Adaptive responses of marine Vibrio species to phthalic acid esters: implications for biodegradation, antibiotic resistance, and biofilm formation

Phthalic acid esters (PAEs) are synthetic organic contaminants widely detected in marine environments, posing serious ecological and health concerns. This study investigated and characterized Vibrio species isolated from fish gills to assess their potential for phthalic acid ester degradation, as well as the impact of PAE exposure on biofilm formation, antibiotic susceptibility, and stress adaptation. A total of 22 Vibrio species were isolated from 51 fish gill samples, comprising Vibrio parahaemolyticus (9), Vibrio alginolyticus (9), Vibrio cholerae (3), and Vibrio fluvialis (1). Mixed populations of V. alginolyticus, V. fluvialis, and V. parahaemolyticus were detected in two samples. Antibiotic susceptibility testing revealed that 55% of isolates were resistant to ampicillin, with no synergistic effect observed between PAEs and antimicrobials. Exposure of Vibrio isolates to PAEs increased ampicillin MIC values by 2–3 fold in V. parahaemolyticus and V. alginolyticus. Salt tolerance was altered while acid tolerance remained unchanged across all isolates. Biofilm formation and adherence to glass surfaces were enhanced in the presence of di(2-ethylhexyl) phthalate (DEHP) and dibutyl phthalate (DBP), with V. alginolyticus showing significantly higher enhancement. All isolates utilized DEHP as a carbon source in the absence of fermentable sugars, and were able to biodegrade it. GC/MS analysis of biodegraded metabolites revealed phthalic acid. The study demonstrates that marine Vibrio species exhibit diverse and adaptive phenotypic responses to PAE exposure, including altered antibiotic resistance, salt tolerance, biofilm formation, and the ability to metabolize DEHP. It provides insights into how Vibrio species naturally attenuate PAEs and how these pollutants drive microbial adaptation. The findings open new research avenues for identifying enzymes responsible for PAE biotransformation, which may be harnessed for the eco-friendly cleanup of plastic-derived pollutants in aquatic systems.