Hydrogen Metabolism by Decomposing Cyanobacterial Aggregates in Big Soda Lake, Nevada

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Abstract
H2 production by incubated cyanobacterial epiphytes occurred only in the dark, was stimulated by C2H2, and was inhibited by O2. Addition of NO3- inhibited dark, anaerobic H2 production, whereas the addition of NH4+ inhibited N2 fixation (C2H2 reduction) but not dark H2 production. Aerobically incubated cyanobacterial aggregates consumed H2, but light-incubated rates (3.6 .mu.mol of H2 g-1 h-1) were statistically equivalent to dark uptake rates (4.8 .mu.mol of H2 g-1 h-1), which were statistically equivalent to dark, anaerobic production rates (2.5-10 .mu.mol of H2 g-1 h-1). Production rates of H2 were 4-fold higher for aggregates in a more advanced stage of decomposition. Enrichment cultures of H2-producing fermentative bacteria were recovered from freshly harvested, H2-producing cyanobacterial aggregates. H2 production in these cyanobacterial communities appears to be caused by the resident bacterial flora and not by the cyanobacteria. In situ area estimates of dark H2 production by submerged epiphytes (6.8 .mu.mol of H2 m-2 h-1) were much lower than rates of light-driven N2 fixation by the epiphytic cyanobacteria (310 .mu.mol of C2H4 m-2 h-1).