Evaluation of a yeast co-culture for cellulase and xylanase production under solid state fermentation of sugarcane bagasse using multivariate approach

Sugarcane bagasse (SB), an abundantly found lignocellulosic material in many countries, has been exploited for the production of industrially important enzymes by filamentous fungi and bacteria. Yeasts have not been reported to utilize SB, particularly under solid-state fermentation (SSF). In this work, two yeast strains, MK-157 and MK-118 were co-cultured to produce a multienzyme preparation comprised of endoglucanase (EG), β-glucosidase (BGL) and xylanase (XYL). Two Plackett-Burman Designs (PBDs) were executed separately to screen the factors affecting SSF of acid-pretreated and alkali pretreated SB for the production of multienzyme. The analysis depicted that SSF of alkali pretreated SB yielded higher titers of multienzyme than acid pretreated SB and three of the factors (temperature, inoculum size and incubation period) were exerting significant effect on the process. Consequently, the three factors were optimized by employing Box-Behnken Design (BBD). Under optimum conditions, i.e. inoculation of 0.5 ml g−1 yeast co-culture in alkali pretreated SB and cultivation at 35 °C for 94 h gave the EG titers of 9.81 IU mL−1 that was comparable to the predicted value of 9.61 IU mL−1. Gravimetric analysis of untreated, pretreated and fermented SB showed that cultivation of the yeasts resulted in decrease in the quantity of cellulose, indicating utilization of this component. Moreover, alkaline pretreatment caused more delignification and disruption of the structure that was evident from scanning electron (SE) micrographs. SE microscopy also revealed that there were more changes in the structure of SB when cultivated with co-culture than with mono-culture. Furthermore, the fermented SB by co-culture adsorbed more dye (congo red) than the other SB indicating formation of pores in SB by the yeasts.