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Symbiotic bacteria often navigate complex environments before colonizing privileged sites in their host organism. Chemical gradients are known to facilitate directional taxis of these bacteria, guiding them towards their eventual destination. However, less is known about the role of physical features in shaping the path the bacteria take and defining how they traverse a given space. The flagellated marine bacteriumVibrio fischeri,which forms a binary symbiosis with the Hawaiian bobtail squid,Euprymna scolopes, must navigate tight physical confinement, squeezing through a bottleneck constricting to ~2 μm in width on the way to its eventual home. Using microfluidicin vitroexperiments, we discovered thatV. fischericells alter their behavior upon entry into confined space, straightening their swimming paths and promoting escape from confinement. Using a computational model, we attributed this escape response to two factors: reduced directional fluctuation and a refractory period between reversals. Additional experiments in asymmetric capillary tubes confirmed thatV. fischeriquickly escape from tapered ends, even when drawn into the ends by chemoattraction. This avoidance was apparent down to a limit of confinement approaching the diameter of the cell itself, resulting in a balance between chemoattraction and evasion of physical confinement. Our findings demonstrate that non-trivial distributions of swimming bacteria can emerge from simple physical gradients in the level of confinement. Tight spaces may serve as an additional, crucial cue for bacteria while they navigate complex environments to enter specific habitats.Significance StatementSymbiotic bacteria that navigate to and through specific host tissues often face tight physical confinement. This work reveals that confinement-associated changes in swimming can dramatically alter taxis, shaping bacterial localization in conjuncture with other motility-directing cues. This work helps explain how bacteria can avoid getting stuck in confined areas while transiting to privileged spaces, adding confinement as an environmental cue that symbiotic bacteria use to shape their motility behavior.

The wheat aphid, Sitobion miscanthi, is one of the most destructive pests of wheat plants in the temperate regions of China. Little is known about the genetic structure evolution of the different geographic populations of S. miscanthi with its migration. In this study, we investigated the population genetic structure and demographic history of S. miscanthi by analysing 18 geographical populations across China using one mitochondrial gene, COI; one nuclear gene, EF-1α; and two endosymbiont Buchnera genes, gnd and trpA. Analysis of data from the various groups showed high haplotype diversity and low nucleotide variation. SAMOVA analysis did not find a correlation between genetic distance and geographic distance. However, areas with high population diversity exhibited high haplotype diversity. Therefore, we speculate that there are two main natural migration pathways of S. miscanthi in China. One is from Yunnan to the Sichuan Basin, and the other is from Wuhan, Xinyang and Jiaodong Peninsula areas to the northwest. Based on this hypothesis, we inferred that these aphid populations appear first in the southwestern and southern regions and spread to the north with the help of the southeastern and southwestern monsoons, which occur in spring and summer. In autumn, the aphids spread southward with the northeastern and northwestern monsoons.

Since the outset of the coronavirus disease 2019 (COVID-19) pandemic, the gut microbiome in COVID-19 has garnered substantial interest, given its significant roles in human health and pathophysiology. Accumulating evidence is unveiling that the gut microbiome is broadly altered in COVID-19, including the bacterial microbiome, mycobiome, and virome. Overall, the gut microbial ecological network is significantly weakened and becomes sparse in patients with COVID-19, together with a decrease in gut microbiome diversity. Beyond the existence of severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2), the gut microbiome of patients with COVID-19 is also characterized by enrichment of opportunistic bacteria, fungi, and eukaryotic viruses, which are also associated with disease severity and presentation. Meanwhile, a multitude of symbiotic bacteria and bacteriophages are decreased in abundance in patients with COVID-19. Such gut microbiome features persist in a significant subset of patients with COVID-19 even after disease resolution, coinciding with ‘long COVID’ (also known as post-acute sequelae of COVID-19). The broadly-altered gut microbiome is largely a consequence of SARS-CoV-2 infection and its downstream detrimental effects on the systemic host immunity and the gut milieu. The impaired host immunity and distorted gut microbial ecology, particularly loss of low-abundance beneficial bacteria and blooms of opportunistic fungi including Candida, may hinder the re-assembly of the gut microbiome post COVID-19. Future investigation is necessary to fully understand the role of the gut microbiome in host immunity against SARS-CoV-2 infection, as well as the long-term effect of COVID-19 on the gut microbiome in relation to the host health after the pandemic.

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.

The dialog between microbes and immune cells is critical for the establishment and maintenance of immune homeostasis. Bacterial-derived metabolites or structural components initiate immune signaling pathways and transcriptional factors, inducing a broad range of specificities and functional repertoires of the immune cells. Conversely, the immune system regulates the composition and function of bacterial communities. Elements of the adaptive immunity, including maternal antibodies and mucosal antibody responses, play crucial roles in protecting the hosts from pathogens in addition to promoting colonization of symbiotic bacteria at mucosal surfaces. The complex interactions set from an early stage in life between the microbiota and adaptive immunity, impact other major physiological systems. In this review, we summarize recent advances in our understanding of how gut bacteria regulate systemic homeostasis by highlighting the finely orchestrated interactions between gut bacteria, immune responses and the nervous system.

Entomopathogenic nematodes (EPNs) and their symbiotic bacteria play a great role in pest bio-control and therefore have been used widely in agricultural production. However, immunologic mechanisms on how they kill their hosts remain little known. Here we investigated the response of cellular immunity to infection by Enterobacter gergoviae LY2W, which is entomopathogenic bacterium of EPN Heterorhabditis megidis 90. Hemocytes started distortion and disintegration after 12 h with a decrease of hemolymph by 34.9%. More interestingly, hemocyte density decreased dramatically to less than 35% of the control at 12 h before larva death. Moreover, the expression of genes coding diptericin and drosomycin responsible for the signaling regulation of humoral immunity indicated that LY2W cells promoted the signaling regulation of humoral immunity mainly by activating Toll and Imd pathways. Therefore, immunosuppression of entomopathogenic bacteria against G. mellonella depended mainly upon disordering the signaling regulation of humoral immunity, destroying hemocyte, and decreasing hemolymph.

Intestinal bacteria play an important role in the health and provide a variety of beneficial effects to host. Immunosuppressant can reduce the immunity of host and increase the susceptibility to pathogens. But it is not clear whether the increased susceptibility caused by immunosuppressant is related to changes of gut microbiota. In this study, we used crucian carp administrated with dexamethasone to explore the effects of immunosuppressants on gut microbial communities and further evaluate the potential association between changes in gut microbiota and susceptibility to pathogens. The results of MANOVA based on the top 10 PCoA axis scores from unweighed/weighted UniFrac distances showed that administration of dexamethasone (P = 0.021) and the administration time (P = 0.027) had a significant impact on the gut microbial composition, regardless of pathogens infection status (P = 0.35). After administration with dexamethasone, the fish had higher abundance of Cetobacterium and lower abundance of Bacillus and Lactococcus, and the abundance of genus Bacillus, Pseudomonas and Lactococcus decreased along with prolong administration time of dexamethasone. The results may help us understand the correlation between the host susceptibility to pathogenic bacteria and gut microbial community shift, and extend our knowledge regarding the role of gut microbiota in keeping the balance between pathogenic and symbiotic bacteria.

