Biodegradation of tannic acid by Citrobacter freundii isolated from a tannery effluent

A bacterial strain capable of utilizing tannic acid as sole carbon source w as isolated from the effluent of a tannery and was identified as Citrobacte r freundii. This organism could grow at concentrations as high as 5% (w/v) of tannic acid and produced extracellular tannase to hydrolyze the same. Wh en grown in minimal medium containing 1% tannic acid (w/v) at 30 degrees C, this strain produced 1.87 U/ml of tannase at 6 h. At that time, tannic aci d degradation products, namely glucose and gallic acid, were detectable in the culture filtrate, the other intermediate metabolites formed were pyroga llol (extracellular) and pyruvate (intracellular). 2-hydroxymuconic acid is presumed to form as a result of ortho-cleavage of pyrogallol. The proposed biochemical pathway for the degradation of tannic acid by Citrobacter freu ndii is: Tannic acid --> [Glucose + Gallic acid] --> Pyrogallol --> 2 hydro xymuconic acid --> [?] --> Pyruvate.