., a chemolithoheterotroph isolated from sulfide and organic rich coastal waters off Peru.

Abstract

Members of the epsilonproteobacterial genus have been identified as potentially important sulfide oxidizers in marine coastal, seep and stratified basin environments. In the highly productive upwelling waters off the coast of Peru, cells comprised 3-25% of the total microbial community at a near-shore station where sulfide concentrations exceeded 20 μM in bottom waters. From the chemocline where the population exceeded 10 cells ml, and where high rates of denitrification (up to 6.5 ± 0.4 μM N d) and dark carbon fixation (2.8 ± 0.2 μM C d) were measured, we isolated a previously uncultivated species - (BCCM LMG-31510) Genomic analysis showed that possesses genes encoding for sulfide oxidation and denitrification pathways, but lacks the ability to fix CO via autotrophic carbon fixation pathways. Genes encoding transporters for organic carbon compounds, however, were present in the genome. Physiological experiments demonstrated that grew best on a mix of sulfide, nitrate and acetate. Isotope labeling experiments further verified that completely reduced nitrate to N and assimilate acetate, but did not fix CO, thus coupling heterotrophic growth to sulfide oxidation and denitrification. Single-cell nanoSIMS analysis of samples taken from shipboard isotope labeling experiments also confirmed that the spp. population did not substantially fix CO The efficient growth yield associated with the chemolithoheterotrophic metabolism of may allow this species to rapidly bloom in eutrophic and sulfide-rich waters off the coast of Peru. Our multidisciplinary approach provides new insights into the ecophysiology of a newly-isolated environmental species, as well as the physiological flexibility within the genus and sulfide-oxidizing, denitrifying microbial communities within oceanic oxygen minimum zones (OMZs). The chemolithoheterotrophic may play a substantial role in the diverse consortium of bacteria that is capable of coupling denitrification and fixed nitrogen loss to sulfide oxidation in eutrophic, sulfidic coastal waters. With increasing anthropogenic pressures on coastal regions, e.g. eutrophication and deoxygenation (D. Breitburg, et al., 359:eaam7240, 2018 DOI: 10.1126/science.aam7240), niches where sulfide-oxidizing, denitrifying heterotrophs such as thrive are likely to expand.