Cadmium and Selenate Exposure Affects the Honey Bee Microbiome and Metabolome, and Bee-Associated Bacteria Show Potential for Bioaccumulation

Urban wild bee well-being revealed by gut metagenome data: A mason bee model

Wild bees are ecologically vital but increasingly threatened by anthropogenic activities, leading to uncertain survival and health outcomes in urban environments. The gut microbiome contains features indicating host health and reflecting long-term evolutionary adaptation and acute reactions to real-time stressors. Moving beyond bacteria, we propose a comprehensive analysis integrating diet, bacteriome, virome, resistome, and their association to understand the survival status of urban lives better. We conducted a study on mason bees (Osmia excavata) across 10 urban agricultural sites in Suzhou, China, using shotgun gut metagenome sequencing for data derived from total gut DNA. Our findings revealed that most ingested pollen originated from Brassica crops and the unexpected garden tree Plantanus, indicating that floral resources at the 10 sites supported Osmia but with limited plant diversity. Varied city landscapes revealed site-specific flowers that all contributed to Osmia sustenance. The gut bacterial community, dominated by Gammaproteobacteria, showed remarkable structural stability across 8 sites but suggested perturbations at 2 sites. Antibiotic resistance gene profiles highly varied across 10 sites with prevalent unclassified drug classes, highlighting environmental threats to both bees and humans. The virome analysis identified honeybee pathogens, suggesting potential virus spillover. Many unknown bacteriophages were detected, some of which targeted the core gut bacteria, underscoring their role in maintaining gut homeostasis. These multifaceted metagenomic insights hold the potential to predict bee health and identify environmental threats, thereby guiding probiotic development and city management for effective bee conservation.

Effects of chronic metal exposure and metamorphosis on the microbiomes of larval and adult insects and riparian spiders through the aquatic-riparian food web

The macroinvertebrate microbiome controls various aspects of the host's physiology, from regulation of environmental contaminants to reproductive output. Aquatic insects provide critical nutritional subsidies linking aquatic and riparian food webs while simultaneously serving as a contaminant pathway for riparian insectivores in polluted ecosystems. Previous studies have characterized the transport and transfer of contaminants from aquatic to riparian ecosystems through insect metamorphosis, but both contaminant exposure and metamorphosis are energetically intensive processes that may cause host microbiomes to undergo radical transformation in structure and function, potentially affecting the host's physiology. We collected arthropods from three sites within Torch Lake, a historical copper mine in the Keweenaw Peninsula, Michigan, USA, and three sites within a nearby reference lake. Our objectives were to: 1) characterize the variation in microbiome communities and predicted metagenomic functions with legacy copper mining activity across space, among host types and family-level host taxonomy, 2) characterize how insect metamorphosis alters the microbiome community, including the degree of endosymbiotic infection, and predicted metagenomic function. We field-collected organisms, extracted their DNA, and sequenced the 16S region of the rRNA gene to characterize microbiome communities, then predicted metagenomic function. Site, lake, and host taxonomy affected the host microbiome community composition. Copper exposure increased the abundance of xenobiotic and lipid metabolism pathways in the Araneidae spider microbiome. Insect metamorphosis reduced the alpha diversity, altered the community composition, and predicted metagenomic function. We observed a bioconcentration of endosymbiotic bacteria in adult insects, especially holometabolous insects. Through metamorphosis, we observed a transition in function from xenobiotic degradation pathways to carbohydrate metabolism. Overall, contaminant exposure alters the microbiome composition in aquatic insects and riparian spiders and alters the function of the microbiome across the aquatic-riparian interface. Furthermore, metamorphosis is a critical element in shaping the aquatic insect microbiome across its life history.

Trace Metals in Nectar of Important Urban Pollinator Forage Plants: A Direct Exposure Risk to Pollinators and Nectar-Feeding Animals in Cities

Pollinators are exposed to metals while foraging in the landscape and accumulate detectable concentrations of trace metals within their bodies, although major exposure routes remain unclear. As nectar is the main source of food for pollinators, we analyzed trace metal content within floral rewards to identify if nectar contained detectable metals and may serve as an oral exposure route. Nectar from flowering plant species growing within vacant lots in the city of Cleveland, OH, USA was extracted using a centrifuge and tested for the metals arsenic, cadmium, chromium, and lead using ICP-MS. We collected volunteer flower species that are common pollinator forage plants. Nectar metal content varied by plant and metal species, but not by location. Nectar arsenic concentrations ranged from 0 to 8.44 μg/L, cadmium from 0 to 32.99 μg/L, chromium from 0 to 45.69 μg/L, and lead from 0 to 135.31 μg/L. The presence of these soil contaminants in nectar indicates that the uptake and concentration of metals within nectar resources is likely a major route of metal exposure for pollinators and nectar-feeding animals.

Metal concentration in honeybees along an urbanization gradient in Central Mexico

Urbanization is rapidly increasing worldwide, leading to rising levels of pollution, one of the major drivers of environmental change; yet little is known about the relationship between urbanization intensity and pollution levels in pollinator taxa. Toxic metals are among the most common contaminants in urban environments, but few data exist on their presence in the flora and fauna of cities in Latin America, one of the world's most urbanized and biologically diverse regions. In this study, we used an urban-rural gradient approach to analyze the relationship between the concentrations of eleven metals present in adult honeybees (Apis mellifera) and the degree of urbanization within twelve landscapes in the metropolitan area of Pachuca, Hidalgo, which forms part of the megalopolis of Mexico City. Metal concentrations were compared with previously reported values contrasting honeybees from urban and rural areas after standardizing urbanization levels among published reports. The concentrations of Ag, Cr, Cu, and Zn in honeybees increased significantly with the degree of urbanization. Urbanization was not found to influence the levels of Al, Ba, Cd, Mn, and Sr in honeybees. The maximum concentrations of six metals in our urban sites (Al, Ba, Cd, Cu, Mn, and Sr) were higher than the maximum values reported for bees in other urban areas. The concentrations of two metals measured in our study (Cr and Zn) were within the range of values previously published for urban areas. Compared to other studies, we did not detect Pb in the body of honeybees. We conclude that the concentrations of Ag, Cr, Cu, and Zn present in honeybees are a quantitative reflection of the degree of urbanization in central Mexico. Our results highlight the need to monitor metal emission sources in this and other areas and investigate their effects on bees and other pollinator taxa.

Effects of heavy metals and metalloids on plant-animal interaction and biodiversity of terrestrial ecosystems-an overview

Heavy metals and metalloids are ubiquitous and persistent in the environment. Anthropogenic activities, including land use change, industrial emissions, mining, chrome plating, and smelting, escalate their distribution and accumulation in terrestrial ecosystems. Priority metals, including lead, chromium, arsenic, nickel, copper, cadmium, and mercury, pose enormous risks to public health, ecological safety, and biodiversity. The adverse effects of heavy metals on plant-animal interactions, pollen viability, species fitness, richness, and abundance are poorly understood. Hence, this review summarises the critical insights from primary investigations on the key sources of heavy metal pollution, distribution pathways, and their adverse effects on plants and pollinators. This study provides insights into how heavy metals compromise nectar quality, pollen viability, plant-pollinator growth, and reproduction. Biotic pollinators are responsible for approximately 90% of the reproduction of flowering plants. Heavy metals adversely affect pollinators that rely on angiosperms for nectar and pollen. Heavy metals interrupt pollinators' and plants' growth, reproduction, and survival. Evidence showed that bees near gold mines had their olfactory learning performances and head sizes reduced by 36% and 4% due to heavy metals exposure. Cadmium (Cd) interrupts the redox balance, causes oxidative stress, alters gut microbiota, and reduces the survival rate of Apis cerana cerana. Excess Cd exposure reduced the flight capacity, loss of mitochondria, and damaged muscle fibre of Bombus terrestris, while Zn stress reduced egg production and hatchability of Harmonia axyridis. Furthermore, heavy metals alter flower visitation, foraging behaviour, and pollination efficiency.

