The endosymbiont Wolbachia increases insulin/IGF-like signalling in Drosophila

Insulin/IGF-like signalling (IIS) is an evolutionarily conserved pathway that has diverse functions in multi-cellular organisms. Mutations that reduce IIS can have pleiotropic effects on growth, development, metabolic homeostasis, fecundity, stress resistance and lifespan. IIS is also modified by extrinsic factors. For instance, in the fruitfly Drosophila melanogaster, both nutrition and stress can alter the activity of the pathway. Here, we test experimentally the hypothesis that a widespread endosymbiont of arthropods, Wolbachia pipientis, can alter the degree to which mutations in genes encoding IIS components affect IIS and its resultant phenotypes. Wolbachia infection, which is widespread in D. melanogaster in nature and has been estimated to infect 30 per cent of strains in the Bloomington stock centre, can affect broad aspects of insect physiology, particularly traits associated with reproduction. We measured a range of IIS-related phenotypes in flies ubiquitously mutant for IIS in the presence and absence of Wolbachia. We show that removal of Wolbachia further reduces IIS and hence enhances the mutant phenotypes, suggesting that Wolbachia normally acts to increase insulin signalling. This effect of Wolbachia infection on IIS could have an evolutionary explanation, and has some implications for studies of IIS in Drosophila and other organisms that harbour endosymbionts.     

Action of genotypical surrounding of host Drosophila melanogaster on biological effects of endosymbiont Wolbachia (strain wMelPop)

In this work, a comparative study of the structure of symbiotic bacteria Wolbachia (strain wMelPop decreasing the fly lifespan) in genotypically different Drosophila melanogaster, as well as the effect of the bacteria on the host cell ultrastructure was investigated out. As a result of special crossings, the Drosophila melanogaster [w]Trl ³⁶² and [w]Trl ^en82 lines, which are carried of mutations for the gene Trithorax-like, are synthesized (lines infected with Wolbachia are designated as [w]). The Drosophila melanogaster line free of Wolbachia was obtained by treatment with antibiotics of the initially infected [w]w ¹¹¹⁸ line. The complex of the used methods and approaches has allowed us to perform a comparative study of the morphology of cell structures for the first time before and after the infestation of insects with bacteria and to evaluate effect of the bacteria on viability and fertility of flies of these lines. Electron microscopy analysis has shown that the embryos of the analyzed lines contain typical Wolbachia in contact with various host cell compartments; the ultrastructural organization of the bacteria indicates the preservation of their functional activity. In the cytoplasm of embryos that are mutant for the gene Trithorax-like, morphologically atypical mitochondria were revealed, as well as Wolbachia (wMelPop) of unusual morphology with a modified form of membtane envelopes. The presence of Wolbachia in ovarian cells of the female mutant fly lines has been found to produce no effect on the amount of the female-ovipositioned eggs. It has been established for the first time that lifespans of the infected and Wolbachia-free Drosophila melanogaster mutant lines TM3 containing chromosome 3 as a balancer are equal. However, it is significantly shorter in the imago of the [w]w ¹¹¹⁸ line than in flies of the mutant lines. This has allowed us to suggest that either the chromosome-balancer TM3 or mutation of the gene Trl play an important role in the host-symbiont interactions. On checking this suggestion, it was found that the lifespan of homozygotes [w]Trl ³⁶² and [w]Trl ^en82 after the infection of flies with bacteria decreased markedly and was close to the lifespan of [w]w ¹¹¹⁸ line. The obtained data indicate that the chromosome-balancer TM3 can have a significant effect on the symbiont-host interaction.     

Variable fitness effects of Wolbachia infection in Drosophila melanogaster

Maternally inherited Wolbachia bacteria are extremely widespread among insects and their presence is usually associated with parasitic modifications of host fitness. Wolbachia pipientis infects Drosophila melanogaster populations from all continents, but their persistence in this species occurs despite any strong parasitic effects. Here, we have investigated the symbiosis between Wolbachia and D. melanogaster and found that Wolbachia infection can have significant survival and fecundity effects. Relative to uninfected flies, infected females from three fly strains showed enhanced survival or fecundity associated with Wolbachia infection, one strain showed both and one strain responded positively to Wolbachia removal. We found no difference in egg hatch rates (cytoplasmic incompatibility) for crosses between infected males and uninfected females, although there were fecundity differences. Females from this cross consistently produced fewer eggs than infected females and these fecundity differences could promote the spread of infection just like cytoplasmic incompatibility. More surprising, we found that infected females often had the greatest fecundity when mated to uninfected males. This could also promote the spread of Wolbachia infection, though here the fitness benefits would also help to spread infection when Wolbachia are rare. We suggest that variable fitness effects, in both sexes, and which interact strongly with the genetic background of the host, could increase cytoplasmic drive rates in some genotypes and help explain the widespread persistence of Wolbachia bacteria in D. melanogaster populations. These interactions may further explain why many D. melanogaster populations are polymorphic for Wolbachia infection. We discuss our results in the context of host-symbiont co-evolution.     

