Introducing a "core steel microbiome" and community functional analysis associated with microbially influenced corrosion.

Microorganisms attached to aquatic steel structures play key roles in nutrient cycling and structural degradation processes. Corrosion-causing microbes are often the focus of studies involving microbially influenced corrosion, yet the roles of remaining community members remain unclear. This study characterizes the composition and functional potential of a 'core steel microbiome' across stainless steel types (304 and 316) and historic shipwreck steel along salinity gradients in North Carolina estuaries. We found higher phylogenetic evenness and diversity on steel surfaces compared to sediment, and at lower salinities. The core steel microbiome was composed of heterotrophic generalist taxa, and community composition was most strongly influenced by salinity. Substrate type was a secondary factor becoming more influential at higher salinities. The core steel microbiome included members of Sphingobacteriia, Cytophagia, Anaerolineaceae, Verrucomicrobiaceae, Chitinophagaceae, and Rheinheimera. While salinity differences led to phylogenetic separations across microbial community assemblages, functional genes were conserved across salinity and steel type. Generalist taxa on steel surfaces likely provide functional stability and biofilm protection for the community with limited functional trade-offs compared to surrounding environments. Further, characterization of a core steel microbiome increases the understanding of these complex steel surface microbial communities and their similarities to core microbiomes in other environments.