Secondary metabolite gene clusters in the entomopathogen fungus Metarhizium anisopliae: genome identification and patterns of expression in a cuticle infection model

Abstract

BackgroundThe described species from the Metarhizium genus are cosmopolitan fungi that infect arthropod hosts. Interestingly, while some species infect a wide range of hosts (host-generalists), other species infect only a few arthropods (host-specialists). This singular evolutionary trait permits unique comparisons to determine how pathogens and virulence determinants emerge. Among the several virulence determinants that have been described, secondary metabolites (SMs) are suggested to play essential roles during fungal infection. Despite progress in the study of pathogen-host relationships, the majority of genes related to SM production in Metarhizium spp. are uncharacterized, and little is known about their genomic organization, expression and regulation. To better understand how infection conditions may affect SM production in Metarhizium anisopliae, we have performed a deep survey and description of SM biosynthetic gene clusters (BGCs) in M. anisopliae, analyzed RNA-seq data from fungi grown on cattle-tick cuticles, evaluated the differential expression of BGCs, and assessed conservation among the Metarhizium genus. Furthermore, our analysis extended to the construction of a phylogeny for the following three BGCs: a tropolone/citrinin-related compound (MaPKS1), a pseurotin-related compound (MaNRPS-PKS2), and a putative helvolic acid (MaTERP1).ResultsAmong 73 BGCs identified in M. anisopliae, 20 % were up-regulated during initial tick cuticle infection and presumably possess virulence-related roles. These up-regulated BGCs include known clusters, such as destruxin, NG39x and ferricrocin, together with putative helvolic acid and, pseurotin and tropolone/citrinin-related compound clusters as well as uncharacterized clusters. Furthermore, several previously characterized and putative BGCs were silent or down-regulated in initial infection conditions, indicating minor participation over the course of infection.Interestingly, several up-regulated BGCs were not conserved in host-specialist species from the Metarhizium genus, indicating differences in the metabolic strategies employed by generalist and specialist species to overcome and kill their host. These differences in metabolic potential may have been partially shaped by horizontal gene transfer (HGT) events, as our phylogenetic analysis provided evidence that the putative helvolic acid cluster in Metarhizium spp. originated from an HGT event.ConclusionsSeveral unknown BGCs are described, and aspects of their organization, regulation and origin are discussed, providing further support for the impact of SM on the Metarhizium genus lifestyle and infection process.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-3067-6) contains supplementary material, which is available to authorized users.

Biosynthesis of helvolic acid and identification of an unusual C-4-demethylation process distinct from sterol biosynthesis

“…Among them, HelB3 is able to catalyze the dual oxidation of C-6 and C-7, to which a similar mechanism is only observed in the fungal meroterpenoid terretonin biosynthesis 28 . Sequence alignment of the P450 enzymes from the helvolic acid gene cluster reported by us and those identified from Sarocladium oryzae 29 and Metarhizium anisopliae 30 revealed some amino acid residues are specifically conserved in HelB3 homologs, but not in other P450 enzymes (Supplementary Fig. 27 ), which might account for its intriguing property.…”

Identification of Secondary Metabolite Gene Clusters in the Pseudovibrio Genus Reveals Encouraging Biosynthetic Potential toward the Production of Novel Bioactive Compounds

“…These analyses revealed that for some families (bacteriocin, NPRS, T1-T3PKS, terpene) the overall identity of the BGCs within the genus is considerably high (> = 75%; Figure 2 ). Given that the majority of the Pseudovibrio strains investigated have been isolated from marine invertebrates, it is tempting to speculate that these metabolites could play a role in interactions with the host or be used by Pseudovibrio to interact with the rest of the bacterial community while establishing itself in the host microbiome, as has been previously described for other bacteria and fungi ( Sharon et al, 2014 ; Sbaraini et al, 2016 ). However, some significant degree of variability existed among the strains.…”

Natural Products from Actinobacteria Associated with Fungus-Growing Termites

“…In contrast, extracts obtained from isolates belonging to Arthrobacter , Cellulosimicrobium , Aeromicrobium, Luteimicrobium and Mycobacterium showed almost no inhibitory activity against any of the investigated test strains. Thirty-seven extracts with moderate to strong antifungal activity were subjected to a second antifungal assay against ecologically-relevant co-occurring fungi derived from termite nests, four different fungal cultivar isolates (two species) and two entomopathogenic fungi ( Beauvaria bassiana ST 17960 and Metarhizium anisopliae ATCC 24942) [ 32 , 33 ]. As depicted in Figure 5 , the majority of culture extracts inhibited none of the representative competing or mutualistic fungi.…”