Two metabolic stages of SRB strain Desulfovibrio bizertensis affecting corrosion mechanism of carbon steel Q235

Desulfovibrio bizertensis (D. bizertensis), an SRB isolated and cultured from the rust layer of the South China Sea, is widespread in the corrosive microbial communities on steel surface. Although the corrosion mechanism of SRB was widely studied, the mechanism of different metabolic stages inducing corrosion was still unclear. In this work, D. bizertensis was used to study the corrosion process of carbon steel Q235 at different metabolic stages by surface analysis and electrochemical methods. Combined with the metabolic process of SRB, corrosion pits of carbon steel could be influenced by two stages. In the first stage, the rapid growth of planktonic D. bizertensis cells in culture medium was accompanied by quick consumption of the electron donor (lactate) till complete consumption. D. bizertensis cells began to adhere to Q235 surface and promote anodic dissolution of iron. In the second stage, the growth of planktonic cells was suppressed, thus the colonized D. bizertensis cell in the pitting could obtain energy directly from Fe(0) through DET, which would further aggravate pitting corrosion and the maximum depth of the pits approached 15.7 µm. Sulfides produced by D. bizertensis metabolism would accumulate on steel coupon and form FeS coverage. Thus D. bizertensis could survive for a long time in this conductive FeS particles network. Electrochemical results showed the promotion effect of D. bizertensis on cathodic reaction, and the values of R_ct in the SRB medium were much lower than that in the sterile medium.