131 Unraveling nitrogen, sulfur and carbon microbial bioreactor responses to stress N. versatile” and anammox bacteria for nitrite and nitric oxide. These results are contrasting to estuary ecosystems in which anammox activity could be sustained by DNRA, positively correlating to sulfide and sediment organic carbon content (Lisa et al., 2014). High sediment organic carbon to nitrate ratio and ferrous iron availability have been reported to favor DNRA over denitrification in estuary ecosystems (Kessler et al., 2018). Having methane as the only organic carbon source (at saturation) and a high nitrate load (3 mmol/day) could have thus modulated DNRA activity to become insufficient to sustain anammox and changed microbial community structure. We also targeted the enrichment of sulfide-oxidizing NO reducers while characterizing microbial community responses to sulfide and NO toxicity. We found genomic potential and transcriptional evidence for this metabolism in “Ca. Nitrobium versatile”, the dominant microorganism in the bioreactor community before the ammonium removal experiment (Figure 3). However, “Ca. Nitrobium versatile” became a rare community member after this experiment and could no longer be enriched. Instead, MAG 65 Thiohalobacteraceae, representing an organism likely performing sulfide oxidation coupled to denitrification, increased in abundance (Figure 3, 4 and 5). The sulfide and NO toxicity experiment revealed unusual resiliency of “Ca. M. nitroreducens” and “Ca. M. tolerans”, which persisted as the most abundant community members (Figure 3) even though methane and nitrate were no longer provided to the reactor for the 7 weeks of the experiment, consistent with the downregulation of mcrA and pmoA (Figure 5, Supplementary Table 3). Given that the hydraulic retention time of the reactor was 5 days, it is unlike that our sequencing results and the dominance of “Ca. M. nitroreducens” and “Ca. M. tolerans” simply reflect older decaying biomass, which would have been removed. MAG 65 Thiohalobacteraceae, MAG 44 Plantomycetes 1, MAG 60 Thermoanaerobaculia 1, and “Ca. Kuenenia stuttgartiensis” followed as the most abundant community members at the end of the experiment. While the first three could make use of sulfide or organic carbon from decaying biomass as electron donors and residual nitrate or nitrite and nitric oxide as electron acceptors, “Ca. K. stuttgartiensis” could have used ammonium generated from decaying biomass and 4
RkJQdWJsaXNoZXIy MTk4NDMw