Term of Award

Spring 1998

Degree Name

Master of Science in Biology

Document Type and Release Option

Thesis (restricted to Georgia Southern)


Department of Biology

Committee Chair

Sara Neville Bennett

Committee Member 1

Wayne A. Krissinger

Committee Member 2

Donald Drapalik


Osmotic-sensitive mutants of the fungus Neurospora crassa fail to grow on medium of increased osmotic pressure. The usual test is their failure to grow on medium with 4% NaCI or with 6% NaCI. These mutants have an accompanying altered morphology resulting in short, cropped aerial hyphae that exude pigmented cytoplasm. A faulty cell wall is thought to be responsible for the phenotype of these mutants. An osmotic-sensitive mutant SS-18 whose morphology resembled the morphology of wild type and differed from that of the typical earlier described osmotic-sensitive mutants was isolated at the Georgia Southern University Laboratory following UV irradiation of the wild type strain. The two backcrosses of SS-18 to wild type 74 each resulted in a 1:1 segregation of wild type to mutant progeny (34:29 and 43:28). These results indicated that the osmotic sensitivity observed was due to a single gene under Mendelian control. Since SS-18 resembled SS-462, another osmotic sensitive mutant isolated in our laboratory, a complementation test between the two mutant was performed. Results of this test ruled out allelism of the two mutants. A cross of SS-18 was made to the multi-marker tester strain alcoy. The results indicated that SS-18 was linked to ylo and Linkage Group III or Linkage Group VI. Complementation tests indicated that SS-18 was not an allele of os-8 in LG III or of os-9 in LGVI. Therefore, SS-18 represents a new locus for osmotic sensitivity. Since some osmotic sensitive mutants produce few or no conidia, SS-18 was compared to wild type and to os-5 for abundance of conidia. os-1 did not produce sufficient conidia to be included in this study. SS-18 was found to have 3.5 x105 conidia/ml, wild type 3 x105 conidia/ml, and os-5 76 x 105 conidia/ml. The number of conidia produced by SS-18 was significantly different (p<.05) from the number produced by wild type 74 and by os-5. Sensitivity of SS-18 to minimal media containing various osmotica was compared to that of os-1 and os-5. Wild type 74 served as the control. The results disclosed that SS-18 had no growth (clean) on medium of 1.37 osmolality (6%) NaCI, but did not show sensitivity on medium containing KCI or glucose as the osmotica. SS-18 differed from os-1 which exhibited a greater degree of sensitivity to media containing NaCI, and was also sensitive to media with KCI or glucose as the osmotica; os-5 was leaky on media with NaCI and was sensitive to 1.71 osmoles of glucose This suggests that some mechanism other than a faulty cell wall might be responsible for osmotic sensitivity observed in SS-18.


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