Production of β-galactosidase in shake-flask and stirred tank bioreactor cultivations by a newly isolated Bacillus licheniformis strain

β-Galactosidase is an industrially important enzyme with many applications in various health, diagnostic and food processing industries. The present work describes the isolation and identification of a new isolate capable of producing β-galactosidase. The work was further extended to optimize the production medium and investigate the kinetics of cell growth and enzyme production during batch cultivation in shake-flask and 5L-stirred tank bioreactor. The isolated strain was identified as Bacillus licheniformis using 16S rRNA and BLAST analysis. The final optimized production medium contained (g/L): yeast extract, 14.0; lactose, 8.0; NaCl, 16.0; (NH4)H2PO4, 0.1; MgSO4.7H2O, 0.1; K2HPO4, 0.1. The optimized medium afforded maximal β-galactosidase production of 116.4 U/mL with a specific yield coefficient (YP/X) of 27.6 × 103 U/g cells. These results corresponds to an increase of about 4.4- and 2.8-folds, respectively, than the initial un-optimized production medium. Further improvement in the production process was achieved by cultivating cells in 5L-stirred tank bioreactor, which increased volumetric enzyme productivity and specific yield coefficient by 8.5- and 6.0-folds than the initial un-optimized production medium, respectively. A new β-galactosidase producing strain was identified and the volumetric as well as specific productivities were greatly enhanced through medium optimization and bioreactor cultivation