Distribution and characterization of phototrophic bacteria isolated from the water of Bietri Bay (Ebrie Lagoon, Ivory Coast)

Abstract

Phototrophic bacteria were observed forming a brown layer, at the interface between aerobic and anaerobic waters, in a stratified tropical lagoon (Bietri Bay, 5°15′ N, 4 °W, Ivory Coast). Within the brown layer (3.2–4 m depth), a stratification of different genera was observed. In the upper part purple bacteria developed, whereas green and brown Chlorobiaceae abounded mostly in a lower layer (3.5–4 m depth). Among the purple bacteria, some species were isolated and identified as Rhodopseudomonas palustris, Chromatium violascens, Chr. vinosum, and Chr. gracile. The green and brown sulfur bacteria were related to Chlorobium vibrioforme and Chl. phaeobacteroides. Chlorobium phaeobacteroides was the most abundant organism in the whole brown layer as well as in the deepest layer. As the phototrophic bacteria isolated were able to grow at different salt concentrations, the stratification observed could be explained by the gradients of sulfide and light. As shown by experimental data, purple bacteria grew under microaerobic conditions and used light intensities higher than green and brown sulfur bacteria whose growths were highly dependent on strict anaerobic conditions. During the dry season, holomixis involved the disappearance of the brown layer. Some phototrophic bacteria were found in the oxygenated water column. However, only brown Chlorobium was isolated. Although this species was found in a microaerobic environment in Bietri Bay, it never grew under microaerobic conditions in the synthetic media. This bacterium (Chlorobium phaeobacteroides strain BI 28) was able to use thiosulfate, as did Chl. vibrioforme isolated from the brown layer.