Types of Cooperation Among Anaerobic Microorganisms

Whereas aerobic bacteria are usually considered to be able to degrade complex organic matter completely to CO2 and H2O, this is true in the anaerobic world only in some exceptional cases. Complex biomass is typically degraded in several steps, including classical (primary) fermentations, with subsequent further oxidation by sulfate reduction or iron reduction, or by coupling primary fermentations with secondary fermentations to methanogenesis at the very end (Bryant 1979 Mclnerney 1988 Stams...

Methanogens

The flagellate Pentatrichomonoides scroa from the gut of the termite Mas-totermes darwiniensis (Fr hlich and K nig 1999) and certain Dinenympha and Microjoenia species in Reticulitermes speratus and Hodotermopsis sjoestedti (Tokura et al. 2000) are associated with methanogens that seemingly exist within the cell. As in the case of the epibiotic methanogens, the 16S rRNA gene sequences indicate that they belong to the genus Methanobrevibacter. The guts of each termite species usually harbor more...

Bacteroidales

The surface of many of the larger gut flagellates is densely covered with morphologically similar rod-shaped bacteria (Bloodgood and Fitzharris 1976 Tamm 1982 Dolan and Margulis 1997 Stingl et al. 2004 Fig. 1). The epibi-onts of a Staurojoenina sp. from Neotermes cubanus were recently identified as members of a new, termite-associated lineage of Bacteroidales (Stingl et al. 2004) and have been assigned to the candidate taxon 'Vestibaculum illiga-tum' (Fig. 5), and also the epibionts of...

Can Euplotidium and Epixenosomes Survive on their

During the 15 years of studying the association, epixenosomes have been found in every specimen of Euplotidium when examined directly after collection. Secondly, the association can be indefinitely maintained in well-fed lab cultures. Thirdly, the host cell cycle is perfectly coordinated with the multiplication and the differentiation of epixenosomes from form I to form II (Giambelluca and Rosati 1996). This cumulative evidence strongly indicates that the association between Euplotidium and...

Carbon Assimilation

A diverse array of enzymatic and physiological assays has shown that methane is the major source of carbon for methanotroph-hosting mussels. Because methane monooxygenases (MMOs) degrade rapidly (Cavanaugh et al. 1987) and methanol dehydrogenase (MeDH) is unique to methylotrophs, MeDH is commonly employed as a diagnostic enzyme for the detection of methanotroph activity (Cavanaugh et al. 1992 Fisher et al. 1993 Barry et al. 2002 Fiala-Medioni et al. 2002). Stable carbon isotope ratios, based on...

Distribution of Symbionts within Mussel Gill Tissue

In most bathymodioline species, no spatial pattern of symbiont types in the bacteriocytes was detected from TEM analyses (Fisher et al. 1993 Distel et al. 1995 Fiala-Medioni et al. 2002 Won et al. 2003a). In contrast, hybridization of methano- and chemoautotrophic-specific probes to symbionts in the gill bacteriocytes of an undescribed Bathymodiolus species from a recently discovered hydrocarbon seep on the Gabon continental margin revealed a distinct distribution pattern for the two bacterial...

Both Organisms Undergo Developmental Changes in Response to the Symbiosis

The interaction between E. scolopes and V. fischeri induces a number of developmental and morphological changes in each organism (Fig. 1). Ciliated epithelial cells, present on a field that projects outward from the LO, likely function to facilitate recruitment of V. fischeri by drawing the bacteria-laden seawater into the mucus matrix near the LO pores. Once the symbiont has successfully migrated into the LO, apoptosis and subsequently regression of these ciliated fields results in their loss...

Alpha Proteobacterial Symbionts

To date, alpha proteobacterial symbionts have been found in three gutless oligochaete species that are all from similar environments, shallow water coral reef sediments, but from different geographic locations (I. leukodermatus from Bermuda, I. makropetalos from the Bahamas, and 0. loisae from the Australian Great Barrier Reef). All three host species harbor symbionts belonging to a clade of relatively closely related (92.6 sequence similarity) bacteria called Alpha 1 symbionts (Fig. 2). Within...

Concluding Remarks and Future Perspectives

The study of symbiotic associations between ciliates and prokaryotes is of interest from ecological and the evolutionary points of view. Especially, the ectosymbiotic relationship between ciliates of Euplotidium spp. and epixenosomes offers novel cues for studying both these aspects since apparently both partners benefit from living together. For epixenosomes, the association might be even vital, whilst for the ciliate it represents an ecological advantage, a powerful defensive tool in the...

Fermentation of Acetone

A special situation is the fermentative conversion of acetone to methane and CO2, which is catalyzed by syntrophically cooperating bacteria as well, with acetate as the only intermediate transferred between both partners CH3COCH3 + CO2 + H2O 2 CH3COO + 2 H+ A G0' - 25.8 kJ mol-1 2 CH3COO- + 2 H+ 2 CH4 + 2 CO2 A G0' - 71.8 kJ mol-1 Although in this case all partial reactions are exergonic under standard conditions, the primary fermenting bacterium depends on the methanogenic partner, and acetone...

Bathymodioline Symbioses

Thus far, symbiont-hosting mytilid mussels are restricted to deep-sea endemics that colonize whale and wood falls (e.g., mussels of the genus Idas) and species in the subfamily Bathymodiolinae (two genera Bathymodiolus and Tamu) that inhabit vents and seeps (Kenk and Wilson 1985 Distel et al. 2000). Anatomical features of mussels in this subfamily, such as mantle fusion, a simple gut, and pronounced gills, distinguish them from other deep-sea mussels (Kenk and Wilson 1985 Gustafson et al....

Identification of the Ectosymbiotic Spirochetes of Mixotricha paradoxa

Berchtold and K nig (1996) and Wenzel (1998) found about 13 different spirochetal 16S rRNA gene clones in the intestinal tract of Mastotermes darwiniensis. Although spirochetes constitute a main part of the gut flora of termites, the microhabitats and function of the identified spirochetes (Berchtold et al. 1994 Berchtold and K nig 1996 Wenzel 1998) in the gut of Mastotermes darwiniensis remained unclear. Therefore, the bacteria associated with the cell surface of Mixotricha paradoxa were...

