Association of oral microbiome with type 2 diabetes risk.

BACKGROUND AND OBJECTIVE: The oral microbiome may help to maintain systemic health, including how it affects blood glucose levels; however, direct evidence linking the oral microbiome with diabetes is lacking. MATERIAL AND METHODS: We compared the oral microbiome profiles of 98 participants with incident diabetes, 99 obese non-diabetics and 97 normal weight non-diabetics, via deep sequencing of the 16S rRNA gene. RESULTS: We found that the phylum Actinobacteria was present significantly less abundant among patients with diabetes than among the controls (p = 3.9 × 10-3 ); the odds ratio (OR) and 95% confidence interval (CI) was 0.27 (0.11-0.66) for those individuals who had relative abundance higher than the median value. Within this phylum, five families and seven genera were observed, and most of them were less abundant among patients with diabetes. Notably, genera Actinomyces and Atopobium were associated with 66% and 72% decreased risk of diabetes with p-values of 8.9 × 10-3 and 7.4 × 10-3 , respectively. Stratified analyses by race showed that most taxa in this phylum were associated with diabetes in both black and white participants. This phylum was also less abundant among non-diabetic obese subjects compared to normal weight individuals, particularly genera Mobiluncus, Corynebacterium and Bifidobacterium, which showed p < 0.05. CONCLUSION: Our study revealed that multiple bacteria taxa in the phylum Actinobacteria are associated with the risk of type 2 diabetes. Some are also associated with the prevalence of obesity, suggesting that the oral microbiome may play an important role in diabetes etiology.

Effects of A and B Wolbachia and host genotype on interspecies cytoplasmic incompatibility in Nasonia.

Wolbachia endosymbionts cause postmating reproductive isolation between the sibling species Nasonia vitripennis and N. giraulti. Most Nasonia are doubly infected with a representative from each of the two major Wolbachia groups (A and B). This study investigates the role of single (A or B) and double (A and B) Wolbachia infections in interspecies cytoplasmic incompatibility (CI) and host genomic influences on the incompatibility phenotype. Results show that the single A Wolbachia harbored in N. vitripennis (wAv) is bidirectionally incompatible with the single A Wolbachia harbored in N. giraulti (wAg). Results also indirectly show that the N. vitripennis wBv is bidirectionally incompatible with the N. giraulti wBg. The findings support current phylogenetic evidence that suggests these single infections have independent origins and were acquired via horizontal transfer. The wAv Wolbachia expresses partial CI in the N. vitripennis nuclear background. However, following genomic replacement by introgression, wAv expresses complete CI in the N. giraulti background and remains bidirectionally incompatible with wAg. Results show that double infections can reinforce interspecies reproductive isolation through the addition of incompatibility types and indicate that the host genome can influence incompatibility levels. This study has implications for host-symbiont coevolution and the role of Wolbachia in speciation.

Intraspecific variation in sexual isolation in the jewel wasp Nasonia.

Divergence in mate recognition systems can lead to reproductive isolation. In this study, we investigate patterns of intraspecific variation that contribute to premating isolation within and between two haplodiploid species, Nasonia vitripennis and N. longicornis. In a broad-scale survey of 17 North American isofemale lines encompassing the two species, we report strong asymmetric sexual isolation between species and a dramatic level of intraspecific variation for mate discrimination between species. A general lack of incipient speciation was found, with the exception of low levels of interpopulational sexual isolation within N. vitripennis. Regression analysis shows that the degree of intraspecific variation for within-species mating frequency is not associated with the degree for between-species mating frequency. Reinforcement or reproductive character displacement may be involved in some of the variation in interspecies premating isolation.

Bidirectional incompatibility among divergent Wolbachia and incompatibility level differences among closely related Wolbachia in Nasonia.

Most insect groups harbor obligate bacterial symbionts from the alpha-proteobacterial genus Wolbachia. These bacteria alter insect reproduction in ways that enhance their cytoplasmic transmission. One of the most common alterations is cytoplasmic incompatibility (CI) - a post-fertilization modification of the paternal genome that renders embryos inviable or unable to complete diploid development in crosses between infected males and uninfected females or infected females harboring a different strain. The parasitic wasp species complex Nasonia (N. vitripennis, N. longicornis and N. giraulti) harbor at least six different Wolbachia that cause CI. Each species have double infections with a representative from both the A and B Wolbachia subgroups. CI relationships of the A and B Wolbachia of N. longicornis with those of N. giraulti and N. vitripennis are investigated here. We demonstrate that all pairwise crosses between the divergent A strains are bidirectionally incompatible. We were unable to characterize incompatibility between the B Wolbachia, but we establish that the B strain of N. longicornis induces no or very weak CI in comparison to the closely related B strain in N. giraulti that expresses complete CI. Taken together with previous studies, we show that independent acquisition of divergent A Wolbachia has resulted in three mutually incompatible strains, whereas codivergence of B Wolbachia in N. longicornis and N. giraulti is associated with differences in CI level. Understanding the diversity and evolution of new incompatibility strains will contribute to a fuller understanding of Wolbachia invasion dynamics and Wolbachia-assisted speciation in certain groups of insects.

Disruption of the Wolbachia surface protein gene wspB by a transposable element in mosquitoes of the Culex pipiens complex (Diptera, Culicidae).

