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Title: Production of destruxins from Metarhizium spp. fungi in artificial medium and in endophytically colonized Cowpea Plants

item GOLO, PATRICIA - Universidade Federal Do Rio De Janeiro
item Gardner, Dale
item GRILLEY, MICHELLE - Utah State University
item TAKEMOTO, JON - Utah State University
item Krasnoff, Stuart
item PIRES, MARCUS - Universidade Federal Do Rio De Janeiro
item FERNANDES, EVERTON - Federal University Of Goias
item BITTENCOURT, VANIA - Universidade Federal Do Rio De Janeiro
item ROBERTS, DONALD - Utah State University

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/17/2014
Publication Date: 8/15/2014
Citation: Golo, P.S., Gardner, D.R., Grilley, M.M., Takemoto, J.Y., Krasnoff, S., Pires, M.S., Fernandes, E.K., Bittencourt, V.R., Roberts, D.W. 2014. Production of destruxins from Metarhizium spp. fungi in artificial medium and in endophytically colonized Cowpea Plants. PLoS One. DOI: 10.1371/journal.pone.0104946.

Interpretive Summary: Metarhizium fungi include strains that are widespread geographically and infect a wide range of injurious insect species. Thus, these fungi are important because of their potential as biocontrol agents of insects, and several related species have been commercialized as biopesticides and are now important components of integrated pest management programs. Destruxins, peptidal compounds produced by many strains of Metarhizium, are among the best known low molecular weight metabolites produced by insect pathogenic fungi, but their contribution, if any, to the effectiveness of these strains as biocontrols is still controversial. Data presented in this paper confirm previous findings indicating that destruxins are dispensable for virulence against insects. Despite a wealth of data indicating potent biological activity in many types of bioassays the biological role of destruxins, which are produced at great metabolic expense, remains obscure. Thus new insights into how they function are needed. Data presented in this paper indicate that destruxins are detectable in plants in which the producing strains were induced to grow as endophytes. This opens new lines of inquiry into how these compounds contribute to the success of these fungi as biocontrols and how they might be exploited for pest control in novel ways.

Technical Abstract: Destruxins (DTXs) are cyclic depsipeptides produced by many Metarhizium isolates that have long been assumed to contribute to virulence of these entomopathogenic fungi. We evaluated the virulence of 20 Metarhizium isolates against insect larvae and measured the concentration of DTXs A, B, and E produced by these same isolates in submerged (shaken) cultures. Eight of the isolates (ARSEF 324, 724, 760, 1448, 1882, 1883, 3479, and 3918) did not produce DTXs A, B, or E during the five days of submerged culture. DTXs were first detected in culture medium at 2–3 days in submerged culture. Galleria mellonella and Tenebrio molitor showed considerable variation in their susceptibility to the Metarhizium isolates. The concentration of DTXs produced in vitro did not correlate with percent or speed of insect kill. We established endophytic associations of M. robertsii and M. acridum isolates in Vigna unguiculata (cowpeas) and Cucumis sativus (cucumber) plants. DTXs were detected in cowpeas colonized by M. robertsii ARSEF 2575 12 days after fungal inoculation, but DTXs were not detected in cucumber. This is the first instance of DTXs detected in plants endophytically colonized by M. robertsii. This finding has implications for new approaches to fungus-based biological control of pest arthropods.