Evidence of environmental and vertical transmission of Burkholderia symbionts in the oriental chinch bug, Cavelerius saccharivorus (Heteroptera: Blissidae)

Large-Scale Sampling Reveals the Strain-Level Diversity of Burkholderia Symbionts in Riptortus pedestris and R. linearis (Hemiptera: Alydidae)

Burkholderia (sensu lato) is a diverse group of β-Proteobacteria that exists worldwide in various environments. The SBE clade of this group was thought to be mutualistic with stinkbugs. Riptortus-Burkholderia was suggested as an ideal model system for studying insect-microbe symbiosis. To explore the strain-level diversity of Burkholderia at the individual and population levels of Riptortus stinkbugs (Hemiptera: Alydidae), and to uncover the factors affecting the Burkholderia community, large-scale sampling of two Riptortus species and deep sequencing data (16S amplicon) were used in the present study. Our results showed that: (1) the proportions of facultative symbiotic bacteria Burkholderia were very high, with an average proportion of 87.1% in the samples; (2) only six out of 1373 Burkholderia amplicon sequence variants (ASVs) did not belong to the SBE clade, accounting for only 0.03% of Burkholderia; (3) a relatively small number of Burkholderia ASVs had a large number of sequences, with 22, 54, and 107 ASVs accounting for more than 1.0%, 0.1%, and 0.01% of the total Burkholderia sequences, respectively; (4) multiple Burkholderia ASVs were present in most Riptortus individuals, but there was one dominant or two codominant ASVs, and codominance was more likely to occur when the genetic distance between the two codominant ASVs was small; and (5) the beta diversity of Burkholderia was significantly different between the two host species (PerMANOVA: both Jaccard and Bray-Curtis, p < 0.001) and among localities (PerMANOVA: both Jaccard and Bray-Curtis, p < 0.001). Two-way PerMANOVA also indicated that both the host (Bray-Curtis, p = 0.020; Jaccard, p = 0.001) and geographical location (Bray-Curtis, p = 0.041; Jaccard, p = 0.045) influence Burkholderia communities; furthermore, Mantel tests showed that the Burkholderia communities were significantly correlated with the geographical distance of sample locations (R = 0.056, p = 0.001). Together, our findings demonstrate the fine-scale diversity of Burkholderia symbionts and suggest a region- and host-dependent pattern of Burkholderia in Riptortus stinkbugs.

The burrower bug Macroscytus japonensis (Hemiptera: Cydnidae) acquires obligate symbiotic bacteria from the environment

Many plant-feeding stinkbugs belonging to the infraorder Pentatomomorpha possess a specialized symbiotic organ at the posterior end of the midgut, in which mutualistic bacterial symbionts are harbored extracellularly. In species of the superfamily Pentatomoidea, these symbionts typically are verticallytransmitted from host mothers to offspring, whereas in species of the superfamilies Coreoidea and Lygaeoidea they are acquired from the environment. In the pentatomoid family Cydnidae, vertical symbiont transmission has been reported in several species. Here, we report the first case of environmental symbiont acquisition in Cydnidae, observed in the burrower bug Macroscytus japonensis. A comprehensive survey of 72 insect samples from 23 sites across the Japanese archipelago revealed that (1) symbionts exhibit remarkably high diversity, forming six distinct phylogenetic groups within the Enterobacteriaceae of the γ-Proteobacteria, (2) most symbionts are cultivable and closely related to free-living Pantoea-allied bacteria, and (3) symbiont phylogenetic groups do not reflect the host phylogeny. Microbial inspection of eggs revealed the absence of bacteria on the egg surface. These results strongly suggest that symbionts are acquired from the environment, not vertical transmission. Rearing experiments confirmed environmental symbiont acquisition. When environmental symbiont sources were experimentally withheld, nymphs became aposymbiotic and died before molting to the second instar, indicating that nymphs environmentally acquire symbionts during the first-instar stage and that symbionts are essential for nymphal growth and survival. This study highlights Cydnidae as the only pentatomoid family that includes species that environmentally acquire symbionts and those that vertically transmit symbionts, providing an ideal platform for comparative studies of the ecological and environmental factors that influence the evolution of symbiont transmission modes.

Ecological drift during colonization drives within-host and between-host heterogeneity in an animal-associated symbiont

Specialized host-microbe symbioses canonically show greater diversity than expected from simple models, both at the population level and within individual hosts. To understand how this heterogeneity arises, we utilize the squash bug, Anasa tristis, and its bacterial symbionts in the genus Caballeronia. We modulate symbiont bottleneck size and inoculum composition during colonization to demonstrate the significance of ecological drift, the noisy fluctuations in community composition due to demographic stochasticity. Consistent with predictions from the neutral theory of biodiversity, we found that ecological drift alone can account for heterogeneity in symbiont community composition between hosts, even when 2 strains are nearly genetically identical. When acting on competing strains, ecological drift can maintain symbiont genetic diversity among different hosts by stochastically determining the dominant strain within each host. Finally, ecological drift mediates heterogeneity in isogenic symbiont populations even within a single host, along a consistent gradient running the anterior-posterior axis of the symbiotic organ. Our results demonstrate that symbiont population structure across scales does not necessarily require host-mediated selection, as it can emerge as a result of ecological drift acting on both isogenic and unrelated competitors. Our findings illuminate the processes that might affect symbiont transmission, coinfection, and population structure in nature, which can drive the evolution of host-microbe symbioses and microbe-microbe interactions within host-associated microbiomes.

Environmental Transmission of Symbionts in the Mangrove Crabs Aratus pisonii and Minuca rapax: Acquisition of the Bacterial Community through Larval Development to Juvenile Stage

Aratus pisonii and Minuca rapax are two brachyuran crabs living with bacterial ectosymbionts located on gill lamellae. One previous study has shown that several rod-shaped bacterial morphotypes are present and the community is dominated by Alphaproteobacteria and Bacteroidota. This study aims to identify the mode of transmission of the symbionts to the new host generations and to identify the bacterial community colonizing the gills of juveniles. We tested for the presence of bacteria using PCR with universal primers targeting the 16S rRNA encoding gene from gonads, eggs, and different larval stages either obtained in laboratory conditions or from the field. The presence of bacteria on juvenile gills was also characterized by scanning electron microscopy, and subsequently identified by metabarcoding analysis. Gonads, eggs, and larvae were negative to PCR tests, suggesting that bacteria are not present at these stages in significant densities. On the other hand, juveniles of both species display three rod-shaped bacterial morphotypes on gill lamellae, and sequencing revealed that the community is dominated by Bacteroidota and Alphaproteobacteria on A. pisonii juveniles, and by Alphaprotobacteria, Bacteroidota, and Acidimicrobia on M. rapax juveniles. Despite the fact that juveniles of both species co-occur in the same biotope, no shared bacterial phylotype was identified. However, some of the most abundant bacteria present in adults are also present in juveniles of the same species, suggesting that juvenile-associated communities resemble those of adults. Because some of these bacteria were also found in crab burrow water, we hypothesize that the bacterial community is established gradually during the life of the crab starting from the megalopa stage and involves epibiosis-competent bacteria that occur in the environment.

Anti-biofouling performance and microbial communities of an integrated fixed-film activated sludge membrane bioreactor with a fibrous carrier material: Pilot-scale demonstration

Widespread use of membrane bioreactors for high-performance wastewater treatment depends on the prevention of biofouling during membrane filtration, which can reduce operating costs. Biofouling is usually prevented using mechanical and chemical membrane treatment methods, which can be time-consuming and expensive. In this study, we developed bio-capsules as a fluidizing carrier material in an integrated fixed-film activated sludge membrane bioreactor (IFAS-MBR). The bio-capsules were prepared from moniliform polyvinylidene chloride fibrous balls enclosed in a spherical plastic basket, and could harbor protozoa and metazoa. A pilot-scale anoxic-oxic IFAS-MBR system with a total volume of 132 m3 was operated to remove organic carbon and nitrogen from municipal wastewater at a high permeate flux (0.84 m3/m2/day). The efficacy of the bio-capsules and the prokaryotic/eukaryotic community structures in the system were investigated. After operation for 1 year, the system demonstrated stable removal of organic carbon (76.0 % ± 15.5 % as total organic carbon, 93.1 ± 5.3 % as BOD, and 88.5 ± 5.2 % as CODMn) and nitrogen (71.3 % ± 9.3 %) despite fluctuations in the influent concentrations. Increases in transmembrane pressure (TMP) were retarded from its increase rates from 0.56 kPa/day to 0.149-0.224 kPa/day by the bio-capsules, and the TMP was kept constant at around 20 kPa throughout the operational period. High-throughput sequencing of 16S rRNA gene amplicons showed that the prokaryotic family Pirellulaceae was metabolically active and correlated with the TMP. According to the 18S rRNA gene sequencing, the eukaryotic metazoan Bdelloidea was more abundant in the bio-capsules than in activated sludge, which was supported by microscopic observations. These results suggest that the application of bio-capsules prevents increases in the TMP by harboring the procaryotes and eukaryotes responsible for biofouling mitigation in the IFAS-MBR system.

