From genes to Black Rust: genomic insights into corrosive methanogens

Within the past ten years, genetic evidence has been increasing for the direct role that microbes play in microbiologically influenced corrosion (MIC), also known as biocorrosion or biodeterioration. One prominent example is the correlation between the corrosion of metal and the presence of genes encoding an extracellular [NiFe]-hydrogenase (MIC hydrogenase) in the methanogenic archaeon, Methanococcus maripaludis. In this study, DNA sequencing and bioinformatic analysis were used to classify the MIC hydrogenase as belonging to a core set of genes, the MIC core, found so far in Methanococci and Methanobacteria classes of methanogens. Genetic evidence is provided for the mobilization of the MIC core via multiple mechanisms, including a horizontal gene transfer event from Methanobacteria to Methanococci and a newly described MIC-transposon. A detailed comparison of M. maripaludis genomes further pointed to the relevance that cell wall modifications involving N-glycosylation of S-layer proteins and the MIC hydrogenase likely play in methanogen-induced MIC (Mi-MIC). Microscopic analysis of corrosive methanogens encoding the MIC core indicated that Methanobacterium-affiliated strain IM1 can form extensive biofilms on the surface of corrosion products whereas individual cells of M. maripaludis Mic1c10 were only found localized to crevices in the corrosion layer. An updated model of Mi-MIC involving two modes of action is presented, which predicts that the propensity of cells to adhere to iron surfaces directly influences the rate of corrosion due to the localization of the MIC hydrogenase at the metal-microbe interface.