Molecular evidence for single Wolbachia infections among geographic strains of the flour beetle Tribolium confusum.

Infections with the rickettsial microorganism Wolbachia are cytoplasmically inherited and occur in a wide range of insect species and several other arthropods. Wolbachia infection often results in unidirectional cytoplasmic incompatibility (CI): crosses between infected males and uninfected females are incompatible and show a reduction of progeny or complete inviability. Unidirectional CI can also occur when males harbouring two incompatible Wolbachia strains are crossed with females infected with only one of the two strains. In the flour beetle Tribolium confusum, Wolbachia infections are of particular interest because of the severity of incompatibility. Typically, no progeny results from the incompatible cross, whereas only partial incompatibility is observed in most other hosts. Werren et al. (1995a) reported that Wolbachia infections in T. confusum consist of two bacterial strains belonging to distinct phylogenic groups, based on PCR amplification and sequence analysis of the bacterial cell division gene ftsZ. However, Fialho & Stevens (1996) showed that eight strains of T. confusum were infected with a single and common incompatibility type. Here we report analysis of the ftsZ gene by specific PCR amplification. Diagnostic restriction enzyme assays revealed no evidence of double infections in 11 geographic strains of T. confusum, including the strain examined by Werren et al. (1995a). Further, sequence analysis of the Wolbachia ftsZ gene and an internal transcribed spacer (ITS) region in two of these strains displayed no nucleotide variation or evidence of polymorphisms. Results suggest that T. confusum is infected with B-group Wolbachia only.     

Infection density of Wolbachia and level of cytoplasmic incompatibility in the Mediterranean flour moth,Ephestia kuehniella

Wolbachia, a causative agent of various reproductive changes in arthropods, induces cytoplasmic incompatibility (CI) in the Mediterranean flour moth, Ephestia kuehniella. Two strains of E. kuehniella, Yokohama and Tsuchiura, harbor closely related Wolbachia, but the Yokohama strain expresses stronger CI than the Tsuchiura strain. A transinfected E. kuehniella strain that harbors the Wolbachia derived from the almond moth Cadra cautella, expresses weak CI at a similar level to the Tsuchiura strain. In the present study, we measured the Wolbachia density in the testis of the three E. kuehniella strains in order to examine the effects of bacterial strain and infection load on the expression of CI. When individuals of the same strain were compared, a correlation of bacterial density to CI level was observed. In addition, the Wolbachia density was higher in the Yokohama strain than the Tsuchiura strain in agreement with the CI levels expressed. However, this relationship did not hold in the comparison between the naturally infected and transinfected strains that carried phylogenetically distant Wolbachia.     

Characterization of non-cytoplasmic incompatibility inducing Wolbachia in two continental African populations of Drosophila simulans

Wolbachia is an endocellular bacterium infecting arthropods and nematodes. In arthropods, it invades host populations through various mechanisms, affecting host reproduction, the most common of which being cytoplasmic incompatibility (CI). CI is an embryonic mortality occurring when infected males mate with uninfected females or females infected by a different Wolbachia strain. This phenomenon is observed in Drosophila simulans, an intensively studied Wolbachia host, harbouring at least five distinct bacterial strains. In this study, we investigate various aspects of the Wolbachia infections occurring in two continental African populations of D. simulans: CI phenotype, phylogenetic position based on the wsp gene and associated mitochondrial haplotype. From the East African population (Tanzania), we show that (i) the siIII mitochondrial haplotype occurs in continental populations, which was unexpected based on the current views of D. simulans biogeography, (ii) the wKi strain (that rescues from CI while being unable to induce it) is very closely related to the CI-inducing strain wNo, (iii) wKi and wNo might not derive from a unique infection event, and (iv) wKi is likely to represent the same entity as the previously described wMa variant. In the West African population (Cameroon), the Wolbachia infection was found identical to the previously described wAu, which does not induce CI. This finding supports the view that wAu might be an ancient infection in D. simulans.     

