Cultivable bacteria associated with larval gut of prothiofos-resistant, prothiofos-susceptible and field-caught populations of diamondback moth, Plutella xylostella and their potential for, antagonism towards entomopathogenic fungi and host insect nutriti

Progress in the Study of Natural Antimicrobial Active Substances in Pseudomonas aeruginosa

The prevalence of antimicrobial resistance reduces the effectiveness of antimicrobial drugs in the prevention and treatment of infectious diseases caused by pathogens such as bacteria, fungi, and viruses. Microbial secondary metabolites have been recognized as important sources for new drug discovery and development, yielding a wide range of structurally novel and functionally diverse antimicrobial drugs for the treatment of a variety of diseases that are considered good producers of novel antimicrobial drugs. Bacteria produce a wide variety of antimicrobial compounds, and thus, antibiotics derived from natural products still dominate over purely synthetic antibiotics among the antimicrobial drugs developed and introduced over the last four decades. Among them, Pseudomonas aeruginosa secondary metabolites constitute a richly diverse source of antimicrobial substances with good antimicrobial activity. Therefore, they are regarded as an outstanding resource for finding novel bioactive compounds. The exploration of antimicrobial compounds among Pseudomonas aeruginosa metabolites plays an important role in drug development and biomedical research. Reports on the secondary metabolites of Pseudomonas aeruginosa, many of which are of pharmacological importance, hold great promise for the development of effective antimicrobial drugs against microbial infections by drug-resistant pathogens. In this review, we attempt to summarize published articles from the last twenty-five years (2000-2024) on antimicrobial secondary metabolites from Pseudomonas aeruginosa.

Functions and regulations of insect gut bacteria

The insect gut is a complicated ecosystem that inhabits a large number of symbiotic bacteria. As an important organ of the host insect, the symbiotic bacteria of the insect gut play very important roles in regulating physiological and metabolic processes. Recently, much progress has been made in the study of symbiotic bacteria in insect guts with the development of high-throughput sequencing technology and molecular biology. This review summarizes the primary functions of symbiotic bacteria in insect guts, such as enhancing insecticide resistance, facilitating food digestion, promoting detoxification, and regulating mating behavior and egg hatching. It also addresses some possible pathways of gut bacteria symbiont regulation governed by external habitats, physiological conditions and immunity of the host insect. This review provides solid foundations for further studies on novel theories, new technologies and practical applications of symbiotic bacteria in insect guts. © 2024 Society of Chemical Industry.

Comparative study of the gut microbial community structure of Spodoptera frugiperda and Spodoptera literal (Lepidoptera)

Background

Spodoptera frugiperda, the fall armyworm is a destructive invasive pest, and S. litura the tobacco cutworm, is a native species closely related to S. frugiperda. The gut microbiota plays a vital role in insect growth, development, metabolism and immune system. Research on the competition between invasive species and closely related native species has focused on differences in the adaptability of insects to the environment. Little is known about gut symbiotic microbe composition and its role in influencing competitive differences between these two insects.

Methods

We used a culture-independent approach targeting the 16S rRNA gene of gut bacteria of 5th instar larvae of S. frugiperda and S. litura. Larvae were reared continuously on maize leaves for five generations. We analyzed the composition, abundance, diversity, and metabolic function of gut microbiomes of S. frugiperda and S. litura larvae.

Results

Firmicutes, Proteobacteria, and Bacteroidetes were the dominant bacterial phyla in both species. Enterococcus, ZOR0006, Escherichia, Bacteroides, and Lactobacillus were the genera with the highest abundance in S. frugiperda. Enterococcus, Erysipelatoclostridium, ZOR0006, Enterobacter, and Bacteroides had the highest abundance in S. litura. According to α-diversity analysis, the gut bacterial diversity of S. frugiperda was significantly higher than that of S. litura. KEGG analysis showed 15 significant differences in metabolic pathways between S. frugiperda and S. litura gut bacteria, including transcription, cell growth and death, excretory system and circulatory system pathways.

Conclusion

In the same habitat, the larvae of S. frugiperda and S. litura showed significant differences in gut bacterial diversity and community composition. Regarding the composition and function of gut bacteria, the invasive species S. frugiperda may have a competitive advantage over S. litura. This study provides a foundation for developing control strategies for S. frugiperda and S. litura.

The role of insect gut microbiota in host fitness, detoxification and nutrient supplementation

Insects are incredibly diverse, ubiquitous and have successfully flourished out of the dynamic and often unpredictable nature of evolutionary processes. The resident microbiome has accompanied the physical and biological adaptations that enable their continued survival and proliferation in a wide array of environments. The host insect and microbiome's bidirectional relationship exhibits their capability to influence each other's physiology, behavior and characteristics. Insects are reported to rely directly on the microbial community to break down complex food, adapt to nutrient-deficit environments, protect themselves from natural adversaries and control the expression of social behavior. High-throughput metagenomic approaches have enhanced the potential for determining the abundance, composition, diversity and functional activities of microbial fauna associated with insect hosts, enabling in-depth investigation into insect-microbe interactions. We undertook a review of some of the major advances in the field of metagenomics, focusing on insect-microbe interaction, diversity and composition of resident microbiota, the functional capability of endosymbionts and discussions on different symbiotic relationships. The review aims to be a valuable resource on insect gut symbiotic microbiota by providing a comprehensive understanding of how insect gut symbionts systematically perform a range of functions, viz., insecticide degradation, nutritional support and immune fitness. A thorough understanding of manipulating specific gut symbionts may aid in developing advanced insect-associated research to attain health and design strategies for pest management.

Diversity and functional characteristics of culturable bacterial endosymbionts from cassava whitefly biotype Asia II-5, Bemisia tabaci

Whitefly Bemisia tabaci, a carrier of cassava mosaic disease (CMD), poses a significant threat to cassava crops. Investigating culturable bacteria and their impact on whiteflies is crucial due to their vital role in whitefly fitness and survival. The whitefly biotype associated with cassava and transmitting CMD in India has been identified as Asia II 5 through partial mitochondrial cytochrome oxidase I gene sequencing. In this study, bacteria associated with adult B. tabaci feeding on cassava were extracted using seven different media. Nutrient Agar (NA), Soyabean Casein Digest Medium (SCDM), Luria Bertani agar (LBA), and Reasoner's 2A agar (R2A) media resulted in 19, 6, 4, and 4 isolates, respectively, producing a total of 33 distinct bacterial isolates. Species identification through 16SrRNA gene sequencing revealed that all isolates belonged to the Bacillota and Pseudomonadota phyla, encompassing 11 genera: Bacillus, Cytobacillus, Exiguobacterium, Terribacillus, Brevibacillus, Enterococcus, Staphylococcus, Brucella, Novosphingobium, Lysobacter, and Pseudomonas. All bacterial isolates were tested for chitinase, protease, siderophore activity, and antibiotic sensitivity. Nine isolates exhibited chitinase activity, 28 showed protease activity, and 23 displayed siderophore activity. Most isolates were sensitive to antibiotics such as Vancomycin, Streptomycin, Erythromycin, Kanamycin, Doxycycline, Tetracycline, and Ciprofloxacin, while they demonstrated resistance to Bacitracin and Colistin. Understanding the culturable bacteria associated with cassava whitefly and their functional significance could contribute to developing effective cassava whitefly and CMD control in agriculture.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-024-03949-0.

Toward an Integrated Understanding of the Lepidoptera Microbiome

Research over the past 30 years has led to a widespread acceptance that insects establish widespread and diverse associations with microorganisms. More recently, microbiome research has been accelerating in lepidopteran systems, leading to a greater understanding of both endosymbiont and gut microorganisms and how they contribute to integral aspects of the host. Lepidoptera are associated with a robust assemblage of microorganisms, some of which may be stable and routinely detected in larval and adult hosts, while others are ephemeral and transient. Certain microorganisms that populate Lepidoptera can contribute significantly to the hosts' performance and fitness, while others are inconsequential. We emphasize the context-dependent nature of the interactions between players. While our review discusses the contemporary literature, there are major avenues yet to be explored to determine both the fundamental aspects of host-microbe interactions and potential applications for the lepidopteran microbiome; we describe these avenues after our synthesis.

