Is marine sediment the source of microbes associated with accelerated low water corrosion?

Accelerated low water corrosion (ALWC) is a form of microbiologically influenced corrosion (MIC) associated with the degradation of marine structures around the low tide water level. A better understanding of the role of microbes in this degradation and the source of these microbes is required to improve the prediction and mitigation of the costly failures occurring due to ALWC. The microbial communities present in a sediment sample and on an ALWC tubercle on adjacent steel sheet piling from a tidal estuary were studied using culture-based isolation and metabarcoding. A total of 43 pure cultures were isolated from the sediment using a variety of culture conditions. Phylogenetic analysis of their 16S rRNA genes placed them in the Actinobacteria, Bacteroidetes, Firmicutes, and Proteobacteria (Alphaproteobacteria and Gammaproteobacteria). 16S rRNA gene metabarcoding of the sediment and tubercle revealed similar microbial groups at varying relative abundances. No Deltaproteobacteria were isolated from the sediment but they were present in both samples according to metabarcoding and their high abundance (49.3%) in the tubercle could indicate an important functional role. Although some sediment isolates and operational taxonomic units from the metabarcoding have previously been associated with surface colonisation or biofilm formation in MIC, there was no strong evidence for the notion that the sediment adjacent to ALWC was the source of tubercle microbes. Further isolation strategies and functional investigations of representative bacteria at different stages of corrosion are being carried out for additional laboratory-based corrosion studies.