Plants can facilitate attraction of herbivore predators and parasites with herbivore-induced volatiles (HIPVs). However, a central unknown of manipulating a natural environment is how the interactive effects of multiple plant stressors impacts belowground multi-trophic interactions. Agricultural systems, while disturbed, are useful model systems for investigating the effects of multiple stressors on plants and their related interactions because of the redundancy of pests and pathogens and thus, the predictability of the species occurring in these environments. Chemical communication among plants and animals belowground remains behind analogous current understanding of terrestrial systems both fundamentally, and from an applied perspective. Entomopathogenic nematodes (EPNs) infect and kill insects with the aid of symbiotic bacteria and can serve a biological control function in agro-ecosystems. EPNs are known to respond to herbivore-induced plant volatiles (HIPVs) that act as attractant cues increasing nematodes numbers in response to herbivory and concurrently increasing mortality of root pests. Microcosm and semi-field investigations have shown evidence that small scale numerical increases of EPN can be artificially caused by targeted applications or increases in HIPV production near the location of herbivore feeding. Community scale field experiments will be necessary to fully describe plant-herbivore-EPN interactions that also include other players such as plant parasitic nematodes (PPNs) and nematophagous fungi (NF), which may have unintended, negative consequences on plant production and natural enemy numerical response, respectively. Drawing upon the existing body of information on multi-trophic belowground communication, we propose development of a method to strategically and dynamically manipulate systems in a manner analogous to ‘tuning an audio mixer’ with hypothetical ‘knobs’ that could be adjusted by the user for human benefit. We suggest that biological control could be artificially up-regulated or down regulated by the action of a pest management practitioner using external forces such as HIPVs to regulate predator-prey interactions with the ultimate goal of sustainable plant production.

Deep-sea Bathymodiolus mussels depend on the organic carbon supplied by symbionts inside their gills. In this study, optimized methods of quantitative real-time PCR and fluorescence in situ hybridization targeted to both mRNA and 16S rRNA were used to investigate the gill symbionts of the cold-seep mussel Bathymodiolus platifrons, including species composition, environmental dependency and immune control by the host. Our results showed that methanotrophs were the major symbiotic bacteria in the gills of B. platifrons, while thiotrophs were scarce. In the mussels freshly collected from the deep sea, methanotrophs were housed in bacteriocytes in a unique circular pattern, and a lysosome-related gene (VAMP) encoding a vesicle-associated membrane protein was expressed at a high level and presented exactly where the methanotrophs occurred. After the mussels were reared for three months in aquaria without methane supply, the abundance of methanotrophs decreased significantly and their circle-shaped distribution pattern disappeared; in addition, the expression of VAMP decreased significantly. These results suggest that the symbiosis between B. platifrons and methanotrophs is influenced by the environment and that the lysosomal system plays an important immune role in controlling the abundance of endosymbionts in host. This study provides a reliable method for investigating symbionts in deep-sea mussels and enriches the knowledge about symbionts in B. platifrons.

Ascidians belonging to Phlebobranchia accumulate vanadium to an extraordinary degree (≤ 350 mM). Vanadium levels are strictly regulated and vary among ascidian species; thus, they represent well-suited models for studies on vanadium accumulation. No comprehensive study on metal accumulation and reduction in marine organisms in relation to their symbiotic bacterial communities has been published. Therefore, we performed comparative 16S rRNA amplicon sequence analyses on samples from three tissues (branchial sac, intestine, and intestinal lumen) involved in vanadium absorption, isolated from two vanadium-rich (Ascidia ahodori and Ascidia sydneiensis samea) and one vanadium-poor species (Styela plicata). For each sample, the abundance of every bacteria and an abundance value normalized to their abundance in seawater were calculated and compared. Two bacterial genera, Pseudomonas and Ralstonia, were extremely abundant in the branchial sacs of vanadium-rich ascidians. Two bacterial genera, Treponema and Borrelia, were abundant and enriched in the intestinal content of vanadium-rich ascidians. The results suggest that specific selective forces maintain the bacterial population in the three ascidian tissues examined, which contribute to successful vanadium accumulation. This study furthers the understanding of the relationship between bacterial communities and metal accumulation in marine life.

Bulb mites of the genus Rhizoglyphus are cosmopolitan pests of onion, garlic and ornamental plants. Despite the growing awareness against the use of pesticides, growers continue to use insecticides as the main control method. Thus, the search for environmentally safe alternative control methods, such as effective biocontrol agents, is of paramount importance. In the present study, the bulb mites were exposed to the infected juveniles of 20 strains of Steinernema and Heterorhabditis species applied at a single dose of 300 IJs per mite, and the invasion rate and mite mortality were assessed. Furthermore, the effect of the culture supernatants of the selected symbiotic bacteria of the genus Xenorhabdus on bulb mite mortality was tested. Our data show that both Steinernema and Heterorhabditis nematodes are able to invade and kill bulb mites, but in general, the invasion and resulting mortality were relatively low. The highest invasion rate of ca 30 IJs per mite was observed in Heterorhabditis taysearae. The mortality reached the maximum of 30% in the most efficient species, namely Steinernema huense, H. bacteriophora and H. amazonensis. The effect of the culture supernatants was generally low, though there were considerable differences in the efficacy among Xenorhabdus species and strains. To conclude we demonstrate that some EPN species are able to invade and kill bulb mites but their effect is in general quite low. Based on present data, EPNs and the metabolites of their symbiotic bacteria do not seem to represent a viable option for bulb mite biocontrol as a standalone approach.

Meloidogyne hapla and Nacobbus aberrans are plant-parasitic nematodes that form galls in the roots of infected plants and cause important economic losses. Entomopathogenic nematodes (EPNs) of the genera Steinernema and Heterorhabditis infect and kill insects via toxins produced by their symbiotic bacteria. EPNs have shown to have an antagonistic effect on different plant-parasitic nematode species in field and greenhouse trials. The aim of the present work was to evaluate, in tomato plants in greenhouse, the effect of the application of three Argentine EPN isolates, their symbiotic bacteria and cell-free supernatants, on a population of M. hapla and two populations of N. aberrans. Sixty days after inoculation, the number of galls and egg masses, the nematode reproduction factor (RF) and plant biomass were calculated. With a few exceptions, biomass was not affected by the different treatments. None of the plant-parasitic nematode populations was reduced by infective juvenile inoculation of the different EPN isolates. Bacterial action differed among populations; M. hapla was the most susceptible one, with a significant reduction in the number of galls, egg masses and RF caused by the application of the three bacterial strains. The most significant effect was produced by the cell-free supernatants on nematode RF, with reductions of 62–90%, caused by bacterial metabolites. The different inoculation alternatives of the EPN-bacterial symbiont complex tested in the present work (infective juveniles, bacteria and cell-free supernatant) are compared for the first time for plant-parasitic nematode species. Fil: Caccia, Milena Guadalupe. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Diversidad y Ecología Animal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Diversidad y Ecología Animal; Argentina Fil: Marro, Nicolás Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto Multidisciplinario de Biología Vegetal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto Multidisciplinario de Biología Vegetal; Argentina Fil: Rondan Dueñas, Juan. Pabellón CEPROCOR. Laboratorio de Biología Molecular; Argentina Fil: Doucet, Marcelo Edmundo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Diversidad y Ecología Animal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Diversidad y Ecología Animal; Argentina Fil: Lax, Paola. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Diversidad y Ecología Animal. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Diversidad y Ecología Animal; Argentina

Selected marine fishes with different feeding habits were screened for the presence of symbiotic cellulolytic bacteria in their gut. Four cellulolytic species of symbiotic bacteria were isolated from GI tract of marine fishes namely Carangoides praeustus, Filimanus similis, Sardinella longiceps and Sillago sihama. The strains were identified after polyphasic phenotypic and genotypic (16S rRNA gene) characterization as Bacillus subtilis strain TCPC1, Vibrio alginolyticus strain CFSS2C2, Pseudomonas stutzeri strain KSLS4C3 and Klebsiella oxytoca strain MSSC4. (Genbank Accession nos.: JN710380, JN710378, JN710377, JN712301).The results indicated the presence of cellulolytic bacteria in GI tract of marine fishes of carnivorous, phytoplanktivorous and omnivorous feeding habits. Cellulolytic activity was the maximum for B. subtilis strain TCPC1 (0.45 mg glucose ml−1) and V. alginolyticus strain CFSS2C2 (0.24 mg glucose ml−1) at 234 h. While P. stutzeri strain KSLS4C3 showed the maximum utilization (0.22 mg glucose ml−1) from 240 to 258 h. K. oxytoca strain MSSC4 (0.47 mg glucose ml−1) showed three peaks during the study. The maximum rate of cellulose utilization was shown by P. stutzeri strain KSLS4C3 (0.05 mg glucose ml−1 medium h−1) followed by K. oxytoca strain MSSC4 (0.03 mg glucose ml−1 medium h−1).