Gut bacteria mediated adaptation of diamondback moth, Plutella xylostella, to secondary metabolites of host plants

IMPORTANCE

In this study, we identify an important role of gut bacteria in mediating the adaptation of diamondback moth (DBM) to plant secondary metabolites. We demonstrate that kaempferol's presence in radish seedlings greatly reduces the fitness of DBM with depleted gut biota. Reinstatement of gut biota, particularly Enterobacter sp. EbPXG5, improved insect performance by degrading kaempferol. This bacterium was common in the larval gut of DBM, lining the epithelium as a protective film. Our work highlights the role of symbiotic bacteria in insect herbivore adaptation to plant defenses and provides a practical and mechanistic framework for developing a more comprehensive understanding of insect-gut microbe-host plant co-evolution.

Impact of gut microbiota composition on black cutworm, Agrotis ipsilon (hufnagel) metabolic indices and pesticide degradation

Endosymbionts are known to have significant effects on their insect hosts, including nutrition, reproduction, and immunity. Insects gut microbiota is a critical component that affects their physiological and behavioral characteristics. The black cutworm (BCW), Agrotis ipsilon, is an economically important lepidopteran pest that has a diverse gut microbiome composed of nine species belonging to three phyla: Proteobacteria, Actinobacteria, and Firmicutes. This study was conducted to investigate the diversity of gut bacteria isolated from BCW larvae and moths and their effects on metabolism and pesticide degradation. The bacterial isolates were identified using the 16 S rRNA gene. The study showed that the gut microbiome composition significantly affected the metabolism of BCW larvae. Based on the screening results of synthesis of digestive enzymes and pesticide degradation, Brachybacterium conglomeratum and Glutamicibacter sp were selected to perform the remaining experiments as single isolates and consortium. The consortium-fed larvae showed high metabolic indices compared to antibiotic-fed larvae and the control. The gut bacteria were also shown to degrade three pesticide groups. Concerns regarding the health risk of chlorpyrifos have been raised due to its extensive use in agriculture. The isolated B. conglomeratum was more effective in chlorpyrifos degradation than the consortium. Furthermore, the study also examined the presence of sex related endosymbionts (Wolbachia, Spiroplasma, and Rickettsia) in the reproductive tissues of adults. The outcomes demonstrated that none of the examined endosymbionts existed. In conclusion, the study highlights the importance of the gut microbiome in insect physiology and behavior and its potential applications in biotechnology. It provides insights into developing eco-friendly pest control and bioremediation strategies using gut bacteria.

The comparison of gut gene expression and bacterial community in Diaphorina citri (Hemiptera: Liviidae) adults fed on Murraya exotica and 'Shatangju' mandarin (Citrus reticulate cv. Shatangju)

BACKGROUND

Diaphorina citri Kuwayama is an important citrus pest. It serves as the vector for the transmission of Candidatus Liberibacter asiaticus (CLas), which induced a destructive disease, Huanglongbing, and caused huge economic losses. During the interaction between insects and plants, insects have evolved a series of mechanisms to adapt to various host plants. Murraya exotica and 'Shatangju' mandarin (Citrus reticulate cv. Shatangju) are the Rutaceae species from different genera that have been discovered as suitable hosts for D. citri adults. While the adaptation mechanism of this pest to these two host plants is unclear.

RESULTS

In this study, RNA-seq and 16 S rDNA amplification sequencing were performed on the gut of D. citri adults reared on M. exotica and 'Shatangju' mandarin. RNA-seq results showed that a total of 964 differentially expressed genes were found in different gut groups with two host plant treatments. The impacted genes include those that encode ribosomal proteins, cathepsins, and mitochondrial respiratory chain complexes. According to 16 S rDNA sequencing, the compositions of the gut bacterial communities were altered by different treatments. The α and β diversity analyses confirmed that the host plant changes influenced the gut microbial diversity. The functional classification analysis by Tax4Fun revealed that 27 KEGG pathways, mostly those related to metabolism, including those for nucleotide metabolism, energy metabolism, metabolism of cofactors and vitamins, amino acid metabolism, carbohydrate metabolism, xenbiotics biodegradation and metabolism, lipid metabolism, and biosynthesis of other secondary metabolites, were significantly altered.

CONCLUSION

Our preliminary findings shed light on the connection between D. citri and host plants by showing that host plants alter the gene expression profiles and bacterial community composition of D. citri adults.

Comparison of bacterial diversity in Bactrocera cucurbitae (Coquillett) ovaries and eggs based on 16S rRNA sequencing

Next-generation sequencing allows for fine-scale studies of microbial communities. Herein, 16S ribosomal RNA high-throughput sequencing was used to identify, classify, and predict the functions of the bacterial communities in the eggs and ovaries of Bactrocera cucurbitae (Coquillett) (Diptera: Tephritidae), which is a pest that infests a variety of cucurbit fruits at different developmental stages. Taxonomic analyses indicate that bacteria associated with B. cucurbitae represent 19 phyla, which were spread across different developmental stages. Specifically, the egg microbiota had a higher alpha diversity than those of microbiota in the primary and mature ovaries. Significant differences were not observed between the primary and mature ovaries in terms of their microbiota's alpha diversities. Pseudomonadota, Deinococcota, Bacteroidota, Bacillota, and Actinomycetota were the dominant phyla in all three developmental stages of B. cucurbitae, and Pseudomonadaceae and Enterobacteriaceae were the most abundant families. Owing to the unique physiological environment of the ovaries, the diversity of their bacterial community was significantly lower than that in the eggs. This study provides new insights into the structure and abundance of the microbiota in B. cucurbitae at different developmental stages and contributes to forming management strategies for this pest.

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.

Host-Adapted Strains of Spodoptera frugiperda Hold and Share a Core Microbial Community Across the Western Hemisphere

The fall armyworm Spodoptera frugiperda is an important polyphagous agricultural pest in the Western Hemisphere and currently invasive to countries of the Eastern Hemisphere. This species has two host-adapted strains named "rice" and "corn" strains. Our goal was to identify the occurrence of core members in the gut bacterial community of fall armyworm larvae from distinct geographical distribution and/or host strain. We used next-generation sequencing to identify the microbial communities of S. frugiperda from corn fields in Brazil, Colombia, Mexico, Panama, Paraguay, and Peru, and rice fields from Panama. The larval gut microbiota of S. frugiperda larvae did not differ between the host strains nor was it affected by the geographical distribution of the populations investigated. Our findings provide additional support for Enterococcus and Pseudomonas as core members of the bacterial community associated with the larval gut of S. frugiperda, regardless of the site of collection or strain. Further investigations are required for a deeper understanding of the nature of this relationship.

Insect Gut Bacteria Promoting the Growth of Tomato Plants (Solanum lycopersicum L.)

We investigated gut bacteria from three insect species for the presence of plant growth properties (PGP). Out of 146 bacterial strains obtained from 20 adult specimens of Scolytidae sp., 50 specimens of Oulema melanopus, and 150 specimens of Diabrotica virgifera, we selected 11 strains displaying the following: PGP, phosphate solubility, production of cellulase, siderophore, lipase, protease, and hydrogen cyanide. The strains were tested for growth promotion ability on tomato (Lycopersicon esculentum) plants. Each strain was tested individually, and all strains were tested together as a bacterial consortium. Tomato fruit yield was compared with the negative control. The plants treated with bacterial consortium showed a significant increase in fruit yield, in both number of fruits (+41%) and weight of fruits (+44%). The second highest yield was obtained for treatment with Serratia liquefaciens Dv032 strain, where the number and weight of yielded fruits increased by 35% and 30%, respectively. All selected 11 strains were obtained from Western Corn Rootworm (WCR), Diabrotica virgifera. The consortium comprised: Ewingella americana, Lactococcus garvieae, L. lactis, Pseudomonas putida, Serratia liquefaciens, and S. plymuthica. To our knowledge, this is the first successful application of D. virgifera gut bacteria for tomato plant growth stimulation that has been described.

