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Hirsutella thompsonii (Ht) is a fungal pathogen of acarines and the primary cause of epizootics among mites. The draft genomes of two isolates of Ht (MTCC 3556: Ht3, 34.6 Mb and MTCC 6686: Ht6, 34.7 Mb) are presented and compared with the genomes of Beauveria bassiana (Bb) ARSEF 2860 and Ophiocordyceps sinensis (Os) CO18. Comparative analysis of carbohydrate active enzymes, pathogen–host interaction genes, metabolism-associated genes, and genes involved in biosynthesis of secondary metabolites in the four genomes was carried out. Reduction in gene family sizes in Ht3 and Os as compared with Ht6 and Bb is observed. Analysis of the mating type genes in Ht reveals the presence of MAT idiomorphs which is suggestive of cryptic sexual traits in Ht. We further identify and classify putative chitinases that may function as virulence factors in fungal entomopathogens due to their role in degradation of arthropod cuticle.

Beauveria is an insect-associated fungal genus and it represents a monophyletic lineage within the Cordycipitaceae (Hypocreales, Sordariomycetes). Beauveria species are economically important as mycoinsecticides and a good source of secondary metabolites. In this study, we employed the genealogical concordance phylogenetic species recognition criterion to resolve the evolutionary relationships of 125 Beauveria and Beauveria-like isolates from India. In ITS-based phylogenetic analysis, 111 fungal isolates clustered within Beauveria clade (Cordycipitaceae), while 14 Beauveria-like isolates showed phylogenetic affinities with Isaria (Cordycipitaceae) and Tolypocladium (Clavicipitaceae) clades. In a multi-gene phylogenetic analysis involving the partial Bloc, EF1α, RPB1 and RPB2 gene sequence-data, a novel Beauveria lineage was recovered that has been described here as Beauveria rudraprayagi sp. nov. This is the first study from India on the molecular taxonomy of Beauveria using GCPSR criterion.

BackgroundAschersonia badia [(Ab) Teleomorph: Hypocrella siamensis] is an entomopathogenic fungus that specifically infects scale insects and whiteflies. We present the whole genome sequence of Ab and its comparison with two clavicipitaceous fungi Metarhizium robertsii (MR: generalist entomopathogen) and M. acridum (MAC: acridid-specific entomopathogen) that exhibit variable host preferences. Here, through comparative analysis of pathogen-host interacting genes, carbohydrate active enzymes, secondary metabolite biosynthesis genes, and sexuality genes, we explore the proteins with possible virulence functions in clavicipitaceous fungi. Comprehensive overview of GH18 family chitinases has been provided to decipher the role of chitinases in claviceptaceous fungi that are either host specific or generalists.ResultsWe report the 28.8 Mb draft genome of Ab and its comparative genome analysis with MR and MAC. The comparative analyses suggests expansion in pathogen-host interacting gene families and carbohydrate active enzyme families in MR, whilst their contraction in Ab and MAC genomes. The multi-modular NRPS gene (dtxS1) responsible for biosynthesis of the secondary metabolite destruxin in MR is not conserved in Ab, similar to the specialist pathogen MAC. An additional siderophore biosynthetic gene responsible for acquisition of iron was identified in MR. Further, the domain survey of chitinases suggest that the CBM50 (LysM) domains, which participate in chitin-binding functions, were not observed in MAC, but were present in Ab and MR. However, apparent differences in frequency of CBM50 domains associated with chitinases of Ab and MR was identified, where MR chitinases displayed a higher proportion of associated CBM50 domains than Ab chitinases.ConclusionsThis study suggests differences in distribution of dtxS1 and chitinases in specialists (Ab and MAC) and generalists (MR) fungi. Our analysis also suggests the presence of a siderophore biosynthetic gene in the MR genome which perhaps aids in enhanced virulence potential and host range. The variation in association of CBMs, being higher in generalists (MR) and lower in specialists (Ab and MAC) fungi may further be responsible for the differences in host affiliation.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-2710-6) contains supplementary material, which is available to authorized users.