Stable States of a Microbial Community Are Formed by Dynamic Metabolic Networks with Members Functioning to Achieve Both Robustness and Plasticity

A more detailed understanding of the mechanisms underlying the formation of microbial communities is essential for the efficient management of microbial ecosystems. The stable states of microbial communities are commonly perceived as static and, thus, have not been extensively examined. The present study investigated stabilizing mechanisms, minority functions, and the reliability of quantitative ana-lyses, emphasizing a metabolic network perspective. A bacterial community, formed by batch transferred cultures supplied with phenol as the sole carbon and energy source and paddy soil as the inoculum, was analyzed using a principal coordinate ana-lysis (PCoA), mathematical models, and quantitative parameters defined as growth activity, community-changing activity, community-forming activity, vulnerable force, and resilience force depending on changes in the abundance of operational taxonomic units (OTUs) using 16S rRNA gene amplicon sequences. PCoA showed succession states until the 3rd transferred cultures and stable states from the 5th to 10th transferred cultures. Quantitative parameters indicated that the bacterial community was dynamic irrespective of the succession and stable states. Three activities fluctuated under stable states. Vulnerable and resilience forces were detected under the succession and stable states, respectively. Mathematical models indicated the construction of metabolic networks, suggesting the stabilizing mechanism of the community structure. Thirteen OTUs coexisted during stable states, and were recognized as core OTUs consisting of majorities, middle-class, and minorities. The abundance of the middle-class changed, whereas that of the others did not, which indicated that core OTUs maintained metabolic networks. Some extremely low abundance OTUs were consistently exchanged, suggesting a role for scavengers. These results indicate that stable states were formed by dynamic metabolic networks with members functioning to achieve robustness and plasticity.

Protective effects of yeast extract against alcohol-induced liver injury in rats

Oxidative stress, inflammatory response, and gut-liver axis dysbiosis have been suggested as the primarily involved in the pathogenesis of alcoholic liver injury. Previous research established that yeast extract (YE) has antioxidant, immune-boosting or microbiota-regulating properties. However, there is currently lack of information regarding the efficacy of YE on alcoholic liver injury. This study seeks to obtain data that will help to address this research gap using a Wistar male rat experimental model. Histologic and biochemical analysis results showed that the groups treated with both low-dose yeast extract (YEL) and high-dose yeast extract (YEH) had lower degrees of alcohol-induced liver injury. The abundance of Peptococcus and Ruminococcus reduced in the low-dose yeast extract (YEL) group, while that of Peptococcus, Romboutsia, Parasutterella, and Faecalibaculum reduced in the high-dose (YEH) group. Furthermore, Spearman analysis showed that the gut microbes were significantly associated with several liver-related indicators. For the analysis of differential metabolites and enriched pathways in the YEL group, the abundance of lysophosphatidylcholine (16:0/0:0) significantly increased, and then the levels of histamine, adenosine and 5' -adenine nucleotide were remarkedly elevated in the YEH group. These findings suggest that both high and low doses of YE can have different protective effects on liver injury in alcoholic liver disease (ALD) rats, in addition to improving gut microbiota disorder. Besides, high-dose YE has been found to be more effective than low-dose YE in metabolic regulation, as well as in dealing with oxidative stress and inflammatory responses.

Role of gut symbionts of insect pests: A novel target for insect-pest control

Insects possess beneficial and nuisance values in the context of the agricultural sector and human life around them. An ensemble of gut symbionts assists insects to adapt to diverse and extreme environments and to occupy every available niche on earth. Microbial symbiosis helps host insects by supplementing necessary diet elements, providing protection from predators and parasitoids through camouflage, modulation of signaling pathway to attain homeostasis and to trigger immunity against pathogens, hijacking plant pathways to circumvent plant defence, acquiring the capability to degrade chemical pesticides, and degradation of harmful pesticides. Therefore, a microbial protection strategy can lead to overpopulation of insect pests, which can drastically reduce crop yield. Some studies have demonstrated increased insect mortality via the destruction of insect gut symbionts; through the use of antibiotics. The review summarizes various roles played by the gut microbiota of insect pests and some studies that have been conducted on pest control by targeting the symbionts. Manipulation or exploitation of the gut symbionts alters the growth and population of the host insects and is consequently a potential target for the development of better pest control strategies. Methods such as modulation of gut symbionts via CRISPR/Cas9, RNAi and the combining of IIT and SIT to increase the insect mortality are further discussed. In the ongoing insect pest management scenario, gut symbionts are proving to be the reliable, eco-friendly and novel approach in the integrated pest management.

Obligate Gut Symbiotic Association with Caballeronia in the Mulberry Seed Bug Paradieuches dissimilis (Lygaeoidea: Rhyparochromidae)

Many insects possess symbiotic bacteria in their bodies, and microbial symbionts play pivotal metabolic roles for their hosts. Members of the heteropteran superfamilies Coreoidea and Lygaeoidea stinkbugs harbor symbionts of the genus Caballeronia in their intestinal tracts. Compared with symbiotic associations in Coreoidea, those in Lygaeoidea insects are still less understood. Here, we investigated a symbiotic relationship involving the mulberry seed bug Paradieuches dissimilis (Lygaeoidea: Rhyparochromidae) using histological observations, cultivation of the symbiont, 16S rRNA gene amplicon sequencing, and infection testing of cultured symbionts. Histological observations and cultivation revealed that P. dissimilis harbors Caballeronia symbionts in the crypts of its posterior midgut. 16S rRNA gene amplicon sequencing of field-collected P. dissimilis confirmed that the genus Caballeronia is dominant in the midgut of natural populations of P. dissimilis. In addition, PCR diagnostics showed that the eggs were free of symbiotic bacteria, and hatchlings horizontally acquired the symbionts from ambient soil. Infection and rearing experiments revealed that symbiont-free aposymbiotic individuals had abnormal body color, small body size, and, strikingly, a low survival rate, wherein no individuals reached adulthood, indicating an obligate cooperative mutualism between the mulberry seed bug and Caballeronia symbionts.

Complexities of Inferring Symbiont Function: Paraburkholderia Symbiont Dynamics in Social Amoeba Populations and Their Impacts on the Amoeba Microbiota

The relationship between the social amoeba Dictyostelium discoideum and its endosymbiotic bacteria Paraburkholderia provides a model system for studying the development of symbiotic relationships. Laboratory experiments have shown that any of three species of the Paraburkholderia symbiont allow D. discoideum food bacteria to persist through the amoeba life cycle and survive in amoeba spores rather than being fully digested. This phenomenon is termed "farming," as it potentially allows spores dispersed to food-poor locations to grow their own. The occurrence and impact of farming in natural populations, however, have been a challenge to measure. Here, we surveyed natural D. discoideum populations and found that only one of the three symbiont species, Paraburkholderia agricolaris, remained prevalent. We then explored the effect of Paraburkholderia on the amoeba microbiota, expecting that by facilitating bacterial food carriage, it would diversify the microbiota. Contrary to our expectations, Paraburkholderia tended to infectiously dominate the D. discoideum microbiota, in some cases decreasing diversity. Similarly, we found little evidence for Paraburkholderia facilitating the carriage of particular food bacteria. These findings highlight the complexities of inferring symbiont function in nature and suggest the possibility that Paraburkholderia could be playing multiple roles for its host. IMPORTANCE The functions of symbionts in natural populations can be difficult to completely discern. The three Paraburkholderia bacterial farming symbionts of the social amoeba Dictyostelium discoideum have been shown in the laboratory environment to allow the amoebas to carry, rather than fully digest, food bacteria. This potentially provides a fitness benefit to the amoebas upon dispersal to food-poor environments, as they could grow their food. We expected that meaningful food carriage would manifest as a more diverse microbiota. Surprisingly, we found that Paraburkholderia tended to infectiously dominate the D. discoideum microbiota rather than diversifying it. We determined that only one of the three Paraburkholderia symbionts has increased in prevalence in natural populations in the past 20 years, suggesting that this symbiont may be beneficial, however. These findings suggest that Paraburkholderia may have an alternative function for its host, which drives its prevalence in natural populations.

