Chironomid microbiome

Vibrio cholerae O1 Inhabit Intestines and Spleens of Fish in Aquaculture Ponds

Vibrio cholerae is the causative agent of cholera, an acute diarrheal disease that spreads locally and globally in epidemics and pandemics. Although it was discovered that fish harbor V. cholerae strains in their intestines, most investigations revealed non-toxic V. cholerae serogroups in fish. Due to the rarity of toxigenic V. cholerae serogroups, it is difficult to cultivate these strains from environmental samples. Hence, here we aimed to uncover evidence of the occurrence of toxigenic V. cholerae in the intestines and spleens of various fish species. By using molecular detection tools, we show that V. cholerae O1 and strains positive for the cholera toxin inhabit both healthy and diseased fish intestines and spleens, suggesting that fish may serve as intermediate vectors of toxigenic V. cholerae. No significant differences were found between the abundance of toxigenic V. cholerae (either O1 or cholera toxin positive strains) in the healthy and the diseased fish intestines or spleens. In conclusion, a variety of fish species may serve as potential vectors and reservoirs of toxigenic V. cholerae as they form a link between the other reservoirs of V. cholerae (chironomids, copepods, and waterbirds). Similarly, they may aid in the spread of this bacterium between water bodies.

Chironomus riparius Larval Gut Bacteriobiota and Its Potential in Microplastic Degradation

Chironomus riparius are sediment-dwelling invertebrates in freshwater ecosystems and are used as indicators of environmental pollution. Their habitat is threatened by high levels of contaminants such as microplastics and organic matter. A promising strategy for the eco-friendly degradation of pollutants is the use of bacteria and their enzymatic activity. The aim of this study was to characterize for the first time bacteriobiota associated with the gut of C. riparius larvae from nature and laboratory samples, to compare it with sediment and food as potential sources of gut microbiota, and to assess its ability to degrade cellulose, proteins, and three different types of microplastics (polyethylene, polyvinyl chloride, and polyamide). The metabarcoding approach highlighted Proteobacteria, Firmicutes, Bacteroidota, and Actinobacteriota as most abundant in both gut samples. Culturable microbiota analysis revealed Metabacillus idriensis, Peribacillus simplex, Neobacillus cucumis, Bacillus thuringiensis/toyonensis, and Fictibacillus phosphorivorans as five common species for nature and laboratory samples. Two P. simplex and one P. frigoritolerans isolates showed the ability for intensive growth on polyethylene, polyvinyl chloride, and polyamide. Both cellulolytic and proteolytic activity was observed for Paenibacillus xylanexedens and P. amylolyticus isolates. The characterized strains are promising candidates for the development of environmentally friendly strategies to degrade organic pollution and microplastics in freshwater ecosystems.

Magnetized vermiculite as a tool for the treatment of produced water generated by oil companies: Effects on aquatic organisms before and after treatment

Produced water (PW) generated by oil companies is a highly impacting waste that contains chemicals such as metals and organic and inorganic compounds. Given its polluting potential, PW requires effective treatment before being discharged into the environment. Conventional treatments have limited efficiency in removing PW toxicity, so alternative approaches must be developed and standardized. In this context, treatment with adsorbent materials like magnetized vermiculite (VMT-mag) is highlighted. This work aimed to evaluate the efficiency of treatment with VMT-mag in reducing PW toxicity to aquatic biota. For this purpose, three aquatic species (the midge Chironomus riparius, the planarian Girardia tigrina, and the crustacean Daphnia magna) were exposed to untreated PW and to PW treated with VMT-mag at laboratory conditions. The assessed endpoints included mortality, growth, emergence, and developmental time of C. riparius; mortality, locomotion, feeding, and head regeneration of G. tigrina; and intrinsic population growth rate (r) and reproductive output of D. magna. The results showed that all the species exposed to raw PW were impaired: C. riparius had delayed development, G. tigrina had reduced locomotor activity and delayed head regeneration, and D. magna had reduced reproduction and delayed intrinsic population growth rate (r). Most of the analyzed parameters showed that treatment with VMT-mag diminished PW toxicity. Therefore, using VMT-mag to treat PW may be the key to reducing the PW effects on aquatic organisms.

