ORIGINAL RESEARCH PAPER Biodegradation of crystal violet by Pseudomonas putida Chiing-Chang Chen Æ Hung-Ju Liao Æ Chiu-Yu Cheng Æ Chia-Yuen Yen Æ Ying-Chien Chung Received: 25 September 2006 / Revised: 9 November 2006 / Accepted: 22 November 2006 / Published online: 6 January 2007 Ó Springer Science+Business Media B.V. 2007 Abstract Crystal violet (CV), which has been extensively used as a biological stain and a commercial textile dye, is a recalcitrant molecule. A strain of Pseudomonas putida was isolated that effectively degraded CV: up to 80% of 60 lM CV as the sole carbon source, was degraded in liquid media within 1 week. Nine degradation products were isolated and identified. We propose that CV degradation occurs via a stepwise demethylation process to yield mono-, di-, tri-, tetra-, penta- and hexa-demethylated CV species. Keywords Biodegradation Á Crystal violet Á N-de-methylation Á Pseudomonas putida Introduction The triphenylmethane dye, crystal violet (CV), has been extensively used in human and veterinary medicine as a biological stain and in various commercial textile processes as a dye (Bumpus and Brock 1988). CV has been classified as a recalcitrant molecule, thereby indicating that it is poorly metabolized by microbes and, consequently, is long-lived in a variety or environments. Conven- tional biological wastewater treatment systems are therefore often incapable of effectively removing CV from the wastewater, resulting in its dispersal into the environment. This was demonstrated by Nelson and Hites (1980) who found CV in soil and river sediments that could be traced back to the dumping of improperly treated chemical waste. An additional worrying factor is that some triphenyl- methane dyes, including CV, are potent clastogens, possibly responsible for promoting tumor growth in some species of fish (Cho et al. 2003). Many alternative processes aimed at removing CV from wastewater have been investigated, including chemical oxidation and reduction, phys- ical precipitation and flocculation, photolysis, adsorption, electrochemical treatment, advanced oxidation, reverse osmosis and biodegradation (Azmi et al. 1998). Of these, biological processes have attracted a great deal of attention because, in general, such systems are regarded as more cost-effective and environmentally friendly than physical and chemical treatment methods, and they produce less sludge. There have been very few reports of CV biodegradation by bacteria. Azmi et al. (1998) C.-C. Chen Department of General Education, National Taichung Nursing College, Taichung 403, Taiwan H.-J. Liao Department of Food Science, China Institute of Technology, Taipei 115, Taiwan C.-Y. Cheng Á C.-Y. Yen Á Y.-C. Chung (&) Department of Biological Science and Technology, China Institute of Technology, 245, Sec 3 Yen-Chu Yuan Rd., Taipei 115, Taiwan e-mail: ycchung@cc.chit.edu.tw 123 Biotechnol Lett (2007) 29:391–396 DOI 10.1007/s10529-006-9265-6