AimInsect frass samples were collected from Drosophila melanogaster, Plodia interpunctella, Rhyzopertha dominica, Sitophilus granarius, Sitophilus oryzae, Sitophilus zeamais, Tribolium confusum and Tribolium castaneum to elucidate if they can be the origin of Type I sourdough micro-organisms (Lactobacillus sanfranciscensis and Candida milleri). Methods and ResultsSelective enrichments were carried out to isolate lactic acid bacteria (LBA) and yeast. A metagenetic analysis, targeted on bacterial 16S rRNA gene and fungal ITS region, was performed by using Illumina MiSeq protocol. In cultivation conditions, Lactococcus garvieae and Rhodotorula mucilaginosa were the most frequently species among LAB and yeasts respectively. The Next Generation Sequencing approach revealed that Enterobacteriaceae, Pseudomonadacae and Bacillaceae were the dominating taxa, accounting for 61% of the bacterial community. Lactobacillus genus showed a relative abundance of only 036%, but L. sanfranciscensis proved to be the species most frequent between lactobacilli and predominant in faecal samples of T. castaneum and T. confusum larvae. The core fungal microbiota was constituted by Saccharomycetales, Pleosporaceae and Nectriaceae that attained the 51% of recognized OTUs. While the most abundant yeast genus was Candida (171%), sequences belonging to C. milleri were not found. ConclusionsFrass released by the insects of stored cereal products can be the natural reservoir of L. sanfranciscensis. Significance and Impact of the StudyInsect dejections are potential sources of novel strains for controlled bakery productions.