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Insect pathogens as biological control agents: Back to the future.

Phylogenetic classification of Cordyceps and the clavicipitaceous fungi

Metarhizium spp. are being used as environmentally friendly alternatives to chemical insecticides, as model systems for studying insect-fungus interactions, and as a resource of genes for biotechnology. We present a comparative analysis of the genome sequences of the broad-spectrum insect pathogen Metarhizium anisopliae and the acridid-specific M. acridum. Whole-genome analyses indicate that the genome structures of these two species are highly syntenic and suggest that the genus Metarhizium evolved from plant endophytes or pathogens. Both M. anisopliae and M. acridum have a strikingly larger proportion of genes encoding secreted proteins than other fungi, while ∼30% of these have no functionally characterized homologs, suggesting hitherto unsuspected interactions between fungal pathogens and insects. The analysis of transposase genes provided evidence of repeat-induced point mutations occurring in M. acridum but not in M. anisopliae. With the help of pathogen-host interaction gene database, ∼16% of Metarhizium genes were identified that are similar to experimentally verified genes involved in pathogenicity in other fungi, particularly plant pathogens. However, relative to M. acridum, M. anisopliae has evolved with many expanded gene families of proteases, chitinases, cytochrome P450s, polyketide synthases, and nonribosomal peptide synthetases for cuticle-degradation, detoxification, and toxin biosynthesis that may facilitate its ability to adapt to heterogenous environments. Transcriptional analysis of both fungi during early infection processes provided further insights into the genes and pathways involved in infectivity and specificity. Of particular note, M. acridum transcribed distinct G-protein coupled receptors on cuticles from locusts (the natural hosts) and cockroaches, whereas M. anisopliae transcribed the same receptor on both hosts. This study will facilitate the identification of virulence genes and the development of improved biocontrol strains with customized properties.

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Genome sequencing and comparative transcriptomics of the model entomopathogenic fungi Metarhizium anisopliae and M. acridum.

Metarhizium anisopliae, the type species of the anamorph entomopathogenic genus Metarhizium, is currently composed of four varieties, including the type variety, and had been demonstrated to be closely related to M. taii, M. pingshaense and M. guizhouense. In this study we evaluate phylogenetic relationships within the M. anisopliae complex, identify monophyletic lineages and clarify the species taxonomy. To this end we have employed a multigene phylogenetic approach using near-complete sequences from nuclear encoded EF-1alpha, RPB1, RPB2 and beta-tubulin gene regions and evaluated the morphology of these taxa, including ex-type isolates whenever possible. The phylogenetic and in some cases morphological evidence supports the monophyly of nine terminal taxa in the M. anisopliae complex that we recognize as species. We propose to recognize at species rank M. anisopliae, M. guizhouense, M. pingshaense, M. acridum stat. nov., M. lepidiotae stat. nov. and M. majus stat. nov. In addition we describe the new species M. globosum and M. robertsii, resurrect the name M. brunneum and show that M. taii is a later synonym of M. guizhouense.

A multilocus phylogeny of the Metarhizium anisopliae lineage

A multi-gene phylogeny of Clavicipitaceae (Ascomycota, Fungi): identification of localized incongruence using a combinational bootstrap approach.

Paecilomyces lilacinus was described more than a century ago and is a commonly occurring fungus in soil. However, in the last decade this fungus has been increasingly found as the causal agent of infections in man and other vertebrates. Most cases of disease are described from patients with compromised immune systems or intraocular lens implants. In this study, we compared clinical isolates with strains isolated from soil, insects and nematodes using 18S rRNA gene, internal transcribed spacer (ITS) and partial translation elongation factor 1-α (TEF) sequences. Our data show that P. lilacinus is not related to Paecilomyces, represented by the well-known thermophilic and often pathogenic Paecilomyces variotii. The new genus name Purpureocillium is proposed for P. lilacinus and the new combination Purpureocillium lilacinum is made here. Furthermore, the examined Purpureocillium lilacinum isolated grouped in two clades based on ITS and partial TEF sequences. The ITS and TEF sequences of the Purpureocillium lilacinum isolates used for biocontrol of nematode pests are identical to those causing infections in (immunocompromised) humans. The use of high concentrations of Purpureocillium lilacinum spores for biocontrol poses a health risk in immunocompromised humans and more research is needed to determine the pathogenicity factors of Purpureocillium lilacinum.

Purpureocillium, a new genus for the medically important Paecilomyces lilacinus

On the relationships of Paecilomyces sect. Isarioidea species.

Insect pathogenic fungi have opened up a relatively untapped area of natural product research which, unfortunately, has not received much attention to date. Found in wild abundance in wet tropical Thailand, the insect fungi are shown to contribute not only as controllers of insect populations but also as rich sources of structurally novel biologically active substances.

Nigel L. Hywel-Jones

Papers

Phylogenetic classification of Cordyceps and the clavicipitaceous fungi

A multi-gene phylogeny of Clavicipitaceae (Ascomycota, Fungi): identification of localized incongruence using a combinational bootstrap approach.

Purpureocillium, a new genus for the medically important Paecilomyces lilacinus

On the relationships of Paecilomyces sect. Isarioidea species.

Bioactive Substances from Insect Pathogenic Fungi