Response surface optimization for cellulase production from Enterococcus faecium and Stutzerimonas stutzeri isolated from Gossypium arboretum and Solanum melongena soil

The rapid utilization of fossil fuel-based energy sources increased demand for alternate sustainable energy sources. One of the best alternate energy sources can be lignocellulosic biomass. The major constituent of lignocellulosic biomass is cellulose that can be converted into simple sugar using cellulase enzymes followed by fermentation for ethanol production. Two potential mesophilic cellulolytic bacteria, BS5 and CS7, from brinjal and cotton soil samples were screened based on high zones of hydrolysis on CMC agar plates and identified as Enterococcus faecium and Stutzerimonas stutzeri, respectively. It is the first instance of a mesophilic cellulase being reported from an S. stutzeri. CMCase production was enhanced by methods like one factor at a time (OFAT) and response surface methodology (RSM). The optimal conditions for maximum CMCase production by isolate BS5 were pH 5.0, 41℃, 1.25% inocula volume, and 56 h of incubation, whereas isolate CS7 produced maximum CMCase at pH 7.0, 43℃, 2.0% inocula volume, and 42 h of incubation. Following optimization through RSM-CCD, CMCase productivity of isolate BS5 increased 2.43 times, reaching 20.4 U/mL compared to 8.22 U/mL under unoptimized conditions, while CMCase productivity of isolate CS7 increased 2.18 times, reaching 24.08 U/mL compared to initial unoptimized activity of 11.05 U/mL. The crude enzyme produced by both isolates demonstrated effective potential in biopolishing cotton fabrics. Cotton fabrics treated with crude enzymes from BS5 and CS7 isolates lost 2.20% and 2.06% of their weight, respectively, showing that the enzymes removed tiny fibers from the surface of the cotton, making it smoother. Crude enzyme of both isolates showed optimum activity at mesophilic temperature, which makes them suitable for industrial applications like bioethanol production using simultaneous saccharification and fermentation, biopolishing and biostoning in the textile industry, and deinking in the paper and pulp industry.