Exploring the risk of microplastics to pollinators: focusing on honey bees

The rapid increase in global plastic production and usage has led to global environmental contamination, with microplastics (MPs) emerging as a significant concern. Pollinators provide a crucial ecological service, while bee populations have been declining in recent years, and MPs have been recognized as a new risk factor contributing to their losses. Despite the pervasive distribution and persistence of MPs, understanding their risks to honey bees remains a critical knowledge gap. This review summarizes recent studies that investigate the toxicity of MPs on honey bee health from different perspectives. The findings revealed diverse and material-/size-/dosage-dependent outcomes, emphasizing the need for comprehensive assessments in the follow-up studies. MPs have been detected in honey and in bees' organs (e.g., gut and brain), posing potential threats to bee fitness, including altered behavior, cognitive abilities, compromised immunity, and dysfunction of the gut microbiota. It should be noticed that despite several laboratory studies suggesting the aforementioned adverse effects of MPs, field/semi-field experiments are still warranted. The synergistic toxicity of MPs with other environmental contaminants (pesticides, antibiotics, fungicides, heavy metals, etc.) still requires further investigation. Our review highlights the critical need to understand the relationships between MPs, pollinators, and the ecosystem to mitigate potential risks and ensure the sustainability of vital services provided by honey bees.

Prospects of probiotics in beekeeping: a review for sustainable approach to boost honeybee health

Honeybees are vital for global crop pollination, making indispensable contributions to agricultural productivity. However, these vital insects are currently facing escalating colony losses on a global scale, primarily attributed to parasitic and pathogenic attacks. The prevalent response to combat these infections may involve the use of antibiotics. Nevertheless, the application of antibiotics raises concerns regarding potential adverse effects such as antibiotic resistance and imbalances in the gut microbiota of bees. In response to these challenges, this study reviews the utilization of a probiotic-supplemented pollen substitute diet to promote honeybee gut health, enhance immunity, and overall well-being. We systematically explore various probiotic strains and their impacts on critical parameters, including survival rate, colony strength, honey and royal jelly production, and the immune response of bees. By doing so, we emphasize the significance of maintaining a balanced gut microbial community in honeybees. The review also scrutinizes the factors influencing the gut microbial communities of bees, elucidates the consequences of dysbiosis, and evaluates the potential of probiotics to mitigate these challenges. Additionally, it delineates different delivery mechanisms for probiotic supplementation and elucidates their positive effects on diverse health parameters of honeybees. Given the alarming decline in honeybee populations and the consequential threat to global food security, this study provides valuable insights into sustainable practices aimed at supporting honeybee populations and enhancing agricultural productivity.

Acute toxicity and bioaccumulation of common urban metals in Bombus impatiens life stages

Metal contamination is ubiquitous in urban areas and represents a risk to arthropod species. Bees are exposed to metals while foraging within contaminated landscapes from multiple sources. Eliminating the risk of bee exposure to metals is complex, and requires an understanding of how bees become contaminated, how metals accumulate within bee bodies, and how this exposure influences their health. We selected Bombus impatiens, the common eastern bumble bee, as our focal species because it is the most frequently encountered bumble bee species in the eastern United States and common within urban greenspaces. The aims of this study were to quantify the lethal concentration exposure limit (LC50) for B. impatiens foragers, assess the bioaccumulation ability of environmentally relevant concentrations of common urban metals in adults, larvae, and pupae, and compare the LC50 values against field relevant concentrations collected by foraging bumble bees within a legacy city. Bumble bees were orally exposed to arsenic oxide, cadmium chloride, or chromium oxide in sucrose solution to encourage consumption. The LC50 for arsenic (As2O3 36.4 mg/L), cadmium (CdCl2 10.3 mg/L), and chromium (CrO3 189.6 mg/L) are 202×, 79×, and 1459× greater than concentrations found within urban bumble bee collected provisions, respectively. Adult bumble bees fed field realistic concentrations of metals accumulate significant amounts of cadmium and lead within their bodies, but do not accumulate chromium and arsenic. Additionally, adults accumulate significantly higher concentrations of metals than brood. While bumble bee foragers are unlikely to encounter lethal metal concentrations while foraging in contaminated landscapes, it is crucial to consider and understand how sublethal concentrations impact overall colony functioning. The results from this study highlight the need to identify hazards and bioaccumulation ability of common metals as bees respond differently to each metal species, as well as the impacts of metal mixtures on bioaccumulation and toxicity.

Antagonistic effect of the beneficial bacterium Enterobacter hormaechei against the heavy metal Cu2+ in housefly larvae

Vermicomposting via housefly larvae can be used to efficiently treat manure and regenerate biofertilizer; however, the uptake of heavy metals could negatively influence the growth and development of larvae. Intestinal bacteria play an important role in the development of houseflies, but their effects on resistance to heavy metal damage in houseflies are still poorly understood. In this study, the life history traits and gut microbiota of housefly larvae were evaluated after exposure to an environment with Cu2+ -Enterobacter hormaechei. The data showed that exposure to 300 μg/mL Cu2+ significantly inhibited larval development and locomotor activity and reduced immune capacity. However, dietary supplementation with a Cu2+ -Enterobacter hormaechei mixture resulted in increased body weight and length, and the immune capacity of the larvae returned to normal levels. The abundances of Providencia and Klebsiella increased when larvae were fed Cu2+ -contaminated diets, while the abundances of Enterobacter and Bacillus increased when larvae were exposed to a Cu2+ -Enterobacter hormaechei mixture-contaminated environment. In vitro scanning electron microscopy analysis revealed that Enterobacter hormaechei exhibited obvious adsorption of Cu2+ when cultured in the presence of Cu2+, which reduced the damage caused by Cu2+ to other bacteria in the intestine and protected the larvae from Cu2+ injury. Overall, our results showed that Enterobacter hormaechei can absorb Cu2+ and increase the abundance of beneficial bacteria, thus protecting housefly larvae from damage caused by Cu2+. These results may fill the gaps in our understanding of the interactions between heavy metals and beneficial intestinal bacteria, offering valuable insights into the interplay between housefly larvae and metal contaminants in the environment. This approach could enhance the efficiency of converting manure contaminated with heavy metals to resources using houseflies.

Toxic effects of the heavy metal Cd on Apis cerana cerana (Hymenoptera: Apidae): Oxidative stress, immune disorders and disturbance of gut microbiota

Cadmium (Cd) is a toxic non-essential metal element that can enter the honey bee body through air, water and soil. Currently, there is a lack of sufficient research on the effects of Cd on A. cerana cerana, especially the potential risks of long-term exposure to sublethal concentrations. In order to ascertain the toxicological effects of the heavy metal Cd on bees, we performed laboratory-based toxicity experiments on worker bees and conducted analyses from three distinctive facets: antioxidative, immunological, and gut microbiota. The results showed that exposure of bees to high concentrations of Cd resulted in acute mortality, and the increase in mortality was concentration dependent. In long-term exposure to sublethal concentrations, Cd reduced the number of transcripts of antioxidant genes (AccSOD1, AccTPx3 and AccTPx4) and superoxide dismutase activity, causing an increase in malondialdehyde content. Simultaneously, the transcription of immune-related genes (AccAbaecin and AccApidaecin) and acetylcholinesterase activities was inhibited. Furthermore, Cd changes the structural characteristics of bacterial and fungal communities in the gut, disrupting the balance of microbial communities. In conclusion, the health and survival of honey bees are affected by Cd. This study provides a scientific basis for investigating the toxicological mechanisms and control strategies of the heavy metal Cd on honey bees, while facilitating a better understanding and protection of these valuable honey bees.

Klebsiella pneumoniae in the intestines of Musca domestica larvae can assist the host in antagonizing the poisoning of the heavy metal copper

BACKGROUND

Musca domestica larvae are common saprophytes in nature, promoting the material-energy cycle in the environment. However, heavy metal pollution in the environment negatively affects their function in material circulation. Our previous research found that some intestinal bacteria play an important role in the development of housefly, but the responses of microbial community to heavy metal stresses in Musca domestica is less studied.