Determination of Wolbachia diversity in butterflies from Western Ghats, India, by a multigene approach

Members of the genus Wolbachia are intracellular bacteria that are widespread in arthropods and establish diverse symbiotic associations with their hosts, ranging from mutualism to parasitism. Here we present the first detailed analyses of Wolbachia in butterflies from India with screening of 56 species. Twenty-nine species (52%) representing five families were positive for Wolbachia. This is the first report of Wolbachia infection in 27 of the 29 species; the other two were reported previously. This study also provides the first evidence of infection in the family Papilionidae. A striking diversity was observed among Wolbachia strains in butterfly hosts based on five multilocus sequence typing (MLST) genes, with 15 different sequence types (STs). Thirteen STs are new to the MLST database, whereas ST41 and ST125 were reported earlier. Some of the same host species from this study carried distinctly different Wolbachia strains, whereas the same or different butterfly hosts also harbored closely related Wolbachia strains. Butterfly-associated STs in the Indian sample originated by recombination and point mutation, further supporting the role of both processes in generating Wolbachia diversity. Recombination was detected only among the STs in this study and not in those from the MLST database. Most of the strains were remarkably similar in their wsp genotype, despite divergence in MLST. Only two wsp alleles were found among 25 individuals with complete hypervariable region (HVR) peptide profiles. Although both wsp and MLST show variability, MLST gives better separation between the strains. Completely different STs were characterized for the individuals sharing the same wsp alleles.     

Influence of aging on cytoplasmic incompatibility, sperm modification and Wolbachia density in Culex pipiens mosquitoes

Wolbachia are maternally inherited endocellular bacteria, widespread in invertebrates and capable of altering several aspects of host reproduction. Cytoplasmic incompatibility (CI) is commonly found in arthropods and induces hatching failure of eggs from crosses between Wolbachia-infected males and uninfected females (or females infected by incompatible strains). Several factors such as bacterial and host genotypes or bacterial density contribute to CI strength and it has been proposed, mostly from Drosophila data, that older males have a lower Wolbachia load in testes which, thus, induces a lighter CI. Here, we challenge this hypothesis using different incompatible Culex pipiens mosquito strains and show that CI persists at the same intensity throughout the mosquito life span. Embryos from incompatible crosses showed even distributions of abortive phenotypes over time, suggesting that host ageing does not reduce the sperm-modification induced by Wolbachia. CI remained constant when sperm was placed in the spermathecae of incompatible females, indicating that sperm modification is also stable over time. The capacity of infected females to rescue CI was independent of age. Last, the density of Wolbachia in whole testes was highly strain-dependent and increased dramatically with age. Taken together, these data stress the peculiarity of the C.pipiens/Wolbachia interaction and suggest that the bacterial dosage model should be rejected in the case of this association.     

Wolbachia and genetic variability in the birdnest blowfly Protocalliphora sialia

Wolbachia are widespread cytoplasmically inherited bacteria that induce various reproductive alterations in host arthropods, including cytoplasmic incompatibility (CI), an incompatibility between sperm and egg that typically results in embryonic death. CI has been invoked as a possible mechanism for reproductive isolation and speciation in arthropods, by restricting gene flow and promoting maintenance (and evolution) of genetic divergence between populations. Here we investigate patterns of Wolbachia infection and nuclear and mitochondrial differentiation in geographical populations of the birdnest blowfly Protocalliphora sialia. Blowflies in western North America are infected with two A-group Wolbachia, with some individuals singly and others doubly infected. Individuals in eastern North America mostly show single infections with a B-group Wolbachia. Populations in the Midwest are polymorphic for infections and show A- or B-group infection. There is a low level of mitochondrial divergence and perfect concordance of mitochondrial haplotype with infection type, suggesting that two Wolbachia-associated selective sweeps of the mitochondrion have occurred in this species. Amplified fragment length polymorphism analysis of nuclear genetic variation shows genetic differentiation between the eastern-Midwestern and western populations. Both Midwestern and eastern flies infected with A-Wolbachia show eastern nuclear genetic profiles. Current results therefore suggest that Wolbachia has not acted as a major barrier to gene flow between western and eastern-Midwestern populations, although some genetic differentiation between A-Wolbachia infected and B-Wolbachia infected individuals in eastern-Midwestern populations cannot be ruled out.     

