Sub-minimum inhibitory concentration of tetrakis(hydroxymethyl)phosphonium sulfate enhances biocorrosion of carbon steel by Pseudomonas aeruginosa

Biocide treatments are commonly employed to mitigate unwanted microbial activities in industrial water systems. This study illuminates the intriguing phenomenon wherein sub-minimum inhibitory concentration (sub-MIC) of tetrakis(hydroxymethyl)phosphonium sulfate (THPS), a frequently used biocide, stimulates the formation of biofilms by Pseudomonas aeruginosa, consequently intensifying the corrosion of carbon steel. Introducing 160 µg/ml THPS, constituting a sub-MIC level, into the culture medium resulted in a notable increase in biofilm thickness and corrosion rate, elevating them from 82 µm and 10 mpy to 97 µm and 18.7 mpy, respectively. Electrochemical impedance spectroscopy, Tafel polarization and linear polarization resistance measurements substantiated the extent of corrosion. Furthermore, the treated biofilm exhibited a heightened presence of extracellular polymeric substances, improved adherence to the metal surface, enhanced structural integrity, and an extended dispersal phase. Confocal laser scanning microscopy (CLSM) images revealed a greater abundance of viable sessile cells within the inner layers of the treated biofilm. These findings underscore the role of sub-MIC levels of biocides as a potential driving force for developing more corrosive biofilms on industrial materials, emphasizing the critical importance of precise biocide dosing.