Bacterial-derived uracil as a modulator of mucosal immunity and gut-microbe homeostasis in Drosophila

Anti-inflammation mechanisms of a homogeneous polysaccharide from Phyllanthus emblica L. on DSS induced colitis mice via the gut microbiota and metabolites alteration

Phyllanthus emblica L. offers promising therapeutic potential for inflammatory diseases. This study revealed the molecular structure of a homogeneous polysaccharide purified from Phyllanthus emblica L. (PEP-1) and evaluated its anti-inflammatory effects on ulcerative colitis (UC) in mice. In the in vivo experiment, administered in varying dosages to dextran sulfate sodium (DSS)-induced UC models, PEP-1 significantly alleviated colonic symptoms, histological damages and reshaped the gut microbiota. Notably, it adjusted the Firmicutes/Bacteroidetes ratio and reduced pro-inflammatory species, closely aligning with shifts in the fecal metabolites and metabolic pathways such as the metabolism of pyrimidine, beta-alanine, and purine. These findings underscore the potential of PEP-1 as a therapeutic agent for UC, providing insights into the mechanisms through gut microbiota and metabolic modulation.

The Future Exploring of Gut Microbiome-Immunity Interactions: From In Vivo/Vitro Models to In Silico Innovations

Investigating the complex interactions between microbiota and immunity is crucial for a fruitful understanding progress of human health and disease. This review assesses animal models, next-generation in vitro models, and in silico approaches that are used to decipher the microbiome-immunity axis, evaluating their strengths and limitations. While animal models provide a comprehensive biological context, they also raise ethical and practical concerns. Conversely, modern in vitro models reduce animal involvement but require specific costs and materials. When considering the environmental impact of these models, in silico approaches emerge as promising for resource reduction, but they require robust experimental validation and ongoing refinement. Their potential is significant, paving the way for a more sustainable and ethical future in microbiome-immunity research.

Ingestion of Bacillus cereus spores dampens the immune response to favor bacterial persistence

Strains of the Bacillus cereus (Bc) group are sporulating bacteria commonly associated with foodborne outbreaks. Spores are dormant cells highly resistant to extreme conditions. Nevertheless, the pathological processes associated with the ingestion of either vegetative cells or spores remain poorly understood. Here, we demonstrate that while ingestion of vegetative bacteria leads to their rapid elimination from the intestine of Drosophila melanogaster, a single ingestion of spores leads to the persistence of bacteria for at least 10 days. We show that spores do not germinate in the anterior part of the intestine which bears the innate immune defenses. Consequently, spores reach the posterior intestine where they germinate and activate both the Imd and Toll immune pathways. Unexpectedly, this leads to the induction of amidases, which are negative regulators of the immune response, but not to antimicrobial peptides. Thereby, the local germination of spores in the posterior intestine dampens the immune signaling that in turn fosters the persistence of Bc bacteria. This study provides evidence for how Bc spores hijack the intestinal immune defenses allowing the localized birth of vegetative bacteria responsible for the digestive symptoms associated with foodborne illness outbreaks.

Involvement of bacteria in the development of fungal infections in the Colorado potato beetle

Entomopathogenic fungi may interact with insects' symbiotic bacteria during infection. We hypothesized that topical infection with Beauveria bassiana may alter the microbiota of the Colorado potato beetle (CPB) and that these modifications may alter the course of mycoses. We used a model with two concentrations of conidia: (1) high concentration that causes rapid (acute) pathogenesis with fast mortality followed by bacterial decomposition of insects; (2) lower concentration that leads to prolonged pathogenesis ending in conidiation on cadavers. The fungal infections increased loads of enterobacteria and bacilli on the cuticle surface and in hemolymph and midgut, and the greatest increase was detected during the acute mycosis. By contrast, stronger activation of IMD and JAK-STAT signaling pathways in integuments and fat body was observed during the prolonged mycosis. Relatively stable (nonpathogenic) conditions remained in the midgut during both scenarios of mycosis with slight changes in bacterial communities, the absence of mesh and stat expression, a decrease in reactive oxygen species production, and slight induction of Toll and IMD pathways. Oral administration of antibiotic and predominant CPB bacteria (Enterobacteriaceae, Lactococcus, Pseudomonas) led to minor and mainly antagonistic effects in survival of larvae infected with B. bassiana. We believe that prolonged mycosis is necessary for successful development of the fungus because such pathogenesis allows the host to activate antibacterial reactions. Conversely, after infection with high concentrations of the fungus, the host's resources are insufficient to fully activate antibacterial defenses, and this situation makes successful development of the fungus impossible.

Chronic PM2.5 exposure disrupts intestinal barrier integrity via microbial dysbiosis-triggered TLR2/5-MyD88-NLRP3 inflammasome activation

BACKGROUND

PM2.5, a known public health risk, is increasingly linked to intestinal disorders, however, the mechanisms of its impact are not fully understood.

PURPOSE

This study aimed to explore the impact of chronic PM2.5 exposure on intestinal barrier integrity and to uncover the underlying molecular mechanisms.

METHODS

C57BL/6 J mice were exposed to either concentrated ambient PM2.5 (CPM) or filtered air (FA) for six months to simulate urban pollution conditions. We evaluated intestinal barrier damage, microbial shifts, and metabolic changes through histopathology, metagenomics, and metabolomics. Analysis of the TLR signaling pathway was also conducted.

RESULTS

The mean concentration of PM2.5 in the CPM exposure chamber was consistently measured at 70.9 ± 26.8 μg/m³ throughout the study period. Our findings show that chronic CPM exposure significantly compromises intestinal barrier integrity, as indicated by reduced expression of the key tight junction proteins Occludin and Tjp1/Zo-1. Metagenomic sequencing revealed significant shifts in the microbial landscape, identifying 35 differentially abundant species. Notably, there was an increase in pro-inflammatory nongastric Helicobacter species and a decrease in beneficial bacteria, such as Lactobacillus intestinalis, Lactobacillus sp. ASF360, and Eubacterium rectale. Metabolomic analysis further identified 26 significantly altered metabolites commonly associated with intestinal diseases. A strong correlation between altered bacterial species and metabolites was also observed. For example, 4 Helicobacter species all showed positive correlations with 13 metabolites, including Lactate, Bile acids, Pyruvate and Glutamate. Additionally, increased expression levels of TLR2, TLR5, Myd88, and NLRP3 proteins were noted, and their expression patterns showed a strong correlation, suggesting a possible involvement of the TLR2/5-MyD88-NLRP3 signaling pathway.

CONCLUSIONS

Chronic CPM exposure induces intestinal barrier dysfunction, microbial dysbiosis, metabolic imbalance, and activation of the TLR2/5-MyD88-NLRP3 inflammasome. These findings highlight the urgent need for intervention strategies to mitigate the detrimental effects of air pollution on intestinal health and identify potential therapeutic targets.