Compositional Dynamics of Gastrointestinal Tract Microbiomes Associated with Dietary Transition and Feeding Cessation in Lake Sturgeon Larvae

Compromised nutritional conditions associated with dietary transitions and feeding cessation in the wild and during fish aquaculture operations are common and can impact growth and survival. These effects are especially prevalent during early ontogenetic stages. We quantified phenotypic and GI tract microbial community responses with an emphasis on protease-producing bacteria of lake sturgeon (Acipenser fulvescens) larvae, a species of aquacultural and conservational importance. To quantify responses associated with experimental food transition and feeding cessation, we performed a 36-day feeding experiment using two treatments: control and diet transition. However, larvae in the diet transition treatment failed to undergo transition and ceased feeding. Larvae in the diet transition treatment exhibited lower growth (total length and body weight) and survival than control larvae. Treatment had a greater effect than ontogenetic changes on taxonomic composition and diversity of the GI tract microbial community. Proteobacteria dominated the GI tract microbial community of the diet transition larvae whereas Firmicutes dominated the GI tracts of control larvae. Most of the 98 identified protease-producing isolates in both treatments were from genera Pseudomonas and Aeromonas: taxonomic groups that include known fish pathogens. Overall, failing to transition diets affected responses in growth and GI tract microbiome composition and diversity, with the later dysbiosis being an indicator of morbidity and mortality in larval lake sturgeon. Thus, microbiological interrogations can characterize responses to dietary regimes. The results can inform fish culturalists and microbiologists of the importance of dietary practices consistent with the establishment and maintenance of healthy GI tract microbiota and optimal growth during early ontogeny.

Accumulation of nylon microplastics and polybrominated diphenyl ethers and effects on gut microbial community of Chironomus sancticaroli

Microplastics (MP) are emerging contaminants with the capacity to bind and transport hydrophobic organic compounds of environmental concern, such as polybrominated diphenyl ethers (PBDEs). The aim of this study was to investigate the ingestion of nylon (polyamide) MP alone and when associated with PBDEs and their effects on Chironomus sancticaroli larvae survival and microbiome structure. Survival, PBDE uptake and microbial community composition were measured in fourth instar larvae exposed for 96 h to BDEs- 47, 99, 100 and 153 in the presence and absence of 1% w/w MP in sediment. Microbiome community structures were determined through high throughput sequencing of 16S small subunit ribosomal RNA gene (16S rRNA). Initial experiments showed that larvae ingested MP faster at 0.5% w/w MP, while depuration was more efficient at 1% w/w MP, although retention of MP was seen even after 168 h depuration. No mortality was observed as a result of PBDEs and MP exposure. MP had a negative effect on PBDE concentration within larvae (η² = 0.94) and a negative effect on sediment concentrations (η² = 0.48). In all samples, microbial communities were dominated by Alphaproteobacteria, Betaproteobacteria, Actinobacteria and Gammaproteobacteria. Bacterial alpha diversity was not significantly affected by PBDEs or MP exposure. However, the abundance of discrete bacterial taxa was more sensitive to MP (X² = 45.81, p = 0.02), and PBDE exposure. Our results highlight that C. sancticaroli showed no acute response to MPs and PBDEs, but that MPs influenced bacterial microbiome structure even after only short-term acute exposure.

Beyond canonical models: why a broader understanding of Diptera-microbiota interactions is essential for vector-borne disease control

Vector-borne diseases constitute a major global public health threat. The most significant arthropod disease vectors are predominantly comprised of members of the insect order Diptera (true flies), which have long been the focus of research into host-pathogen dynamics. Recent studies have revealed the underappreciated diversity and function of dipteran-associated gut microbial communities, with important implications for dipteran physiology, ecology, and pathogen transmission. However, the effective parameterization of these aspects into epidemiological models will require a comprehensive study of microbe-dipteran interactions across vectors and related species. Here, we synthesize recent research into microbial communities associated with major families of dipteran vectors and highlight the importance of development and expansion of experimentally tractable models across Diptera towards understanding the functional roles of the gut microbiota in modulating disease transmission. We then posit why further study of these and other dipteran insects is not only essential to a comprehensive understanding of how to integrate vector-microbiota interactions into existing epidemiological frameworks, but our understanding of the ecology and evolution of animal-microbe symbiosis more broadly.

