Screening and Production of Xylanase by Thermophilic Microorganisms Isolated from Compost Using Sorghum Straw as Substrate Under Solid and Submerged Fermentation

Abstract

The development of renewable energy from lignocelluloic biomass is an economical and eco-friendly approach to the global energy crisis. The enzymatic hydrolysis of the biomass leads to xylose, as one of the fermenting sugars for bioethanol production. However, selection of a suitable microorganism for enzyme (xylanase) production plays a significant role in biomass conversion. This, however, requires selection of efficient xylanolytic organisms. The current study focuses on producing xylanase from selected bacteria (Bacillus pumilus, Bacillus subtilis, and Micrococcus sp.) and fungi species (Aspergillus flavus, Aspergillus niger and Trichoderma viridae) and enhancing their production capacities on sorghum straw substrate through solid state and submerge fermentation. Ability to produce xylanase was established by hydrolysis zone produced on xylan-agar plate. Among the fungi isolates, hydrolytic capacity reached the highest (2.0 mm) for Aspergillus niger, while Bacillus subtilis produced the highest (1.6 mm) among the bacteria species. Aspergillus niger showed the highest xylanase production (62.42 ± 0.78 U/mL) after 96 h. As for the bacteria isolates, the maximum xylanase activity (29.84±0.06 U/mL) was obtained at 48 h by Bacillus subtilis. Xylanase activity was further enhanced by mixed culture of bacteria species. Mixed culture of Bacillus subtilis and Bacillus pumilus improved xylanase activity to 33.58 U/mL. Xylanase production by the mixed culture grown on sorghum straw biomass resulted in a 1.7 – fold increase compared to commercial xylan. Findings suggest that sorghum straw has more economic advantage over xylan as a substrate for xylanase production by the test isolates.