Conclusions

The large number of symbioses among termite gut flagellates and prokaryotes, the high level of integration evidenced by the elaborate attachment structures or the intracellular location, and the large proportion of the prokaryotic gut microbiota that is associated with the protozoa suggest a major importance of such symbioses for the hindgut metabolism of lower termites. Molecular tools allow the identification of the phylogeny of the partners involved in the symbioses, and although these...

Co

Metabiotic cooperations in defined cocultures degrading glucose (A) and trimethoxybenzoate to methane and CO (B) Fig. 2. Carbon and electron flow in the methanogenic degradation of complex organic matter. Groups of prokaryotes involved 1 primary fermentative bacteria 2 hydrogen-oxidizing methanogens 3 acetate-cleaving methanogens 4 secondary fermenting bacteria (syntrophs) and 5 homoacetogenic bacteria Fig. 2. Carbon and electron flow in the methanogenic degradation of complex organic...

Future Directions

The initiation of the symbiosis between E. scolopes and V. fischeri involves several regulatory systems, many of which affect traits known to be involved in colonization (Fig. 3). Many important questions remain. First, what is the relation of these regulatory circuits to one another Both FlrA and the luminescence regulator LuxO modulate transcription by o54-containing RNA polymerase (Lilley and Bassler 2000 Millikan and Ruby 2003). Not surprisingly, a o54 mutant is defective for colonization,...

Epixenosomes

Analyses with an electron microscope clearly showed that epixenosomes are always external to the Euplotidium cortex. Since the epixenosome number is quite constant throughout the ciliate's life cycle, their number must increase prior to the binary fission of Euplotidium. These observations led us to interpret epixenosomes not as extrusomes but, rather, as epibionts. Initial evidence for a cellular nature of the epixenosomes was obtained by DAPI staining that showed the presence of DNA within...

Environment

Until recently, it was assumed that gutless oligochaetes only occur in large numbers in shallow water calcareous sediments, living interstitially in the pore waters. The discovery of high abundances of gutless oligochaetes in silicate sediments near sea-grass beds off the coast of Elba in the Mediterranean (Perner 2003) and in 100-400 m water depth in muds off the coast of Chile and Peru (Levin et al. 2002, 2003) indicate that gutless oligochaetes may be much more widespread and occur in many...

Bacterial Symbionts

Phylogenetic analyses based on 16S rRNA have revealed that two types of gamma Proteobacteria are housed within the bacteriocytes of bathymodioline mussels. One type of symbiont includes lineages that cluster with free-living, type I methanotrophs, while the others form a monophyletic group of chemoautotrophic endosymbionts associated with mytilid mussels and vesicomyid clams (Fig. 4). Overall, six of the sixteen species of Bathymodiolus host dual symbionts, while an additional three harbor only...

Functional Aspects

The phylogenetic diversity of the oligochaete symbionts is mirrored in their physiological diversity. Before the discovery that gutless oligochaetes harbor multiple symbionts, it was assumed that these associations are driven solely by chemoautotrophy. Evidence for a symbiosis fueled by sulfur-oxidizing, CO2-fixing bacteria was based on rapid uptake and incorporation of radiolabeled bicarbonate as well as the presence of characteristic enzymes for the fixation of CO2, such as...

Butyrate Oxidation

In syntrophically butyrate-oxidizing bacteria (Mclnerney et al. 1979), 1 ATP is synthesized by substrate-level phosphorylation through thiolytic acetoace-tyl-CoA cleavage (Wofford et al. 1986), but part of this energy has to be reinvested in reverse electron transport to allow proton reduction with electrons from the butyryl CoA dehydrogenase reaction at a hydrogen partial pressure of 10-4 to 10-5 bar (Thauer and Morris 1984). Experimental evidence of a reverse electron transport system between...

Introduction

A fundamental feature of symbioses is the colonization of the host by specific microorganisms. The degree of specificity is reflected both in the number of microbial species associated with the host and in the frequency of detecting any given microbe in the host. Some associations such as the light organ symbiosis of Vibrio fischeri and the squid Euprymna scolopes are highly specific involving one microbial species that is always detectable in the functional symbiotic association to the...

Identification of the Ectosymbiotic Rodshaped Bacterium of Mixotricha paradoxa

Wenzel (1998) obtained 16S rDNA amplificates (e.g., clone B6 ca. 400 bp) from Mixotricha paradoxa, which were related to Bacteroides sp. With the specific primer B6.1 derived from the obtained sequence of clone B6 1338 bp were amplified. The Bacteroides sp.-related clone B6 and some of its phylogenetic relatives were used to construct the Bacteroides tree. Figure 5.6 shows the phylo-genetic relationship of clone B6 to representatives of Bacteroides-related species. This indicates that the...

Conclusions and Outlook

Considering the known physiology of the leech and the mutant phenotypes that we have characterized so far, possible mechanisms can be deduced that may interfere with microbial growth and thus contribute to the specificity of this symbiosis. These mechanisms are likely to play important roles at different times, immediately after feeding, during the rapid growth period and during the persistence phase (Fig. 2). The first powerful layer of defense is the antimicrobial properties of the ingested...

Evolution and Biogeography of Bathymodioline Symbioses

The historical biogeography of bathymodioline symbioses, inferred by placing portraits of relationships among individuals in a geographic context, provides a basis for understanding the current distribution and magnitude of diversity in the invertebrate host and symbionts. The disjunct distribution of hydrothermal vent and hydrocarbon seep communities, due to factors such as topography, physical oceanography, and tectonic activity, could promote genetic differentiation, local adaptation, and...

Gamma Proteobacterial Symbionts

In all gutless oligochaete species examined to date, the large oval-shaped symbiont morphotype with sulfur and PHB vesicles (see Sect. 4.2) has been identified as a Gamma 1 phylotype (Fig. 2 and 3) that falls within a closely related cluster of sequences in the gamma subdivision of the Proteobacteria. The oligochaete Gamma 1 symbionts are most closely related to the ectosymbionts of the marine nematode Laxus (Polz et al. 1994), and build a monophyletic group with these in all phylogenetic...

