Isolation of strains and their genome sequencing to analyze the mating system of Ophiocordyceps robertsii.

The fungal genus Ophiocordyceps contains a number of insect pathogens. One of the best known of these is Ophiocordyceps sinensis, which is used in Chinese medicine and its overharvesting threatens sustainability; hence, alternative species are being sought. Ophiocordyceps robertsii, found in Australia and New Zealand, has been proposed to be a close relative to O. sinensis, but little is known about this species despite being also of historical significance. Here, O. robertsii strains were isolated into culture and high coverage draft genome sequences obtained and analyzed. This species has a large genome expansion, as also occurred in O. sinensis. The mating type locus was characterized, indicating a heterothallic arrangement whereby each strain has an idiomorphic region of two (MAT1-2-1, MAT1-2-2) or three (MAT1-1-1, MAT1-1-2, MAT1-1-3) genes flanked by the conserved APN2 and SLA2 genes. These resources provide a new opportunity for understanding the evolution of the expanded genome in the homothallic species O. sinensis, as well as capabilities to explore the pharmaceutical potential in a species endemic to Australia and New Zealand.

Identification of the ergC gene involved in polyene drug sensitivity in the Mucorales species Phycomyces blakesleeanus.

BACKGROUND: A strain of Phycomyces blakesleeanus (Mucorales, Mucoromycota) that was previously isolated after ultraviolet mutagenesis has altered responses to polyene antifungal drugs, sterol profiles, and phototropism of its sporangia. In this study, the genetic basis for these changes was sought. METHODS AND RESULTS: Two base pair substitutions were identified in the mutant within a P. blakelesleeanus gene that is homologous to others characterized from fungi, such as the Saccharomyces cerevisiae ERG3 gene, encoding sterol Δ5,6-desaturase. The polyene resistance and growth reduction phenotypes co-segregated with mutations in the gene in genetic crosses. The P. blakelesleeanus wild type ergC gene complemented a S. cerevisiae deletion strain of ERG3. CONCLUSIONS: This gene discovery may contribute towards better antifungal use in treating mucormycoses diseases caused by related species in the order Mucorales.