Bee-associated Orbaceae species aid in the metabolism of plant polysaccharides, toxic sugars and urea and stimulate the immune system. In honeybees and other eusocial bees, microbial transmission occurs through hive contact and social interactions, favouring the emergence of host-specific strains. While most solitary bees acquire their microbiota from the environment, large carpenter bees (genus Xylocopa ) exhibit facultative or incipient social behaviour that might enable direct transmission. This behaviour might have contributed to host specialization of Xylocopa -associated bacteria, such as the genus Xylocopilactobacillus and novel species belonging to the genus Lactobacillus and the family Bifidobacteriaceae . Evidence of an apparent Xylocopa -specific Orbaceae clade has also been observed. Here, we isolated and characterized AC157Xtp T , a novel strain in the family Orbaceae , from the gut of Xylocopa tabaniformis parkinsoniae . The optimal growth occurs anaerobically at 30–35°C, 0–0.5% salinity and pH 6–7. The predominant fatty acids were C 18:1 ω 6c and/or C 18:1 ω 7c (45.9%), followed by C 16:0 (35.0%) and C 14:0 (7.8%), consistent with those reported for members of the family Orbaceae . The cell size of AC157XtpT was ~0.5–1.6 µm in length and 0.4–0.7 µm in width, with coccoid to small rod-shaped morphology under scanning electron microscopy. The average nucleotide identity (ANI) and digital DNA–DNA hybridization (dDDH) scores between AC157Xtp T and other Orbaceae ranged from 69.99 to 72.88% for ANIb, from 0.59 to 0.83 for TETRA values and from 20.1 to 26.7% for dDDH, measures far below species thresholds. Combined with the average amino acid identity (AAI) and percentage of conserved proteins (POCP) at the lower end of the Orbaceae -specific genus boundary range, and the phylogenomic tree placing AC157Xtp T in a separate monophyletic clade sister to Orbus and Frischella , these data support the classification of AC157Xtp T as a representative of a novel genus within the family Orbaceae . In conclusion, AC157XtpT (=NCIMB 15593T=ATCC TSD-486 T ) represents the type strain of Neffella xylocopae gen. nov., sp. nov. The GenBank accession numbers are CP133583 (genome) and PQ456091 (16S rRNA gene).
Cerqueira et al. (Wed,) studied this question.