Biodegradation of rice husks for glucose production using Streptomyces coelicolor STRP-19

Biodegradation is an effective approach to safely dispose of agricultural biomasses and produce useful materials that can be used in various fields. In this study, soil and rice husks samples were collected from different locations in Sakha, Kafr El-Sheikh governorate. Soil extracts were used to recover 70 mesophilic Streptomyces isolates, which were screened qualitatively and quantitatively for their ability to degrade rice husks and release reducing sugars. Although several Streptomyces isolates showed rice husks-degrading activity, STRP-19 isolate was the most potent and was identified as S. coelicolor using phenotypic and genetic methods based on 16S rRNA gene sequencing. Saturated ammonium sulfate (80%) was used to precipitate cellulase with a total activity of 75,420 U mL−1, specific activity of 302 U mg−1, purification fold of 1.5, and recovery of 81.5%. Gel filtration technique was used to purify the obtained cellulase which was electrophoresed at 70 kDa. Biodegradation of rice husks resulted in production of glucose as reducing sugar at 85 mg dL−1 on the 7th day of incubation at 28 °C and pH 7.5. Adding 20 g of calcium carbonate to the biodegradation medium improved glucose production by 110 mg dL−1, because calcium carbonate acts as a buffer salt that maintains pH and promotes the logarithmic phase. This study highlighted the agricultural biomasses biodegradation, which may help in the safe disposal of the agricultural biomasses with the production of glucose as a reducing sugar, which can be used in many medicinal uses. Accumulation of rice husks as a by-product of rice milling represents an environmental issue, as their disposal by burning leads to significant air pollution and serious respiratory diseases.