Page 63 - Microbial methane cycling in a warming world From biosphere to atmosphere Michiel H in t Zandt

relatively stable and can protect metal surfaces from further corrosion. Several recent studies focused on biological corrosion inhibition by natural corrosion protective layers (CPLs) (Zuo 2007; Videla and Herrera 2009; Esnault et al. 2011; Kip and van Veen 2015). Kip et al. detected limonite as candidate enriched mineral in the deposit layer (Kip et al. 2017). Furthermore, X- ray crystallography (XRD) analysis indicated wustite, calcite (CaCO3), siderite, and chukanovite [Fe2(CO3)(OH)2] in two mineral layers on Westerkade sheet piles (Kip et al. 2017).
16S rRNA gene-based phylogeny indicated the presence of an organic carbon-degrading consortium with enrichment of methanogens in deposit layers
The microbial compositions of BS, AS and DL were analyzed using 16S rRNA gene reads derived from 14 metagenomic data sets (Fig. 3; see also Table S2 in the supplemental material) and metagenome-assembled genomes (MAGs) (Table 1; see also Table S3). 16S rRNA gene- based analysis showed equal relative abundances of Bacillales (12.4%), Clostridiales (10.1%), and Flavobacteriales (5.8%) in all locations. Anaerolineales (2.9%), Betaproteobacteriales (2.4%), and Bacteroidales (1.9%) were also omnipresent, but overall relatively less abundant. The Bathyarchaeota phylum was more abundant in AS (14.7%), less abundant in DL (5.1%), and least abundant in BS (1.7%). The Bathyarchaeota relative abundances strongly differed between AS sample 1 and 2 (21.5% and 8.0%, respectively). This, however, could not be explained by geochemical properties (Table S1). The same pattern was found for the candidate phylum Atribacteria (JS1), which showed highest relative abundance in AS sample 1 (7.6%), but showed only low abundance in DL (0.9%) and was not detected in BS.
The potential organic matter-degrading community is dominated by Bacillales, Clostridiales and Flavobacteriales
The average total organic matter content was high (76%) in the metal sheet pile environment due to presence of peat sediments. Organic matter degrading guilds are essential for the formation of a methanogenic food web resulting in local changes that can induce CPL formation. Bacillales (12%), Clostridiales (10%), and Flavobacteriales (5.8%) were relatively highly abundant in all samples. These phyla are common members of soil microbial communities (Kuramae et al. 2012; Tracy et al. 2012; Pold, Melillo and DeAngelis 2015). A study on crude oil contaminated soils indicated their preference for organic carbon-rich
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