Microbial Communities Associated with Carbon Steel Corrosion in Model Seawater Compensated Fuel Ballast Tanks

Duplicate rotating reactors containing carbon steel coupons were inoculated with seawater and either a petro- or Fischer-Tropsch F76 or a mix of both fuels. Controls included reactors without fuel and reactors containing sterilized seawater and fuels. After 389 days, one replicate of each treatment received either heat-sterilized or non-sterile sediments. The reactors were disassembled after 730 days and the coupons, reactor fluids and sediment samples were obtained for sequencing analysis and assessed for evidence of corrosion.Dissolved O2 was not detected in any reactor after day 11, and differences in pH, ORP and corrosion rates (based on dissolved Fe and Mn) were observed by day 82. By these measures, reactors with fuel enhanced corrosion over seawater-amended controls. Addition of sediments caused pH to drop in the non-sterile seawater reactors, suggesting microbial activity was stimulated by exogenous organic carbon. SRA was generally insignificant, but transiently higher after sediment addition.Microbial profiles from the seawater and sediment inocula were more diverse than samples from the reactors. In general, microbial profiles from coupons were similar in that all contained a high % Deltaproteobacteria. Desulfovibrio dominated coupons from reactors without fuel, while coupons from reactors with fuel were more diverse and varied between replicates which received non-sterile rather than heat-treated sediments. The coupon communities from the 6 reactors that received non-sterile seawater and fuel were more similar to each other than to the fuel-unamended reactors, but the type of fuel did not determine the community profile. Compared to results from seawater-compensated fuel ballast tanks, a higher % Deltaproteobacteria and lower % aerobic hydrocarbon-degrading Gammaproteobacteria was typically observed in the reactors.