Statistical optimization of medium components for wickerhamomyces anomalus killer toxin production

Abstract

Yeast killer toxin (KT) was associated with the killer system group where yeast is able to synthesize and export proteins or glycoproteins with toxic effects to control citrus postharvest diseases. In this study strains belonging to the species Kazachstania exigua, Saccharomyces cerevisiae and Wickerhamomyces anomalus isolated from citrus plants of Tucuman city at Argentina were screening in vitro as a potential biocontrol agents (BCAs) against of Aspergillus niger. W. anomalus was chosen to further develop and established to ensure good growth with high activity cells for killer toxin used for industrial application. Medium formulation is an essential stage in the design of pilot scale development in order to optimize (KT) production with the medium must satisfy the elemental requirement for (KT) biosynthesis and cell maintenance. Therefore, the aim of this study is to enhance production of (KT) by applying two-stage statistical approach, Plackett-Burman design and response surface methodology (RSM) using central composite design (CCD) of the medium composition through the shake flask levels. In the first stage of optimization, among the studied variables, peptone, glycerol, and pH were selected based on their high positive significant effect on the productivity of (KT). The second stage of experimental design (RSM) using (CCD) was utilized to create a polynomial quadratic model correlating the relationship between the three variables and the productivity of (KT). The optimal combination of the major medium constituents for (KT) production evaluated using the non-linear optimization algorithm of EXCEL-Solver and JMP program, was as follows: 6% peptone, 30% glycerol and pH 4. The predicted optimum production of (KT) against A. niger was 1904 arbitrary units (AU) per ml via Plackett-Burman design. By using the optimal fermentation medium of (RSM) design as follows 6.69%, 15.1% at pH 4.3, the (KT) production was improved approximate two times higher over the previous production in the un-optimized medium.