Abstract
A marine yeast strain, DD21-2 was isolated from sediments in Dandong, China, which has killer activity against yeast Metschnikowia bicuspidata WCY (pathogenic to crab, Portunus trituberculatus). Routine identification, sequence analysis of 26S rDNA and ITS sequencing showed that the strain was M. saccharicola DD21-2, and has not been previously reported as having killer activity against M. bicuspidata WCY. To optimize the production of the killer toxin by M. saccharicola DD21-2, the interaction effects of fermentation process variables were investigated by Response Surface Methodology (RSM). The following reaction factors were selected in screening experiments: Inoculum concentration (2 to 6%), pH (5.0 to 6.0), temperature (20 to 28°C), and fermentation time (2 to 3 days), and the diameter of the inhibition zone produced by the killer toxin was used as a response variable. A quadratic regression model of killer toxin activity was established by regression analysis and significance testing (P test). The results identified the following parameters as optimal for maximal production of the killer toxin by M. saccharicola DD21-2: Fermentation temperature 28°C, pH 5.5, fermentation time 2.7 days, and inoculum concentration 4.1% (v/v). Thus, RSM was effective in determining the best conditions for killer toxin production, suggesting the practical usage of this marine yeast in the investigation of process variables. Key words: Marine killer yeast, killer toxin, response surface methodology (RSM), fermentation, optimization.
Highlights
Many studies have shown that some marine yeast species are pathogenic to marine animals (Xu, 2005; Wang et al, 2008; Kaewwichian et al, 2012)
Anti-yeast compounds such as nystatin, benzalkonium bromide, and extracts of gold thread root and garlic are toxic to the crab, so killer toxins produced by some yeast species against pathogenic yeasts may be a good alternative (Philliskink and Young, 1975)
The yeast strain DD21-2 isolated from river bed sediments could secrete killer toxins onto culture medium and kill pathogenic yeast M. bicuspidata WCY, C. tropicalis Ct, and C. albicans YTS-03 (Figure 1)
Summary
Many studies have shown that some marine yeast species are pathogenic to marine animals (Xu, 2005; Wang et al, 2008; Kaewwichian et al, 2012). Studies have shown that killer yeasts and the killer toxins they produce have antimicrobial activity and can be used to control the growth of pathogenic yeasts in humans, animals and plants (Comitini et al, 2004; Magliani et al, 2008; Chi et al, 2010; Wang et al, 2013). Yeast-derived killer toxins have been widely used to control harmful yeast growth in industrial fermentation systems, food production, animal breeding, agriculture, and medicine as antifungal drug formulations (Magliani et al, 2008; Wang et al, 2013). Some diseases of marine animals, including P. trituberculatus can be controlled by certain marine killer toxin-producing yeast (Wang et al, 2007; Chi et al, 2010)
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