Phylogeny and species composition of five European species of Branchiobdella (Annelida: Clitellata: Branchiobdellida) reflect the biogeographic history of three endangered crayfish species

Branchiobdellid annelids are usually found as commensal symbionts associated with crayfish populations, but knowledge of their dispersion and ecology in Europe is generally scarce. We hypothesized that their geographic extension of species and populations may mirror the distribution history of their hosts. We analysed potential host specificities and the geographic distribution of species from the Italian and Austrian Tyrol and Carinthia by characterizing the morphological and genetic features. On the three indigenous crayfish species Astacus astacus, Austropotamobius pallipes and Austropotamobius torrentium , we identified four branchiobdellid species based on morphological characteristics: Branchiobdella hexodonta, Branchiobdella pentodonta, Branchiobdella balcanica and Branchiobdella parasita . In contrast to the morphological classification, phylogenetic analysis using mitochondrial cytochrome c oxidase I (CO-I) sequences identified five main lineages: B. balcanica, B. hexodonta, Branchiobdella italica, B. parasita and B. pentodonta . The arrangement of branchiobdellid species corresponded generally to the geographical distribution of their crayfish hosts' locations but also confirmed previous assumptions of crayfish translocations. Our study provides the first application of ideas on the association of freshwater crayfish and their ectosymbionts to be used for discussing the biogeography of crayfish populations. The phenotypical and genotypical analysis also demonstrated so far ignored effects of human activities at both macro-ecological and micro-ecological levels.     

造礁石珊瑚与其共生藻(Symbiodinium)共生研究进展

对造礁石珊瑚与其共生藻共生研究现状及其在全球变化下的适应能力进行较全面的综述.造礁石珊瑚与遗传和生理功能独特的共生藻组成内共生关系是成功演化的范例.近年来对珊瑚共生体的分子系统学研究表明共生藻遗传多样性极为丰富,当前认为共生藻属至少包括8个(A-H)各自包含亚系群的世系或系群.珊瑚-共生藻共生功能体对诸如全球变化引起的海水温度上升等环境变化十分敏感.由于珊瑚以及珊瑚礁面临气候变化的严峻挑战,对珊瑚与其共生藻共生关系和共生功体适应能力的研究将是未来重要的研究领域之一.     

Survey and phylogenetic analysis of culturable microbes in the oral secretions of three bark beetle species

In a recent study, we reported a previously undescribed behavior in which a bark beetle exuded oral secretions containing bacteria that have antifungal properties, and hence defend their galleries against pervasive antagonistic Hyphomycete fungi. Actinobacteria, a group known for their antibiotic properties, were the most effective against fungi that invade the spruce beetle galleries. In the present study, we describe the isolation and identification of microorganisms from oral secretions of three bark beetles (Coleoptera: Curculionidae: Scolytinae): the spruce beetle, Dendroctonus rufipennis Kirby, the mountain pine beetle, Dendroctonus ponderosae Hopkins, and the pine engraver, Ips pini Say. Bacteria isolated from these three species span the major bacterial classes α-, β-, and γ-Proteobacteria, Firmicutes, Bacteroidetes, and Actinobacteria, except for D. ponderosae , which yielded no α-proteobacteria or Bacteroidetes isolates. Spruce beetles and pine engraver beetles had similar numbers of α-proteobacteria isolates, but pine engravers yielded twice as many Bacteroidetes isolates as spruce beetles. In contrast, mountain pine beetles yielded more isolates in the β- and γ-proteobacteria than spruce beetles and pine engravers. The highest percentage of Actinobacteria was obtained from spruce beetles, followed by pine engravers and mountain pine beetles. All of the fungal isolates obtained from the three beetle species were Ascomycetes. The greatest fungal diversity was obtained in spruce beetles, which had nine species, followed by pine engravers with five, and mountain pine beetles with one.     

