A novel strain of Stenotrophomonas acidaminiphila produces super-active alkaline protease during cassava effluent fermentation: process optimization, kinetic modeling and scale-up

Abstract

Microbial fermentations for value-added metabolites production are exploited for efficient bioconversion of agro-industrial wastes for the dual purposes of pollution abatement and cost-effectiveness. In the present study, the regular 2-level factorial design was employed to screen fermentation parameters that enhance production of a novel alkaline protease by a strain of Stenotrophomonas acidaminiphila using cassava processing effluent as substrate. Data from randomized experiments of central composite rotatable design for improved enzyme activity, guided by path of steepest ascent experiments, were modeled and optimized by response surface methodology (RSM). Shake flask kinetics of production under optimized conditions was modeled by logistic and modified Gompertz models and determinations of maximum specific growth rate, µmax, maximum volumetric rate of substrate consumption, rsm, maximum volumetric rate of biomass formation, rxm and specific yield of product, Yp/x were made. Logistic model poorly fitted RSM-generated product formation and substrate consumption data. However, biomass formation was accurately fitted (adjusted r2 >99%), with µmax of 0.471 h-1. The modified Gompertz model, on the contrary, more accurately fitted all three major response data with minimal mean squared error. Potential for scale-up of bioprocess evaluated in 5-L bioreactor satisfactorily revealed 8.5-fold more substrate consumption in bioreactor than in shake flask. The 86.76-fold aqueous two-phase system-purified protease had a specific activity of 1416.73 Umg-1 which improved with increasing surfactant concentration. These results suggest significant bioprocess potential for sustainable cassava effluent management and concomitant commercial production of alkaline protease for industrial detergent application.