Prokaryotic Epibionts

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 a tight association. In some cases, the epibionts seem to be responsible for the locomotion of the host (Cleveland and Grimstone 1964; Tamm 1982; see also Chapter by H. König, L. Li, M. Wenzel, and J. Fröhlich). Advances in molecular ecology made it possible to elucidate the identity of the microorganisms involved in these associations and the specificity of these symbioses.

Epibiont Bacterial

Fig. 1. 'Candidatus Vestibaculum illigatum' colonizing Staurojoenina sp. from Neo-termes cubanus. A Scanning electron micrograph illustrating the whole cell covered with rod-shaped and spirochetal epibionts (b bacteria, f flagella). B Scanning electron micrograph of the flagellate surface, showing the morphotype and the dense arrangement of 'Vestibaculum illigatum'. Arrows point to cells in division stages. C Transmission electron micrograph of a thin section of the flagellate cell, showing (1) the Gram-negative cell wall structure of 'Vestibaculum illigatum' (dl diffuse layer, om outer membrane, im inner membrane), (2) the presence of special attachment sites (arrow), and (3) the presence of 'Vestibaculum illigatum' in vacuoles within the cytoplasm of the host cell. (Figures from Stingl et al. 2004)

Fig. 1. 'Candidatus Vestibaculum illigatum' colonizing Staurojoenina sp. from Neo-termes cubanus. A Scanning electron micrograph illustrating the whole cell covered with rod-shaped and spirochetal epibionts (b bacteria, f flagella). B Scanning electron micrograph of the flagellate surface, showing the morphotype and the dense arrangement of 'Vestibaculum illigatum'. Arrows point to cells in division stages. C Transmission electron micrograph of a thin section of the flagellate cell, showing (1) the Gram-negative cell wall structure of 'Vestibaculum illigatum' (dl diffuse layer, om outer membrane, im inner membrane), (2) the presence of special attachment sites (arrow), and (3) the presence of 'Vestibaculum illigatum' in vacuoles within the cytoplasm of the host cell. (Figures from Stingl et al. 2004)

Prokaryotes Climate

Fig. 2. Symbiotic bacteria attached to the oxymonad flagellate Streblomastix strix from Zootermopsis angusticollis. A Scanning electron micrograph showing a S. strix cell covered with epibiotic bacteria. Bar 5 |m. B Transmission electron micrograph of a thin section of a S. strix cell. The host is organized as a central core (c) with seven thin vanes radiating outward (arrows). Seven to ten epibiotic bacteria with distinctive morphotypes were clustered around each vane (arrowheads). Bar 1 |m. (Figure from Leander and Keeling 2004)

Fig. 2. Symbiotic bacteria attached to the oxymonad flagellate Streblomastix strix from Zootermopsis angusticollis. A Scanning electron micrograph showing a S. strix cell covered with epibiotic bacteria. Bar 5 |m. B Transmission electron micrograph of a thin section of a S. strix cell. The host is organized as a central core (c) with seven thin vanes radiating outward (arrows). Seven to ten epibiotic bacteria with distinctive morphotypes were clustered around each vane (arrowheads). Bar 1 |m. (Figure from Leander and Keeling 2004)

Fig. 3. Transmission-electron micrographs of ultra-thin sections of Trichonympha agilis (A) and Pyrsonympha vertens (B) showing the ultrastructure of Termite Group 1 (TG-1) bacteria, which are very abundant in the cytoplasm of these flagellate species. TG-1 cells are surrounded by two membranes; the outer-most membrane forms tube-like elongations at the tapered cell poles (arrow in A). g glycogen. Bars 0.2 |m. (Figure from Stingl et al. 2005)

Fig. 3. Transmission-electron micrographs of ultra-thin sections of Trichonympha agilis (A) and Pyrsonympha vertens (B) showing the ultrastructure of Termite Group 1 (TG-1) bacteria, which are very abundant in the cytoplasm of these flagellate species. TG-1 cells are surrounded by two membranes; the outer-most membrane forms tube-like elongations at the tapered cell poles (arrow in A). g glycogen. Bars 0.2 |m. (Figure from Stingl et al. 2005)

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