Evolution and invasion dynamics of multiple infections with Wolbachia investigated using matrix based models

Endosymbiotic bacteria are often transmitted vertically from one host generation to the next via oocytes cytoplasm. The generally small number of colonizing bacteria in the oocytes leads to a bottleneck at each generation, resulting in genetic homogenization of the symbiotic population. Nevertheless, in many of the species infected by Wolbachia (maternally transmitted bacteria), individuals do sometimes simultaneously harbor several bacterial strains, owing to the fact that Wolbachia induces cytoplasmic incompatibility (CI) that maintains multiple infections. CI occurs in crosses in which the male is infected by at least one Wolbachia strain that the female lacks, and consequently it favors individuals with the greatest symbiotic diversity. CI results in death of offspring in diploid species. In haplodiploid individuals, unfertilized eggs hatch normally into males and fertilized ones, which would lead to females, either die (female mortality type: FM) or develop into males (male development type: MD). Until now, only one theoretical study, restricted to diploid species, has investigated the associations where multiple CI-inducing Wolbachia co-exist, and explored the conditions under which multiple infections can spread. The consequences of double infections on Wolbachia maintenance in host populations, and the selective pressures to which it is subjected have not yet been analysed. Here, we have re-written a model previously developed for single infection in matrix form, which allows easy extension to multiple infections and introduction of mutant strains. We show that (i) the CI type has a strong influence on invasiveness and maintenance of multiple infections; (ii) double infection lowers the invasion threshold of less competitive strains that hitch-hike with their companion strain; (iii) when multiple infections occur, as in single infections, the strains selected are those which maximize the production of infected offspring; and (iv) for the MD CI type, invasion of mutant strains can carry the whole infection to extinction.     

Many compatible Wolbachia strains coexist within natural populations of Culex pipiens mosquito

Maternally inherited Wolbachia often manipulate the reproduction of arthropods to promote their transmission. In most species, Wolbachia exert a form of conditional sterility termed cytoplasmic incompatibility (CI), characterized by the death of embryos produced by the mating between individuals with incompatible Wolbachia infections. From a theoretical perspective, no stable coexistence of incompatible Wolbachia infections is expected within host populations and CI should induce the invasion of one strain or of a set of compatible strains. In this study, we investigated this prediction on CI dynamics in natural populations of the common house mosquito Culex pipiens. We surveyed the Wolbachia diversity and the expression of CI in breeding sites of the south of France between 1990 and 2005. We found that geographically close C. pipiens populations harbor considerable Wolbachia diversity, which is stably maintained over 15 years. We also observed a very low frequency of infertile clutches within each sampled site. Meanwhile, mating choice experiments conducted in laboratory conditions showed that assortative mating does not occur. Overall, this suggests that a large set of compatible Wolbachia strains are always locally dominant within mosquito populations thus, fitting with the theoretical expectations on CI dynamics.     

