d-Phenylalanine Alleviates the Corrosion by Desulfovibrio vulgaris in Saline Water

A biofilm is a major contributor to microbiologically influenced corrosion (MIC) in cooling water systems, resulting in severe economical and environmental impacts. d-Amino acids offer a potential alternative for preventing biofilm formation in these systems, where salinity levels vary due to diverse water sources, such as freshwater and diluted seawater. However, the impact of d-amino acids on corrosion inhibition under saline conditions remains unexplored. In this study, we evaluated the effect of d-phenylalanine (d-Phe) on corrosion by Desulfovibrio vulgaris at three salinity levels. d-Phe (10 mg/L) played little role in corrosion inhibition at low salinity (5 g/L) but obviously decreased the corrosion by 40.6% and 59.6% at moderate salinity (15 g/L) and high salinity (20 g/L), respectively. It was attributed to that d-Phe reduced the secretion of extracellular protein from 292.5 μg/mg to 245.6 μg/mg and decreased the biofilm thickness from 25.46 μm to 20.87 μm on the coupon surface. Besides, d-Phe decreased the sessile cells from 15.1 × 10⁷ cells/cm² to 12.8 × 10⁷ cells/cm² at high salinity. Furthermore, transcriptome analysis found that indole, the signal molecule negatively regulating the biofilm formation, was increased by adding d-Phe at high salinity. Moreover, peptidoglycan reorganization was strengthened at high osmotic pressure via absorbing additional d-Phe, leading to weak bacterial adhesion. The work provides mechanistic insights into the application of d-Phe for biofilm inhibition and MIC mitigation in industries.