Heterothallic sexual life cycle was recently discovered in the environmental strains of Aspergillus fumigatus (AF) isolated in Ireland. The discovery evoked excitement among mycologists since heterothallism enables genetic studies via recombinational analysis. However, the 6-month incubation period required for the formation of sexual spores in these strains significantly stifles progress for genetic research. Thus, we aimed to identify MAT-1 and MAT-2 strains that could produce viable ascospores in a shorter period.
50 AF strains isolated in Ireland, USA and England were screened for their MAT types and those of opposite type were crossed on oatmeal agar at 30oC. Viability of the resulting ascospores was tested on malt extract agar plates at 37oC. Virulence of the strains was analyzed in CGD and hydrocortisone treated balb/C mice.
Out of 49 crosses, 39 produced cleistothecia containing ascospores. The remaining 10 crosses lacked the sexual structures. MAT-1 strains were evenly divided into three categories; good, poor and non-maters whereas MAT-2 strains were mostly poor maters. A pair of MAT-1 and MAT-2 strains that produced abundant cleiostothecia (>>100) containing over 10,000 ascospores/cleistothecium was chosen and designated as the pair of "œsupermaters". The supermater MAT-1 and MAT-2 strains showed similar virulence in both animal models. Although viability of the ascospores at 4 weeks was relatively low (10%), percent viability of the spores increased as the cleistothecia aged (over 90% in 5 months).
Different degrees of fertility were observed among the 50 isolates; fertility of MAT-2 strains was generally inferior to that of the MAT-1 strains. The pair of MAT-1 and MAT-2 strains that produced abundant cleistothecia with viable ascospores by 4 weeks was designated as "œsupermaters". The discovery of supermaters enables recombinational analysis in a shorter time period. Segregation patterns of genetic markers are currently being analyzed.
Full conference title:
- ASM 111th (2011)