Metagenomics and metatranscriptomics uncover the microbial community associated with high S0 production in a denitrifying desulfurization granular sludge reactor

The denitrification desulfurization process is a promising technology for elemental sulfur (S-0) production from sulfide containing wastewater. However, the microbial community associated with high S-0 production still is not well studied. This study describes an efficient denitrification S-0 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 similar to 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-0 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-0 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-0, 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-0 production.