SIMULTANEOUS PHOTOTROPHIC AND CHEMOTROPIC GROWTH IN THE PURPLE SULFURBACTERIUM THIOCAPSA-ROSEOPERSICINA M1

The anoxygenic phototrophic purple sulfur bacterium Thiocapsa roseoper sicina was grown in illuminated continuous cultures with thiosulfate a s growth limiting substrate. Aeration resulted in completely colorless cells growing chemotrophically, whereafter the conditions were change d to a 23 h oxic/1 h anoxic regime. After 11 volume changes at a dilut ion rate of 0.031 h(-1) (35% of mu(max)) a time dependent equilibrium was established. During the 23 h oxic periods bacteriochlorophyll a sy nthesis (BChla) was not observed, whereas during the 1 h anoxic period s synthesis was maximal (i.e. 1.1 mu g (mg protein)(-1) h(-1)). As a r esult the BChla concentration gradually increased from zero to an aver age value over 24 h of 1.9 pg (mg protein)(-1). Concomitantly,the prot ein concentration increased from 13.9 mg l(-1) during continuous oxic conditions to 28.8 mg l(-1). For comparison, the protein concentration during fully phototrophic growth at an identical thiosulfate concentr ation in the inflowing medium was 53.7 mg l(-1) The specific respirati on rate was 8 mu mol O-2 (mg protein)(-1) h(-1) during full chemotroph ic growth and gradually decreased to 3.5 mu mol O-2 (mg protein)(-1) h (-1) after 11 volume changes at the regime employed. These data show t hat T. roseopersicina is able to simultaneously utilize light and aero bic respiration of thiosulfate as sources of energy. The ecological re levance of the data is discussed.