Extractive fermentation for improved production of endoglucanase by an intergeneric fusant of Trichoderma reesei/ Saccharomyces cerevisiae using aqueous two-phase system

Abstract

Extractive aqueous two-phase fermentation of endoglucanase, a key enzyme for the conversion of cellulosic substances to fermentable sugars, from an intergeneric fusant of Trichoderma reesei/ Saccharomyces cerevisiae is a meaningful approach for better production and simple recovery of this enzyme. A phase composition of 6.5% (w/w) dextran and 7.5% (w/w) polyethylene glycol 6000, having a partition coefficient of 2.89 and 1.31 for endoglucanase from an intergeneric fusant of T. reesei/ S. cerevisiae and T. reesei (WT) (being a control in this study), respectively, was chosen for extractive fermentation of the enzyme. Endoglucanase production is higher in medium containing polyethylene glycol (PEG) 6000 than in medium without PEG 6000. Comparative analysis of endoglucanase fermentation by fusant and T. reesei was carried out in shake culture and environment-controlled bioreactor conditions. The fusant produced 0.43 U of endoglucanase (overall production: 0.34 U) in the top phase of an aqueous two-phase system (ATPS), compared to 0.3 U in medium without the phase system in shake culture. In a batch reactor, the endoglucanase level for the fusant in the top phase of ATPS was 0.49 U (overall production: 0.40 U), compared to 0.38 U produced in medium without aqueous two-phase components. To corroborate this study, T. reesei produced 8.41 U of endoglucanase (overall production: 5.96 U) in the top phase of ATPS, compared to 7.18 U in the medium without the phase system in shake culture. On the other hand, in a batch bioreactor, T. reesei produced 10.13 U of endoglucanase (overall production: 6.90 U) in the top phase of ATPS, compared to 8.56 U of the enzyme in medium without aqueous two-phase components. The lower overall enzyme production by T. reesei in the two-phase system might be due to limitation in oxygen transfer to the dispersed phase where the enzyme is produced. A higher cell concentration and a reduced lag phase was obtained in ATPS, compared to a similar medium without phase forming polymers for both the intergeneric fusant of T. reesei/ S. cerevisiae and T. reesei.