Fluoropyrimidines affect de novo pyrimidine synthesis impairing biofilm formation in Escherichia coli

Antivirulence agents are considered a promising strategy to treat bacterial infections. Fluoropyrimidines possess antivirulence and antibiofilm activity against Gram-negative bacteria; however, their mechanism of action is yet unknown. Consistent with their known antibiofilm activity, fluoropyrimidines, particularly 5-fluorocytosine (5-FC), impair curli-dependent surface adhesion by Escherichia coli MG1655 via downregulation of curli fimbriae gene transcription. Curli inhibition requires fluoropyrimidine conversion into fluoronucleotides and is not mediated by c-di-GMP or the ymg-rcs envelope stress response axis, previously suggested as the target of fluorouracil antibiofilm activity in E. coli. In contrast, 5-FC hampered the transcription of curli activators RpoS and stimulated the expression of Fis, a curli repressor affected by nucleotide availability. This last observation suggested a possible perturbation of the de novo pyrimidine biosynthesis by 5-FC: indeed, exposure to 5-FC resulted in a ca. 2-fold reduction of UMP intracellular levels while not affecting ATP. Consistently, expression of the de novo pyrimidine biosynthesis genes carB and pyrB was upregulated in the presence of 5-FC. Our results suggest that the antibiofilm activity of fluoropyrimidines is mediated, at least in part, by perturbation of the pyrimidine nucleotide pool. We screened a genome library in search of additional determinants able to counteract the effects of 5-FC. We found that a DNA fragment encoding the unknown protein D8B36_18,480 and the N-terminal domain of the penicillin-binding protein 1b (PBP1b), involved in peptidoglycan synthesis, could restore curli production in the presence of 5-FC. Deletion of the PBP1b-encoding gene mrcB, induced csgBAC transcription, while overexpression of the gene encoding the D8B36_18,480 protein obliterated its expression, possibly as part of a coordinated response in curli regulation with PBP1b. While the two proteins do not appear to be direct targets of 5-FC, their involvement in curli regulation suggests a connection between peptidoglycan biosynthesis and curli production, which might become even more relevant upon pyrimidine starvation and reduced availability of UDP-sugars needed in cell wall biosynthesis. Overall, our findings link the antibiofilm activity of fluoropyrimidines to the redirection of at least two global regulators (RpoS, Fis) by induction of pyrimidine starvation. This highlights the importance of the de novo pyrimidines biosynthesis pathway in controlling virulence mechanisms in different bacteria and makes the pathway a potential target for antivirulence strategies.

DeepIDA-GRU: a deep learning pipeline for integrative discriminant analysis of cross-sectional and longitudinal multiview data with applications to inflammatory bowel disease classification

Biomedical research now commonly integrates diverse data types or views from the same individuals to better understand the pathobiology of complex diseases, but the challenge lies in meaningfully integrating these diverse views. Existing methods often require the same type of data from all views (cross-sectional data only or longitudinal data only) or do not consider any class outcome in the integration method, which presents limitations. To overcome these limitations, we have developed a pipeline that harnesses the power of statistical and deep learning methods to integrate cross-sectional and longitudinal data from multiple sources. In addition, it identifies key variables that contribute to the association between views and the separation between classes, providing deeper biological insights. This pipeline includes variable selection/ranking using linear and nonlinear methods, feature extraction using functional principal component analysis and Euler characteristics, and joint integration and classification using dense feed-forward networks for cross-sectional data and recurrent neural networks for longitudinal data. We applied this pipeline to cross-sectional and longitudinal multiomics data (metagenomics, transcriptomics and metabolomics) from an inflammatory bowel disease (IBD) study and identified microbial pathways, metabolites and genes that discriminate by IBD status, providing information on the etiology of IBD. We conducted simulations to compare the two feature extraction methods.

How infection-triggered pathobionts influence virulence evolution

Host-pathogen interactions can be influenced by the host microbiota, as the microbiota can facilitate or prevent pathogen infections. In addition, members of the microbiota can become virulent. Such pathobionts can cause co-infections when a pathogen infection alters the host immune system and triggers dysbiosis. Here we performed a theoretical investigation of how pathobiont co-infections affect the evolution of pathogen virulence. We explored the possibility that the likelihood of pathobiont co-infection depends on the evolving virulence of the pathogen. We found that, in contrast to the expectation from classical theory, increased virulence is not always selected for. For an increasing likelihood of co-infection with increasing pathogen virulence, we found scenario-specific selection for either increased or decreased virulence. Evolutionary changes, however, in pathogen virulence do not always translate into similar changes in combined virulence of the pathogen and the pathobiont. Only in one of the scenarios where pathobiont co-infection is triggered above a specific virulence level we found a reduction in combined virulence. This was not the case when the probability of pathobiont co-infection linearly increased with pathogen virulence. Taken together, our study draws attention to the possibility that host-microbiota interactions can be both the driver and the target of pathogen evolution. This article is part of the theme issue 'Sculpting the microbiome: how host factors determine and respond to microbial colonization'.

Duox activation in Drosophila Malpighian tubules stimulates intestinal epithelial renewal through a countercurrent flow

The gut must perform a dual role of protecting the host against toxins and pathogens while harboring mutualistic microbiota. Previous studies suggested that the NADPH oxidase Duox contributes to intestinal homeostasis in Drosophila by producing reactive oxygen species (ROS) in the gut that stimulate epithelial renewal. We find instead that the ROS generated by Duox in the Malpighian tubules leads to the production of Upd3, which enters the gut and stimulates stem cell proliferation. We describe in Drosophila the existence of a countercurrent flow system, which pushes tubule-derived Upd3 to the anterior part of the gut and stimulates epithelial renewal at a distance. Thus, our paper clarifies the role of Duox in gut homeostasis and describes the existence of retrograde fluid flow in the gut, collectively revealing a fascinating example of inter-organ communication.

Ingested soil bacteria breach gut epithelia and prime systemic immunity in an insect

Insects lack acquired immunity and were thought to have no immune memory, but recent studies reported a phenomenon called immune priming, wherein sublethal dose of pathogens or nonpathogenic microbes stimulates immunity and prevents subsequential pathogen infection. Although the evidence for insect immune priming is accumulating, the underlying mechanisms are still unclear. The bean bug Riptortus pedestris acquires its gut microbiota from ambient soil and spatially structures them into a multispecies and variable community in the anterior midgut and a specific, monospecies Caballeronia symbiont population in the posterior region. We demonstrate that a particular Burkholderia strain colonizing the anterior midgut stimulates systemic immunity by penetrating gut epithelia and migrating into the hemolymph. The activated immunity, consisting of a humoral and a cellular response, had no negative effect on the host fitness, but on the contrary protected the insect from subsequent infection by pathogenic bacteria. Interruption of contact between the Burkholderia strain and epithelia of the gut weakened the host immunity back to preinfection levels and made the insects more vulnerable to microbial infection, demonstrating that persistent acquisition of environmental bacteria is important to maintain an efficient immunity.

Larval microbiota primes the Drosophila adult gustatory response

The survival of animals depends, among other things, on their ability to identify threats in their surrounding environment. Senses such as olfaction, vision and taste play an essential role in sampling their living environment, including microorganisms, some of which are potentially pathogenic. This study focuses on the mechanisms of detection of bacteria by the Drosophila gustatory system. We demonstrate that the peptidoglycan (PGN) that forms the cell wall of bacteria triggers an immediate feeding aversive response when detected by the gustatory system of adult flies. Although we identify ppk23+ and Gr66a+ gustatory neurons as necessary to transduce fly response to PGN, we demonstrate that they play very different roles in the process. Time-controlled functional inactivation and in vivo calcium imaging demonstrate that while ppk23+ neurons are required in the adult flies to directly transduce PGN signal, Gr66a+ neurons must be functional in larvae to allow future adults to become PGN sensitive. Furthermore, the ability of adult flies to respond to bacterial PGN is lost when they hatch from larvae reared under axenic conditions. Recolonization of germ-free larvae, but not adults, with a single bacterial species, Lactobacillus brevis, is sufficient to restore the ability of adults to respond to PGN. Our data demonstrate that the genetic and environmental characteristics of the larvae are essential to make the future adults competent to respond to certain sensory stimuli such as PGN.

Lactic acid bacteria modulate the CncC pathway to enhance resistance to β-cypermethrin in the oriental fruit fly

The gut microbiota of insects has been shown to regulate host detoxification enzymes. However, the potential regulatory mechanisms involved remain unknown. Here, we report that gut bacteria increase insecticide resistance by activating the cap "n" collar isoform-C (CncC) pathway through enzymatically generated reactive oxygen species (ROS) in Bactrocera dorsalis. We demonstrated that Enterococcus casseliflavus and Lactococcus lactis, two lactic acid-producing bacteria, increase the resistance of B. dorsalis to β-cypermethrin by regulating cytochrome P450 (P450) enzymes and α-glutathione S-transferase (GST) activities. These gut symbionts also induced the expression of CncC and muscle aponeurosis fibromatosis. BdCncC knockdown led to a decrease in resistance caused by gut bacteria. Ingestion of the ROS scavenger vitamin C in resistant strain affected the expression of BdCncC/BdKeap1/BdMafK, resulting in reduced P450 and GST activity. Furthermore, feeding with E. casseliflavus or L. lactis showed that BdNOX5 increased ROS production, and BdNOX5 knockdown affected the expression of the BdCncC/BdMafK pathway and detoxification genes. Moreover, lactic acid feeding activated the ROS-associated regulation of P450 and GST activity. Collectively, our findings indicate that symbiotic gut bacteria modulate intestinal detoxification pathways by affecting physiological biochemistry, thus providing new insights into the involvement of insect gut microbes in the development of insecticide resistance.

