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

Abstract A halo-tolerant glutaminase gene (Bl gls A) was isolated from Bacillus licheniformis . Heterologous expression of Bl gls A 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 °C was found to be the optimum temperature. The enzyme retained about 92 and 97% stability at pH 12 and temperature (40 °C) respectively. Subsequent immobilization of Bl gls A on nano magnetic cellulose sheet (NMCS) led to an enhanced tolerance to higher temperature. NMCS-Bl gls A showed optimum activity at 45 °C, although it was stable even at 60 °C. NaCl tolerance (≥90% in 0.3 M) was almost similar to Bl gls A and NMCS-Bl gls A. The metal ions Fe 2+ (5 mM) and Mn 2+ (2.5 mM) improved the Bl gls A relative activity by 61 and 48%, respectively. In contrast, 5 mM Mn 2+ was found suitable to enhance the activity of NMCS-Bl gls A up to 72%. The production of glutamic acid by NMCS-Bl gls A was 1.61 g/l in 48 h. Reusability test of NMCS-Bl gls A showed 76 and 35% retention of the actual activity after 4th and 7th cycle, respectively. Such remarkable biochemical properties of NMCS-Bl gls A make it an attractive enzyme for food industries.