摘要：SummaryElectrotrophic microorganisms have not been well studied in extreme environments. Here, we report on the nitrate-reducing cathodic microbial biofilm from a haloalkaline environment. The biofilm enrichedviaelectrochemical approach under 9.5 pH and 20 g NaCl/L salinity conditions achieved−43.5±7.2μA/cm2current density and49.5±13.2%nitrate reduction efficiency via partial and complete denitrification. Voltammetric characterization of the biocathodes revealed a redox center with−0.294±0.003V(vs.Ag/AgCl) formal potential putatively involved in the electron uptake process. The lack of soluble redox mediators and hydrogen-driven nitrate reduction suggests direct-contact cathodic electron uptake by the nitrate-reducing microorganisms in the enriched biofilm. 16S-rRNA amplicon sequencing of the cathodic biofilm revealed the presence of unreportedPseudomonas, Natronococcus,andPseudoalteromonasspp. at31.45%,11.82%,and9.69%relative sequence abundances, respectively. The enriched nitrate-reducing microorganisms also reduced nitrate efficiently using soluble electron donors found in the lake sediments, thereby suggesting their role in N-cycling in such environments.Graphical abstractDisplay OmittedHighlights•Enrichment of haloalkaliphilic nitrate-reducing microbial biofilm at the cathode•Cathodic reduction current corresponded to the nitrate reduction process•Pseudomonas,Natronococcus, andPseudoalteromonas spp.enriched in the cathodic biofilm•Enriched culture reduced nitrate efficiently with soluble electron donor sourcesBio-electrochemistry; Microbiofilms
