Optimisation of filtrationenrichment methods in fungi lacking asexual spores: mutagenesis, filtration and isolation of mutants

ABSTRACT

Filtration-enrichment is a very successful method for obtaining auxotrophs in fungi, where traditional methods can not applied directly to fungi lacking suitable asexual spores. This is mainly because of a heavy carry-over of parental nutrients into sexual spores such as ascospores. A procedure has been devised to apply filtration-enrichment to such fungi by using hyphal mutagenesis, crossing, germination of sexual spores, fragmentation of germination hyphae into small propagules, followed by two cycles of filtration-enrichment in liquid minimal medium. This technique was first applied by Helmi [1985] and then by others [Zwolinski, 1988]. In the present work this technique has been optimised with Ascobolus --immersus for mutagenesis, hyphal fragmentation and recovery, filtration pore size, duration and number of growth periods, and final isolation of colonies. It was possible to get yields of about 30% auxotrophs. This technique is easily applicable to other fungi, such as Sordaria