Genome Evolution of Bartonellaceae Symbionts of Ants at the Opposite Ends of the Trophic Scale.

Many insects rely on bacterial symbionts to supply essential amino acids and vitamins that are deficient in their diets, but metabolic comparisons of closely related gut bacteria in insects with different dietary preferences have not been performed. Here, we demonstrate that herbivorous ants of the genus Dolichoderus from the Peruvian Amazon host bacteria of the family Bartonellaceae, known for establishing chronic or pathogenic infections in mammals. We detected these bacteria in all studied Dolichoderus species, and found that they reside in the midgut wall, that is, the same location as many previously described nutritional endosymbionts of insects. The genomic analysis of four divergent strains infecting different Dolichoderus species revealed genes encoding pathways for nitrogen recycling and biosynthesis of several vitamins and all essential amino acids. In contrast, several biosynthetic pathways have been lost, whereas genes for the import and conversion of histidine and arginine to glutamine have been retained in the genome of a closely related gut bacterium of the carnivorous ant Harpegnathos saltator. The broad biosynthetic repertoire in Bartonellaceae of herbivorous ants resembled that of gut bacteria of honeybees that likewise feed on carbohydrate-rich diets. Taken together, the broad distribution of Bartonellaceae across Dolichoderus ants, their small genome sizes, the specific location within hosts, and the broad biosynthetic capability suggest that these bacteria are nutritional symbionts in herbivorous ants. The results highlight the important role of the host nutritional biology for the genomic evolution of the gut microbiota-and conversely, the importance of the microbiota for the nutrition of hosts.

Absence of zoonotic Bartonella species in questing ticks: first detection of Bartonella clarridgeiae and Rickettsia felis in cat fleas in the Netherlands.

BACKGROUND: Awareness for flea- and tick-borne infections has grown in recent years and the range of microorganisms associated with these ectoparasites is rising. Bartonella henselae, the causative agent of Cat Scratch Disease, and other Bartonella species have been reported in fleas and ticks. The role of Ixodes ricinus ticks in the natural cycle of Bartonella spp. and the transmission of these bacteria to humans is unclear. Rickettsia spp. have also been reported from as well ticks as also from fleas. However, to date no flea-borne Rickettsia spp. were reported from the Netherlands. Here, the presence of Bartonellaceae and Rickettsiae in ectoparasites was investigated using molecular detection and identification on part of the gltA- and 16S rRNA-genes. RESULTS: The zoonotic Bartonella clarridgeiae and Rickettsia felis were detected for the first time in Dutch cat fleas. B. henselae was found in cat fleas and B. schoenbuchensis in ticks and keds feeding on deer. Two Bartonella species, previously identified in rodents, were found in wild mice and their fleas. However, none of these microorganisms were found in 1719 questing Ixodes ricinus ticks. Notably, the gltA gene amplified from DNA lysates of approximately 10% of the questing nymph and adult ticks was similar to that of an uncultured Bartonella-related species found in other hard tick species. The gltA gene of this Bartonella-related species was also detected in questing larvae for which a 16S rRNA gene PCR also tested positive for "Candidatus Midichloria mitochondrii". The gltA-gene of the Bartonella-related species found in I. ricinus may therefore be from this endosymbiont. CONCLUSIONS: We conclude that the risk of acquiring Cat Scratch Disease or a related bartonellosis from questing ticks in the Netherlands is negligible. On the other hand fleas and deer keds are probable vectors for associated Bartonella species between animals and might also transmit Bartonella spp. to humans.

Functional genomics of bacterial pathogens: from post-genomics to therapeutic targets.

A wealth of new data have become available to the scientific community as a result of the sequencing of many pathogen genomes. A recent meeting devoted to functional genomics of pathogenic microorganisms confirmed the notion that bacterial genomes are not static, because large blocks of genes can be acquired or deleted. Less complex environments usually result in reduction in genome size, while genome expansion is usually associated with environmental change and complexity. During the meeting, pathogenicity and evolutionary aspects were illustrated for enteric pathogens, as well as the microevolution of the plague bacillus Yersinia pestis. New clues for evolution and pathogenicity were derived from comparative genomics of Listeria species. The genomic organization of Bartonellae, an emerging human pathogen, was also discussed in an evolutionary context. Population and functional genomics of Anthrax-causing bacteria highlighted current scientific interest in this potential biothreat.