Host-microbiota interaction in intestinal stem cell homeostasis

Intestinal stem cells (ISCs) play a pivotal role in gut physiology by governing intestinal epithelium renewal through the precise regulation of proliferation and differentiation. The gut microbiota interacts closely with the epithelium through myriad of actions, including immune and metabolic interactions, which translate into tight connections between microbial activity and ISC function. Given the diverse functions of the gut microbiota in affecting the metabolism of macronutrients and micronutrients, dietary nutrients exert pronounced effects on host-microbiota interactions and, consequently, the ISC fate. Therefore, understanding the intricate host-microbiota interaction in regulating ISC homeostasis is imperative for improving gut health. Here, we review recent advances in understanding host-microbiota immune and metabolic interactions that shape ISC function, such as the role of pattern-recognition receptors and microbial metabolites, including lactate and indole metabolites. Additionally, the diverse regulatory effects of the microbiota on dietary nutrients, including proteins, carbohydrates, vitamins, and minerals (e.g. iron and zinc), are thoroughly explored in relation to their impact on ISCs. Thus, we highlight the multifaceted mechanisms governing host-microbiota interactions in ISC homeostasis. Insights gained from this review provide strategies for the development of dietary or microbiota-based interventions to foster gut health.

Recent trends in insect gut immunity

The gut is a crucial organ in insect defense against various pathogens and harmful substances in their environment and diet. Distinct insect gut compartments possess unique functionalities contributing to their physiological processes, including immunity. The insect gut's cellular composition is vital for cellular and humoral immunity. The peritrophic membrane, mucus layer, lumen, microvilli, and various gut cells provide essential support for activating and regulating immune defense mechanisms. These components also secrete molecules and enzymes that are imperative in physiological activities. Additionally, the gut microbiota initiates various signaling pathways and produces vitamins and minerals that help maintain gut homeostasis. Distinct immune signaling pathways are activated within the gut when insects ingest pathogens or hazardous materials. The pathway induced depends on the infection or pathogen type; include immune deficiency (imd), Toll, JAK/STAT, Duox-ROS, and JNK/FOXO regulatory pathways. These pathways produce different antimicrobial peptides (AMPs) and maintain gut homeostasis. Furthermore, various signaling mechanisms within gut cells regulate insect gut recovery following infection. Although some questions regarding insect gut immunity in different species require additional study, this review provides insights into the insect gut's structure and composition, commensal microorganism roles in Drosophila melanogaster and Tenebrio molitor life cycles, different signaling pathways involved in gut immune systems, and the insect gut post-infection recovery through various signaling mechanisms.

Perish in the Attempt: Regulated Cell Death in Regenerative and Nonregenerative Tissue

Significance: A cell plays its roles throughout its life span, even during its demise. Regulated cell death (RCD) is one of the key topics in modern biomedical studies. It is considered the main approach for removing stressed and/or damaged cells. Research during the past two decades revealed more roles of RCD, such as coordinating tissue development and driving compensatory proliferation during tissue repair. Recent Advances: Compensatory proliferation, initially identified in primitive organisms during the regeneration of lost tissue, is an evolutionarily conserved process that also functions in mammals. Among various types of RCD, apoptosis is considered the top candidate to induce compensatory proliferation in damaged tissue. Critical Issues: The roles of apoptosis in the recovery of nonregenerative tissue are still vague. The roles of other types of RCD, such as necroptosis and ferroptosis, have not been well characterized in the context of tissue regeneration. Future Directions: In this review article, we attempt to summarize the recent insights on the role of RCD in tissue repair. We focus on apoptosis, with expansion to ferroptosis and necroptosis, in primitive organisms with significant regenerative capacity as well as common mammalian research models. After gathering hints from regenerative tissue, in the second half of the review, we take a notoriously nonregenerative tissue, the myocardium, as an example to discuss the role of RCD in terminally differentiated quiescent cells. Antioxid. Redox Signal. 39, 1053-1069.

Dextran sulfate sodium and uracil induce inflammatory effects and disrupt the chitinous peritrophic matrix in the midgut of Tribolium castaneum

Dextran sulfate sodium is used in inflammatory bowel disease (IBD) mice models to trigger chronic intestinal inflammation. In this study, we have analyzed DSS effects in the genetic model and pest beetle, Tribolium castaneum, which can be easily and cost-effectively cultivated and examined in very large quantities compensating for individual variations. We fed the larvae with DSS and uracil, which is known to induce the production of reactive oxygen species by activating DUOX, a member of the NADPH oxidase family. Both chemicals induced IBD-like phenotypes, including impaired growth and development, midgut thickening, epithelial swelling, and a loss of epithelial barrier function. RNAi mediated knockdown of DUOX expression enhanced the effects of DSS and uracil on mortality. Finally, we showed that both treatments result in an altered activity of the intestinal microbiome, similar as observed in IBD patients. Our findings suggest that both chemicals impair the epithelial barrier by increasing the permeability of the peritrophic matrix. The loss of the barrier function may facilitate the entry of midgut bacteria triggering innate immune responses that also affect the intestinal microbiome. As the observed effects resemble those induced by DSS treatment in mice, T. castaneum might be suitable high-throughput invertebrate model for IBD research and preclinical studies.

Differential expression of immunity-related genes in larval Manduca sexta tissues in response to gut and systemic infection

Introduction

The midgut epithelium functions as tissue for nutrient uptake as well as physical barrier against pathogens. Additionally, it responds to pathogen contact by production and release of various factors including antimicrobial peptides, similar to the systemic innate immune response. However, if such a response is restricted to a local stimulus or if it appears in response to a systemic infection, too is a rather underexplored topic in insect immunity. We addressed the role of the midgut and the role of systemic immune tissues in the defense against gut-borne and systemic infections, respectively.

Methods

Manduca sexta larvae were challenged with DAP-type peptidoglycan bacteria - Bacillus thuringiensis for local gut infection and Escherichia coli for systemic stimulation. We compared the immune response to both infection models by measuring mRNA levels of four selected immunity-related genes in midgut, fat body, hematopoietic organs (HOs), and hemocytes, and determined hemolymph antimicrobial activity. Hemocytes and HOs were tested for presence and distribution of lysozyme mRNA and protein.

Results

The midgut and circulating hemocytes exhibited a significantly increased level of lysozyme mRNA in response to gut infection but did not significantly alter expression in response to a systemic infection. Conversely, fat body and HOs responded to both infection models by altered mRNA levels of at least one gene monitored. Most, but not all hemocytes and HO cells contain lysozyme mRNA and protein.

Discussion

These data suggest that the gut recruits immune-related tissues in response to gut infection whereas systemic infections do not induce a response in the midgut. The experimental approach implies a skewed cross-talk: An intestinal infection triggers immune activity in systemic immune organs, while a systemic infection does not elicit any or only a restricted immune response in the midgut. The HOs, which form and release hemocytes in larval M. sexta, i) synthesize lysozyme, and ii) respond to immune challenges by increased immune gene expression. These findings strongly suggest that they not only provide phagocytes for the cellular immune response but also synthesize humoral immune components.