Mining the diversity and functional profile of bacterial symbionts from the larvae of Chironomus circumdatus (bloodworms)

Chironomids are the most abundant aquatic insects in freshwater habitats that can survive in extreme conditions. In this study, as the microbiome provides extended genotype to the host to perform various functions, we explored the microbiota of the Chironomus circumdatus larvae to find out the putative role played by the symbiotic bacteria for the host. The metabarcoding analyses of the larvae revealed that the insect harbors 1771 phylotypes. Out of the various microbial communities found, the majority corresponded to the phyla Proteobacteria (52.59%) and Actinobacteria (20.56%), respectively. The midges also harbored Klebsiella (2.57%), Enterobacter (1.32%), Bacillus (2.29%), and Acinetobacter (2.13%) genera that are involved in detoxification of xenobiotics present in the water. The presence of radiation-resistant genera like Deinococcus, including bacterial species like radiodurans, a highly radiation-resistant bacterium, indicates its potential to support the host's ability to sustain in adverse environments. The functional profiling of the bacteria showed the relative abundance of many enzyme groups, such as transferases (40.62%), oxidoreductases (23.49%), and hydrolases (3.77%). The results indicate that the larvae harbor a considerable variety of bacteria that help the host adapt and survive in the polluted waters. The present study provides thorough insights into the microbiome of the C. circumdatus larvae that can be exploited for the bioremediation of certain pollutants through biomimetic strategies. It also gives us a wake-up call to take a good look at the guts of these disease-carrying insects' inabilities to spread deadly human diseases.

Climate Change: Water Temperature and Invertebrate Propagation in Drinking-Water Distribution Systems, Effects, and Risk Assessment

This paper provides a summary of the knowledge of drinking-water temperature increases and present daily, seasonal, and yearly temperature data of drinking-water distribution systems (DWDS). The increasing water temperatures lead to challenges in DWDS management, and we must assume a promotion of invertebrates as pipe inhabitants. Macro-, meio-, and microinvertebrates were found in nearly all DWDS. Data in relation to diversity and abundance clearly point out a high probability of mass development, and invertebrate monitoring must be the focus of any DWDS management. The water temperature of DWDS is increasing due to climate change effects, and as a consequence, the growth and reproduction of invertebrates is increasing. The seasonal development of a chironomid (Paratanytarus grimmii) and longtime development of water lice (Asellus aquaticus) are given. Due to increased water temperatures, a third generation of water lice per year has been observed, which is one reason for the observed mass development. This leads to an impact on drinking-water quality and an increased health risk, as invertebrates can serve as a host or vehicle for potential harmful microbes. More research is needed especially on (i) water temperature monitoring in drinking-water distribution systems, (ii) invertebrate development, and (iii) health risks.

The Chironomid Microbiome Plays a Role in Protecting Its Host From Toxicants

Organisms are assemblages of the host and their endogenous bacteria, which are defined as microbiomes. The host and its microbiome undergo a mutual evolutionary process to adapt to changes in the environment. Chironomids (Diptera; Chironomidae), are aquatic insects that grow and survive in polluted environments; however, the mechanisms that protect them under these conditions are not fully understood. Here we present evidence that the chironomids’ microbiome enables them to survival in polluted environments. It has been demonstrated that about 40% of the microbiota that inhabit Chironomus transvaalensis egg masses and larvae has the potential to detoxify different toxicants. Metagenomic analysis of Chironomus ramosus larvae demonstrated the presence of genes in the insects’ microbiome that can help the insects to survive in hostile environments. A set of experiments demonstrated that short exposure of C. transvaalensis larvae to metals significantly changed their microbiota composition in comparison to unexposed larvae. Another experiment, that followed Koch’s postulates, demonstrated that disinfected C. transvaalensis larvae can survive toxic lead and chromium exposure when they are recolonized with bacteria that can detoxify these toxic metals. This accumulating research, points to the conclusion that the chironomid microbiome plays a role in protecting its host from toxicants.

Comparative Microbiota Composition Across Developmental Stages of Natural and Laboratory-Reared Chironomus circumdatus Populations From India

Chironomids are aquatic insects that undergo a complete metamorphosis of four life stages. Here we studied, for the first time, the microbiota composition of Chironomus circumdatus, a tropical midge species, both from the Mula and Mutha Rivers in Pune, India and as a laboratory-reared culture. We generated a comparative microbial profile of the eggs, larvae and pupae, the three aquatic life stages of C. circumdatus. Non-metric multidimensional scaling analysis (NMDS) demonstrated that the developmental stage had a more prominent effect on the microbiota composition compared to the sampling location. Notably, the microbiota composition of the egg masses from the different sampling points clustered together and differed from laboratory culture larvae. Proteobacteria was the dominant phylum in all the environmental and laboratory-reared egg masses and pupal samples, and in the laboratory-reared larvae, while Fusobacteria was the dominant phylum in the larvae collected from the field environment. The most abundant genera were Cetobacterium, Aeromonas, Dysgonomonas, Vibrio, and Flavobacterium. The ten amplicon sequence variants (ASVs) that most significantly contributed to differences in microbiota composition between the three sampled locations were: Burkholderiaceae (ASVs 04 and 37), C39 (Rhodocyclaceae, ASV 14), Vibrio (ASV 07), Arcobacter (ASV 21), Sphaerotilus (ASV 22), Bacteroidia (ASVs 12 and 28), Flavobacterium (ASV 29), and Gottschalkia (ASV 10). No significant differences were found in the microbial richness (Chao1) or diversity (Shannon H’) of the three sampled locations. In contrast, significant differences were found between the microbial richness of the three life stages. Studying the microbiota of this Chironomus species may contribute to a better understanding of the association of C. circumdatus and its microbial inhabitants.

