Interactions between Perchlorate and Nitrate Reductions in the Biofilm of a Hydrogen-Based Membrane Biofilm Reactor

We studied the microbial functional and structural interactions between nitrate (NO3-) and perchlorate (ClO4-) reductions in the hydrogen (H-2)-based membrane biofilm reactor (MBfR). When H-2 was not limiting, ClO4- and NO3- reductions were complete, and the MBfR's biofilm was composed mainly of bacteria from the epsilon- and beta-proteobacteria classes, with autotrophic genera Sulfuricurvum, Hydrogenophaga, and Dechloromonas dominating the biofilm. Based on functional-gene and pyrosequencing assays, Dechloromonas played the most important role in ClO4- reduction, while Sulfuricurvum and Hydrogenophaga were responsible for NO3- reduction. When H-2 delivery was insufficient to completely reduce both electron acceptors, NO3- reduction out-competed ClO4- reduction for electrons from H-2 and mixotrophs become important in the MBfR biofilm. beta-Proteobacteria became the dominant class, and Azonexus replaced Sulfuricurvum as a main genus. The changes suggest that facultative, NO3--reducing bacteria had advantages over strict autotrophs when H-2 was limiting, because organic microbial products became important electron donors when H-2 was severely limiting.