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Appl Microbiol Biotechnol (2008) 77:11391144 DOI 10.1007/s00253-007-1212-5
ENVIRONMENTAL BIOTECHNOLOGY
Azoreductase and dye detoxification activities of Bacillus velezensis strain AB
Amit Bafana & Tapan Chakrabarti &
Sivanesan Saravana Devi
Received: 27 July 2007 /Revised: 7 September 2007 /Accepted: 16 September 2007 / Published online: 22 November 2007 # Springer-Verlag 2007
Abstract Azo dyes are known to be a very important and widely used class of toxic and carcinogenic compounds. Although lot of research has been carried out for their removal from industrial effluents, very little attention is given to changes in their toxicity and mutagenicity during the treatment processes. Present investigation describes isolation of a Bacillus velezensis culture capable of degrading azo dye Direct Red 28 (DR28). Azoreductase enzyme was isolated from it, and its molecular weight was found to be 60 kDa. The enzyme required NADH as cofactor and was oxygen-insensitive. Toxicity and mutagenicity of the dye during biodegradation was monitored by using a battery of carefully selected in vitro tests. The culture was found to degrade DR28 to benzidine and 4-aminobiphenyl, both of which are potent mutagens. However, on longer incubation, both the compounds were degraded further, resulting in reduction in toxicity and mutagenicity of the dye. Thus, the culture seems to be a suitable candidate for further study for both decolourization and detoxification of azo dyes, resulting in their safe disposal.
Keywords Direct red 28 . Azoreductase . Zymogram .
Ames test . Biodegradation
Introduction
Azo dyes constitute the largest and most versatile class of synthetic dyes used for textile dyeing and other industrial applications. As fixation of these dyes to textile fibers is never complete, a significant amount of dyes is lost in wastewater. Release of such coloured compounds into the environment is undesirable not only because of their aesthetic appearance, which may drastically affect photo-synthesis in aquatic ecosystem, but also because many of the dyes and/or their breakdown products are toxic and mutagenic to life (Chung and Cerniglia 1992). Unfortunately, azo dyes present in the wastewater are normally unaffected by conventional treatment processes. Their persistence is mainly due to sulfo and azo groups, which do not occur naturally, making the dyes xenobiotic and recalcitrant to oxidative biodegradation (Kulla et al. 1983). The persistence of azo dyes has resulted in several reports,...