The Factors Involved in Plant–Insect–Microbe Interactions Expanded: Genome Analysis and Description of <i>Frigoribacterium adelgis</i> <scp>sp. nov.</scp>

Actinobacteria of the genus Frigoribacterium were isolated from adelgid Adelges (Aphrastasia) pectinatae collected from a Korean fir tree. Genomic analyses revealed that these bacteria encode a range of factors that may be involved in the interactions among Frigoribacterium strains, adelgids and/or conifers. Secreted carbohydrate-active enzymes were identified in the genomes, which allow these bacteria to degrade plant polysaccharides such as cellulose, xylan, pectin and mannan, the main hemicellulose component of softwood. The degradation potential of insect cuticles was investigated, and secreted chitinases belonging to the GH18 family were predicted to be present in the genomes. However, no phenotypic chitinolytic activity was detected. The potential interactions between these bacterial strains and either plants or insects were assessed, resulting in a few high-scoring hits. The related Frigoribacterium genomes were compared, revealing several unique features, such as numerous orthologous gene clusters specific to these strains and five biosynthetic gene clusters. Ten genomic islands were predicted in the genomes of the adelgid-associated strains, which contained genes responsible for adapting to environmental changes, resisting heavy metals and expanding metabolic capabilities. We propose a new species, Frigoribacterium adelgis, belonging to the genus Frigoribacterium, based on these results.