Low nitrous oxide concentration and spatial microbial community transition across an urban river affected by treated sewage

Urban rivers receive used water derived from anthropogenic activities and are a crucial source of the potent greenhouse gas nitrous oxide (N₂O). However, considerable uncertainties still exist regarding the variation and mechanisms of N₂O production in response to the discharge of treated sewage from municipal wastewater treatment plants (WWTPs). This study investigated N₂O concentrations and microbial processes responsible for nitrogen conversion upstream and downstream of WWTPs along the Tama River flowing through Tokyo, Japan. We evaluated the effect of treated sewage on dissolved N₂O concentrations and inherent N₂O consumption activities in the river sediments. In summer and winter, the mean dissolved N₂O concentrations were 0.67 µg-N L^-1 and 0.82 µg-N L^-1, respectively. Although the dissolved N₂O was supersaturated (mean 288.7% in summer, mean 240.7% in winter) in the river, the N₂O emission factors (EF_5r, 0.013%-0.025%) were significantly lower than those in other urban rivers and the Intergovernmental Panel on Climate Change default value (0.25%). The nitrate (NO₃^-) concentration in the Tama River increased downstream of the WWTPs discharge sites, and it was the main nitrogen constituent. An increasing trend of NO₃^- concentration was observed from upstream to downstream, along with an increase in the N₂O consumption potential of the river sediment. A multiple regression model showed that NO₃^- is the crucial factor influencing N₂O saturation. The diversity in the upstream microbial communities was greater than that in the downstream ones, indicating the involvement of treated sewage discharge in shaping the microbial communities. Functional gene quantification for N₂O production and consumption suggested that nirK-type denitrifiers likely contributed to N₂O production. Structural equation models (SEMs) revealed that treated sewage discharged from WWTPs increased the NO₃^- loading from upstream to downstream in the river, inducing changes in the microbial communities and enhancing the N₂O consumption activities. Collectively, aerobic conditions limited denitrification and in turn facilitated nitrification, leading to low N₂O emissions even despite high NO₃^- loadings in the Tama River. Our findings unravel an overestimation of the N₂O emission potential in an urban oxygen-rich river affected by treated sewage discharge.

Prevalence of an Insect-Associated Genomic Region in Environmentally Acquired Burkholderiaceae Symbionts

Microbial symbionts are critical for the development and survival of many eukaryotes. Recent research suggests that the genes enabling these relationships can be localized in horizontally transferred regions of microbial genomes termed "symbiotic islands." Recently, a putative symbiotic island was found that may facilitate symbioses between true bugs and numerous Burkholderia species, based on analysis of five Burkholderia symbionts. We expanded on this work by exploring the putative island's prevalence, origin, and association with colonization across the bacterial family Burkholderiaceae. We performed a broad comparative analysis of 229 Burkholderiaceae genomes, including 8 new genomes of insect- or soil-associated Burkholderia sequenced for this study. We detected the region in 23% of the genomes; these were located solely within two Burkholderia clades. Our analyses suggested that the contiguous region arose at the common ancestor of plant- and insect-associated Burkholderia clades, but the genes themselves are ancestral. Although the region was initially discovered on plasmids and we did detect two likely instances of horizontal transfer within Burkholderia, we found that the region is almost always localized to a chromosome and does not possess any of the mobility elements that typify genomic islands. Finally, to attempt to deduce the region's function, we combined our data with information on several strains' abilities to colonize the insect's symbiotic organ. Although the region was associated with improved colonization of the host, this relationship was confounded with, and likely driven by, Burkholderia clade membership. These findings advance our understanding of the genomic underpinnings of a widespread insect-microbe symbiosis. IMPORTANCE Many plants and animals form intricate associations with bacteria. These pairings can be mediated by genomic islands, contiguous regions containing numerous genes with cohesive functionality. Pathogen-associated islands are well described, but recent evidence suggests that mutualistic islands, which benefit both host and symbiont, may also be common. Recently, a putative symbiosis island was found in Burkholderia symbionts of insects. We determined that this genomic region is located in only two clades of Burkholderia (the plant- and insect-associated species) and that although it has undergone horizontal transfer, it is most likely a symbiosis-associated region rather than a true island. This region is associated with improved host colonization, although this is may be due to specific Burkholderia clades' abilities to colonize rather than presence of the region. By studying the genomic basis of the insect-Burkholderia symbiosis, we can better understand how mutualisms evolve in animals.

Development of common leaf-footed bug pests depends on the presence and identity of their environmentally-acquired symbionts

Many beneficial symbioses between bacteria and their terrestrial arthropod hosts are vertically transmitted from mother to offspring, ensuring the progeny acquire necessary partners. Unusually, in several families of coreoid and lygeoid bugs (Hemiptera), nymphs must instead ingest the beneficial symbiont, Burkholderia (sensu lato), from the environment early in development. We studied the effects of Burkholderia on development of two species of leaf-footed bug (Coreidae) in the genus Leptoglossus, L. zonatus and L. phyllopus. We found no evidence for vertical transmission of the symbiont, but found stark differences in performance between symbiotic and aposymbiotic individuals. Symbiotic nymphs grew more rapidly, were approximately four times more likely to survive to adulthood than aposymbiotic bugs, and were two times larger. These findings suggest that Burkholderia is an obligate symbiont for Leptoglossus species. We also tested for variation in fitness effects conferred by four symbiont isolates representing different species within Burkholderia's insect-associated Stinkbug Beneficial and Environmental (SBE) clade. While three isolates conferred similar benefits to hosts, nymphs associated with the fourth isolate grew more slowly and weighed significantly less as adults. The effects of the four isolates were similar for both Leptoglossus species. This work indicates that both Burkholderia acquisition and isolate identity play critical roles in the growth and development of Leptoglossus. Importance Leptoglossus zonatus and L. phyllopus are important polyphagous pests and both species have been well-studied, but generally without regard to their dependance on a bacterial symbiont. Our results indicate that the central role of Burkholderia in the biology of these insects, as well as in other leaf-footed bugs, should be considered in future studies of coreid life history, ecology and pest management. Our work suggests acquisition of Burkholderia is critical for the growth and development of Leptoglossus species. Further, we found that there was variation in performance outcomes according to symbiont identity, even among members of the Stinkbug Beneficial and Environmental clade. This suggests that although environmental acquisition of a symbiont can provide extraordinary flexibility in partner associations, it also carries a risk if the partner is sub-optimal.

Exploring bycatch diversity of organisms in whole genome sequencing of Erebidae moths (Lepidoptera)

Models estimate that up to 80% of all butterfly and moth species host vertically transmitted endosymbiotic microorganisms, which can affect the host fitness, metabolism, reproduction, population dynamics, and genetic diversity, among others. The supporting empirical data are however currently highly biased towards the generally more colourful butterflies, and include less information about moths. Additionally, studies of symbiotic partners of Lepidoptera predominantly focus on the common bacterium Wolbachia pipientis, while infections by other inherited microbial partners have more rarely been investigated. Here, we mine the whole genome sequence data of 47 species of Erebidae moths, with the aims to both inform on the diversity of symbionts potentially associated with this Lepidoptera group, and discuss the potential of metagenomic approaches to inform on host associated microbiome diversity. Based on the result of Kraken2 and MetaPhlAn2 analyses, we found clear evidence of the presence of Wolbachia in four species. Our result also suggests the presence of three other bacterial symbionts (Burkholderia spp., Sodalis spp. and Arsenophonus spp.) in three other moth species. Additionally, we recovered genomic material from bracovirus in about half of our samples. The detection of the latter, usually found in mutualistic association to braconid parasitoid wasps, may inform on host-parasite interactions that take place in the natural habitat of the Erebidae moths, suggesting either contamination with material from species of the host community network, or horizontal transfer of members of the microbiome between interacting species.

Worker-dependent gut symbiosis in an ant

The hallmark of eusocial insects, honeybees, ants, and termites, is division of labor between reproductive and non-reproductive worker castes. In addition, environmental adaption and ecological dominance are also underpinned by symbiotic associations with beneficial microorganisms. Microbial symbionts are generally considered to be maintained in an insect colony in two alternative ways: shared among all colony members or inherited only by a specific caste. Especially in ants, the reproductive caste plays a crucial role in transmission of the symbionts shared among colony members over generations. Here, we report an exceptional case, the worker-dependent microbiota in an ant, Diacamma cf. indicum from Japan. By collecting almost all the individuals from 22 colonies in the field, we revealed that microbiota of workers is characterized by a single dominant bacterium localized at the hindgut. The bacterium belonging to an unclassified member within the phylum Firmicutes, which is scarce or mostly absent in the reproductive castes. Furthermore, we show that the gut symbiont is acquired at the adult stage. Collectively, our findings strongly suggest that the specific symbiont is maintained by only workers, demonstrating a novel pattern of ant-associated bacterial symbiosis, and thus further our understanding of host-microbe interactions in the light of sociobiology.

