β-Glucosidase production by mixed culture using crude hemicellulose from rice straw black liquor and peat moss as an inert support

Background and objectives
Rice straw black liquor (RSBL) has no commercial significance and causes environmental pollution because of its poor disposal, although it holds promise as a cheap substrate for the production of β-glucosidase. The objective of the present work was to improve and optimize the cultural conditions of mixed cultures of NRRL 6165 and NRC 9A under solid-state fermentation (SSF) for the production of β-glucosidase using crude hemicellulose (CHC) prepared from RSBL and peat moss as an inert support.
Materials and methods
Mixed cultures of the mycelial fungi NRRL 11236 and NRRL 6165 and strains (NRC 5A, NRC 7A, and NRC 9A) were evaluated for their ability to produce β-glucosidase using CHC prepared from RSBL and peat moss as an inert support under SSF. Optimization of initial pH (4–8), supplementation with different concentrations of corn steep liquor and ammonium sulfate, the initial moisture content (63.6–87.4% v/w), inoculum size and ratio of microorganisms, CHC/peat moss ratio, and incubation time (0–14 day) were studied. The extracted enzyme was assayed using p-nitrophenyl-β-d-glucopyranoside as a substrate. Data analysis was performed by one-way analysis of variance using computer software Minitab 16.
Results and conclusion
Mixed cultures of the mycelial fungi NRRL 11236 and NRRL 6165 and (NRC 5A, NRC 7A, and NRC 9A) were evaluated for their ability to produce β-glucosidase using CHC prepared from RSBL and peat moss as an inert support under SSF. The most potent coculture composed of NRC 9A (192.39 ± 7.37 U/g CHC) and NRRL 6165 (12.56 ± 0.42 U/g CHC) was used in a mixed culture to enhance β-glucosidase production by coculturing under SSF. In mixed culture, β-glucosidase of the coculture (265.32 ± 0.25 U/g CHC) was nearly 1.3-fold and 10.6-fold than that of monocultures of NRC 9A and NRRL 6165, respectively. Optimization of the environmental and culture parameters, different solid supports, concentration of nitrogen sources (ammonium sulfate and corn steep liquor), initial pH value, CHC/peat moss ratio, inoculum size and ratios of the two strains, moisture content, and incubation time exhibited a significant increase (466 ± 5.42 U/g CHC) in β-glucosidase production compared with before optimization. The study demonstrated that a substrate that does not find any commercial significance and causes environmental pollution because of its poor disposal holds promise as a cheap substrate for the production of β-glucosidase.