Biosynthesis of Autoinducer-2 as the Possible Mechanism to Enhance Decolourisation of Azo Dye by Citrobacter freundii A1

In this study, we attempted to understand possible mechanism associated with bacterial azo dye decolourisation via mass spectral analysis and shotgun cloning of genomic DNA from C. freundii A1. The presence of S-ribosylhomocysteine, a precursor in biosynthesis of autoinducer-2 after complete decolourisation of Amaranth shed light on quorum sensing as the possible related mechanism. Screening of recombinants from E. coli strain ABLE C library on plates supplemented with Amaranth dye resulted in the isolation of a positive recombinant clone, designated ABLE C-pTrueBlue-ropA12 (or in short AC-A12) which showed enhanced Amaranth decolourisation activity. Molecular identification of the cloned DNA fragment revealed an autoinducer-2 synthase (luxS) gene that codes for the final enzyme in the biosynthetic pathway for production of autoinducer-2, which involves in bacterial quorum sensing mechanism. This is the first time the biosynthesis of autoinducer is reported to be related to azo dye decolourisation.