Sponges are sessile benthic filter-feeding animals, which harbor numerous microorganisms. The enormous diversity and abundance of sponge associated bacteria envisages sponges as hot spots of microbial diversity and dynamics. Many theories were proposed on the ecological implications and mechanism of sponge-microbial association, among these, the biosynthesis of sponge derived bioactive molecules by the symbiotic bacteria is now well-indicated. This phenomenon however, is not exhibited by all marine sponges. Based on the available reports, it has been well established that the sponge associated microbial assemblages keep on changing continuously in response to environmental pressure and/or acquisition of microbes from surrounding seawater or associated macroorganisms. In this review, we have discussed nutritional association of sponges with its symbionts, interaction of sponges with other eukaryotic organisms, dynamics of sponge microbiome and sponge-specific microbial symbionts, sponge-coral association etc.

Although alkaloids are frequent in the poison glands of ants of the genus Aphaenogaster, this is not the case for A. iberica. Hypothesizing that in the genus Aphaenogaster, alkaloids are produced by symbiotic bacteria, except for A. iberica, we treated an experimental lot of both A. iberica and a 'classical' Aphaenogaster species, A. senilis, with an antibiotic. Compared to workers from a control lot, this treatment reduced considerably alkaloid production in A. senilis, whereas A. iberica did not react to the treatment. Furthermore, the treatment induced an increase in cuticular hydrocarbon quantities in A. senilis, but not in A. iberica. An analysis of the ant microbiota will be the next step to confirm our hypothesis.

In many microalgal cultivation systems, microalgae co-exist with bacteria, while little is known about the characteristics of their symbiotic relationships. In this study, twenty-six microalgae growth-promoting bacteria were isolated from a culture system of Scenedesmus sp. LX1 cultivated in the secondary effluent from domestic wastewater by using the high-throughput multiple well plate screening method. Ten strains were found to produce and secrete indole acetic acid (IAA), promoting the growth of microalgae. Meanwhile, the microalgae might have secreted signal substances to induce IAA production in bacteria, which was amplified in the tryptophan abundant environment. This indicates that bacteria may mainly promote the growth of the co-existing microalgae through secreting IAA, and microalgae would selectively enhance IAA secretion in turn. Microalgae cultured with microalgal growth-promoting bacteria would be a new potential strategy for improving large-scale microalgal cultivation in an economic and environmentally-friendly way.

The Chinese black honeybees is an ecotype of the European honeybee that is formed by the natural hybridization of Apis mellifera mellifera and A. m. carnica. It is distributed in nature reserves in North China and has been an important breeding resource for disease resistance and other desirable traits. Compared to the areas outside of reserves, the nature reserves offer significant biodiversity benefits not only to the Chinese black honey bees but also to the other valuable plants and animals. In recent years there has been growing evidence that environmental factors including food choices play an important role in shaping the composition and activity of gut microbiota, which in turn can impact host health. In the previous studies on Chinse black honeybees, little attention has been paid to the diverse population of microbes in the gut that play a vital role in host health. In order to achieve a better understanding on the role of environmental factors in diversity and composition of gut microbiota of honey bees, in the present study, we analyzed the gut bacterial communities of Chinese black honeybees using terminal restriction fragment length polymorphism (T-RFLP). The results showed that the samples from the national nature reserves that are protected and managed so as to preserve and enrich their natural condition and resources for Chinese black honeybees had higher variety and richness of gut bacteria than that collected from unreserved regions that also harbor populations of Chinese black honeybees. The four terminal restriction fragments (T-RFs), 201, 223, 247 and 320 bp, were identified to be the dominant bacteria of Chinese black honeybees. Of which 247 and 320 bp had greater differences between bee groups sampled in different regions and therefore could be used as genetic markers to separate samples collected from the national nature reserves to samples collected from unreserved regions. The results clearly indicate that national nature reserve protects biological diversity and ecological and evolutionary processes which have had a significant influence on the diversity of gut bacteria of Chinese black honeybees. The ubiquity of gut symbiotic bacteria identified in Chinese black honeybee suggests that environmental factors could play an important role in diversity and composition of gut bacteria and warrant further investigation into the functional significance of these gut bacteria for the honeybee health.

The gut microbiota that resides in the mammalian intestine plays a critical role in host health, nutrition, metabolic and immune homeostasis. As symbiotic bacteria, these microorganisms depend mostly on non-digestible fibers and polysaccharides as energy sources. Dietary polysaccharides that reach the distal gut are fermented by gut microbiota and thus exert a fundamental impact on intestinal ecology. Marine polysaccharides contain a class of dietary fibers that are widely used in food and pharmaceutical industries (e.g., agar and carrageenan). In this regard, insights into fermentation of marine polysaccharides and its effects on intestinal ecology are of vital importance for understanding the beneficial effects of these glycans. Here, in this review, to provide an overlook of current advances and facilitate future studies in this field, we describe and summarize up-to-date findings on how marine polysaccharides are metabolized by gut microbiota and what effects these polysaccharides have on intestinal ecology.

Coral-associated bacterial communities are paramount for coral ecosystems and holobiont health. However, the role of symbiotic bacteria in the adaptation of high-latitude corals to seasonal fluctuations remains underexplored. Therefore, we used 16S rRNA-based high-throughput sequencing to analyze the symbiotic bacterial diversity, composition, and core bacterial community in high-latitude coral and explored the seasonal fluctuation characteristics of symbiotic bacterial communities. We found that bacterial richness and α-diversity changed significantly across different seasons. Additionally, the community structure recombined seasonally, with different dominant bacterial phyla and genera in different seasons. However, the symbiotic bacterial community structures of Acropora pruinosa in winter and spring were similar. Proteobacteria were the dominant bacteria in spring, autumn, and winter. In summer, the dominant bacterial taxa were Bacteroidota and Proteobacteria. Ralstonia was the dominant bacterial genus in spring and winter, whereas in autumn, BD1-7_clade was dominant. Linear discriminant analysis effect size identified 20 abundant genera between the different groups. Core microbiome analysis revealed that 12 core bacterial operational taxonomic units were associated with A. pruinosa in all seasons, seven of which varied with the seasons, changing between dominant and rare. Distance-based redundancy and variation partitioning analyses revealed that sea surface temperature was the major contributor of variation in the microbial community structure. We hypothesized that the high diversity and abundance of symbiotic bacteria and the increase in Prosthecochloris abundance in coral in summer can help A. pruinosa maintain its physiological functions, ameliorating the negative physiological effects of the decrease in Symbiodiniaceae density under high-temperature stress. Thus, the rapid reorganization of the symbiotic bacterial community structure and core microflora in different seasons may allow the corals to adapt to large seasonal environmental fluctuations. In conclusion, seasonal variation of bacteria plays an important role in coral adaptation to large environmental fluctuations.

Mosquito-borne diseases are global health problems, which mainly affect low-income populations in tropics and subtropics. In order to prevent the transmission of mosquito-borne diseases, the intracellular symbiotic bacteria named as Wolbachia is becoming a promising candidate to interrupt the virus transmission. In this paper, an impulsive mosquito population model with general birth and death rate functions is established to study the cytoplasmic incompatibility (CI) effect caused by mating of Wolbachia-infected males and uninfected females. The dynamics of the spread of Wolbachia in mosquito population are studied, and the strategies of mosquito extinction or replacing Wolbachia-uninfected mosquitoes with Wolbachia-infected mosquitoes are analyzed. Moreover, the results are applied to models with specific birth and death rate functions. It is shown that strategies may be different due to different birth and death rate functions, the type of Wolbachia strains and the initial number of Wolbachia-infected mosquitoes. Furthermore, numerical simulations are conducted to illustrate our conclusions.

