Vibrio fischeri strains are specifically recruited from the seawater

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: [email protected])

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 (Boettcher and Ruby 1990). Furthermore, inoculation in the laboratory with bacteria closely related to V. fischeri, including V. harveyi and V. parahaemolyticus, fails to result in colonization (McFall-Ngai and Ruby 1991; Nyholm et al. 2000). In addition to this species-specific selection, strain-specific enrichment also occurs. Both visibly luminescent and non-visibly luminescent strains of V. fischeri co-exist in the seawater, but only the latter strains colonize the squid LO in nature (Lee and Ruby 1994b). This strict limitation on the species and strains of bacteria capable of colonizing the LO suggests that a specific exchange of signals must occur between the squid and the bacteria early during colonization.

Within hours of hatching, E. scolopes recruits V. fischeri from the surrounding seawater. The presence of bacteria or the bacterial cell wall component peptidoglycan in the seawater causes the squid to secrete mucus (Nyholm et al. 2002), allowing V. fischeri cells to aggregate near pores leading into the LO (Fig. 1). Other bacteria such as V. parahaemolyticus also exhibit the ability to aggregate in squid mucus, suggesting that E. scolopes does not distinguish between V. fischeri and other Gram negative bacteria at this stage (Nyholm et al. 2000). However, when both V. parahaemolyticus and V. fischeri are present, the latter organism becomes the dominant species in the aggregate (Nyholm and McFall-Ngai 2003), indicating that V. fischeri may participate in establishing specificity at this stage.

Fig. 1. Cartoon depicting the structure of and developmental changes in the juvenile squid LO during colonization. The position of the LO in a juvenile squid is shown on the left, while an enlarged cross section is shown on the right. The juvenile LO contains three pores on each side (six total), only one of which is depicted at the opening of the duct. Arrows indicate developmental events that occur within the first 4 days after exposure to V. fischeri. Dashed lines indicate an enlargement of the boxed area. V. fischeri cells are shown as black ovals aggregated in the mucus (depicted as wavy lines) outside the pore and in the crypt spaces (without flagella). This depiction of the light organ is based on Visick and McFall-Ngai (2000) and references described therein.

Vibrio Colonization Squid

Fig. 1. Cartoon depicting the structure of and developmental changes in the juvenile squid LO during colonization. The position of the LO in a juvenile squid is shown on the left, while an enlarged cross section is shown on the right. The juvenile LO contains three pores on each side (six total), only one of which is depicted at the opening of the duct. Arrows indicate developmental events that occur within the first 4 days after exposure to V. fischeri. Dashed lines indicate an enlargement of the boxed area. V. fischeri cells are shown as black ovals aggregated in the mucus (depicted as wavy lines) outside the pore and in the crypt spaces (without flagella). This depiction of the light organ is based on Visick and McFall-Ngai (2000) and references described therein.

volume and microvilli density „ j-

Was this article helpful?

0 0

Post a comment