Isolation of microbes associated with field-collected populations of the egg parasitoid,Trichogramma chilonis capable of enhancing biotic fitness

Four bacterial and one yeast species, cultured and identified as Stenotrophomonas maltophilia, Acinetobacter sp., Pseudomonas sp. and Ochrobactrum sp. and the yeast as Metschnikowia reukaufii, were isolated from the internal organs of four collections of field-sourced egg parasitoid, Trichogramma chilonis, obtained as parasitised Helicoverpa armigera eggs. Bacteria were identified through 16 rRNA amplification and sequencing. The single species of yeast was identified through internal transcribed spacer sequences. A single bacterial species could be isolated from each of the four T. chilonis collections; however, all four T. chilonis collections yielded the yeast, M. reukaufii. In order to study the influence of the association of each of the bacterial species and the yeast, microbe-free laboratory-bred populations of T. chilonis were fed with the individual cultures and fitness parameters as parasitisation vigour and female bias were studied in T. chilonis over 10 generations. T. chilonis fed with either S. maltophilia or Acinetobacter sp. and Pseudomonas sp. showed a mean percent increase in female ratio of 26.2%, 30% and 30.3% and mean percent parasitisation of H. armigera eggs significantly increased by 38%, 32.2% and 31.3%, respectively. However, T. chilonis fed with Acinetobacter sp. did not positively influence the two T. chilonis fitness factors. The ubiquitous yeast, M. reukaufii, which could be isolated from all four collections of T. chilonis, could significantly increase both female count and percent parasitism ratio by 22% and 65%, respectively. This study has opened the possibility of modulating the parasitisation fitness of laboratory-bred T. chilonis, prior to field release, using microbes associated with them in the wild.     

Fungal associates of the tree-killing bark beetle,Ips typographus,vary in virulence,ability to degrade conifer phenolics and influence bark beetle tunneling behavior

The bark beetle Ips typographus carries numerous fungi that could be assisting the beetle in colonizing live Norway spruce (Picea abies) trees. Phenolic defenses in spruce phloem are degraded by the beetle's major tree-killing fungus Endoconidiophora polonica, but it is unknown if other beetle associates can also catabolize these compounds. We compared the ability of five fungi commonly associated with I. typographus to degrade phenolic compounds in Norway spruce phloem. Grosmannia penicillata and Grosmannia europhioides were able to degrade stilbenes and flavonoids faster than E. polonica and grow on minimal growth medium with spruce bark constituents as the only nutrients. Furthermore, beetles avoided medium amended with phenolics but marginally preferred medium colonized by fungi. Taken together our results show that different bark beetle-associated fungi have complementary roles in degrading host metabolites and thus might improve this insect's persistence in well defended host tissues.     

Diversity of symbiotic bacteria associated with Bemisia tabaci (Homoptera: Aleyrodidae) in cassava mosaic disease pandemic areas of Tanzania

All Bemisia tabaci individuals harbour an obligate bacterial symbiont (Portiera aleyrodidarum), and many also harbour non‐essential facultative symbionts. The association of symbiotic bacteria with the various genetic groups of B. tabaci remains unknown for East Africa. This study aimed to assess any association between the various whitefly genetic groups and the endosymbionts they harbour; to investigate if a unique endosymbiont is associated with super‐abundant whiteflies, and to provide baseline information on endosymbionts of whiteflies for a part of East Africa. Whiteflies collected during surveys in Tanzania were genotyped and screened for the presence of the obligate and six secondary symbionts (SS): Rickettsia (R), Hamiltonella (H), Arsenophonus (A), Wolbachia (W), Cardinium (C) and Fritschea (F). The results revealed the presence of Mediterranean (MED), East Africa 1 (EA1), Indian Ocean (IO) and Sub‐Saharan Africa 1 (SSA1) genetic groups of Bemisia tabaci, with SSA1 further clustered into four sub‐groups: SSA1‐SG1, SSA1‐SG2, SSA1‐SG1/2 and SSA1‐SG3. F was completely absent from all of the whiteflies tested while R was always found in double or multiple infections. In general, no particular symbiont appeared to be associated with the super‐abundant SSA1‐SG1 B. tabaci, although A or AC infections were common among infected individuals. The most striking feature of these super‐abundant whiteflies, dominating cassava mosaic disease pandemic areas, was the high prevalence of individuals uninfected by any of the six SS tested. This study of the endosymbionts of B. tabaci in East Africa showed contrasting patterns of infection in crop and weed hosts.     

