Mating type segregation in Choanephora cucurbitarum following sexual reproduction

Zygospore progeny from the cross between + and − isolates of Choanephora cucurbitarum consisted of +, −, and ± types. The + and − zygospore isolates were stable, giving rise to hyphal fragment cultures and sporangiospores with the same mating type as their respective parent. However, the ± zygospore isolates were unstable, segregating to +, −, and ± types during asexual propagations. During long-term storage, the + and − isolates were also very stable, but ± isolates were not. All the ± isolates originating from single zygospores, hyphal fragments, or sporangiospores produced azygospores, suggesting that azygospores of this fungus are produced by mating-type heterokaryotic mycelia. Keywords: azygospore, Choanephora cucurbitarum, germsporangiospore, germsporangium, zygospore germination.

Differentiation of mutants of Cephalosporium acremoniun in complex medium: the formation of unicellular arthrospores and their germination

Differentiation of swollen hyphal fragments to unicellular arthrospores accompanied the synthesis of cephalosporin C by a series of Cephalosporium acremonium mutants during propagation in a complex medium. The complex medium supported significantly higher synthesis than the defined medium used in previous studies of differentiation in C. acremonium. The mutants differed in their ability to form unicellular arthrospores and to synthesize cephalosporin C, but a one-to-one correspondence between the two properties was not observed. An inverse relation was observed between the growth rates of the mutants and their ability to synthesize cephalosporin C: each mutant produced more antibiotic but grew more slowly than its parent strain. Germination of the unicellular arthrospores occurred in complex medium but differed significantly from the germination of conidia in seed medium. The unicellular arthrospores were examined by electron microscopy and compared with swollen hyphal fragments and slender hyphal filaments. The unicellular arthrospores had a thicker cell wall, rougher cell surface, and had one or more small indentations in their surface. The internal structure of the unicellular arthrospore resembled those of the swollen hyphal fragment and slender hyphal filament. Filaments had lower concentrations of lipid-containing vacuoles which were prevalent in both the swollen hyphal fragments and the unicellular arthrospores.