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 μmol of H 2 g −1 h −1 ) were statistically equivalent to dark uptake rates (4.8 μmol of H 2 g −1 h −1 ), which were statistically equivalent to dark, anaerobic production rates (2.5 to 10 μmol of H 2 g −1 h −1 ). 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 μmol of H 2 m −2 h −1 ) were much lower than rates of light-driven N 2 fixation by the epiphytic cyanobacteria (310 μmol of C 2 H 4 m −2 h −1 ).