Exploring triclosan degradation potential of Citrobacter freundii KS2003

The removal of triclosan from the environment is a very challenging task owing to its persistent nature and lipophilic property. Citrobacter freundii KS2003, isolated from wastewater sample collected from a healthcare setting, was exploited for effective degradation of triclosan. Cell elongation was observed as a major morphological change in this isolate, when grown in the presence of triclosan. One-factor-at-a-time (OFAT) approach was applied to optimize various nutritional and environmental parameters. Citrobacter freundii KS2003 degraded 99.57 ± 0.6% of 250 mg/L of triclosan in M9 MSM at 30 ℃ and pH 8 under static condition within 96 h of incubation. Mass spectroscopy and Fourier transform infrared spectroscopy confirmed the formation of non-toxic 2,4-dichlorophenol as the main by-product by this isolate. Ion chromatography revealed partial dechlorination of triclosan. Also, the cell-free extract of Citrobacter freundii KS2003 showed the activity of catechol 1,2-dioxygenase enzyme (specific enzyme activity = 0.159 U/mg). 4-chlorocatechol was used as an inhibitor of catechol 1,2-dioxygenase enzyme. The absence of triclosan degradation in the presence of inhibitor suggested the involvement of dioxygenase enzyme in triclosan degradation by Citrobacter freundii KS2003. These findings proposed an ortho -cleavage pathway being followed by KS2003 for triclosan degradation.