Immunometabolic regulation during the presence of microorganisms and parasitoids in insects

Multicellular organisms live in environments containing diverse nutrients and a wide variety of microbial communities. On the one hand, the immune response of organisms can protect from the intrusion of exogenous microorganisms. On the other hand, the dynamic coordination of anabolism and catabolism of organisms is a necessary factor for growth and reproduction. Since the production of an immune response is an energy-intensive process, the activation of immune cells is accompanied by metabolic transformations that enable the rapid production of ATP and new biomolecules. In insects, the coordination of immunity and metabolism is the basis for insects to cope with environmental challenges and ensure normal growth, development and reproduction. During the activation of insect immune tissues by pathogenic microorganisms, not only the utilization of organic resources can be enhanced, but also the activated immune cells can usurp the nutrients of non-immune tissues by generating signals. At the same time, insects also have symbiotic bacteria in their body, which can affect insect physiology through immune-metabolic regulation. This paper reviews the research progress of insect immune-metabolism regulation from the perspective of insect tissues, such as fat body, gut and hemocytes. The effects of microorganisms (pathogenic bacteria/non-pathogenic bacteria) and parasitoids on immune-metabolism were elaborated here, which provide guidance to uncover immunometabolism mechanisms in insects and mammals. This work also provides insights to utilize immune-metabolism for the formulation of pest control strategies.

Intake of caffeine containing sugar diet remodels gut microbiota and perturbs Drosophila melanogaster immunity and lifespan

The diet-microbiome-immunity axis is one among the many arms that draw up the "we are what we intake" proclamation. As such, studies on the effect of food and beverage intake on the gut environment and microbiome and on modulating immunological responses and the host's susceptibility to pathogens are on the rise. A typical accompaniment in different sustenance we consume on daily basis is the trimethylxanthine alkaloid caffeine. Being a chief component in our regular aliment, a better understanding of the effect of caffeine containing food and beverages on our gut-microbiome-immunity axis and henceforth on our health is much needed. In this study, we shed more light on the effect of oral consumption of caffeine supplemented sugar diet on the gut environment, specifically on the gut microbiota, innate immunity and host susceptibility to pathogens using the Drosophila melanogaster model organism. Our findings reveal that the oral intake of a dose-specific caffeine containing sucrose/agarose sugar diet causes a significant alteration within the fly gut milieu demarcated by microbial dysbiosis and an elevation in the production of reactive oxygen species and expression of immune-deficiency (Imd) pathway-dependent antimicrobial peptide genes. The oral intake of caffeine containing sucrose/agarose sugar diet also renders the flies more susceptible to bacterial infection and shortens their lifespan in both infection and non-infection settings. Our findings set forth additional insight into the potentiality of diet to alter the gut milieu and highlight the importance of dietary control on health.

Homeostatic Regulation of the Duox-ROS Defense System: Revelations Based on the Diversity of Gut Bacteria in Silkworms (Bombyx mori)

The Duox-ROS defense system plays an important role in insect intestinal immunity. To investigate the role of intestinal microbiota in Duox-ROS regulation herein, 16S rRNA sequencing technology was utilized to compare the characteristics of bacterial populations in the midgut of silkworm after different time-periods of treatment with three feeding methods: 1-4 instars artificial diet (AD), 1-4 instars mulberry leaf (ML) and 1-3 instars artificial diet + 4 instar mulberry leaf (TM). The results revealed simple intestinal microbiota in the AD group whilst microbiota were abundant and variable in the ML and TM silkworms. By analyzing the relationship among intestinal pH, reactive oxygen species (ROS) content and microorganism composition, it was identified that an acidic intestinal environment inhibited the growth of intestinal microbiota of silkworms, observed concurrently with low ROS content and a high activity of antioxidant enzymes (SOD, TPX, CAT). Gene expression associated with the Duox-ROS defense system was detected using RT-qPCR and identified to be low in the AD group and significantly higher in the TM group of silkworms. This study provides a new reference for the future improvement of the artificial diet feeding of silkworm and a systematic indicator for the further study of the relationship between changes in the intestinal environment and intestinal microbiota balance caused by dietary alterations.

HMG-like DSP1 is a damage signal to mediate the western flower thrips, Frankliniella occidentalis, immune responses to tomato spotted wilt virus infection

Tomato spotted wilt virus (TSWV) causes a serious plant disease and is transmitted by specific thrips including the western flower thrips, Frankliniella occidentalis. The persistent and circulative virus transmission suggests an induction of immune defenses in the thrips. We investigated the immune responses of F. occidentalis to TSWV infection. Immunofluorescence assay demonstrated viral infection in the larval midguts at early stage and subsequent propagation to the salivary gland in adults. In the larval midgut, TSWV infection led to the release of DSP1, a damage-associated molecular pattern, from the gut epithelium into the hemolymph. DSP1 up-regulated PLA₂ activity, which would lead to biosynthesis of eicosanoids that activate cellular and humoral immune responses. Phenoloxidase (PO) activity was enhanced following induction of PO and its activating protease gene expressions. Antimicrobial peptide genes and dual oxidase, which produces reactive oxygen species, were induced by the viral infection. Expression of four caspase genes increased and TUNEL assay confirmed apoptosis in the larval midgut after the virus infection. These immune responses to viral infection were significantly suppressed by the inhibition of DSP1 release. We infer that TSWV infection induces F. occidentalis immune responses, which are activated by the release of DSP1 from the infection foci within midguts.

Colonization Resistance of Symbionts in Their Insect Hosts

The symbiotic microbiome is critical in promoting insect resistance against colonization by exogenous microorganisms. The mechanisms by which symbionts contribute to the host's immune capacity is referred to as colonization resistance. Symbionts can protect insects from exogenous pathogens through a variety of mechanisms, including upregulating the expression of host immune-related genes, producing antimicrobial substances, and competitively excluding pathogens. Concordantly, insects have evolved fine-tuned regulatory mechanisms to avoid overactive immune responses against symbionts or specialized cells to harbor symbionts. Alternatively, some symbionts have evolved special adaptations, such as the formation of biofilms to increase their tolerance to host immune responses. Here, we provide a review of the mechanisms about colonization resistance of symbionts in their insect hosts. Adaptations of symbionts and their insect hosts that may maintain such symbiotic relationships, and the significance of such relationships in the coevolution of symbiotic systems are also discussed to provide insights into the in-depth study of the contribution of symbionts to host physiology and behavior.

The Drosophila tumor necrosis factor receptor, Wengen, couples energy expenditure with gut immunity

It is well established that tumor necrosis factor (TNF) plays an instrumental role in orchestrating the metabolic disorders associated with late stages of cancers. However, it is not clear whether TNF/TNF receptor (TNFR) signaling controls energy homeostasis in healthy individuals. Here, we show that the highly conserved Drosophila TNFR, Wengen (Wgn), is required in the enterocytes (ECs) of the adult gut to restrict lipid catabolism, suppress immune activity, and maintain tissue homeostasis. Wgn limits autophagy-dependent lipolysis by restricting cytoplasmic levels of the TNFR effector, TNFR-associated factor 3 (dTRAF3), while it suppresses immune processes through inhibition of the dTAK1/TAK1-Relish/NF-κB pathway in a dTRAF2-dependent manner. Knocking down dTRAF3 or overexpressing dTRAF2 is sufficient to suppress infection-induced lipid depletion and immune activation, respectively, showing that Wgn/TNFR functions as an intersection between metabolism and immunity allowing pathogen-induced metabolic reprogramming to fuel the energetically costly task of combatting an infection.

