Characterization of Phycomyces blakesleeanus mutants temperature-sensitive for heat-shock induced germination

Altered expression of chitin synthetase activity and biochemical changes in the cell wall in a developmental mutant of Phycomyces

The Phycomyces developmental mutant S356 elaborates spores which show a much poorer viability and a higher affinity for Calcofluor White than the wild-type spores. Protease-activated extracts of the mutant spores showed higher levels of chitin synthetase activity than the parental strain-derived spores. High levels of enzyme activity in the mutant extracts, but not in the corresponding wild-type extracts, could be detected in the absence of an exogenous protease. The high basal active chitin synthetase is not the result of activation by endogeneous proteases during cell breakage since protease inhibitors did not reduce, but rather increased, the activity levels. The analysis of cell wall composition in the mutant spores revealed significant changes in the proportion of uronic acids and protein but not in chitin. The mutant phenotype is discussed in relation to the developmental stage at which the alterations connected with cell wall metabolism occurred.

Expression of Tn5-derived kanamycin resistance in the fungus Phycomyces blakesleeanus

A plasmid, carrying the Tn5 gene for kanamycin resistance lacking its own promoter, has successfully been used in the selection of DNA sequences of the fungus Phycomyces blakesleeanus having promoter activity in Escherichia coli. Many of these sequences were also effective in promoting resistance to kanamycin when the corresponding chimeric plasmids were introduced in the fungus via spheroplast transformation. The selected phenotype was easily propagated through vegetative spores and behaved as a stable character since it was not appreciably lost in the absence of selection.