Dual anaerobic reactor model to study biofilm and microbiologically influenced corrosion interactions on UNS G10180carbon steel

Continual challenges due to microbial corrosion are faced by the maritime, offshore renewable and energy sectors. Understanding the biofilm and microbiologically influenced corrosion interaction is hindered by the lack of robust and reproducible physical models that reflect operating environments. A novel dual anaerobic biofilm reactor, using a complex microbial consortium sampled from a marine littoral sediment, was used to investigate biofilms under conditions that mimic the MIC environment of interest. Overall, the aim is to develop a reproducible bioreactor-based model for MIC that will be able to: (i) gain new scientific insight and mechanistic MIC understanding that will improve predictive measures including next-generation sequencing of the MIC-associated microbiome and (ii) progress the first standard model and biofilm-relevant test method for the industry. Moreover, the protocol incorporates a multi-disciplinary
approach, using multiple lines of evidence (MLOE) to gain a holistic understanding of biofilms and MIC. Electrochemical data indicated that the biofilm caused an increased incidence of localised pitting, resulting in active pit growth. Coupon analysis further confirmed that the biotic reactor had a significantly greater pit density, with a greater pit depth and size. Critically, DNA extraction and 16S rRNA amplicon sequencing demonstrated the principal biofilm activity was due to respiratory electrogens, specifically sulphate reducing and iron reducing bacteria. The dual anaerobic reactor model provided key insights into the different abiotic and biotic corrosion mechanisms under relevant environmental conditions. From this, we can start to rationalise an idealised representation of the mixed-species biofilm and the microbial mechanisms that lead to corrosion of carbon steel under anoxic conditions at the electrode/electrolyte interface. Using multiple lines of evidence to gain a holistic understanding of biofilms and MIC, more sustainable prevention and mitigation strategies can be designed. Hopefully, the novel
dual bioreactor protocol described here helps to progress the first standard model and biofilm-relevant test method for biocide efficacy testing within industry.

Acknowledgements:
This work was supported by the South Coast Biosciences Doctoral Training Partnership (SoCoBio DTP), a Biotechnology and Biological Sciences Research Council (BBSRC) funded research training programme (reference number BB/T008768/1) in affiliation with DNV, and the National Biofilms Innovation Centre (NBIC).