Primary Study On The Diversity Of Marine Killer Yeasts

The yeast Metchnikowia bicuspidata WCY (the pathogenic yeast to the crab Portunus trituberculatus) can be inhibited or killed by many 'killer' yeast strains. To identify if a yeast can produce killer toxin, first the plates is seeded with sensitive yeast strains. Then, the killer yeast is inoculated on the plate. After incubation, the killer yeast can secrete killer toxin and kill the sensitive cells and the clear zone will appear around the killer yeast clony.After 300 yeast strains preserved in our lab were screened for killer yeasts, we found that 5 strains of them can produce killer toxins,and these five yeast strains are name 2E00688,2E00797,2E00814,2E00871 and 2E01035. The results of the routine identifications based on microbial morphologies, colony morphologies, carbon source fermentation and assimilation show that the five yeast strains belong to Kluyveromyces aestuarii, Mrakia frigida, Yarrowia lipolytica, Kluyveromyces siamensis, Kluyveromyces lactis, respectively. Molecular identification of the five yeast strains using their 26S rDNA sequences shows that they also belong to K. aestuarii, Mrakia sp., Y. lipolytica, K. siamensis, K. lactis, respetctively. The accession numbers of them at GenBank are EU651844, EU680778, EU596441, FJ483911, FJ437050, respectively.In order to test the killing spectra of the five killer yeasts, the sensitive strains which belong to M. bicuspidate (WCY), Candida tropicalis, Saccharomyces cerevisiae, Schizosaccharomyces pombe, Trichosporon montevideense, Yarrowia lipolytica, Candida albicans and Cryptococcus aureus were used. The results show that Kluyveromyces lactis has killing activity against Candida albicans. Kluyveromyces aestuarii has killing activity against Schizosaccharomyces pombe. Mrakia frigida has killing activity against Candida albicans and Candida tropicalis. Yarrowia lipolytica has killing activity against Candida tropicalis. Kluyveromyces siamensis has killing activity against Candida albicans, and all of the five yeast strains have killing activity against Metschnikowia bicuspidate WCY, a pathogenic yeast to the crab.