Purification and characterization of the cold-active killer toxin from the psychrotolerant yeast Mrakia frigida isolated from sea sediments in Antarctica

The psychrotolerant yeast Mrakia frigida 2E00797 isolated from sea sediments in Antarctica was found to be able to produce killer toxin against Metschnikowia bicuspidata, Candida tropicalis and Candida albicans. In the present study, the killer toxin was purified and characterized. The molecular weight of the purified killer toxin was estimated to be 55.6 kDa and the purified killer toxin shared 35.1% sequence homology with a protein kinase. The purified killer toxin's optimal temperature and pH for killing activity were 16 °C and 4.5, respectively, and it was stable in the temperature range from 10 to 25 °C at pH 4.5. The toxin's highest killing activity was observed in the presence of 3.0 g/100 ml NaCl. The purified killer toxin was able to actively kill whole cells of M. bicuspidata but could not kill the protoplast of the sensitive yeast. Of the eight yeast species tested in this study, the killer toxin was able to kill C. tropicalis and C. albicans in addition to M. bicuspidata.

► The purified killer toxin from the psychrotolerant yeast had an estimated molecular weight of 55.6 kDa.
► The optimal temperature and pH of killing activity for the purified killer toxin were 16 °C and 4.5.
► The purified killer toxin actively killed only the whole cells of Metschnikowia bicuspidata.
► The killer toxin also killed Candida tropicalis and Candida albicans.