Chironomus ramosus Larval Microbiome Composition Provides Evidence for the Presence of Detoxifying Enzymes

Chironomids (Diptera; Chironomidae) are aquatic insects that are abundant in freshwater. We aimed to study the endogenous microbiota composition of Chironomus ramosus larvae that were sampled from the Mutha River and a laboratory culture in India. Furthermore, we performed a metagenomic analysis of the larval microbiome, sampled from the Mutha River. Significant differences were found between the bacterial community composition of C. ramosus larvae that were sampled from the Mutha River and the laboratory culture. A total of 54.7% of the amplicon sequence variants (ASVs) that were identified in the larvae from the Mutha River were unique, compared to only 12.9% of unique ASVs that were identified from the laboratory-reared larvae. The four most abundant phyla across all samples were: Proteobacteria, Fusobacteria, Firmicutes, and Bacteroidetes, while the nine most abundant genera were: Aeromonas, Alkanindiges, Breznakia, Cetobacterium, Chryseobacterium, Desulfovibrio, Dysgonomonas, Thiothrix, and Vibrio. Moreover, in the metagenomic analysis, we detected bacterial genes and bacterial pathways that demonstrated the ability to degrade different toxic compounds, detoxify metal, and confer resistance to antibiotics and UV radiation, amongst other functions. The results illuminate the fact that there are detoxifying enzymes in the C. ramosus larval microbiome that possibly play a role in protecting the insect in polluted environments.

Copper and chromium exposure affect chironomid larval microbiota composition

Chironomids are aquatic insects that are known to be pollution tolerant. We have recently demonstrated that endogenous chironomid microbiota protects its host from toxic metals. Following these findings, we hypothesized that under different environmental conditions, a different bacterial consortium will evolve. Our aim was to explore the change in chironomid larval microbiota composition triggered by exposure to toxic copper and hexavalent chromium. Chironomid larvae were collected from the environment and treated in the laboratory with copper, hexavalent chromium, and no metal (control). After six days, the microbial composition of the surviving larvae was examined. We found a significant change in larval microbiota composition between the three treatments and for different copper concentrations. The abundance of specific taxa varied significantly between the treatments. At the genus level, the abundance of some genera (e.g. Yersinia, Acinetobacter) increased in the presence of copper, and some genera (e.g. Yersinia, Dysgonomonas, Delftia, Enterococcus) increased in the presence of hexavalent chromium, compared to the control. The change in the larval microbiota composition was rapid and metal-specific. We suggest that each larva hosts a consortium of bacterial species that can proliferate under a specific environmental change and thus, protect the insect under unstable environmental conditions.

Interspecies bacterial communication produces a delicate balance between Vibrio cholerae and the chironomid egg mass microbiome

The evolution of antimicrobial resistance in bacterial pathogens is considered by the World Health Organization to be one of the ten most concerning public health threats facing humanity (World Health Organization, 2020). Bacterial diseases previously controllable by antibiotics are resurging and treatment options are dwindling. Cholera is one such disease. Human pathogenic strains of Vibrio cholerae cause as many as 4 million cases of disease resulting in over 100,000 deaths each year (Ali et al. 2015) and multidrug-resistant V. cholerae is now established where pandemic cholera persists. Vibrio cholerae is fundamentally an aquatic species thriving in brackish and estuarial waters. Its environmental prevalence, together with both extracellular and intracellular infection of alternative arthropod and mollusc hosts, produces a highly complex ecological milieu that is not well understood. With the absence of reliable antibiotic-based treatment options, it is necessary to build a better understanding of V. cholerae biology and ecology in order to develop alternative methods for risk modelling and disease control. In this issue of Molecular Ecology, authors Sela, Hammer, and Halpern experimentally investigated a mechanism by which V. cholerae pathogenicity is affected by interspecies quorum sensing involving an array of bacterial species from the microbiome of an alternative arthropod host, the egg mass of a chironomid midge (Diptera:Chironomidae) (Sela et al. 2020). Quorum sensing is a mechanism whereby bacteria communicate with each other using autoinducers and is known to be important, for example, in shaping virulence in a variety of pathogenic bacteria. The innovative methodologies they used, both in molecular and protein biology and reductive investigative microbiomics, are helping to develop the tools needed for understanding this understudied ecological system and fighting cholera in a post-antibiotic world.