The Importance of Environmentally Acquired Bacterial Symbionts for the Squash Bug (Anasa tristis), a Significant Agricultural Pest

Most insects maintain associations with microbes that shape their ecology and evolution. Such symbioses have important applied implications when the associated insects are pests or vectors of disease. The squash bug, Anasa tristis (Coreoidea: Coreidae), is a significant pest of human agriculture in its own right and also causes damage to crops due to its capacity to transmit a bacterial plant pathogen. Here, we demonstrate that complete understanding of these insects requires consideration of their association with bacterial symbionts in the family Burkholderiaceae. Isolation and sequencing of bacteria housed in the insects’ midgut crypts indicates that these bacteria are consistent and dominant members of the crypt-associated bacterial communities. These symbionts are closely related to Caballeronia spp. associated with other true bugs in the superfamilies Lygaeoidea and Coreoidea. Fitness assays with representative Burkholderiaceae strains indicate that the association can significantly increase survival and decrease development time, though strains do vary in the benefits that they confer to their hosts, with Caballeronia spp. providing the greatest benefit. Experiments designed to assess transmission mode indicate that, unlike many other beneficial insect symbionts, the bacteria are not acquired from parents before or after hatching but are instead acquired from the environment after molting to a later developmental stage. The bacteria do, however, have the capacity to escape adults to be transmitted to later generations, leaving the possibility for a combination of indirect vertical and horizontal transmission.

Transmission of Bacterial Symbionts With and Without Genome Erosion Between a Beetle Host and the Plant Environment

Many phytophagous insects harbor symbiotic bacteria that can be transmitted vertically from parents to offspring, or acquired horizontally from unrelated hosts or the environment. In the latter case, plants are a potential route for symbiont transfer and can thus foster a tripartite interaction between microbe, insect, and plant. Here, we focus on two bacterial symbionts of the darkling beetle Lagria villosa that belong to the genus Burkholderia; the culturable strain B. gladioli Lv-StA and the reduced-genome strain Burkholderia Lv-StB. The strains can be transmitted vertically and confer protection to the beetle’s eggs, but Lv-StA can also proliferate in plants, and both symbiont strains have presumably evolved from plant pathogens. Notably, little is known about the role of the environment for the transmission dynamics and the maintenance of the symbionts. Through manipulative assays, we demonstrate the transfer of the symbionts from the beetle to wheat, rice and soybean plants, as well as leaf litter. In addition, we confirm that aposymbiotic larvae can pick up Lv-StA from dry leaves and the symbiont can successfully establish in the beetle’s symbiotic organs. Also, we show that the presence of plants and soil in the environment improves symbiont maintenance. These results indicate that the symbionts of L. villosa beetles are still capable of interacting with plants despite signatures of genome erosion and suggest that a mixed-mode of bacterial transmission is likely key for the persistence of the symbiosis.

Experimental infection of bed bugs (Cimex lectularius L.) with Burkholderia multivorans

The bacterium Burkholderia multivorans is an opportunistic nosocomial pathogen of humans. A previous study reported molecular detection of this bacterium in several specimens of the common bed bug (Cimex lectularius L.) collected from an elderly care facility in the U.S.A., raising questions about the possibility of vector-borne transmission. However, the ability of B. multivorans to colonize bed bugs and the ability of bed bugs to transmit the bacteria both remained untested. To resolve this knowledge gap, here we performed a set of experiments to examine the persistence and shedding of B. multivorans following ingestion by bed bugs in a blood meal. We isolated viable B. multivorans from the bodies of bed bugs for up to 13 days post-ingestion, but bacterial load substantially diminished over time. By 16 days post-ingestion, the bacteria could not be isolated. Further, B. multivorans was not shed in the saliva of infected bugs during feeding nor was it transmitted vertically from infected insects to their progeny. Based on these results, significant biological or mechanical transmission of B. multivorans to humans by bed bugs appears unlikely. Nonetheless, some viable bacteria were passively shed into the environment through defecation, a process which could potentially contribute to transmission through indirect contamination under rare circumstances.

Combination of 15N Tracer and Microbial Analyses Discloses N2O Sink Potential of the Anammox Community

Although nitrogen removal by partial nitritation and anammox is more cost-effective than conventional nitrification and denitrification, one downside is the production and accumulation of nitrous oxide (N₂O). The potential exploitation of N₂O-reducing bacteria, which are resident members of anammox microbial communities, for N₂O mitigation would require more knowledge of their ecophysiology. This study investigated the phylogeny of resident N₂O-reducing bacteria in an anammox microbial community and quantified individually the processes of N₂O production and N₂O consumption. An up-flow column-bed anammox reactor, fed with NH₄⁺ and NO₂^- and devoid of oxygen, emitted N₂O at an average conversion ratio (produced N₂O: influent nitrogen) of 0.284%. Transcriptionally active and highly abundant nosZ genes in the reactor biomass belonged to the Burkholderiaceae (clade I type) and Chloroflexus genera (clade II type). Meanwhile, less abundant but actively transcribing nosZ strains were detected in the genera Rhodoferax, Azospirillum, Lautropia, and Bdellovibrio and likely act as an N₂O sink. A novel ¹⁵N tracer method was adapted to individually quantify N₂O production and N₂O consumption rates. The estimated true N₂O production rate and true N₂O consumption rate were 3.98 ± 0.15 and 3.03 ± 0.18 mg_N·g_VSS^-1·day^-1, respectively. The N₂O consumption rate could be increased by 51% (4.57 ± 0.51 mg_N·g_VSS^-1·day^-1) with elevated N₂O concentrations but kept comparable irrespective of the presence or absence of NO₂^-. Collectively, the approach allowed the quantification of N₂O-reducing activity and the identification of transcriptionally active N₂O reducers that may constitute as an N₂O sink in anammox-based processes.

We and herbivores eat endophytes

Health depends on the diet and a vegetal diet promotes health by providing fibres, vitamins and diverse metabolites. Remarkably, plants may also provide microbes. Fungi and bacteria that reside inside plant tissues (endophytes) seem better protected to survive digestion; thus, we investigated the reported evidence on the endophytic origin of some members of the gut microbiota in animals such as panda, koala, rabbits and tortoises and several herbivore insects. Data examined here showed that some members of the herbivore gut microbiota are common plant microbes, which derived to become stable microbiota in some cases. Endophytes may contribute to plant fibre or antimetabolite degradation and synthesis of metabolites with the plethora of enzymatic activities that they display; some may have practical applications, for example, Lactobacillus plantarum found in the intestinal tract, plants and in fermented food is used as a probiotic that may defend animals against bacterial and viral infections as other endophytic-enteric bacteria do. Clostridium that is an endophyte and a gut bacterium has remarkable capabilities to degrade cellulose by having cellulosomes that may be considered the most efficient nanomachines. Cellulose degradation is a challenge in animal digestion and for biofuel production. Other endophytic-enteric bacteria may have cellulases, pectinases, xylanases, tannases, proteases, nitrogenases and other enzymatic capabilities that may be attractive for biotechnological developments, indeed many endophytes are used to promote plant growth. Here, a cycle of endophytic-enteric-soil-endophytic microbes is proposed which has relevance for health and comprises the fate of animal faeces as natural microbial inoculants for plants that constitute bacterial sources for animal guts.

Environmental Acquisition of Gut Symbiotic Bacteria in the Saw-Toothed Stinkbug, Megymenum gracilicorne (Hemiptera: Pentatomoidea: Dinidoridae)

Many plant-sucking stinkbugs possess a specialized symbiotic organ with numerous crypts in a posterior region of the midgut. In stinkbugs of the superfamily Pentatomoidea, specific γ-proteobacteria are hosted in the crypt cavities, which are vertically transmitted through host generations and essential for normal growth and survival of the host insects. Here we report the discovery of an exceptional gut symbiotic association in the saw-toothed stinkbug, Megymenum gracilicorne (Hemiptera: Pentatomoidea: Dinidoridae), in which specific γ-proteobacterial symbionts are not transmitted vertically but acquired environmentally. Histological inspection identified a very thin and long midgut symbiotic organ with two rows of tiny crypts whose cavities harbor rod-shaped bacterial cells. Molecular phylogenetic analyses of bacterial 16S rRNA gene sequences from the symbiotic organs of field-collected insects revealed that (i) M. gracilicorne is stably associated with Pantoea-allied γ-proteobacteria within the midgut crypts, (ii) the symbiotic bacteria exhibit a considerable level of diversity across host individuals and populations, (iii) the major symbiotic bacteria represent an environmental bacterial lineage that was reported to be capable of symbiosis with the stinkbug Plautia stali, and (iv) the minor symbiotic bacteria also represent several bacterial lineages that were reported as cultivable symbionts of P. stali and other stinkbugs. The symbiotic bacteria were shown to be generally cultivable. Microbial inspection of ovipositing adult females and their eggs and nymphs uncovered the absence of stable vertical transmission of the symbiotic bacteria. Rearing experiments showed that symbiont-supplemented newborn nymphs exhibit improved survival, suggesting the beneficial nature of the symbiotic association.

