152 Chapter 5 Table 1. Methyl-coenzyme M reductase (MCR) complex and nitrate reductase (narG) gene transcript expression from “Ca. Methanoperedens”. Methyl-coenzyme M reductase alpha subunit [EC:2.8.4.1] (mrcA), methyl-coenzyme M reductase gamma subunit [EC:2.8.4.1] (mcrG), methyl-coenzyme M reductase subunit D (mcrD), methyl-coenzyme M reductase beta subunit (mcrB) [EC:2.8.4.1]. Padj<0.05 is indicated in bold. Condition differences (T0-T1, T0-T2 and T0-T3) indicate log2 fold chain (FC) values. “NA” (Not Available). Gene (contig) T0-T1 T0-T2 T0-T3 mcrA (812_16) 2.31 -0.59 -2.31 mcrG (812_17) 2.20 -0.50 -1.99 mcrD (812_18) 2.23 -0.86 -2.11 mcrB (812_19) 2.09 -0.31 -1.92 narG (750_30) 3.96 -1.46 -5.65 Rare phyla apparently detoxified sulfide via Sqr and FccAB during the first sulfide exposure (T0-T1) To determine the potential for sulfide detoxification/oxidation across conditions, we investigated the sulfide quinone oxidoreductase transcripts (sqr) across all MAGs (Supplementary Table 3). We observed that the rare microbial community, that is, not belonging to the top > 4% MAGs (Figure 1), was most likely responsible for the the most significantly changed (Padj<0.05 and log2FC min 2) transcripts for the first step of sulfide oxidation (Table 2). MAGs “Nordella 1”, “Hypomicrobium 1”, “Burkholderiales g SHXO01”, “Rubrivivax”, “Xanthobacteraceae” and others, probably catalyzed the first step of sulfide oxidation from T0 to T1. Conversely, from T0 to T2 (downward trend, non-significant) and T0 to T3 (mostly significant), almost all MAGs, except for “Hyphomicrobiaceae g AWTP1 13” showed lowered expression values for sqr.
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