Enrichment of anaerobic methanotrophs in biotrickling filters using different sulfur compounds as electron acceptor

Anaerobic oxidation of methane (AOM) coupled to sulfate reduction is a biological process regulating the methane cycle with potential application in desulfurization of industrial wastewater using methane as an electron donor. However, it has been difficult to control and fully understand this process, mainly due to the slow-growing nature of the AOM-mediating microorganisms. A biotrickling filter (BTF) operating at ambient pressure and temperature was used to enrich microorganisms from a deep-sea anaerobic methane-oxidizing sediment (Alpha Mound, Gulf of Cadiz). Different sulfur compounds namely, sulfate, elemental sulfur, and thiosulfate were used as electron acceptors to understand their effects on the AOM, sulfate reduction rates, and the microbial community distribution. The highest AOM and sulfate reduction rates were obtained in the BTF fed with thiosulfate as the electron acceptor (∼0.4 mmol/[L·day]). Use of thiosulfate triggered the enrichment of sulfate-reducing bacteria (SRB) in the BTF, whereas the highest number of anaerobic methanotrophs (ANME) was visualized in the sulfate-fed BTF (ANME-2 43% of the total visualized archaea), where sulfate was reduced at a maximum rate of 0.3 mmol/[L·day]. This study shows that ANME and SRB obtained from deep-sea conditions (528 m below sea level) can be enriched in a BTF at ambient pressure and temperature with a relatively short start-up time (42 days).