Enhanced transformation of triclosan by laccase in the presence of redox mediators.
Triclosan (TCS), an antimicrobial agent, is an emerging and persistent environmental pollutant that is often found as a contaminant in surface waters and sediments; hence, knowledge of its degradability is important. In this study we investigated laccase-mediated TCS transformation and detoxification, using laccase (from the fungus Ganoderma lucidum) in the presence and absence of redox mediators. Transformation products were identified using HPLC, ESI-MS and GC-MS, and transformation mechanisms were proposed. In the absence of redox mediator, 56.5% TCS removal was observed within 24h, concomitant with formation of new products with molecular weights greater than that of TCS. These products were dimers and trimers of TCS, as confirmed by ESI-MS analysis. Among the various mediators tested, 1-hydroxybenzotriazole (HBT) and syringaldehyde (SYD) significantly enhanced TCS transformation ( approximately 90%). The presence of these mediators resulted in products with lower molecular weights than TCS, including 2,4-dichlorophenol (2,4-DCP; confirmed by GC-MS) and dechlorinated forms of 2,4-DCP. When SYD was used as the mediator, dechlorination resulted in 2-chlorohydroquinone (2-CHQ). Bacterial growth inhibition studies revealed that laccase-mediated transformation of TCS effectively decreased its toxicity, with ultimate conversion to less toxic or nontoxic products. Our results confirmed the involvement of two mechanisms of laccase-catalyzed TCS removal: (i) oligomerization in the absence of redox mediators, and (ii) ether bond cleavage followed by dechlorination in the presence of redox mediators. These results suggest that laccase in combination with natural redox mediator systems may be a useful strategy for the detoxification and elimination of TCS from aqueous systems.
School of Environmental Science and Engineering, Pohang University of Science and Technology (POSTECH), San 31, Hyoja-dong, Nam-gu, Pohang 790-784, Republic of Korea.
Kumarasamy
K
Murugesan
Yoon-Young
YY
Chang
Young-Mo
YM
Kim
Jong-Rok
JR
Jeon
Eun-Ju
EJ
Kim
Yoon-Seok
YS
Chang
D000890:Anti-Infective Agents / Q000737:chemistry* / Q000378:metabolism*; D042845:Laccase / Q000378:metabolism*; D010084:Oxidation-Reduction; D014230:Triazoles / Q000737:chemistry; D014260:Triclosan / Q000737:chemistry* / Q000378:metabolism*; D014874:Water Pollutants, Chemical / Q000737:chemistry* / Q000378:metabolism*; D018508:Water Purification / Q000379:methods
D000890:Anti-Infective Agents; D014230:Triazoles; D014874:Water Pollutants, Chemical; D014260:Triclosan; C011852:1-hydroxybenzotriazole; D042845:Laccase