共生菌Wolbachia引起宿主细胞质不亲和的研究进展

Wolbachia 是一类广泛存在于节肢动物以及线虫体内细胞质中呈母系遗传的共生细菌,能够在宿主中产生细胞质不亲和、孤雌生殖、雌性化及杀雄等多种生殖调控作用,其中细胞质不亲和是指被 Wolbachia 感染的雄性个体与未感染的雌性个体（单向不亲和）,或者感染不同株系 Wolbachia 的雌性个体（双向不亲和）交配后不能或很少产生后代,或者后代偏雄性的现象。细胞质不亲和作用使感染的雌性个体在种群中具有很大的生殖优势,凭借这种生殖优势,Wolbachia 能够迅速在宿主种群中扩张。细胞质不亲和的机理探索主要集中在细胞学水平上,其中广为接受的精子“修饰”和“拯救”理论认为,精巢中的 Wolbachia 能够修饰宿主的精细胞,使其不能和卵细胞正常融合,但是当母本感染相同的 Wolbachia 时,就能够将“修饰”过的精子细胞“拯救”过来,使其恢复与卵细胞的正常融合。而分子机理上的探索也开始在转录组、基因组和miRNA水平上对部分昆虫展开了研究。影响细胞质不亲和的因素有很多,包括宿主遗传背景、 Wolbachia 株系、Wolbachia 基因型、共生菌密度（浓度、滴度）、雄虫年龄、环境因素以及共生菌在宿主生殖组织的分布等。近年来,人类也应用细胞质不亲和控制害虫（主要是蚊虫）和人类疾病,取得了较好的进展。     

Wolbachia segregation dynamics and levels of cytoplasmic incompatibility in Drosophila sechellia

In Drosophila sechellia, the endocellular bacterium Wolbachia induces cytoplasmic incompatibility (CI): in crosses involving infected males, a partial or complete embryonic mortality occurs unless the female bears the same Wolbachia. D. sechellia is known to harbour two Wolbachia variants, namely wSh and wSn, closely related to wHa and wNo, respectively, two strains infecting the populations of D. simulans from the Seychelles archipelago and New Caledonia. Strikingly, the two species show similar infection patterns: in D. sechellia, wSh can be present on its own or in double infection with wSn, but individuals carrying wSn only do not occur; in D. simulans, wHa can be present on its own or in double infection with wNo, but individuals carrying wNo only do not occur, or occur at very low frequency. Previous experiments on D. simulans showed that lines singly infected by wNo can be obtained by segregation, and stably maintained. Here we investigate this issue in D. sechellia through an 18 generation experiment, and show that wSn and wSh singly infected lines can arise by segregation. Using singly infected lines obtained in this experiment, we estimate the CI intensities of wSh and wSn in D. sechellia, and compare these to the CI intensities of the same Wolbachia injected into D. simulans. Our results do not suggest any consistent effect of the host species on the CI induced by wSh. On the contrary, it seems that wSn expression is repressed by host factors in D. sechellia.     

Widespread Wolbachia infection in terrestrial isopods and other crustaceans

Wolbachia bacteria are obligate intracellular alpha-Proteobacteria of arthropods and nematodes. Although widespread among isopod crustaceans, they have seldom been found in non-isopod crustacean species. Here, we report Wolbachia infection in fourteen new crustacean species. Our results extend the range of Wolbachia infections in terrestrial isopods and amphipods (class Malacostraca). We report the occurrence of two different Wolbachia strains in two host species (a terrestrial isopod and an amphipod). Moreover, the discovery of Wolbachia in the goose barnacle Lepas anatifera (subclass Thecostraca) establishes Wolbachia infection in class Maxillopoda. The new bacterial strains are closely related to B-supergroup Wolbachia strains previously reported from crustacean hosts. Our results suggest that Wolbachia infection may be much more widespread in crustaceans than previously thought. The presence of related Wolbachia strains in highly divergent crustacean hosts suggests that Wolbachia endosymbionts can naturally adapt to a wide range of crustacean hosts. Given the ability of isopod Wolbachia strains to induce feminization of genetic males or cytoplasmic incompatibility, we speculate that manipulation of crustacean-borne Wolbachia bacteria might represent potential tools for controlling crustacean species of commercial interest and crustacean or insect disease vectors.     

