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

Abstract

Hydrogen production by incubated cyanobacterial epiphytes occurred only in the dark, was stimulated by C(2)H(2), and was inhibited by O(2). Addition of NO(3) inhibited dark, anaerobic H(2) production, whereas the addition of NH(4) inhibited N(2) fixation (C(2)H(2) reduction) but not dark H(2) production. Aerobically incubated cyanobacterial aggregates consumed H(2), but light-incubated rates (3.6 mumol of H(2) g h) were statistically equivalent to dark uptake rates (4.8 mumol of H(2) g h), which were statistically equivalent to dark, anaerobic production rates (2.5 to 10 mumol of H(2) g h). Production rates of H(2) were fourfold higher for aggregates in a more advanced stage of decomposition. Enrichment cultures of H(2)-producing fermentative bacteria were recovered from freshly harvested, H(2)-producing cyanobacterial aggregates. Hydrogen production in these cyanobacterial communities appears to be caused by the resident bacterial flora and not by the cyanobacteria. In situ areal estimates of dark H(2) production by submerged epiphytes (6.8 mumol of H(2) m h) were much lower than rates of light-driven N(2) fixation by the epiphytic cyanobacteria (310 mumol of C(2)H(4) m h).