Effects of the pyrE deletion mutant from Bacillus thuringiensis on gut microbiota and immune response of Spodoptera exigua

The gut microbiota is essential for the growth and development of insects, and the intestinal immune system plays a critical role in regulating the homeostasis of intestinal microorganisms and their interactions with pathogenic bacteria. Infection with Bacillus thuringiensis (Bt) can disrupt the gut microbiota of insects, but the regulatory factors governing the interaction between Bt and gut bacteria are not well understood. Uracil secreted by exogenous pathogenic bacteria can activate DUOX-mediated reactive oxygen species (ROS) production, which helps maintain intestinal microbial homeostasis and immune balance. To elucidate the regulatory genes involved in the interaction between Bt and gut microbiota, we investigate the effects of uracil derived from Bt on gut microbiota, and host immunity using a uracil deficient Bt strain (Bt GS57△pyrE) obtained by homologous recombination. We analyze the biological characteristics of the uracil deficient strain and found that the deletion of uracil in Bt GS57 strain changed the diversity of gut bacteria in Spodoptera exigua, as investigated using Illumina HiSeq sequencing. Furthermore, qRT-PCR analysis showed that compared with Bt GS57 (control), the expression of the SeDuox gene and the level of ROS were significantly decreased after feeding with Bt GS57△pyrE. Adding uracil to Bt GS57△pyrE restored the expression level of DUOX and ROS to a higher level. Additionally, we observed that PGRP-SA, attacin, defensin and ceropin genes were significant different in the midgut of S. exigua infected by Bt GS57 and Bt GS57△pyrE, with a trend of increasing first and then decreasing. These results suggest that uracil regulates and activates the DUOX-ROS system, affects the expression of antimicrobial peptide genes, and disturb intestinal microbial homeostasis. We preliminarily speculate that uracil is a key factor in the interaction between Bt and gut microbiota, and these findings provide a theoretical basis for clarifying the interaction between Bt, host, and intestinal microorganisms, as well as for gaining new insights into the insecticidal mechanism of B. thuringiensis in insects.

The tracheal immune system of insects - A blueprint for understanding epithelial immunity

The unique design of respiratory organs in multicellular organisms makes them prone to infection by pathogens. To cope with this vulnerability, highly effective local immune systems evolved that are also operative in the tracheal system of insects. Many pathogens and parasites (including viruses, bacteria, fungi, and metazoan parasites) colonize the trachea or invade the host via this route. Currently, only two modules of the tracheal immune system have been characterized in depth: 1) Immune deficiency pathway-mediated activation of antimicrobial peptide gene expression and 2) local melanization processes that protect the structure from wounding. There is an urgent need to increase our understanding of the architecture of tracheal immune systems, especially regarding those mechanisms that enable the maintenance of immune homeostasis. This need for new studies is particularly exigent for species other than Drosophila.

Administration of Bifidobacterium animalis subsp. lactis strain BB-12® in healthy children: characterization, functional composition, and metabolism of the gut microbiome

Introduction

The consumption of probiotics may influence children's gut microbiome and metabolome, which may reflect shifts in gut microbial diversity composition and metabolism. These potential changes might have a beneficial impact on health. However, there is a lack of evidence investigating the effect of probiotics on the gut microbiome and metabolome of children. We aimed to examine the potential impact of a two (Streptococcus thermophilus and Lactobacillus delbrueckii; S2) vs. three (S2 + Bifidobacterium animalis subsp. lactis strain BB-12) strain-supplemented yogurt.

Methods

Included in this study were 59 participants, aged one to five years old, recruited to phase I of a double-blinded, randomized controlled trial. Fecal samples were collected at baseline, after the intervention, and at twenty days post-intervention discontinuation, and untargeted metabolomics and shotgun metagenomics were performed.

Results

Shotgun metagenomics and metabolomic analyses showed no global changes in either intervention group's gut microbiome alpha or beta diversity indices, except for a lower microbial diversity in the S2 + BB12 group at Day 30. The relative abundance of the two and three intervention bacteria increased in the S2 and S2 + BB12 groups, respectively, from Day 0 to Day 10. In the S2 + BB12 group, the abundance of several fecal metabolites increased at Day 10, including alanine, glycine, lysine, phenylalanine, serine, and valine. These fecal metabolite changes did not occur in the S2 group.

Discussion

In conclusion, there were were no significant differences in the global metagenomic or metabolomic profiles between healthy children receiving two (S2) vs. three (S2 + BB12) probiotic strains for 10 days. Nevertheless, we observed a significant increase (Day 0 to Day 10) in the relative abundance of the two and three probiotics administered in the S2 and S2 + BB12 groups, respectively, indicating the intervention had a measurable impact on the bacteria of interest in the gut microbiome. Future research using longer probiotic intervention durations and in children at risk for gastrointestinal disorders may elucidate if functional metabolite changes confer a protective gastrointestinal effect.

Recognition of commensal bacterial peptidoglycans defines Drosophila gut homeostasis and lifespan

Commensal microbes in animals have a profound impact on tissue homeostasis, stress resistance, and ageing. We previously showed in Drosophila melanogaster that Acetobacter persici is a member of the gut microbiota that promotes ageing and shortens fly lifespan. However, the molecular mechanism by which this specific bacterial species changes lifespan and physiology remains unclear. The difficulty in studying longevity using gnotobiotic flies is the high risk of contamination during ageing. To overcome this technical challenge, we used a bacteria-conditioned diet enriched with bacterial products and cell wall components. Here, we demonstrate that an A. persici-conditioned diet shortens lifespan and increases intestinal stem cell (ISC) proliferation. Feeding adult flies a diet conditioned with A. persici, but not with Lactiplantibacillus plantarum, can decrease lifespan but increase resistance to paraquat or oral infection of Pseudomonas entomophila, indicating that the bacterium alters the trade-off between lifespan and host defence. A transcriptomic analysis using fly intestine revealed that A. persici preferably induces antimicrobial peptides (AMPs), while L. plantarum upregulates amidase peptidoglycan recognition proteins (PGRPs). The specific induction of these Imd target genes by peptidoglycans from two bacterial species is due to the stimulation of the receptor PGRP-LC in the anterior midgut for AMPs or PGRP-LE from the posterior midgut for amidase PGRPs. Heat-killed A. persici also shortens lifespan and increases ISC proliferation via PGRP-LC, but it is not sufficient to alter the stress resistance. Our study emphasizes the significance of peptidoglycan specificity in determining the gut bacterial impact on healthspan. It also unveils the postbiotic effect of specific gut bacterial species, which turns flies into a "live fast, die young" lifestyle.

Regulating metabolism to shape immune function: Lessons from Drosophila

Infection with pathogenic microbes is a severe threat that hosts manage by activating the innate immune response. In Drosophila melanogaster, the Toll and Imd signaling pathways are activated by pathogen-associated molecular patterns to initiate cellular and humoral immune processes that neutralize and kill invaders. The Toll and Imd signaling pathways operate in organs such as fat body and gut that control host nutrient metabolism, and infections or genetic activation of Toll and Imd signaling also induce wide-ranging changes in host lipid, carbohydrate and protein metabolism. Metabolic regulation by immune signaling can confer resistance to or tolerance of infection, but it can also lead to pathology and susceptibility to infection. These immunometabolic phenotypes are described in this review, as are changes in endocrine signaling and gene regulation that mediate survival during infection. Future work in the field is anticipated to determine key variables such as sex, dietary nutrients, life stage, and pathogen characteristics that modify immunometabolic phenotypes and, importantly, to uncover the mechanisms used by the immune system to regulate metabolism.

Eucommia Polysaccharides Ameliorate Aging-Associated Gut Dysbiosis: A Potential Mechanism for Life Extension in Drosophila

The gut microbiota is increasingly considered to play a key role in human immunity and health. The aging process alters the microbiota composition, which is associated with inflammation, reactive oxygen species (ROS), decreased tissue function, and increased susceptibility to age-related diseases. It has been demonstrated that plant polysaccharides have beneficial effects on the gut microbiota, particularly in reducing pathogenic bacteria abundance and increasing beneficial bacteria populations. However, there is limited evidence of the effect of plant polysaccharides on age-related gut microbiota dysbiosis and ROS accumulation during the aging process. To explore the effect of Eucommiae polysaccharides (EPs) on age-related gut microbiota dysbiosis and ROS accumulation during the aging process of Drosophila, a series of behavioral and life span assays of Drosophila with the same genetic background in standard medium and a medium supplemented with EPs were performed. Next, the gut microbiota composition and protein composition of Drosophila in standard medium and the medium supplemented with EPs were detected using 16S rRNA gene sequencing analysis and quantitative proteomic analysis. Here, we show that supplementation of Eucommiae polysaccharides (EPs) during development leads to the life span extension of Drosophila. Furthermore, EPs decreased age-related ROS accumulation and suppressed Gluconobacter, Providencia, and Enterobacteriaceae in aged Drosophila. Increased Gluconobacter, Providencia, and Enterobacteriaceae in the indigenous microbiota might induce age-related gut dysfunction in Drosophila and shortens their life span. Our study demonstrates that EPs can be used as prebiotic agents to prevent aging-associated gut dysbiosis and reactive oxidative stress.