Transposable element polymorphism of Wolbachia in the mosquito Culex pipiens: evidence of genetic diversity, superinfection and recombination

Wolbachia is a group of maternally inherited endosymbiotic bacteria that infect and induce cytoplasmic incompatibility (CI) in a wide range of arthropods. In contrast to other species, the mosquito Culex pipiens displays an extremely high number of CI types suggesting differential infection by multiple Wolbachia strains. Attempts so far failed to detect Wolbachia polymorphism that might explain this high level of CI diversity found in C. pipiens populations. Here, we establish that Wolbachia infection is near to or at fixation in worldwide populations of the C. pipiens complex. Wolbachia polymorphism was addressed by sequence analysis of the Tr1 gene, a unique transposable element of the IS5 family, which allowed the identification of five C. pipiens Wolbachia strains, differing either by nucleotide substitution, presence or absence pattern, or insertion site. Sequence analysis also showed that recombination, transposition and superinfection occurred at very low frequencies. Analysis of the geographical distributions of each Wolbachia strain among C. pipiens populations indicated a strong worldwide differentiation independent from mosquito subspecies type, except in the UK. The availability of this polymorphic marker now opens the way to investigate evolution of Wolbachia populations and CI dynamics, in particular in regions where multiple crossing types coexist among C. pipiens populations.     

Evolution of Wolbachia-induced cytoplasmic incompatibility in Drosophila simulans and D. sechellia

Abstract.— The intracellular bacterium Wolbachia invades arthropod host populations through various mechanisms, the most common of which being cytoplasmic incompatibility (CI). CI involves elevated embryo mortality when infected males mate with uninfected females or females infected with different, incompatible Wolbachia strains. The present study focuses on this phenomenon in two Drosophila species: D. simulans and D. sechellia . Drosophila simulans populations are infected by several Wolbachia strains, including w Ha and w No. Drosophila sechellia is infected by only two Wolbachia : w Sh and w Sn. In both Drosophila species, double infections with Wolbachia are found. As indicated by several molecular markers, w Ha is closely related to w Sh, and w No to w Sn. Furthermore, the double infections in the two host species are associated with closely related mitochondrial haplotypes, namely si I (associated with w Ha and w No in D. simulans ) and se (associated with w Sh and w Sn in D. sechellia ). To test the theoretical prediction that Wolbachia compatibility types can diverge rapidly, we injected w Sh and w Sn into D. simulans , to compare their CI properties to those of their sister strains w Ha and w No, respectively, in the same host genetic background. We found that within each pair of sister strains CI levels were similar and that sister strains were fully compatible. We conclude that the short period for which the Wolbachia sister strains have been evolving separated from each other was not sufficient for their CI properties to diverge significantly.     

我国三地区黑腹果蝇中Wolbachia的系统发育关系及其对宿主生殖的影响

【目的】Wolbachia 是广泛存在于节肢动物和丝状线虫体内的一类共生菌, 能够以多种方式对宿主产生影响。精卵细胞质不亲和（CI）是其引起的最普遍的表型, 即感染Wolbachia的雄性宿主与未感染或感染不同品系的雌性宿主交配后, 不能产生后代或后代极少, 而感染同品系Wolbachia的雌雄宿主交配后则能正常产生后代。我们前期研究发现, 湖北武汉、 云南六库和天津3个地区黑腹果蝇Drosophila melanogaster被Wolbachia感染。本研究旨在明确这3个地区黑腹果蝇中Wolbachia的系统发育关系及其对宿主生殖的影响。【方法】利用Clustal X软件对Wolbachia的wsp基因序列进行比对, 利用MEGA软件构建系统发育树。采用多位点序列分型（MLST）的方法对Wolbachia进行分型。通过区内交配和区之间杂交的方式研究不同地区黑腹果蝇体内Wolbachia 的关系及其对果蝇生殖的影响。【结果】湖北武汉、 云南六库和天津3个地区黑腹果蝇中感染的Wolbachia都是属于A大组的Mel亚群。这3个地区果蝇感染的Wolbachia的序列类型（ST）不同, Wolbachia之间存在一定的差异。湖北武汉和天津果蝇中的Wolbachia能引起强烈的CI表型, 而云南六库果蝇中的Wolbachia引起的CI强度相对较弱。武汉果蝇中Wolbachia不能完全挽救天津果蝇中Wolbachia引起的CI表型, 而天津果蝇中Wolbachia也不能完全挽救武汉果蝇中Wolbachia引起的CI表型。【结论】武汉和天津地区黑腹果蝇中的Wolbachia可能距离较远。Wolbachia的长期共生可能对黑腹果蝇的进化产生了一定的影响, 湖北武汉与云南六库的黑腹果蝇中感染的Wolbachia属于不同的序列类型, 这2个地区的黑腹果蝇已发生了一定的分歧, 产生了一定的生殖隔离。     