Detection of Multiple Symbiont Phylotypes

The gene of choice for studying the phylogeny of the bacterial symbionts has been the 16S ribosomal RNA (rRNA) gene. Crucial to the study of these hosts has been the full cycle rRNA approach, in which comparative 16S rRNA sequence analysis is coupled with fluorescence in situ hybridization (FISH) (Amann et al. 1995). Oligonucleotide probes of 18-22 bp length are designed based on the 16S rRNA sequences isolated from the hosts, labeled with a fluorescent dye, and hybridized to sections of the...

Differentiation in the Free Living State

In the free-living state, heterocyst differentiation is repressed by the presence of a source of combined nitrogen. When the combined nitrogen is exhausted, heterocysts appear in the filaments in a nonrandom spacing pattern, typically as a single heterocyst flanked by 10 to 15 vegetative cells (Fig. 1B). There are two interrelated phenomena with respect to the presence and position of heterocysts in a filament. The first is the sequence of heterocyst appearance following exhaustion of combined...

Concept of Syntrophic Energy Metabolism

The effect of hydrogen- and acetate-scavenging partner organisms on syntro-phic fermentations becomes obvious if one compares such fermentations under standard conditions (which are roughly comparable to those prevailing in pure cultures) and under conditions that are similar to those prevailing in natural or semi-natural environments. As shown in Table 1, the endergonic fermentations of ethanol, alanine and butyrate turn into exergonic reactions if conditions are assumed that are comparable to...

Nitrogen Acquisition

Riftia pachyptila must also obtain all of the other macro- and micro-nutrients used in biosynthesis by both host and symbiont. While the pathways mediating assimilation and conversion of most metabolites are unknown for this symbiosis, researchers have identified some of the mechanisms of nitrogen metabolism in R. pachyptila. Laboratory incubations measuring the uptake of 15N-nitrate (15NO3-) showed that nitrate, which is abundant in situ ( 40 M Johnson et al. 1988b), is the predominant...

Importance of the Vertebrate Complement System

This colonization assay allowed us to evaluate the specificity of the symbiosis experimentally. For these experiments, a portion of the inoculated blood was incubated in vitro under the same conditions as the animal. This modification allowed us to compare the growth potential of the strain in blood and perhaps detect modifications of the ingested blood inside the leech (Indergand and Graf 2000). One Escherichia coli strain, EcR1, had an interesting colonization phenotype (Fig. 3). The number...

Substage 5 Heterocyst Differentiation and Behavior

Physiologically, heterocysts are microoxic, heterotrophic, N2-fixing cells whose differentiation from oxygenic photoautotrophic vegetative cells involves a hypothetically large, but unknown, extent of differential gene expression estimates range from 140 (Wolk 2000) to 600 (Ehira et al. 2003), to more than 1,000 (Lynn et al. 1986) genes. A number of regulatory and structural genes for heterocyst differentiation and function have been identified in Anabaena sp. strain PCC 7120 (see Wolk 1996,...

Outlook

The few examples mentioned here should illustrate that there are many different types of cooperation between prokaryotes, especially among anaerobic bacteria. Especially in syntrophic associations of fermenting bacteria and methanogenic partners, which catalyze the last steps in methanogenic degradation of organic matter, the partner organisms are forced to very close cooperation in order to exploit the very small amounts of energy available to these steps, which range at the lowermost limit of...

Other Invertebrate Hosts

While this chapter focuses on the association between bathymodioline mussels and their endosymbionts, because those are the best understood of methane-based symbioses, the two other known examples, a pogonophoran tubeworm and a carnivorous sponge, illustrate the diversity of invertebrate taxa that can harbor methanotrophs. The pogonophoran Siboglinum poseidoni from methane-rich reducing sediments is the only tubeworm known to host methanotrophic endosymbionts (Schmaljohann 1991). Siboglinum...

Molecular Basis of Symbiosis

Progress in Molecular and Subcellular Biology Series Editors W.E.G. M ller (Managing Editor), Ph. Jeanteur, Y. Kuchino, A. Macieira-Coelho, R. E. Rhoads Progress in Molecular and Subcellular Biology Signaling Pathways for Translation Insulin and Nutrients Signaling Pathways for Translation Stress, Calcium, and Rapamycin A.-P. Arrigo and W.E.G. M ller (Eds.) Protein Degradation in Health and Disease Guidance Cues in the Developing Brain I. Kostovic (Ed.) Invertebrate Cytokines and the Phylogeny...

Phylogeny

Termite gut flagellates belong to three distinct taxa trichomonads, hypermas-tigids, and oxymonads (Yamin 1979). Originally, all were considered primitive, primarily amitochondriate eukaryotes, but recent molecular data proved that they represent two separate eukaryotic lineages. Phylogenetic analyses of the termite gut flagellates by various groups (reviewed by Ohkuma 2003 Gerbod et al. 2004), mainly based on 18S rRNA gene sequence analysis, confirmed the presence of two classes of the phylum...

Morphology of the Symbiosis

In the first two descriptions of gutless oligochaetes, namely Inanidrilus albidus (albus Latin white) and I. leukodermatus (leukos Greek white), the intensive white color of the worms, now known to be common to all gutless oligochaetes, was mentioned but not further investigated (Fig. 4a) (Jamieson 1977 Giere 1979). This white coloring comes from the refraction of light by the symbiotic sulfur-oxidizing bacteria just below the cuticle of the worm that are filled with sulfur and the storage...

Hindgut Protozoa

Symbiotic flagellates are found exclusively in the phylogenetically lower termites and the closely related cockroaches of the genus Cryptocercus the higher termites harbor a largely prokaryotic microbiota. The first studies that revealed the beneficial nature of these peculiar symbionts - discovered in 1856 by Lespes (see Leidy 1881) and initially considered as parasites - were reported by Cleveland (1925, 1926), who demonstrated that termites do not survive for long after elimination of their...

Info

Cluster of Caedibacter caryophilus in the macronucleus of Paramecium cauda-tum. Some bacteria contain R bodies (arrows) with phage capsids (arrowheads). Electron micrograph, courtesy of Michael Schweikert, University of Stuttgart. Bar 0.5 m Fig. 2. R bodies are coiled protein ribbons that are refractile in phase contrast. a The unrolled ribbons have a length of up to 20 m and a width of 0.4 to 0.8 m. b By appropriated triggers, such as low pH, they are induced to unroll. Certain R...

