AN ATOMIC-FORCE MICROSCOPY STUDY OF THE BIODETERIORATION OF STAINLESS-STEEL IN THE PRESENCE OF BACTERIAL BIOFILMS

Atomic Force Microscopy (AFM), a technique requiring little or no preparation of biological samples prior to viewing and allowing observation of bacteria and bacterial exopolymers in their hydrated forms, has been used to elucidate the phenomena of stainless steel corrosion due to the development of bacterial biofilms. Biofilms formed by pure and mixed cultures of Pseudomonas aeruginosa, the sulphate-reducing bacterium Desulfovibrio gigas and a consortium isolated from a corroding, cast iron pipe carrying potable water were grown for 7 and 14 days in batch cultures at 25 degrees C on surfaces of stainless steel (316) coupons, polished to obtain a 1 mu m finish. Surfaces with biofilms present and removed were examined by AFM and by scanning electron microscopy (SEM). The study revealed that the greatest deterioration of steel, in a form of pitting corrosion, occurred in the presence of an isolated pipe consortium. The degree of corrosion observed in mixed cultures of P. aeruginosa and D. gigas was higher than that recorded in pure cultures of these bacteria. The advantage of using AFM as a qualitative method of biocorrosion assessment and its potential for quantitative analysis of micrabially influenced corrosion are emphasised.