Abstract
The crosstalk between gut microbiota and host immunity has emerged as one of the research foci of microbiome studies in recent years. The purpose of this study was to determine how gut microbes respond to fungal infection in termites, given their reliance on gut symbionts for food intake as well as maintaining host health. Here, we used Metarhizium robertsii, an entomopathogenic fungus, to infect Odontotermes formosanus, a fungus-growing termite in the family Termitidae, and documented changes in host gut microbiota via a combination of bacterial 16S rDNA sequencing, metagenomic shotgun sequencing, and transmission electron microscopy. Our analyses found that when challenged with Metarhizium, the termite gut showed reduced microbial diversity within the first 12 h of fungal infection and then recovered and even surpassed pre-infection flora levels. These combined results shed light on the role of gut flora in maintaining homeostasis and immune homeostasis in the host, and the impact of gut flora dysbiosis on host susceptibility to infection.
Highlights
Metarhizium is an entomopathogenic fungus widely present in the natural environment, whose conidia come into contact with the surface of the insect cuticle through the secreted protein MAD1 adhesin (Wang and St Leger, 2007)
Disruption of Termite Gut Flora Caused by Metarhizium robertsii Infection
We did not observe the production of M. robertsii mycelia, suggesting that M. robertsii did not multiply in the hindgut (Wang and St Leger, 2007; Schrank and Vainstein, 2010)
Summary
Metarhizium is an entomopathogenic fungus widely present in the natural environment, whose conidia come into contact with the surface of the insect cuticle through the secreted protein MAD1 adhesin (Wang and St Leger, 2007) Afterward, several enzymes such as chitinase are secreted and mechanical pressure is applied causing the attached fungal cell to produce hyphae that penetrate the cuticle and shed budding spores from the hyphae into the body of the host. Insects show active avoidance of pathogenic fungi before they break through the cuticle barrier, which is evident in group-living social insects In these species, social immunity occurs at the group level, which is manifested by positive social contact between individuals grooming each other, corpse removal, and use of oral gland secretions. Studies have confirmed that social immunity depends in part on the regulation of exogenous enzymes associated with the body’s immune system (Esparza-Mora et al, 2020)
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