Kinetic Study of Cell Growth and Production of Amylase, Cellulase and Xylanase by Bacillus subtilis Using Barley Husk as the Prime Carbon Source

Bacillus spp have been widely adopted as one of the vital producers of the industrial enzymes including amylase, cellulase and xylanase. In fact, submerged fermentation (SmF) with the presence of excess water is the best suited technique for the culture of bacteria especially Bacillus that required high moisture content to grow. Pure carbon sources besides being expensive, are not economically viable for the production of enzymes. Therefore, inexpensive yet effective agricultural residues such as barley husk was used in this study.

Aims: The primary aim of this study was to investigate the kinetic of cell growth and enzymes production of amylase, cellulase and xylanase by Bacillus subtilis ATCC 6633 using barley husk as the main carbon source under SmF.

Methodology: In the present study, the standard inoculum size of 1 × 108 cells of B. subtilis was inoculated into culture flask containing barley husk for the production of enzymes in SmF. Samples were collected every 12 h for analysis.

Results: In this study, B. subtilis possessed the maximum specific growth rate (µmax) of 0.55 h-1 at 48 h with the maximum cell productivity of 1.98 × 1010 cells/L/h was attained during the exponential growth phase. On the other hand, the highest enzyme activity by B. subtilis obtained in this study was identified to be amylase with its activity of 1.991 U/mL, followed by xylanase activity of 1.492 U/mL and lastly cellulase with the lowest activity of 0.304 U/mL. In addition, the specific enzymes activity and productivity were also elucidated to describe the kinetic study of enzymes production. The maximum specific xylanase activity of 6.81 U/mg, followed by specific amylase activity of 6.68 U/mg and the least specific cellulase activity of 0.73 U/mg were attained from B. subtilis. In fact, cellulase productivity of 18.23 U/mL/h was found to be relatively low compared to amylase with 119.48 U/mL/h and xylanase with 89.52 U/mL/h. Cellulase production was determined as growth associated process where its maximum production was attained at the end of the exponential growth phase. On the contrary, the production of amylase and xylanase were partially growth associated due to their maximal production observed after the exponential phase of cell growth.

Conclusion: In a nutshell, B. subtilis is anticipated to be potential bacteria for the optimisation of enzymes production for amylase, cellulase and xylanase using barley husk as the sole carbon source in SmF.