The microbiome of the wood-dwelling Cossus cossus (Lepidoptera: Cossidae): a functional approach

Microorganisms associated with insects can offer diverse benefits to their host, but the degree to which hosts rely on them varies across insect groups. Although research has increasingly focused on Lepidoptera, many of which are important pest species, key aspects of their microbiome's stability and functional importance remain ambiguous and seem context-dependent. The caterpillars of the goat moth, Cossus cossus (Linnaeus), which develop over 2 to 5 years within trunks of deciduous trees and consume a wood-based diet rich in recalcitrant lignin, provide an intriguing model to examine potential microbial contributions to lignocellulose degradation. Full-length 16S rRNA gene sequencing revealed a gut microbiome dominated by Enterococcus spp. and a high Leuconostoc spp. presence in the mandibular glands. Concurrent culturomics approaches recovered 64 taxa identified by sequencing and uncovered additional diversity, such as Brevibacterium spp. and Streptomyces spp. Notably, several isolates, including strains of Acinetobacter johnsonii, Citrobacter gillenii, Leucobacter sp., and Pseudomonas sp., demonstrated growth on minimal media supplemented with wood, lignin, or lignin-derived aromatics as the sole carbon and energy sources. These findings provide the first evidence that specific bacterial members of the goat moth caterpillar's microbiome may contribute to wood digestion, suggesting a functional symbiosis suited to a challenging dietary niche.