Draft genome sequences of Enterobacter sp. isolate Ag1 from the midgut of the malaria mosquito Anopheles gambiae

Enterobacter sp. AA26 as a Protein Source in the Larval Diet of Drosophila suzukii

The Spotted-Wing Drosophila fly, Drosophila suzukii, is an invasive pest species infesting major agricultural soft fruits. Drosophila suzukii management is currently based on insecticide applications that bear major concerns regarding their efficiency, safety and environmental sustainability. The sterile insect technique (SIT) is an efficient and friendly to the environment pest control method that has been suggested for the D. suzukii population control. Successful SIT applications require mass-rearing of the strain to produce competitive and of high biological quality males that will be sterilized and consequently released in the wild. Recent studies have suggested that insect gut symbionts can be used as a protein source for Ceratitis capitata larval diet and replace the expensive brewer's yeast. In this study, we exploited Enterobacter sp. AA26 as partial and full replacement of inactive brewer's yeast in the D. suzukii larval diet and assessed several fitness parameters. Enterobacter sp. AA26 dry biomass proved to be an inadequate nutritional source in the absence of brewer's yeast and resulted in significant decrease in pupal weight, survival under food and water starvation, fecundity, and adult recovery.

Trained Immunity in Anopheles gambiae: Antibacterial Immunity Is Enhanced by Priming via Sugar Meal Supplemented With a Single Gut Symbiotic Bacterial Strain

Mosquitoes have evolved an effective innate immune system. The mosquito gut accommodates various microbes, which play a crucial role in shaping the mosquito immune system during evolution. The resident bacteria in the gut microbiota play an essential role in priming basal immunity. In this study, we show that antibacterial immunity in Anopheles gambiae can be enhanced by priming via a sugar meal supplemented with bacteria. Serratia fonticola S1 and Enterobacter sp. Ag1 are gut bacteria in mosquitoes. The intrathoracic injection of the two bacteria can result in an acute hemocoelic infection in the naïve mosquitoes with mortality of ∼40% at 24 h post-infection. However, the Enterobacter orSerratia primed mosquitoes showed a better 24 h survival upon the bacterial challenge. The priming confers the protection with a certain degree of specificity, the Enterobacter primed mosquitoes had a better survival upon the Enterobacter but not Serratia challenge, and the Serratia primed mosquitoes had a better survival upon the Serratia but not Enterobacter challenge. To understand the priming-mediated immune enhancement, the transcriptomes were characterized in the mosquitoes of priming as well as priming plus challenges. The RNA-seq was conducted to profile 10 transcriptomes including three samples of priming conditions (native microbiota, Serratia priming, and Enterobacter priming), six samples of priming plus challenges with the two bacteria, and one sample of injury control. The three priming regimes resulted in distinctive transcriptomic profiles with about 60% of genes affected by both bacteria. Upon challenges, different primed mosquitoes displayed different transcriptomic patterns in response to different bacteria. When a primed cohort was challenged with a heterogenous bacterium, more responsive genes were observed than when challenged with a homogenous bacterium. As expected, many canonical immune genes were responsive to the priming and challenge, but much more non-immune genes with various functions were also responsive in the contexts, which implies that the prior priming triggers a delicately coordinated systemic regulation that results in an enhanced immunity against the subsequent challenge. Besides the participation of typical immune pathways, the transcriptome data suggest the involvement of lysosome and metabolism in the context. Overall, this study demonstrated a trained immunity via priming with bacteria in diet.

Coculturing of Mosquito-Microbiome Bacteria Promotes Heme Degradation in Elizabethkingia anophelis

Anopheles mosquito microbiomes are intriguing ecological niches. Within the gut, microbes adapt to oxidative stress due to heme and iron after blood meals. Although metagenomic sequencing has illuminated spatial and temporal fluxes of microbiome populations, limited data exist on microbial growth dynamics. Here, we analyze growth interactions between a dominant microbiome species, Elizabethkingia anophelis, and other Anopheles-associated bacteria. We find E. anophelis inhibits a Pseudomonas sp. via an antimicrobial-independent mechanism and observe biliverdins, heme degradation products, upregulated in cocultures. Purification and characterization of E. anophelis HemS demonstrates heme degradation, and we observe hemS expression is upregulated when cocultured with Pseudomonas sp. This study reveals a competitive microbial interaction between mosquito-associated bacteria and characterizes the stimulation of heme degradation in E. anophelis when grown with Pseudomonas sp.

