Metagenomics and metatranscriptomics uncover the microbial community associated with high S production in a denitrifying desulfurization granular sludge reactor.

The denitrification desulfurization process is a promising technology for elemental sulfur (S) production from sulfide containing wastewater. However, the microbial community associated with high S production still is not well studied. This study describes an efficient denitrification S production bioreactor based on inoculation with anaerobic granular sludge. At an optimal S/N molar ratio of 7:2, 80 % of the influent sulfide was transformed to high quality elemental sulfur with a purity of 92.5% while the total inorganic nitrogen removal efficiency was stable at ∼80%. Metatranscriptomic analysis found that community expression of the gene encoding the sulfide-quinone reductase (SQR) was 10-fold greater than that of the flavocytochrome-c sulfide dehydrogenase subunit B (fccB). Moreover, the expression level of SQR was also significantly higher than the Dsr gene encoding for dissimilatory sulfate reductase, which encodes a critical S oxidation enzyme. Metagenomic binning analysis confirmed that sulfide-oxidizing bacteria (SOB) utilizing SQR were common in the community and most likely accounted for high S production. An unexpected enrichment in methanogens and high expression activity of bacteria carrying out Stickland fermentation as well as in other bacteria with reduced genomes indicated a complex community supporting stable sulfide oxidation to S, likely aiding in performance stability. This study establishes this treatment approach as an alternative biotechnology for sulfide containing wastewater treatment and sheds light on the microbial interactions associated with high S production.