Gymnodinium aeruginosum (Dinophyta): A blue-green dinoflagellate with a vestigial,anucleate, cryptophycean endosymbiont

Gymnodinium aeruginosum has the usual fine structure of a dinoflagellate but does not seem to contain a well elaborated peduncle or a microtubular basket. Naked cells are surrounded by a single large amphiesmal vesicle. It houses an endosymbiont with typical blue-green cryptophycean chloroplasts (generally only one), cryptophycean starch grains in the periplastidal cytoplasm without a nucleomorph, and two membranes separating the periplastidal cytoplasm from the cryptophycean cytoplasm which contains mitochondria, ER, vesicles and ribosomes, but no eukaryotic nucleus. The endosymbiont is surrounded by a single membrane. Possible ways of the acquisition of the endosymbiont and the problem of the existence of ribosomes within a compartment without nucleus are discussed.Devoted to Prof. Dr.L. Geitler, the Nestor of phycology and endosymbiosis research, on the occasion of the 90th anniversary of his birthday.     

ag13 is expressed in Alnus glutinosa nodules in infected cells during endosymbiont degradation and in the nodule pericycle

We isolated and characterized an Alnus glutinosa cDNA clone, pAg13, which corresponds to a gene expressed at higher levels in nodules induced by Frankia than in roots. The deduced polypeptide sequence is rich in glutamic acid and proline and contains a putative signal peptide indicating an extracellular location of Ag13. In situ hybridization showed that ag13 is expressed in the pericycle of the nodule vascular bundle and in infected cells that exhibited degradation of the endosymbiont.     

Wolbachia host shifts: routes,mechanisms, constraints and evolutionary consequences

Wolbachia is one of the most abundant endosymbionts on earth, with a wide distribution especially in arthropods. Effective maternal transmission and the induction of various phenotypes in their hosts are two key features of this bacterium. Here, we review our current understanding of another central aspect of Wolbachia's success: their ability to switch from one host species to another. We build on the proposal that Wolbachia host shifts occur in four main steps: (i) physical transfer to a new species; (ii) proliferation within that host; (iii) successful maternal transmission; and (iv) spread within the host species. Host shift can fail at each of these steps, and the likelihood of ultimate success is influenced by many factors. Some stem from traits of Wolbachia (different strains have different abilities for host switching), others on host features such as genetic resemblance (e.g. host shifting is likely to be easier between closely related species), ecological connections (the donor and recipient host need to interact), or the resident microbiota. Host shifts have enabled Wolbachia to reach its enormous current incidence and global distribution among arthropods in an epidemiological process shaped by loss and acquisition events across host species. The ability of Wolbachia to transfer between species also forms the basis of ongoing endeavours to control pests and disease vectors, following artificial introduction into uninfected hosts such as mosquitoes. Throughout, we emphasise the many knowledge gaps in our understanding of Wolbachia host shifts, and question the effectiveness of current methodology to detect these events. We conclude by discussing an apparent paradox: how can Wolbachia maintain its ability to undergo host shifts given that its biology seems dominated by vertical transmission?     

Drosophila melanogaster brain invasion: pathogenic Wolbachia in central nervous system of the fly

The pathogenic Wolbachia strain wMelPop rapidly over‐replicates in the brain, muscles, and retina of Drosophila melanogaster, causing severe tissue degeneration and premature death of the host. The unique features of this endosymbiont make it an excellent tool to be used for biological control of insects, pests, and vectors of human diseases. To follow the dynamics of bacterial morphology and titer in the nerve cells we used transmission electron microscopy of 3‐d‐old female brains. The neurons and glial cells from central brain of the fly had different Wolbachia titers ranging from single bacteria to large accumulations, tearing cell apart and invading extracellular space. The neuropile regions of the brain were free of wMelPop. Wolbachia tightly interacted with host cell organelles and underwent several morphological changes in nerve cells. Based on different morphological types of bacteria described we propose for the first time a scheme of wMelPop dynamics within the somatic tissue of the host.     