HGT is widespread in insects and contributes to male courtship in lepidopterans

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Diversity and functional analysis of luxS genes in Vibrios from marine sponges Mycale laxissima and Ircinia strobilina

Sponges harbor highly diverse and dense microbial communities, providing an environment in which bacterial signaling may be important. Quorum sensing (QS) is a cell density-dependent signaling process that bacteria employ to coordinate and regulate their gene expression. Previous studies have found that bacteria isolated from sponges are able to produce acyl-homoserine lactones (AHLs), an important class of QS molecules found in proteobacteria. Autoinducer-2 (AI-2) is a second class of QS molecule, and is considered to be an interspecies signal. However, AI-2 signaling has not been reported in sponge bacterial symbionts. In this study, degenerate primers were designed based on known Vibrio luxS sequences to amplify the luxS genes encoding AI-2 synthases of several Vibrio isolates from marine sponges Mycale laxissima and Ircinia strobilina. All the vibrios isolated from these two sponges had luxS genes and were able to produce signals with AI-2 activity as detected using a biological reporter. A novel group of luxS sequences was found, thus extending the known diversity of luxS genes. One isolate was chosen for further analysis of its luxS gene by expression of the gene in Escherichia coli DH5α and by characterization of the profile of AI-2 activity. This work provides the first information about luxS genes and AI-2 activity in sponge-associated bacterial communities.     

Population dynamics,hunting nature on insect pests and existence of symbiotic bacterial microbes among leading transgenic cotton spiders

The genetically modified cotton holding Bt proteins, is noxious to bollworms larvae but very little is known about its impact on population of non-target spiders within the field. Studies conducted with the aim to identify spiders along with their abundance, prevalence pattern, preying habit on insect pests in Bt cotton (L280, Cry2Ab4) and commonness of symbiotic bacteria in these spiders. Spiders collections were made via vial tapping/jarring, from May to end of October (2018). In total, 13,342 spiders were recorded during the entire cropping season. Least relative abundance was in May (0.28%), highest in August (30.39%) while ahead decline was observed, reached to 12% in October. The 27 species were verified, least richness was in May (3 species), high in August (19 species), later in the end, reduced to 7 species. High abundance was of Hylyphantes graminicola (68.56%) and Neoscona theisi (19.98%). Existence of H. graminicola and Pardosa astrigera observed during the whole cropping season. Presence of seven guilds among spiders had a diverse nature of hunting insect pests and on number of species existed in the crop, maximum was from direct hunting habit. Composition and community structure of microbiota varied as of spider species. Proteobacteria was the most abundant bacterial phylum and topmost genus was Wolbachia in observed spiders. Five groups of bacteria distinguished across 4 clusters of spiders depending on core community of symbiotic bacterial genera. This effort is an initial step to get knowhow about spiders in Bt cotton, which will facilitate future research studies concerning spiders.     

Antimicrobial activity of certain essential oils against hindgut symbionts of the drywood termite Kalotermes flavicollis Fabr. and prevalent fungi on termite-infested wood

Abstract:  When the kalotermitid Kalotermes flavicollis Fabr. pseudergates exposed to Casuarina wood wafers treated separately with different concentrations (5, 15 and 30  μ l/2 g wood wafer) of the essential oils, their spirochaete and flagellate populations abnormally reduced in numbers and vigour. The lophomonadids Joenia sp. and Mesojoenia sp. were the most adversely affected flagellates followed by the polymastigid Foaina sp. and the trichomonadid Tricercomitus sp. The Taxodium distichum essential oil evidently appeared to have the greatest adverse effect on the flagellates (95–100% decline in numbers within 2–4 days) followed by the Eucalyptus citriodora (89–100%) and the Cupressus sempervirens oils (31–100%). While with the hindgut spirochaetes, the adverse effect seemed to be reversed where the E. citriodora essential oil had the greatest effect (54–100%) followed by C. sempervirens (46–100%) and T. distichum (8–100%) oils. Moreover, the essential oils were assayed for their antifungal activity, at 15, 20, 25, 30, and 50  μ l/1 ml acetone/15 ml Czapek-Dox medium, against isolates of four woodrotting fungi associated with Casuarina timber, Aspergillus sp., Penicillium sp., Fusarium sp. and Mucor sp. by a method based on inhibition of the fungus growth on agar plates. E. citriodora exhibited the most potent fungicidal activity against the tested four fungi, followed by T. distichum oil. While the C. sempervirens essential oil appeared to have the least significant antifungal property.     