Impact of environmental stress on aphid clonal resistance to parasitoids: Role of Hamiltonella defensa bacterial symbiosis in association with a new facultative symbiont of the pea aphid

Resistance to endoparasitoids in aphids involves complex interactions between insect and microbial players. It is now generally accepted that the facultative bacterial symbiont Hamiltonella defensa of the pea aphid Acyrthosiphon pisum is implicated in its resistance to the parasitoid Aphidius ervi. It has also been shown that heat negatively affects pea aphid resistance, suggesting the thermosensitivity of its defensive symbiosis. Here we examined the effects of heat and UV-B on the resistance of A. pisum to A. ervi and we relate its stability under heat stress to different facultative bacterial symbionts hosted by the aphid. For six A. pisum clones harboring four different facultative symbiont associations, the impact of heat and UV-B was measured on their ability to resist A. ervi parasitism under controlled conditions. The results revealed that temperature strongly affected resistance, while UV-B did not. As previously shown, highly resistant A. pisum clones singly infected with H. defensa became more susceptible to parasitism after exposure to heat. Interestingly, clones that were superinfected with H. defensa in association with a newly discovered facultative symbiont, referred to as PAXS (pea aphid X-type symbiont), not only remained highly resistant under heat stress, but also expressed previously unknown, very precocious resistance to A. ervi compared to clones with H. defensa alone. The prevalence of dual symbiosis involving PAXS and H. defensa in local aphid populations suggests its importance in protecting aphid immunity to parasitoids under abiotic stress.     

On the mechanisms of cadmium stress alleviation in Medicago truncatula by arbuscular mycorrhizal symbiosis: A root proteomic study

The arbuscular mycorrhizal (AM) symbiosis belongs to the strategies plants have developed to cope with adverse environmental conditions including contamination by heavy metals such as cadmium (Cd). In the present work, we report on the protective effect conferred by AM symbiosis to the model legume Medicago truncatula grown in presence of Cd, and on the 2‐D‐based proteomic approach further used to compare the proteomes of M. truncatula roots either colonised or not with the AM fungus Glomus intraradices in Cd‐free and Cd‐contaminated substrates. The results indicated that at the proteome level, 9 out of the 15 cadmium‐induced changes in nonmycorrhizal roots were absent or inverse in those Cd‐treated and colonized by G. intraradices, including the G. intraradices‐dependent down‐accumulation of Cd stress‐responsive proteins. Out of the twenty‐six mycorrhiza‐related proteins that were identified, only six displayed changes in abundance upon Cd exposure, suggesting that part of the symbiotic program, which displays low sensitivity to Cd, may be recruited to counteract Cd toxicity through the mycorrhiza‐dependent synthesis of proteins having functions putatively involved in alleviating oxidative damages, including a cyclophilin, a guanine nucleotide‐binding protein, an ubiquitin carboxyl‐terminal hydrolase, a thiazole biosynthetic enzyme, an annexin, a glutathione S‐transferase (GST)‐like protein, and a S‐adenosylmethionine (SAM) synthase.     

Effects of elimination of Wolbachia on oogenesis of the uzifly Exorista sorbillans,a parasitoid of the silkworm Bombyx mori

Maternally inherited bacteria of the genus Wolbachia are known to affect the physiology and reproduction of several arthropod and nematode hosts. This paper presents the effects of using tetracycline to eliminate Wolbachia on the oogenesis of its host uzifly Exorista sorbillans (Diptera: Tachinidae), a parasitoid of silkworm Bombyx mori L. Earlier we reported cytoplasmic incompatibility, nucleo‐cytoplasmic conflict, male biased sex ratio and reduction in fecundity upon curing of Wolbachia infection using an antibiotic. This paper presents the abnormal growth and proliferation of oocytes in the uninfected/cured uziflies. The anomalies include abnormal/arrested oocyte production with inhibition of normal functioning of nurse cell nuclei, malformation and agglutination in egg chambers, empty egg chambers due to arrested vitellogenesis and undeveloped ovarian tubules. These anomalies further lead to reduction in growth of the ovarian tubules, which resulted in a 20% reduction of fecundity. It is hypothesized that normal oocyte production in uzifly requires the infection of Wolbachia bacteria. Further, in the uzifly, infection is at transition stage from a facultative to an obligatory mode of symbiosis. In light of this, this paper discusses the relationship between Wolbachia and oocyte production.     