Contribution of insect gut microbiota and their associated enzymes in insect physiology and biodegradation of pesticides

Synthetic pesticides are extensively and injudiciously applied to control agriculture and household pests worldwide. Due to their high use, their toxic residues have enormously increased in the agroecosystem in the past several years. They have caused many severe threats to non-target organisms, including humans. Therefore, the complete removal of toxic compounds is gaining wide attention to protect the ecosystem and the diversity of living organisms. Several methods, such as physical, chemical and biological, are applied to degrade compounds, but as compared to other methods, biological methods are considered more efficient, fast, eco-friendly and less expensive. In particular, employing microbial species and their purified enzymes makes the degradation of toxic pollutants more accessible and converts them into non-toxic products by several metabolic pathways. The digestive tract of insects is usually known as a superior organ that provides a nutrient-rich environment to hundreds of microbial species that perform a pivotal role in various physiological and ecological functions. There is a direct relationship between pesticides and insect pests: pesticides reduce the growth of insect species and alter the phyla located in the gut microbiome. In comparison, the insect gut microbiota tries to degrade toxic compounds by changing their toxicity, increasing the production and regulation of a diverse range of enzymes. These enzymes breakdown into their derivatives, and microbial species utilize them as a sole source of carbon, sulfur and energy. The resistance of pesticides (carbamates, pyrethroids, organophosphates, organochlorines, and neonicotinoids) in insect species is developed by metabolic mechanisms, regulation of enzymes and the expression of various microbial detoxifying genes in insect guts. This review summarizes the toxic effects of agrochemicals on humans, animals, birds and beneficial arthropods. It explores the preferential role of insect gut microbial species in the degradation process and the resistance mechanism of several pesticides in insect species. Additionally, various metabolic pathways have been systematically discussed to better understand the degradation of xenobiotics by insect gut microbial species.

Diversity of culturable gut bacteria of diamondback moth, Plutella xylostella (Linnaeus) (Lepidoptera: Yponomeutidae) collected from different geographical regions of India

Diamondback moth, Plutella xylostella is one of the important pests of cole crops, the larval stages cause damage to leaves from seedling stage to the harvest thus reducing the quality and quantity of the yield. The insect gut posses a large variety of microbial communities among which, the association of bacteria is the most spread and common. Due to variations in various agro-climatic factors, the insect often assumes the status of major pest. These geographical variations in insects influence various biological parameters including insecticide resistance due to diversity of microbes/bacteria. The diverse role of gut bacteria in insect fitness traits has now gained perspectives for biotechnological exploration. The present study was aimed to determine the diversity of larval gut bacteria of diamondback moth collected from five different geographical regions of India. The gut bacteria of this pest were found to be influenced by different geographical regions. A total of 14 larval gut bacterial isolates were obtained. Majority of these bacteria belong to Enterobacteriaceae followed by Yersiniaceae, Morganellaceae and Enterococcaceae. Phylogeny analysis of all the bacterial isolates collected from five different geographical regions of India revealed that all the isolated strains are resolved in well-defined clades with their closest type species.

Functional characterization of cultivable gut bacterial communities associated with rugose spiralling whitefly, Aleurodicus rugioperculatus Martin

Gut symbiotic bacteria provide protection and nutrition to the host insect. A high reproductive rate and dispersal ability of the rugose spiralling whitefly help this polyphagous species to develop and thrive on many horticultural crops. In this study, we isolated the cultivable gut bacteria associated with rugose spiralling whitefly and demonstrated their role in the host insect. We also studied the influence of antibiotics on the rugose spiralling whitefly oviposition. A total of 70 gut bacteria were isolated from the second nymphal stage of rugose spiralling whitefly reared on coconut, banana, and sapota using seven growth media. From the 70 isolates, chitinase, siderophore (51), protease (44), and Glutathione-S-Transferase producers (16) were recorded. The activities of chitinase, siderophore, protease, and Glutathione-S-Transferase in the gut bacterial isolates of rugose spiralling whitefly ranged from 0.07 to 3.96 µmol^-1 min^-1 mL^-1, 10.01 to 76.93%, 2.10 to 83.40%, and 5.21 to 24.48 nmol^-1 min^-1 mL^-1 μg^-1 protein, respectively. The16S rRNA gene sequence analysis revealed that bacterial genera associated with the gut of rugose spiralling whitefly included Bacillus, Exiguobacterium, Acinetobacter, Lysinibacillus, Arthrobacter, and Pseudomonas. Based on the susceptibility of the gut bacteria to antibiotics, 11antibiotic treatments were administered to the host plant leaves infested with the nymphal stages. The antibiotics were evaluated for their effect on rugose spiralling whitefly oviposition. Among the antibiotic treatments, carbenicillin (100 µg mL^-1) + ciprofloxacin (5 µg mL^-1) significantly reduced the oviposition (13 eggs spiral^-1) and egg hatchability (61.54%) of rugose spiralling whitefly. Disruption of chitinase, siderophore, protease, and detoxification enzyme producers and elimination of these symbionts through antibiotics altered the host insect physiology and indirectly affected whitefly oviposition. In conclusion, gut bacteria-based management strategies might be used as insecticides for the effective control of whiteflies.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-03081-3.

Endosymbiotic Bacteria Aid to Overcome Temperature Induced Stress in the Oriental Fruit Fly, Bactrocera dorsalis

Endosymbiotic microbiota are known to have an enormous impact on their host, influencing its physiology, behavior, fitness, and various other aspects. The present study hypothesizes that certain bacterial symbionts aid the Oriental fruit fly, Bactrocera dorsalis in its adaptation to survive thermal stress encountered in the environment. Investigative studies on the change in gut and reproductive tract microbiota diversity of male and female B. dorsalis revealed that certain genera of Acinetobacter, Brevibacillus, Bacillus, Enterobacter, Enterococcus, Pseudomonas, and Staphylococcus were involved in the adaptation of B. dorsalis to temperature stresses. The intestinal and reproductive tract bacterial community of B. dorsalis varied depending on the temperature the insects were reared at. We hypothesized that the microbiota present in B. dorsalis' gut helped it endure temperature stresses over prolonged periods. Out of 54 bacterial isolates, 25, 15, and 14 isolates were obtained from flies reared at 27 °C, 18 °C, and 35 °C, respectively. A 16S rDNA analysis revealed that the bacterial isolates (reared at different temperatures) belonged to different genera. The flies were supplemented with antibiotics to suppress the existing gut microbiota and subsequently fed with bacterial isolates from flies reared at 18 °C, 27 °C (control) or 35 °C separately. When these flies were placed in incubators pre-set at the above temperatures, the survival rate exhibited by the flies differed significantly. The flies fed with bacterial isolates from 18 °C could survive only in incubators pre-set at 18 °C, while flies fed with bacterial isolates from 35 °C could survive only at 35 °C and not vice versa. The microbiota supplementation assay established that the presence of specific bacterial isolates aided the flies' survival under varied thermal stresses.

Immune Response and Hemolymph Microbiota of Apis mellifera and Apis cerana After the Challenge With Recombinant Varroa Toxic Protein

The honey bee is a significant crop pollinator and key model insect for understanding social behavior, disease transmission, and development. The ectoparasitic Varroa destructor mite put threats on the honey bee industry. A Varroa toxic protein (VTP) from the saliva of Varroa mites contributes to the toxicity toward Apis cerana and the deformed wing virus elevation in Apis mellifera. However, the immune response and hemolymph microbiota of honey bee species after the injection of recombinant VTP has not yet been reported. In this study, both A. cerana and A. mellifera worker larvae were injected with the recombinant VTP. Then the expressions of the honey bee immune genes abaecin, defensin, and domeless at three time points were determined by qRT-PCR, and hemolymph microbial community were analyzed by culture-dependent method, after recombinant VTP injection. The mortality rates of A. cerana larvae were much higher than those of A. mellifera larvae after VTP challenge. VTP injection induced the upregulation of defensin gene expression in A. mellifera larvae, and higher levels of abaecin and domeless mRNAs response in A. cerana larvae, compared with the control (without any injection). Phosphate buffer saline (PBS) injection also upregulated the expression levels of abaecin, defensin, and domeless in A. mellifera and A. cerana larvae. Three bacterial species (Enterococcus faecalis, Staphylococcus cohnii, and Bacillus cereus) were isolated from the hemolymph of A. cerana larvae after VTP injection and at 48 h after PBS injections. Two bacterial species (Stenotrophomonas maltophilia and Staphylococcus aureus) were isolated from A. mellifera larvae after VTP challenge. No bacterial colonies were detected from the larval hemolymph of both honey bee species treated by injection only and the control. The result indicates that abaecin, defensin, and domeless genes and hemolymph microbiota respond to the VTP challenge. VTP injection might induce the dramatic growth of different bacterial species in the hemolymph of the injected larvae of A. mellifera and A. cerana, which provide cues for further studying the interactions among the honey bee, VTP, and hemolymph bacteria.

