(175n) Mechanisms of Microbially Influenced Corrosion Enabled By Acidithiobacillus Ferrooxidans

Acidithiobacillus ferrooxidans are acidophilic chemolithoautotrophic bacteria that are able to oxidize iron and/or sulfur¹. They are commonly associated with metallic, sulfidic ores and the acid mine drainages that result because of the acid generated from the oxidation of these minerals. These and related microorganisms are key players in commercial biomining operations as they generate ferric iron which is able to oxidize copper and other metals from sulfidic ore deposits. There is also increasing interest in developing these cells for urban biomining, bioremediation of contaminated sites, and recycling of waste metals from e-waste and spent batteries. In these applications, there are conditions and materials that create resistance to microbial oxidation and thus, new strategies are needed to enhance these capabilities.

Microbially influenced corrosion (MIC) is a process that affects a variety of industries with severe economic consequences. There are many microbes that can participate in a range of mechanisms leading to MIC, and there is great interest in understanding and inhibiting these interactions. However, many of the characterized conditions for MIC involve anoxic environments and anaerobic bacteria. Despite the relatively mature understanding of role of A. ferrooxidans in biomining, the role that these cells can play in MIC is poorly understood. Therefore, we have set out to determine aerobic conditions where A. ferrooxidans can contribute to MIC. Ferrous iron is readily oxidized by the cells to ferric iron which is a potent oxidant that can cause corrosion of most metals and alloys, except for stainless steel. We have uncovered a mechanism of aggressive corrosive attack on SS304 and SS316 steels involving the in situ production of thiosulfate in the presence of chloride². Beyond the dominant players of thiosulfate, sulfate, and chloride which are known to control the extent of pitting corrosion at circumneutral or alkaline pH in the paper industry, ferric iron and proton concentrations are key species important in acidic environments controlling the severity of corrosion mediated by A. ferrooxidans.

Therefore, we are developing strategies to enhance MIC by A. ferrooxidans and these insights may be used in the future to inhibit MIC in different environments. By genetically engineering A. ferrooxidans with tools we have developed and modulating the activity of the native sulfur metabolism, the complex interactions between the sulfur cycle and MIC are being explored and enhanced^3-5. The latest results involving the genetic control of corrosion events by A. ferrooxidans will be presented.

1. Banerjee I, Burrell B, Reed C, West AC, & Banta S. (2017). Metals and minerals as a biotechnology feedstock: engineering biomining microbiology for bioenergy applications. Curr Opin Biotechnol 45:144-155.
2. Inaba Y, West AC, & Banta S. Microbially influenced corrosion of stainless steel enhanced via pyrite oxidation by Acidithiobacillus ferrooxidans. (In Preparation).
3. Kernan T, Majumdar S, Li X, Guan J, West AC, & Banta S. (2016). Engineering the iron-oxidizing chemolithoautotroph Acidithiobacillus ferrooxidans for biochemical production. Biotechnol Bioeng 113(1):189-197.
4. Kernan T, West AC, & Banta S. (2017). Characterization of endogenous promoters for control of recombinant gene expression in Acidithiobacillus ferrooxidans. Biotechnol Appl Biochem 64(6):793-802.
5. Inaba Y, Banerjee I, Kernan T, & Banta S. (2018). Transposase-Mediated Chromosomal Integration of Exogenous Genes in Acidithiobacillus ferrooxidans. Appl. Environ. Microbiol. 84(21).