Enhanced tannase production by Bacillus subtilis PAB2 with concomitant antioxidant production

Abstract

Abstract The present study was aimed at finding the optimal conditions for tannin biodegradation by Bacillus subtilis PAB2, a newly isolated soil bacterium, and to study its fermentative byproducts. Tannase production by B. subtilis PAB2 in optimum level was studied by one variable at a time (OVAT) approach followed by Box–Behnken response surface methodology (RSM) using six important variables. The maximum tannase production (10.69 U/ml) was achieved in the presence of 0.47% (w/v) tannic acid, 0.23% (w/v) ammonium chloride (NH 4 Cl), 0.1% (w/v) potassium dihydrogen phosphate (KH 2 PO 4 ) and 0.046% (w/v) magnesium sulphate (MgSO 4 ) with the initial medium pH of 5.9 and incubation at 34.1 °C for 36 h under shaking condition (120 rpm). An overall 2.06 fold increase in tannase production was achieved after RSM global formulation. One of the major end product of tannin degradation i.e. gallic acid, was accumulated in the highest level (6.45 mg/ml) in 36 h of fermentation. Liquid chromatography and mass spectroscopy results indicated the presence of both gallic acid and pyrogallol in the fermentative end product. Purification of gallic acid and pyrogallol was achieved through high pressure liquid chromatography followed by crystallization and confirmed by Fourier transform infrared spectroscopy. Associated production of tannase as well as gallic acid and pyrogallol by B. subtilis PAB2 makes it obvious in different biotechnological interest.