Microbiomes of a specialist caterpillar are consistent across different habitats but also resemble the local soil microbial communities

BACKGROUND

Insect-associated microorganisms can provide a wide range of benefits to their host, but insect dependency on these microbes varies greatly. The origin and functionality of insect microbiomes is not well understood. Many caterpillars can harbor symbionts in their gut that impact host metabolism, nutrient uptake and pathogen protection. Despite our lack of knowledge on the ecological factors driving microbiome assemblages of wild caterpillars, they seem to be highly variable and influenced by diet and environment. Several recent studies have shown that shoot-feeding caterpillars acquire part of their microbiome from the soil. Here, we examine microbiomes of a monophagous caterpillar (Tyria jacobaeae) collected from their natural host plant (Jacobaea vulgaris) growing in three different environments: coastal dunes, natural inland grasslands and riverine grasslands, and compare the bacterial communities of the wild caterpillars to those of soil samples collected from underneath each of the host plants from which the caterpillars were collected.

RESULTS

The microbiomes of the caterpillars were dominated by Proteobacteria, Actinobacteria, Firmicutes and Bacteroidetes. Only 5% of the total bacterial diversity represented 86.2% of the total caterpillar's microbiome. Interestingly, we found a high consistency of dominant bacteria within the family Burkholderiaceae in all caterpillar samples across the three habitats. There was one amplicon sequence variant belonging to the genus Ralstonia that represented on average 53% of total community composition across all caterpillars. On average, one quarter of the caterpillar microbiome was shared with the soil.

CONCLUSIONS

We found that the monophagous caterpillars collected from fields located more than 100 km apart were all dominated by a single Ralstonia. The remainder of the bacterial communities that were present resembled the local microbial communities in the soil in which the host plant was growing. Our findings provide an example of a caterpillar that has just a few key associated bacteria, but that also contains a community of low abundant bacteria characteristic of soil communities.

Gut bacteria of the silkworm Bombyx mori facilitate host resistance against the toxic effects of organophosphate insecticides

Organophosphate insecticides that are heavily used in agriculture for pest control have caused growing environmental problems and public health concerns worldwide. Ironically, insecticide resistance develops quickly in major lepidopteran pests, partially via their microbial symbionts. To investigate the possible mechanisms by which the microbiota confers insecticide resistance to Lepidoptera, the model organism silkworm Bombyx mori (Lepidoptera: Bombycidae) was fed different antibiotics to induce gut dysbiosis (microbiota imbalance). Larvae treated with polymyxin showed a significantly lower survival rate when exposed to chlorpyrifos. Through high-throughput sequencing, we found that the abundances of Stenotrophomonas and Enterococcus spp. changed substantially after treatment. To assess the roles played by these two groups of bacteria in chlorpyrifos resistance, a germ-free (GF) silkworm rearing protocol was established to avoid the influence of natural microbiota and antibiotics. Monoassociation of GF silkworms with Stenotrophomonas enhanced host resistance to chlorpyrifos, but not in Enterococcus-fed larvae, consistent with larval detoxification activity. GC-μECD detection of chlorpyrifos residues in feces indicated that neither Stenotrophomonas nor Enterococcus degraded chlorpyrifos directly in the gut. However, gut metabolomics analysis revealed a highly species-specific pattern, with higher levels of essential amino acid produced in the gut of silkworm larvae monoassociated with Stenotrophomonas. This critical nutrient provisioning significantly increased host fitness and thereby allowed larvae to circumvent the deleterious effects of these toxic chemicals more efficiently. Altogether, our study not only suggests a new mechanism for insecticide resistance in notorious lepidopteran pests but also provides a useful template for investigating the interplay between host and gut bacteria in complex environmental systems.

Developmental stage-associated microbiota profile of the peach fruit fly, Bactrocera zonata (Diptera: Tephritidae) and their functional prediction using 16S rRNA gene metabarcoding sequencing

The different developmental stage-associated microbiota of the peach fruit fly, Bactrocera zonata (Diptera: Tephritidae), was characterized using 16S rRNA gene (V3-V4 region) metabarcoding on the Illumina HiSeq platform. Taxonomically, at 97% similarity, there were total 16 bacterial phyla, comprising of 24 classes, 55 orders, 90 families and 134 genera. Proteobacteria, Firmicutes, Actinobacteria and Bacteroidetes were the most abundant phyla with Gammaproteobacteria, Alphaproteobacteria, Actinobacteria, Bacteroidia and Bacilli being the most abundant classes. The bacterial genus Enterobacter was dominant in the larval and adult stages and Pseudomonas in the pupal stage. A total of 2645 operational taxonomic units (OTUs) were identified, out of which 151 OTUs (core microbiota) were common among all the developmental stages of B. zonata. The genus Enterobacter, Klebsiella and Pantoea were dominant among the core microbiota. PICURSt analysis predicted that microbiota associated with B. zonata may be involved in membrane transport, carbohydrate metabolism, amino acid metabolism, replication and repair processes as well as in cellular processes and signalling. The microbiota that was shared by all the developmental stages of B. zonata in the present study could be targeted and the foundation for research on microbiota-based management of fruit flies.

Functional Variation in Dipteran Gut Bacterial Communities in Relation to Their Diet, Life Cycle Stage and Habitat

Simple Summary

Like in many other organisms, the guts of insects are full with many different bacteria. These bacteria can help their hosts to overcome toxic diets or can boost their resistance to pathogens. We were curious to learn which factors determine the composition of gut bacterial communities (GBCs) in true flies and mosquitoes, which belong to the order Diptera. We searched for research papers reporting on GBCs in these insects. Using these published data, we investigated whether the GBCs are species-specific, or whether they are determined by the diet, life stage or environment of the host insect. We found that the GBCs in larvae and adults of the same insect species can be very different. Insects on similar diets did not necessarily show similar GBCs. This made us conclude that GBCs are mostly life stage-specific. However, we found that the number of data papers we could use is limited; more data are needed to strengthen our conclusion. Lastly, novel DNA technologies can show ‘who is there’ in GBCs. At the same time, we lack knowledge on the exact function of gut bacteria. Obtaining more knowledge on the function of GBCs may help to design sustainable pest control measures.

Abstract

True flies and mosquitos (Diptera) live in habitats and consume diets that pose specific demands on their gut bacterial communities (GBCs). Due to diet specializations, dipterans may have highly diverse and species-specific GBCs. Dipterans are also confronted with changes in habitat and food sources over their lifetime, especially during life history processes (molting, metamorphosis). This may prevent the development of a constant species- or diet-specific GBC. Some dipterans are vectors of several human pathogens (e.g., malaria), which interact with GBCs. In this review, we explore the dynamics that shape GBC composition in some Diptera species on the basis of published datasets of GBCs. We thereby focus on the effects of diet, habitats, and life cycle stages as sources of variation in GBC composition. The GBCs reported were more stage-specific than species- or diet-specific. Even though the presence of GBCs has a large impact on the performance of their hosts, the exact functions of GBCs and their interactions with other organisms are still largely unknown, mainly due to the low number of studies to date. Increasing our knowledge on dipteran GBCs will help to design pest management strategies for the reduction of insecticide resistance, as well as for human pathogen control.

Comparative Genomic and Metabolomic Analyses of Two Pseudomonas aeruginosa Strains With Different Antifungal Activities

Pseudomonas aeruginosa isolated from the plant rhizosphere has been widely used as an effective strain in biological control against plant disease. This bacterium promotes plant growth and protect plants against various phytopathogens through the production of phenazine metabolites. In this study, the strain P. aeruginosa Y12 with anti-Beauveria bassiana activity was isolated from the gut of housefly larvae. It was comparatively analyzed with the strain P. aeruginosa P18, which showed no anti-B. bassiana activity. Genomic and metabolomic methods were used to obtain a comprehensive understanding of the antimicrobial mechanism of Y12. After whole-genome resequencing of the two strains, a total of 7,087 non-synonymous single-nucleotide polymorphisms (nsSNPs), 1079 insertions and deletions (InDels), 62 copy-number variations (CNVs) and 42 structural variations (SV) were found in both strains. We analyzed the differentially abundant metabolites between Y12 and P18, and identified six bioactive compounds that could be associated with the antimicrobial activity of Y12. Additionally, we found that, unlike other previously reported rhizospheric P. aeruginosa strains, Y12 could produce both phenazine-1,6-dicarboxylic acid (PDC) and pyocyanin (PYO) at significantly higher concentrations than P18. As B. bassiana is an effective biological insecticide that can cause high mortality in adult houseflies but has little effect on housefly larvae, we believe that P. aeruginosa Y12, identified in housefly larvae but not in adults, were beneficial for the development of housefly larvae and could protect them from B. bassiana infection through the production of toxic metabolites.