Known Environments Inhabited by Methanotrophic Symbioses

Fluids rich in methane are released from hydrothermal vents, cold seeps, and mud volcanoes in the deep-sea. Hydrothermal vents, discovered in 1977, TYPE II METHANOTROPHS (Serine pathway) Fig. 3. Methane oxidation and carbon assimilation pathways for type I and type II methanotrophs via the RuMP (ribulose monophosphate) and serine pathways (compiled from Hanson and Hanson 1996). Enzymes involved in the oxidation of methane are abbreviated as follows pMMO (particulate methane monooxygenase), sMMO...

Other Environmental Factors

As described above, when gutless oligochaetes were first discovered it was assumed that they gained their nutrition by uptake of dissolved organic compounds from the environment. At the Bermuda site where I. leukodermatus occurs in high abundances, concentrations of dissolved free amino acids and organic carbon, as well as total carbohydrates were higher than in other Bermudian carbonate sediments (Giere et al. 1982). However, in uptake experiments with radiolabeled substrates, organic carbon...

References

Abrahamsen MS, Templeton TJ, Enomoto S, Abrahante JE, Zhu G, Lancto CA, Deng M, Liu C, Widmer G, Tzipori S, Buck GA, Xu P, Bankier AT, Dear PH, Konfortov BA, Spriggs HF, Iyer L, Anantharaman V, Aravind L, Kapur V (2004) Complete genome sequence of the Apicomplexan, Cryptosporidium parvum. Science 304 441-445 Adams MWW (1990) The structure and mechanism of iron-hydrogenases. Biochim Biophys Acta 1020 115-145 Akhmanova A, Voncken FG, van Alen A, van Hoek A, Boxma B, Vogels GD, Veenhuis M,...

Nutritional Basis of the Symbiosis

Nutrition in Riftia pachyptila depends on bacterial symbionts that fix carbon dioxide into organic matter using energy derived from the oxidation of reduced sulfur compounds. Figure 2 presents an overview of symbiont sulfur oxidation, as inferred from studies of free-living sulfur bacteria (see Kelly 1982 Nelson and Hagen 1995 Friedrich et al. 2001 for reviews of sulfur- based chemoautotrophy). The pathways by which the first half of this process, 2 2 2 the oxidation of sulfide (H2S, HS-, S )...

Quorum Sensing Regulatory Systems

First described in V. fischeri, quorum sensing is used by many bacteria to detect the presence of other bacteria in their surroundings (reviewed in Taga and Bassler 2003). This method of monitoring the environment involves the production of a small molecule known as an autoinducer (AI) by an autoinducer synthase. Secreted into the environment, Als can be recognized in recipient cells either by a specific two-component sensor kinase, or more frequently in Gram-negative bacteria, by a DNA-binding...

Organic Compound Transfer and Symbiont Growth

In chemosynthetic endosymbioses the transfer of fixed carbon from the symbiont to the host for use in biomass synthesis or energy metabolism can occur via two mechanisms 1) the symbiont excretes autotrophically-fixed carbon in the form of soluble organic molecules that are then translocated to host cells, or 2) the host directly digests bacterial cells (Fig. 2). Both translocation and digestion appear to contribute to host nutrition in Riftia pachyptila. Felbeck and Jarchow (1998), using...

Reduced Sulfur Compounds

The close timing between the discovery of sulfur-oxidizing bacteria in the gutless tube worms from hydrothermal vents and the symbiotic bacteria in gutless oligochaetes, led to the assumption that the oligochaete symbionts were also dependent on reduced sulfur compounds such as sulfide and thiosulfate from the environment. Most ecological studies have centered on a single species, Inanidrilus leukodermatus, from a single site in Bermuda (Giere et al. 1982). Sulfide concentrations at this site...

Secreted Proteins

Bacteria have evolved several different ways of secreting proteins into the environment including the type I, II, III, IV and V secretion systems. Not all bacteria dispose of every one of the five secretion systems and so far, only type I, III and IV secretion systems have been shown to be relevant for the establishment of symbioses. Type IV secretion systems (T4SSs) are being unveiled in ever more bacteria (Nagai and Roy 2003) and a T4SS was found to be encoded by the symbiotic plasmid of R....

Spirochaetes

Although spirochetes are extremely abundant in the intestinal tract of most wood-feeding termites, only a few species have been characterized in pure culture (Breznak and Leadbetter 2002 Graber et al. 2004). Termite gut spiro-chetes display an enormous morphological diversity (Margulis and Hinkle 1999 Breznak and Leadbetter 2002), but several cultivation-independent analyses have documented that they belong exclusively to the Treponema branch of the Spirochaetes, forming two distinct clusters...

Nutrient Assimilation

The metabolic needs of the host are met by the transfer of nutrients from endosymbionts. Our discussion focuses on assimilation of nutrients from the methanotrophic symbionts, since the previous chapter discusses nutrient acquisition by invertebrates hosting chemoautotrophs. Enzymatic and physiological assays have indicated that, in methanotrophic symbioses, the majority of carbon attained by the host is derived from utilization of methane by the symbiont. Evidence suggests that nitrogen, in...

Symbiosis Genes of the Epibiont

All epibionts analyzed to date represent 16S rRNA gene sequence types that could not be detected in any free-living green sulfur bacterium (see (2.)3.1). Although phylogenetically distinct, the epibiont of Chlorochromatium ag-gregatum did not exhibit unusual physiological properties with respect to the capability of assimilating organic carbon sources, the temperature dependence or the pH dependence of growth. The only phenotypic trait that clearly differed between epibionts and free-living...

Preface

Symbiotic associations involving prokaryotes are known from many different phylogenetic lineages and occur ubiquitously. The significance of these associations is well established for insects, where 15-20 (i.e., up to 190,000) of the species depend on symbioses with bacteria (Buchner 1965). As another example, up to 85 of all prokaryotes in the termite hindgut occur in ecto- or endosymbiotic associations with flagellates (Berchtold et al. 1999). In some aquatic environments, essentially all...