Water Lice and Other Macroinvertebrates in Drinking Water Pipes: Diversity, Abundance and Health Risk

Activities to ensure and maintain water quality in drinking water networks, including flushing, are presented after standardized hydrant sampling combined with a stainless-steel low pressure–high flow rate (NDHF) filter and a 100 µm mesh size was used to separate pipe inhabitants. A databank of more than 1000 hydrant samples in European lowland areas was developed and used to analyze the diversity and abundance of macroinvertebrates in drinking water networks. Load classes for water louse (Asellus aquaticus) and oligochaetes are given with three evaluation classes: normal colonization, increased colonization, and mass development. The response of Asellus aquaticus in drinking water networks to environmental conditions are presented as are their growth and reproduction, promotion of a third generation by climate change effects, food limitations, and the composition and stability of their feces. Finally, the health risks posed by dead water lice and water lice feces with bacterial regrowth and the promotion of microbe development on house filters are analyzed.

Multi-Level Gene Expression in Response to Environmental Stress in Aquatic Invertebrate Chironomids: Potential Applications in Water Quality Monitoring

In freshwater ecosystems, aquatic invertebrates are influenced continuously by both physical stress and xenobiotics. Chironomids (Diptera; Chironomidae), or non-biting midges, are the most diverse and abundant invertebrates in freshwater habitats. They are a fundamental link in food chains of aquatic ecosystems. Chironomid larvae tolerate stress factors in their environments via various physiological processes. At the molecular level, environmental pollutants induce multi-level gene responses in Chironomus that regulate cellular protection through the activation of defense processes. This paper reviews literature on the transcriptional responses of biomarker genes to environmental stress in chironomids at the molecular level, in studies conducted from 1991 to 2020 (120 selected literatures of 374 results with the keywords "Chironomus and gene expression" by PubMed search tool). According to these studies, transcriptional responses in chironomids vary depending on the type of stress factor and defensive responses associated with antioxidant activity, the endocrine system, detoxification, homeostasis and stress response, energy metabolism, ribosomal machinery, apoptosis, DNA repair, and epigenetics. These data could provide a comprehensive overview of how Chironomus species respond to pollutants in aquatic environments. Furthermore, the transcriptomic data could facilitate the development of genetic tools for water quality and environmental monitoring based on resident chironomid species.

Identification of chironomid species as natural reservoirs of toxigenic Vibrio cholerae strains with pandemic potential

Vibrio cholerae causes the fatal cholera diarrhea. Chironomids (Diptera; Chironomidae) are abundant in freshwater aquatic habitats and estuaries and are natural reservoirs of V. cholerae. Until now, only the non-O1/O139 serogroups of V. cholerae were identified in chironomids. Here, we explored whether chironomids are natural reservoirs of V. cholerae O1/O139 serogroups, which are associated with cholera endemics and pandemics. All four life stages of chironomids were sampled from two rivers, and a laboratory culture in Pune, India, and from a pond in Israel. In total, we analyzed 223 chironomid samples. The presence of V. cholerae O1/O139 serogroups was verified using molecular tools. Nine chironomid species were identified; of them, Chironomus circumdatus was the most abundant. The presence of V. cholerae serogroup O1 and the cholera toxin genes were detected in samples from all chironomid species. However, serogroup O139 was detected in only two chironomid species. Besides PCR to detect specific genes, a metagenomic analysis that was performed in three selected C. ramosus larvae, identified a list of virulence genes associated with V. cholerae. The findings provide evidence that chironomids are natural reservoirs of toxigenic V. cholerae O1/O139. Chironomid populations and V. cholerae show biannual peak patterns. A similar pattern is found for cholera epidemics in the Bengal Delta region. Thus, we hypothesize that monitoring chironomids in endemic areas of the disease may provide a novel tool for predicting and preventing cholera epidemics. Moreover, serogroup O139 was detected only in two chironomid species that have a restricted distribution in the Indian subcontinent, possibly explaining why the distribution of the O139 serogroup is limited.