RESULTS

In this study, CuSO4, CuSO4-Klebsiella pneumoniae mixture and CuSO4-K. pneumoniae phage mixture were added to the larval diet to analyze whether K. pneumoniae can protect housefly larvae against Cu2+ injury. Our results showed that larval development was inhibited when were fed with CuSO4, the bacterial abundance of Providencia in the intestine of larvae increased. However, the inhibition effects of CuSO4 was relieved when K. pneumoniae mixed and added in larval diets, the abundance of Providencia decreased. Electron microscope results revealed that K. pneumoniae showed an obvious adsorption effect on copper ion in vitro.

CONCLUSIONS

Based on the results we assume that K. pneumoniae could adsorb Cu2+, reduce Cu2+ impact on gut community structure. Our study explains the role of K. pneumoniae antagonizing Cu2+, which could be applied as a probiotic to saprophytic bioantagonistic metal contamination.

The honeybee gut resistome and its role in antibiotic resistance dissemination

There is now general concern about widespread antibiotic resistance, and growing evidence indicates that gut microbiota is critical in providing antibiotic resistance. Honeybee is an important pollinator; the incidence of antibiotic resistance genes in honeybee gut causes potential risks to not only its own health but also to public and animal health, for its potential disseminator role, thus receiving more attention from the public. Recent analysis results reveal that the gut of honeybee serves as a reservoir of antibiotic resistance genes, probably due to antibiotics application history in beekeeping and horizontal gene transfer from the highly polluted environment. These antibiotic resistance genes accumulate in the honeybee gut and could be transferred to the pathogen, even having the potential to spread during pollination, tending, social interactions, etc. Newly acquired resistance traits may cause fitness reduction in bacteria whereas facilitating adaptive evolution as well. This review outlines the current knowledge about the resistome in honeybee gut and emphasizes its role in antibiotic resistance dissemination.

Integration of Untargeted Metabolomics and Microbial Community Analyses to Characterize Distinct Deep-Sea Methane Seeps

Deep-sea methane seeps host highly diverse microbial communities whose biological diversity is distinct from other marine habitats. Coupled with microbial community analysis, untargeted metabolomics of environmental samples using high resolution tandem mass spectrometry provides unprecedented access to the unique specialized metabolisms of these chemosynthetic microorganisms. In addition, the diverse microbial natural products are of broad interest due to their potential applications for human and environmental health and well-being. In this exploratory study, sediment cores were collected from two methane seeps (-1000 m water depth) with very different gross geomorphologies, as well as a non-seep control site. Cores were subjected to parallel metabolomic and microbial community analyses to assess the feasibility of representative metabolite detection and identify congruent patterns between metabolites and microbes. Metabolomes generated using high resolution liquid chromatography tandem mass spectrometry were annotated with predicted structure classifications of the majority of mass features using SIRIUS and CANOPUS. The microbiome was characterized by analysis of 16S rRNA genes and analyzed both at the whole community level, as well as the small subgroup of Actinobacteria, which are known to produce societally useful compounds. Overall, the younger Dagorlad seep possessed a greater abundance of metabolites while there was more variation in abundance, number, and distribution of metabolites between samples at the older Emyn Muil seep. Lipid and lipid-like molecules displayed the greatest variation between sites and accounted for a larger proportion of metabolites found at the older seep. Overall, significant differences in composition of the microbial community mirrored the patterns of metabolite diversity within the samples; both varied greatly as a function of distance from methane seep, indicating a deterministic role of seepage. Interdisciplinary research to understand microbial and metabolic diversity is essential for understanding the processes and role of ubiquitous methane seeps in global systems and here we increase understanding of these systems by visualizing some of the chemical diversity that seeps add to marine systems.

Trace metals with heavy consequences on bees: A comprehensive review

The pervasiveness of human imprint on Earth is alarming and most animal species, including bees (Hymenoptera: Apoidea: Anthophila), must cope with several stressors. Recently, exposure to trace metals and metalloids (TMM) has drawn attention and has been suggested as a threat for bee populations. In this review, we aimed at bringing together all the studies (n = 59), both in laboratories and in natura, that assessed the effects of TMM on bees. After a brief comment on semantics, we listed the potential routes of exposure to soluble and insoluble (i.e. nanoparticle) TMM, and the threat posed by metallophyte plants. Then, we reviewed the studies that addressed whether bees could detect and avoid TMM in their environment, as well as the ways bee detoxify these xenobiotics. Afterwards, we listed the impacts TMM have on bees at the community, individual, physiological, histological and microbial levels. We discussed around the interspecific variations among bees, as well as around the simultaneous exposure to TMM. Finally, we highlighted that bees are likely exposed to TMM in combination or with other stressors, such as pesticides and parasites. Overall, we showed that most studies focussed on the domesticated western honey bee and mainly addressed lethal effects. Because TMM are widespread in the environment and have been shown to result in detrimental consequences, evaluating their lethal and sublethal effects on bees, including non-Apis species, warrants further investigations.

Recent Review on Selected Xenobiotics and Their Impacts on Gut Microbiome and Metabolome

As it is well known, the gut is one of the primary sites in any host for xenobiotics, and the many microbial metabolites responsible for the interactions between the gut microbiome and the host. However, there is a growing concern about the negative impacts on human health induced by toxic xenobiotics. Metabolomics, broadly including lipidomics, is an emerging approach to studying thousands of metabolites in parallel. In this review, we summarized recent advancements in mass spectrometry (MS) technologies in metabolomics. In addition, we reviewed recent applications of MS-based metabolomics for the investigation of toxic effects of xenobiotics on microbial and host metabolism. It was demonstrated that metabolomics, gut microbiome profiling, and their combination have a high potential to identify metabolic and microbial markers of xenobiotic exposure and determine its mechanism. Further, there is increasing evidence supporting that reprogramming the gut microbiome could be a promising approach to the intervention of xenobiotic toxicity.

Whole genome analyses of toxicants tolerance genes of Apis mellifera gut-derived Enterococcus faecium strains

BACKGROUND

Because of its social nature, the honeybee is regularly exposed to environmental toxicants such as heavy metals and xenobiotics. These toxicants are known to exert strong selective pressure on the gut microbiome's structure and diversity. For example, resistant microbial members are more likely to dominate in maintaining a stable microbiome, which is critical for bee health. Therefore, the aim of this study was to examine the Enterococcus faecium strains isolated from bee guts for their in vitro growth and tolerability to diverse heavy metals and xenobiotics. An additional aim was to analyze the genomes of E. faecium isolates to assess the molecular bases of resistance and compare them with E. faecium species isolated from other environmental sources.

RESULTS

The E. faecium bee isolates were able to tolerate high levels (up to 200 mg/L) of toxicants, including cadmium, zinc, benzoate, phenol and hexane. Moreover, the isolates could tolerate toluene and copper at up to 100 mg/L. The genome of E. faecium Am5, isolated from the larval stage of Apis mellifera gut, was about 2.7 Mb in size, had a GC content of 37.9% and 2,827 predicted coding sequences. Overall, the Am5 genome features were comparable with previously sequenced bee-gut isolates, E. faecium Am1, Bee9, SM21, and H7. The genomes of the bee isolates provided insight into the observed heavy metal tolerance. For example, heavy metal tolerance and/or regulation genes were present, including czcD (cobalt/zinc/cadmium resistance), cadA (exporting ATPase), cutC (cytoplasmic copper homeostasis) and zur (zinc uptake regulation). Additionally, genes associated with nine KEGG xenobiotic biodegradation pathways were detected, including γ-hexachlorocyclohexane, benzoate, biphenyl, bisphenol A, tetrachloroethene, 1,4-dichlorobenzene, ethylbenzene, trinitrotoluene and caprolactam. Interestingly, a comparative genomics study demonstrated the conservation of toxicant resistance genes across a variety of E. faecium counterparts isolated from other environmental sources such as non-human mammals, humans, avians, and marine animals.

