The bean beetle (Callosobruchus maculatus) is both a pervasive pest of stored bean crops and a model for incorporating entomological research into undergraduate curricula. Over the years, bean beetles have been used in undergraduate laboratories to study everything from development to ecology. Given the propensity of many insects to benefit from association with microbial symbionts, we began investigations of the bean beetle microbiome as a way to foster student understanding of the techniques associated with the study of microbiomes and of the importance of microbes for animal functioning. We have revealed that the beetles’ microbiome consists of a conserved bacterial assembly shared between larvae and adults. This community is localized extracellularly along the epithelial lining of the bean beetles’ digestive tracts. Only one species, Staphylococcus gallinarum (phylum Firmicutes), is shared across all developmental stages, indicative of a vertical transmission route. One cultivated strain encodes complete biosynthetic pathways for the production of B vitamins and amino acids, including tyrosine, which is increasingly recognized as an important precursor for cuticle biosynthesis in beetles. Relative to free-living Staphylococcus gallinarum, the genomes of host-associated lineages are enriched in carbohydrate active enzymes, reflecting the nutritional ecology of their herbivorous hosts. These findings set the stage for undergraduate researchers to ask questions about how the microbiome composition changes with diet and whether association with the microbiome alters host fitness, giving students from diverse institutions a pathway to conduct authentic research with an easily maintained insect and its microbes.