Diversity and Composition of the Gut Microbiota in the Developmental Stages of the Dung Beetle Copris incertus Say (Coleoptera, Scarabaeidae)

Dung beetles are holometabolous insects that feed on herbivorous mammal dung and provide services to the ecosystem including nutrient cycling and soil fertilization. It has been suggested that organisms developing on incomplete diets such as dungs require the association with microorganisms for the synthesis and utilization of nutrients. We describe the diversity and composition of the gut-microbiota during the life cycle of the dung beetle Copris incertus using 16S rRNA gene sequencing. We found that C. incertus gut contained a broad diversity of bacterial groups (1,699 OTUs and 302 genera). The taxonomic composition varied during the beetle life cycle, with the predominance of some bacterial genera in a specific developmental stage (Mothers: Enterobacter and Serratia; Eggs: Nocardioides and Hydrogenophaga; Larval and pupal stages: Dysgonomonas and Parabacteroides; offspring: Ochrobactrum). The beta diversity evidenced similarities among developmental stages, clustering (i) the adult stages (mother, male and female offsprings), (ii) intermediate developmental (larvae and pupa), and (iii) initial stage (egg). Microbiota differences could be attributed to dietary specialization or/and morpho-physiological factors involved in the transition from a developmental stage to the next. The predicted functional profile (PICRUSt2 analysis) for the development bacterial core of the level 3 categories, indicated grouping by developmental stage. Only 36 categories were significant in the SIMPER analysis, including the metabolic categories of amino acids and antibiotic synthesis, which were enriched in the larval and pupal stages; both categories are involved in the metamorphosis process. At the gene level, we found significant differences only in the KOs encoding functions related to nitrogen fixation, uric acid metabolism, and plant cell wall degradation for all developmental stages. Nitrogen fixation and plant cell wall degradation were enriched in the intermediate stages and uric acid metabolism was enriched in mothers. The data reported here suggested the influence of the maternal microbiota in the composition and diversity of the gut microbiota of the offspring.

Pyrosequencing Uncovers a Shift in Bacterial Communities Across Life Stages of Octodonta nipae (Coleoptera: Chrysomelidae)

Bacterial symbionts of insects affect a wide array of host traits including fitness and immunity. Octodonta nipae (Maulik), commonly known as hispid leaf beetle is a destructive palm pest around the world. Understanding the dynamics of microbiota is essential to unravel the complex interplay between O. nipae and its bacterial symbionts. In this study, bacterial 16S rRNA V3-V4 region was targeted to decipher the diversity and dynamics of bacterial symbionts across different life stages [eggs, larvae, pupae, and adult (male and female)] and reproductive organs (ovaries and testis) of O. nipae. Clustering analysis at ≥97% similarity threshold produced 3,959 operational taxonomic units (OTUs) that belonged to nine different phyla. Proteobacteria, Actinobacteria, and Firmicutes represented the bulk of taxa that underwent notable changes during metamorphosis. Enterobacteriaceae and Dermabacteraceae were the most abundant families in immature stages (eggs, larvae, and pupae), while Anaplasmataceae family was dominated in adults (male and female) and reproductive organs (ovaries and testis). The genus Serratia and Lactococcus were most abundant in eggs, whereas Pantoea and Brachybacterium represented the bulk of larvae and pupae microbiota. Interestingly the genus Wolbachia found positive to all tested samples and was recorded extremely high (>64%) in the adults and reproductive organs. The bacteria varied across the developmental stages and responsible for various metabolic activities. Selection choice exerted by the insect host as a result of its age or developmental stage could be the main reason to ascertain the shift in the bacteria populations. Maternally inherited Wolbachia was found to be an obligate endosymbiont infecting all tested life stages, body parts, and tissues. These outcomes foster our understanding of the intricate associations between bacteria and O. nipae and will incorporate in devising novel pest control strategies against this palm pest.

Honeydew-associated microbes elicit defense responses against brown planthopper in rice

Feeding of sucking insects, such as the rice brown planthopper (Nilaparvata lugens; BPH), causes only limited mechanical damage on plants that is otherwise essential for injury-triggered defense responses against herbivores. In pursuit of complementary BPH elicitors perceived by plants, we examined the potential effects of BPH honeydew secretions on the BPH monocot host, rice (Oryza sativa). We found that BPH honeydew strongly elicits direct and putative indirect defenses in rice, namely accumulation of phytoalexins in the leaves, and release of volatile organic compounds from the leaves that serve to attract natural enemies of herbivores, respectively. We then examined the elicitor active components in the honeydew and found that bacteria in the secretions are responsible for the activation of plant defense. Corroborating the importance of honeydew-associated microbiota for induced plant resistance, BPHs partially devoid of their microbiota via prolonged antibiotics ingestion induced significantly less defense in rice relative to antibiotic-free insects applied to similar groups of plants. Our data suggest that rice plants may additionally perceive herbivores via their honeydew-associated microbes, allowing them to discriminate between incompatible herbivores-that do not produce honeydew-and those that are compatible and therefore dangerous.

Characterization of a Lipase From the Silkworm Intestinal Bacterium Bacillus pumilus With Antiviral Activity Against Bombyx mori (Lepidoptera: Bombycidae) Nucleopolyhedrovirus In Vitro

To investigate whether Bombyx mori Linnaeus (Lepidoptera: Bombycidae) intestinal microorganism play a role in the host defence system against viral pathogens, a lipase gene from the silkworm intestinal bacterium Bacillus pumilus SW41 was characterized, and antiviral activity of its protein against B. mori nucleopolyhedrovirus (BmNPV) was tested. The lipase gene has an open-reading frame of 648 bp, which encodes a 215-amino-acid enzyme with a 34-amino-acid signal peptide. The recombinant lipase (without signal peptide) was expressed and purified by using an Escherichia coli BL21 (DE3) expression system. The total enzyme activity of this recombinant lipase reached 277.40 U/mg at the optimum temperature of 25°C and optimum pH value of 8.0. The antiviral test showed that a relative high concentration of the recombinant lipase reduced BmNPV infectivity in vitro, which resulted in decreased viral DNA abundance and viral occlusion bodies. Besides, the preincubation method also suggested that the lipase probably directly acting on the budded virions. The results suggest that the lipase from intestinal bacterium B. pumilus SW41 is a potential antiviral factor for silkworm against BmNPV.

Bacterial community structure and diversity in the gut of the muga silkworm, Antheraea assamensis (Lepidoptera: Saturniidae), from India

The muga silkworm, Antheraea assamensis, is exclusively present in the northeastern regions of India and rearing of this silkworm is a vocation unique to this region in the world. Through culture-dependent techniques, generic identification using 16S ribosomal RNA probes, diversity analysis and qualitative screening for enzyme activities, our studies have identified a number of bacterial isolates, viz. Bacillus spp., Serratia marcescens, Stenotrophomonas maltophilia, Pseudomonas stutzeri, Acinetobacter sp. and Alcaligens sp., inhabiting the gut of the muga silkworm. Analysis of the culturable bacterial community from the gut of An. assamensis revealed that Bacillus (54%) was the predominant bacterial genus followed by Serratia (24%), Pseudomonas (10%) and Alcaligens (6%). Significant differences in the Shannon-Wiener (H') and Simpson (D) diversity indices of gut bacteria were recorded for An. assamensis collected from different regions. H' and D values were found to be highest for An. assamensis from the Titabar region (H' = 4.73 ± 0.43; D = 10.00 ± 0.11) and lowest for individuals from the Mendipathar region (H' = 2.1 ± 0.05; D = 0.04 ± 0.00) of northeastern India. Qualitative screening for enzyme activities identified about 26 gut bacterial isolates having significantly higher cellulose, amylase and lipase activities. These isolates probably contribute to the digestion and nutrition of their host insect, An. assamensis.