This study addressed the modulation of immune responses of the white grub larvae Polyphylla adspersa Motschulsky (Col., Melolonthidae) when challenged with entomopathogenic nematodes (EPNs) Heterorhabditis bacteriophora and Steinernema glaseri. To investigate the immunity system, 20 infective juvenile (IJs) of the EPNs were injected into the larval haemolymph at incubation time. Haemocytic reactions of the larvae against the EPNs at different times post-injection (hpi) showed changes in total haemocyte count (THC) and differential haemocyte count (DHC). Encapsulation as a prominent and typical cellular reaction reached its maximum rate at 8 hpi of H. bacteriophora and 12 hpi of S. glaseri. The encapsulation reaction against H. bacteriophora was significantly different from that against S. glaseri. In contrast to the second instar larvae, the third larval stage had a higher encapsulation rate and specific phenoloxidase activity when injected with both species of EPNs. The humoral reaction related to this enzymatic activity could create initial melanization at 18 hpi of S. glaseri and 12 hpi of H. bacteriophora. However, EPNs probably reduced the number of circulating haemocytes in haemolymphs by their pathogenic potentials and symbiotic bacteria. This occurrence, which was followed by a reduction in the THC, decreased the intensity of the cellular and humoral responses of the larvae. Therefore, the immune system of the grub was activated by the initial infection with EPNs, but was finally suppressed by their activity. This study showed the weak immune response of the white grub larvae of P. adspersa against EPNs, S. glaseri, and H. bacteriophora. This finding could aid biocontrol management by facilitating the selection of a suitable EPN species for its virulence and ability to suppress insect defense systems.

The crustacean zooplankton Daphnia magna has been widely used for chemical toxicity tests. Although abiotic factors have been well documented in ecotoxicological test protocols, biotic factors that may affect the sensitivity to chemical compounds remain limited. Recently, we identified symbiotic bacteria that are critical for the growth and reproduction of D. magna. The presence of symbiotic bacteria on Daphnia raised the question as to whether these bacteria have a positive or negative effect on toxicity tests. In order to evaluate the effects of symbiotic bacteria on toxicity tests, bacteria-free Daphnia were prepared, and their chemical sensitivities were compared with that of Daphnia with symbiotic bacteria based on an acute immobilization test. The Daphnia with symbiotic bacteria showed higher chemical resistance to nonylphenol, fenoxycarb, and pentachlorophenol than bacteria-free Daphnia. These results suggested potential roles of symbiotic bacteria in the chemical resistance of its host Daphnia.

Cowpea (Vigna unguiculata) is a promiscuous grain legume, capable of establishing efficient symbiosis with diverse symbiotic bacteria, mainly slow-growing rhizobial species belonging to the genus Bradyrhizobium. Although much research has been done on cowpea-nodulating bacteria in various countries around the world, little is known about the genetic and symbiotic diversity of indigenous cowpea rhizobia in European soils. In the present study, the genetic and symbiotic diversity of indigenous rhizobia isolated from field-grown cowpea nodules in three geographically different Greek regions were studied. Forty-five authenticated strains were subjected to a polyphasic approach. ERIC-PCR based fingerprinting analysis grouped the isolates into seven groups and representative strains of each group were further analyzed. The analysis of the rrs gene showed that the strains belong to different species of the genus Bradyrhizobium. The analysis of the 16S-23S IGS region showed that the strains from each geographic region were characterized by distinct IGS types which may represent novel phylogenetic lineages, closely related to the type species of Bradyrhizobium pachyrhizi, Bradyrhizobium ferriligni and Bradyrhizobium liaoningense. MLSA analysis of three housekeeping genes (recA, glnII, and gyrB) showed the close relatedness of our strains with B. pachyrhizi PAC48T and B. liaoningense USDA 3622T and confirmed that the B. liaoningense-related isolate VUEP21 may constitute a novel species within Bradyrhizobium. Moreover, symbiotic gene phylogenies, based on nodC and nifH genes, showed that the B. pachyrhizi-related isolates belonged to symbiovar vignae, whereas the B. liaoningense-related isolates may represent a novel symbiovar.

Aphis gossypii is one of the most economically important insect pests for agriculture worldwide. Aphids have developed symbiotic associations with bacterial species, which has led to morphological and molecular differences, such as body color and insecticide resistance. Adults and 3rd instar nymphs of a laboratory-selected spirotetramat-resistant strain of cotton aphid presented 579-fold and 15-fold higher resistance to spirotetramat, respectively, than a susceptible strain (Pan et al., 2015; Peng et al., 2016). In this study, we found that antibiotics, especially ampicillin and tetracycline, increased spirotetramat toxicity in resistant aphids. We also characterized all of the bacterial endosymbionts in these two clones by sequencing the 16S rRNA genes of the endosymbiont. The total reads could be clustered into 3534 operational taxonomic units (OTUs) that showed 97% similarity and belonged to six abundant phyla. Proteobacteria and Firmicutes dominated in the two strains, and the most abundant families were Enterobacteriaceae, Lactobacillaceae and Rhodobiaceae. The genera Arsenophonus, Anderseniella, Buchnera and Lactobacillus were most abundant in the susceptible strain, whereas a significant decrease in abundance of Anderseniella and a great increase in abundance of Arsenophonus and Lactobacillus were observed in the resistant strain. Certain identified species had low sequence similarity to the reported species, which indicates the possibility of novel taxa. The type and abundance of different bacterial groups varied significantly between the two strains. The insecticide selection pressure could be the reason for the observed shift in the bacteria groups. These results increase our understanding of the symbiotic relationships between bacteria and their hosts under insecticide stress and provide clues for the development of potential control techniques against this cotton aphid.

There is increasing interest to understand the interspecies interactions between microbes of anaerobic ammonium oxidation (anammox) consortia. However, the microbial nitrogen and carbon interactions in inorganic suspended growth anammox consortia are still elusive. Here, we operated a long-term Continuous Stirred Tank Reactor (CSTR) with synthetic inorganic wastewater, which achieved 80% of total nitrogen removal at the steady-state, representing a nitrogen removal rate (NRR) of 1.032 kg-N/(m3·d). Our meta-omics analyses yielded 16 high-quality draft genomes and reconstructed their potential metabolic pathways. Elevated expressions of gene transcripts encoding for enzymes involved in nitrogen and carbon metabolisms were detected in isolates obtained from the same anammox consortia, suggesting their potential metabolic roles and possible microbial interaction capacity in anammox consortia. The expressed genes encoding NO support, nitrite/ammonium loop, dissimilatory nitrate reduction to ammonium, and denitrification in anammox bacteria, and its symbiotic bacteria could have benefits to the bacterial survival and reactor performance. The Carbohydrate-active enzyme analysis revealed that carbohydrate cross-feeding in autotrophic anammox consortia might shift the microbial community. Proteobacteria and anammox bacteria might contribute acetate and glycogen for other symbiotic microorganisms to support their survival. Proteobacteria-affiliated bacteria encoded the potentials of biotin synthesis, hinting at the possibility of the regulation of the diversity of the microbial community. The observed microbial interactions in anammox consortia with inorganic feeding facilitate the purification of anammox bacteria and their engineering application.

Environmental pollution can disrupt the interactions between animals and their symbiotic bacteria, which can lead to adverse effects on the host even in the absence of direct chemical toxicity. It is therefore crucial to understand how environmental pollutants affect animal microbiomes, especially for those chemicals that are designed to target microbes. Here, we study the effects of two biocidal nanoparticles (NPs) (Ag and CuO) on the soil bacterial community and the resident gut microbiome of the earthworm Eisenia fetida over a 28-day period using metabarcoding techniques. Exposures to NPs were conducted following OECD test guidelines and effects on earthworm reproduction and juvenile biomass were additionally recorded in order to compare effects on the host to effects on microbiomes. By employing a full concentration series, we were able to link pollutants to microbiome effects in high resolution. Multivariate analysis, differential abundance analysis and species sensitivity distribution analysis showed that Ag-NPs are more toxic to soil bacteria than CuO-NPs. In contrast to the strong effects of CuO-NPs and Ag-NPs on the soil bacterial community, the earthworm gut microbiome is largely resilient to exposure to biocidal NPs. Despite this buffering effect, CuO-NPs did negatively affect the relative abundance of some earthworm symbionts, including 'Candidatus Lumbricincola'. Changes in the soil bacterial community and the earthworm microbiome occur at total copper concentrations often found or modelled to occur in agricultural fields, demonstrating that soil bacterial communities and individual taxa in the earthworm microbiome may be at risk from environmental copper exposure including in nanomaterial form.

