Competition between anoxygenic phototrophic bacteria and colorless sulfur bacteria in a microbial mat


H. van Gemerden, Department of Microbiology, University of Groningen, Kerklaan 30, 9751 NN Haren, The Netherlands.


Abstract The populations of chemolithoautotrophic (colorless) sulfur bacteria and anoxygenic phototrophic bacteria were enumerated in a marine microbial mat. The highest population densities were found in the 0–5 mm layer of the mat: 2.0 × 109 cells cm−3 sediment, and 4.0 × 107 cells cm−3 sediment for the colorless sulfur bacteria and phototrophs, respectively. Kinetic parameters for thiosulfate-limited growth were assessed for Thiobacillus thioparus T5 and Thiocapsa roseopersicina M1, both isolated from microbial mats. For Thiobacillus T5, growing at a constant oxygen concentration of 43 μmol l−1, μmax was 0.336 h−1 and Ks 0.8 μmol l−1. Phototrophically grown Thiocapsa strain M1 displayed a μmax of 0.080 h−1 and a Ks of 8 μmol l−1 when anoxically grown under thiosulfate limitation. In a competition experiment with thiosulfate as electron donor, Thiocapsa became dominant during a 10-h oxic/14-h anoxic regimen at continuous illumination, despite the higher affinity for thiosulfate of Thiobacillus.