Summary and Conclusions

The symbioses between invertebrates and chemosynthetic bacteria allow both host and symbiont to colonize and thrive in otherwise inhospitable deep-sea habitats. Given the global distribution of the bathymodioline symbioses, this association is an excellent model for evaluating co-speciation and evolution of symbioses. Thus far, the methanotroph and chemoautotroph endosymbionts of mussels are tightly clustered within two independent clades of gamma Proteobacteria, respectively. Further...

Nitrogen and other Essential Nutrients

Both partners in the symbioses are dependent on environmental sources of nitrogen, typically available at deep-sea vents and seeps in the form of ammonium, nitrate, and or organic nitrogen (Lee et al. 1992, 1999 Lee and Childress 1994). N2 fixation, originally postulated for both chemoautotrophic and methanotrophic symbionts (based on depleted 815N values for mussel tissues), has not been detected. In retrospect, this is to be expected given the availability of other fixed nitrogen sources....

Phylogeny of the Hosts

Over 80 gutless oligochaete species have been described, and there are numerous undescribed species, mainly from the Indo-Pacific region and the East Atlantic Ocean, still available for identification. Given that a collection trip to a novel region can yield as many as 9 new species (Erseus 2003), the diversity of gutless oligochaetes may be even higher. There is a broad range from primitive to highly derived species, indicating that the symbiotic condition has led to a radiative evolution in...

Syntrophic Oxidation of Hexoses

Fermentation of hexose to 2 acetate, 2 CO2 and 4 H2 as sole products is exer-gonic (-216 kJ per mol) but does not yield sufficient energy to synthesize 4 ATP by substrate level phosphorylation that are directly linked with this fermentation via glycolysis. Hydrogen removal to a low concentration makes this reaction exergonic enough to allow fermentation according to this pattern. We could recently show that there is a considerable number of primary fermenting bacteria in a lake sediment that...

Transmission of the Symbionts

When gutless oligochaetes become fully mature they develop so-called genital pads, a pair of sack-like pockets on the ventral side of the worms close to the oviporus, the opening through which eggs are deposited. These genital pads are packed with symbiotic bacteria and are only separated from the environment by a very thin cuticle layer of the worm (Giere and Langheld 1987). While all genital organs and the maturing eggs inside of the worm appear to be free of bacteria, the freshly laid egg is...

Springer

J rg Overmann Section of Microbiology Department of Biology Maria-Ward-Str. 1a 80638 Munich Germany ISBN-10 3-540-28210-6 Springer-Verlag Berlin Heidelberg New York ISBN-13 978-3-540-28210-5 Library of Congress Control Number 2005934306 This work is subject to copyright. All rights are reserved, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilm or...

Sulfide Acquisition

Thioautotrophy requires simultaneous access to both sulfide and oxygen. This dual requirement poses a unique challenge given that sulfide and oxygen occur in distinct habitat zones in contrast to ambient seawater, the reduced vent fluid from which vent thioautotrophs obtain sulfide is typically anoxic or contains oxygen only at very low levels. In addition, sulfide spontaneously reacts with oxygen to form less-reduced sulfur compounds (S0, S2O32-, or SO4 - Zhang and Millero 1993). Such abiotic...

Types of Interspecies Metabolite Transfer

In most syntrophic methanogenic associations, hydrogen is the electron carrier between oxidative and reductive metabolic processes. Its small size and ease of diffusibility make it an excellent candidate for such interspecies electron transfer reactions. Nonetheless, in several cases, formate has also been shown to act as an electron carrier through a formate C 2 cycle. Theoretical considerations indicate that the formate system has certain advantages in an aqueous phase, whereas hydrogen might...

Symbiotic Associations that Depend on Intracellularly Generated Hydrogen

Aerobically functioning mitochondria are unlikely to support any symbiotic association since - besides a number of functions in anabolic and catabolic cellular pathways - they produce ATP to the benefit of their hosts and, in addition, just CO2 and H2O. Anaerobically functioning mitochondria, on the other hand, may excrete succinate and acetate besides CO2, and a hydrogeno-some is likely to excrete substantial amounts of acetate, (formate), CO2, and hydrogen (M ller 1993 Tielens et al. 2002)....

Vibrio fischeri cells navigate physical and chemical barriers to colonize Euprymna scolopes

From the aggregates, the V. fischeri cells migrate through LO pores, reaching ducts that ultimately lead into crypts, the sites of colonization (Fig. 1). In the ducts, the bacteria must move through mucus against an outward current generated by ciliated cells lining the passageway (McFall-Ngai and Ruby 1998). As a further barrier to colonization, the ducts contain high levels of nitric oxide, an anti-microbial agent that may function as a layer of defense against invasion by non-specific...

Syntrophic Ethanol Oxidation

Although the case of Methanobacillus omelianskii is the classical example of interspecies hydrogen transfer, numerous further syntrophically ethanol-oxidizing bacteria have been isolated, such as Thermoanaerobium brockii (Ben-Bassat et al. 1981) and various Pelobacter strains (Eichler and Schink 1986). Also certain ethanol-oxidizing sulfate reducers such as Desulfovibrio vulgaris oxidize ethanol in the absence of sulfate by hydrogen transfer to a hydrogen-oxidizing methanogenic partner....

Host Specificity of Caedibacter

Parasites are believed to have a major impact on host evolution. On the other hand, it is necessary for a parasite to adapt its growth dynamics to the host species or even to its genotype because the host must not be killed before the parasite has developed infectious stages. Optimal virulence should result in high parasite fitness in a host, whereas maladapted virulence could drive a parasite or the host extinct ('Suicide King' hypothesis e.g., Dybdahl and Stor-fer 2003). Co-evolution between...

The Ejection Mechanism and its Significance

The EA is a very efficiently engineered structure. In its resting position, its organisation is compact, fitting well into the intact epixenosome. During the ejection, it unrolls starting from inside, whereby the layers slip relative to each other. Thus, a tube is formed which fits exactly through the hole of the DZ. The tube penetrates the hole, and reaches the opening of the cell membrane formed as the first step of the ejecting process. As a result, the apical portion of the epixenosome...