Microbiota in insect fungal pathology

Significant progress has been made in the biochemical and genetic characterization of the host-pathogen interaction mediated by insect pathogenic fungi, with the most widely studied being the Ascomycetes (Hypocrealean) fungi, Metarhizium robertsii and Beauveria bassiana. However, few studies have examined the consequences and effects of host (insect) microbes, whether compatible or antagonistic, on the development and survival of entomopathogenic fungi. Host microbes can act on the insect cuticular surface, within the gut, in specialized insect microbe hosting structures, and within cells, and they include a wide array of facultative and/or obligate exosymbionts and endosymbionts. The insect microbiome differs across developmental stages and in response to nutrition (e.g., different plant hosts for herbivores) and environmental conditions, including exposure to chemical insecticides. Here, we review recent advances indicating that insect-pathogenic fungi have evolved a spectrum of strategies for exploiting or suppressing host microbes, including the production of antimicrobial compounds that are expressed at discrete stages of the infection process. Conversely, there is increasing evidence that some insects have acquired microbes that may be specialized in the production of antifungal compounds to combat infection by (entomopathogenic) fungi. Consideration of the insect microbiome in fungal insect pathology represents a new frontier that can help explain previously obscure ecological and pathological aspects of the biology of entomopathogenic fungi. Such information may lead to novel approaches to improving the efficacy of these organisms in pest control efforts.

The interactions between gut microbiota and entomopathogenic fungi: a potential approach for biological control of Blattella germanica (L.)

BACKGROUND

Metarhizium anisopliae and Beauveria bassiana mainly infect insects through the cuticle; gut infection occasionally occurs. Micro-organisms existing in the gut may play a crucial role in the evolution and ecology of host defenses against fungal pathogens. To evaluate whether the gut bacteria participate in antifungal activity, and to determine their role in host protection, the interactions between gut bacteria and M. anisopliae and the diversity of gut microbiota in cockroaches were studied.

RESULTS

An oral feeding test showed that the mortality of conventional cockroaches was significantly lower than that of germ-free cockroaches; both gut homogenates and aqueous fecal extracts showed antifungal activity, but the samples from germ-free cockroaches did not. Twenty-two bacterial strains with antifungal activity and siderophore-producing ability were isolated from the gut and feces of cockroaches. Using high-throughput sequencing techniques, a total of 23 different phyla and 212 genera were detected. The composition of the microbiota of the hindgut was vastly different from those of the foregut and midgut; higher diversity and abundance of Bacteroides and Pseudomonas were found in the hindgut.

CONCLUSION

The gut microbiota of German cockroaches may play a critical role in protecting cockroaches from fungal invasion and colonization. Removing certain bacteria from the B. germanica microbiota may facilitate microbial control using fungal pathogens. © 2017 Society of Chemical Industry.

The folA gene from the Rickettsia endosymbiont of Ixodes pacificus encodes a functional dihydrofolate reductase enzyme

Although nonpathogenic bacterial endosymbionts have been shown to contribute to their arthropod host's fitness by supplying them with essential vitamins and amino acids, little is known about the nutritional basis for the symbiotic relationship of endosymbionts in ticks. Our lab has previously reported that Rickettsia species phylotype G021 in Ixodes pacificus carries all five genes for de novo folate synthesis, and that these genes are monophyletic with homologs from other Rickettsia species. In this study, the rickettsial folate synthesis folA gene, coding for dihydrofolate reductase, was PCR amplified, cloned into an expression vector, and overexpressed in E. coli. Bioinformatic analysis identified that the FolA protein of phylotype G021 has the conserved DHFR domain, NADP binding sites, and substrate binding sites of bacterial dihydrofolate reductase. SDS-PAGE results showed that recombinant rickettsial FolA protein was overexpressed in BL21(DE3) E. coli in its soluble form. Affinity chromatography was used to purify the protein, and in vitro enzyme assays were performed to assess the biochemical activity of dihydrofolate reductase. The specific activity of recombinant FolA from phylotype G021 was determined to be 16.1 U/mg. This study has revealed that Rickettsia species phylotype G021 of I. pacificus is capable of producing a functional enzyme of the folate biosynthesis pathway, addressing the nutritional interactions behind the symbiosis between Rickettsia species phylotype G021 and its host.

The Gut Entomotype of Red Palm Weevil Rhynchophorus ferrugineus Olivier (Coleoptera: Dryophthoridae) and Their Effect on Host Nutrition Metabolism

For invasive insects, the potential roles of gut microbiota in exploiting new food resources and spreading remain elusive. Red palm weevil (RPW), Rhynchophorus ferrugineus Olivier, is an invasive destructive pest which feeds on nutrient-poor tender tissues and has caused extensive mortality of palm trees. The microbes associated with insects can improve their nutrition assimilation. However, experimental evidence on the interactions between RPW and its gut microbiota is still absent. The aim of this study is to determine the dynamics changes and the bacterial entomotype in the RPW gut and its potential physiological roles. Here, we confirmed RPW harbors a complex gut microbiota mainly constituted by bacteria in the families Enterobacteriaceae, Lactobacillaceae, Entomoplasmataceae, and Streptococcaceae. RPW gut microbiota exhibited a highly stable microbial community with low variance in abundance across different life stages and host plants. Furthermore, the abundance of Enterobacteriaceae was markedly increased but that of Acetobacteraceae was reduced significantly after administration of antibiotics. Although no significant effects were found on the body weight gain of RPW larvae, these alterations dramatically decreased the concentration of hemolymph protein and glucose while that of hemolymph triglyceride increased. In the gut of wild-caught RPW larvae, seven bacterial species in the genera Klebsiella, Serratia, Enterobacter, and Citrobacter were shown to have an ability to degrade cellulose. Together, RPW accommodate a stable gut microbiota which can degrade plant polysaccharides and confer their host optimal adaptation to its environment by modulating its metabolism.

Midgut bacteria in deltamethrin-resistant, deltamethrin-susceptible, and field-caught populations of Plutella xylostella, and phenomics of the predominant midgut bacterium Enterococcus mundtii

Gut bacteria play a significant role in host insect. This study evaluated detail difference of midgut bacteria in deltamethrin-resistant, deltamethrin-susceptible and field-caught populations of diamondback moth, and studied phenomics of the predominant midgut bacterium Enterococcus mundtii. Cultivable bacteria revealed that E. mundtii and Carnobacterium maltaromaticum dominated the bacterial populations from deltamethrin-resistant and deltamethrin-susceptible larval midguts, whereas E. mundtii was predominant in field-caught population. Illumina sequencing analysis indicated that 97% of the midgut bacteria were from the phyla Firmicutes, Proteobacteria and Cyanobacteria. Both resistant and susceptible populations had more Enterococcus and Carnobacterium. Enterococcus, Carnobacterium, Bacillus, and Pseudomonas were predominant in the field-caught population. A phenomics analysis revealed that E. mundtii was able to metabolize 25.26% of the tested carbon sources, 100% of the nitrogen sources, 100% of the phosphorus sources and 97.14% of the sulfur sources, had a wide range of osmolytes and pH conditions, and showed active deaminase activity but no decarboxylase activity. This is the first report regarding different populations of DBM midgut bacteria analyzed using both high-throughput DNA sequencing and cultivation methods, and also first report concerning the phenomics of E. mundtii. The phenomics of E. mundtii provide a basis for the future study of gut bacteria functions.

Metagenomic Sequencing of Diamondback Moth Gut Microbiome Unveils Key Holobiont Adaptations for Herbivory

Herbivore specialists adapt to feed on a specific group of host plants by evolving various mechanisms to respond to plant defenses. Insects also possess complex gut microbiotas but their potential role in adaptation is poorly understood. Our previous study of the genome of diamondback moth, Plutella xylostella, revealed an intrinsic capacity to detoxify plant defense compounds, which is an important factor in its success as a pest. Here we expand on that work with a complete taxonomic and functional profile of the P. xylostella gut microbiota obtained by metagenomic sequencing. Gene enrichment in the metagenome, accompanied by functional identification, revealed an important role of specific gut bacteria in the breakdown of plant cell walls, detoxification of plant phenolics, and synthesis of amino acids. Microbes participating in these pathways mainly belonged to three highly abundant bacteria: Enterobacter cloacae, Enterobacter asburiae, and Carnobacterium maltaromaticum. Results show that while the gut microbial community may be complex, a small number of functionally active species can be disproportionally important. The presence of specific enzymes in the microbiota community, such as supporting amino acid synthesis, digestion and detoxification functions, demonstrates the beneficial interactions between P. xylostella and its gut microbiota. These interactions can be potential targets for manipulation to provide novel pest management approaches.