Changes in Microbiota Composition Along the Metamorphosis Developmental Stages of Chironomus transvaalensis

Chironomids (Diptera; Chironomidae), also known as non-biting midges, are one of the most abundant insects in freshwater habitats. Our aim was to understand whether the metamorphosis developmental stages affect the endogenous microbiota composition of Chironomus transvaalensis. Toward our objective, we analyzed the endogenous microbiota composition of C. transvaalensis' four life stages: egg masses, larvae, pupae, and adults. Significant differences were found between the microbiota compositions of the different developmental stages of this Chironomus species. We observed a decline in bacterial diversity as the insect evolved from egg mass to adult, while the highest richness was observed in the pupal stage. Although there were significant differences between the microbiota compositions of each life stage, a bacterial core, which included 27 Amplicon Sequence Variants (ASVs), was found in all the developmental life stages (in ≥75% of samples). Chironomids are natural reservoirs of Vibrio cholerae and Aeromonas species, and the Vibrio and Aeromonas ASVs were part of the core bacteria. The presence of the ompW gene, which is specific to V. cholerae, confirmed the presence of this species in all the chironomid's life stages. Thus, the results provide important insights about the host-microbe interactions in chironomids with a specific understanding of chironomids-Vibrio-Aeromonas-microbiota interactions.

Quorum-sensing signaling by chironomid egg masses' microbiota, affects haemagglutinin/protease (HAP) production by Vibrio cholerae

Vibrio cholerae, the causative agent of cholera, is commonly isolated, along with other bacterial species, from chironomid insects (Diptera: Chironomidae). Nevertheless, its prevalence in the chironomid egg masses' microbiota is less than 0.5%. V. cholerae secretes haemagglutinin/protease (HAP) that degrades the gelatinous matrix of chironomid egg masses and prevents hatching. Quorum sensing (QS) activates HAP production in response to accumulation of bacterial autoinducers (AIs). Our aim was to define the impact of chironomid microbiota on HAP production by V. cholerae. To study QS signaling, we used V. cholerae bioluminescence reporter strains (QS-proficient O1 El-Tor wild-type and QS-deficient mutants) and different bacterial species that we isolated from chironomid egg masses. These egg mass isolates, as well as a synthetic AI-2, caused an enhancement in lux expression by a V. cholerae QS-deficient mutant. The addition of the egg mass bacterial isolate supernatant to the QS-deficient mutant also enhanced HAP production and egg mass degradation activities. Moreover, the V. cholerae wild-type strain was able to proliferate using egg masses as their sole carbon source, while the QS-deficient was not. The results demonstrate that members of the chironomid bacterial consortium produce external chemical cues that, like AI-2, induce expression of the hapA gene in V. cholerae. Understanding the interactions between V. cholerae and the insects' microbiota may help uncover the interactions between this pathogen and the human gut microbiota.

Seasonal dynamics of Chironomus transvaalensis populations and the microbial community composition of their egg masses

Chironomids (Diptera; Chironomidae) are the most abundant insects in freshwater environments and are considered natural reservoirs of Vibrio cholerae. We monitored the annual dynamics of chironomid populations along with their microbiota in order to better understand host–microbiota interactions. Chironomus transvaalensis populations peaked biannually in August and May–June. The composition of the endogenous bacterial communities of their egg masses clustered in two groups according to the sampling periods August–November and May–July. Nevertheless, a core bacterial community (43%) was present in all egg-mass samples. The most abundant phyla were: Proteobacteria, Firmicutes, Cyanobacteria and Bacteroidetes. The abundance of several genera (e.g. Rheinheimera and Pseudomonas) was positively correlated with C. transvaalensis population dynamics, while a predator–prey interaction was observed between the relative abundance of Vibrio OTUs and C. transvaalensis population size. Chironomids are known to tolerate toxic and stress conditions, and our results demonstrated that bacterial genera that may protect the insect under these conditions are present in the egg masses. After hatching, the first larval meal is the gelatinous matrix that surrounds the eggs. This meal contains a probiotic consortium that may protect the larva during its metamorphosis. The results provide important insights into the host–microbe interactions of chironomids.