Vent Habitat

Riftia pachyptila inhabits hydrothermal vent sites along the East Pacific Rise and the Galapagos Rift in the Eastern Pacific. The distribution of the tubeworm is intimately tied to the unique physiochemical characteristics of hydrothermal vents. Vent sites are typified by steep gradients between cold ( 1.8 C), oxygen-rich (110 M) bottom water and hot (up to 400 C), acidic (pH 3 to 6) vent fluid. Hydrothermal fluids are usually laden with volcanic gases (e.g., methane and carbon dioxide) and...

Surface Polysaccharides

Nod-factors are essential signal molecules that permit rhizobia to enter legume roots, but they are not the only bacterial determinants required for successful symbiosis. Other determinants include secreted proteins and surface polysaccharides (SPS). SPS include exo-polysaccharides (EPS), lipo-polysaccharides (LPS), capsular polysaccharides (CPS and K-Antigens) and cyclic glucans (Fraysse et al. 2003). SPS are abundant extra-cellular components that are exported to the cell surface and into the...

Why Does Euplotidium Maintain its Epixenosomes

As described above, the association between Euplotidium and epixenosomes appears to be obligatory in the natural environment. In a non-competitive environment, however, the ciliate survives well without its symbionts. Epixenosomes may therefore provide their host with an important ecological advantage, such as defence against predators. This hypothesis was experimentally verified by comparing the behaviour of Litonotus lamella when preying upon E. itoi with and without epixenosomes. L. lamella,...

Geographic Distribution

The first gutless oligochaetes were found in coral reef sediments in the Pacific (Jamieson 1977), and North Atlantic (Erseus 1979b Giere 1979), and the highest diversity of oligochaete species is still regularly found in shallow water calcareous sediments (Erseus 1984, 1990). For example, as many as 18 species have been described from sediments around a small island in the Bahamas (Erseus 2003). While tropical and subtropical coral reef sediments clearly represent hotspots for gutless...

Biogeography of the Hosts

Gutless oligochaetes are an ideal host group for studying the biogeography and evolution of marine symbioses as they occur throughout the world in a wide range of different habitats with some species widely distributed and others highly endemic (Erseus 1992). They are also one of the few marine groups in which such a large number of host species (> 100) are so closely related to each other, forming a monophyletic group with all gutless oligochaetes descendents from a single common ancestor...

Establishment of the Association Differentiation and Behavior of Hormogonia

This general stage can be viewed as three substages (1) induction of hor-mogonium differentiation (2) control of the direction of hormogonium gliding and (3) colonization and repression of hormogonium differentiation. Physiologically, hormogonia are analogous to non-growing swarmer cells of certain prosthecate bacteria, such as Caulobacter crescentus (Roberts et al. 1996 Shimkets and Brun 2000). In response to a variety of environmental signals, including light quality, nutrient stress and the...

The Ciliate Host

Blepharisma

The eukaryotic partners of the consortium are marine, sand-dwelling, hypotrich ciliates. They have been assigned to the Euplotidium genus. Since Noland (1937) erected this genus, six species have been described. Euplotidium itoi and E. arenarium are the only two species characterised at the electron microscopical level. A lateral view of E. itoi at SEM is shown in Fig. 1. The organism is oval in shape, 60-90 m long and 40-52 m wide. The somatic ciliature on the flat ventral surface consists of...

Glycolytic Activities of Mastotermes darwiniensis and its Flagellates

Up to now, it has been believed that the hindgut flagellates produce nutrients using their own cellulolytic enzymes for the benefit of their termite host. The glycolytic activities found in separated cells of Mixotricha paradoxa are compiled in Table 5.3 (Berchtold and K nig, unpubl. res.). Surprisingly, not all of these activities seemed to be produced by the flagellates themselves, but rather taken up with the gut contents. Two endoglucanases, Cel I and Cel II, Monotrichomonas sp....

Symbiont Transmission and Evolution

The evolutionary dynamics between symbiont and host depend largely on the symbiont transmission strategy. Symbiont transmission between successive host generations can occur environmentally (acquisition from a free-living population of symbiotic bacteria), horizontally (transfer between hosts sharing the same habitat), or vertically (transfer from parent to offspring via the egg). Vertically transmitted endosymbionts experience a unique selective regime within the host. These symbionts are...

Characterization of the Microbiota in the Crop of the Leech

The early bacteriological investigations in the 1940s and 1950s described the isolation of a single bacterium from the crop of the medicinal leech (Lehmensick 1941 Hornbostel 1942 Busing 1951 Busing et al. 1953). The consistent isolation of this bacterium and the absence of other microorganisms lead the early investigators to suggest a symbiotic association. Three functions have been proposed for the symbiont (Busing et al. 1953 Graf 2000, 2002) (1) digestion of the ingested blood meal, (2)...

Hydrogen Metabolism

The symbiosis with methanogens is likely based on the interspecies transfer of molecular hydrogen. Little is known about the physiology of the protozoa, but from thermodynamic considerations, any fermentative metabolism releasing part of the reducing equivalents as H2 will become more exergonic if this product is not allowed to accumulate (Schink 1997 see also Chapter by B. Schink). Virtually all 16S rRNA gene clones of methanogens obtained from lower termites fall into the phylogenetic...

Differentiation in Symbiosis

Symbiotic heterocyst differentiation differs from that in the free-living state in at least two ways the signal that activates the differentiation cascade and an enhanced frequency and altered spacing pattern. Signal. Symbiotic heterocyst differentiation is hypothetically independent of the presence and concentration of combined nitrogen in the immediate environment (Meeks 1998, 2003 Meeks and Elhai 2002). Three lines of evidence support this hypothesis. First, approximately 10 M NH4+ represses...

The Digestive Tract Symbiosis of Hirudo medicinalis

Diagram Hirudo

In contrast to the digestive tract communities residing in most animals (Savage 1977 Demaio et al. 1996 Lilburn et al. 1999), the digestive tract of Hirudo medicinalis appears to be colonized by a relatively simple microbial community (Lehmensick 1941 Busing et al. 1953 Graf 2000). Only one symbiont, an Aeromonas sp., was consistently cultured in several investigations and culture independent approaches suggest the presence of only a few additional taxa (described below). This apparent...