Transstadial immune activation in a mosquito: Adults that emerge from infected larvae have stronger antibacterial activity in their hemocoel yet increased susceptibility to malaria infection

Larval and adult mosquitoes mount immune responses against pathogens that invade their hemocoel. Although it has been suggested that a correlation exists between immune processes across insect life stages, the influence that an infection in the hemocoel of a larva has on the immune system of the eclosed adult remains unknown. Here, we used Anopheles gambiae to test whether a larval infection influences the adult response to a subsequent bacterial or malaria parasite infection. We found that for both female and male mosquitoes, a larval infection enhances the efficiency of bacterial clearance following a secondary infection in the hemocoel of adults. The adults that emerge from infected larvae have more hemocytes than adults that emerge from naive or injured larvae, and individual hemocytes have greater phagocytic activity. Furthermore, mRNA abundance of immune genes-such as cecropin A, Lysozyme C1, Stat-A, and Tep1-is higher in adults that emerge from infected larvae. A larval infection, however, does not have a meaningful effect on the probability that female adults will survive a systemic bacterial infection, and increases the susceptibility of females to Plasmodium yoelii, as measured by oocyst prevalence and intensity in the midgut. Finally, immune proficiency varies by sex; females exhibit increased bacterial killing, have twice as many hemocytes, and more highly express immune genes. Together, these results show that a larval hemocoelic infection induces transstadial immune activation-possibly via transstadial immune priming-but that it confers both costs and benefits to the emerged adults.

Anopheles gambiae larvae mount stronger immune responses against bacterial infection than adults: evidence of adaptive decoupling in mosquitoes

BACKGROUND

The immune system of adult mosquitoes has received significant attention because of the ability of females to vector disease-causing pathogens while ingesting blood meals. However, few studies have focused on the immune system of larvae, which, we hypothesize, is highly robust due to the high density and diversity of microorganisms that larvae encounter in their aquatic environments and the strong selection pressures at work in the larval stage to ensure survival to reproductive maturity. Here, we surveyed a broad range of cellular and humoral immune parameters in larvae of the malaria mosquito, Anopheles gambiae, and compared their potency to that of newly-emerged adults and older adults.

RESULTS

We found that larvae kill bacteria in their hemocoel with equal or greater efficiency compared to newly-emerged adults, and that antibacterial ability declines further with adult age, indicative of senescence. This phenotype correlates with more circulating hemocytes and a differing spatial arrangement of sessile hemocytes in larvae relative to adults, as well as with the individual hemocytes of adults carrying a greater phagocytic burden. The hemolymph of larvae also possesses markedly stronger antibacterial lytic and melanization activity than the hemolymph of adults. Finally, infection induces a stronger transcriptional upregulation of immunity genes in larvae than in adults, including differences in the immunity genes that are regulated.

CONCLUSIONS

These results demonstrate that immunity is strongest in larvae and declines after metamorphosis and with adult age, and suggest that adaptive decoupling, or the independent evolution of larval and adult traits made possible by metamorphosis, has occurred in the mosquito lineage.

The impact of metagenomic interplay on the mosquito redox homeostasis

Mosquitoes are exposed to oxidative challenges throughout their life cycle. The primary challenge comes from a blood meal. The blood digestion turns the midgut into an oxidative environment, which imposes pressure not only on mosquito fecundity and other physiological traits but also on the microbiota in the midgut. During evolution, mosquitoes have developed numerous oxidative defense mechanisms to maintain redox homeostasis in the midgut. In addition to antioxidants, SOD, catalase, and glutathione system, sufficient supply of the reducing agent, NADPH, is vital for a successful defense against oxidative stress. Increasing evidence indicates that in response to oxidative stress, cells reconfigure metabolic pathways to increase the generation of NADPH through NADP-reducing networks including the pentose phosphate pathway and others. The microbial homeostasis is critical for the functional contributions to various host phenotypes. The symbiotic microbiota is regulated largely by the Duox-ROS pathway in Drosophila. In mosquitoes, Duox-ROS pathway, heme-mediated signaling, antimicrobial peptide production and C-type lectins work in concert to maintain the dynamic microbial community in the midgut. Microbial mechanisms against oxidative stress in this context are not well understood. Emerging evidence that microbial metabolites trigger host oxidative response warrants further study on the metagenomic interplay in an oxidative environment like mosquito gut ecosystem. Besides the classical Drosophila model, hematophagous insects like mosquitoes provide an alternative model system to study redox homeostasis in a symbiotic metagenomic context.

