New insights in the metabolic functions of freshwater sulfate reducing communities during steel corrosion by biophysicochemical, 16S rRNA gene sequence and metaproteomic analysis

Abstract

To date, the focus of microbially induced corrosion (MIC) studies has largely been on marine environments. In this study, biocorrosion of steel enrichment cultures from a freshwater corrosion site was investigated under sulfate reducing conditions. Biomass and metabolic processes were monitored by measuring the time-dependent biophysicochemical parameters and with Fe⁰ (steel) as the sole electron source, or with H₂ as control. Although yields and sulfate reduction rates were higher with H₂ due to its greater bioavailability, the yield coefficients indicated that bacterial growth with Fe⁰ was equally efficient. Upon imaging of the steel surface by SEM, patches of cells embedded in an iron sulfide matrix on top of larger carbonate and phosphate minerals were observed. Cell number determination indicated that the cells on the steel surface constituted only a minor proportion (<4%) of the total counts. The 16S rRNA gene sequencing revealed the enrichment of sulfate reducers next to acetogens, indicating a syntrophic relationship. In compliance with biophysicochemical analysis and estimated yield coefficients, metaproteomics indicated no major differences in the pathways of energy metabolism between treatments with H₂ and Fe⁰. Highly abundant proteins namely periplasmic hydrogenases and c-cytochromes associated with H₂-mediated electron transfer coupled to dissimilatory sulfate reduction indicated this mechanism to be dominant (except for a few putative outer membrane proteins identified with Fe⁰). In conclusion, using a multiphasic approach including metaproteomics to elucidate metabolic pathways improved the overall understanding of microbial processes associated with freshwater MIC.