Growth of the phototrophic purple sulfur bacterium Thiocapsa roseopersicina under oxic/anoxic regimens in the light

Abstract

The phototrophic purple sulfur bacterium Thiocapsa roseopersicina was grown in sulfide-limited continuous cultures exposed to oxic/anoxic regimens in continuous light. Synthesis of bacteriochlorophyll a (BChl a) did not occur during the oxic periods, but started immediately upon the creation of anoxic conditions. In contrast, protein synthesis continued during both oxic and anoxic periods. Consequently, the specific content of BChla fluctuated. Despite the presence of oxygen and the fluctuating BChl a content, growth occurred predominantly in a phototrophic mode and respiration was virtually zero. BChl a synthesis continued at high rates during anoxic periods, thus compensating for the lack of synthesis during oxic periods. When cultivated under regimens with oxic periods shorter than 12 h the highest specific BCh a content was 27 μg·mg − protein. In contrast, when cultivated under regimens with oxic periods longer than 12 h the specific BChl a content was always lower than 27μg·mg − length of the oxic periods. During the anoxic periods, BChl a synthesis occurred at the maximal velocity of 1.2 μg·mg −1 protein·h −, but the length of the anoxic periods was not sufficient to allow the BChl a content to reach the maximum level. Cultivation under continuously oxic conditions eventually resulted in pigmentless cells growing chemolithotrophically. The BChl a synthesizing ability was not lost during prolonged exposure to oxygen. It was concluded that T. roseopersicina is very well adapted to oxic/anoxic cycles.