Administration of Bifidobacterium animalis subsp. lactis Strain BB-12 ® in Healthy Children: Characterization, Functional Composition, and Metabolism of the Gut Microbiome

The consumption of probiotics may influence children's gut microbiome and metabolome, which may reflect shifts in gut microbial diversity composition and metabolism. These potential changes might have a beneficial impact on health. However, there is a lack of evidence investigating the effect of probiotics on the gut microbiome and metabolome of children. We aimed to examine the potential impact of a two ( Streptococcus thermophilus and Lactobacillus delbrueckii ; S2) vs . three (S2 + Bifidobacterium animalis subsp. lactis strain BB-12) strain-supplemented yogurt. Included in this study were 59 participants, aged one to five years old, recruited to phase I of a double-blinded, randomized controlled trial. Fecal samples were collected at baseline, after the intervention, and at twenty days post-intervention discontinuation, and untargeted metabolomics and shotgun metagenomics were performed. Shotgun metagenomics and metabolomic analyses showed no global changes in either intervention group's gut microbiome alpha or beta diversity indices. The relative abundance of the two and three intervention bacteria increased in the S2 and S2 + BB12 groups, respectively, from Day 0 to Day 10 . In the S2+BB12 group, the abundance of several fecal metabolites was reduced at Day 10 , including alanine, glycine, lysine, phenylalanine, serine, and valine. These fecal metabolite changes did not occur in the S2 group. Future research using longer probiotic intervention durations and in children at risk for gastrointestinal disorders may elucidate if functional metabolite changes confer a protective gastrointestinal effect.

The endocrine disruptor, fenoxycarb modulates gut immunity and gut bacteria titer in the cotton bollworm, Helicoverpa armigera

The endocrine system modulates several physiological functions such as development and metamorphosis in insects. The normal growth and development of insects is interfered with insect growth regulators (IGRs), which act as mimics of insect hormones like juvenile hormone (JH) and ecdysone hormone. The effects of JH and its analogs on systemic immunity have been identified. However the effect of these compounds on local gut immunity is largely unknown. In this study, the effects of JH analog fenoxycarb on the local gut immunity of Helicoverpa armigera, gut bacteria population, and their role in the pathogenicity of Bacillus thuringiensis (Bt) were analyzed. The results showed that feeding fenoxycarb causes a decrease in the transcription level of IMD (Relish and PGPR-LC), ROS (DUOX and SOD) related genes and antimicrobial peptides (AMPs), followed by an overpopulation of gut bacteria. The fenoxycarb-treated larvae showed higher susceptibility to Bt compared to the control larvae. Overall, these findings collectively suggest that JH analog affects local gut immunity and gut bacteria titer.

Damage signal induced by Bacillus thuringiensis infection triggers immune responses via a DAMP molecule in lepidopteran insect, Spodoptera exigua

Insect immunity defends the infection of an insect pathogenic bacterium, Bacillus thuringiensis (Bt). However, it was not clear on the recognition of Bt infection by the insect immune system. This study tested a physiological function of dorsal switch protein 1 (DSP1) in the Bt infection. DSP1 is classified into HMGB1-like damage-associated molecular pattern (DAMP) in insects. Upon Bt infection in a lepidopteran Spodoptera exigua, DSP1 was released from the nuclei of the midgut epithelium and activated immune responses. For this DSP1 release, a functional binding between Bt and its receptors on the midgut epithelium was required because any RNA interference (RNAi) treatments of Bt receptor (cadherin or ABCC) prevented the DSP1 release and became susceptible to the bacterial infection. The DSP1 release was required for the gene induction of Repat33, which is a member of response to pathogen gene family and its gene product mediated cellular and humoral immune responses against pathogen infection in S. exigua. The released DSP1 activated phospholipase A₂ (PLA₂) to produce eicosanoids, which induced the Repat33 expression because a hemocoelic injection of a recombinant DSP1 induced the Repat33 expression without Bt infection. However, any inhibition of PLA₂ activity impaired the DAMP signaling between DSP1 and Repat33. DSP1 also up-regulated two other immune mediators, nitric oxide (NO) and a cytokine called plasmatocyte-spreading peptide (PSP). Either NO or PSP activated PLA₂ to up-regulate Repat33 expression. These results suggest that Bt infection of the insect midgut generates a DAMP signal via DSP1 release, which turns on NO or the cytokine-PLA₂-Repat33 immune signaling pathway.

Experimental bacterial dysbiosis with consequent immune alterations increase intrarectal SIV acquisition susceptibility

Variations in the composition of the intestinal bacterial microbiome correlate with acquisition of some sexually transmitted pathogens. To experimentally assess the contribution of intestinal dysbiosis to rectal lentiviral acquisition, we induce dysbiosis in rhesus macaques (RMs) with the antibiotic vancomycin prior to repeated low-dose intrarectal challenge with simian immunodeficiency virus (SIV) SIVmac239X. Vancomycin administration reduces T helper 17 (TH17) and TH22 frequencies, increases expression of host bacterial sensors and antibacterial peptides, and increases numbers of transmitted-founder (T/F) variants detected upon SIV acquisition. We observe that SIV acquisition does not correlate with measures of dysbiosis but rather associates with perturbations in the host antimicrobial program. These findings establish a functional association between the intestinal microbiome and susceptibility to lentiviral acquisition across the rectal epithelial barrier.

The role of Drosophila microbiota in gut homeostasis and immunity

The gut epithelia of virtually all animals harbor complex microbial communities that play an important role in maintaining immune and cellular homeostasis. Gut microbiota have evolutionarily adapted to the host gut environment, serving as key regulators of intestinal stem cells to promote a healthy gut barrier and modulate epithelial self-renewal. Disruption of these populations has been associated with inflammatory disorders or cancerous lesions of the intestine. However, the molecular mechanisms controlling gut-microbe interactions are only partially understood due to the high diversity and biologically dynamic nature of these microorganisms. This article reviews the current knowledge on Drosophila gut microbiota and its role in signaling pathways that are crucial for the induction of distinct homeostatic and immune responses. Thanks to the genetic tractability of Drosophila and its cultivable and simple microbiota, this association model offers new efficient tools for investigating the crosstalk between a host and its microbiota while providing a framework for a better understanding of the ecological and evolutionary roles of the microbiome.

Comparative analysis of gut microbiota and immune genes linked with the immune system of wild and captive Spodoptera frugiperda (Lepidoptera: Noctuidae)

The fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith), is one of the most highly polyphagous invasive pests causing serious damage to maize crops in China. However, little is known about the gut immune responses to the environment, particularly along the migration routes in Jianghuai, China, throughout the autumn and winter. In this study, high-throughput sequencing and real-time quantitative PCR (RT-qPCR) were employed to examine the variations in immune genes and gut microbiome communities between captive and wild fall armyworm populations. Results showed that the diversity and community of the gut's microbes were higher in wild populations, and the average weighted UniFrac distance between bacterial taxa varied. A wide variety of immune genes were more abundant in the wild populations than in others. Results indicated that diets and different survival conditions impacted the gut microbiota and immune system of S. frugiperda, which was crucial for environmental adaptation. These differences in gut microbiota and immune responses between wild and captive Fall armyworms are critical for comprehending the symbiotic relationship between microbes, immune genes, and hosts. They also highlight the need for increased focus on developing more effective and environmentally friendly pest control methods.