The termite gut contains different kinds of lignin and lignocellulose degrading microbes. This study was conducted to isolate and identify termite gut symbiotic bacteria with lignocellulose-degrading potential, and evaluate their effects on the chemical composition and in vitro digestibility of wheat straw and date leaves. Termite gut contents were extracted and cultured in 9 different culture media containing lignin and lignocellulosic materials that had been prepared from water-extracted sawdust and wheat straw. Three superior bacteria capable of growing on all media, and with higher lignin peroxidase activity, were selected and subjected to molecular identification. Following this, wheat straw and date leaves were incubated with the isolated bacteria in liquid medium for 6 weeks. 16S rRNA sequence analysis showed that these isolates possessed 97, 99 and 97% similarity with Bacillus licheniformis , Ochrobactrum intermedium and Microbacterium paludicola , respectively. The highest (P B. licheniformis . In the case of wheat straw, the organic matter (OM) and neutral detergent fiber (NDF), and for date leaves OM, NDF and acid detergent lignin (ADL) contents were not influenced by the treatments (P > 0.05). The greatest and lowest (P B. licheniformis and O. intermedium , respectively. However, bacterial treatments decreased (P M. paludicola and O. intermedium treatments, respectively. For date leaves, the CP content of the control treatment was highest (P O. intermedium and M. paludicola , respectively. For date leaves, treatment with B. licheniformis significantly increased (P 0.05) between experimental groups. Overall, the results of this study showed that the isolated bacteria partially changed the chemical composition of wheat straw and date leaves while, they improved digestibility of nutrients. These bacteria are suitable candidates for increasing nutritive value of by-products for ruminants.

A total of 212 symbiotic bacteria were isolated from nodules of Vicia ervilia, a traditional crop cultivated in Northern Morocco. The isolates were recovered from 10 different sites, trapped each time with the local cultivar grown in the same field. Four loci were sequenced in order to characterize the isolates, including two housekeeping genes (recA and glnII), one plasmidic symbiotic gene (nodC) and one locus from another plasmid (prL11). In several isolates, two different copies of glnII were detected and sequenced, suggesting a unique duplication event, which has never been reported previously. There was no correlation between the genetic differentiation among cultivars and among bacteria, showing that the evolution of the bacterial population was independent, at least partially, from the host plant. By placing the haplotypes in a wide-ranging phylogenetic reconstruction, it was shown that the diversity detected in Morocco was spread throughout the different clades detected worldwide. The differentiation between areas relied on frequency variations of haplotypes rather than a presence/absence pattern. This finding raises new questions concerning bacterial genetic resource preservation, and confirms the old tenet "everything is everywhere but the environment selects".

The leafhopper Cicadella viridis (Hemiptera: Cicadellidae), a sap-sucking insect, is a notorious pest of fruit trees and seedlings. They harbor “ Candidatus sulcia merii ” which is an obligatory symbiotic bacterium housed in a special organ called the bacteriome. In this study universal eubacterial primers 27F and 1513R were used to amplify approximately 1462 bp of symbiotic bacteria 16S rRNA gene from C. viridis . Cloning, sequencing, and phylogenetic analysis targeting the 16S rRNA gene revealed the presence of bacteria stably associated with C. viridis , and a Rickettsia endosymbiont was detected for the first time in this species. Rickettsia endosymbiont localization was studied using quantitative PCR which showed that it was found in all developmental stages. It was also co-localized in the bacteriomes, ovaries, testes, guts, and salivary glands. By an antibiotic treatment, the antibiotic-treated insects exhibited lower Rickettsia infection density than the untreated.

In the fat body cells of the scale insects, Gossyparia spuria and Acanthococcus aceris, numerous rod-shaped symbiotic bacteria occur. Molecular analyses have revealed that these microorganisms are closely related to the widely distributed bacterium Burkholderia. Ultrastructural observations have revealed that the bacteria are transovarially (vertically) transmitted from the mother to offspring. The microorganisms leave the fat body cells and invade ovarioles containing vitellogenic oocytes. They pass through the follicular epithelium in the neck region of the ovariole and enter the perivitelline space. Next, the symbionts infest the anterior region of the oocyte.

Extracellular polysaccharide (EPS) of symbiotic bacteria is indispensible for the invasion of root that leads to formation of nodule in legume plant. The chemical structure of the EPS is important for structural recognition at the early stage of infection in highly host specific legume-bacteria symbiosis. Two bacterial strains A3CK and A7CK isolated from the root nodule of legume Abrus precatorius and identified as Enterobacter spp. based on 16S rDNA sequence homology. Both the strains were found to produce copious amount of EPS (88 and 122 µg/ml respectively) in yeast extract mineral medium. The EPS production was increased 485 µg/ml and 656 µg/ml by A3CK and A7CK strain respectively after the medium supplemented with preferable carbon (mannitol), nitrogen (L-asparagine), and vitamin (B12). Gas chromatography coupled with mass spectrometry (GC–MS) analysis of EPS was performed to determine the presence of sugar monomers. GC–MS analysis of alditol-acetate derivatives of acid hydrolyzed EPS of these two strains revealed that presence of sugars such as mannose, glucose and galactose in A3CK strain, whereas glucose and galactose present in A7CK strain. FT-IR spectrum of the EPS indicated the presence of hydroxyl, methyl and carboxylate groups in both the two strains. The possible role of bacterial EPS production in root nodule and their roles in plant – bacteria interaction are briefly discussed.

TheSteinernema carpocapsae-Xenorhabdus nematophilaassociation is a nematobacterial complex (NBC) used in biological control of insect crop pests. The ability of this dual pathogen to infest and kill an insect strongly depends on the dialogue between the host’s immune system and each partner of the complex. Even though this dialogue has been extensively studied from the two partners’ points of view in several insect models, still little is known about the structure and the molecular aspects of the insects’ immune response to the dual infection. Here, we used the lepidopteran pestSpodoptera frugiperdaas a model to analyze the respective impact of each NBC partner in the spatiotemporal immune responses that are induced after infestation. To this aim, we first analyzed the expression variations of the insect’s immune genes in the fat bodies and hemocytes of infested larvae by using previously obtained RNAseq data. We then selected representative immune genes for RT-qPCR investigations of the temporal variations of their expressions after infestation and of their induction levels after independent injections of each partner. We found that the fat body and the hemocytes both produce potent and stable immune responses to the infestation by the NBC, which correspond to combinations of bacterium- and nematode-induced ones. Consistent with the nature of each pathogen, we showed thatX. nematophilamainly induces genes classically involved in antibacterial responses, whereasS. carpocapsaeis responsible for the induction of lectins and of genes expected to be involved in melanization and cellular encapsulation. In addition, we found that two clusters of unknown genes dramatically induced by the NBC also present partner-specific induction profiles, which paves the way for their functional characterization. Finally, we discuss putative relationships between the variations of the expression of some immune genes and the NBC’s immunosuppressive strategies.Author summaryEntomopathogenic nematodes (EPNs) are living in the soil and prey upon insect larvae. They enter the insect by the natural orifices, and reach the hemocoel through the intestinal epithelium. There, they release their symbiotic bacteria that will develop within the insect and eventually kill it. Nematodes can then feed and reproduce on the insect cadaver. By using transcriptomic approaches, we previously showed that Lepidoptera larvae (caterpillars of the fall armywormSpodoptera frugiperda) produce a strong immune response in reaction to infestation by EPNs. However, we do not know if this immune reaction is triggered by the nematode itself -Steinernema carpacapsae- or its symbiotic bacteria -Xenorhabdus nematophila. To answer this question, we present in this work a careful annotation of immunity genes inS. frugiperdaand surveyed their activation by quantitative PCR in reaction to an injection of the bacteria alone, the axenic nematode or the associated complex. We found that the immune genes are selectively activated by either the bacteria or the nematode and we discuss the implication of which pathway are involved in the defense against various pathogens. We also show that a cluster of newly discovered genes, present only in Lepidoptera, is activated by the nematode only and could represent nematicide genes.

