[Acetate photometabolism in Ectothiorhodospira shaposhnikovii]

The cells of Ectothiorhodospira were cultivated under autotrophic conditions and assimilated 14C-acetate in the presence of bicarbonate. The label was incorporated rapidly into phosphoglyceric acid (PGA) and phosphorous esters (PE) of sugars, into compounds of the tricarboxylic acid cycle (TAC), aspartate, glutamate. After some time the content of the label became the highest in glutamate and decreased in other compounds. The same products were formed upon the assimilation of acetate by the cells cultivated in its presence. However, the amount of PGA and PE of sugars, especially those formed in the presence of sulphides, was less, and their curve had a positive slope. Fluoroacetate inhibited the incorporation of 14C from acetate in the cells and caused an increase of labeled citrate. Iodacetate inhibited almost completely the fixation of CO2 by the cells in the presence of sulphide; the fixation of carbon dioxide constituted about 60 percent of the control if both sulphide and acetate were present in the medium. Therefore, the assimilation of acetate by Ect. shaposhnikovii can be accomplished via the glyoxylate shunt and TAC, and also as a result of action of pyruvate synthase and the production of C4- and C5-organic acids with the participation of CO2. The pathways of acetate metabolism depend on the growth conditions and on the presence of sulphide in the medium.