Vibrio fischeri strains are specifically recruited from the seawater

Vibrio Colonization Squid

V. fischeri comprises less than 0.1 of the total bacterial population in the seawater inhabited by the squid (Lee and Ruby 1992), yet this organism alone K. Geszvain, K. Visick (e-mail kvisick lumc.edu) Dept. Microbiology and Immunology, Loyola University Chicago, 2160 S. First Ave. Bldg. 105, Maywood, IL 60153, USA Progress in Molecular and Subcellular Biology Jorg Overmann (Ed.) Molecular Basis of Symbiosis Springer-Verlag Berlin Heidelberg 2005 is found in the light organ association...

Methanotrophic Symbioses

Methanotrophic endosymbioses have only been characterized in a few marine invertebrate taxa and deep-sea habitats. Symbioses involving methanotrophs were first described in bathymodioline mussels inhabiting deep-sea cold seeps (Childress et al. 1986 Cavanaugh et al. 1987) and subsequently found in other bathymodioline mussels, a pogonophoran Table 1. The taxonomic and biogeographic distribution of methanotroph-hosting invertebrates Species_Type of symbiontb Habitat_Collection...

Morphology of Mixotrixa paradoxa

Microbes Protists

One of the larger wood-ingesting flagellates in the hindgut of Mastotermes darwiniensis is Mixotricha paradoxa, a member of the order Trichomonadida (Table 5.2). The pear-shaped cells are about 500 m long and 250 m in diameter (Fig. 5.3). The surface of Mixotricha paradoxa shows a highly ordered pattern of rod-shaped bacteria and in addition it is covered by a dense carpet Fig. 5.3. Scanning electron micrograph of Mixotricha paradoxa. The white line indicates the borderline between the anterior...

Specificity of the Symbiosis

A powerful tool for the molecular investigation of a symbiosis is a colonization assay that allows one to evaluate the ability of specific strains to colonize the medicinal leech (Graf 1999, 2002 Indergand and Graf 2000). In order to differentiate the introduced test strain from the native microbiota, we use spontaneous rifampin-resistant mutants as test strains. The strains are added to a blood meal that was preheated to 37 C and is fed to the leech in a parafilm covered disposable centrifuge...

Types of Phototrophic Consortia

To date, a total of 10 morphologically different types of consortia have been detected. Most of them have repeatedly been observed in freshwater habitats. The majority of the phototrophic consortia are round to spindle-shaped, motile, and consist of 13-69 colored cells that form a layer surrounding one colorless central bacterium in the center (Fig. 1B, Fig. 2A,B). Previously, the different types of phototrophic consortia were distinguished based on the color of their epibionts and the...

Prokaryotic Epibionts

Epibiont Bacterial

Many of the termite gut flagellates are colonized by epibiotic bacteria. Some of the associations are already evident by observation with a light microscope, but only the electron microscope reveals the enormous variety and complexity of these associations (e.g., Cleveland and Grimstone 1964 Leander and Keeling 2004 Figs. 1-3). The presence of special attachment sites on the cell envelope of the flagellates (e.g., Tamm 1980 Radek et al. 1992 Dolan and Margulis 1997 Stingl et al. 2004) indicates...

Modes and Specificity of Interaction between the Bacterial Partners

Theoretically, phototrophic consortia could form randomly from bacterial cells which encounter each other just by chance. Under these conditions, morphologically identical consortia would be expected to harbor different types of green sulfur bacteria and, secondly, free-living epibiont cells should also be detected in the habitat of phototrophic consortia. However, when the epibionts associated with a particular phototrophic consortium were analyzed, all epibi-ont cells invariably contained the...

Phylogenetic Position of Mixotricha paradoxa

Figure 5.4 shows a phylogenetic tree of parabasalids. The SSU rDNA sequences were added to an existing database of 36 parabasalid sequences. This data set included 1,210 nucleotides which were analyzed with distance matrix, maximum parsomony, and maximum likelihood methods (Li 2003). The phylogenetic tree shows that four hindgut protozoa of Mastotermes darwiniensis form one subdivision the small flagellate Metadevescovina extranea and the three large flagellates Koruga bonita, Deltotrichonympha...

Substage 4 Growth and Metabolic Control

The physiological characteristics of Nostoc in symbiotic and free-living growth states are summarized in Table 3. In all plant associations, the Nostoc partners grow obviously slower than do free-living cultures. The mechanistic basis of this growth control is unknown, but it clearly influences the most fundamental developmental direction of N. punctiforme, the vegetative cell cycle. Although the rates of CO2 and NH4+ assimilation are depressed (see below), they are so in proportion to the...

Multiple Bacterial Morphotypes

The first ultrastructural studies of oligochaete symbionts described two bacterial morphotypes (Giere 1981, 1985) large oval bacteria 2-7 m in length filled with sulfur and PHB vesicles and smaller cocci- to rod-shaped bacteria 0.7-1.5 m in length without any conspicuous inclusions or structures in their cytoplasm (Fig. 1) (also see Bright and Giere 2005 for a more detailed review of the ultrastructure of the symbiosis). The large oval bacteria are now known to be sulfur-oxidizing gamma...

The Endomicrobia

For a long time, the nature and identity of the endosymbionts of the larger gut flagellates was completely obscure. Recently, the cytoplasmic symbionts of the hypermastigid Trichonympha agilis and the oxymonad Pyrsonympha vertens in the gut of Reticulitermes santonensis were identified as members of the so-called 'Termite Group 1' (TG-1) (Stingl et al. 2005). Based on their 16S rRNA gene sequences, whose origin was verified by fluorescence in situ hybridization with clone-specific probes, and...

Syntrophic Propionate Oxidation

For syntrophic propionate oxidation according to the equation 4 CH3CH2COO- + 4 H + + 2 H2O 7 CH4 + 5 CO2 A G0' -249 kJ per 4 mol of propionate a metabolic flow scheme can be drawn, leaving a free energy change in the range of -22 to -23 kJ per mol reaction (11 partial reactions) to all partners involved under standard conditions (Stams et al. 1989 Schink 1991), and this values decreases to -19 kJ in laboratory cultures and to -12 kJ at propionate concentrations prevailing in sediments or sludge...