Wolbachia在玉米螟赤眼蜂内的三重感染

Wolbachia是一类广泛存在于节肢动物体内的共生菌。玉米螟赤眼蜂Trichogramma ostriniae是我国玉米田间的优势赤眼蜂种, 据报道, 赤眼蜂种内有Wolbachia感染。本文利用Wolbachia的16s rDNA和wsp基因引物通过PCR方法对玉米螟赤眼蜂的野生种群进行了调查, 发现以wsp基因为鉴定依据, 检测的所有个体都感染了3种Wolbachia ［wOstGDAa (GenBank accession no. EU157103), wOstGDAb (GenBank accession no. EU157104) 和 wOstGDB (GenBank accession no. EU157105)］。本文首次报道了野生赤眼蜂种群内Wolbachia的三重感染率几乎为100%。根据本研究的结果, 可以推测当不同种赤眼蜂寄生同一寄主时, Wolbachia可能会在不同赤眼蜂种间进行横向传播。     

Diversity and phylogeny of Wolbachia infecting Bactrocera dorsalis (Diptera: Tephritidae) populations from China

Wolbachia are a common and widespread group of symbiotic bacteria found in the reproductive tissues of arthropods. Bactrocera dorsalis (Hendel) is an important pest causing considerable economic losses of fruits and vegetables in several southern provinces of China. In this study, polymerase chain reaction (PCR) with general Wolbachia surface protein (wsp) primers was used to test the presence of Wolbachia in 1,500 individuals of B. dorsalis from five geographical populations of China. We detected 19 individuals of B. dorsalis infected by Wolbachia, and the infection rates of different populations varied. Comparison of wsp gene sequences from 19 individuals and search of the GenBank identified four new sequences, probably representing four Wolbachia strains. Sequence comparison showed that the four Wolbachia strains from B. dorsalis in China belonged to three groups (Kue, Mel, and Cuc). Phylogenetic analysis of the wsp sequences suggests that geographical isolation of Wolbachia exists among the populations of B. dorsalis in China, and gene flow of Wolbachia might have occurred between B. dorsalis populations of China and Thailand. Phylogenetic analysis performed on the host mitochondrial cytochrome oxidase I (COI) gene and wsp gene suggests that host has coevolved with Wolbachia.     

Wolbachia infections and superinfections in cytoplasmically incompatible populations of the European cherry fruit fly Rhagoletis cerasi (Diptera,Tephritidae)

Wolbachia is an obligately intracellular, maternally inherited bacterium which has been detected in many arthropods. Wolbachia infections disperse in host populations by mechanisms such as cytoplasmic incompatibility (CI). CI leads to embryonic mortality which occurs when infected males mate with uninfected females or females with a different Wolbachia strain. Populations of the European cherry fruit fly Rhagoletis cerasi (Diptera, Tephritidae) were found to be infected by two different Wolbachia strains, wCer1 and wCer2. Superinfections with both strains occurred throughout southern and central Europe and infections with wCer1 were found in northern, western and eastern Europe. Strong unidirectional CI between European populations of R. cerasi were first reported in the 1970s. From the conformity in the recent geographical distribution of the Wolbachia infections and the CI expression patterns found 25 years ago it was deduced that wCer2 potentially causes CI in R. cerasi. The comparison of the geographical distributions indicated that wCer1 + 2 must have spread into wCer1-infected populations in some areas. In other regions, a spread of wCer1 + 2 was probably prevented by dispersal barriers. There, a sharp transition from infected to superinfected populations suggested regional isolation between wCer1 and wCer1 + 2-infected populations.     

