The anaerobic photodissimilation of acetate by Chlamydomonas reinhardii F-60 adapted to a hydrogen metabolism was studied utilizing manometric and isotopic techniques. The rate of photoanaerobic (N2) acetate uptake was approximately 20 moles per milligram chlorophyll per hour or one-half that of the photoaerobic (air) rate. Under N2, cells produced 1.7 moles H2 and 0.8 mole CO2 per mole of acetate consumed. Gas production and acetate uptake were inhibited by monofluoroacetic acid (MFA), 3-(3',4'-dichlorophenyl)-1,1-dimethylurea (DCMU) and by H2. Acetate uptake was inhibited about 50% by 5% H2 (95% N2 (3) suggested that acetate increased gas production by consuming ATP which regulated the unspecified sequence of reactions giving rise to CO2 and H2. Healey (18) modifying a mechanism put forward by Jones and Myers (20) to explain the Kok effect in blue-green algae, proposed a flow of electrons from acetate via the citric acid cycle into PSI resulting in the photoevolution of H2 from reduced Fd. The operation of an anaerobic and light-dependent citric acid cycle which affects the stoichiometric conversion of acetate to CO2 and H2 had been documented in the photosynthetic purple bacteria ( 13).The present communication summarizes the results of a detailed investigation of the anaerobic photometabolism of acetate by C. reinhardii F-60, with reference to stoichiometry of gas (CO2 and H2) production, incorporation into cellular components, and sensitivity of the process to a variety of inhibitors. The stoichiometric relationships observed, together with the isotopic distribution following assimilation of ["4C]acetate, constitute strong evidence for the conclusion that anaerobic carbon oxidation occurs in part through the reactions of the glyoxylate and citric acid cycles.
MATERIALS AND METHODSAlgal Growth Conditions. Chlamydomonas reinhardii (Dangeard) F-60, a mutant strain with an incomplete photosynthetic carbon reduction cycle but with an intact photosynthetic electron transport chain, was obtained from R. K. Togasaki, Indiana University. Cells were grown in batch cultures on an acetatesupplemented medium (14)