PICRUSt2 functionally predicts organic compounds degradation and sulfate reduction pathways in an acidogenic bioreactor

? Over 70% reduction of sulfate was achieved for sulfate less than 12000 mg/L. ? The decrease of genes encoding (EC: 1.3.8.1) induced the accumulation of VFAs. ? The sulfate reduction genes were primary carried by genus Desulfovibrio. ? Sulfate favored assimilatory, but inhibited dissimilatory sulfate reduction process. For comprehensive insights into the influences of sulfate on performance, microbial community and metabolic pathways in the acidification phase of a two-phase anaerobic system, a laboratory-scale acidogenic bioreactor was continuously operated to treat wastewater with elevated sulfate concentrations from 2000 to 14000 mg/L. The results showed that the acidogenic bioreactor could achieve sulfate reduction efficiency of greater than 70% for influent sulfate content less than 12000 mg/L. Increased sulfate induced the accumulation of volatile fatty acids (VFAs), especially propionate and butyrate, which was the primary negative effects to system performance under the high-sulfate environment. High-throughput sequencing coupled with PICRUSt2 uncovered that the accumulation of VFAs was triggered by the decreasing of genes encoding short-chain acyl-CoA dehydrogenase (EC: 1.3.8.1), regulating the transformation of propanoyl-CoA to propenoyl-CoA and butanoyl-CoA to crotonyl-CoA of propionate and butyrate oxidation pathways, which made these two process hardly proceed. Besides, genes encoding (EC: 1.3.8.1) were mainly carried by order Clostridiales. Desulfovibrio was the most abundant sulfate-reducing bacteria and identified as the primary host of dissimilatory sulfate reduction functional genes. Functional analysis indicated the dissimilatory sulfate reduction process predominated under a low sulfate environment, but was not favored under the circumstance of high-sulfate. With the increase of sulfate, the assimilatory sulfate reduction process finally overwhelmed dissimilatory as the dominant sulfate reduction pathway in acidogenic bioreactor.