Variation of gut microbiota caused by an imbalance diet is detrimental to bugs' survival

Diet is an important factor in shaping and influencing both an insect's phenotype and gut bacterial community, which commonly establishes diversely symbiotic interactions with the host. Efforts to leverage the connection between diet, insects, and gut microbiome primarily focus on how diet alters insect's phenotype or gut microbial composition and relatively few studies have illuminated the link between the diet-induced insect phenotypic difference and variation of gut microbiota. Mirids bugs, Adelphocoris suturalis, are plant sap-feeding omnivores that sometimes complementarily prey on other insects, like aphids (the dietary regime is referred to hereafter as balanced diet). In this study, we found that an imbalanced diet (exclusive ingestion of aphids) induced significantly higher mortality in A. suturalis (86.66%). Further gut microbial community analysis showed that the dietary difference significantly changed both the abundance and composition of the bug's gut microbiome. Most notably, an abundance of entomopathogenic Serratia bacteria in the A. suturalis gut was positively correlated with the proportion of aphids in A. suturalis diet, and Serratia marcescens was found to transfer into the hemocoels of carnivorous bugs. Injection of S. marcescens to the hemocoels further confirmed its detrimental effect to the bugs. Collectively, our study suggests that the diet-altered variation of gut microbiota may be detrimental to host insect, advancing the knowledge of omnivorous insects' strategy in forage allocation of different foods.

Insecticide resistance governed by gut symbiosis in a rice pest, Cletus punctiger, under laboratory conditions

Resistance to toxins in insects is generally thought of as their own genetic trait, but recent studies have revealed that gut microorganisms could mediate resistance by detoxifying phytotoxins and man-made insecticides. By laboratory experiments, we here discovered a striking example of gut symbiont-mediated insecticide resistance in a serious rice pest, Cletus punctiger. The rice bug horizontally acquired fenitrothion-degrading Burkholderia through oral infection and housed it in midgut crypts. Fenitrothion-degradation test revealed that the gut-colonizing Burkholderia retains a high degrading activity of the organophosphate compound in the insect gut. This gut symbiosis remarkably increased resistance against fenitrothion treatment in the host rice bug. Considering that many stinkbug pests are associated with soil-derived Burkholderia, our finding strongly supports that a number of stinkbug species could gain resistance against insecticide simply by acquiring insecticide-degrading gut bacteria.

The Gut Microbiota of the Insect Infraorder Pentatomomorpha (Hemiptera: Heteroptera) for the Light of Ecology and Evolution

The stinkbugs of the infraorder Pentatomomorpha are a group of important plant sap-feeding insects, which host diverse microorganisms. Some are located in their complex morphological midgut compartments, while some within the specialized bacteriomes of insect hosts. This perpetuation of symbioses through host generations is reinforced via the diverse routes of vertical transmission or environmental acquisition of the symbionts. These symbiotic partners, reside either through the extracellular associations in midgut or intracellular associations in specialized cells, not only have contributed nutritional benefits to the insect hosts but also shaped their ecological and evolutionary basis. The stinkbugs and gut microbe symbioses present a valuable model that provides insights into symbiotic interactions between agricultural insects and microorganisms and may become potential agents for insect pest management.

Direct comparison of bacterial communities in soils contaminated with different levels of radioactive cesium from the first Fukushima nuclear power plant accident

The Great East Japan Earthquake caused a serious accident at the first Fukushima nuclear power plant (NPP), which in turn released a large amount of radionuclides. Little attention has been paid to in-situ soil microorganisms exposed to radioactive contamination by the actual NPP accident. We herein investigated bacterial communities in the radioactive cesium (Cs)-contaminated and non-contaminated soils by high-throughput sequencing. The uppermost and ectorhizosphere soil samples were collected from the base of mugwort grown in the same soil type with the same soil-use history in order to compare the bacterial communities at geographically separated areas. The concentrations of radioactive Cs in the soils ranged from 10 to 563,000 Bq ¹³⁷Cs/kg dry soil, with the highest concentration being detected at 1 km from the NPP. Alpha-diversity indices, i.e., Chao1, Shannon and Simpson reciprocal, of the sequence data showed the lower bacterial diversity in the most highly Cs-contaminated soil. Principal coordinate analysis with principle components 1 and 3 based on unweighted UniFrac distances indicated the significant difference in bacterial communities of the most contaminated area from those of the other areas. Operational taxonomic unit-based assay revealed higher abundance of the radio-resistant Geodermatophilus bullaregiensis relative in the most contaminated soil. Thus, it was strongly suggested that the radioactive accident facilitated the growth and/or survival of radio-resistant bacteria in the Cs-contaminated soils. The results of this study show that information on the soil type, vegetation and soil-use history enhances the direct comparison of geographically distant soil bacterial communities exposed to different levels of radioactive contamination.

Continent-Scale Sampling Reveals Fine-Scale Turnover in a Beneficial Bug Symbiont

Many members of animal-associated microbial communities, including the gut flora, are acquired from their host’s environment. While many of these communities are species rich, some true bugs (Hemiptera) in the superfamilies Lygaeoidea and Coreidae allow only ingested Burkholderia to colonize and reproduce in a large portion of the midgut. We studied the spatial structuring of Burkholderia associated with a widespread omnivorous bug genus, Jalysus (Berytidae). We sampled Wickham’s stilt bug, Jalysus wickhami, across the United States and performed limited sampling of its sister species, the spined stilt bug Jalysus spinosus. We asked: (1) What Burkholderia strains are hosted by Jalysus at different locations? (2) Does host insect species, host plant species, or location influence the strain these insects acquire? (3) How does Burkholderia affect the development and reproductive fitness of J. wickhami? We found: (1) Sixty-one Burkholderia strains were present across a sample of 352 individuals, but one strain dominated, accounting for almost half of all symbiont reads. Most strains were closely related to other hemipteran Burkholderia symbionts. (2) Many individuals hosted more than one strain of Burkholderia. (3) J. wickhami and J. spinosus did not differ in the strains they hosted. (4) Insects that fed on different plant species tended to host different Burkholderia, but this accounted for only 4% of the variation in strains hosted. In contrast, the location at which an insect was collected explained 27% of the variation in symbiont strains. (5) Burkholderia confers important fitness benefits to J. wickhami. In laboratory experiments, aposymbiotic (Burkholderia-free) insects developed more slowly and laid fewer eggs than symbiotic (Burkholderia-colonized) insects. (6) In the lab, nymphs sometimes acquired Burkholderia via indirect exposure to adults, indicating that horizontal symbiont transmission can occur via adult insect-mediated enrichment of Burkholderia in the local environment – a phenomenon not previously reported in bug-Burkholderia relationships. Taken together, the results suggest that for these bugs, critical nutritional requirements are outsourced to a highly diverse and spatially structured collection of Burkholderia strains acquired from the environment and, occasionally, from conspecific adults.

Genomic Comparison of Insect Gut Symbionts from Divergent Burkholderia Subclades

Stink bugs of the superfamilies Coreoidea and Lygaeoidea establish gut symbioses with environmentally acquired bacteria of the genus Burkholderia sensu lato. In the genus Burkholderia, the stink bug-associated strains form a monophyletic clade, named stink bug-associated beneficial and environmental (SBE) clade (or Caballeronia). Recently, we revealed that members of the family Largidae of the superfamily Pyrrhocoroidea are associated with Burkholderia but not specifically with the SBE Burkholderia; largid bugs harbor symbionts that belong to a clade of plant-associated group of Burkholderia, called plant-associated beneficial and environmental (PBE) clade (or Paraburkholderia). To understand the genomic features of Burkholderia symbionts of stink bugs, we isolated two symbiotic Burkholderia strains from a bordered plant bug Physopellta gutta (Pyrrhocoroidea: Largidae) and determined their complete genomes. The genome sizes of the insect-associated PBE (iPBE) are 9.5 Mb and 11.2 Mb, both of which are larger than the genomes of the SBE Burkholderia symbionts. A whole-genome comparison between two iPBE symbionts and three SBE symbionts highlighted that all previously reported symbiosis factors are shared and that 282 genes are specifically conserved in the five stink bug symbionts, over one-third of which have unknown function. Among the symbiont-specific genes, about 40 genes formed a cluster in all five symbionts; this suggests a "symbiotic island" in the genome of stink bug-associated Burkholderia.

