Bartonella apis sp. nov., a honey bee gut symbiont of the class Alphaproteobacteria.

Here, we report the culture and characterization of an alphaproteobacterium of the order Rhizobiales, isolated from the gut of the honey bee Apis mellifera. Strain PEB0122T shares >95 % 16S rRNA gene sequence similarity with species of the genus Bartonella, a group of mammalian pathogens transmitted by bloodsucking arthropods. Phylogenetic analyses showed that PEB0122T and related strains from the honey bee gut form a sister clade of the genus Bartonella. Optimal growth of strain PEB0122T was obtained on solid media supplemented with defibrinated sheep blood under microaerophilic conditions at 35-37 °C, which is consistent with the cultural characteristics of other species of the genus Bartonella. Reduced growth of strain PEB0122T also occurred under aerobic conditions. The rod-shaped cells of strain PEB0122T had a mean length of 1.2-1.8 μm and revealed hairy surface structures. Strain PEB0122T was positive for catalase, cytochrome c oxidase, urease and nitrate reductase. The fatty acid composition was comparable to those of other species of the genus Bartonella, with palmitic acid (C16 : 0) and isomers of 18- and 19-carbon chains being the most abundant. The genomic DNA G+C content of PEB0122T was determined to be about 45.5 mol%. The high 16S rRNA gene sequence similarity with species of Bartonella and its close phylogenetic position suggest that strain PEB0122T represents a novel species within the genus Bartonella, for which we propose the name Bartonella apis sp. nov. The type strain is PEB0122T ( = NCIMB 14961T = DSM 29779T)

Genomic changes associated with the evolutionary transition of an insect gut symbiont into a blood-borne pathogen.

The genus Bartonella comprises facultative intracellular bacteria with a unique lifestyle. After transmission by blood-sucking arthropods they colonize the erythrocytes of mammalian hosts causing acute and chronic infectious diseases. Although the pathogen-host interaction is well understood, little is known about the evolutionary origin of the infection strategy manifested by Bartonella species. Here we analyzed six genomes of Bartonella apis, a honey bee gut symbiont that to date represents the closest relative of pathogenic Bartonella species. Comparative genomics revealed that B. apis encodes a large set of vertically inherited genes for amino acid and cofactor biosynthesis and nitrogen metabolism. Most pathogenic bartonellae have lost these ancestral functions, but acquired specific virulence factors and expanded a vertically inherited gene family for harvesting cofactors from the blood. However, the deeply rooted pathogen Bartonella tamiae has retained many of the ancestral genome characteristics reflecting an evolutionary intermediate state toward a host-restricted intraerythrocytic lifestyle. Our findings suggest that the ancestor of the pathogen Bartonella was a gut symbiont of insects and that the adaptation to blood-feeding insects facilitated colonization of the mammalian bloodstream. This study highlights the importance of comparative genomics among pathogens and non-pathogenic relatives to understand disease emergence within an evolutionary-ecological framework

Bacterial communities within Phengaris (Maculinea) alcon caterpillars are shifted following transition from solitary living to social parasitism of Myrmica ant colonies

Bacterial symbionts are known to facilitate a wide range of physiological processes and ecological interactions for their hosts. In spite of this, caterpillars with highly diverse life histories appear to lack resident microbiota. Gut physiology, endogenous digestive enzymes, and limited social interactions may contribute to this pattern, but the consequences of shifts in social activity and diet on caterpillar microbiota are largely unknown. Phengaris alcon caterpillars undergo particularly dramatic social and dietary shifts when they parasitize Myrmica ant colonies, rapidly transitioning from solitary herbivory to ant tending (i.e., receiving protein‐rich regurgitations through trophallaxis). This unique life history provides a model for studying interactions between social living, diet, and caterpillar microbiota. Here, we characterized and compared bacterial communities within P. alcon caterpillars before and after their association with ants, using 16S rRNA amplicon sequencing and quantitative PCR. After being adopted by ants, bacterial communities within P. alcon caterpillars shifted substantially, with a significant increase in alpha diversity and greater consistency in bacterial community composition in terms of beta dissimilarity. We also characterized the bacterial communities within their host ants (Myrmica schencki), food plant (Gentiana cruciata), and soil from ant nest chambers. These data indicated that the aforementioned patterns were influenced by bacteria derived from caterpillars’ surrounding environments, rather than through transfers from ants. Thus, while bacterial communities are substantially reorganized over the life cycle of P. alcon caterpillars, it appears that they do not rely on transfers of bacteria from host ants to complete their development.ISSN:2045-775