Germination and physiological properties of Frankia spores

Spores from four Frankia strains were isolated and purified to homogeneity. The purified spores were biochemically and physiologically characterized and compared to vegetative cells. Frankia spores exhibited low levels of endogenous respiration that were at least ten-fold lower than the endogenous respiration rate of vegetative cells. The macromolecular content of purified spores and vegetative cells differed. One striking difference among the Frankia spores was their total DNA content. From DAPI staining experiments, only 9% of strain ACN1^AG spore population contained DNA. With strains DC12 and EuI1c, 92% and 67% of their spore population contained DNA. The efficiency of spore germination was correlated to the percentage of the spore population containing DNA. These results suggest that the majority of strain ACN1^AG spores were immature or nonviable. The presence of a solidifying agent inhibited the initial stages of spore germination, but had no effect once the process had been initiated. The optimal incubation temperature for spore germination was 25°C and 30°C for strains DC12 and EuI1c, respectively. A mild heat shock increased the efficiency of spore germination, while root extracts also stimulated spore germination. These results suggest that strains DC12 and EuI1c may be suitable strains for further germination and genetic studies.     

Diversity of Rhizobium-Phaseolus vulgaris symbiosis: overview and perspectives

Common bean (Phaseolus vulgaris) has become a cosmopolitan crop, but was originally domesticated in the Americas and has been grown in Latin America for several thousand years. Consequently an enormous diversity of bean nodulating bacteria have developed and in the centers of origin the predominant species in bean nodules is R. etli. In some areas of Latin America, inoculation, which normally promotes nodulation and nitrogen fixation is hampered by the prevalence of native strains. Many other species in addition to R. etli have been found in bean nodules in regions where bean has been introduced. Some of these species such as R. leguminosarum bv. phaseoli, R. gallicum bv. phaseoli and R. giardinii bv. phaseoli might have arisen by acquiring the phaseoli plasmid from R. etli. Others, like R. tropici, are well adapted to acid soils and high temperatures and are good inoculants for bean under these conditions. The large number of rhizobia species capable of nodulating bean supports that bean is a promiscuous host and a diversity of bean-rhizobia interactions exists. Large ranges of dinitrogen fixing capabilities have been documented among bean cultivars and commercial beans have the lowest values among legume crops. Knowledge on bean symbiosis is still incipient but could help to improve bean biological nitrogen fixation.     

Phylogenetic analyses of symbiotic genes and characterization of functional traits of Mesorhizobium spp. strains associated with the promiscuous species Acacia seyal Del.

Aims: To assess the phenotypic, symbiotic and genotypic diversity scope of Mesorhizobium spp. strains associated with Acacia seyal (Del.) isolated from different agro‐ecological zones in Senegal, and uses of susceptible microbial inoculum in a reafforestation process. Methods and Results: A polyphasic approach including phenotypic and genotypic techniques was used to study the diversity and their relationships with other biovars and species of rhizobia. The geographical origins of the strains have limited effect on their phylogenetic and phenotypic classification. Nodulation tests indicated promiscuity of the strains studied, because they were capable of nodulating six woody legume species (Acacia auriculiformis, Acacia senegal, A. seyal, Acacia tortilis ssp. raddiana, Leucaena leucocephala and Prosopis juliflora). Sequencing and phylogenetic analyses of nodA, nodC and nifH genes pointed out that in contrast to nodA gene, the phylogenies of nodC and nifH genes were not consistent with that of 16S rRNA, indicating that these genes of the A. seyal‐nodulating rhizobia might have different origins. Microbial inoculation on nonsterile soil had significant effect on the nodules number and the growth of the seedlings, indicating that these strains of rhizobia might be used as inoculum. Conclusions: The results indicated that A. seyal is a nonselective host that can establish effective symbiosis with Mesorhizobium spp. strains from diverse genomic backgrounds and that the selected A. seyal‐nodulating rhizobia could enhance plant growth. Significance and Impact of the Study: These results showed the important role that A. seyal could play in the improvement of reafforestation process as a promiscuous host, which can establish effective symbiosis with rhizobia from diverse genomic backgrounds.