Enhanced thermostability of halo-tolerant glutaminase from Bacillus licheniformis ATCC 14580 by immobilization onto nano magnetic cellulose sheet and its application in production of glutamic acid

A halo-tolerant glutaminase gene (BlglsA) was isolated from Bacillus licheniformis. Heterologous expression of BlglsA revealed that it encodes for a 36 kDa protein containing 327 amino acid residues. The purified enzyme showed optimal activity at a pH of 9.5 while 35 degrees C was found to be the optimum temperature. The enzyme retained about 92 and 97% stability at pH 12 and temperature (40 degrees C) respectively. Subsequent immobilization of BIgIsA on nano magnetic cellulose sheet (NMCS) led to an enhanced tolerance to higher temperature. NMCS-BlglsA showed optimum activity at 45 degrees C, although it was stable even at 60 degrees C. NaCI tolerance (>= 90% in 0.3 M) was almost similar to BIgIsA and NMCS-BIgIsA. The metal ions Fe2+ (5 mM) and Mn2+ (2.5 mM) improved the BIgIsA relative activity by 61 and 48%, respectively. In contrast, 5 mM Mn2+ was found suitable to enhance the activity of NMCS-BlglsA up to 72%. The production of glutamic acid by NMCS-BIgIsA was 1.61 g/l in 48 h. Reusability test of NMCS-BIgIsA showed 76 and 35% retention of the actual activity after 4th and 7th cycle, respectively. Such remarkable biochemical properties of NMCS-BIgIsA make it an attractive enzyme for food industries. (C) 2018 Elsevier B.V. All rights reserved.