Microbial polysaccharides and corrosion

Polysaccharides were extracted from culture supernatants and biofilms on mild steel surfaces incubated for 7 and 28 days in pure and mixed cultures of Pseudomonas fluorescens and Desulfovibrio desulfuricans P. fluorescens produced the highest quantities of free extracellular polysaccharides (EPS) but yielded the lowest hexose content in biofilms. The major neutral hexoses detected in all extracted polysaccharides were glucose and mannose, glucose being prevalent in biofilms and mannose in free EPS. Uronic acids were found only in biofilm polysaccharides.

Scanning electron microscopy and kinetic polarisation studies showed that little corrosion occurred on mild steel incubated in P. fluorescens cultures. High levels of corrosion were seen in mixed and, to a somewhat greater extent, in pure D. desulfuricans cultures. Extracellular polysaccharides on metal surfaces help to maintain the structure of the biofilm and in this way may serve to facilitate corrosion. There is no correlation between the levels of free EPS and corrosion.