An Examination of Flying Insects in Seven Hospitals in the United Kingdom and Carriage of Bacteria by True Flies (Diptera: Calliphoridae, Dolichopodidae, Fanniidae, Muscidae, Phoridae, Psychodidae, Sphaeroceridae)

Insects are efficient vectors of bacteria and in the hospital environment may have a role in spreading nosocomial infections. This study sampled the flying insect populations of seven hospitals in the United Kingdom and characterized the associated culturome of Diptera, including the antibiotic resistance profile of bacterial isolates. Flying insects were collected in seven U.K. hospitals between the period March 2010 to August 2011. The bacteria carried by Diptera were isolated using culture-based techniques, identified and characterized by antimicrobial susceptibility testing. A total of 19,937 individual insects were collected with Diptera being the most abundant (73.6% of the total), followed by Hemiptera (13.9%), Hymenoptera (4.7%), Lepidoptera (2.9%), and Coleoptera (2%). From Diptera, 82 bacterial strains were identified. The majority of bacteria belonged to the Enterobacteriaceae (42%), followed by Bacillus spp. (24%) and Staphylococcus spp. (19%). Less abundant were bacteria of the genus Clostridium (6%), Streptococcus (5%), and Micrococcus (2%). A total of 68 bacterial strains were characterized for their antibiotic resistance profile; 52.9% demonstrated a resistant phenotype to at least one class of antibiotic. Staphylococcus spp. represented the highest proportion of resistant strains (83.3%), followed by Bacillus spp. (60%) and Enterobacteriaceae (31.3%). Diptera were the predominant flying insects present in the U.K. hospital environments sampled and found to harbor a variety of opportunistic human pathogens with associated antimicrobial resistance profiles. Given the ability of flies to act as mechanical vectors of bacteria, they present a potential to contribute to persistence and spread of antimicrobial-resistant pathogenic bacteria in the hospital environment.

The cholera epidemic in Yemen - How did it start? The role of El Niño conditions followed by regional winds

The largest cholera epidemic of modern times began during the autumn of 2016 in Yemen, under ongoing war conditions. What exactly caused the epidemic to emerge is unclear. It is suggested that a combination of the impact of the strong El Niño of 2015-16 on cholera incidence in Somalia, followed by southwestern winds over the Gulf of Aden throughout the summer of 2016, contributed to the disease spreading through dissemination of cholera-contaminated flying insects (chironomids) from the Horn of Africa to Yemen.

Accumulating evidence suggests that some waterbird species are potential vectors of Vibrio cholerae

Vibrio cholerae is the causative agent of cholera, a life-threatening diarrheal disease. Cholera causes epidemics and pandemics, but the ways this disease spreads worldwide is still unclear. This review highlights a relatively new hypothesis regarding the way V. cholerae can be globally dispersed. Copepods and chironomids are natural reservoirs of V. cholerae and are part of different fish species’ diet. Furthermore, V. cholerae inhabits marine and freshwater fish species. Waterbird species feed on fish or on small invertebrates such as copepods and chironomids. Waterbirds have also been found to carry living copepods and/or chironomids internally or externally from one waterbody to another. All of the above points to the fact that some waterbird species might be vectors of V. cholerae. Indeed, we and others have found evidence for the presence of V. cholerae non-O1 as well as O1 in waterbird cloacal swabs, feces, and intestine samples. Moreover, hand-reared cormorants that were fed on tilapia, a fish that naturally carries V. cholerae, became infected with this bacterial species, demonstrating that V. cholerae can be transferred to cormorants from their fish prey. Great cormorants as well as other waterbird species can cover distances of up to 1,000 km/day and thus may potentially transfer V. cholerae in a short time across and between continents. We hope this review will inspire further studies regarding the understanding of the waterbirds' role in the global dissemination of V. cholerae.

Comparative Analysis of Intestine Microbiota of Four Wild Waterbird Species

Waterbirds are ubiquitous and globally distributed. Yet, studies on wild waterbirds' gut microbiota are still rare. Our aim was to explore and compare the gut microbial community composition of wild waterbird species. Four wild waterbird species that are either wintering or all-year residents in Israel were studied: great cormorants, little egrets, black-crowned night herons and black-headed gulls. For each bird, three intestinal sections were sampled; anterior, middle and posterior. No significant differences were found among the microbiota compositions in the three intestine sections of each individual bird. Each waterbird species had a unique microbial composition. The gut microbiota of the black-headed gulls' fundamentally deviated from that of the other bird species, probably due to a very high abundance (58.8%) of the genus Catellicoccus (Firmicutes). Our results suggest a correlation between the waterbird species' phylogeny and their intestine microbial community hierarchical tree, which evinced phylosymbiosis. This recent coinage stands for eco-evolutionary patterns between the host phylogeny and its microbiota composition. We conclude that eco-evolutionary processes termed phylosymbiosis may occur between wild waterbird species and their gut microbial community composition.

