THE USE OF BIOCIDES TO CONTROL SULFATE-REDUCING BACTERIA IN BIOFILMS ON MILD-STEEL SURFACES

Three different types of biocides, viz, formaldehyde (FM), glutaraldeh yde (GA) and isothiozolone (ITZ) were used to control planktonic and s essile populations of two marine isolates of sulphate-reducing bacteri a (SRB). The influence of these biocides on the initial attachment of cells to mild steel surfaces, on subsequent biofilm formation and on t he activity of hydrogenase enzymes within developed biofilms was evalu ated. In the presence of biocides the rate and degree of colonization of mild steel by SRB depended on incubation time, bacterial isolate an d the type of biocide used. Although SRB differed in their susceptibil ity to biocides, for all isolates the biofilm population was more resi stant to the treatment than the planktonic population. GA showed highe st efficiency in controlling planktonic and sessile SRB compared with the other two biocides. The activity of the enzyme hydrogenase measure d in SRB biofilms varied between isolates and with the biocide treatme nt. No correlation was found between the number of sessile cells and h ydrogenase activity.