Biofilm Effects and MIC of Carbon Steel in Electrolytic Media Contaminated with Microbial Strains Isolated from Cutting-Oil Emulsions

Abstract

SAE 1020 carbon steel samples were tested in laboratory experiments using two different microbial strains isolated from cutting-oil emulsions: Pseudomonas fluorescens and Desulfovibrio vulgaris to evaluate their resistance to microbial attack. Several electrodes were immersed during different periods of time either in a Pseudomonas fluorescens or in a Desulfovibrio vulgaris pure culture and in a mixed culture of Pseudomonas fluorescens + Desulfovibrio vulgaris. The relationship between the corrosive attack and bacterial biofilms was assessed in each case by using electrochemical experiments complemented with scanning electron microscopic (SEM) observation of the samples. SEM observations show that the strains of bacteria used were able to attach to steel surface, leading to the formation of biofilms. Bacteria were mixed with corrosion products hindering the formation of a continuous protective passive layer. Electrochemical experiments showed that passivity breakdown of steel was facilitated in P. fluorescens contaminated media whereas repassivation was delayed in D. vulgaris contaminated media.