Addressing the diversity of the honeybee gut symbiont Gilliamella: Description of Gilliamella apis sp. nov., isolated from the gut of honeybees (Apis mellifera)

The gut microbiota of honeybees (Apis) and bumblebees (Bombus) include the symbiotic bacterial genus Gilliamella. This genus shows a high degree of functional and genomic diversity and separates into distinct lineages. Gilliamella apicola wkB1^T, which was isolated from Apis, was the first species to be described. Recently four new species, isolated from Bombus, were identified. In this paper, we compare several genomes/strains from previous studies spanning this diversity, which gives insight into the phylogenetic relationship among different Gilliamella species. We show that one lineage, isolated only from Apis, is different from other gilliamellas described, based on average nucleotide identity calculation (about 80 %) and phenotypic characterizations. We propose the new species name for this lineage: Gilliamella apis sp. nov. We present the characterization of the type strain NO3^T (=DSM 105629^T=LMG 30293^T), a strain isolated from the Western honeybee Apis mellifera, which clusters within this lineage. Cells of strain NO3T grow best in a microaerophilic atmosphere with enhanced CO₂ levels at 36 ºC and pH 7.0-7.5. Cells also grow well in anaerobic conditions, but not in aerobic conditions. Cells are approximately 1μm in length and rod-shaped, and the genomic G+C content is 34.7 mol%. Differential characteristics between strain NO3T and the different type strains of Gilliamella were revealed based on API kit tests and genomic content comparisons. The main respiratory quinone of strain NO3T was ubiquinone-8, and the predominant fatty acids were C_{18: 1}ω7c/C_{18: 1}ω6c, C_{16: 0}, consistent with the genus Gilliamella.