Microbes affected the TYLCCNV transmission rate by the Q biotype whitefly under high O3

Ozone (O3) is a major air pollutant that has a profound effect on whole ecosystems. In this study we studied how hO3 affected the transmission of the Tomato yellow leaf curl China virus (TYLCCNV), a begomovirus, by the Q biotype Bemisia tabaci in a persistent, circulative manner. We found hO3 affected the transmission of TYLCCNV via the effect of it on the microbial community of the transmitting insect, such as Candidatus Hamiltonella, Ralstonia, Diaphorobacter, Caldilineaceae, Deinococcus, Rickettsia, Thysanophora penicillioides and Wallemia ichthyophaga. We concluded that hO3 decreased the resistance of acquiring virus tomatoes, and decreased the immune response and increased the endurance to extreme environments of viruliferous whiteflies by altering the composition and abundance of the microbial environments inside the body and on the surface of whitefly, as a result, it enhanced the TYLCV transmission rate by the Q biotype whitefly.

Otitis Media Caused by V. cholerae O100: A Case Report and Review of the Literature

Infections due to Vibrio cholerae are rarely documented in Israel. Here we report a case of recurrent otitis media in a young male, caused by V. cholerae non-O1/O139. This extra-intestinal infection was caused by V. cholerae O100 and has been associated with freshwater exposure and travel. Symptoms of chronic periodic earaches along with purulent exudate began about one week after the patient suffered a water skiing accident on a river in Australia. The condition lasted for three years, until his ear exudate was examined in a clinical laboratory, diagnosed and treated. Five bacterial isolates were identified as V. cholerae O100. The isolates were screened for genetic characteristics and were found positive for the presence of hapA, hlyA, and ompU virulence genes. All isolates were negative for the presence of ctxA. Based on antibiogram susceptibility testing, ciprofloxacin ear drops were used until the patient’s symptoms disappeared. This case demonstrates that exposure to freshwater can cause otitis media by V. cholerae non-O1/O139 in young and otherwise healthy humans.

Fish as Hosts of Vibrio cholerae

Vibrio cholerae, the causative agent of pandemic cholera, is abundant in marine and freshwater environments. Copepods and chironomids are natural reservoirs of this species. However, the ways V. cholerae is globally disseminated are as yet unknown. Here we review the scientific literature that provides evidence for the possibility that some fish species may be reservoirs and vectors of V. cholerae. So far, V. cholerae has been isolated from 30 fish species (22 freshwater; 9 marine). V. cholerae O1 was reported in a few cases. In most cases V. cholerae was isolated from fish intestines, but it has also been detected in gills, skin, kidney, liver and brain tissue. In most cases the fish were healthy but in some, they were diseased. Nevertheless, Koch postulates were not applied to prove that V. cholerae and not another agent was the cause of the disease in the fish. Evidence from the literature correlates raw fish consumption or fish handling to a few cholera cases or cholera epidemics. Thus, we can conclude that V. cholerae inhabits some marine and freshwater fish species. It is possible that fish may protect the bacteria in unfavorable habitats while the bacteria may assist the fish to digest its food. Also, fish may disseminate the bacteria in the aquatic environment and may transfer it to waterbirds that consume them. Thus, fish are reservoirs of V. cholerae and may play a role in its global dissemination.

Chironomids' Relationship with Aeromonas Species

Chironomids (Diptera: Chironomidae), also known as non-biting midges, are one of the most abundant groups of insects in aquatic habitats. They undergo a complete metamorphosis of four life stages of which three are aquatic (egg, larva, and pupa), and the adult emerges into the air. Chironomids serve as a natural reservoir of Aeromonas and Vibrio cholerae species. Here, we review existing knowledge about the mutual relations between Aeromonas species and chironomids. Using 454-pyrosequencing of the 16S rRNA gene, we found that the prevalence of Aeromonas species in the insects’ egg masses and larvae was 1.6 and 3.3% of the insects’ endogenous microbiota, respectively. Aeromonas abundance per egg mass remained stable during a 6-month period of bacterial monitoring. Different Aeromonas species were isolated and some demonstrated the ability to degrade the insect’s egg masses and to prevent eggs hatching. Chitinase was identified as the enzyme responsible for the egg mass degradation. Different Aeromonas species isolated from chironomids demonstrated the potential to protect their host from toxic metals. Aeromonas is a causative agent of fish infections. Fish are frequently recorded as feeding on chironomids. Thus, fish might be infected with Aeromonas species via chironomid consumption. Aeromonas strains are also responsible for causing gastroenteritis and wound infections in humans. Different virulence genes were identified in Aeromonas species isolated from chironomids. Chironomids may infest drinking water reservoirs, hence be the source of pathogenic Aeromonas strains in drinking water. Chironomids and Aeromonas species have a complicated mutual relationship.