Investigations of the Thermophobic Character in Neurospora crassa, Especially of the Relationships Between Temperature and Carbohydrate Utilization

Citation

Pao, Wen Kwe (1950) Investigations of the Thermophobic Character in Neurospora crassa, Especially of the Relationships Between Temperature and Carbohydrate Utilization. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/7M5A-FG46. https://resolver.caltech.edu/CaltechTHESIS:12122012-103207950

Abstract

The thermophobic character is a temperature mutant which is unable to grow at 35°C on certain sugars in tube culture. This character is controlled by a single gene located far away from the centromere on the chromosome of Paba linkage group.

A limited growth of thermophobic strain on lactose minimal medium can be forced at 35° after activation at 25° for as little as 2 hours. The experiments show that the inhibition of growth at higher temperature is not due to nutritional deficiency, change of permeability of cell membrane to certain sugars or inhibition of hydrolytic enzymes of oligosaccharides. At 40° the thermophobic strain can not grow on any sugar, while the normal strain can grow on certain sugars but not others, just as the thermophobic strain did at 35°. The difference of effective temperature between the strains is only 5°C. This led to the studies of the common step of carbohydrate degradation, e.g., glycolysis and Krebs' cycle. All Krebs' acids were found to have a strong thermophobic effect at 35° on the thermophobic strain on sucrose. But the manometric studies of certain of the enzyme systems in Krebs' cycle reveal no significant differences between the strains.

In liquid culture on lactose at 35° there appears a morphological difference between the strains, i.e., semicolonial for the thermophobic strain and usual filamentous for the normal. This led to the studies of cell wall material in Neurospora, and it was found that there is a difference in response to chlorozinc iodine staining. The staining reaction is quantitatively related to the length of unacetylated end group of chitin. Estimates show that the chitin of the thermophobic strain has a length of half molecule only about 1/5 that of normal. A length of chitin half mol ecule less than 100 acetylglucosamine units will induce a growth of semicolonial form in liquid culture, and will have very little measurable growth in tube culture. The length of chitin molecule is influenced by glucose-acetate ratio. Temperature and type of sugar will influence the ratio greatly, and will thus change the habit of growth of both strains, but different quantitatively as the thermophobic gene causes a shortness of chitin molecule from the start.

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