Unexpected diversity of acetate degraders in anaerobic membrane bioreactor treating organic solid waste revealed by high-sensitivity stable isotope probing

In anaerobic membrane bioreactor (AnMBR) treating organic solid waste, acetate is one of the most important precursors to CH₄. However, the identity and diversity of anaerobic acetate degraders are largely unknown, possibly due to their slow growth rates and low abundances. Here, we identified acetate-degrading microorganisms in the AnMBR sludges by high-sensitivity stable isotope probing. Degradation of the amended ¹³C-acetate coincided with production of ¹³CH₄ and ¹³CO₂ during the sludge incubation. High-throughput sequencing of RNA density fractions indicated that the aceticlastic and hydrogenotrophic methanogens, i.e., Methanosaeta sp. (acetate dissimilator) and Methanolinea sp. (acetate assimilator), incorporated ¹³C-acetate significantly. Remarkably, 22 bacterial species incorporating ¹³C-acetate were identified, whereas their majority was distantly related to the cultured representatives. Only two of them were the class Deltaproteobacteria-affiliated lineages with syntrophic volatile fatty acid oxidation activities. Phylogenetic tree analysis and population dynamics tracing revealed that novel species of the hydrolyzing and/or fermenting taxa, such as the phyla Bacteroidetes, Chloroflexi and Lentisphaerae, exhibited low relative abundances comparable to that of Methanolinea sp. (0.00011%) during the AnMBR operation, suggesting that these bacteria were involved in anaerobic acetate assimilation. Meanwhile, novel species of the phyla Firmicutes, Synergistetes and Caldiserica, the candidate phyla Aminicenantes and Atribacteria and the candidate division GOUTA4-related clade, as well as the known Deltaproteobacteria members, existed at relatively high abundances (0.00031%-0.31121%) in the reactor, suggesting that these bacterial species participated in anaerobic dissimilation of acetate, e.g., syntrophic acetate oxidation. The results of this study demonstrated the unexpected diversity and ecophysiological features of the anaerobic acetate degraders in the AnMBR treating organic solid waste.

Relevance of microbial symbiosis to insect behavior

Microbial symbiosis is widespread among insects. This article reviews our understanding of insect behaviors relevant to commensalistic and mutualistic microbial symbiosis, which has received relatively less attention compared to insect behaviors in parasitic symbiosis. First, we review our knowledge of symbiont transmission behaviors by which the host insects maintain associations with beneficial microorganisms over generations. Some insects that extracellularly harbor mutualistic symbionts exhibit particularly sophisticated behaviors for vertical symbiont transmission. Next, we highlight notable studies on behavioral changes induced by symbiont infection. In the last decade, a number of studies have demonstrated or suggested that mutualistic or commensalistic symbiont infections affect their host behaviors. Finally, future directions regarding these research topics are discussed.

Versatile and Dynamic Symbioses Between Insects and Burkholderia Bacteria

Symbiotic associations with microorganisms represent major sources of ecological and evolutionary innovations in insects. Multiple insect taxa engage in symbioses with bacteria of the genus Burkholderia, a diverse group that is widespread across different environments and whose members can be mutualistic or pathogenic to plants, fungi, and animals. Burkholderia symbionts provide nutritional benefits and resistance against insecticides to stinkbugs, defend Lagria beetle eggs against pathogenic fungi, and may be involved in nitrogen metabolism in ants. In contrast to many other insect symbioses, the known associations with Burkholderia are characterized by environmental symbiont acquisition or mixed-mode transmission, resulting in interesting ecological and evolutionary dynamics of symbiont strain composition. Insect-Burkholderia symbioses present valuable model systems from which to derive insights into general principles governing symbiotic interactions because they are often experimentally and genetically tractable and span a large fraction of the diversity of functions, localizations, and transmission routes represented in insect symbioses.

Host-symbiont specificity determined by microbe-microbe competition in an insect gut

Despite the omnipresence of specific host-symbiont associations with acquisition of the microbial symbiont from the environment, little is known about how the specificity of the interaction evolved and is maintained. The bean bug Riptortus pedestris acquires a specific bacterial symbiont of the genus Burkholderia from environmental soil and harbors it in midgut crypts. The genus Burkholderia consists of over 100 species, showing ecologically diverse lifestyles, and including serious human pathogens, plant pathogens, and nodule-forming plant mutualists, as well as insect mutualists. Through infection tests of 34 Burkholderia species and 18 taxonomically diverse bacterial species, we demonstrate here that nonsymbiotic Burkholderia and even its outgroup Pandoraea could stably colonize the gut symbiotic organ and provide beneficial effects to the bean bug when inoculated on aposymbiotic hosts. However, coinoculation revealed that the native symbiont always outcompeted the nonnative bacteria inside the gut symbiotic organ, explaining the predominance of the native Burkholderia symbiont in natural bean bug populations. Hence, the abilities for colonization and cooperation, usually thought of as specific traits of mutualists, are not unique to the native Burkholderia symbiont but, to the contrary, competitiveness inside the gut is a derived trait of the native symbiont lineage only and was thus critical in the evolution of the insect gut symbiont.

Repeated evolution of bacteriocytes in lygaeoid stinkbugs

Host-microbe symbioses often evolved highly complex developmental processes and colonization mechanisms for establishment of stable associations. It has long been recognized that many insects harbour beneficial bacteria inside specific symbiotic cells (bacteriocytes) or organs (bacteriomes). However, the evolutionary origin and mechanisms underlying bacterial colonization in bacteriocyte/bacteriome formation have been poorly understood. In order to uncover the origin of such evolutionary novelties, we studied the development of symbiotic organs in five stinkbug species representing the superfamily Lygaeoidea in which diverse bacteriocyte/bacteriome systems have evolved. We tracked the symbiont movement within the eggs during the embryonic development and determined crucial stages at which symbiont infection and bacteriocyte formation occur, using whole-mount fluorescence in situ hybridization. In summary, three distinct developmental patterns were observed: two different modes of symbiont transfer from initial symbiont cluster (symbiont ball) to presumptive bacteriocytes in the embryonic abdomen, and direct incorporation of the symbiont ball without translocation of bacterial cells. Across the host taxa, only closely related species seemed to have evolved relatively conserved types of bacteriome development, suggesting repeated evolution of host symbiotic cells and organs from multiple independent origins.

Enrichment, Isolation, and Characterization of High-Affinity N2O-Reducing Bacteria in a Gas-Permeable Membrane Reactor

The recent discovery of nitrous oxide (N₂O)-reducing bacteria suggests a potential biological sink for the potent greenhouse gas N₂O. For an application toward N₂O mitigation, characterization of more isolates will be required. Here, we describe the successful enrichment and isolation of high-affinity N₂O-reducing bacteria using a N₂O-fed reactor (N₂OFR). Two N₂OFRs, where N₂O was continuously and directly supplied as the sole electron acceptor to a biofilm grown on a gas-permeable membrane, were operated with acetate or a mixture of peptone-based organic substrates as an electron donor. In parallel, a NO₃^- -fed reactor (NO₃FR), filled with a nonwoven sheet substratum, was operated using the same inoculum. We hypothesized that supplying N₂O vs NO₃^- would enhance the dominance of distinct N₂O-reducing bacteria. Clade II type nosZ bacteria became rapidly enriched over clade I type nosZ bacteria in the N₂OFRs, whereas the opposite held in the NO₃FR. High-throughput sequencing of 16S rRNA gene amplicons revealed the dominance of Rhodocyclaceae in the N₂OFRs. Strains of the Azospira and Dechloromonas genera, canonical denitrifiers harboring clade II type nosZ, were isolated with high frequency from the N₂OFRs (132 out of 152 isolates). The isolates from the N₂OFR demonstrated higher N₂O uptake rates (V_max: 4.23 × 10^-3-1.80 × 10^-2 pmol/h/cell) and lower N₂O half-saturation coefficients (K_m,N2O: 1.55-2.10 μM) than a clade I type nosZ isolate from the NO₃FR. Furthermore, the clade II type nosZ isolates had higher specific growth rates on N₂O than nitrite as an electron acceptor. Hence, continuously and exclusively supplying N₂O in an N₂OFR allows the enrichment and isolation of high-affinity N₂O-reducing strains, which may be used as N₂O sinks in bioaugmentation efforts.

Bacterial associates of Orthezia urticae, Matsucoccus pini, and Steingelia gorodetskia - scale insects of archaeoccoid families Ortheziidae, Matsucoccidae, and Steingeliidae (Hemiptera, Coccomorpha)

The biological nature, ultrastructure, distribution, and mode of transmission between generations of the microorganisms associated with three species (Orthezia urticae, Matsucoccus pini, Steingelia gorodetskia) of primitive families (archaeococcoids = Orthezioidea) of scale insects were investigated by means of microscopic and molecular methods. In all the specimens of Orthezia urticae and Matsucoccus pini examined, bacteria Wolbachia were identified. In some examined specimens of O. urticae, apart from Wolbachia, bacteria Sodalis were detected. In Steingelia gorodetskia, the bacteria of the genus Sphingomonas were found. In contrast to most plant sap-sucking hemipterans, the bacterial associates of O. urticae, M. pini, and S. gorodetskia are not harbored in specialized bacteriocytes, but are dispersed in the cells of different organs. Ultrastructural observations have shown that bacteria Wolbachia in O. urticae and M. pini, Sodalis in O. urticae, and Sphingomonas in S. gorodetskia are transovarially transmitted from mother to progeny.