Fitness effects of Wolbachia and Spiroplasma in Drosophila melanogaster

Maternally inherited endosymbionts that manipulate the reproduction of their insect host are very common. Aside from the reproductive manipulation they produce, the fitness of these symbionts depends in part on the direct impact they have on the female host. Although this parameter has commonly been investigated for single infections, it has much more rarely been established in dual infections. We here establish the direct effect of infection with two different symbionts exhibiting different reproductive manipulation phenotypes, both alone and in combination, in the fruit fly Drosophila melanogaster. This species carries a cytoplasmic incompatibility inducing Wolbachia and a male-killing Spiroplasma, occurring as single or double (co-) infections in natural populations. We assessed direct fitness effects of these bacteria on their host, by comparing larval competitiveness and adult fecundity of uninfected, Wolbachia, Spiroplasma and Wolbachia–Spiroplasma co-infected females. We found no effect of infection status on the fitness of females for both estimates, that is, no evidence of any benefits or costs to either single or co-infection. This leads to the conclusion that both bacteria probably have other sources of benefits to persist in D. melanogaster populations, either by means of their reproductive manipulations (fitness compensation from male death in Spiroplasma infection and cytoplasmic incompatibility in Wolbachia infection) or by positive fitness interactions on other fitness components.     

Evidence for a global Wolbachia replacement in Drosophila melanogaster

Wolbachia are maternally inherited intracellular alpha-Proteobacteria found in numerous arthropod and filarial nematode species. They influence the biology of their hosts in many ways. In some cases, they act as obligate mutualists and are required for the normal development and reproduction of the host. They are best known, however, for the various reproductive parasitism traits that they can generate in infected hosts. These include cytoplasmic incompatibility (CI) between individuals of different infection status, the parthenogenetic production of females, the selective killing of male embryos, and the feminization of genetic males. Wolbachia infections of Drosophila melanogaster are extremely common in both wild populations and long-term laboratory stocks. Utilizing the newly completed genome sequence of Wolbachia pipientis wMel, we have identified a number of polymorphic markers that can be used to discriminate among five different Wolbachia variants within what was previously thought to be the single clonal infection of D. melanogaster. Analysis of long-term lab stocks together with wild-caught flies indicates that one of these variants has replaced the others globally within the last century. This is the first report of a global replacement of a Wolbachia strain in an insect host species. The sweep is at odds with current theory that cannot explain how Wolbachia can invade this host species given the observed cytoplasmic incompatibility characteristics of Wolbachia infections in D. melanogaster in the field.     

Wolbachia感染导致果蝇dHira基因表达下调

Wolbachia是广泛存在于节肢动物体内的一类共生微生物,可通过宿主卵的细胞质传递给子代.     

亚洲不同地理种群褐飞虱内共生菌Wolbachia的分子检测

褐飞虱Nilaparvata lugens Stl是水稻的重要害虫,而Wolbachia是其重要的次生共生细菌之一。为了解褐飞虱种群感染Wolbachia的情况,本研究对采自世界褐飞虱主要分布区的22个地理种群感染Wolbachia的情况进行了检测和分析。qPCR结果表明,除杭州2009年种群没有检测出Wolbachia外,其它21个种群中都有不同程度的Wolbachia感染。对Wolbachia的wsp基因序列的比较和进化分析表明,褐飞虱各地理种群Wolbachia都属于B群,并可进一步分为Ori和Con两个亚群。其中18个褐飞虱种群中的Wolbachia属于Ori亚群,广东清远和浙江桐乡褐飞虱种群中的Wolbachia则属于Con亚群,而菲律宾Iloilo褐飞虱种群分别检测到同时有2个亚群Wolbachia感染。本结果可为进一步研究褐飞虱与共生菌的共生关系、褐飞虱致害性变异和迁飞路线分析及利用Wolbachia防治褐飞虱提供依据。     

Infection with Wolbachia does not influence crossing-over in Drosophila melanogaster

The influence of endosymbiotic bacterium Wolbachia on the recombination processes in the sex chromosome of Drosophila melanogaster on the region between white and cut genes has been studied. The analysis of the crossing-over frequency in various variants of strain crossing, infected and noninfected, with bacteria has been carried out. The results have shown the absence of the influence of infection with Wolbachia on the frequency of crossing-over in the studied region of the X chromosome of D. melanogaster.     

