Isolation and biochemical analysis of Mucor bacilliformis monomorphic mutants

Abstract

Fourteen stable mutants of Mucor bacilliformis which grew yeastlike under both aerobic and anaerobic conditions were isolated after treatment of growing mycelium with N-methyl-N'-nitro-N-nitrosoguanidine. Biochemical characterization of the mutants included determination of growth in different carbon and nitrogen sources, determination of sensitivity of respiration to cyanide and salicylhydroxamate, analysis of cytochrome spectra, determination of glutamate dehydrogenases, glutamine synthase, and ornithine decarboxylase activities, and measurement of cyclic AMP levels. Data showed that all mutants were defective in some aspect of oxidative metabolism and had low levels of ornithine decarboxylase, whereas other characters were variable. It was concluded that morphological transition in M. bacilliformis is probably associated with mitochondrial functions and expression of omithine decarboxylase, but may be independent of cyclic AMP and glutamate dehydrogenase levels. The importance of genetic studies in the analysis of dimorphism is stressed.

Mucor dimorphism.

“…However, Orlowski and Ross (155) reexamined this issue and corroborated the initial assertion of Larsen and Sypherd (118) that Mucor morphology and intracellular cyclic-AMP levels are inextricably linked. The cyclic-AMP levels reported in the study by Paznokas and Sypherd (169) seem anomalously high when compared with results obtained by other investigators (118,155,167,196 These concentrations drop precipitously when either type of culture is shifted to an air atmosphere. The levels of cyclic AMP stay the same if the CO2 is changed to nitrogen or vice versa, implying that the decline in nucleotide concentration observed during morphogenesis is not due simply to a reduction in CO2 tension.…”

“…to the yeast phase. Similarly, mutants deficient in aerobic respiration are reported to be locked into the yeast morphology (208), and mutants selected as monomorphic are reportedly all respiratory deficient (196). All these findings might suggest an obligatory link between aerobic respiration and Mucor morphology.…”

“…Respiratory-deficient monomorphic mutants have been isolated from M. bacilliformis by Ruiz-Herrera et al (196). Two of these mutants display a reduced level of NADdependent GDH activity, and both possess high levels of intracellular cyclic AMP.…”

Respiratory-competent conditional developmental mutant of Mucor racemosus

“…The isolation and characterization of Mucor bacilliformis mutants unable to grow in the mycelial morphology has been reported by Storck and Morrill (16) and Ruiz-Herrera et al (14). The obligate yeast variants described in these studies were defective in various aspects of oxidative energy metab-olism (i.e., respiratory deficient, defective in the tricarboxylic acid [TCA] cycle, or uncoupled).…”

“…Thus its role as an indicator of oxidative activity is already established. The use of a small-molecule intermediate of oxidative metabolism such as citrate as an inducer or corepressor for both glycolytic enzyme synthesis and for polypeptides involved in morphogenesis would explain why anaerobiosis, a variety of different mutations (14,16) in oxidative metabolism, or various inhibitors of oxidative metabolism (3,18,22) lead to growth in the yeast morphology and to a highly fermentative metabolic mode. Each of these would be expected to lead to relatively low citrate pools.…”