Suggested mitochondrial ancestry of nonmitochondrial ATP/ADP carrier

One of the major evolutionary events that transformed an endosymbiotic bacterium into a mitochondrion was the acquisition of the ATP/ADP carrier (AAC) in order to supply the host with respiration-derived ATP. Along with the mitochondrial carrier, an unrelated carrier is known, which is characteristic of intracellular chlamydiae, plastids, parasitic intracellular eukaryote Encephalitozoon cuniculi, and the genus Rickettsia of obligate endosymbiotic α-proteobacteria. This nonmitochondrial carrier was recently described in rickettsia-like endosymbionts (RLE), a group of obligate intracellular bacteria classified with the order Rickettsiales, which have diverged after free-living α-proteobacteria but before sister groups of the Rickettsiaceae assemblage (true rickettsiae) and mitochondria. Published controversial phylogenetic data on nonmitochondrial AAC were re-analyzed in the present work, using both DNA and protein sequences and various methods including Bayesian analysis. The data presented are consistent with the classic endosymbiont theory for the origin of mitochondria and suggest that even the last but one common ancestor of rickettsiae and organelles was an endosymbiotic bacterium, in which AAC first originated.     

Genomic conflict in scale insects: the causes and consequences of bizarre genetic systems

It is now clear that mechanisms of sex determination are extraordinarily labile, with considerable variation across all taxonomic levels. This variation is often expressed through differences in the genetic system (XX‐XY, XX‐XO, haplodiploidy, and so on). Why there is so much variation in such a seemingly fundamental process has attracted much attention, with recent ideas concentrating on the possible role of genomic conflicts of interest. Here we consider the role of inter‐ and intra‐genomic conflicts in one large insect taxon: the scale insects. Scale insects exhibit a dizzying array of genetic systems, and their biology promotes conflicts of interest over transmission and sex ratio between male‐ and female‐expressed genes, parental‐ and offspring‐expressed genes (both examples of intra‐genomic conflict) and between scale insects and their endosymbionts (inter‐genomic conflict). We first review the wide range of genetic systems found in scale insects and the possible evolutionary transitions between them. We then outline the theoretical opportunities for genomic conflicts in this group and how these might influence sex determination and sex ratio. We then consider the evidence for these conflicts in the evolution of sex determination in scale insects. Importantly, the evolution of novel genetic systems in scale insects has itself helped create new conflicts of interest, for instance over sex ratio. As a result, a major obstacle to our understanding of the role of conflict in the evolution of sex‐determination and genetic systems will be the difficulty in identifying the direction of causal relationships. We conclude by outlining possible experimental and comparative approaches to test more effectively how important genomic conflicts have been.     

Symbiosis interruption in the olive fly: Effect of copper and propolis on Candidatus Erwinia dacicola

The relationship between Bactrocera oleae (Rossi 1790) and its endosymbiont Candidatus Erwinia dacicola is important to achieving effective control of the olive fly population in the field. This bacterium plays a crucial role in the life of B. oleae and is necessary for its fitness. Thus, in the absence of the endosymbiont, B. oleae wild populations in the field might decrease considerably. Copper is one of the most used antimicrobials for horticultural crops worldwide, and its efficacy against Ca. E. dacicola has been demonstrated in field trials. Propolis is another natural antimicrobial compound largely used for its activity in several fields. If propolis and copper prove to be efficient against wild populations of the endosymbiont B. oleae in the field, such a biological restraint might improve sustainable agriculture. We evaluated, under laboratory conditions, the effect of two different copper products (at two different concentrations, 5% and 20%) and propolis on the content of Ca. E. dacicola in the eggs and in the adult oesophageal bulbs of B. oleae. Bulbs were extracted twice, after 2 and 5 weeks of exposure. Real‐time PCR on the bulbs showed a reduction in Ca. E. dacicola content in flies treated with copper (at both 5% and 20%), and from the first to the second extraction, while flies treated with propolis showed an increment of the relative abundance of Ca. E. dacicola. Both copper products (5% and 20%) reduced the egg production after 2 and 5 weeks in comparison with the control and propolis treatments. Moreover, adult mortality was significantly higher with propolis compared with the other treatments. Thus, our results encourage further research in order to develop new tools for the control of the olive fly in the framework of an integrated pest management strategy.     

