Inhibition of metal corrosion by bacteria

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Abstract
Corrosion inhibition of steel (ASTM A619) by two marine isolates, Pseudomonas sp.S9 and Serratia marces‐cens EF190, was investigated by weight loss measurements of metal coupons placed in static batch cultures. Artificial seawater with (VNSS) and without (NSS) nutrients was used. The effects of bulk‐ and surface localised cells were compared. Adhesion of cells to the metal surface was quantified microscopically. Corrosion was inhibited in suspensions of high cell density (109.ml−1). The protective effect remained when the metal coupons were separated from the cells by a dialysis membrane. Also, a monolayer of cells on the metal surface lowered the corrosion if immersed in a suspension of sterile filtered spent NSS, but not in fresh sterile NSS. When the metal in fresh sterile NSS was coated with stearic acid however, the attached cells exerted a limited protection. Corrosion of metal coupons occurred in cell‐free suspensions of both VNSS and NSS and in low cell‐density (106.ml−1). Glutaraldehyde‐fixed cells (109.ml−1) did not inhibit corrosion. Protection is suggested to be caused by cellular metabolic activity, including a decrease of the oxygen content. The attached cells may also form a protective film which may lower the diffusion or corrosion products from the surface.