Interaction between Metarhizium anisopliae and Its Host, the Subterranean Termite Coptotermes curvignathus during the Infection Process.

Samsuddin Ahmad Syazwan,Wei Hong Lau,Ahmad Said Sajap,Rozi Mohamed,Shiou Yih Lee,Dzolkhifli Omar

doi:10.3390/biology10040263

Samsuddin Ahmad Syazwan, Wei Hong Lau + Show 4 more

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https://doi.org/10.3390/biology10040263

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Abstract

Simple SummaryThe use of Metarhizium anisopliae as a biological control of insect pests has been experimented in the laboratory as well as in field trials. This includes against the termite Coptotermes curvignathus, however the results have varying degrees of success. One reason could be due to the lack of detailed knowledge on the molecular pathogenesis of M. anisopliae. In the current study, the conidial suspension of M. anisopliae isolate PR1 was first inoculated on the C. curvignathus, after which the pathogenesis was examined using two different approaches: electron microscopy and protein expression. At the initiation stage, the progression observed and documented including adhesion, germination, and penetration of the fungus on the cuticle within 24 h after inoculation. Later, this was followed by colonization and spreading of the fungus at the cellular level. Proteomics of C. curvignathus witnessed the expression of proteins related to cell regulation and defense, while in M. anisopliae, protein related to transport and fungal virulence were expressed throughout the infection. These findings offer relevant knowledge for use in the development of M. anisopliae as a prospective biological control agent for termites in the future.Metarhizium anisopliae (Metchnikoff) Sorokin, a pathogenic fungus to insects, infects the subterranean termite, Coptotermes curvignathus Holmgren, a devastating pest of plantation trees in the tropics. Electron microscopy and proteomics were used to investigate the infection and developmental process of M. anisopliae in C. curvignathus. Fungal infection was initiated by germ tube penetration through the host’s cuticle as observed at 6 h post-inoculation (PI), after which it elongated into the host’s integumental tissue. The colonization process continued as seen from dissemination of blastospores in the hemocoel at 96 h PI. At this time point, the emergent mycelia had mummified the host and forty-eight hours later, new conidia were dispersed on the termites’ body surface. Meanwhile, hyphal bodies were observed in abundance in the intercellular space in the host’s body. The proteomes of the pathogen and host were isolated separately using inoculated termite samples withdrawn at each PI-time point and analyzed in two-dimensional electrophoresis (2-DE) gels. Proteins expressed in termites showed evidence of being related to cell regulation and the immune response, while those expressed in M. anisopliae, to transportation and fungal virulence. This study provides new information on the interaction between termites and its entomopathogen, with potential utilization for developing future biopesticide to control the termite population.

Highlights

Metarhizium anisopliae is an entomopathogenic fungus of a wide range of hosts, including subterranean termites and other insect members from the class Insecta [1]
The pathogenesis process continued with germination of the hyphal tips or germ tubes from the conidia (Figure 1b), which progressed into appressoria as observed at 6 h PI
We found that M. anisopliae had begun with a germ tube penetrating the C. curvignathus cuticles as early as 6 h PI

Summary

Introduction

Metarhizium anisopliae is an entomopathogenic fungus of a wide range of hosts, including subterranean termites and other insect members from the class Insecta [1]. Subterranean termites are social insects [4]; it has been suggested that their behavior could be the reason that stops M. anisopliae from spreading to other healthy members such as alarming by vibration and aggregation, grooming, defecating, and burying the infected colonies member [5,6,7,8]. These actions are commonly not taken into consideration during in vitro pathogenicity studies because the experimental termites were kept solitary after exposure to fungal spores [9,10,11]. This explains why promising laboratory results were not always reproducible in the field [12,13]

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