Chironomid Microbiome: Exploring Dietary Habits of Cold‐Adapted Species Using DNA Metabarcoding

We focused on non-biting midges (Diptera Chironomidae), the dominant insects in the food-poor and ice-cold aquatic glacial habitats selected as study sites. Glacial habitats and their dwelling fauna (i.e., species of the genus Diamesa) are at risk of extinction due to climate change in the Alps. In this study, we investigated the gut microbial structure of Diamesa and a few other cold-adapted chironomid larvae (34) and adults (2) via 16S rRNA metabarcoding. In all, we analysed 36 specimens belonging to 10 species and 12 environmental samples (e.g., melted ice water, soil, mud, debris) collected in three glacial sites, in Trentino (NE-Italy): the two glacier-fed streams Amola and Mandrone and the proglacial pond Agola. Bacterial diversity, and significant inter-site and inter-species differences were analysed by Shannon and Chao-1 indices, Cluster Analysis, Principal Coordinates Analysis and Heat Tree Analysis. New insights were provided on which bacteria ingested from the environment can be configured as “food” and which, among those present in the gut, can be considered the stable, resident metabolic “chefs” of the host animal, allowing glacial species to feed on hard-to-digest or nutrient-poor foods available in glacial habitats. A first list of bacteria with potential physiological functions was produced, including: the Proteobacteria Massilia, Serratia, Pseudomonas, Providencia, Undibacterium, Janthinobacterium and Iodobacter; the Bacteroidota Flavobacterium; the Actinobacteriota Arthorbacter. As symbiotic bacteria, they could also help these insects cope with abiotic stressors e.g., enhancing their tolerance to extreme temperatures so influencing the host ecology.