Interspecific transfer of Wolbachia between two lepidopteran insects expressing cytoplasmic incompatibility: a Wolbachia variant naturally infecting Cadra cautella causes male killing in Ephestia kuehniella

Wolbachia is known as the causative agent of various reproductive alterations in arthropods. The almond moth Cadra cautella is doubly infected with A- and B-group Wolbachia and expresses complete cytoplasmic incompatibility (CI). The Mediterranean flour moth Ephestia kuehniella carries A-group Wolbachia and expresses partial CI. In the present study, the Wolbachia in C. cautella was transferred to E. kuehniella from which the original Wolbachia had been removed. We obtained transfected lines of three different infection states: single infection with A, single infection with B, and double infection with A and B. The doubly transfected lines and those transfected with only A produced exclusively female progeny. Two lines of evidence suggested that the sex ratio distortion was due to male killing. First, reduced egg hatch rate was observed. Second, removal of the Wolbachia from the transfected lines resulted in the recovery of a normal sex ratio of approximately 1:1. The occurrence of male killing following transfection showed that host factors influence the determination of the reproductive phenotype caused by Wolbachia. The transfected E. kuehniella males carrying exclusively B-group Wolbachia expressed partial incompatibility when crossed with the uninfected females. In addition, the transfected lines were bidirectionally incompatible with the naturally infected strain, which was the first demonstration of bidirectional CI in a lepidopteran.     

Incidence of a new sex-ratio-distorting endosymbiotic bacterium among arthropods

Many intracellular micro-organisms are now known to cause reproductive abnormalities and other phenomena in their hosts. The endosymbiont Wolbachia is the best known of these reproductive manipulators owing to its extremely high incidence among arthropods and the diverse host effects it has been implicated as causing. However, recent evidence suggests that another intracellular bacterium, a Cytophaga-like organism (CLO), may also induce several reproductive effects in its hosts. Here, we present the first survey of arthropod hosts for infection by the CLO. We use a sensitive hemi-nested polymerase chain reaction method to screen 223 species from 20 arthropod orders for infection by the CLO and Wolbachia. The results indicate that, although not as prevalent as Wolbachia, the CLO infects a significant number of arthropod hosts (ca. 7.2%). In addition, double infections of the CLO and Wolbachia were found in individuals of seven arthropod species. Sequencing analysis of the 16S rDNA region of the CLO indicates evidence for horizontal transmission of the CLO strains. We discuss these results with reference to future studies on host effects induced by intracellular micro-organisms.     

小麦和大豆蚜虫中内共生菌Wolbachia的感染检测和系统发育分析

Wolbachia是一类在节肢动物中广泛感染的胞内共生菌。为了了解其在我国蚜虫中的感染情况, 本研究通过扩增wsp基因片段对采集自我国多个地区的3种小麦蚜虫（荻草谷网蚜Sitobion miscanthi、 麦二叉蚜Schizaphis graminum和禾谷缢管蚜Rhopalosiphum padi）和1种大豆蚜虫（大豆蚜Aphis glycines）样品进行了内共生菌Wolbachia的感染检测。结果显示： 3种小麦蚜虫中均未检测出Wolabchia。大豆蚜也仅在采集自北京和杭州的种群中发现了Wolbachia的感染, 感染率分别为95.8%和22.9%, 并且所检测的个体均为单株系感染。wsp基因序列的比对分析显示, 大豆蚜感染的Wolbachia株系与多个亲缘关系较远的昆虫物种中所感染的Wolbachia株系间具有高度一致的基因序列。wsp基因序列构建的系统发育关系和序列一致性均表明大豆蚜感染的Wolbachia株系属于B大组CauB组。本研究为今后探讨Wolbachia在我国蚜虫中的寄主范围和株系多样性提供了数据支持。