Insect Pathogenic Fungus Metarhizium Research Articles

Regulation of production of a trypsin-like protease by the insect pathogenic fungus Metarhizium anisopliae

The entomopathogenic fungus metarhizium anisopliae produces several cuticle-degrading proteases which may play a role in pathogenesis. The regulation of one of these, a trypsin-like protease PR2, has been investigated using depressed mycelia. Three insoluble protein sources, insect cuticle, elastin and collagen, as well as two soluble proteins, BSA and gelatin, induced PR2. The polymeric carbon sources cellulose and xylan resulted in derepressed basal levels but not induced production of PR2. An approximately 15-fold increase in PR2 activity per mg dry weight of mycelium was observed when the fungus was grown in the presence of bovine serum albumin (BSA), as compared with conditions of derepression alone. This indicates that PR2 is induced by BSA, and probably by other proteins. Basal levels of PR2 were detected after 8 h when mycelium was starved for both carbon and nitrogen but only after 16 h when starved for either nitrogen or carbon. In the presence of a protein source, nitrogen strongly repressed PR2 whereas carbon had little effect. There was no effect of sulphur on PR2 production.

Regulation of production of a trypsin-like protease by the insect pathogenic fungus Metarhizium anisopliae

The entomopathogenic fungus metarhizium anisopliae produces several cuticle-degrading proteases which may play a role in pathogenesis. The regulation of one of these, a trypsin-like protease PR2, has been investigated using depressed mycelia. Three insoluble protein sources, insect cuticle, elastin and collagen, as well as two soluble proteins, BSA and gelatin, induced PR2. The polymeric carbon sources cellulose and xylan resulted in depressed basal levels but not induced production of PR2. An approximately 15-fold increase in PR2 activity per mg dry weight of mycelium was observed when the fungus was grown in the presence of bovine serum albumin (BSA), as compared with conditions of depression alone. This indicates that PR2 is induced by BSA, and probably by other proteins. Basal levels of PR2 were detected after 8 h when mycelium was starved for both carbon and nitrogen but only after 16 h when starved for either nitrogen or carbon. In the presence of a protein source, nitrogen strongly repressed PR2 whereas carbon had little effect. There was no effect of sulphur on PR2 production.

Inhibition of ecdysteroid secretion from Manduca prothoracic glands in vitro by destruxins—Cyclic depsipeptide toxins from the insect pathogenic fungus Metarhizium anisopliae

Incubation of prothoracic glands (PG) from Manduca sexta with destruxins (DTX) (principally destruxin-A) inhibited ecdysteroid secretion in vitro in a dose-dependent manner over a 6 h test period. A concentration of 0.5 μg ml −1 DTX gave ca 50% inhibition of the basal rate of secretion. The effect of a 1 h preincubation of PG with 1 μg ml −1 DTX was completely reversed by washing and incubation in normal medium. DTX (1 μg ml −1) effectively completely prevented (93% inhibition) the large stimulatory effects on ecdysteroid secretion of exposure to dibutyryl cAMP in the presence of the phosphodiesterase inhibitor isobutylmethylxanthine (IBMX). DTX also significantly inhibited ecdysteroid secretion stimulated by the adenylyl cyclase activator forskolin, and by the calcium ionophore A23187. These results suggest that in Manduca PG, DTX may act at a level beyond these second messengers.

Control of the black vine weevil,otiorhynchus sulcatus, with the fungusmetarhizium anisopliae

The insect-pathogenic fungusMetarhizium anisopliae attacks larvae of the black vine weevil,Otiorhynchus sulcatus, an important pest of soft fruit and ornamental plants. In trials on strawberries and potted ornamental plants growing outdoors, a strain of this fungus has given promising results for control of the pest. Further work is required to determine the most effective dose rates, methods and timing of application.

Preliminary field tests on the use ofMetarhizium anisopliaefor the control ofNasutitermes exitiosus(Hill) (Isoptera: Termitidae)

AbstractThe insect-pathogenic fungusMetarhizium anisopliaecaused heavy mortality in laboratory groups of the Australian termiteNasutitermes exitiosus(Hill) to which infected workers had been added. Conidia ofM. anisopliaestarted an epizootic when introduced into field colonies ofN. exitiosusnear Canberra, irrespective of whether the termites were treated by dusting or spraying in the mound itself, or dusting in nearby feeding sites. In some cases, the disease persisted for at least 15 weeks, and by this time few healthy termites could be found in almost half the treated colonies. Samples of workers taken from treated colonies showed high levels of contamination byMetarhizium, irrespective of the state of the colony, but the factors that inhibited the completion of fungal development in the nest are unknown.