Genomic versatility and functional variation between two dominant heterotrophic symbionts of deep-sea Osedax worms

An unusual symbiosis, first observed at ∼3000 m depth in the Monterey Submarine Canyon, involves gutless marine polychaetes of the genus Osedax and intracellular endosymbionts belonging to the order Oceanospirillales. Ecologically, these worms and their microbial symbionts have a substantial role in the cycling of carbon from deep-sea whale fall carcasses. Microheterogeneity exists among the Osedax symbionts examined so far, and in the present study the genomes of the two dominant symbionts, Rs1 and Rs2, were sequenced. The genomes revealed heterotrophic versatility in carbon, phosphate and iron uptake, strategies for intracellular survival, evidence for an independent existence, and numerous potential virulence capabilities. The presence of specific permeases and peptidases (of glycine, proline and hydroxyproline), and numerous peptide transporters, suggests the use of degraded proteins, likely originating from collagenous bone matter, by the Osedax symbionts. ¹³C tracer experiments confirmed the assimilation of glycine/proline, as well as monosaccharides, by Osedax. The Rs1 and Rs2 symbionts are genomically distinct in carbon and sulfur metabolism, respiration, and cell wall composition, among others. Differences between Rs1 and Rs2 and phylogenetic analysis of chemotaxis-related genes within individuals of symbiont Rs1 revealed the influence of the relative age of the whale fall environment and support possible local niche adaptation of ‘free-living'' lifestages. Future genomic examinations of other horizontally-propogated intracellular symbionts will likely enhance our understanding of the contribution of intraspecific symbiont diversity to the ecological diversification of the intact association, as well as the maintenance of host diversity.     

Facultative 'secondary' bacterial symbionts and the nutrition of the pea aphid, Acyrthosiphon pisum

Abstract.  Facultative 'secondary' bacterial symbionts influence various traits of aphids, including plant utilization patterns and resistance to parasitoids. The present study is designed to test the hypothesis that these multiple effects are underlain by symbiont-mediated changes to the aphid requirement for the dominant dietary nutrients, sucrose and amino acids. The performance of pea aphids ( Acyrthosiphon pisum ) on chemically defined diets of systematically altered sucrose and amino acid content varies among eight parthenogenetic clones, with a pattern that does not match the aphid complements of secondary symbionts, Hamiltonella defensa , Regiella insecticola and Serratia symbiotica . Aphid performance is reduced, increased and unaffected by elimination of S. symbiotica , R. insecticola and H. defensa , respectively, but with no significant effect on the range of diets on which aphids performed well. It is concluded that the impact of secondary symbionts on aphid traits is most unlikely to have a purely nutritional basis.     

微藻与细菌作用关系的研究进展

藻类是水生环境中的初级生产者,它的生长常常伴随着细菌并受菌的影响。有研究者指出藻类和细菌有着密不可分的关系。一些研究表明与藻相关的主体细菌是特定的细菌群体,特别是α-变形菌频繁地发现,说明这类菌可能能够开启和维持共生关系。最近的研究提出了营养物质交换是菌藻共生的基础,这类相关化合物是复杂的和特定的分子,可能参与信号处理和监控作用,而不只是被动扩散。同时,这种作用很明显不是静态的,它的开启和终止可能是对环境和发育的响应。需要指出的是明确菌藻关系的作用机理还有待于进一步的深入研究,本篇综述结合新提出的理论,对细菌与微藻作用关系的研究进展进行总结,概括了微藻与菌的作用关系(进化关系,营养依赖,代谢互补和协作生物合成),这种作用关系涉及到的菌的分类(膜菌和藻际微环境菌,促生菌PGPB和溶藻菌)以及菌藻作用的应用(废水处理和生物燃料生产)的情况,并对菌藻关系的未来发展做了展望。