Enterococcus faecalis is one of the main components of symbiotic bacteria in the intestine of silkworm (Bombyx mori L.). The abundance of E. faecalis in the intestine of silkworm is affected by fluoride exposure. However, the response mechanism of E. faecalis toward fluoride remains largely unknown. In this study, a strain of E. faecalis (named TV4), which is a symbiotic bacteria of silkworm, was isolated and characterized. Inhibition assay showed that fluoride can significantly inhibit the growth of the TV4 strain (P 0.05) after culture for 4 h. Finally, Illumina X-Ten platform was used to investigate the response mechanism of E. faecalis TV4 under fluoride exposure. We found that the TV4 strain demonstrated significant changes in its carbohydrate transport and metabolism and energy metabolism. The transcriptome sequencing results revealed that 237 genes were differentially expressed for TV4 grown after fluoride exposure, i.e., 92 genes were differentially up-regulated and 145 genes were differentially down-regulated. Many of the down-regulated genes were involved in cell carbohydrate transport and metabolism and energy production, whereas the up-regulated genes were mostly related to ethanolamine utilization and amino acid synthesis and metabolism. Our results revealed that strain TV4 reduced its carbohydrate metabolism and energy metabolism and increased ethanolamine utilization and amino acid metabolism to adapt and survive under fluoride exposure. This study enhances our understanding about the response mechanism of E. faecalis after fluoride exposure and has important implications for investigations on the three-way interaction among fluoride, symbiotic bacteria and silkworm.

Large-scale cultivation of microalgae benefits from co-cultivation with model growth-promoting microorganisms to increase algal biomass and lipids production. Nevertheless, the effect of natural symbiotic bacteria on microalgae cultivation and lipid production is still unclear. Here, the effects of nitrogen-fixing, symbiotic Rhizobium on nitrogen content and algal growth, lipid accumulation, and gene expression were investigated in the green microalga Chlorella variabilis. The results demonstrated that compared to axenic C. variabilis cultures, the bacterial-derived nitrogen supply and algal growth were enhanced by 32.8% and 27% in cocultures, respectively. Transcriptome analyses revealed that C. variabilis growing with R. radiobacter TH729 upregulated genes involved in fatty acid oxidation and downregulated genes related to nitrogen metabolism. Our findings indicated that bacterial fixed nitrogen reduces lipid accumulation in microalgae, which is not beneficial for biodiesel production. Further studies on the effects of other bacteria on microalgae are needed to assess most optimal practices for biodiesel production.

Microbial symbionts in humans, animals, and plants are unparalleled sources of compounds for drug discovery. However, methods are needed to access natural biodiversity and make it amenable to pharmaceutical and biotechnological development. Here, we employ a novel approach marrying traditional natural products chemistry with modern metagenomics and synthetic biology in Escherichia coli to discover, synthesize, and analogue divamides, anti‐HIV molecules from rare coral reef animals. We demonstrate that divamides are produced by Prochloron symbiotic bacteria, which have eluded cultivation for >40 years. This represents a new paradigm of direct compound discovery from a true symbiotic relationship. We show that the divamides arise from a diversitygenerating biosynthetic pathway, which was exploited to generate derivatives for mechanism of action studies. The synthesis of closely related, yet functionally distinct compounds by a single biosynthetic pathway provides the first direct evidence supporting the "speculative metabolism" hypothesis of chemical diversity.

Toxic goby fish (Yongeichthys criniger) containing tetrodotoxin (TTX), from Zhanjiang, Guangdong province, China, were screened for TTX-producing bacteria. Two toxic bacterial strains were isolated from the liver of Y. criniger and respectively denoted XC3-3 and XL-1. TTX production by the strains was confirmed by mouse bioassay, enzyme-linked immunosorbent assay and high performance liquid chromatography coupled with mass spectrometry. Based on morphological, physiological and biochemical characteristics and 16S rDNA phylogenetic analysis, strain XC3-3 was identified as Enterobacter cloaca and XL-1 was closely related to Rahnella aquatilis. These findings show for the first time that TTX-producing bacteria are symbiotic bacteria in goby and suggest that bacterial strains are at least partially responsible for TTX accumulation in Y. criniger.

Deep-sea mytilid mussels harbor symbiotic bacteria in their gill epithelial cells that are horizontally or environmentally transmitted to the next generation of hosts. To understand the immune defense system in deep-sea symbiotic mussels, we examined the hemocyte populations of the symbiotic Bathymodiolus mussel species Bathymodiolus japonicus, Bathymodiolus platifrons, and Bathymodiolus septemdierum, and characterized three types of hemocytes: agranulocytes (AGs), basophilic granulocytes (BGs), and eosinophilic granulocytes (EGs). Of these, the EG cells were the largest (diameter, 8.4–10.0 μm) and had eosinophilic cytoplasm with numerous eosinophilic granules (diameter, 0.8–1.2 μm). Meanwhile, the BGs were of medium size (diameter, 6.7–8.0 μm) and contained small basophilic granules (diameter, 0.3–0.4 μm) in basophilic cytoplasm, and the AGs, the smallest of the hemocytes (diameter, 4.8–6.0 μm), had basophilic cytoplasm lacking granules. A lectin binding assay revealed that concanavalin A bound to all three hemocyte types, while wheat germ agglutinin bound exclusively to EGs and BGs. The total hemocyte population densities within the hemolymph of all three Bathymodiolus mussel species were similar (8.4–13.3 × 105 cells/mL), and the percentages of circulating AGs, BGs, and EGs in the hemolymph of these organisms were 44.7–48.5%, 14.3–17.6%, and 34.3–41.0%, respectively. To analyze the functional differences between these hemocytes, the phagocytic activity and post-phagocytic phagosome–lysosome fusion events were analyzed in each cell type using a fluorescent Alexa Fluor® 488-conjugated Escherichia coli bioparticle and a LysoTracker® lysosomal marker, respectively. While the AGs exhibited no phagocytic activity, both types of granulocytes were phagocytic. Of the three hemocyte types, the EGs exhibited the highest level of phagocytic activity as well as rapid phagosome–lysosome fusion, which occurred within 2 h of incubation. Meanwhile, the BGs showed lower phagocytic activity and lower rates of phagosome–lysosome fusion than the EGs. These findings indicate that the two types of granulocyte play distinct roles in the defense system.

The acquisition and maintenance of symbiont-host associations is considered an important prerequisite for the successful colonisation of land by animals because symbionts allowed the hosts to dwell on low-quality food sources. Digestive tract symbionts are suggested to either enhance digestive efficiency of cellulose or supply the host with nutrients otherwise limited in the food. Terrestrial isopods are the most successful land colonisers among the Crustacea, and although symbiotic bacteria have been identified in digestive tract, the mechanism of transmission and the nutritional role of the symbionts are at present poorly understood. We used a novel in vitro approach to isolate and culture juveniles of Porcellio scaber at a time when only the vertical mode of symbiont acquisition could have occurred, which allowed us to follow juvenile growth and to simulate alternative modes of symbiont acquisition through feeding manipulations. Thus, we experimentally obtained groups of juveniles that could have acquired symbionts only through vertical transfer (mother-offspring), or additionally, through horizontal (through faeces or contact with conspecifics) and environmental (through leaves) transfer. We quantified survival and growth rates over two months for the different experimental acquisition modes, and significantly different growth rates were observed ( p p = 0.051), juveniles supplemented with potential sources of symbionts showed a tendency towards increased survival. The successful invasion of land may thus have been facilitated through the uptake of symbionts from the surroundings.

