Ascocarp production by Nannizzia otae on keratinous and non-keratinous agar media and mating behavior of N. otae and 123 Japanese isolates of Microsporum canis

Abstract

Ascocarp production byNannizzia otae, VUT 77054‘+’x VUT 77055‘−’, was compared on 8 different (1 keratinous and 7 non-keratinous) agar media.

Oatmeal salts agar and diluted Sabouraud dextrose salts agar with or without yeast extract were found to be unsuitable for ascocarp production in this species. In contrast, three different variants of oatmeal salts agar enriched with yeast extract proved to be satisfactory for the same purpose, while oatmeal salts agar with both yeast extract and horsehair powder was not necessarily superior to the former three media in this regard. Niger seed salts agar enriched with yeast extract was the most superior to any other seven media in all of the following respects; i.e., the number of gymnothecia produced per plate, the germination rate of ascospores, and the suppression of sporulation.

Asci from the cross VUT 77054‘+’ x VUT 77055‘−’ that yielded abundant fertile gymnothecia on niger seed salts agar with yeast extract were dissected and 51 ascospores were randomly isolated. Of the 51 ascospores, 47 (92%) germinated to form mature colonies. Of the 47 monoascospore F₁ progeny back crossed to the parentals, 21 (45%) mated or reacted with the ‘+’ mating type, 18 (38%) did with the ‘−’ mating type, and the remaining 8(17%) were sexually nonreactive.

One hundred and twenty-three Japanese isolates ofMicrosporum canis, obtained from human and animal ringworms for the past 12 years, were also crossed with the tester strains ofN. otae on selected 3 of the 8 media to determine their mating type. Out of these 123, 113 (92%) produced fertile gymnothecia in crosses with VUT 77054 ‘+’, 9(7%) were non-reactive, and the only one isolated from human in Osaka city produced fertile gymnothecia in crosses with VUT 77055‘−’. The data suggest thatM. canis (N. otae) exists predominantly as ‘−’ mating type in Japan. A possible explanation for this unequal distribution of mating type is presented.