The Intestinal Immune Defense System in Insects

Over a long period of evolution, insects have developed unique intestinal defenses against invasion by foreign microorganisms, including physical defenses and immune responses. The physical defenses of the insect gut consist mainly of the peritrophic matrix (PM) and mucus layer, which are the first barriers to pathogens. Gut microbes also prevent the colonization of pathogens. Importantly, the immune-deficiency (Imd) pathways produce antimicrobial peptides to eliminate pathogens; mechanisms related to reactive oxygen species are another important pathway for insect intestinal immunity. The janus kinase/STAT signaling pathway is involved in intestinal immunity by producing bactericidal substances and regulating tissue repair. Melanization can produce many bactericidal active substances into the intestine; meanwhile, there are multiple responses in the intestine to fight against viral and parasitic infections. Furthermore, intestinal stem cells (ISCs) are also indispensable in intestinal immunity. Only the coordinated combination of the intestinal immune defense system and intestinal tissue renewal can effectively defend against pathogenic microorganisms.

High-throughput screening of caterpillars as a platform to study host-microbe interactions and enteric immunity

Mammalian models of human disease are expensive and subject to ethical restrictions. Here, we present an independent platform for high-throughput screening, using larvae of the tobacco hornworm Manduca sexta, combining diagnostic imaging modalities for a comprehensive characterization of aberrant phenotypes. For validation, we use bacterial/chemical-induced gut inflammation to generate a colitis-like phenotype and identify significant alterations in morphology, tissue properties, and intermediary metabolism, which aggravate with disease progression and can be rescued by antimicrobial treatment. In independent experiments, activation of the highly conserved NADPH oxidase DUOX, a key mediator of gut inflammation, leads to similar, dose-dependent alterations, which can be attenuated by pharmacological interventions. Furthermore, the developed platform could differentiate pathogens from mutualistic gastrointestinal bacteria broadening the scope of applications also to microbiomics and host-pathogen interactions. Overall, larvae-based screening can complement mammals in preclinical studies to explore innate immunity and host-pathogen interactions, thus representing a substantial contribution to improve mammalian welfare.

Dorsal switch protein 1 as a damage signal in insect gut immunity to activate dual oxidase via an eicosanoid, PGE2

Various microbiota including beneficial symbionts reside in the insect gut. Infections of pathogens cause dysregulation of the microflora and threaten insect survival. Reactive oxygen species (ROS) have been used in the gut immune responses, in which its production is tightly regulated by controlling dual oxidase (Duox) activity via Ca2+ signal to protect beneficial microflora and gut epithelium due to its high cytotoxicity. However, it was not clear how the insects discriminate the pathogens from the various microbes in the gut lumen to trigger ROS production. An entomopathogenic nematode (Steinernema feltiae) infection elevated ROS level in the gut lumen of a lepidopteran insect, Spodoptera exigua. Dorsal switch protein 1 (DSP1) localized in the nucleus in the midgut epithelium was released into plasma upon the nematode infection and activated phospholipase A2 (PLA2). The activated PLA2 led to an increase of PGE2 level in the midgut epithelium, in which rising Ca2+ signal up-regulated ROS production. Inhibiting DSP1 release by its specific RNA interference (RNAi) or specific inhibitor, 3-ethoxy-4-methoxyphenol, treatment failed to increase the intracellular Ca2+ level and subsequently prevented ROS production upon the nematode infection. A specific PLA2 inhibitor treatment also prevented the up-regulation of Ca2+ and subsequent ROS production upon the nematode infection. However, the addition of PGE2 to the inhibitor treatment rescued the gut immunity. DSP1 release was not observed at infection with non-pathogenic pathogens but detected in plasma with pathogenic infections that would lead to damage to the gut epithelium. These results indicate that DSP1 acts as a damage-associated molecular pattern in gut immunity through DSP1/PLA2/Ca2+/Duox.

Drosophila melanogaster as a model to study innate immune memory

Over the last decades, research regarding innate immune responses has gained increasing importance. A growing body of evidence supports the notion that the innate arm of the immune system could show memory traits. Such traits are thought to be conserved throughout evolution and provide a survival advantage. Several models are available to study these mechanisms. Among them, we find the fruit fly, Drosophila melanogaster. This non-mammalian model has been widely used for innate immune research since it naturally lacks an adaptive response. Here, we aim to review the latest advances in the study of the memory mechanisms of the innate immune response using this animal model.

Tiny Drosophila intestinal stem cells, big power

The signaling pathways are highly conserved between Drosophila and mammals concerning intestinal development, regeneration, and disease. The powerful genetic tools of Drosophila make it a valuable and convenient alternative to answer basic biological questions that can not be addressed using mammalian models. In this review, we discuss recent advances in how we use fly midgut to answer the following key questions: (1) How intestine stem cell niches are established; (2) which factors control asymmetric division of stem cells; (3) how intestinal cells interact with environmental factors, such as tissue damage, microbiota, and diet; (4) how to screen aging/cancer-related factors or drugs by fly intestine stem cells.

Comparison of Gut Bacterial Communities of Locusta migratoria manilensis (Meyen) Reared on Different Food Plants

Simple Summary

Although locusts can cause major agricultural damage, they also constitute a valuable food resource. At present, L. migratoria manilensis has been largely domesticated, being considered an edible insect in China. Feeding variety is one of the main characteristics of L. migratoria manilensis. There are apparent differences in the capacity of locusts to adapt to different food plants. To elucidate the effect of different food plants (i.e., goosegrass, maize leaves, soybean leaves, and pakchoi) on the growth and development of L. migratoria manilensis, the gut bacterial community composition of L. migratoria manilensis fifth instars fed on different plants was analyzed by high-throughput sequencing. Gut bacterial communities were affected by food plants and may play an essential role in host adaption. Feeding on different food plants has significant effects on the growth and development of L. migratoria manilensis. The present study establishes a theoretical foundation for studying the interplay between gut bacteria structure and L. migratoria manilensis adaptation.

Abstract

Locusts, in particular Locusta migratoria manilensis (Meyen), have been associated with major damages in agriculture, forestry, and animal husbandry in China. At present, L. migratoria manilensis has been largely domesticated, being considered an edible insect in China. Feeding variety is one of the main characteristics of L. migratoria manilensis. It has been demonstrated that microorganisms inhabiting the insect gut impact nutrition, development, defense, and reproduction of the insect host. The aim of the present study was to search for the adaptation mechanism of L. migratoria manilensis feeding on four different food plants (goosegrass, maize leaves, soybean leaves, and pakchoi) and explore changes in the gut bacterial community structure of the insect at the fifth instar nymph stage. Proteobacteria and Firmicutes were the dominant phyla, whereas Kluyvera, Enterobacter, Pseudocitrobacter, Klebsiella, Cronobacter, Citrobacter, Lactococcus, and Weissella were the dominant genera in the gut of L. migratoria manilensis. Principal component analysis and permutational multivariate analysis of variance (PERMANOVA) revealed significant differences in the gut microbiota structure of L. migratoria manilensis fed on different food plants. Moreover, functional prediction analysis revealed that metabolic and cellular processes were the most enriched categories. Within the category of metabolic processes, the most enriched pathways were carbohydrate transport and metabolism; amino acid transport and metabolism; translation, ribosomal structure, and biogenesis; cell wall/membrane/envelope biogenesis; inorganic ion transport and metabolism; and energy production and conversion. Collectively, the present results revealed that the structure of gut bacterial communities in L. migratoria manilensis fed on different food plants is impacted by food plants, which may play an essential part in the adaptation of the host.

Microbiota aggravates the pathogenesis of Drosophila acutely exposed to vehicle exhaust

Vehicle exhaust (VE) is the primary cause of urban air pollution, which adversely affects the respiratory system, exacerbates lung diseases, and results in high mortality rates. However, the underlying mechanism of the pathogenesis is largely unclear. Here, we developed a Drosophila model to systematically investigate the effects of VE on their health and physiology. We found that VE significantly impaired life span and locomotion in Drosophila. Interestingly, there was an increase in bacterial load in the guts upon VE exposure, suggesting VE is able to induce dysbiosis in the guts. Microbiota depletion can ameliorate the impairment of life span and locomotion. VE causes permeability of intestinal epithelial cells and increases proliferation of intestinal cells, suggesting VE disrupts intestinal homeostasis. We elucidate the underlying mechanism by which VE triggers Imd and DUOX gene expression. Taken together, this Drosophila model provides insight into the pathogenesis of Drosophila exposure to VE, enabling us to better understand the specific role of microbiota.

