Kinetics of cell growth and invertase production by the biotherapeutic yeast, Saccharomyces boulardii

Abstract

Invertase (β-D-fructofuranoside fructohydrolase; EC 3.2.1.26) is a highly glycosylated enzyme which hydrolyzes sucrose to glucose and fructose. Therefore, it finds many applications in food and feed industries. In addition, this enzyme become more attractive for its potential application in pharmaceutical industries based on its antimicrobial activities and its ability to reduce the side effects of cancer therapy. In this work, the biotherapeutic yeast Saccharomyces boulardii has been used as a potential biofactory for extracellular invertase production using semi-defind cultivation medium in different submerged cultivtion systems. The initial results showed that the optimal sucrose cocnentration for invertase production was 30 g L-1 which yielded volumetric enzyme production of 6540 U L-1. Further studies for bioprocess optimization were carried out in shake flask, bioreactor cultivations under uncontrolled and controlled pH conditions. The results clearly demonstrated that, scaling up of process from shake flask to bioreactor level increased volumetric enzyme production up to 8111 U L-1. However, this increase was due to the incrase in biomass production (from 3.6 g L-1 up to 4.4 g L-1) rather than cell productivity as both cultures showed almost the same specific enzyme production of about 1980 U g-1. Further improvment in the production process was achieved in pH-controlled bioreactor culture (pH 5.5). The maximal invertase production in the controlled culture was increased up to 14830 U L-1 concomitant with a significant increase in biomass up to 7.5 g L-1. However, on calculating the specific growth rate, the specific enzyme production was about 2269 U g-1. Thus, we can conclude that the increase in invertase production in bioreactor under controlled pH condition was not only due to the increase in biomass but also due to the increase of cell productivity.