Discovery of a sexual cycle in Aspergillus lentulus, a close relative of A. fumigatus.
Eukaryot Cell. 2013 May 6;
Authors: Swilaiman SS, O'Gorman CM, Balajee SA, Dyer PS
Aspergillus lentulus was described in 2005 as a new species within the A. fumigatus sensu lato complex. It is an opportunistic human pathogen causing invasive aspergillosis with high mortality rates, and has been isolated from clinical and environmental sources. The species is morphologically nearly identical to A. fumigatus sensu stricto and this similarity has resulted in their frequent misidentification. Comparative studies show that A. lentulus has some distinguishing growth features and decreased in vitro susceptibility to several antifungal agents including amphotericin B and caspofungin. Similar to the once-presumed asexual A. fumigatus, it is only known to reproduce mitotically. However, we now show that A. lentulus has a heterothallic sexual breeding system. A PCR-based mating-type diagnostic detected isolates of either MAT1-1 or MAT1-2 genotype and examination of 26 worldwide clinical and environmental isolates revealed a similar ratio of the two mating types (38% vs. 62%, respectively). MAT1-1 and MAT1-2 idiomorph regions were analysed, revealing the presence of characteristic alpha- and HMG-domain genes, together with other more unusual features such as a MAT1-2-4 gene. We then demonstrated that A. lentulus possesses a functional sexual cycle with mature cleistothecia, containing heat-resistant ascospores, being produced after three weeks incubation. Recombination was confirmed using molecular markers. However, isolates of A. lentulus failed to cross with highly-fertile strains of A. fumigatus, demonstrating reproductive isolation between these sibling species. The discovery of the A. lentulus sexual stage has significant implications for the management of drug resistance and control of invasive aspergillosis associated with this emerging fungal pathogen.
PMID: 23650087 [PubMed - as supplied by publisher]