Wolbachia effects in Drosophila melanogaster: in search of fitness benefits

Insect endosymbionts often influence host nutrition but these effects have not been comprehensively investigated in Wolbachia endosymbionts that are widespread in insects. Using strains of Drosophila melanogaster with the wMel Wolbachia infection, we showed that Wolbachia did not influence adult starvation resistance. Wolbachia also had no effect on larval development time or the size of emerging adults from a low nutrition medium. While Wolbachia may influence the expression of heat shock proteins, we found that there was no effect on adult heat resistance when tested in terms of survival or virility following heat stress. The absence of nutrition or stress effects suggests that other processes maintain wMel frequencies in natural populations of Drosophila melanogaster.     

The Bacterial Symbiont Wolbachia Induces Resistance to RNA Viral Infections in Drosophila melanogaster

Wolbachia are vertically transmitted, obligatory intracellular bacteria that infect a great number of species of arthropods and nematodes. In insects, they are mainly known for disrupting the reproductive biology of their hosts in order to increase their transmission through the female germline. In Drosophila melanogaster, however, a strong and consistent effect of Wolbachia infection has not been found. Here we report that a bacterial infection renders D. melanogaster more resistant to Drosophila C virus, reducing the load of viruses in infected flies. We identify these resistance-inducing bacteria as Wolbachia. Furthermore, we show that Wolbachia also increases resistance of Drosophila to two other RNA virus infections (Nora virus and Flock House virus) but not to a DNA virus infection (Insect Iridescent Virus 6). These results identify a new major factor regulating D. melanogaster resistance to infection by RNA viruses and contribute to the idea that the response of a host to a particular pathogen also depends on its interactions with other microorganisms. This is also, to our knowledge, the first report of a strong beneficial effect of Wolbachia infection in D. melanogaster. The induced resistance to natural viral pathogens may explain Wolbachia prevalence in natural populations and represents a novel Wolbachia–host interaction.     

Physiological Aspects of Wolbachia pipientis–Drosophila melanogaster Relationship

Journal of Evolutionary Biochemistry and Physiology - The intracellular bacterium Wolbachia pipientis is one of the most common prokaryotic symbionts of invertebrates. It is able to affect host...     

Wolbachia and other endosymbiont infections in spiders

Maternally inherited endosymbiotic bacteria, such as Wolbachia, Rickettsia and Spiroplasma, have been shown to have wide-ranging effects on the reproduction of their hosts. We present data on the presence of each of these sorts of bacteria in spiders, a group for which there are currently few data, but where such infections could explain many observed reproductive characteristics, such as sex ratio skew. The Wolbachia and Spiroplasma variants that we find in spiders belong to the same clades previously found to infect other arthropods, but many of the rickettsias belong to two, novel, hitherto spider-specific bacterial lineages. We find evidence for coexistence of different bacterial types within species, and in some cases, within individuals. We suggest that spiders present a useful opportunity for studying the effect of these sorts of bacteria on the evolution of host traits, such as those that are under sexual selection.     

Sex-specific behavioural symptoms of viral gut infection and Wolbachia in Drosophila melanogaster

All organisms are infected with a range of symbionts spanning the spectrum of beneficial mutualists to detrimental parasites. The fruit fly Drosophila melanogaster is a good example, as both endosymbiotic Wolbachia, and pathogenic Drosophila C Virus (DCV) commonly infect it. While the pathophysiology and immune responses against both symbionts are the focus of intense study, the behavioural effects of these infections have received less attention. Here we report sex-specific behavioural responses to these infections in D. melanogaster. DCV infection caused increased sleep in female flies, but had no detectable effect in male flies. The presence of Wolbachia did not reduce this behavioural response to viral infection. We also found evidence for a sex-specific cost of Wolbachia, as male flies infected with the endosymbiont became more lethargic when awake. We discuss these behavioural symptoms as potentially adaptive sickness behaviours.     