CONCLUSIONS

Honeybee gut-derived E. faecium strains can tolerate a variety of heavy metals. Moreover, their genomes encode many xenobiotic biodegradation pathways. Further research is required to examine E. faecium strains potential to boost host resistance to environmental toxins.

The impact of selenium on insects

Selenium, a naturally occurring metalloid, is an essential trace element for many higher organisms, including humans. Humans primarily become exposed to selenium by ingesting food products containing trace amounts of selenium compounds. Although essential in these small amounts, selenium exhibits toxic effects at higher doses. Previous studies investigating the effects on insects of order Blattodea, Coleoptera, Diptera, Ephemeroptera, Hemiptera, Hymenoptera, Lepidoptera, Odonata, and Orthoptera revealed impacts on mortality, growth, development, and behavior. Nearly every study examining selenium toxicity has shown that insects are negatively affected by exposure to selenium in their food. However, there were no clear patterns of toxicity between insect orders or similarities between insect species within families. At this time, the potential for control will need to be determined on a species-by-species basis. We suspect that the multiple modes of action, including mutation-inducing modification of important amino acids as well as impacts on microbiome composition, influence this variability. There are relatively few studies that have examined the potential effects of selenium on beneficial insects, and the results have ranged from increased predation (a strong positive effect) to toxicity resulting in reduced population growth or even the effective elimination of the natural enemies (more common negative effects). As a result, in those pest systems where selenium use is contemplated, additional research may be necessary to ascertain if selenium use is compatible with key biological control agents. This review explores selenium as a potential insecticide and possible future directions for research.

Cobalt-induced neuro-behavioural alterations are accompanied by profound Purkinje cell and gut-associated responses in rats

Metal ions including cobalt (Co) ions reportedly exhibit neurotoxic and antimicrobial properties. We hypothesized that oral exposure to Co may have implications for gut-dysbiosis with possible alterations of microbiota-gut-brain signaling in the host. In this preliminary study, we sought to examine whether exposure of male Wistar rats to cobalt chloride (CoCl2) at 0, 25, 50 and 100 mg/kg for two weeks affects select neurobehavioural indices, vagus nerve and brain morphology along with evaluation of associated changes in faecal bacterial flora, faecal fatty acids and the morphology of the intestines. CoCl2-exposed rats showed a dose-dependent reduction in hanging latency in the hanging wire (HW) test, reduced tendency to recognize novel objects in a Novel Object recognition (NOR) test, but increased interaction with open arms in the elevated plus maze (EPM) test, compared to controls. There were dose-dependent reductions in total heterotrophic count, coliforms, E. coli, Enterococcal and Lactobacilli counts in the faeces. Administration of CoCl2 at 100 mg/kg evoked the appearance of unsaturated fatty acids including palmitoleic, oleic and linoleic acids in the faeces as detected by gas chromatography-flame ion detection (GD-FID) analysis using fatty acid methyl esters (FAME) standards. Histopathological examination revealed chromatolysis of Purkinje cells in the cerebellum, although no significant lesions were present in the vagus nerve isolated from all the groups. In the intestines, there was moderate to severe infiltration of inflammatory cells into the duodenum, ileum, jejunum and colon while villi erosions were seen prominently in the ileum. These initial findings suggest that short-term exposure to Co can lead to gut-associated changes that may underlie neurotoxicity and alterations in behavior induced by Co.

Comparison of gut bacterial communities of Hyphantriacunea Drury (Lepidoptera, Arctiidae), based on 16S rRNA full-length sequencing

There are a large number of microorganisms in the gut of insects, which form a symbiotic relationship with the host during the long-term co-evolution process and have a significant impact on the host's nutrition, physiology, development, immunity, stress tolerance and other aspects. However, the composition of the gut microbes of Hyphantriacunea remains unclear. In order to investigate the difference and diversity of intestinal microbiota of H.cunea larvae feeding on different host plants, we used PacBio sequencing technology for the first time to sequence the 16S rRNA full-length gene of the intestinal microbiota of H.cunea. The species classification, β diversity and function of intestinal microflora of the 5th instar larvae of four species of H.cunea feeding on apricot, plum, redbud and Chinese ash were analysed. The results showed that a total of nine phyla and 65 genera were identified by PacBio sequencing, amongst which Firmicutes was the dominant phylum and Enterococcus was the dominant genus, with an average relative abundance of 59.29% and 52.16%, respectively. PERMANOVA analysis and cluster heat map showed that the intestinal microbiomes of H.cunea larvae, fed on different hosts, were significantly different. LEfSe analysis confirmed the effect of host diet on intestinal community structure and PICRUSt2 analysis showed that most of the predictive functions were closely related to material transport and synthetic, metabolic and cellular processes. The results of this study laid a foundation for revealing the interaction between the intestinal microorganisms of H.cunea and its hosts and provided ideas for exploring new green prevention and control strategies of H.cunea.

The sulfoximine insecticide sulfoxaflor exposure reduces the survival status and disrupts the intestinal metabolism of the honeybee Apis mellifera

Honeybees (Apis mellifera) are indispensable pollinators in agricultural production, biodiversity conservation, and nutrients provision. The abundance and diversity of honeybees have been rapidly diminishing, possibly related to the extensive use of insecticides in ecosystems. Sulfoxaflor is a novel sulfoximine insecticide that, like neonicotinoids, acts as a competitive modulator of nicotinic acetylcholine receptors (nAChR) in insects. However, few studies have addressed the negative effects of sulfoxaflor on honeybees at environmentally relevant concentrations. In the present study, adult workers were fed a 50% (w/v) of sugar solution containing different concentrations (0, 0.05, 0.5 and 2.0 mg/L) of sulfoxaflor for two weeks consecutively. The survival rates, food intake, and body weight of the honeybees significantly decreased after continuous exposure at higher doses (0.5 and 2.0 mg/L) of sulfoxaflor when compared with the control. The change in the metabolites in the honeybee gut was determined using high-throughput non-targeted metabolomics on day 14 after sulfoxaflor treatment. The results revealed that 24 and 105 metabolites changed after exposure to 0.5 and 2.0 mg/L sulfoxaflor, respectively, compared with that of the control groups. A total of 12 changed compounds including pregenolone and glutathione were detected as potential biomarkers, which were eventually found to be enriched in pathways of the steroid hormone biosynthesis (p = 0.0001) and glutathione metabolism (p = 0.021). These findings provide a new perspective on the physiological influence of sulfoxaflor stress in honeybees.

What happens to gut microorganisms and potential repair mechanisms when meet heavy metal(loid)s

Heavy metal (loid) pollution is a significant threat to human health, as the intake of heavy metal (loid)s can cause disturbances in intestinal microbial ecology and metabolic disorders, leading to intestinal and systemic diseases. Therefore, it is important to understand the effects of heavy metal (loid)s on intestinal microorganisms and the necessary approaches to restore them after damage. This review provides a summary of the effects of common toxic elements, such as lead (Pb), cadmium (Cd), chromium (Cr), and metalloid arsenic (As), on the microbial community and structure, metabolic pathways and metabolites, and intestinal morphology and structure. The effects of heavy metal (loid)s on metabolism are focused on energy, nitrogen, and short-chain fatty acid metabolism. We also discussed the main solutions for recovery of intestinal microorganisms from the effects of heavy metal (loid)s, namely the supplementation of probiotics, recombinant bacteria with metal resistance, and the non-toxic transformation of heavy metal (loid) ions by their own intestinal flora. This article provides insight into the toxic effects of heavy metals and As on gut microorganisms and hosts and provides additional therapeutic options to mitigate the damage caused by these toxic elements.