Methane Utilizing Bacteria

The identification of symbionts, since none have been cultured, has depended on comparison with free-living aerobic methanotrophs. Methanotrophic bacteria, unique in their ability to use methane as a substrate, form a subset of methylotrophs, which utilize C1 compounds for energy and carbon acquisition (Anthony 1982). Symbiotic methanotrophs are most closely related to free-living type I aerobic methanotrophs in the gamma Proteobacteria, based on their membrane organization, C1 assimilation...

Inorganic Carbon Acquisition

The Riftia symbiont uses the Calvin cycle for autotrophic carbon fixation and therefore requires access to dissolved organic carbon (DIC) in the form of CO2, the DIC species that diffuses most readily through biological membranes (Fig. 2). While the majority of DIC in seawater (pH 8.0 ) is bicarbonate (HCO3- pKa of 6.1 at in situ temperature and pressure of 10 C and 101.3 kPa Dickson and Millero 1987), the lower pH associated with diffuse flow vents (pH 6.0 around R. pachyptila plumes)...

Discovery of the Riftia pachyptila Symbiosis

Riftia Metabolism Images

Scientific understanding of chemosynthetic symbioses derives in large part from studies of the unique fauna associated with deep-sea hydrothermal vents. Early explorations revealed that, in contrast to common perceptions, the deep benthos was not a cold, food-limited habitat but instead contained flourishing ecosystems localized at hot springs emanating from mid-ocean spreading centers. First characterized along the Galapagos Rift and the East Pacific Rise in the eastern Pacific Ocean,...

Anatomy and Ultrastructure

Riftia pachyptila occurs in dense clumps attached to the seafloor substrate (e.g., basalt) at low flow vents. A narrow, elongate tube composed of chitin and scleroproteins and up to three meters in length protects the soft body of the worm, which is divided into four major regions. The branchial plume lies at the anterior of the worm in direct contact with the surrounding seawater. Infused with blood vessels, this gill-like organ allows an efficient exchange of metabolites (e.g., sulfide,...

The Termite Gut Microecosystem

The symbiotic digestion of lignocellulose by termites is a complex series of events involving both the host and its intestinal microbiota (Brune 2003, 2005). While the digestive activities in the foregut and midgut seem to be mainly caused by the host, the processes in the hindgut are largely controlled by the symbionts. The recalcitrance of the lignocellulosic diet and the dynamics of physicochemical gut conditions contribute to the heterogeneity of ecological niches and are reflected in a...

Hydrogenosomes Organelles that Can Use Protons as Electron Acceptors

Deep Mind Dreams

In marked contrast to the mitochondrial remnant organelles mentioned above, hydrogenosomes retained an ATP generating function (M ller 1993, 1998). They compartmentalize the terminal reactions of the cellular energy metabolism. Characteristically, hydrogenosomes import pyruvate (or malate) which is oxidatively decarboxylated to acetyl-CoA by the action of a pyru-vate ferredoxin oxidoreductase (PFO), and not, as in aerobic mitochondria, by the action of a pyruvate dehydrogenase (PDH). An acetate...

Pseudocaedibacter

Anderson RM, May RM (1982) Coevolution of hosts and parasites. Parasitology 85 411-426 Anderson RM, May RM (1991) Infectious diseases of humans. Oxford Univ Press, Oxford Atlas RM (1999) Legionella from environmental habitats to disease pathology, detection and control. Environ Microbiol 1 283-293 Balsley M (1967) Dependence of the kappa particles of stock 7 of Paramecium aurelia on a single gene. Genetics 56 125-131 Barker J, Brown MRW (1994) Trojan Horses of the microbial world protozoa and...

The Gut Microenvironment

Based on the oxygen sensitivity and the fermentative metabolism of the intestinal protozoa, the high concentrations of microbial fermentation products, the presence of anaerobic or oxygen-sensitive activities such as methanogenesis and nitrogen fixation, and the isolation of obligately anaerobic bacteria, it was initially assumed that the termite hindgut is an anoxic habitat (for literature, see Breznak 2000 Brune 2005). However, the maintenance of anoxia in an environment of such minute...

The Epibiont

Early electron microscopic studies of phototrophic consortia from the natural samples revealed the presence of chlorosomes in the epibiont cells (Truper and Pfennig 1971 Caldwell and Tiedje 1974), suggesting that they belonged to the group of green sulfur bacteria. This conclusion was supported by the observation that maximum concentrations of green sulfur bacterial pigments (bacterio-chlorophylls c, d and e) in freshwater lakes coincided with population maxima of phototrophic consortia. The...

Evolutionary Ecology of the Caedibacter Symbiosis and R Body Production

Intracellular Bacteria Phylogeny

Intracellular bacteria are favorable for the host and may be regarded as mutu-alists when uninfected competitors are killed due to these bacterial symbionts. This view, however, may be too simple, as ecological and molecular studies revealed fascinating details on the evolutionary ecology of this long known occurrence of killer-bacteria in paramecia. The bacteria are closely related to pathogens and exploit the host cells just as invasive agents in metazoans do. Caedibacter species are energy...

Two Component Signal Transduction Systems

Many bacteria, including V. fischeri, recognize and respond to their environments using two-component regulatory systems (Fig. 2A, reviewed in Stock et al. 2000). These systems are composed of a sensor histidine kinase Fig. 2. Two-component regulatory systems. A. The phospho-relay in orthodox (top) and hybrid (bottom) two-component systems. Upon detection of signal, phosphate generated from a bound ATP is passed from conserved His to Asp residues until finally being transferred to an Asp in the...

Nod Factors

Plants initiate the molecular dialogue with rhizobia by releasing flavonoids into their rhizospheres (Schultze and Kondorosi 1998 Broughton et al. 2003). These flavonoids are then taken up by the bacteria where they bind NodD proteins of the LysR family of transcriptional regulators (Broughton et al. 2000). The promoters of genes relevant for Nod-factor synthesis (nol, noe and nod genes) contain conserved 49 bp motifs called nod-boxes (Feng et al. 2003). NodD proteins bind nod-boxes as...