Pathogenicity of Life-Shortening Wolbachia in Aedes albopictus after Transfer from Drosophila melanogaster

Maternally inherited Wolbachia bacteria have evolved mechanisms to manipulate the reproduction of their invertebrate hosts, promoting infection spread. A high fitness cost to the host is maladaptive for obligate endosymbionts, and prior studies show rapid selection of new Wolbachia associations toward commensal or mutualistic symbioses. Here, wMelPop Wolbachia is transferred from Drosophila melanogaster into the mosquito Aedes albopictus. Characterization of the resulting strain provides an extreme example of Wolbachia as a pathogen. In addition to reduced longevity and fecundity, abnormally high Wolbachia density is associated with embryonic mortality that masks the typical pattern of cytoplasmic incompatibility. The results are consistent with earlier reports that show unpredictable shifts in the Wolbachia phenotype after interspecific transfer, which can complicate proposed strategies to modify the age structure of medically important vector populations.Wolbachia bacteria have been identified within a diverse array of invertebrates, where infections are responsible for a variety of host effects including male killing, parthenogenesis, feminization and cytoplasmic incompatibility (CI) (29). The CI phenotype is characterized by early embryonic arrest and a reduction in the number of viable progeny (7, 8, 18, 39). Strict maternal inheritance via embryonic cytoplasm is observed with Wolbachia, and although Wolbachia numbers can be high in testes (24), transmission of the infection to offspring via males has not been reported (17, 41). Instead, an unidentified “modification” of sperm acts to initiate CI in fertilized embryos, unless “rescued” by a compatible Wolbachia infection in their mates (8). The cost of CI to hosts falls upon uninfected females and infected males within the host population, and since males are a dead-end for Wolbachia infection, the resulting dynamics can lead to the spread of infection above an unstable equilibrium threshold (18).Wolbachia bacteria are generally described as “reproductive parasites,” and Wolbachia-host interactions include examples that span the symbiosis spectrum. Field and laboratory studies support hypothesized trends from pathogenicity toward commensalisms and/or mutualism (16, 25, 40). Since mutualistic examples are hypothesized to represent older associations, it follows that maladapted symbioses will be more common among new associations, including artificially generated infections. It is surprising, therefore, that additional examples of pathogenic Wolbachia symbioses have not been identified to date, especially given examples of Wolbachia transinfection. To date, there are two reported examples of pathogenic Wolbachia: an artificially generated association between the isopod Porcellio dilatatus and Wolbachia injected from Armadillium (2) and the wMelPop Wolbachia infection in Drosophila (27). Both examples are similar in that host mortality occurs relatively late and is associated with Wolbachia overproliferation in adult tissues (22, 27). A prior artificial transfer of the wMelPop infection into D. simulans led to a transient exaggeration of pathogenic effects, which were ameliorated in later generations (24, 25).A recent report of the stable introduction of wMelPop into the medically important mosquito disease vector Aedes aegypti (26) suggests a potential strategy to control disease transmission utilizing the heritable Wolbachia infection. Since female mosquitoes must survive an extrinsic incubation period to transmit dengue or other pathogens, a Wolbachia-induced shift in the population age structure toward younger females is expected to reduce pathogen transmission (6, 9).Aedes albopictus (Asian tiger mosquito) is a globally invasive mosquito that has spread via accidental human transport and competitive dominance, resulting in its displacement of numerous resident mosquito populations (15, 30, 31). Its relevance as a disease vector has been elevated recently due to its role in recent chikungunya outbreaks (1, 14, 21, 36).Populations of A. albopictus are normally superinfected with two Wolbachia strains: wAlbA and wAlbB (23, 37). The infection is among the most mutualistic of associations described for Wolbachia in insects (12). Here, we introduced wMelPop into A. albopictus as the first step toward modifying age structure of an A. albopictus population in order to decrease disease transmission such as dengue. However, the wMelPop infection in A. albopictus was maladaptive and provided an extreme example of Wolbachia as a pathogen.     

Genotype of Wolbachia pipientis Endosymbiont Affects Octopamine Metabolism in Drosophila melanogaster Females

Russian Journal of Genetics - The effect of the genotype of the endosymbiont Wolbachia pipientis on the metabolism of octopamine (one of the main biogenic amines in insects) was studied in young...     

Enzyme polymorphism in Drosophila melanogaster populations in Iraq

Electrophoretic studies of the degree and pattern of polymorphism at two third-chromosome loci, esterase-6 (Est-6) and phosphoglucomutase (PGM), were carried out in three Drosophila melanogaster populations collected from different localities in Iraq: Mosul, Tuwaitha, and Basrah. The results show that only the Tuwaitha population was polymorphic for both loci; the other two populations were polymorphic for Est-6 and monomorphic for PGM. The allele frequency changes at both loci were followed for 20 generations in an experimental cage derived from the Tuwaitha population; it was found that there is a deviation from Hardy-Weinberg equilibrium at both loci toward the homozygote.