Diet and its impact on gut microbial essential amino acid provisioning in the viviparous Pacific beetles, Diploptera punctata

Diet has been shown to be a determinant of insect gut microbiome composition. In this study we assessed indications of gut microbial EAA provisioning in D. punctata, using a plant-only diet Gari (starchy and granulated root tubers of Yucca, Manihot esculenta), and dog food diet (DF) and cellulose-amended dog food (CADF) diets. Overall, DF-fed insects exhibited significantly higher mass-specific standard metabolic rare (SMR) (P = 0.04) by day 28 relative to the CADF-fed insects (least) and the Gari-fed insects (intermediate). Differences in SMR were accompanied by significant differential abundances of 14 bacterial families in across the gut microbiomes of the three groups. Cellulolytic and nitrogen-fixing bacteria families Streptococcaceae and Xanthomonadaceae dominated CADF-fed insect gut microbiomes, whiles anaerobic lignocellulolytic bacteria families Paludibacteraceae and Dysgonomonadaceae, and proteolytic anaerobes Williamwhitmaniaceae and sulfate-reducing bacteria Desulfovibrionaceae dominated in the Gari-fed and DF-fed insect gut microbiomes, respectively. Finally, higher ¹³C-enrichments across all six EAAs quantified in the Gari-fed insects relative to Gari diet, as anticipated. This was followed by determination of microbial EAAs (mix of fungi and bacteria from the gut microbiome) as the alternate sources of EAAs causing the offsets in the insect samples in a linear discriminant analysis. These results corroborate previous assertions that alterations in gut microbiome compositions on different diets can regulate SMR responses, mediated by changes in gut microbial functions (EAA provisioning). Further understanding of the relative importance of gut microbial functions known to underscore SMR responses in insects under varying dietary conditions is needed.