154 Chapter 5 transcript expression across all conditions and MAGs (Supplementary Table 3) (Padj<0.05 and log2FC min 2). Here, we observed similar trends to sqr, with general upregulation trends from T0-T1 vs downregulation from T0-T2 and T0-T3. MAGs “Desulfobacillus 2” and “Casimicrobiaceae g JACPUX01” fccA showed increased significant expression from T0-T1 and T0-T3, respectively (Supplementary Table 4). The rest of fccB or fccA transcripts got downregulated in almost all MAGs with significant expression from T0-T2 and T0-T3. All in all, the sulfide scavenging was most likely carried out by the rare community members indicated by upregulation of sqr and fccAB during the first sulfide exposure (Table 3 and Supplementary Table 4) with a general downregulation after long-term exposure for the same 0.5 mM sulfide pulse (Figure 2). This observation is suggestive of the overall response of the community towards more efficient processes or, alternative sulfur metabolism pathways. One example is the sulfite reductase that might be cycling sulfur through assimilatory or dissimilatory pathways (Susanti & Mukhopadhyay, 2012; Yu et al., 2018). The methanotrophic community activated sulfite reductase after longterm sulfide exposure (T2 and T3) We screened for sulfite detoxification potential by a query search of “Nitrite and sulfite reductase 4Fe-4S domain” (PFAM: PF01077.27) protein family genes in our metagenome (Supplementary Table 3). We found a total of 33 sulfite/nitrite reductase genes that were significantly up/downregulated upon sulfide exposure (Table 3). These sulfite/nitrite reductases were divided into four categories: dissimilatory sulfite reductase alpha (dsrA) or beta subunit (dsrB), large (nirB) or small (nirD) subunit of nitrite reductase (NADH), an assimilatory sulfite reductase (aSir) (IPR051329), an aSir- Group I Dissimilatory Reductase-Like Protein (aSir/DsrLP) (IPR045854) and, a Group III Dsr-LP sulfite reductase (IPR045169) of unknown physiological function. We found a marked increase and subsequent decrease for dsrAB expression during the first sulfide pulse and subsequent time points, coinciding with increased sqr and fccAB expression, respectively (Table 3). On the contrary, the assimilatory sulfite reductases from Group I Dsr-LP (IPR045854), assimilatory aSir, (IPR051329)
RkJQdWJsaXNoZXIy MTk4NDMw