Intestinal Bacteria Aid Termites in Response to Entomopathogen Infection According to the Metagenome and Meta-transcriptome

Abstract

Intestinal symbionts live in insects’ digestive systems and help with food digestion, nitrogen cycling, and energy use. Numerous symbionts, including bacteria, fungi, and protozoa, colonize the posterior gut of termites. Intestinal microbiota affects the Toll or Imd pathways during viral or entomopathogenic fungus infection in mosquitoes, but the role of intestinal symbionts in individual termite immunity is unclear. In the present research, Odontotermes formosanus and Metarhizium robertsii were selected to investigate the potential mechanism of the intestinal bacteria influencing termite innate immune while encountering an entomopathogen using metagenome sequencing and meta-transcriptome sequencing. We found that termite mortality declined within 48 hours under high spore infections and reached semi-lethal status within 72 hours. We sequenced the control and infestation termite and found that the dominant phyla changed below low-abundance flora during infestation. According to function annotation, the functions of spirochetes are significantly different from those of the rest of the phyla, which are mainly enriched in metabolism and cellular processes. There are 261 upregulated and 459 down-regulated DEGs derived from bacteria after infestation. We identified the glutamate-cysteine ligase gene, gshA, which is significantly upregulated in the infected group, and the GSH content in the regular infected group was higher than the 5% kanamycin-infected group. We speculated on a potential mechanism that one or more bacteria belonging to Spirochetes that upregulated gshA gene expression and increased GSH content in the hindgut to integrate with metarhizium toxins and then excrete out of the intestine.