Phytoplankton and bacteria play the foremost role in primary production and often act in unison in biogeochemical cycling. Studies conducted so far are inconclusive on species specificity of phycosphere bacteria as the overarching function of specific clades of algae-associated bacteria, for instance Roseobacter in sulfur cycling, is widely held. In this study, we attempt to demonstrate the diversity of phycosphere bacteria in phylogenetically divergent unialgal green algae from vastly different environmental samples like soil, freshwater, marine, and wastewater with diatom and cyanobacteria as an outgroup. Diversity analyses using Differential Gel Gradient Electrophoresis (DGGE) revealed the predominant presence of bacteria belonging to Bacteroidetes phylum (46% of all strains). 454 pyrosequencing of selected strains from different habitats not only confirmed the presence of Bacteroidetes (33.1% of total reads) but also revealed the presence of bacteria belonging to α-Proteobacteria (52.6%), all in close association with their host. Majority of those symbiotic bacteria have been classified as Plant Growth Promoting Bacteria (PGPB) including prominent Sphingomonads and Rhizobacter. Results suggest that although host algae might encourage species specific interactions, specific functional traits are prerequisite for proximal adhesion in nutrient-rich phycosphere. While Bacteroidetes is known to have significant role in nutrient cycling through degradation of plant and algal macromolecules and for its attached growth, PGPB have proven symbiosis with plants and the overwhelming presence of these bacteria in green algae points to possible co-evolution.

Deep-sea hydrothermal vents are extreme habitats that are distributed worldwide in association with volcanic and tectonic events, resulting thus in the establishment of particular environmental conditions, in which high pressure, steep temperature gradients, and potentially toxic concentrations of sulfur, methane and heavy metals constitute driving factors for the foundation of chemosynthetic-based ecosystems. Of all the different macroorganisms found at deep-sea hydrothermal vents, the mussel Bathymodiolus azoricus is the most abundant species inhabiting the vent ecosystems from the Mid-Atlantic Ridge (MAR). In the present study, the effect of long term acclimatization at atmospheric pressure on host–symbiotic associations were studied in light of the ensuing physiological adaptations from which the immune and endosymbiont gene expressions were concomitantly quantified by means of real-time PCR. The expression of immune genes at 0 h, 12 h, 24 h, 36 h, 48 h, 72 h, 1 week and 3 weeks post-capture acclimatization was investigated and their profiles compared across the samples tested. The gene signal distribution for host immune and bacterial genes followed phasic changes in gene expression at 24 h, 1 week and 3 weeks acclimatization when compared to other time points tested during this temporal expression study. Analyses of the bacterial gene expression also suggested that both bacterial density and activity could contribute to shaping the intricate association between endosymbionts and host immune genes whose expression patterns seem to be concomitant at 1 week acclimatization. Fluorescence in situ hybridization was used to assess the distribution and prevalence of endosymbiont bacteria within gill tissues confirming the gradual loss of sulfur-oxidizing (SOX) and methane-oxidizing (MOX) bacteria during acclimatization. The present study addresses the deep-sea vent mussel B. azoricus as a model organism to study how acclimatization in aquaria and the prevalence of symbiotic bacteria are driving the expression of host immune genes. Tight associations, unseen thus far, suggest that host immune and bacterial gene expression patterns reflect distinct physiological responses over the course of acclimatization under aquarium conditions.

The application of entomopathogenic nematodes (EPN) and their symbiotic bacteria as biological control approaches depend on their lethal parasites to pest and antifungal activities against plant pathogenic fungi. We have collected 23 symbiotic bacterial strains from 23 EPN isolates gathered from different regions of China. In the present study, the insecticidal and antifungal activities of all these bacterial isolates were evaluated in the laboratory. Bioassay results showed that the broth and crude extract of all these 23 EPN symbiotic bacteria strains have, to a certain extent, oral insecticidal activity and/or growth inhibition to the larvae of Ostrinia furnacalis and antifungal activity against Bipolaris maydis and Curvularia lunata. Among these strains, SY5 exhibited highest insecticidal and antifungal activities to O. furnacalis, B. maydis and C. lunata. The adversity resistance of strain SY5 showed that the antifungal activity of the broth was more stable than the insecticidal activity, and the stability of antifungal activity to B. maydis and C. lunata was different.

International audience; The Wolbachia are symbiotic bacteria vertically transmitted from one host generation to another. However, a growing amount of data shows that horizontal transfers of Wolbachia also frequently occur within and between host species. The consequences of the arrival of new symbionts on host physiology can be studied by their experimental introduction in asymbiotic hosts. After experimental transfers of the eight major isopod Wolbachia strains in the isopod Porcellio dilatatus only two of them (wCon and wDil) were found to (1) have no pathogenic effect on the host and (2) be able to pass vertically to the host offspring. In the present work, we studied the influence of these two strains, able to complete an horizontal transfer, on immunity and reproduction of P. dilatatus at two stages of the transfer: (1) in recipient hosts that encounter the symbionts: to test the influence of symbiont when acquired during host life and (2) in vertically infected offspring: to test the influence of a symbiotic interaction occurring all lifelong. The impact of Wolbachia varied depending on the stage: there were clearer effects in vertically infected individuals than in those that acquired the symbionts during their lives. Moreover, the two Wolbachia strains showed contrasted effects: the strain wCon tended to reduce the reproductive investment but to maintain or increase immune parameters whilst wDil had positive effects on reproductive investment but decreased the investment in some immune parameters. These results suggest that horizontally acquisition of Wolbachia can influence the balance between host immune and reproductive traits.

There is evidence of competition within and between helminth species, but the mechanisms involved are not well described. In interference competition, organisms prevent each other from using the contested resource through direct negative interactions, either chemical or physical. Steinernema spp. are entomopathogenic nematodes; they enter a living insect host which they kill and consume with the aid of symbiotic bacteria. Several studies have demonstrated intra- and interspecific competition in Steinernema, mediated by a scramble for resources and by incompatibility of the bacterial symbiont. Here we describe a mechanism by which male Steinernema may compete directly for resources, both food (host) and females, by physically injuring or killing members of another species as well as males of their own species. A series of experiments was conducted in hanging drops of insect haemolymph. Males of each of four species (Steinernema longicaudum, Steinernema carpocapsae, Steinernema kraussei and Steinernema feltiae), representing three of the five phylogenetic clades of the genus, killed each other. Within 48 h, up to 86% of pairs included at least one dead male, compared with negligible mortality in single male controls. There was evidence of intraspecific difference: one strain of S. feltiae (4CFMO) killed while another (UK76) did not. Males also killed both females and males of other Steinernema spp. There was evidence of a hierarchy of killing, with highest mortality due to S. longicaudum followed by S. carpocapsae, S. kraussei and S. feltiae. Wax moth larvae were co-infected with members of two Steinernema spp. to confirm that killing also takes place in the natural environment of an insect cadaver. When insects were co-infected with one infective juvenile of each species, S. longicaudum males killed both S. feltiae UK76 and Steinernema hermaphroditum. Wax moths co-infected with larger, equal numbers of S. longicaudum and S. feltiae UK76 produced mainly S. longicaudum progeny, as expected based on hanging drop experiments.

Bean plants from the Phaseolus genus are widely consumed and represent a nitrogen source for human nutrition. They provide biological fertilization by establishing root nodule symbiosis with nitrogen-fixing bacteria. To establish a successful interaction, bean plants and their symbiotic bacteria need to synchronize a proper molecular crosstalk. Within the Phaseolus genus, P. vulgaris has been the prominent species to study nodulation with Rhizobium symbionts. However the Phaseolus genus comprises diverse species whose symbionts have not been analyzed. Here we identified and studied nodule bacteria from representative Phaseolus species not previously analyzed and from all the described wild species related to P. vulgaris. We found Bradyrhizobium in nodules from most species representing all Phaseolus clades except in five phylogenetically related species from the P. vulgaris clade. Therefore we propose that Bradyrhizobium nodulation is common in Phaseolus and that there was a symbiont preference shift to Rhizobium nodulation in few related species. This work sets the basis to further study the genetic basis of this symbiont substitution.