TIR-only protein RBA1 recognizes a pathogen effector to regulate cell death in Arabidopsis

Detection of pathogens by plants is mediated by intracellular nucleotide-binding site leucine-rich repeat (NLR) receptor proteins. NLR proteins are defined by their stereotypical multidomain structure: an N-terminal Toll-interleukin receptor (TIR) or coiled-coil (CC) domain, a central nucleotide-binding (NB) domain, and a C-terminal leucine-rich repeat (LRR). The plant innate immune system contains a limited NLR repertoire that functions to recognize all potential pathogens. We isolated Response to the bacterial type III effector protein HopBA1 (RBA1), a gene that encodes a TIR-only protein lacking all other canonical NLR domains. RBA1 is sufficient to trigger cell death in response to HopBA1. We generated a crystal structure for HopBA1 and found that it has similarity to a class of proteins that includes esterases, the heme-binding protein ChaN, and an uncharacterized domain of Pasteurella multocida toxin. Self-association, coimmunoprecipitation with HopBA1, and function of RBA1 require two previously identified TIR-TIR dimerization interfaces. Although previously described as distinct in other TIR proteins, in RBA1 neither of these interfaces is sufficient when the other is disrupted. These data suggest that oligomerization of RBA1 is required for function. Our identification of RBA1 demonstrates that "truncated" NLRs can function as pathogen sensors, expanding our understanding of both receptor architecture and the mechanism of activation in the plant immune system.

Diversity of bacteriome associated with Phlebotomus chinensis (Diptera: Psychodidae) sand flies in two wild populations from China

Sand fly Phlebotomus chinensis is a primary vector of transmission of visceral leishmaniasis in China. The sand flies have adapted to various ecological niches in distinct ecosystems. Characterization of the microbial structure and function will greatly facilitate the understanding of the sand fly ecology, which would provide critical information for developing intervention strategy for sand fly control. In this study we compared the bacterial composition between two populations of Ph. chinensis from Henan and Sichuan, China. The phylotypes were taxonomically assigned to 29 genera of 19 families in 9 classes of 5 phyla. The core bacteria include Pseudomonas and enterobacteria, both are shared in the sand flies in the two regions. Interestingly, the endosymbionts Wolbachia and Rickettsia were detected only in Henan, while the Rickettsiella and Diplorickettsia only in Sichuan. The intracellular bacteria Rickettsia, Rickettsiella and Diplorickettsia were reported for the first time in sand flies. The influence of sex and feeding status on the microbial structure was also detected in the two populations. The findings suggest that the ecological diversity of sand fly in Sichuan and Henan may contribute to shaping the structure of associated microbiota. The structural classification paves the way to function characterization of the sand fly associated microbiome.

The reproductive tracts of two malaria vectors are populated by a core microbiome and by gender- and swarm-enriched microbial biomarkers

Microbes play key roles in shaping the physiology of insects and can influence behavior, reproduction and susceptibility to pathogens. In Sub-Saharan Africa, two major malaria vectors, Anopheles gambiae and An. coluzzii, breed in distinct larval habitats characterized by different microorganisms that might affect their adult physiology and possibly Plasmodium transmission. We analyzed the reproductive microbiomes of male and female An. gambiae and An. coluzzii couples collected from natural mating swarms in Burkina Faso. 16S rRNA sequencing on dissected tissues revealed that the reproductive tracts harbor a complex microbiome characterized by a large core group of bacteria shared by both species and all reproductive tissues. Interestingly, we detected a significant enrichment of several gender-associated microbial biomarkers in specific tissues, and surprisingly, similar classes of bacteria in males captured from one mating swarm, suggesting that these males originated from the same larval breeding site. Finally, we identified several endosymbiotic bacteria, including Spiroplasma, which have the ability to manipulate insect reproductive success. Our study provides a comprehensive analysis of the reproductive microbiome of important human disease vectors, and identifies a panel of core and endosymbiotic bacteria that can be potentially exploited to interfere with the transmission of malaria parasites by the Anopheles mosquito.

