GROWTH AND METABOLISM OF THE PURPLE SULFUR BACTERIUM THIOCAPSA-ROSEOPERSICINA UNDER COMBINED LIGHT DARK AND OXIC ANOXIC REGIMENS

The dominant purple sulfur bacterium of laminated sediment ecosystems in temperate environments, Thiocapsa roseopersicina, was cultivated in sulfide-limited continuous cultures (D=0.03 h-1) subjected to various combined diel regimen of aeration and illumination in order to simulate environmental conditions in microbial mats. For comparison, cultures were grown under similar illumination regimens but continuously anoxic conditions. Bacteriochlorophyll a (BChl a) and carotenoid synthesis was restricted to anoxic-dark periods and did not occur during oxic-light periods. An increase in the length of the oxic-light periods resulted in decreased pigment contents. However, phototrophic growth remained possible even at 20 h oxic-light/4 h anoxic-dark regimens. When anoxic conditions were maintained throughtout, BChl a synthesis occurred both during light and dark periods. Glycogen was synthesized in the light and degraded in the dark. Calculations showed that degradation of 1/4-1/5 of the glycogen is sufficient to account for the BChl a and carotenoid synthesis in the dark. The data showed that T. roseopersicina is very well adapted to cope with the combined oxygen and light regimes as they occur in microbial mats, which may explain the dominance of this bacterium in the purple layer of these sediment ecosystems. © 1990 Springer-Verlag.