Cooperation of burying beetles and their microbiota on carcasses

Researchers look into the mechanisms by which insects preserve and provision food for their larvae in competitive environments

19 May 2017

A team of researchers from the Max Planck Institute for Chemical Ecology in Jena, the Fraunhofer Institute for Molecular Biology and Applied Ecology, Giessen University, and Johannes Gutenberg University Mainz (JGU) has studied the role of the burying beetle (Nicrophorus vespilloides) and its microbiota in carrion digestion and chemical preservation during breeding. Burying beetles utilize carrion, a highly nutritious but ephemeral resource, that they bury and chemically preserve by applying oral and anal secretions. The research team found a metabolically rich beetle gut transcriptome producing a diverse set of enzymes and antimicrobial proteins that may help to digest and preserve the carcass, as well as a consistent bacterial and fungal gut microbiota that is transmitted to the larvae through anal secretions applied to the carcass.

With more than one million described species, insects represent the group of organisms exhibiting the greatest biodiversity. This tremendous evolutionary success of insects is at least in part owed to their microbial symbionts which help them to explore novel ecological niches such as the ability to utilize unusual diets. Insects that use ephemeral and sporadic resources minimize larval development times to avoid competition and predation. A highly efficient digestive mechanism is required by such insects to support rapid nutrient assimilation and biomass conversion during larval development. At the same time, insects that provision food for their larvae must evolve behavioral and chemical food-preservation strategies that suppress competitors.

An intriguing example are burying beetles (Nicrophorus spp) that feed and reproduce on cadavers of small mammals or birds. Once a carcass has been located, parent beetles cooperate to bury it underground to hide it from competing fly maggots, remove hair or feathers, and shape it into a "meatball" to prepare it for consumption by their offspring. Carrion is a valuable but ephemeral resource, so there is intense competition with bacterial and fungal decomposers, which decrease its nutritional value and render it unpalatable or even toxic to animals.

The burying beetle transcriptome and microbiome together shed light on the potential mechanisms by which insects preserve and provision food for their larvae in competitive and pathogen-rich environments. The differential expression of digestive enzymes, antimicrobial proteins, and the characteristic bacteria and fungi in these species may underlie basic parental behavior such as the transfer of oral regurgitates and sanitization of food resources. Such behaviors are common across many insects exhibiting parental care and may therefore serve similar functions for digestion, detoxification, and preservation as in Nicrophorus. "We were particularly surprised by the fact that the identified dominant yeast is not only present in anal secretions of the burying beetles, but is transmitted to their offspring and is metabolically active also on the carcass," said Heiko Vogel from the Max Planck Institute for Chemical Ecology.

The obtained results indicate that metabolic cooperation with a diverse community of bacteria and yeasts may at least in part underlie the ecological success of burying beetles. "Our results also support recent concepts in biology that distinguish between a flexible, environmentally modulated microbial community and a host-adapted core community, differing in their contributions to host adaptation," explained Professor Andreas Vilcinskas from the Institute for Insect Biotechnology in Giessen.

The study is part of a project entitled "Application of Insect-associated Microbes in Industrial Biotechnology" (AIM-Biotech), which is co-funded by both the Max Planck Society and the Fraunhofer Society and aims to expand the toolbox for the industrial (white) biotechnology. The latter focuses on the biotransformation of raw materials into useful industrial products, predominantly using microbes and/or enzymes. Insects and their coevolved microorganisms potentially cooperate to convert unusual or challenging biomass such as cadavers into diet for their offspring. Insect-derived beneficial microbes which can be cultured in fermenters are of particular interest because they enable the bioconversion of organic waste into higher value products. The novel yeasts found to be associated with the burying beetle are promising sources of novel enzymes for biotechnological applications.