Indispensable role of melatonin, a scavenger of reactive oxygen species (ROS), in the protective effect of Akkermansia muciniphila in cadmium-induced intestinal mucosal damage

The gastrointestinal tract is the main target of cadmium toxicity. However, whether Akkermansia muciniphila (A. muciniphila), which has been reported to be the next generation of promising probiotics, can alleviate cadmium-induced intestinal damage has not been investigated. In this study, we found that compared to the cadmium exposure group, mice gavaged with A. muciniphila showed less severe intestinal mucosal damage, with improved bodyweight, colon length, a decline in inflammation, and significantly increased glutathione and goblet cell numbers. Meanwhile, melatonin was interestingly found to be strikingly increased after A. muciniphila treatment. We then demonstrated that melatonin also could ameliorate the intestinal mucosal damage caused by cadmium through scavenging reactive oxygen species (ROS) and increasing the number of goblet cells. Furthermore, mice treated with inhibitors had a low level of melatonin and could not reproduce the beneficial effects of the A. muciniphila. Our results implied that the regulation of melatonin production by A. muciniphila is associated with an increase in enterochromaffin cells number, which determine melatonin secretion. This study indicated that the A. muciniphila-melatonin axis reduces cadmium-induced damage by increasing the goblet cells and scavenging the ROS, which may guide the prevention of the toxic effects of heavy metals.

Chronic Cadmium Exposure Induces Impaired Olfactory Learning and Altered Brain Gene Expression in Honey Bees (Apis mellifera)

The honey bee (Apis mellifera) plays vital ecological roles in the pollination of crops and the maintenance of ecological balance, and adult honey bees may be exposed to exogenous chemicals including heavy metals during their foraging activities. Cadmium (Cd) is regarded as a nonessential toxic metal and is readily accumulated in plants; honey bees can therefore acquire Cd through the collection of contaminated nectar. In the present study, honey bees were chronically exposed to Cd to investigate the effects of sublethal cadmium doses on the olfactory learning and brain gene expression profiles of honey bees. The results showed that Cd-treated bees exhibited significantly impaired olfactory learning performances in comparison with control bees. Moreover, the head weight was significantly lower in Cd-treated bees than in control bees after chronic exposure to Cd. Gene expression profiles between the Cd treatment and the control revealed that 79 genes were significantly differentially expressed. Genes encoding chemoreceptors and olfactory proteins were downregulated, whereas genes involved in response to oxidative stress were upregulated in Cd-treated bees. The results suggest that Cd exposure exerts oxidative stress in the brain of honey bees, and the dysregulated expression of genes encoding chemoreceptors, olfactory proteins, and cytochrome P450 enzymes is probably associated with impaired olfactory learning in honey bees.

Effects of in situ experimental selenium exposure on finescale dace (Phoxinus neogaeus) gut microbiome

Selenium (Se) is an environmental contaminant of global concern that can cause adverse effects in fish at elevated levels. Fish gut microbiome play essential roles in gastrointestinal function and host health and can be perturbed by environmental contaminants, including metals and metalloids. Here, an in-situ Se exposure of female finescale dace (Phoxinus neogaeus) using mesocosms was conducted to determine the impacts of Se accumulation on the gut microbiome and morphometric endpoints. Prior to this study, the gut microbiome of finescale dace, a widespread Cyprinid throughout North America, had not been characterized. Exposure to Se caused a hormetic response of alpha diversity of the gut microbiome, with greater diversity at the lesser concentration of 1.6 μg Se/L, relative to that of fish exposed to the greater concentration of 5.6 μg Se/L. Select gut microbiome taxa of fish were differentially abundant between aqueous exposure concentrations and significantly correlated with liver-somatic index (LSI). The potential effects of gut microbiome dysbiosis on condition of wild fish might be a consideration when assessing adverse effects of Se in aquatic environments. More research regarding effects of Se on field-collected fish gut microbiome and the potential adverse effects or benefits on the host is warranted.

Pollen diet mediates how pesticide exposure impacts brain gene expression in nest-founding bumble bee queens

A primary goal in biology is to understand the effects of multiple, interacting environmental stressors on organisms. Wild and domesticated bees are exposed to a wide variety of interacting biotic and abiotic stressors, with widespread declines in floral resources and agrochemical exposure being two of the most important. In this study, we used examinations of brain gene expression to explore the sublethal consequences of neonicotinoid pesticide exposure and pollen diet composition in nest-founding bumble bee queens. We demonstrate for the first time that pollen diet composition can influence the strength of bumble bee queen responses to pesticide exposure at the molecular level. Specifically, one pollen mixture in our study appeared to buffer bumble bee queens entirely against the effects of pesticide exposure, with respect to brain gene expression. Additionally, we detected unique effects of pollen diet and sustained (versus more temporary) pesticide exposure on queen gene expression. Our findings support the hypothesis that nutritional status can help buffer animals against the harmful effects of other stressors, including pesticides, and highlight the importance of using molecular approaches to explore sublethal consequences of stressors.

Host and gut microbiome modulate the antiparasitic activity of nectar metabolites in a bumblebee pollinator

Antimicrobial nectar secondary metabolites can support pollinator health by preventing or reducing parasite infections. To better understand the outcome of nectar metabolite-parasite interactions in pollinators, we determined whether the antiparasitic activity was altered through chemical modification by the host or resident microbiome during gut passage. We investigated this interaction with linden (Tilia spp.) and strawberry tree (Arbutus unedo) nectar compounds. Unedone from A. unedo nectar inhibited the common bumblebee gut parasite Crithidia bombi in vitro and in Bombus terrestris gynes. A compound in Tilia nectar, 1-[4-(1-hydroxy-1-methylethyl)-1,3-cyclohexadiene-1-carboxylate]-6-O-β-d-glucopyranosyl-β-d-glucopyranose (tiliaside), showed no inhibition in vitro at naturally occurring concentrations but reduced C. bombi infections of B. terrestris workers. Independent of microbiome status, tiliaside was deglycosylated during gut passage, thereby increasing its antiparasitic activity in the hindgut, the site of C. bombi infections. Conversely, unedone was first glycosylated in the midgut without influence of the microbiome to unedone-8-O-β-d-glucoside, rendering it inactive against C. bombi, but subsequently deglycosylated by the microbiome in the hindgut, restoring its activity. We therefore show that conversion of nectar metabolites by either the host or the microbiome modulates antiparasitic activity of nectar metabolites. This article is part of the theme issue 'Natural processes influencing pollinator health: from chemistry to landscapes'.

Bee Stressors from an Immunological Perspective and Strategies to Improve Bee Health

Honeybees are the most prevalent insect pollinator species; they pollinate a wide range of crops. Colony collapse disorder (CCD), which is caused by a variety of biotic and abiotic factors, incurs high economic/ecological loss. Despite extensive research to identify and study the various ecological stressors such as microbial infections, exposure to pesticides, loss of habitat, and improper beekeeping practices that are claimed to cause these declines, the deep understanding of the observed losses of these important insects is still missing. Honeybees have an innate immune system, which includes physical barriers and cellular and humeral responses to defend against pathogens and parasites. Exposure to various stressors may affect this system and the health of individual bees and colonies. This review summarizes and discusses the composition of the honeybee immune system and the consequences of exposure to stressors, individually or in combinations, on honeybee immune competence. In addition, we discuss the relationship between bee nutrition and immunity. Nutrition and phytochemicals were highlighted as the factors with a high impact on honeybee immunity.

Understanding effects of floral products on bee parasites: Mechanisms, synergism, and ecological complexity

Floral nectar and pollen commonly contain diverse secondary metabolites. While these compounds are classically thought to play a role in plant defense, recent research indicates that they may also reduce disease in pollinators. Given that parasites have been implicated in ongoing bee declines, this discovery has spurred interest in the potential for 'medicinal' floral products to aid in pollinator conservation efforts. We review the evidence for antiparasitic effects of floral products on bee diseases, emphasizing the importance of investigating the mechanism underlying antiparasitic effects, including direct or host-mediated effects. We discuss the high specificity of antiparasitic effects of even very similar compounds, and highlight the need to consider how nonadditive effects of multiple compounds, and the post-ingestion transformation of metabolites, mediate the disease-reducing capacity of floral products. While the bulk of research on antiparasitic effects of floral products on bee parasites has been conducted in the lab, we review evidence for the impact of such effects in the field, and highlight areas for future research at the floral product-bee disease interface. Such research has great potential both to enhance our understanding of the role of parasites in shaping plant-bee interactions, and the role of plants in determining bee-parasite dynamics. This understanding may in turn reveal new avenues for pollinator conservation.

