Dynamics of the hindgut microbiota of the Japanese honey bees (<i>Apis cerana japonica</i>) throughout the overwintering period

Honey bees play crucial roles as pollinators in natural, agricultural, and ecological systems. The role of gut microbiota in the overwinter survival of honey bees is gaining attention. Compared with Western honey bees (<i>Apis mellifera</i>), Eastern honey bees (<i>Apis cerana</i>) are more tolerant to low-temperature stress. This study compared the hindgut microbiota of the Japanese honey bees (<i>Apis cerana japonica</i>), a subspecies of <i>A</i>. <i>cerana</i>, during the overwintering period (December) with that before overwintering (October) and after overwintering (March) to estimate beneficial hindgut bacteria contributing to survival during the overwintering period. Overall, the hindgut microbiota of <i>A</i>. <i>c</i>. <i>japonica</i> was occupied by Actinobacteriota, Bacteroidota, Firmicutes, and Proteobacteria at the phylum level and <i>Apibacter</i>, <i>Bifidobacterium</i>, <i>Bombilactobacillus, Gilliamella</i>, <i>Lactobacillus</i>, and <i>Snodgrassella</i> at the genus level. The hindgut microbiota composition of <i>A</i>. <i>c</i>. <i>japonica</i> was similar to that of <i>A</i>. <i>cerana</i> in other regions, suggesting that phylogeny influenced the composition. Many sequences assigned to these six core genera showed <98.7% similarity to type strains, indicating potential novel bacterial species. The relative abundance of <i>Bifidobacterium</i>, <i>Bombilactobacillus</i>, and <i>Lactobacillus</i> was higher during overwintering than in other periods. Our findings highlight changes in the core bacteria of the hindgut microbiota of <i>A</i>. <i>c</i>. <i>japonica</i> during overwintering and also suggest the presence of novel candidate bacterial species. The roles of the bacteria that were increased during the overwintering period require further elucidation.