Selection of bacterial probiotics to enhance bioconversion ability and growth performance of mass-reared insects

In recent years insect farming has gained great attention to bioconvert agro-industrial by-products into valuable biomass in the context of circular economy and to partially or fully substitute conventional protein sources used in feed and food systems. Insects have established intricate associations with diverse microbial partners which play crucial roles in host physiological processes, defence, and overall fitness. Gut eubiosis is critical for host health and physiological homeostasis, as alterations of the gut microbial structure may negatively affect host health and physiological functions. Thus, supplementation of beneficial bacteria may help insects improve their growth, bioconversion ability and health in general. Aim of this work was to characterise the cultivable microbiota associated with the yellow mealworm (YM) Tenebrio molitor L. (Coleoptera: Tenebrionidae) to select candidate probiotics that can promote host growth and health, particularly when insects are reared on different agro-industrial by-products. To obtain a detailed description of the gut bacterial community associated to the insects, 16S rRNA gene amplicon sequencing was performed. Guts were dissected from surface-sterilized insects and used for bacterial isolation on selective culture media. The resulting bacterial collections were dereplicated by ITS-PCR fingerprinting and taxonomically identified through 16S rRNA gene sequencing. The isolates were further evaluated for their ability to hydrolyse key dietary polysaccharides, including cellulose, starch, and pectin, which can be found in agro-industrial by-products, as well as for their antimicrobial activity against entomopathogenic microorganisms. Overall, this study provides a comprehensive characterisation of the gut microbiota of an edible insect species, with particular emphasis on its cultivable fraction. This approach enables the identification of potentially beneficial bacterial strains that may be exploited in microbially assisted rearing strategies to enhance insect production and promote the bioconversion of organic wastes into high-quality products. Work funded by PRIN 2022 Project InProFarm (Insect Probiotic-assisted Farming: a promising tool to enhance edible insect health and performances), grant number 2022L4NJMK, European Union — Next Generation EU, Mission 4, Component 1.