The gut microbiota of insecticide-resistant insects houses insecticide-degrading bacteria: A potential source for biotechnological exploitation

The exploration of new niches for microorganisms capable of degrading recalcitrant molecules is still required. We hypothesized the gut microbiota associated with insect-resistant lines carry pesticide degrading bacteria, and predicted they carry bacteria selected to degrade pesticides they were resistant to. We isolated and accessed the pesticide-degrading capacity of gut bacteria from the gut of fifth instars of Spodoptera frugiperda strains resistant to lambda-cyhalothrin, deltamethrin, chlorpyrifos ethyl, spinosad and lufenuron, using insecticide-selective media. Sixteen isolates belonging to 10 phylotypes were obtained, from which four were also associated with the susceptible strain. However, growth of gut bacteria associated with larvae from the susceptible strain was not obtained in any of the insecticide-based selective media tested. Growth of isolates was affected by the concentration of insecticides in the media, and all grew well up to 40 μg/ml. The insecticide-degrading capacity of selected isolates was assessed by GC or LC-MS/MS analyses. In conclusion, resistant strains of S. frugiperda are an excellent reservoir of insecticide-degrading bacteria with bioremediation potential. Moreover, gut-associated bacteria are subjected to the selection pressure imposed by insecticides on their hosts and may influence the metabolization of pesticides in insects.

Draft Genome Sequence of Stenotrophomonas maltophilia SBo1 Isolated from Bactrocera oleae

Bacteria of the genus Stenotrophomonas are ubiquitous in the environment and are increasingly associated with insects. Stenotrophomonas maltophilia SBo1 was cultured from the gut of Bactrocera oleae. The draft genome sequence presented here will inform future investigations into the nature of the interaction between insects and their microbiota.

Midgut Transcriptome of the Cockroach Periplaneta americana and Its Microbiota: Digestion, Detoxification and Oxidative Stress Response

The cockroach, Periplaneta americana, is an obnoxious and notorious pest of the world, with a strong ability to adapt to a variety of complex environments. However, the molecular mechanism of this adaptability is mostly unknown. In this study, the genes and microbiota composition associated with the adaptation mechanism were studied by analyzing the transcriptome and 16S rDNA pyrosequencing of the P. americana midgut, respectively. Midgut transcriptome analysis identified 82,905 unigenes, among which 64 genes putatively involved in digestion (11 genes), detoxification (37 genes) and oxidative stress response (16 genes) were found. Evaluation of gene expression following treatment with cycloxaprid further revealed that the selected genes (CYP6J1, CYP4C1, CYP6K1, Delta GST, alpha-amylase, beta-glucosidase and aminopeptidase) were upregulated at least 2.0-fold at the transcriptional level, and four genes were upregulated more than 10.0-fold. An interesting finding was that three digestive enzymes positively responded to cycloxaprid application. Tissue expression profiles further showed that most of the selected genes were midgut-biased, with the exception of CYP6K1. The midgut microbiota composition was obtained via 16S rDNA pyrosequencing and was found to be mainly dominated by organisms from the Firmicutes phylum, among which Clostridiales, Lactobacillales and Burkholderiales were the main orders which might assist the host in the food digestion or detoxification of noxious compounds. The preponderant species, Clostridium cellulovorans, was previously reported to degrade lignocellulose efficiently in insects. The abundance of genes involved in digestion, detoxification and response to oxidative stress, and the diversity of microbiota in the midgut might provide P. americana high capacity to adapt to complex environments.

Detection of carboxylesterase and esterase activity in culturable gut bacterial flora isolated from diamondback moth, Plutella xylostella (Linnaeus), from India and its possible role in indoxacarb degradation

Diamondback moth (DBM), Plutella xylostella (Linnaeus), is a notorious pest of brassica crops worldwide and is resistant to all groups of insecticides. The insect system harbors diverse groups of microbiota, which in turn helps in enzymatic degradation of xenobiotic-like insecticides. The present study aimed to determine the diversity of gut microflora in DBM, quantify esterase activity and elucidate their possible role in degradation of indoxacarb. We screened 11 geographic populations of DBM in India and analyzed them for bacterial diversity. The culturable gut bacterial flora underwent molecular characterization with 16S rRNA. We obtained 25 bacterial isolates from larvae (n=13) and adults (n=12) of DBM. In larval gut isolates, gammaproteobacteria was the most abundant (76%), followed by bacilli (15.4%). Molecular characterization placed adult gut bacterial strains into three major classes based on abundance: gammaproteobacteria (66%), bacilli (16.7%) and flavobacteria (16.7%). Esterase activity from 19 gut bacterial isolates ranged from 0.072 to 2.32μmol/min/mg protein. Esterase bands were observed in 15 bacterial strains and the banding pattern differed in Bacillus cereus - KC985225 and Pantoea agglomerans - KC985229. The bands were characterized as carboxylesterase with profenofos used as an inhibitor. Minimal media study showed that B. cereus degraded indoxacarb up to 20%, so it could use indoxacarb for metabolism and growth. Furthermore, esterase activity was greater with minimal media than control media: 1.87 versus 0.26μmol/min/mg protein. Apart from the insect esterases, bacterial carboxylesterase may aid in the degradation of insecticides in DBM.

Analysis of Inter-Individual Bacterial Variation in Gut of Cicada Meimuna mongolica (Hemiptera: Cicadidae)

Intestinal bacterial community plays a crucial role in the nutrition, development, survival, and reproduction of insects. When compared with other insects with piercing-sucking mouthparts, the habitats of cicada nymphs and adults are totally different. However, little is known about the differences in the gut bacterial communities in the nymphs and adults within any cicada species. The diversity of bacteria in the gut of nymphs and adults of both genders of Meimuna mongolica (Distant) was studied using the denaturing gradient gel electrophoresis (DGGE) method. Few inter-individual variations among gut microbiota were observed, suggesting that M. mongolica typically harbors a limited and consistent suite of bacterial species. Bacteria in the genera Pseudomonas and Enterobacter were the predominant components of the gut microflora of M. mongolica at all life stages. Bacteria of Pantoea, Streptococcus, and Uruburuella were also widespread in the cicada samples but at relatively lower concentrations. The relative stability and similarity of the PCR-DGGE patterns indicate that all individuals of this cicada species harbor a characteristic bacterial community which is independent from developmental stages and genders. Related endosymbionts that could be harbored in bacteromes of cicadas were not detected in any gut samples, which could be related to the cicada species and the distribution of these endosymbionts in the cicada cavity, or due to some of the possible limitations of PCR-DGGE community profiling. It is worthwhile to further address if related cicada endosymbiont clades distribute in the alimentary canals and other internal organs through diagnostic PCR using group-specific primer sets.

Bacteria abundance and diversity of different life stages of Plutella xylostella (Lepidoptera: Plutellidae), revealed by bacteria culture-dependent and PCR-DGGE methods

Microbial abundance and diversity of different life stages (fourth instar larvae, pupae and adults) of the diamondback moth, Plutella xylostella L., collected from field and reared in laboratory, were investigated using bacteria culture-dependent method and PCR-DGGE analysis based on the sequence of bacteria 16S rRNA V3 region gene. A large quantity of bacteria was found in all life stages of P. xylostella. Field population had higher quantity of bacteria than laboratory population, and larval gut had higher quantity than pupae and adults. Culturable bacteria differed in different life stages of P. xylostella. Twenty-five different bacterial strains were identified in total, among them 20 strains were presented in larval gut, only 8 strains in pupae and 14 strains in adults were detected. Firmicutes bacteria, Bacillus sp., were the most dominant species in every life stage. 15 distinct bands were obtained from DGGE electrophoresis gel. The sequences blasted in GenBank database showed these bacteria belonged to six different genera. Phylogenetic analysis showed the sequences of the bacteria belonged to the Actinobacteri, Proteobacteria and Firmicutes. Serratia sp. in Proteobacteria was the most abundant species in larval gut. In pupae, unculturable bacteria were the most dominant species, and unculturable bacteria and Serratia sp. were the most dominant species in adults. Our study suggested that a combination of molecular and traditional culturing methods can be effectively used to analyze and to determine the diversity of gut microflora. These known bacteria may play important roles in development of P. xylostella.