Functional Properties and Antimicrobial Activity from Lactic Acid Bacteria as Resources to Improve the Health and Welfare of Honey Bees

Simple Summary

Honey bees play a pivotal role in the sustainability of ecosystems and biodiversity. Many factors including parasites, pathogens, pesticide residues, forage losses, and poor nutrition have been proposed to explain honey bee colony losses. Lactic acid bacteria (LAB) are normal inhabitants of the gastrointestinal tract of honey bees and their role has been consistently reported in the literature. In recent years, there have been numerous scientific evidence that the intestinal microbiota plays an essential role in honey bee health. Management strategies, based on supplementation of the gut microbiota with probiotics, may be important to increase stress tolerance and disease resistance. In this review, recent scientific advances on the use of LABs as microbial supplements in the diet of honey bees are summarized and discussed.

Abstract

Honey bees (Apis mellifera) are agriculturally important pollinators. Over the past decades, significant losses of wild and domestic bees have been reported in many parts of the world. Several biotic and abiotic factors, such as change in land use over time, intensive land management, use of pesticides, climate change, beekeeper’s management practices, lack of forage (nectar and pollen), and infection by parasites and pathogens, negatively affect the honey bee’s well-being and survival. The gut microbiota is important for honey bee growth and development, immune function, protection against pathogen invasion; moreover, a well-balanced microbiota is fundamental to support honey bee health and vigor. In fact, the structure of the bee’s intestinal bacterial community can become an indicator of the honey bee’s health status. Lactic acid bacteria are normal inhabitants of the gastrointestinal tract of many insects, and their presence in the honey bee intestinal tract has been consistently reported in the literature. In the first section of this review, recent scientific advances in the use of LABs as probiotic supplements in the diet of honey bees are summarized and discussed. The second section discusses some of the mechanisms by which LABs carry out their antimicrobial activity against pathogens. Afterward, individual paragraphs are dedicated to Chalkbrood, American foulbrood, European foulbrood, Nosemosis, and Varroosis as well as to the potentiality of LABs for their biological control.

Eusociality is linked to caste-specific differences in metabolism, immune system, and somatic maintenance-related processes in an ant species

The social organization of many primate, bird and rodent species and the role of individuals within that organization are associated with specific individual physiological traits. However, this association is perhaps most pronounced in eusocial insects (e.g., termites, ants). In such species, genetically close individuals show significant differences in behavior, physiology, and life expectancy. Studies addressing the metabolic changes according to the social role are still lacking. We aimed at understanding how sociality could influence essential molecular processes in a eusocial insect, the black garden ant (Lasius niger) where queens can live up to ten times longer than workers. Using mass spectrometry-based analysis, we explored the whole metabolome of queens, nest-workers and foraging workers. A former proteomics study done in the same species allowed us to compare the findings of both approaches. Confirming the former results at the proteome level, we showed that queens had fewer metabolites related to immunity. Contrary to our predictions, we did not find any metabolite linked to reproduction in queens. Among the workers, foragers had a metabolic signature reflecting a more stressful environment and a more highly stimulated immune system. We also found that nest-workers had more digestion-related metabolites. Hence, we showed that specific metabolic signatures match specific social roles. Besides, we identified metabolites differently expressed among behavioral castes and involved in nutrient sensing and longevity pathways (e.g., sirtuins, FOXO). The links between such molecular pathways and aging being found in an increasing number of taxa, our results confirm and strengthen their potential universality.

Methodology for Single Bee and Bee Brain 1H-NMR Metabolomics

The feasibility of metabolomic 1H NMR spectroscopy is demonstrated for its potential to help unravel the complex factors that are impacting honeybee health and behavior. Targeted and non-targeted 1H NMR metabolic profiles of liquid and tissue samples of organisms could provide information on the pathology of infections and on environmentally induced stresses. This work reports on establishing extraction methods for NMR metabolic characterization of Apis mellifera, the European honeybee, describes the currently assignable aqueous metabolome, and gives examples of diverse samples (brain, head, body, whole bee) and biologically meaningful metabolic variation (drone, forager, day old, deformed wing virus). Both high-field (600 MHz) and low-field (80 MHz) methods are applicable, and 1H NMR can observe a useful subset of the metabolome of single bees using accessible NMR instrumentation (600 MHz, inverse room temperature probe) in order to avoid pooling several bees. Metabolite levels and changes can be measured by NMR in the bee brain, where dysregulation of metabolic processes has been implicated in colony collapse. For a targeted study, the ability to recover 10-hydroxy-2-decenoic acid in mandibular glands is shown, as well as markers of interest in the bee brain such as GABA (4-aminobutyrate), proline, and arginine. The findings here support the growing use of 1H NMR more broadly in bees, native pollinators, and insects.

Host species identity shapes the diversity and structure of insect microbiota

As for most of the life that inhabits our planet, microorganisms play an essential role in insect nutrition, reproduction, defence, and support their host in many other functions. More recently, we assisted to an exponential growth of studies describing the taxonomical composition of bacterial communities across insects' phylogeny. However, there is still an outstanding question that needs to be answered: Which factors contribute most to shape insects' microbiomes? This study tries to find an answer to this question by taking advantage of publicly available sequencing data and reanalysing over 4000 samples of insect-associated bacterial communities under a common framework. Results suggest that insect taxonomy has a wider impact on the structure and diversity of their associated microbial communities than the other factors considered (diet, sex, life stage, sample origin and treatment). However, when specifically testing for signatures of codiversification of insect species and their microbiota, analyses found weak support for this, suggesting that while insect species strongly drive the structure and diversity of insect microbiota, the diversification of those microbial communities did not follow their host's phylogeny. Furthermore, a parallel survey of the literature highlights several methodological limitations that need to be considered in the future research endeavours.

Parasitic nematode fatty acid- and retinol-binding proteins compromise host immunity by interfering with host lipid signaling pathways

Parasitic nematodes cause significant morbidity and mortality globally. Excretory/secretory products (ESPs) such as fatty acid- and retinol- binding proteins (FARs) are hypothesized to suppress host immunity during nematode infection, yet little is known about their interactions with host tissues. Leveraging the insect parasitic nematode, Steinernema carpocapsae, we describe here the first in vivo study demonstrating that FARs modulate animal immunity, causing an increase in susceptibility to bacterial co-infection. Moreover, we show that FARs dampen key components of the fly immune response including the phenoloxidase cascade and antimicrobial peptide (AMP) production. Our data also reveal that FARs deplete lipid signaling precursors in vivo as well as bind to these fatty acids in vitro, suggesting that FARs elicit their immunomodulatory effects by altering the availability of lipid signaling molecules necessary for an efficient immune response. Collectively, these data support a complex role for FARs in immunosuppression in animals and provide detailed mechanistic insight into parasitism in phylum Nematoda.

