Establishment Of The Marine Yeast Culture Collection And Study On The Diversity Of Special Marine Yeasts

Total 551 marine yeast strains from different marine environments were obtained. The results of routine identification and molecular methods show that they belonged to 22 genera, 58 species. The Marine Yeast Culture Collection, which was the first yeast culture collection in China, was established basing on these strains. An electronic file for each strain was recorded. All the information and strains collected can be shared at the website http://www.mccc.org.cn/ and the collection center.After lipase activity of the yeast cultures was estimated, we found that nine yeast strains obtained in the Marine Yeast Culture Collection grown in the medium with olive oil could produce lipase. The results of routine identification and molecular methods show that they belonged to Candida intermedia YA01a, Pichia guilliermondii N12c, Candida parapsilosis 3eA2, Lodderomyces elongisporus YF12c, Candida quercitrusa JHSb, Candia rugosa wl8, Yarrowia lipolytica N9a, Rhodotorula mucilaginosa L10-2 and Aureobasidium pullulans HN2.3, respectively. The optimal pHs and temperatures of lipases produced by them were between 6.0 and 8.5 and between 35 and 40℃, respectively. Majority of lipases from the yeast strains were cell-bound and only lipase from A. pullulans HN2.3 was extracellular. Some lipases from the yeast strains could actively hydrolyse different oils, indicating that they may have potential applications in industry.After killer toxin activity of the yeast cultures was determined, we found that 17 strains obtained in the Marine Yeast Culture Collection could secrete killer toxin into the medium and killed the pathogenic yeast Metschnikowia bicuspidate WCY in crab. However, only five strains (WC91-2,gao1zhong2,YF07b,hcx-1 and HN2.3) among them had higher killer toxin activity against the pathogenic yeast than others. The results of routine identification and molecular methods show that the five yeast strains belonged to Williopsis saturnus WC91-2, Pichia guilliermondii gao1zhong2, Pichia anomala YF07b, Debaryomyces hansenii hcx-1 and Aureobasidium pullulans HN2.3, respectively. We found that not all the optimal conditions for killer toxin production and action of killer toxin by the marine killer yeasts were in agreement with those of marine environments and for crab cultivation. It was found that the killer toxins produced by the killer yeast strains could kill other yeasts in addition to the pathogenic yeast and NaCl concentration in the medium could change killing activity spectra. All the crude killer toxins produced by them could hydrolyze laminarin and the hydrolysis end products were monosaccharides.We found that the marine yeast strain W14-3 isolated from seawater of China Eastern Sea could produce riboflavin. It is interesting to observe that the marine yeast strain produced a large amount of riboflavin in the medium containing xylose, sucrose, galactose and maltose, respectively under the conditions of vigorous shaking. The yeast strain was found to belong to Candida membranifaciens subsp. flavinogenie based on the results of routine and molecular identification. The protein sequences deduced from the partial genes encoding GTP cyclohydrolase II, DRAP deaminase, 3,4-dihydroxy-2-butanone -4-phosphate synthase and lumazine synthase in the yeast exhibited high identity with those of the corresponding enzymes for riboflavin biosynthesis in other yeasts, respectively. Fe3+ available in the medium repressed riboflavin production and expression of the genes responsible for riboflavin biosynthesis in the yeast. The results have evidenced that riboflavin synthesis pathway indeed existed in the yeast. This is the first time to report that C. membranifaciens subsp. flavinogenie W14-3 from the marine environment could produce riboflavin.