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

在向葡萄糖半定义培养基中加入乙醇后，石油同化酵母从酵母到假菌丝的二态转变发生。对酵母弯曲对照培养物和乙醇补充培养物（乙醇培养物）的cDNA进行减法克隆。从该cDNA片段中分离出了Schizosaccharomyces pombe nmtl^+或Saccharomyces cerevisiae THI5的同源基因，作为乙醇培养的优先表达基因。这个同源物暂时被称为CtTHI5，因为外源硫胺素抑制了它在热带血吸虫生长培养基中的表达。乙醇培养表现为两期生长模式，CtTHI5的表达发生在第一生长期。在第一期乙醇培养中添加硫胺素抑制了CtTHI5的表达，延缓了假菌丝的生长和假菌丝的出现，假菌丝呈短棍状，带有分枝丝。该生物的CtTHI5干扰物即使在对照培养中也没有表现出硫胺素营养不良，并产生假菌丝。在对照培养基中添加类似硫胺素的氧硫胺素后，出现假菌丝。在乙醇培养基中添加丙戊酸抑制了假菌丝的生长，然而，额外添加硫胺素部分抵消了这种抑制作用。这些事实表明，硫胺素参与了该生物的假菌丝生长过程。

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.