Unraveling Metabolic and Proteomic Features in Soybean Plants in Response to Copper Hydroxide Nanowires Compared to a Commercial Fertilizer

Mechanistic understanding of the interaction of copper-based nanomaterials with crops is crucial for exploring their application in precision agriculture and their implications on plant health. We investigated the biological response of soybean (Glycine max) plants to the foliar application of copper hydroxide nanowires (CNWs) at realistic exposure concentrations. A commercial copper based-fungicide (Kocide), dissolved copper ions, and untreated controls were used for comparison to identify unique features at physiological, cellular, and molecular levels. After 32 d of exposure to CNW (0.36, 1.8, and 9 mg CNW/plant), the newly developed tissues accumulated significantly high levels of Cu (18-60 μg/g) compared to Kocide (10 μg/g); however, the rate of Cu translocation from the site of CNW treatment to other tissues was slower compared to other Cu treatments. Like Kocide, CNW exposure at medium and high doses altered Co, Mn, Zn, and Fe accumulation in the tissues and enhanced photosynthetic activities. The proteomic and metabolomic analyses of leaves from CNW-treated soybean plants suggest a dose-dependent response, resulting in the activation of major biological processes, including photosynthesis, energy production, fatty acid metabolism, lignin biosynthesis, and carbohydrate metabolism. In contrast to CNW treatments, Kocide exposure resulted in increased oxidative stress response and amino acid metabolism activation.

The composition of bacteria in gut and beebread of stingless bees (Apidae: Meliponini) from tropics Yunnan, China

Stingless bees are the main pollinators in tropical and subtropical regions. However, there are only a few studies on the structure and composition of bacteria in the gut and beebread of stingless bees, especially in China. To address this shortage of information, we characterized the microbiota of three common species of stingless bees (Lepidotrigona terminata, Lepidotrigona ventralis and Tetragonula pagdeni) and beebread samples of T. pagdeni. The results showed that the gut of stingless bees contained a set of dominant bacteria, including Acetobacter-like, Snodgrassella, Lactobacillus, Psychrobacter, Pseudomonas, Bifidobacterium and other species. The gut microbiota structures of the three stingless bees were different, and the abundances of bacterial species in the gut varied between communities of the same bee species. The reasons for this are manifold and may include food preference, age and genetic differences. In addition, the abundances of Lactobacillus, Carnimonas, Escherichia-Shigella, Acinetobacter and other species were high in the beebread of stingless bees. In conclusion, our findings reveal the bacteria composition and structure of the gut and beebread of stingless bees in China and deepen our understanding of the dominant bacteria of the gut and beebread of stingless bees.

Bio-remediation approaches for alleviation of cadmium contamination in natural resources

Cadmium (Cd) is a harmful heavy metal that can cause potent environmental and health hazards at different trophic levels through food chain. Cd is relatively non-biodegradable and persists for a long time in the environment. Considering the potential toxicity and non-biodegradability of Cd in the environment as well as its health hazards, this is an urgent issue of international concern that needs to be addressed by implicating suitable remedial approaches. The current article specifically attempts to review the different biological approaches for remediation of Cd contamination in natural resources. Further, bioremediation mechanisms of Cd by microbes such as bacteria, fungi, algae are comprehensively discussed. Studies indicate that heavy metal resistant microbes can be used as suitable biosorbents for the removal of Cd (up to 90%) in the natural resources. Soil-to-plant transfer coefficient (TC) of Cd ranges from 3.9 to 3340 depending on the availability of metal to plants and also on the type of plant species. The potential phytoremediation strategies for Cd removal and the key factors influencing bioremediation process are also emphasized. Studies on molecular mechanisms of transgenic plants for Cd bioremediation show immense potential for enhancing Cd phytoremediation efficiency. Thus, it is suggested that nano-technological based integrated bioremediation approaches could be a potential futuristic path for Cd decontamination in natural resources. This review would be highly useful for the biologists, chemists, biotechnologists and environmentalists to understand the long-term impacts of Cd on ecology and human health so that potential remedial measures could be taken in advance.

Characterization of Apis mellifera Gastrointestinal Microbiota and Lactic Acid Bacteria for Honeybee Protection-A Review

Numerous honeybee (Apis mellifera) products, such as honey, propolis, and bee venom, are used in traditional medicine to prevent illness and promote healing. Therefore, this insect has a huge impact on humans’ way of life and the environment. While the population of A. mellifera is large, there is concern that widespread commercialization of beekeeping, combined with environmental pollution and the action of bee pathogens, has caused significant problems for the health of honeybee populations. One of the strategies to preserve the welfare of honeybees is to better understand and protect their natural microbiota. This paper provides a unique overview of the latest research on the features and functioning of A. mellifera. Honeybee microbiome analysis focuses on both the function and numerous factors affecting it. In addition, we present the characteristics of lactic acid bacteria (LAB) as an important part of the gut community and their special beneficial activities for honeybee health. The idea of probiotics for honeybees as a promising tool to improve their health is widely discussed. Knowledge of the natural gut microbiota provides an opportunity to create a broad strategy for honeybee vitality, including the development of modern probiotic preparations to use instead of conventional antibiotics, environmentally friendly biocides, and biological control agents.

Acute and chronic effects of Titanium dioxide (TiO2) PM1 on honey bee gut microbiota under laboratory conditions

Apis mellifera is an important provider of ecosystem services, and during flight and foraging behaviour is exposed to environmental pollutants including airborne particulate matter (PM). While exposure to insecticides, antibiotics, and herbicides may compromise bee health through alterations of the gut microbial community, no data are available on the impacts of PM on the bee microbiota. Here we tested the effects of ultrapure Titanium dioxide (TiO₂) submicrometric PM (i.e., PM₁, less than 1 µm in diameter) on the gut microbiota of adult bees. TiO₂ PM₁ is widely used as a filler and whitening agent in a range of manufactured objects, and ultrapure TiO₂ PM₁ is also a common food additive, even if it has been classified by the International Agency for Research on Cancer (IARC) as a possible human carcinogen in Group 2B. Due to its ubiquitous use, honey bees may be severely exposed to TiO₂ ingestion through contaminated honey and pollen. Here, we demonstrated that acute and chronic oral administration of ultrapure TiO₂ PM₁ to adult bees alters the bee microbial community; therefore, airborne PM may represent a further risk factor for the honey bee health, promoting sublethal effects against the gut microbiota.

High Plasticity of the Gut Microbiome and Muscle Metabolome of Chinese Mitten Crab (Eriocheir sinensis) in Diverse Environments

Phenotypic plasticity is a rapid response mechanism that enables organisms to acclimate and survive in changing environments. The Chinese mitten crab (Eriocheir sinensis) survives and thrives in different and even introduced habitats, thereby indicating its high phenotypic plasticity. However, the underpinnings of the high plasticity of E. sinensis have not been comprehensively investigated. In this study, we conducted an integrated gut microbiome and muscle metabolome analysis on E. sinensis collected from three different environments, namely, an artificial pond, Yangcheng Lake, and Yangtze River, to uncover the mechanism of its high phenotypic plasticity. Our study presents three divergent gut microbiotas and muscle metabolic profiles that corresponded to the three environments. The composition and diversity of the core gut microbiota (Proteobacteria, Bacteroidetes, Tenericutes, and Firmicutes) varied among the different environments while the metabolites associated with amino acids, fatty acids, and terpene compounds displayed significantly different concentration levels. The results revealed that the gut microbiome community and muscle metabolome were significantly affected by the habitat environments. Our findings indicate the high phenotypic plasticity in terms of gut microbiome and muscle metabolome of E. sinensis when it faces environmental changes, which would also facilitate its acclimation and adaptation to diverse and even introduced environments.

Elevated temperature and toxic Microcystis reduce Daphnia fitness and modulate gut microbiota

The gut microbiota has been increasingly recognized to regulate host fitness, which in turn is dependent on stability of community structure and composition. Many biotic and abiotic factors have been demonstrated to shape gut microbiota of cladocerans. However, the interactive effects of these variables on cladocerans fitness due to alteration of gut microbiota and their linkage with life history parameters are poorly understood. Here, we investigated the responses of Daphnia magna gut microbiota to the combined effects of toxic Microcystis aeruginosa and high temperature and its associations with fitness. We found that under good food regime, the temperature has no effect on the composition of the gut microbiota, whereas under high proportion of toxic M. aeruginosa and high temperature conditions, D. magna lost their symbionts. High proportion of toxic M. aeruginosa and high temperature had synergistically negative effects on D. magna performance due to altered gut microbiota. The high abundance of symbiotic Comamonadaceae and good food increased D. magna fitness. The present study illustrates that understanding life history strategies in response to multiple stressors related to changes in the gut microbiota diversity and composition requires integrated approaches that incorporate multiple linked traits and tether them to one another.