The waaL gene mutation compromised the inhabitation of Enterobacter sp. Ag1 in the mosquito gut environment

BACKGROUND

The mosquito gut harbors a variety of bacteria that are dynamically associated with mosquitoes in various contexts. However, little is known about bacterial factors that affect bacterial inhabitation in the gut microbial community. Enterobacter sp. Ag1 is a predominant Gram negative bacterium in the mosquito midgut.

METHODS

In a mutant library that was generated using transposon Tn5-mediated mutagenesis, a mutant was identified, in which the gene waaL was disrupted by the Tn5 insertion. The waaL encodes O antigen ligase, which is required for the attachment of O antigen to the outer core oligosaccharide of the lipopolysaccharide (LPS).

RESULTS

The waaL(-) mutation caused the O antigen repeat missing in the LPS. The normal LPS structure was restored when the mutant was complemented with a plasmid containing waaL gene. The waaL(-) mutation did not affect bacterial proliferation in LB culture, the mutant cells grew at a rate the same as the wildtype (wt) cells. However, when waaL(-) strain were co-cultured with the wt strain or complemented strain, the mutant cells proliferated with a slower rate, indicating that the mutants were less competitive than wt cells in a community setting. Similarly, in a co-feeding assay, when fluorescently tagged wt strain and waaL(-) strain were orally co-introduced into the gut of Anopheles stephensi mosquitoes, the mutant cells were less prevalent in both sugar-fed and blood-fed guts. The data suggest that the mutation compromised the bacterial inhabitation in the gut community. Besides, the mutant was more sensitive to oxidative stress, demonstrated by lower survival rate upon exposure to 20 mM H₂O₂.

CONCLUSION

Lack of the O antigen structure in LPS of Enterobacter compromised the effective growth in co-culture and co-feeding assays. In addition, O-antigen was involved in protection against oxidative stress. The findings suggest that intact LPS is crucial for the bacteria to steadily stay in the gut microbial community.

Draft Genome Sequences of Two Strains of Serratia spp. from the Midgut of the Malaria Mosquito Anopheles gambiae

Here, we report the annotated draft genome sequences of two strains of Serratia spp., Ag1 and Ag2, isolated from the midgut of two different strains of Anopheles gambiae. The genomes of these two strains are almost identical.

Bacterial antimicrobial metal ion resistance

Metals such as mercury, arsenic, copper and silver have been used in various forms as antimicrobials for thousands of years with until recently, little understanding of their mode of action. The discovery of antibiotics and new organic antimicrobial compounds during the twentieth century saw a general decline in the clinical use of antimicrobial metal compounds, with the exception of the rediscovery of the use of silver for burns treatments and niche uses for other metal compounds. Antibiotics and new antimicrobials were regarded as being safer for the patient and more effective than the metal-based compounds they supplanted. Bacterial metal ion resistances were first discovered in the second half of the twentieth century. The detailed mechanisms of resistance have now been characterized in a wide range of bacteria. As the use of antimicrobial metals is limited, it is legitimate to ask: are antimicrobial metal resistances in pathogenic and commensal bacteria important now? This review details the new, rediscovered and 'never went away' uses of antimicrobial metals; examines the prevalence and linkage of antimicrobial metal resistance genes to other antimicrobial resistance genes; and examines the evidence for horizontal transfer of these genes between bacteria. Finally, we discuss the possible implications of the widespread dissemination of these resistances on re-emergent uses of antimicrobial metals and how this could impact upon the antibiotic resistance problem.