Abundance and diversity of gut-symbiotic bacteria, the genus Burkholderia in overwintering Riptortus pedestris (Hemiptera: Alydidae) populations and soil in South Korea

Riptortus pedestris is a major agricultural pest on leguminous plants in South Korea and Japan. Recent studies have revealed that R. pedestris can form beneficial symbiosis with bacteria belonging to genus Burkholderia acquired from soil newly for every generation. Although their physiological interactions are relatively well-understood, infection rate and abundance of the Burkholderia in overwintering natural populations of R. pedestris remain unknown. Therefore, the objective of this study was to characterize Burkholderia infection ratio and clade composition of overwintering R. pedestris populations as well as prevalence and diversity of the genus Burkholderia in soil by conducting a two-year field survey. From the field survey, we found 29 overwintering R. pedestris adults in forested areas nearby soybean fields. Diagnostic PCR analysis revealed that overall infection rate of the symbiotic Burkholderia was 93.1% from overwintering adults. Among the Burkholderia-infected R. pedestris, 70.4% of individuals harbored unclassified Burkholderia clades whereas 22.2% and 7.4% of R. pedestris harbor stinkbug-associated beneficial and environmental (SBE) group and Burkholderia cepacia and complex (BCC), respectively. All R. pedestris were infected with a single clade of Burkholderia. In soil, 56.2% of soil samples were Burkholderia positive, and unlike R. pedestris, multiple Burkholderia clades were detected from 62.2% of those samples. Clade composition of the genus Burkholderia in the samples with the bacteria was 91.1%, 60.0%, 31.1% and 8.8% for plant-associated beneficial and environment (PBE), BCC, SBE and unclassified clade, respectively.

Stratification of Sulfur Species and Microbial Community in Launched Marine Sediment by an Improved Sulfur-Fractionation Method and 16S rRNA Gene Sequencing

With a focus on marine sediment launched by the tsunami accompanying the Great East Japan Earthquake, we examined the vertical (i.e., depths of 0–2, 2–10, and 10–20 mm) profiles of reduced inorganic sulfur species and microbial community using a newly improved sulfur-fractionation method and 16S rRNA gene sequencing. S⁰ accumulated at the largest quantities at a depth of 2–10 mm, while the reduced forms of sulfur, such as iron(II) sulfide and pyrite, were abundant below 2 mm of the sediment. Operational taxonomic units (OTUs) related to chemolithotrophically sulfur-oxidizing Sulfurimonas denitrificans and Sulfurimonas autotrophica were only predominant at 2–10 mm, suggesting the involvement of these OTUs in the oxidation of sulfide to S⁰. In addition, Desulfocapsa sulfexigens, which is capable of chemolithotrophically disproportionating S⁰, prevailed at the same depth, indicating that accumulated S⁰ was converted to sulfate and sulfide. Although no significant differences were observed in sulfate concentrations across the depths examined, specific species of chemoorganotrophic sulfate reducers, i.e., Desulfotignum toluenicum and Desulfosalsimonas propionicica, showed significantly higher abundance at a depth of 2–10 mm than at the other depths examined. Organic matter potentially generated from sulfur oxidation and disproportionation may have served as the carbon source for the growth of these sulfate reducers. The present results demonstrated that sulfur oxidizers, a sulfur disproportionator, and sulfate reducers played vital roles in sulfur cycling with S⁰ as the key inorganic sulfur species in the oxic-anoxic boundary layer of the launched marine sediment.

Burkholderia Gut Symbionts Associated with European and Japanese Populations of the Dock Bug Coreus marginatus (Coreoidea: Coreidae)

Insects of the heteropteran superfamilies Coreoidea and Lygaeoidea are consistently associated with symbionts of a specific group of the genus Burkholderia, called the “stinkbug-associated beneficial and environmental (SBE)” group. The symbiosis is maintained by the environmental transmission of symbionts. We investigated European and Japanese populations of the dock bug Coreus marginatus (Coreoidea: Coreidae). High nymphal mortality in reared aposymbiotic insects suggested an obligate host-symbiont association in this species. Molecular phylogenetic analyses based on 16S rRNA gene sequences revealed that all 173 individuals investigated were colonized by Burkholderia, which were further assigned to different subgroups of the SBE in a region-dependent pattern.

Evidence for a conserved microbiota across the different developmental stages of Plodia interpunctella

Diversity and composition of lepidopteran microbiotas are poorly investigated, especially across the different developmental stages. To improve this knowledge, we characterize the microbiota among different developmental stages of the Indian meal moth, Plodia interpunctella, which is considered one of the major pest of commodities worldwide. Using culture-independent approach based on Illumina 16S rRNA gene sequencing we characterized the microbiota of four developmental stages: eggs, first-, and last-instar larvae, and adult. A total of 1022 bacterial OTUs were obtained, showing a quite diversified microbiota associated to all the analyzed stages. The microbiotas associated with P. interpunctella resulted almost constant throughout the developmental stages, with approximately 77% of bacterial OTUs belonging to the phylum of Proteobacteria. The dominant bacterial genus is represented by Burkholderia (∼64%), followed by Propionibacterium, Delftia, Pseudomonas, and Stenotrophomonas. A core bacterial community, composed of 139 OTUs, was detected in all the developmental stages, among which 112 OTUs were assigned to the genus Burkholderia. A phylogenetic reconstruction, based on the 16S rRNA, revealed that our Burkholderia OTUs clustered with Burkholderia cepacia complex, in the same group of those isolated from the hemipterans Gossyparia spuria and Acanthococcus aceris. The functional profiling, predicted on the base of the bacterial 16S rRNA, indicates differences in the metabolic pathways related to metabolism of amino acids between preimaginal and adult stages. We can hypothesize that bacteria may support the insect host during preimaginal stages.

Cophylogenetic analysis suggests cospeciation between the Scorpion Mycoplasma Clade symbionts and their hosts

Scorpions are predator arachnids of ancient origin and worldwide distribution. Two scorpion species, Vaejovis smithi and Centruroides limpidus, were found to harbor two different Mollicutes phylotypes: a Scorpion Mycoplasma Clade (SMC) and Scorpion Group 1 (SG1). Here we investigated, using a targeted gene sequencing strategy, whether these Mollicutes were present in 23 scorpion morphospecies belonging to the Vaejovidae, Carboctonidae, Euscorpiidae, Diplocentridae, and Buthidae families. Our results revealed that SMC is found in a species-specific association with Vaejovidae and Buthidae, whereas SG1 is uniquely found in Vaejovidae. SMC and SG1 co-occur only in Vaejovis smithi where 43% of the individuals host both phylotypes. A phylogenetic analysis of Mollicutes 16S rRNA showed that SMC and SG1 constitute well-delineated phylotypes. Additionally, we found that SMC and scorpion phylogenies are significantly congruent, supporting the observation that a cospeciation process may have occurred. This study highlights the phylogenetic diversity of the scorpion associated Mollicutes through different species revealing a possible cospeciation pattern.

Effects of glycinin and β-conglycinin on growth performance and intestinal health in juvenile Chinese mitten crabs (Eriocheir sinensis)

This study investigates the effects of two soybean antigens (glycinin and β-conglycinin) as an antinutritional substance in the diet on the growth, digestive ability, intestinal health and microbiota of juvenile Chinese mitten crabs (Eriocheir sinensis). The isonitrogenous and isolipidic diets contained two soybean antigens at two levels each (70 and 140 g/kg β-conglycinin, 80 and 160 g/kg glycinin) and a control diet without β-conglycinin or glycinin supplementation, and were used respectively to feed juvenile E. sinensis for seven weeks. Dietary inclusion of either glycinin or β-conglycinin significantly reduced crab survival and weight gain. The crabs fed diets containing soybean antigens had higher malondialdehyde concentrations and lower catalase activities in the intestine than those in the control. The activities of trypsin and amylase in the intestine were suppressed by dietary β-conglycinin and glycinin. Dietary glycinin or β-conglycinin impaired the immunity and morphological structure of intestine, especially the peritrophic membrane. The mRNA expression of constitutive and inducible immune responsive genes (lipopolysaccharide-induced TNF-α factor and interleukin-2 enhancer-binding factor 2) increased while the mRNA expression of the main genes related to the structural integrity peritrophic membrane (peritrophin-like gene and peritrophic 2) significantly decreased in the groups with soybean antigen addition. Soybean antigen could also change the intestinal microbial community. The abundance of pathogenic bacteria (Ochrobactrum, Burkholderia and Pseudomonas) increased significantly in both soybean antigen groups. Although pathogenic bacteria Vibrio were up-regulated in the glycinin group, the abundance of Dysgonomonas that degraded lignocellulose and ameliorated the gut environment decreased in the glycinin group. This study indicates that existence of soybean antigens (glycinin or β-conglycinin) could induce gut inflammation, reshape the community of gut microbiota, and cause digestive dysfunction, ultimately leading to impaired growth in crabs.