The universality of improved CO₂ fixing upon the addition of mixed electron donors (MEDs) composed of Na₂S, NO₂(-), and S₂O₃(2-) to non-photosynthetic microbial communities (NPMCs) obtained from 12 locations in four oceans of the world was validated. The CO₂ fixing efficiencies of NPMCs were universally enhanced by MED compared with those obtained using H₂ alone as electron donor, with average increase of about 276%. An increase in microbial inoculation concentration could increase the net amount of CO₂ fixing to 853.34 mg/L in the presence of MED. NO₂(-) and S₂O₃(2-) may play the roles of both electron acceptor and electron donor under aerobic conditions, which may improve the energy utilization efficiency of NPMC and enhance the CO₂ fixation efficiency. The sequence determination of 16S ribosomal deoxyribonucleic acid (rDNA) from 150 bacteria of NPMC showed that more than 50% of the bacteria were symbiotic and there were many heterotrophic bacteria such as Vibrio natriegens. These results indicate that NPMC acts as a symbiotic CO₂ fixing system. The interaction between autotrophic and heterotrophic bacteria may be a crucial factor supporting ladder utilization and recycling of energy/carbon source.

Hylotrupes bajulus (Linnaeus) (Coleoptera, Cerambycidae), a wood-boring beetle attacking softwood, utilises both wood starch and cellulose as food. The fibre is digested in variable percentages, depending on the starch content. A role for symbiotic bacteria was presumed as well as the presence of endogenous cellulases. The aim of our investigation was to verify the presence of endogenous endoglucanase genes in H. bajulus larvae. After performing an online search, three sequences for the endoglucanases of the class GHF5 and four for the endoglucanases of the class GHF45 were recovered and aligned in order to develop some primers on the most conserved regions and try the amplification of the genes in H. bajulus . Seven degenerated primers for GHF5 endoglucanase and five for GHF45 endoglucanase were tested. By using two different primer combinations we obtained two fragments: both of them showed homology with significant identity with insect endoglucanases of the GHF45 family available online, and one also with microbial cellulases. The first fragment is undoubtedly of endogenous origin while we cannot exclude that the second one is of microbial origin. No results were obtained for the endoglucanase of the class GHF5.

Recent studies have provided molecular evidence that gut symbiotic bacteria modulate host insect development, fitness and reproduction. However, the molecular mechanisms through which gut symbionts regulate these aspects of host physiology remain elusive. To address these questions, we prepared two different Riptortus-Burkholderia insect models, Burkholderia gut symbiont-colonized (Sym) Riptortus pedestris insects and gut symbiont-noncolonized (Apo) insects. Upon LC-MS analyses, juvenile hormone III skipped bisepoxide (JHSB3) was newly identified from Riptortus Apo- and Sym-female and male adults' insect hemolymph and JHSB3 titer in the Apo- and Sym-female insects were measured because JH is important for regulating reproduction in adult insects. The JHSB3 titer in the Sym-females were consistently higher compared to those of Apo-females. Since previous studies reported that Riptortus hexamerin-α and vitellogenin proteins were upregulated by the topical abdominal application of a JH-analog, chemically synthesized JHSB3 was administered to Apo-females. As expected, the hexamerin-α and vitellogenin proteins were dramatically increased in the hemolymph of JHSB3-treated Apo-females, resulting in increased egg production compared to that in Sym-females. Taken together, these results demonstrate that colonization of Burkholderia gut symbiont in the host insect stimulates biosynthesis of the heteroptera-specific JHSB3, leading to larger number of eggs produced and enhanced fitness in Riptortus host insects.

Recently, there has been a growing interest in bacterial diversity in the phycosphere of microalgae because plant growth promoting bacteria (PGPB) increase algal biomass. However, the phycosphere bacterial community associated with the unicellular microalgae, Haematococcus strains, has not been studied to date, despite the broad industrial applications of these microalgae. Accordingly, in this study, we analyzed the characteristics of phycosphere bacterial communities associated with microalgae. The phycosphere bacterial community structure was dramatically shifted with each growth stage of Haematococcus lacustris. A symbiotic bacterium, Achromobacter sp. CBA4603, was identified and isolated from the Haematococcus culture and was found to produce high levels of auxin compared with other PGPB strains. During co-cultivation of Haematococcus pluvialis, which has high commercial value, with the isolated strain CBA4603, the growth of the microalga was enhanced at all growth stages, and the exponential stage was prolonged. However, the accumulation of astaxanthin was not high, which could be explained by the previously reported characteristics of exogenous auxin. Taken together, our results suggested that this Achromobacter strain may be useful for industrial and biotechnological applications to enhance biomass and for generation of high value-added products of H. pluvialis.

Microbial associations are widespread across the insects. In the olive fruit fly Bactrocera oleae (Diptera: Tephritidae), vertically transmitted gut symbionts contribute to larval development inside the olive host, and to adult nutrition. Nevertheless, their effect on behavioural decisions of adults is unknown. In this study, we show that symbiotic bacteria affect oviposition behaviour in B. oleae. We studied the effect of different fruits as hosts and different gut-bacteria as gut-symbionts on oviposition attempts and fly development in B. oleae. Untreated flies that had native gut-symbionts attempted oviposition significantly more times than axenic flies as well as flies treated with medfly-associated Pantoea or Klebsiella bacteria. Axenic flies provided with a diet containing the homogenized gut of symbiotic flies recovered the same number of oviposition attempts as their symbiotic counterparts. As for as the different hosts, green olives (unripe) and grapes were preferred while black olives (ripe) elicited the least number of oviposition attempts, with an interactive effect of host and bacterial treatments. It appears that both the host attributes and the native gut-symbionts drive oviposition preference towards green olives in B. oleae. Moreover, both bacterial treatments and hosts significantly affected the development of B. oleae larvae. Though grapes elicited as many oviposition attempts as green olives, they yielded no pupae. Taken together, our results suggest that the intimate association between B. oleae and their gut-microbes, extends beyond nutritional support to behaviour.

Photomicrobial fuel cells (pMFCs) are a new technology for transforming the light energy or bioenergy of algae into bioelectricity. However, the current methods of generating algal pMFCs have poor efficiency due to the complex electron transfer network in algal cells. In this study, pMFCs containing the model electricity-producing cyanobacterium Synechocystis sp. PCC6803 contaminated by additional bacteria exhibited a 12.6-fold greater voltage output compared to the control pMFCs with axenic Synechocystis sp. PCC6803. To explain this phenomenon, the compositions of symbiotic bacterial communities in bacterial-contaminated pMFCs were analyzed, and a pure strain WJ04 belonging to the genus Pseudomonas, which was the second most abundant (30.2%) among the total symbiotic bacteria, was obtained. The strain WJ04 was able to raise the voltage output by 8.3 fold compared with the control treatments, meaning that strain WJ04 contributed to the increased voltage output of pMFCs. Through the coculture experiment, strain WJ04 was found to influence the growth of Synechocystis, improve photosynthesis rates by regulating algal genes and further affect algal metabolite production compared with control treatments. In addition, nicotinamide, l -homocysteic acid and 4-aminobutyric acid (fold change analysis, F.C. ≥ 10) could regulate algal gene expression and enhance the coculture current density by 6.1–12.3 fold compared with the control treatments. Thus, these results provide a clear explanation for the high current production in bacterial-contaminated pMFCs, clarify the interaction mechanisms between algae and bacteria in the anode and provide accurate evidence for the role of bacteria in improving algal bioelectricity utilization.