Reduced sulfur and nitrogen compounds and molecular hydrogen as electron donors for anaerobic carbon di oxide photo reduction in anacystis nidulans
Archives of Microbiology 119(3): 313-322
ISSN/ISBN: 0302-8933 DOI: 10.1007/bf00405412
Photosynthesis by A. nidulans was studied in presence of reduced S or N compounds, or of H2. O2 evolution and CO2 fixation were depressed by sulfide, sulfite, cysteine, thioglycollate, hydroxylamine and hydrazine. Sulfite, cysteine and hydrazine inhibited O2 evolution much more strongly than CO2 fixation, indicating ability to supply electrons for CO2 photoreduction; DCMU [dichlorophenyl dimethylurea] suppressed these photoreductions. Some anoxygenic photosynthetic CO2 fixation insensitive to DCMU was found with sulfide, thiosulfate and hydrogen. Emerson enhancement studies confirmed that sulfite, cysteine and hydrazine acted on photosystem II, while photoreduction supported by sulfide, thiosulfate and H2 needed photosystem I only. Sulfite was photooxidized to sulfate, sulfide to elemental S, and thiosulfate to sulfate plus elemental S; the S accumulated inside the cells. Results on the stoichiometries of the photoreductions were consistent with the photooxidation products determined. Inhibitor studies suggested photosynthetic CO2 fixation through the Calvin cycle. While photoreduction by all reductants used was constitutive in Anacystis, the process was stimulated by anaerobic preincubation with the reductants only in the cases of H2 and thiosulfate; this adaptation was prevented by chloramphenicol and by O2. Anaerobic photoautotrophic growth of Anacystis was not observed; the increase in dry weight with H2 and thiosulfate was not accompanied by cell multiplication or by an increase in chlorophyll content. Parallel short-term experiments with Chlorella did not reveal any constitutive photoreduction in this eukaryotic alga.