各種の炭化水素を炭素源とした培地を用いて,309株の供試菌(同定株133株,未同定の分離株176株)から炭化水素資化性の強い菌株を選択した。その結果,M.japanica 316, M.japonica 6226, M.japonica 6229, C.tropicalis 6019, C.tropicalis 6263, C. trioucakus 6264,土壌からの分離母Y191株の7菌株を得た。Y191株, M.japonica 316はCetaneを炭素源とする培地でとくによい生育をしたが,窒素源として硫酸アンモニウムを使用したばあいは培地のpHが極端に低下した。硫酸アンモニウムのかわりに尿素を用いると,培養によるpHの極端な低下が防止でき,生育量も増大した。Y191株においてとくに生育量の増大が顕著であった。つぎに,赤木によって四日市市の油浸土壌から分離された炭化水素資化性の強いY191号菌(Candida sp.に属する)の生育におよぼす種種の窒素源,界面活性剤などの影響を検討した。窒素源としては尿素が適当であり,その濃度は0.2～0.8%が良好であった。供試した10種類の界面活性剤のうち,Candida sp. Y191株の生育に効果があったものは,Span 40, Span 80, Span 85であった。中でもSpan 85がもっとも効果的であり,その適量は0.005～0.01%であった。また,培養フラスコ中の培養液量の増加とともに,一定量の培地からの菌体収量は減少した。しかし,Span 85の添加により,収量の減少は大幅に防止できた。We attempted to obtain yeast strains which utilize hydrocarbon as carbon source. In this report, three hundred and nine strains of yeast were employed. These strains included one hundred and thirty-three strains of identified yeast, i.e., forty-four strains of Pichia, fifty-four strains of Hansenula, six strains of Saccharomyces, ten strains of Candida, three strains of Mycotorula, five strains of Rhodotorula and eleven strains of Debaryomyces, and one hundred and seventy-six strains of unidentified yeast. Seven strains of yeast, Mycotorula japonica 316, Mycotorula japonica 6226, Mycotorula japonica 6229, Candida tropicalis 6019, Candida tropicalis 6263, Candida tropicalis 6264 and unidentified strain Y 191, utilizing hydrocarbon as carbon source were selected. Among these seven strains of yeast, Mycotorula japonica 316 and Y 191 strain, which had been isolated from oily soil by M. Akaki, one of the authors, grew abundantly, especially in the medium containing cetane as carbon source. When ammonium sulphate was used as nitrogen source, the pH of culture media depressed extremely during cultivation. In the culture with media, which used urea instead of ammonium sulphate as nitrogen source, these yeast cultures were prevented from depression of pH during cultivation, and gave high yield of the yeast cell, particularly Y 191 strain. Since Y 191 strain is capable of utilizing various hydrocarbon sources and making rapid growth in the media containing hydrocarbon, it would seem to be a promising strain for cell production from hydrocarbons. The effects of various nitrogen sources and surfactants on the growth of hydrocarbon utilizing yeast Y 191, which identified as Candida sp, by M. Akaki, were investigated in shaking culture on the basal medium B(Table 2) containing 1 per cent cetane as carbon source, Following results were obtained. Four kinds of nitrogen source, i,e., urea, ammonium sulfate, ammonium chloride and ammonium nitrate, were tested. Among these four, urea was most fitted for the growth of the yeast, and gave higher yeast cell yield than the other nitrogen sources tested. Optimal concentration of urea as a nutrient for the yeast growth in the medium containing 1 per cent cetane as carbon source was between 0.2 and 0.8 per cent. Ten kinds of surfactant shown in Table 10 were tested. Among them, Span 40, Span 80, Span 85 gave good effects on the growth of the yeast in the basal medium. Especially, Span 85 was most effective for the yeast growth. Optimal concentration of Span 85 for the growth of the yeast in the medium was between 0.005 and 0.01 per cent. The yeast cell yield on the basis of a definite amount of the medium decreased with the increase of the volume of medium in a culture flask. However, the addition of Span 85 to the basal medium greatly prevented the yeast cell yield on the basis of a definite amount of the medium from decreasing