三种抗生素去除大青叶蝉内共生菌的效果

内共生菌能够为寄主提供营养物质,同时在宿主昆虫的生长及生殖等方面具有特殊作用,大青叶蝉Cicadella viridis与其他昆虫一样具有内共生菌。本文设计了大青叶蝉内共生菌Sulcia muelleri和Sodalis sp.的特异性引物,检测其在大青叶蝉中的感染率;同时分别用利福平、盐酸土霉素和青霉素G钾盐3种抗生素处理大青叶蝉,用TaqMan探针法绝对定量PCR检测不同处理时间下大青叶蝉内共生菌的拷贝数。结果表明:大青叶蝉内共生菌Sulcia muelleri和Sodalis sp.的带菌率均为100%;利福平、盐酸土霉素和青霉素G钾盐均可使内共生菌的量减少,但不能完全消除。3种抗生素均能显著减少大青叶蝉雌虫和雄虫中内共生菌Sulcia muelleri 16S rRNA基因拷贝数。盐酸土霉素和利福平均能显著降低大青叶蝉若虫和雄虫中内共生菌Sodalis sp. 16S rRNA基因拷贝数,但对雌虫影响不显著。     

Sequencing and comparison of the Rickettsia genomes from the whitefly Bemisia tabaci Middle East Asia Minor I

The whitefly, Bemisia tabaci, harbors the primary symbiont ‘Candidatus Portiera aleyrodidarum’ and a variety of secondary symbionts. Among these secondary symbionts, Rickettsia is the only one that can be detected both inside and outside the bacteriomes. Infection with Rickettsia has been reported to influence several aspects of the whitefly biology, such as fitness, sex ratio, virus transmission and resistance to pesticides. However, mechanisms underlying these differences remain unclear, largely due to the lack of genomic information of Rickettsia. In this study, we sequenced the genome of two Rickettsia strains isolated from the Middle East Asia Minor 1 (MEAM1) species of the B. tabaci complex in China and Israel. Both Rickettsia genomes were of high coding density and AT‐rich, containing more than 1000 coding sequences, much larger than that of the coexisted primary symbiont, Portiera. Moreover, the two Rickettsia strains isolated from China and Israel shared most of the genes with 100% identity and only nine genes showed sequence differences. The phylogenetic analysis using orthologs shared in the genus, inferred the proximity of Rickettsia in MEAM1 and Rickettsia bellii. Functional analysis revealed that Rickettsia was unable to synthesize amino acids required for complementing the whitefly nutrition. Besides, a type IV secretion system and a number of virulence‐related genes were detected in the Rickettsia genome. The presence of virulence‐related genes might benefit the symbiotic life of the bacteria, and hint on potential effects of Rickettsia on whiteflies. The genome sequences of Rickettsia provided a basis for further understanding the function of Rickettsia in whiteflies.     

Independent origins of resistance or susceptibility of parasitic wasps to a defensive symbiont

Insect microbe associations are diverse, widespread, and influential. Among the fitness effects of microbes on their hosts, defense against natural enemies is increasingly recognized as ubiquitous, particularly among those associations involving heritable, yet facultative, bacteria. Protective mutualisms generate complex ecological and coevolutionary dynamics that are only beginning to be elucidated. These depend in part on the degree to which symbiont‐mediated protection exhibits specificity to one or more members of the natural enemy community. Recent findings in a well‐studied defensive mutualism system (i.e., aphids, bacteria, parasitoid wasps) reveal repeated instances of evolution of susceptibility or resistance to defensive bacteria by parasitoids. This study searched for similar patterns in an emerging model system for defensive mutualisms: the interaction of Drosophila, bacteria in the genus Spiroplasma, and wasps that parasitize larval stages of Drosophila. Previous work indicated that three divergent species of parasitic wasps are strongly inhibited by the presence of Spiroplasma in three divergent species of Drosophila, including D. melanogaster. The results of this study uncovered two additional wasp species that are susceptible to Spiroplasma and two that are unaffected by Spiroplasma, implying at least two instances of loss or gain of susceptibility to Spiroplasma among larval parasitoids of Drosophila.