Tissue signatures influence the activation of intrahepatic CD8(+) T cells against malaria sporozoites

Plasmodium sporozoites and liver stages express antigens that are targeted to the MHC-Class I antigen-processing pathway. After the introduction of Plasmodium sporozoites by Anopheles mosquitoes, bone marrow-derived dendritic cells in skin-draining lymph nodes are the first cells to cross-present parasite antigens and elicit specific CD8⁺ T cells. One of these antigens is the immunodominant circumsporozoite protein (CSP). The CD8⁺ T cell-mediated protective immune response against CSP is dependent on the interleukin loop involving IL-4 receptor expression on CD8⁺ cells and IL-4 secretion by CD4⁺ T cell helpers. In a few days, these CD8⁺ T cells re-circulate to secondary lymphoid organs and the liver. In the liver, the hepatic sinusoids are enriched with cells, such as dendritic, sinusoidal endothelial and Kupffer cells, that are able to cross-present MHC class I antigens to intrahepatic CD8⁺ T cells. Specific CD8⁺ T cells actively find infected hepatocytes and target intra-cellular parasites through mechanisms that are both interferon-γ-dependent and -independent. Immunity is mediated by CD8⁺ T effector or effector-memory cells and, when present in high numbers, these cells can provide sterilizing immunity. Human vaccination trials with recombinant formulations or attenuated sporozoites have yet to achieve the high numbers of specific effector T cells that are required for sterilizing immunity. In spite of the limited number of specific CD8⁺ T cells, attenuated sporozoites provided multiple times by the endovenous route provided a high degree of protective immunity. These observations highlight that CD8⁺ T cells may be useful for improving antibody-mediated protective immunity to pre-erythrocytic stages of malaria parasites.

Insights from the genome annotation of Elizabethkingia anophelis from the malaria vector Anopheles gambiae

Elizabethkingia anophelis is a dominant bacterial species in the gut ecosystem of the malaria vector mosquito Anopheles gambiae. We recently sequenced the genomes of two strains of E. anophelis, R26^T and Ag1, isolated from different strains of A. gambiae. The two bacterial strains are identical with a few exceptions. Phylogenetically, Elizabethkingia is closer to Chryseobacterium and Riemerella than to Flavobacterium. In line with other Bacteroidetes known to utilize various polymers in their ecological niches, the E. anophelis genome contains numerous TonB dependent transporters with various substrate specificities. In addition, several genes belonging to the polysaccharide utilization system and the glycoside hydrolase family were identified that could potentially be of benefit for the mosquito carbohydrate metabolism. In agreement with previous reports of broad antibiotic resistance in E. anophelis, a large number of genes encoding efflux pumps and β-lactamases are present in the genome. The component genes of resistance-nodulation-division type efflux pumps were found to be syntenic and conserved in different taxa of Bacteroidetes. The bacterium also displays hemolytic activity and encodes several hemolysins that may participate in the digestion of erythrocytes in the mosquito gut. At the same time, the OxyR regulon and antioxidant genes could provide defense against the oxidative stress that is associated with blood digestion. The genome annotation and comparative genomic analysis revealed functional characteristics associated with the symbiotic relationship with the mosquito host.

Draft Genome Sequences of Elizabethkingia anophelis Strains R26T and Ag1 from the Midgut of the Malaria Mosquito Anopheles gambiae

Elizabethkingia anophelis is a species in the family Flavobacteriaceae. It is a dominant resident in the mosquito gut and also a human pathogen. We present the draft genome sequences of two strains of E. anophelis, R26^T and Ag1, which were isolated from the midgut of the malaria mosquito Anopheles gambiae.

Genome sequences published outside of Standards in Genomic Sciences, October - November 2012

The purpose of this table is to provide the community with a citable record of publications of ongoing genome sequencing projects that have led to a publication in the scientific literature. While our goal is to make the list complete, there is no guarantee that we may have omitted one or more publications appearing in this time frame. Readers and authors who wish to have publications added to subsequent versions of this list are invited to provide the bibliographic data for such references to the SIGS editorial office.

Genome sequences published outside of Standards in Genomic Sciences, July - October 2012

The purpose of this table is to provide the community with a citable record of publications of ongoing genome sequencing projects that have led to a publication in the scientific literature. While our goal is to make the list complete, there is no guarantee that we may have omitted one or more publications appearing in this time frame. Readers and authors who wish to have publications added to subsequent versions of this list are invited to provide the bibliographic data for such references to the SIGS editorial office.