Probing the corrosion inhibiting role of a thermophilic Bacillus licheniformis biofilm on steel in a saline axenic culture

Abstract

The growth of some bacterial biofilms has been widely reported to have defined consequences on industrial metals, and their related metabolic activities affect the overall electrochemical process of these metals in any given medium. This work seeks to unravel the role of a thermophilic Bacillus licheniformis biofilm (an isolate from the Jazan spring of Saudi Arabia) on corrosion reduction for stainless steel (316 L grade) in a saline culture medium. Grown on the steel substrate, this bacterial biofilm and the nature of its extracellular polymeric substances have been probed chemically and electrochemically for their influences on the metal dissolution within an incubation period. Corrosion inhibition in the presence of varying concentrations (in CFU ml⁻¹) of this bacterium in the biotic-inoculate systems is explained in terms of corrosion resistance and capacitance of the biofilm. The corrosion rate of steel is found to reduce significantly in the saline culture medium within the range of concentrations of bacterium under study compared with the sterile control. This is attributed to the adhesion of a relatively compact and dense “beneficial” biofilm as well as the secretion of corrosion inhibiting substances from the bacterial biofilm as revealed during surface analysis.