H2-producing bacterial communities from a heat-treated soil inoculum

Hydrogen gas (similar to 60% H-2) was produced in a continuous flow bioreactor inoculated with heat-treated soil, and fed synthetic wastewater containing glucose (9.5 g l(-1)). The pH in the bioreactor was maintained at 5.5 to inhibit consumption of H-2 by methanogens. The objective of this study was to characterize bacterial communities in the reactor operated under two different hydraulic retention times (HRTs of 30-h and 10-h) and temperatures (30 degreesC and 37 degreesC). At 30-h HRT, the H-2 production rate was 80 ml h(-1) and yield was 0.91 mol H-2/ mol glucose. At 10-h HRT, the H-2 production rate was more than 5 times higher at 436 ml h(-1), and yield was 1.61 mol H-2/mol glucose. Samples were removed from the reactor under steady-state conditions for PCR-based detection of bacterial populations by ribosomal intergenic spacer analysis (RISA). Populations detected at 30-h HRT were more diverse than at 10-h HRT and included representatives of Bacillaceae, Clostridiaceae, and Enterobacteriaceae. At 10-h HRT, only Clostridiaceae were detected. When the temperature of the 10-h HRT reactor was increased from 30 degreesC to 37 degreesC, the steady-state H-2 production rate increased slightly to 463 ml h(-1) and yield was 1.8 mol H-2/mol glucose. Compared to 30 degreesC, RISA fingerprints at 37 degreesC from the 10-h HRT bioreactor exhibited a clear shift from populations related to Clostridium acidisoli (subcluster Ic) to populations related to Clostridium acetobutylicum ( subcluster Ib).