The role of vitamin B1 as a regulator of yeast dimorphism (yeast-hypha conversion)

在葡萄糖半限定培养基中添加乙醇后，热带假丝酵母吸收石油的酵母发生了从酵母到假菌丝的二相性转变。对酵母对照培养物和添加乙醇的培养物(乙醇培养物)的cDNA进行了差减基因克隆。从该片段中分离到裂殖酵母nmtl^+或酿酒酵母tHi5的同源物，作为乙醇培养的优势表达基因。由于外源硫胺素抑制了CtTHI5在热带锥虫生长培养基中的表达，因此将该同源物暂定为CtTHI5。乙醇培养呈现双相生长模式，CtTHI5表达出现在第一个生长阶段。在乙醇培养的第一阶段添加硫胺素后，CtTHI5的表达受到抑制，假菌丝的生长和假菌丝体的出现也被延迟。该菌的一种CtTHI5干扰物即使在对照培养中也不显示硫胺素营养不良，并产生假菌丝。在对照培养中添加一种类似硫胺素的氧化硫胺后，出现了假菌丝。在乙醇培养中添加丙戊酸可抑制假菌丝生长，但添加硫胺素可部分消除这种抑制作用。这些事实表明，硫胺参与了该生物体中假菌丝的生长过程。

The dimorphic transition from yeast to pseudohyphae in the petroleum-assimilating yeast Candida tropicalis occurs following the addition of ethanol to glucose semi-defined medium. Subtractive gene cloning was performed on the cDNA from the yeast-bowing control culture and on that from the ethanol-supplemented one (the ethanol culture). A homologue of Schizosaccharomyces pombe nmtl^+ or Saccharomyces cerevisiae THI5 was isolated from the cDNA fraction as a preferentially expressed gene for the ethanol culture. This homologue was tentatively called CtTHI5, since exogenous thiamine repressed its expression in C.tropicalis growth media. The ethanol culture showed biphasic pattern of growth phases and the expression of CtTHI5 occurred at the first growth phase. The supplementation of thiamine to the ethanol culture at the first phase was followed by repression of CtTHI5 expression and also delay of pseudohyphal growth and the occurrence of pseudomycelia in a stubby form with branched filaments. A CtTHI5 disruptant of this organism did not show thiamine auxotrophy and produced pseudohyphal filaments even in the control culture. The supplement of oxythiamine, an analog of thiamine, to the control culture was followed by the appearance of pseudohyphal filaments. Supplementation of valproic acid to the ethanol culture inhibited pseudohyphal growth, however, additional supplementation of thiamine partially cancelled the inhibition. These facts indicate that the participation of thiamine during the process of pseudohyphal growth in this organism.