Solid-state fermentation conditions optimization, homology modelling and molecular docking of beta-mannanase of a novel Streptomyces species LB66 isolated from Sargassum seaweed waste

The applications of beta-mannanase for environmentally friendly manufacture of biofuels, biological detergents and health-promoting manno-oligosaccharides have garnered research interests for sustainable and cost-effective production of this industrially important enzyme by identifying potent microorganisms to be applied as the biocatalyst and by using cheap feedstocks in the fermentation medium. The current study has optimized the solid-state fermentation (SSF) conditions with cow dung as the economical feedstock for maximal production of beta-mannanase by a novel Streptomyces sp. LB66 (GenBank accession no. MT228944) isolated from Sargassum seaweed waste. Furthermore, homology modelling and molecular docking approaches were applied to elucidate the 3D-structure and enzyme-substrate interactions of modelled beta-mannanase. The optimization of SSF components via a 2(3)-factorial central composite design recorded the maximal beta-mannanase production (36.8 +/- 1.74 U/mg-protein) with 18 g cow dung, and at pH 7.5 and 30 degrees C incubation temperature. Molecular docking of modelled beta-mannanase with mannobiose, mannotriose and mannotetraose as substrates displayed participations of six shared active site residues (Arg46, Ala54, Val56, Gln279, Leu281 and Gly282) for the binding. These identified active site residues can be targeted via directed evolution approaches in tailoring the enzymatic traits for overproduction of beta-mannanase and in ecofriendly bioprocessing of diverse lignocellulosic and seaweed waste.