Isolation, Identification and Cultivation of Methanol-Utilizing Yeasts
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A large number of methanol-utilizing yeaste were isolated from a wide variety of nutural sources in Japan. Typical twenty-five strains were identified. These strains were found to belong to five species, Candida boidinii, Torulopsis molischiana, Torulopsis sonorensis, Pichia methanolica and Hansenula polymorpha, on the basis of the biochemical and physiological characteristics, the assimilation of carbon compounds, the GC-content in DNA and the ubiquinone system.Continuous cultures of Pichia methanolica Y-1023,Torulopsis sonorensis MT-8,Hansenula polymorpha U-22 and I-3 were carried out, and the feasibility of single cell protein production from methanol was studied. Optimum cultural conditions of P. methanolica Y-1023 were 28℃, pH 3.5-4.5 and a dilution rate of 0.13-0.19 h^<-1>, those of T. sonorensis Mt-8 were 34℃, pH 4.0-4.5 and a dilution rate of 0.15-0.22 h^<-1>, and those of H. polymorpha U-22 and I-3 were 38℃, pH 4.0-4.5 and a dilution rate of 0.13-0.19 h^<-1>. Of these four strains, H. polymorpha I-3 seems to be the most suitable for commercial production of yeast SCP from methanol in the optimum cultural temperature, the cell yield, the growth rate, the contents of crude protein and amino acids, and the composition of amino acids. H. polymorpha I-3 showed the maximum specific growth rate which was approximately 0.209 h^(-1), a cell yield which was approximately 38 wt%, a content of crude protein which was approximately 56 wt%, a content of amino acids which was approximately 50 wt%, and the maximum content of nucleic acids which was approximately 9 wt%. The methanol consumption rate per unit cell mass for maintenance, m, was about 0.015 g methanol/g cell・h. The value for the Monod constant K_s was about 1.39 ppm of methanol.