Culex pipiens quinquefasciatus Say and Culex pipiens pipiens Linnaeus are sibling species incriminated as important vectors of emerging and re-emerging infectious diseases worldwide. The two forms differ little morphologically and are differentiated mainly based upon ecological, behavioural, physiological and genetic traits. Within the North American zone of sympatry, populations of Cx. p. quinquefasciatus and Cx. p. pipiens undergo extensive introgression and hybrid forms have been reported in nature. Both Cx. p. quinquefasciatus and Cx. p. pipiens are infected with the endosymbiotic bacteria Wolbachia pipientis. Here, we report the presence of a transposable element belonging to the IS256 family (IS256wPip) associated with Wolbachia in both Cx. p. quinquefasciatus and Cx. p. pipiens populations. Using reverse transcriptase PCR and sequence analysis, we show that IS256wPip has disrupted the wspB locus, a paralogue of the Wolbachia outer membrane protein (wspA) gene. The inactivation of the wspB appears to be specific to Cx. p. quinquefasciatus and to hybrids of the two forms, and was not observed in the surveyed Cx. p. pipiens mosquitoes. Our results support the hypothesis of a different origin of North American Cx. p. quinquefasciatus and Cx. p. pipiens populations. The flux of mobile genetic elements in the Wolbachia wPip genome could explain the high level of crossing types observed among different Culex populations. The insertion of IS256wPip into wspB may comprise a genetic candidate for discriminating Wolbachia symbionts in Culex.

Taxonomic status of the intracellular bacterium Wolbachia pipientis.

Wolbachia pipientis is a maternally inherited, intracellular bacterium found in more than 20 % of all insects, as well as numerous other arthropods and filarial nematodes. It has been the subject of a growing number of studies in recent decades, because of the remarkable effects it has on its arthropod hosts, its potential as a tool for biological control of arthropods of agricultural and medical importance and its use as a target for treatment of filariasis. W. pipientis was originally discovered in cells of the mosquito Culex pipiens and is the only formally described member of the genus. Molecular sequence-based studies have revealed a number of phylogenetically diverse strains of W. pipientis. Owing to uncertainty about whether W. pipientis comprises more than one species, researchers in the field now commonly refer to W. pipientis simply as Wolbachia. In this note, we briefly review higher-level phylogenetic and recombination studies of W. pipientis and propose that all the intracellular symbionts known to cluster closely with the type strain of W. pipientis, including those in the currently recognized supergroups (A-H), are officially given this name.

Phylogeny of Wolbachia pipientis based on gltA, groEL and ftsZ gene sequences: clustering of arthropod and nematode symbionts in the F supergroup, and evidence for further diversity in the Wolbachia tree.

Current phylogenies of the intracellular bacteria belonging to the genus Wolbachia identify six major clades (A-F), termed 'supergroups', but the branching order of these supergroups remains unresolved. Supergroups A, B and E include most of the wolbachiae found thus far in arthropods, while supergroups C and D include most of those found in filarial nematodes. Members of supergroup F have been found in arthropods (i.e. termites), and have previously been detected in the nematode Mansonella ozzardi, a causative agent of human filariasis. To resolve the phylogenetic positions of Wolbachia from Mansonella spp., and other novel strains from the flea Ctenocephalides felis and the filarial nematode Dipetalonema gracile, the authors generated new DNA sequences of the Wolbachia genes encoding citrate synthase (gltA), heat-shock protein 60 (groEL), and the cell division protein ftsZ. Phylogenetic analysis confirmed the designation of Wolbachia from Mansonella spp. as a member of the F supergroup. In addition, it was found that divergent lineages from Dip. gracile and Cte. felis lack any clear affiliation with known supergroups, indicating further genetic diversity within the Wolbachia genus. Finally, although the data generated did not permit clear resolution of the root of the global Wolbachia tree, the results suggest that the transfer of Wolbachia spp. from arthropods to nematodes (or vice versa) probably occurred more than once.

Do Wolbachia influence fecundity in Nasonia vitripennis?

This paper reports the influence of a vertically transmitted symbiont, Wolbachia, on host fitness in the parasitic wasp, Nasonia vitripennis. We measured fecundities of uninfected strains and strains infected with either two Wolbachia variants (wAv,wBv) or one (wAv or wBv). Preliminary tests suggested that double-infected females produce more offspring on average than uninfected females. However, further studies failed to yield consistent fitness effects. To control for host genetic effects, the genotype of the double-infected and uninfected strain was 'replaced' with three different host genetic backgrounds by introgression. Contrary to previous results, we found no convincing evidence for positive fitness effects of Wolbachia in Nasonia vitripennis, once host genetic background was controlled for. It can be concluded that under the experimental design used here, the fecundity effects associated with Wolbachia in N. vitripennis are small or absent.

Wolbachia-induced incompatibility precedes other hybrid incompatibilities in Nasonia.

Wolbachia are cytoplasmically inherited bacteria that cause a number of reproductive alterations in insects, including cytoplasmic incompatibility, an incompatibility between sperm and egg that results in loss of sperm chromosomes following fertilization. Wolbachia are estimated to infect 15-20% of all insect species, and also are common in arachnids, isopods and nematodes. Therefore, Wolbachia-induced cytoplasmic incompatibility could be an important factor promoting rapid speciation in invertebrates, although this contention is controversial. Here we show that high levels of bidirectional cytoplasmic incompatibility between two closely related species of insects (the parasitic wasps Nasonia giraulti and Nasonia longicornis) preceded the evolution of other postmating reproductive barriers. The presence of Wolbachia severely reduces the frequency of hybrid offspring in interspecies crosses. However, antibiotic curing of the insects results in production of hybrids. Furthermore, F1 and F2 hybrids are completely viable and fertile, indicating the absence of F1 and F2 hybrid breakdown. Partial interspecific sexual isolation occurs, yet it is asymmetric and incomplete. Our results indicate that Wolbachia-induced reproductive isolation occurred in the early stages of speciation in this system, before the evolution of other postmating isolating mechanisms (for example, hybrid inviability and hybrid sterility).