Distribution of Transferable Antibiotic Resistance Genes in Laboratory-Reared Edible Mealworms (Tenebrio molitor L.)

In the present study, the distribution of antibiotic resistance genes in laboratory-reared fresh mealworm larvae (Tenebrio molitor L.), their feeding substrates (carrots and wheatmeal), and frass was assessed. Microbial counts on selective media added with antibiotics highlighted the presence of lactic acid bacteria resistant to ampicillin and vancomycin and, more specifically, enterococci resistant to the latter antibiotic. Moreover, staphylococci resistant to gentamicin, erythromycin, tetracycline, and vancomycin were detected. Enterobacteriaceae resistant to ampicillin and gentamicin were also found, together with Pseudomonadaceae resistant to gentamicin. Some of the genes coding for resistance to macrolide-lincosamide-streptogramin B (MLSB) [erm(A), erm(C)], vancomycin [vanA, vanB], tetracycline [tet(O)], and β-lactams [mecA and blaZ] were absent in all of the samples. For the feeding substrates, organic wheatmeal was positive for tet(S) and tet(K), whereas no AR genes were detected in organic carrots. The genes tet(M), tet(K), and tet(S) were detected in both mealworms and frass, whereas gene aac-aph, coding for resistance to amynoglicosides was exclusively detected in frass. No residues for any of the 64 antibiotics belonging to 10 different drug classes were found in either the organic wheatmeal or carrots. Based on the overall results, the contribution of feed to the occurrence of antibiotic resistance (AR) genes and/or antibiotic-resistant microorganisms in mealworm larvae was hypothesized together with vertical transmission via insect egg smearing.

Transmission strategies in a chemosynthetic symbiosis: detection and quantification of symbionts in host tissues and their environment

Transmission of bacteria vertically through host tissues ensures offspring acquire symbionts; however, horizontal transmission is an effective strategy for many associations and plays a role in some vertically transmitted symbioses. The bivalve Solemya velum and its gammaproteobacterial chemosynthetic symbionts exhibit evolutionary evidence of both transmission modes, but the dominant strategy on an ecological time scale is unknown. To address this, a specific primer set was developed and validated for the S. velum symbiont using a novel workflow called specific marker design (SMD). Symbionts were quantified in spawned eggs and sediment and seawater samples from S. velum habitats with qPCR. Each egg was estimated to contain 50-100 symbiont genomes. By contrast, symbiont DNA was found at low abundance/occurrence in sediment and seawater, often co-occurring with host mitochondrial DNA, obscuring its origin. To ascertain when eggs become infected, histological sections of S. velum tissues were labelled for symbiont 16S rRNA via in situ hybridization. This revealed symbionts in the ovary walls and mature oocytes, suggesting association in late oogenesis. These data support the hypothesis that S. velum symbionts are vertically transmitted every host generation, thus genetic signatures of horizontal transmission are driven by ecologically infrequent events. This knowledge furthers our understanding of vertical and horizontal mode integration and provides insights across animal-bacterial chemosynthetic symbioses.

Identification of active and taxonomically diverse 1,4-dioxane degraders in a full-scale activated sludge system by high-sensitivity stable isotope probing

1,4-Dioxane is one of the most common and persistent artificial pollutants in petrochemical industrial wastewaters and chlorinated solvent groundwater plumes. Despite its possible biological treatment in natural environments, the identity and dynamics of the microorganisms involved are largely unknown. Here, we identified active and diverse 1,4-dioxane-degrading microorganisms from activated sludge by high-sensitivity stable isotope probing of rRNA. By rigorously analyzing 16S rRNA molecules in RNA density fractions of ¹³C-labeled and unlabeled 1,4-dioxane treatments, we discovered 10 significantly ¹³C-incorporating microbial species from the complex microbial community. 16S rRNA expression assays revealed that 9 of the 10 species, including the well-known degrader Pseudonocardia dioxanivorans, an ammonia-oxidizing bacterium and phylogenetically novel bacteria, increased their metabolic activities shortly after exposure to 1,4-dioxane. Moreover, high-resolution monitoring showed that, during a single year of operation of the full-scale activated sludge system, the nine identified species exhibited yearly averaged relative abundances of 0.001–1.523%, and yet showed different responses to changes in the 1,4-dioxane removal efficiency. Hence, the co-existence and individually distinct dynamics of various 1,4-dioxane-degrading microorganisms, including hitherto unidentified species, played pivotal roles in the maintenance of the biological system removing the recalcitrant pollutant.

Infection dynamics of insecticide-degrading symbionts from soil to insects in response to insecticide spraying

Insecticide resistance is a serious concern in modern agriculture, and an understanding of the underlying evolutionary processes is pivotal to prevent the problem. The bean bug Riptortus pedestris, a notorious pest of leguminous crops, acquires a specific Burkholderia symbiont from the environment every generation, and harbors the symbiont in the midgut crypts. The symbiont's natural role is to promote insect development but the insect host can also obtain resistance against the insecticide fenitrothion (MEP) by acquiring MEP-degrading Burkholderia from the environment. To understand the developing process of the symbiont-mediated MEP resistance in response to the application of the insecticide, we investigated here in parallel the soil bacterial dynamics and the infected gut symbionts under different MEP-spraying conditions by culture-dependent and culture-independent analyses, in conjunction with stinkbug rearing experiments. We demonstrate that MEP application did not affect the total bacterial soil population but significantly decreased its diversity while it dramatically increased the proportion of MEP-degrading bacteria, mostly Burkholderia. Moreover, we found that the infection of stinkbug hosts with MEP-degrading Burkholderia is highly specific and efficient, and is established after only a few times of insecticide spraying at least in a field soil with spraying history, suggesting that insecticide resistance could evolve in a pest bug population more quickly than was thought before.

Yeast-like microorganisms in the scale insect Kermes quercus (Insecta, Hemiptera, Coccomorpha: Kermesidae). Newly acquired symbionts?

Scale insects, like other plant sap-consumers, are host to symbiotic microorganisms which provide them with the substances missing from their diet. In contrast to most scale insects, Kermes quercus (Linnaeus) was regarded as asymbiotic. Our histological and ultrastructural observations show that in the body of the feeding stages of K. quercus collected in two locations (Warsaw and Cracow), numerous yeast-like microorganisms occur. These microorganisms were localized in the cytoplasm of fat body cells. The yeast-like microorganisms were observed neither in other organs of the host insect nor in the eggs. These microorganisms did not cause any damage to the structure of the ovaries and the course of oogenesis of the host insect. The females infected by them produced about 1300 larvae. The lack of these microorganisms in the cytoplasm of eggs indicates that they are not transmitted transovarially from mother to offspring. Molecular analyses indicated that the microorganisms which reside in the body of K. quercus are closely related to the entomopathogenic fungi Cordyceps and Ophiocordyceps, which belong to the Sordariomycetes class within the Ascomycota. The role of yeast-like microorganisms to their host insects remains unknown; however, it has been suggested that they may represent newly acquired symbionts.

Detoxifying symbiosis: microbe-mediated detoxification of phytotoxins and pesticides in insects

Symbiotic microorganisms degrade natural and artificial toxic compounds, and confer toxin resistance on insect hosts.

Symbiont dynamics and strain diversity in the defensive mutualism between Lagria beetles and Burkholderia

Defensive mutualisms are often facultative in nature, and their evolutionary dynamics can be shaped by changes in local antagonist communities or arms races with coevolving antagonists. Under these conditions, selection may favour hosts that flexibly acquire symbionts producing compounds with bioactivity against current antagonists. Here, we study the prevalence, dynamics and strain diversity of Burkholderia gladioli bacteria in Lagria beetles, a recently described protective symbiosis involving vertical transmission and antifungal defense for the host eggs. In Lagria hirta, we investigate the fate of the bacteria during the host life cycle. Despite a transmission route relying solely on the females, the bacteria are present in both sexes during the larval stage, suggesting a potentially multifaceted defensive role. In L. hirta and L. villosa adults, culture-dependent and -independent techniques revealed that individual beetles harbour diverse Burkholderia strains from at least two different phylogenetic clades, yet all closely related to free-living B. gladioli. Interestingly, rearing the beetles in the laboratory strongly impacted symbiont strain profiles in both beetle species. Our findings highlight the dynamic nature of the B. gladioli-Lagria symbiosis and present this as a valuable system for studying multiple strain coinfections, as well as the evolutionary and ecological factors regulating defensive symbiosis.