Direct involvement of an extracellular complex produced by a marine sulfate-reducing bacterium in deterioration of steel

A thermostable polysaccharide-protein complex capable of accelerating the deterioration of mild steel was produced by a marine strain of sulfate-reducing bacterium of the genus Desulfovibrio, and partially purified using low-pressure chromatography. This complex induced pitting of steel in oxic aqueous solution. The increase in the corrosion rate of steel exposed to the complex, determined using linear polarization resistance measurements, correlated with the inferred increase in production of exopolymer during the stationary phase of Desulfovibrio growth. Atomic absorption analysis confirmed that the complex caused rapid dissolution of iron from the steel surface, while light microscopy observations demonstrated that the complex caused grain boundary and intercrystalline attack of the steel, which did not occur in control solutions. The molecular mass of the corrosive complex, determined using gelfiltration, was greater than 200 kD.