Phage delivered CRISPR-Cas system to combat multidrug-resistant pathogens in gut microbiome

The Host-microbiome interactions that exist inside the gut microbiota operate in a synergistic and abnormal manner. Additionally, the normal homeostasis and functioning of gut microbiota are frequently disrupted by the intervention of Multi-Drug Resistant (MDR) pathogens. CRISPR-Cas (CRISPR-associated protein with clustered regularly interspersed short palindromic repeats) recognized as a prokaryotic immune system has emerged as an effective genome-editing tool to edit and delete specific microbial genes for the expulsion of bacteria through bactericidal action. In this review, we demonstrate many functioning CRISPR-Cas systems against the anti-microbial resistance of multiple pathogens, which infiltrate the gastrointestinal tract. Moreover, we discuss the advancement in the development of a phage-delivered CRISPR-Cas system for killing a gut MDR pathogen. We also discuss a combinatorial approach to use bacteriophage as a delivery system for the CRISPR-Cas gene for targeting a pathogenic community in the gut microbiome to resensitize the drug sensitivity. Finally, we discuss engineered phage as a plausible potential option for the CRISPR-Cas system for pathogenic killing and improvement of the efficacy of the system.

Bt Cry1Ab/2Ab toxins disrupt the structure of the gut bacterial community of Locusta migratoria through host immune responses

The gut microbiota of insects plays a vital role in digestion, nutrient acquisition, metabolism of dietary toxins, pathogen immunity and maintenance of gut homeostasis. Bacillus thuringinensis (Bt) poisons target insects through its toxins that are activated in the insect gut. The effects of Bt toxins on gut microbiota of insects and their underlying mechanisms are not well understood. In this study, we found that Cry1Ab/2Ab toxins significantly changed the gut bacterial community's structure and reduced the total load of gut bacteria in the Locusta migratoria. In addition, Cry toxins significantly increased the level of reactive oxygen species (ROS) in the gut of locusts. Our results also showed that Cry1Ab/2Ab toxins induced the host gut's immune response by up-regulating of key genes in the Immune deficiency (IMD) and Toll pathway. RNA interference showed that knocking down Relish could narrow the difference in the load, diversity, and composition in gut bacteria caused by Cry toxins. Our findings suggest that Bt potentially influences the gut bacterial community of L. migratoria through host immune response.

A Black Raspberry-Rich Diet Protects From Dextran Sulfate Sodium-Induced Intestinal Inflammation and Host Metabolic Perturbation in Association With Increased Aryl Hydrocarbon Receptor Ligands in the Gut Microbiota of Mice

Dietary modulation of the gut microbiota recently received considerable attention, and ligand activation of aryl hydrocarbon receptor (AHR) plays a pivotal role in intestinal immunity. Importantly, black raspberry (BRB, Rubus occidentalis) is associated with a variety of beneficial health effects. We aim to investigate effects of a BRB-rich diet on dextran sulfate sodium (DSS)-induced intestinal inflammation and to determine whether its consequent anti-inflammatory effects are relevant to modulation of the gut microbiota, especially its production of AHR ligands. A mouse model of DSS-induced intestinal inflammation was used in the present study. C57BL/6J mice were fed either AIN-76A or BRB diet. Composition and functions of the gut microbiota were assessed by 16S rRNA sequencing and comparative metagenome analysis. Metabolic profiles of host and the gut microbiome were assessed by serum and fecal metabolomic profiling and identification. BRB diet was found to ameliorate DSS-induced intestinal inflammation and host metabolic perturbation. BRB diet also protected from DSS-induced perturbation in diversity and composition in the gut microbiota. BRB diet promoted AHR ligand production by the gut microbiota, as revealed by increased levels of fecal AHR activity in addition to increased levels of two known AHR ligands, hemin and biliverdin. Accordingly, enrichment of bacterial genes and pathways responsible for production of hemin and biliverdin were found, specific gut bacteria that are highly correlated with abundances of hemin and biliverdin were also identified. BRB dietary intervention ameliorated intestinal inflammation in mice in association with promotion of AHR ligand production by the gut microbiota.

The Role of Microbiota in Drosophila melanogaster Aging

Intestinal microbial communities participate in essential aspects of host biology, including nutrient acquisition, development, immunity, and metabolism. During host aging, dramatic shifts occur in the composition, abundance, and function of the gut microbiota. Although such changes in the microbiota are conserved across species, most studies remain descriptive and at most suggest a correlation between age-related pathology and particular microbes. Therefore, the causal role of the microbiota in host aging has remained a challenging question, in part due to the complexity of the mammalian intestinal microbiota, most of which is not cultivable or genetically amenable. Here, we summarize recent studies in the fruit fly Drosophila melanogaster that have substantially progressed our understanding at the mechanistic level of how gut microbes can modulate host aging.

Role of Insect Gut Microbiota in Pesticide Degradation: A Review

Insect pests cause significant agricultural and economic losses to crops worldwide due to their destructive activities. Pesticides are designed to be poisonous and are intentionally released into the environment to combat the menace caused by these noxious pests. To survive, these insects can resist toxic substances introduced by humans in the form of pesticides. According to recent findings, microbes that live in insect as symbionts have recently been found to protect their hosts against toxins. Symbioses that have been formed are between the pests and various microbes, a defensive mechanism against pathogens and pesticides. Insects' guts provide unique conditions for microbial colonization, and resident bacteria can deliver numerous benefits to their hosts. Insects vary significantly in their reliance on gut microbes for basic functions. Insect digestive tracts are very different in shape and chemical properties, which have a big impact on the structure and composition of the microbial community. Insect gut microbiota has been found to contribute to feeding, parasite and pathogen protection, immune response modulation, and pesticide breakdown. The current review will examine the roles of gut microbiota in pesticide detoxification and the mechanisms behind the development of resistance in insects to various pesticides. To better understand the detoxifying microbiota in agriculturally significant pest insects, we provided comprehensive information regarding the role of gut microbiota in the detoxification of pesticides.

HMG-Like DSP1 Mediates Immune Responses of the Western Flower Thrips (Frankliniella occidentalis) Against Beauveria bassiana, a Fungal Pathogen

Western flower thrips, Frankliella occidentalis, is a serious pest by directly infesting host crops. It can also give indirect damage to host crops by transmitting a plant virus called tomato spotted wilt virus. A fungal pathogen, Beauveria bassiana, can infect thrips. It has been used as a biopesticide. However, little is known on the defense of thrips against this fungal pathogen. This study assessed the defense of thrips against the fungal infection with respect to immunity by analyzing immune-associated genes of F. occidentalis in both larvae and adults. Immunity-associated genes of western flower thrips were selected from three immunity steps: nonself recognition, mediation, and immune responses. For the pathogen recognition step, dorsal switch protein 1 (DSP1) was chosen. For the immune mediation step, phospholipase A₂ (PLA₂) and prostaglandin E₂ synthase were also selected. For the step of immune responses, two phenoloxidases (PO) genes and four proPO-activating peptidase genes involved in melanization against pathogens were chosen. Dual oxidase gene involved in the production of reactive oxygen species and four antimicrobial peptide genes for executing humoral immune responses were selected. All immunity-associated genes were inducible to the fungal infection. Their expression levels were induced higher in adults than in larvae by the fungal infections. However, inhibitor treatments specific to DSP1 or PLA₂ significantly suppressed the inducible expression of these immune-associated genes, leading to significant enhancement of fungal pathogenicity. These results suggest that immunity is essential for thrips to defend against B. bassiana, in which DSP1 and eicosanoids play a crucial role in eliciting immune responses.