Isolation and characterization of bacteria from midgut of the rice water weevil (Coleoptera: Curculionidae)

Gut bacteria are known to play important and often essential roles in the biology of insects. Theoretically, they can be genetically manipulated, then reintroduced into insects to negatively modify specific biological features. The weevil superfamily Curculionoidea is one of the most species-rich and successful animal groups on earth, but currently the overall knowledge of the bacterial communities in weevils and their associations with hosts is still limited. In this study, we isolated and characterized the bacteria in the midgut of an invasive weevil, Lissorhoptrus oryzophilus Kuschel, by culturing methods. Female adults of this weevil were collected from four different geographic regions of the United States and mainland China. Sequencing of the bacterial 16S rRNA amplicons demonstrated that the major culturable gut bacteria of rice water weevil are γ-proteobacteria and Bacilli. The gut bacterial composition differs among regions, with many of the bacteria isolated from only a single region while several were detected from more than one region. Overall, the diversity of gut bacteria in rice water weevil is relatively low. The possible origins of certain bacteria are discussed in relation to the weevil, rice plant, and bacteria.

DNA sequencing reveals the midgut microbiota of diamondback moth, Plutella xylostella (L.) and a possible relationship with insecticide resistance

BACKGROUND

Insect midgut microbiota is important in host nutrition, development and immune response. Recent studies indicate possible links between insect gut microbiota and resistance to biological and chemical toxins. Studies of this phenomenon and symbionts in general have been hampered by difficulties in culture-based approach. In the present study, DNA sequencing was used to examine the midgut microbiota of diamondback moth (DBM), Plutella xylostella (L.), a destructive pest that attacks cruciferous crops worldwide. Its ability to develop resistance to many types of synthetic insecticide and even Bacillus thuringiensis toxins makes it an important species to study.

METHODOLOGY/PRINCIPAL FINDINGS

Bacteria of the DBM larval midgut in a susceptible and two insecticide (chlorpyrifos and fipronil) resistant lines were examined by Illumina sequencing sampled from an insect generation that was not exposed to insecticide. This revealed that more than 97% of the bacteria were from three orders: Enterobacteriales, Vibrionales and Lactobacillales. Both insecticide-resistant lines had more Lactobacillales and the much scarcer taxa Pseudomonadales and Xanthomonadales with fewer Enterobacteriales compared with the susceptible strain. Consistent with this, a second study observed an increase in the proportion of Lactobacillales in the midgut of DBM individuals from a generation treated with insecticides.

CONCLUSIONS/SIGNIFICANCE

This is the first report of high-throughput DNA sequencing of the entire microbiota of DBM. It reveals differences related to inter- and intra-generational exposure to insecticides. Differences in the midgut microbiota among susceptible and insecticide-resistant lines are independent of insecticide exposure in the sampled generations. While this is consistent with the hypothesis that Lactobacillales or other scarcer taxa play a role in conferring DBM insecticide resistance, further studies are necessary to rule out other possibilities. Findings constitute the basis for future molecular work on the functions of insect midgut microbiota taxa and their possible role in conferring host resistance to toxins.

Pseudomonas reactans, a bacterial strain isolated from the intestinal flora of Blattella germanica with anti-Beauveria bassiana activity

Anti-Beauveria bassiana activity of aqueous fecal extracts from conventional German cockroaches [Blattella germanica (L.)] was detected, but was not detected in samples from germ-free German cockroaches. Subsequently, bacterial strain BGI-14 was isolated from the gut of conventional German cockroaches and was identified as Pseudomonas reactans based on 16S rDNA sequence. The strain BGI-14 not only inhibited the germination of conidia, but also inhibited the growth of B. bassiana hyphae. Further studies demonstrated that B. bassiana infections in German cockroaches orally treated with the extracts of BGI-14 fermentation were significantly weakened. Compared with the control group, the cumulative mortality rate of treatment group was reduced by 10.3% at 20 d postinoculation. These studies imply that intestinal flora with anti-B. bassiana activity might contribute to resistance of infection by entomopathogenic fungi.

Proteolytic activity of gut bacteria isolated from the velvet bean caterpillar Anticarsia gemmatalis

The development of proteinase inhibitors as potential insect control agents has been constrained by insect adaptation to these compounds. The velvet bean caterpillar (Anticarsia gemmatalis) is a key soybean pest species that is well-adapted to proteinase inhibitors, particularly serine-proteinase inhibitors, which are abundant in the caterpillar host. The expression of diverse proteolytic enzymes by gut symbionts may allow the velvet bean caterpillar to circumvent proteinase inhibitors produced by the host plant. In this study, we characterized the proteolytic activity of the four nonpathogenic species of gut bacteria isolated from the velvet bean caterpillar-Bacillus cereus, Enterococcus gallinarum, Enterococcus mundtii and Staphylococcus xylosus. Two proteinase substrates, N-α-benzoyl-L-Arg-p-nitroanilide (L-BApNA) and N-α-p-tosyl-L-Arg methyl ester (L-TAME) and five proteinase inhibitors [aprotinin, E-64, ethylenediamine tetraacetic acid (EDTA), pepstatin and N-α-tosyl-L-lysine chloromethyl ketone (TLCK)] as well as CaCl2, pH and temperature profiles were used to characterize the expressed proteolytic activity of these bacterial strains in vitro. Kinetic parameters for proteolytic activity were also estimated. The results of these experiments indicated that serine- and cysteine-proteinase activities were expressed by all four gut bacteria symbionts of the velvet bean caterpillar. The cysteine- and serine-proteinase activities of these gut symbionts were distinct and different from that of gut proteinases of the caterpillar itself. This finding provides support for the potential involvement of gut symbionts in the mitigation of the negative effects of serine-proteinase inhibitors in the velvet bean caterpillar.

Pyrosequencing the Bemisia tabaci transcriptome reveals a highly diverse bacterial community and a robust system for insecticide resistance

Background

Bemisia tabaci (Gennadius) is a phloem-feeding insect poised to become one of the major insect pests in open field and greenhouse production systems throughout the world. The high level of resistance to insecticides is a main factor that hinders continued use of insecticides for suppression of B. tabaci. Despite its prevalence, little is known about B. tabaci at the genome level. To fill this gap, an invasive B. tabaci B biotype was subjected to pyrosequencing-based transcriptome analysis to identify genes and gene networks putatively involved in various physiological and toxicological processes.

Methodology and Principal Findings

Using Roche 454 pyrosequencing, 857,205 reads containing approximately 340 megabases were obtained from the B. tabaci transcriptome. De novo assembly generated 178,669 unigenes including 30,980 from insects, 17,881 from bacteria, and 129,808 from the nohit. A total of 50,835 (28.45%) unigenes showed similarity to the non-redundant database in GenBank with a cut-off E-value of 10–5. Among them, 40,611 unigenes were assigned to one or more GO terms and 6,917 unigenes were assigned to 288 known pathways. De novo metatranscriptome analysis revealed highly diverse bacterial symbionts in B. tabaci, and demonstrated the host-symbiont cooperation in amino acid production. In-depth transcriptome analysis indentified putative molecular markers, and genes potentially involved in insecticide resistance and nutrient digestion. The utility of this transcriptome was validated by a thiamethoxam resistance study, in which annotated cytochrome P450 genes were significantly overexpressed in the resistant B. tabaci in comparison to its susceptible counterparts.

Conclusions

This transcriptome/metatranscriptome analysis sheds light on the molecular understanding of symbiosis and insecticide resistance in an agriculturally important phloem-feeding insect pest, and lays the foundation for future functional genomics research of the B. tabaci complex. Moreover, current pyrosequencing effort greatly enriched the existing whitefly EST database, and makes RNAseq a viable option for future genomic analysis.