Characterisation of exopolymers produced by different isolates of marine sulphate-reducing bacteria

This study was undertaken to investigate the influence of carbon steel surfaces on the yield and composition of exopolymers (EPS) secreted by two different isolates of marine sulphate-reducing bacteria (SRB) recovered from severe corrosion failures and to establish whether the yield and the type of EPS varied between these isolates. SRB were purified and grown in the laboratory as static batch cultures with and without the presence of carbon steel surfaces. Characterisation of EPS harvested from the bulk phase of the cultures revealed the presence of carbohydrates, proteins and nucleic acids. Colorimetric and gas chromatographic analysis of EPS polysaccharides showed that although their composition was similar for both SRB isolates, they were synthesised in different quantities. Furthermore, the presence of carbon steel surfaces influenced the type of polysaccharide produced by the SRB. Examination of the EPS protein profiles has revealed the appearance of new bands in exopolymers harvested from bacterial cultures grown with carbon steel. The amount and type of nucleic acid in the EPS varied between the cultures. The results demonstrate the difference in EPS composition between SRB isolates and the ability of SRB to modify their physiological response in the presence of a carbon steel surface. The implication of such modification for the phenomenon of SRB influenced corrosion of carbon steel is discussed.