Ectoparasites of gray squirrels in two different habitats and screening of selected ectoparasites for bartonellae.

Gray squirrels, Sciurus carolinensis, were livetrapped in 2 different habitat types, woodland (67 squirrels) and parkland (53 squirrels), in southeastern Georgia. Ectoparasites were recovered from anesthetized squirrels and compared between hosts from the 2 habitats. Because of the absence of low vegetation in parkland habitats, it was hypothesized that the ectoparasite fauna, especially ticks and chiggers, would be more diverse on woodland squirrels. The results were generally in agreement with this hypothesis. Seventeen species of ectoparasites were recovered from woodland squirrels, compared with 6 species from parkland squirrels. Five species of ticks and 3 species of chiggers parasitized the woodland squirrels compared with no ticks or chiggers on the parkland squirrels. Significantly higher infestation prevalences were recorded on woodland compared with parkland squirrels for the flea Orchopeas howardi, the tick Amblyomma americanum, and the mesostigmatid mite Androlaelaps fahrenholzi. The mean intensity for O. howardi also was significantly higher on woodland than on parkland squirrels. Because a new strain of Bartonella sp. was isolated recently from S. carolinensis in Georgia, selected ectoparasites from this study were screened for bartonellae by polymerase chain reaction (PCR). Some of the fleas and lice, but none of the mites tested, were PCR positive, suggesting that fleas, or lice, or both, might be vectors of bartonellae between squirrels. Six distinct strains of Bartonella sp. were detected, 2 in fleas and 4 in lice.

Grahamella in small woodland mammals in the U.K.: isolation, prevalence and host specificity.

Bacteria isolated from the blood of small woodland mammals were identified as members of the genus Grahamella. The prevalence of Grahamella infection among the 37 small mammals examined, detected by cultivation of blood samples, was 62%. This figure is somewhat higher than previous reports. Further characterization of the isolates, based on restriction enzyme analysis of the 16S rRNA gene, serological reactivity and DNA hybridization studies, revealed three distinct Grahamella species. One of the species was found in five different species of small mammal (Apodemus sylvaticus, A. flavicollis, Clethrionomys glareolus, Microtus agrestis and Neomys fodiens). All three species were found in M. agrestis, although there was no evidence of concurrent infection of an animal by more than one species of Grahamella. These observations demonstrate that Grahamella spp. are not host-specific, as previously thought, and that it is therefore invalid to name Grahamella spp. solely on the basis of the host in which they are observed.

Proposals to unify the genera Bartonella and Rochalimaea, with descriptions of Bartonella quintana comb. nov., Bartonella vinsonii comb. nov., Bartonella henselae comb. nov., and Bartonella elizabethae comb. nov., and to remove the family Bartonellaceae from the order Rickettsiales.

DNA hybridization data (hydroxyapatite method, 50 to 70 degrees C) indicate that Rickettsia prowazekii, the type species of the type genus of the family Rickettsiaceae, is substantially less closely related to Rochalimaea species than was previously thought. The levels of relatedness of Rickettsia prowazekii to Rochalimaea species and to Bartonella bacilliformis under optimal conditions for DNA reassociation were 0 to 14%, with 25.5% or greater divergence in related sequences. When stringent reassociation criteria were used, the levels of relatedness were 0 to 2%. The genera Bartonella and Rochalimaea are currently classified in different families (the Bartonellaceae and the Rickettsiaceae) in the order Rickettsiales. On the basis of DNA relatedness data, previous 16S rRNA sequence data, guanine-plus-cytosine contents, and phenotypic characteristics, neither Bartonella bacilliformis nor Rochalimaea species are closely related to other organisms currently classified in the order Rickettsiales. In fact, the closest relative of these organisms is Brucella abortus. It is therefore proposed that the family Bartonellaceae should be removed from the order Rickettsiales. Previous 16S rRNA sequence data and DNA hybridization data revealed high levels of relatedness between Bartonella bacilliformis and the four Rochalimaea species, indicating that these species are members of a single genus. It is proposed that the genus Rochalimaea should be united with the genus Bartonella in the family Bartonellaceae. The name Bartonella is retained as the genus name since it has nomenclatural priority over the name Rochalimaea. This means that new combinations for the Rochalimaea species must be created. Proposals are therefore made for the creation of Bartonella quintana comb. nov., Bartonella vinsonii comb. nov., Bartonella henselae comb. nov., and Bartonella elizabethae comb. nov.