Polysulfide utilization by Thiocapsa roseopersicina

The purple sulfur bacterium Thiocapsa roseopersicina, being the dominant anoxygenic phototroph in microbial mats, was tested for growth on polysulfide as the electron donor for carbon dioxide fixation. Data collected in continuous cultures revealed _max to be 0.065 h^-1 and the saturation affinity constant K_s to be 6.7 M. The value of the inhibition constant K_i was estimated in batch cultures and was found to be approximately 1100 M. When grown on monosulfide, the organism was capable of trisulfide utilization without lag. Monosulfide-limited growth was established to have a _max of 0.091 h^-1 and K_s of 8.0 M. Field observations revealed polysulfide, present at supra-optimal concentrations, as a major pool of reduced sulfur in a laminated marine sediment ecosystem.Non-standard abbreviations DLP Direct Linear Plot - TS Total Sugar - SS Structural Sugar - P Protein - R_R concentration of growth limiting nutrient in reservoir vessel - S_nutrient residual concentration of growth-limiting nutrient in the culture vessel - S_{sulfur compound} concentration of sulfur in the corresponding compound - D dilution rate - _max maximum specific growth rate - K_s saturation constant - K_i inhibition constantDedicated to Prof. Dr. Norbert Pfennig on the occasion of his 65th birthday