Scale-up thermostable α-amylase production in lab-scale fermenter using rice husk as an elicitor by Bacillus licheniformis-AZ2 isolated from Qinarje Hot Spring (Ardebil Prov. of Iran)

Abstract

Background and purpose: Amylases are commercially important enzymes with various biotechnological, clinical and medical applications. This study aimed at scaling up α-amylase production elicited by rice husk in stirred-fermenter using Bacillus lichneniformis-AZ2 isolated from Qinarje Hot Spring.

Materials and methods: Effect of temperature, aeration rate and agitation speed on bacterial growth and ɑ-amylase production were investigated under batch fermentation process in a 3-Lit stirred-fermenter. OFAT method was followed to select optimum level of each parameter. Other factors were set upon the results of previous experiments carried out in shake-flask scale.

Results: Maximum α-amylase production of 17.66 ± 0.87 U/mL (2.1 folds more than shake-flask cultures) was achieved in stirred-fermenter with optimized agitation speed of 100 rpm and 1 vvm aeration rate at 37ºC after 60 h of incubation. This time was shorter than the corresponding fermentation time obtained from shake-flask experiments by half. A comparison of kinetic parameters of fermentation in stirred-fermenter and shake-flask cultures revealed that B. licheniformis-AZ2 was more active to synthesize ɑ-amylase in fermenter. In shaken cultures Q_x, Q_p, Y_p/x, µmax, q_p and t_d, were 0.27 (g/L/h), 228.6 (U/L/h), 13.64 (U/g), 0.055 (h^-1), 0.76 (U/g/h) and 12.48 h, whereas in stirred-fermenter the above values were 0.40 (g/L/h), 723.1 (U/L/h), 45.17 (U/g), 0.120 (h^-1), 5.42 (U/g/h) and 5.78 h, respectively.

Conclusions: SmF in stirred-fermenter is a potential strategy for ɑ-amylase production. Although for commercialization further studies are needed in pilot-scale. Rice husk as a low-cost agro-waste is preferable to use as the carbon and energy sources, which provides a great ɑ-amylase elicitation.