Isolation and characterization of chlorate resistant mutants from nitrate-nonutilizing fungus Phycomyces blakesleeanus

Abstract

Chlorate resistant mutants, which were first isolated in the zygomycetous fungus Phycomyces blakesleeanus, were found to be resistant up to a concentration of at least 300 mM of potassium chlorate. The dose-response relationship showed that although the mutants could be divided into two groups based on chlorate resistance in the mycelial elongation assay on the solid minimal medium, this was not observed in the assay using liquid culture. Genetic analysis of heterokaryons revealed the mutant alleles to be dominant. Enzymatic activities of three nitrate reductases and chlorate reductase were deficient in both the parent strain and the mutants. Intracellular incorporation of chlorate ion varied from strain to strain; however, the variation could not explain the mechanism of chlorate resistance. One unexpected characteristic of the mutants was that the intracellular sulfate ion concentration was 3.5 to 5.5 times higher than in the parent strain. We designated this mutant genotype crw, chlorate resistant mutant from nitrate-nonutilizing wild type.

Effects of chemical components and nitrogen sources on zygospore development in Phycomyces blakesleeanus

“…Mo acts as an electron carrier in the enzymatic reduction of nitrates. This involvement is, however, unlike that of Phycornyces, which is deficient in nitrate utilization (Garc~s et al, 1985;Fukui et al, 2000). It is well known that Ca is involved in many essential cell functions in eukaryotic cells: maintenance of the structural integrity of the cell membranes, enzyme activity, and the operation of microfilaments and microtubules (Moore-Landecker, 1996).…”