Functional bacteria and their genes encoding for key enzymes in hydrogen-driven autotrophic denitrification with sulfate loading

Functional bacteria and their genes encoding for key enzymes in hydrogen-driven autotrophic denitrification with sulfate loading were studied with metagenomic analysis. H2-based membrane biofilm reactor (H2-MBfR) was set-up for over 170-day operation. Sulfate loading with 25 (Stage 2) and 50 mg S/L (Stage 3) obviously inhibited nitrate reduction from 100 % (Stage 1 without sulfate loading) to below 90 %. Sulfate loading replaced Dechloromonas (Stage 1) with Thauera (Stage 2 and 3) as dominate genus, while both of them contained all functional genes encoding for denitrification enzymes. It was evident that genes encoding for nitrate reductase was the most abundant in all stages, but decreased with sulfate loading. Among them, napB accounted for the maximum proportion of nitrate reductase, and ranged from 3.4 x 10-4 to 1.4 x 10-4 and 1.5 x 10-4 with SO2-4 loading. This study suggests sulfate loading inhibited autotrophic denitrification, especially suppressing Dechloromonas and their functional gene, napB.