Identification of microbes isolated with test kits through culture-dependent and metabarcoding techniques for assessment of microbial corrosion

Abstract

• The diversity of microbes in biofilms/orange tubercles was narrowed through the use of various test kits. • Metabarcoding of enriched biomass confirmed the kits’ selection of microbial phenotypes. • Kit enrichment is useful for isolating specific bacteria for biocorrosion studies. Commercial diagnostic test kits are often used to confirm the presence of specific microbes associated with microbially influenced corrosion (MIC). We evaluated two of these kits in detail to assess their applications, by using biofilm/tubercle samples from a marine steel wall in a southern Australian harbour. The studied biofilms included different layers of orange tubercles (typically associated with accelerated low water corrosion (ALWC), with or without underlying pitting) and non-orange coloured (without underlying corrosion) biofilms. Two kit brands were used to assay sulfate reducing bacteria (SRB), acid producing bacteria and/or iron related bacteria. Significantly different microbial communities were revealed by the two kits. MIC/ALWC have often been attributed to SRB; however, the SRB kit results did not support such a relationship. The SRB abundance determined with both kits was higher in outer orange tubercles than inner orange tubercles (where any aggressive corrosion would have occurred). The non-orange biofilm, in contrast to the orange tubercles, generally had the highest numbers of SRB. We explored the microbes enriched by the test kits through preliminary pure culture isolation and 16S rRNA metabarcoding. Some microbes identified through kit enrichment were likely to have had the properties that the test kits were designed to detect, but several identified microbes did not have the target phenotype.