Physiological study and alcohol oxidase gene(s) of thermotolerant methylotrophic yeasts isolated in Thailand

Nantana Srisuk. Faculty of Science. Department of Microbiology E-mail:fscints@ku.ac.th; Savitree Limtong. Faculty of Science. Department of Microbiology; Yurimoto, Hiroya. Graduate School of Agriculture. Division of Applied Life Sciences. Laboratory of Microbial Biotechnology; Sakai, Yasuyoshi. Graduate School of Agriculture. Division of Applied Life Sciences. Laboratory of Microbial Biotechnology; Kato, Nobuo. Graduate School of Agriculture. Division of Applied Life Sciences. Laboratory of Microbial Biotechnology

Physiological study and alcohol oxidase gene(s) of thermotolerant methylotrophic yeasts isolated in Thailand

2006

Nantana Srisuk(Kasetsart University. Bangkhen Campus, Bangkok (Thailand). Faculty of Science. Department of Microbiology) E-mail:fscints@ku.ac.th | Savitree Limtong(Kasetsart University. Bangkhen Campus, Bangkok (Thailand). Faculty of Science. Department of Microbiology) | Yurimoto, Hiroya(Kyoto University, Kyoto 606-8502 (Japan). Graduate School of Agriculture. Division of Applied Life Sciences. Laboratory of Microbial Biotechnology) | Sakai, Yasuyoshi(Kyoto University, Kyoto (Japan). Graduate School of Agriculture. Division of Applied Life Sciences. Laboratory of Microbial Biotechnology) | Kato, Nobuo(Kyoto University, Kyoto (Japan). Graduate School of Agriculture. Division of Applied Life Sciences. Laboratory of Microbial Biotechnology)

Two thermotolerant methylotrophic yeasts, Candida sithepensis sp. nov. and Pichia siamensis sp. nov. isolated in Thailand were studied for their physiology and alcohol oxidase gene(s). Optimum and maximum temperatures for growth on methanol of C. sithepensis sp. nov. were 34 deg C and 37 deg C whereas those of P. siamensis sp. nov. were 37 deg C and 40 deg C, respectively. Effect of methanol on the methylotrophic growth of the two yeast strains was investigated within the ranges of 0.25 percent to 2 percent (v/v) methanol. At 34 deg C, C. sithepensis sp. nov. exhibited a decline in micro max from 0.16/h to 0.13/h with respect to increase in methanol concentration. When cultivated at 37 deg C, the micro max of C. sithepensis sp. nov. was found to be drastically decreased from 0.16/h to 0.10/h within the same rangew of methanol concentration studied. P. siamensis sp. nov. showed an insignificant decrease of micro max with respect to an increase in methanol supplement when cultivated at 37 deg C. Key enzymes involved in methanol dissimilatory pathway, i.e., alcohol oxidase (AOD), glutathione-dependent formaldehyde dehydrogenase (FLD), formate dehydrogenase (FDH) and catalase (CAT) of the two yeasts were assesed. As for the favorable growth of C. sithepensis sp. nov. at its optimum temperature, fairly high level of specific AOD activity was observed but lower level of specific AOD activity was exhibited at maximum temperature. In contrast, specific FLD and FDH activity profiles were found to be higher when the yeast C. sithepensis sp. nov. was grown at its maximum temperature compared to the methylotrophic growth at its optimum temperature. Catalase production appeared to be slightly disturbed under all conditions studied. In case of P. siamensis sp. nov., stationary phase growth under low methanol supplement at its optimum temperature appeared soon after 24h cultivation. Nucleotide sequences of AOD gene(s) of the two yeasts were investigated. C. sithepensis sp. nov. showed two AOD genes designated as AOD1 and AOD2 whereas P. siamensis sp. nov. revealed only one AOD gene within the genome.

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