Unique niche-specific adaptation of fructophilic lactic acid bacteria and proposal of three Apilactobacillus species as novel members of the group

BACKGROUND

Fructophilic lactic acid bacteria (FLAB) found in D-fructose rich niches prefer D-fructose over D-glucose as a growth substrate. They need electron acceptors for growth on D-glucose. The organisms share carbohydrate metabolic properties. Fructobacillus spp., Apilactobacillus kunkeei, and Apilactobacillus apinorum are members of this unique group. Here we studied the fructophilic characteristics of recently described species Apilactobacillus micheneri, Apilactobacillus quenuiae, and Apilactobacillus timberlakei.

RESULTS

The three species prefer D-fructose over D-glucose and only metabolize D-glucose in the presence of electron acceptors. The genomic characteristics of the three species, i.e. small genomes and thus a low number of coding DNA sequences, few genes involved in carbohydrate transport and metabolism, and partial deletion of adhE gene, are characteristic of FLAB. The three species thus are novel members of FLAB. Reduction of genes involved in carbohydrate transport and metabolism in accordance with reduction of genome size were the common characteristics of the family Lactobacillaceae, but FLAB markedly reduced the gene numbers more than other species in the family. Pan-genome analysis of genes involved in metabolism displayed a lack of specific carbohydrate metabolic pathways in FLAB, leading to a unique cluster separation.

CONCLUSIONS

The present study expanded FLAB group. Fructose-rich environments have induced similar evolution in phylogenetically distant FLAB species. These are examples of convergent evolution of LAB.

Ecological and toxicological assessments of anthropogenic contaminants based on environmental metabolomics

There has long been a great concern with growing anthropogenic contaminants and their ecological and toxicological effects on living organisms and the surrounding environment for decades. Metabolomics, a functional readout of cellular activity, can capture organismal responses to various contaminant-related stressors, acquiring direct signatures to illustrate the environmental behaviours of anthropogenic contaminants better. This review entails the application of metabolomics to profile metabolic responses of environmental organisms, e.g. animals (rodents, fish, crustacean and earthworms) and microorganisms (bacteria, yeast and microalgae) to different anthropogenic contaminants, including heavy metals, nanomaterials, pesticides, pharmaceutical and personal products, persistent organic pollutants, and assesses their ecotoxicological impacts with regard to literature published in the recent five years. Contaminant-induced metabolism alteration and up/down-regulation of metabolic pathways are revealed in typical organisms. The obtained insights of variations in global metabolism provide a distinct understanding of how anthropogenic contaminants exert influences on specific metabolic pathways on living organisms. Thus with a novel ecotechnique of environmental metabolomics, risk assessments of anthropogenic contaminants are profoundly demonstrated.

Insects' potential: Understanding the functional role of their gut microbiome

The study of insect-associated microbial communities is a field of great importance in agriculture, principally because of the role insects play as pests. In addition, there is a recent focus on the potential of the insect gut microbiome in areas such as biotechnology, given some microorganisms produce molecules with biotechnological and industrial applications, and also in biomedicine, since some bacteria and fungi are a reservoir of antibiotic resistance genes (ARGs). To date, most studies aiming to characterize the role of the gut microbiome of insects have been based on high-throughput sequencing of the 16S rRNA gene and/or metagenomics. However, recently functional approaches such as metatranscriptomics, metaproteomics and metabolomics have also been employed. Besides providing knowledge about the taxonomic distribution of microbial populations, these techniques also reveal their functional and metabolic capabilities. This information is essential to gain a better understanding of the role played by microbes comprising the microbial communities in their hosts, as well as to indicate their possible exploitation. This review provides an overview of how far we have come in characterizing insect gut functionality through omics, as well as the challenges and future perspectives in this field.

The direct and indirect effects of environmental toxicants on the health of bumblebees and their microbiomes

Bumblebees (Bombus spp.) are important and widespread insect pollinators, but the act of foraging on flowers can expose them to harmful pesticides and chemicals such as oxidizers and heavy metals. How these compounds directly influence bee survival and indirectly affect bee health via the gut microbiome is largely unknown. As toxicants in floral nectar and pollen take many forms, we explored the genomes of bee-associated microbes for their potential to detoxify cadmium, copper, selenate, the neonicotinoid pesticide imidacloprid, and hydrogen peroxide-which have all been identified in floral nectar and pollen. We then exposed Bombus impatiens workers to varying concentrations of these chemicals via their diet and assayed direct effects on bee survival. Using field-realistic doses, we further explored the indirect effects on bee microbiomes. We found multiple putative genes in core gut microbes that may aid in detoxifying harmful chemicals. We also found that while the chemicals are largely toxic at levels within and above field-realistic concentrations, the field-realistic concentrations-except for imidacloprid-altered the composition of the bee microbiome, potentially causing gut dysbiosis. Overall, our study shows that chemicals found in floral nectar and pollen can cause bee mortality, and likely have indirect, deleterious effects on bee health via their influence on the bee microbiome.

Mechanism of the different metabolome responses between Plutella xylostella and Pieris rapae treated with the diamide insecticides

Diamide insecticides, such as chlorantraniliprole, cyantraniliprole, and tetrachlorantraniliprole, are a new class of insecticides that selectively target insects by affecting calcium homeostasis. While this class of insecticides are effective on a wide range of insect pests, the toxicities of diamide insecticides vary among species and life stages. In this study, we addressed the mechanism underlying the different responses of Plutella xylostella and Pieris rapae to diamide insecticides. The susceptibility to insecticides of P. xylostella and P. rapae larvae was assessed 2 and 4 days after exposure to chlorantraniliprole, cyantraniliprole, and tetrachlorantraniliprole. P. xylostella larvae treated with distilled water (Group A), chlorantraniliprole (Group B), cyantraniliprole (Group C), and tetrachlorantraniliprole (Group D) and P. rapae larvae treated with distilled water (Group E), chlorantraniliprole (Group F), cyantraniliprole (Group G) and tetrachlorantraniliprole (Group H) were subjected to metabolomics analysis. The differential metabolites in the B vs. F, C vs. G, and D vs. H groups were analyzed, followed by pathway enrichment analysis. Chlorantraniliprole, cyantraniliprole, and tetrachlorantraniliprole all showed high toxicities for P. xylostella and P. rapae larvae. P. rapae larvae were more sensitive to the diamide insecticides than P. xylostella larvae. There were 65 overlapped differential metabolites between P. xylostella and P. rapae larvae treated with these three diamide insecticides. Pathway analysis showed that the differential metabolites were closely related with fatty acid biosynthesis and metabolism-related pathways. The differential regulation of fatty acid biosynthesis and metabolism may contribute to the different response to diamide insecticides in P. xylostella and P. rapae.

Pollutants and Their Interaction with Diseases of Social Hymenoptera

Many insect species, including social insects, are currently declining in abundance and diversity. Pollutants such as pesticides, heavy metals, or airborne fine particulate matter from agricultural and industrial sources are among the factors driving this decline. While these pollutants can have direct detrimental effects, they can also result in negative interactive effects when social insects are simultaneously exposed to multiple stressors. For example, sublethal effects of pollutants can increase the disease susceptibility of social insects, and thereby jeopardize their survival. Here we review how pesticides, heavy metals, or airborne fine particulate matter interact with social insect physiology and especially the insects’ immune system. We then give an overview of the current knowledge of the interactive effects of these pollutants with pathogens or parasites. While the effects of pesticide exposure on social insects and their interactions with pathogens have been relatively well studied, the effects of other pollutants, such as heavy metals in soil or fine particulate matter from combustion, vehicular transport, agriculture, and coal mining are still largely unknown. We therefore provide an overview of urgently needed knowledge in order to mitigate the decline of social insects.