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Laccases are multi-copper proteins that can oxidize a wide range of inorganic and aromatic compounds, especially phenols, while reducing molecular oxygen to water [1]. Laccases catalyze the removal of one hydrogen atom from phenolic substrates and aromatic amines by an abstraction of electrons. Free radicals formed during the reaction are also capable of undergoing depolymerization, further repolymerization, demethylation, or quinone formation [2-4]. The low substrate specificity of laccases and their ability to oxidize various pollutants suggest their industrial-technological and biotechnological applications [5,6]. Laccases are widely distributed in fungi and plants [7]. However, it has been found that laccases are also widespread in bacteria [1]. To date, laccases have mostly been isolated and characterized from plants and fungi, but only fungal laccases are currently used in biotechnology applications. In contrast, only a few bacterial laccases have been characterized. Bacterial laccases have the ability to oxidize syringaldazine and 2, 6-dimethoxyphenol, which are typical substrates for laccases, and also possess the canonical four areas for the binding of copper. Nevertheless, overall sequences of bacterial laccases show little resemblance to fungal laccases. Therefore, they are often called “multicopper oxidases” or “(poly) phenol oxidases” and their activity is generally defined as “laccase-like” [8]. The first report of bacterial laccase was from the strain Azospirillum lipoferum, which was isolated from the rhizosphere of rice [9]. This enzyme has been identified as a laccase using a combination of substrates and inhibitors [9] [10]. Laccase activities have also been found in Bacillus sphaericus [11], Escherichia coli [12], Bacillus halodurans [13], and Streptomyces psammoticus [14] to name a few. CotA, the Bacillus subtilis endospore layer component, is the most studied bacterial laccase [15]. Since spores allow microorganisms to survive in harsh conditions, spore coat enzymes can also withstand high temperatures or extreme pH values. As most fungal laccases are unstable at pH values greater than 7.0, their detoxification efficiency for pollutants often decrease under alkaline conditions. This limits the potential industrial application of fungal laccases as many processes are performed under alkaline conditions. Alternatively, spore laccases that are active in the alkaline pH range could be used for bioremediation or application in membrane reactors [4]. Compared to fungal laccases, bacterial laccases have the advantage of being less sensitive to halides and alkaline conditions and the producing strain typically exhibits a rapid growth rate [16]. Despite the importance of bacterial laccase in the degradation of pollutants, only a few new bacterial strains with “laccase-like” activity have been discovered. The lack of a robust and inexpensive commercially available laccase is a major obstacle to the widespread application of laccase in various industrial sectors [17]. Since bacterial genetic tools and biotechnological processes are well established, the development of bacterial laccases would be of great significance [18]. The present study was therefore conducted to isolate and characterize the strain, Bacillus sp. ETL 1979, which was isolated from an industrial textile effluent treatment plant. The spore laccase of this strain was characterized and used to decolorize various synthetic dyes.

Microbial Decolorization of Various Dyes by a Bacillus subtilis Strain Isolated from an Industrial Effluent Treatment Plant