The microbiota drives diurnal rhythms in tryptophan metabolism in the stressed gut

Chronic stress disrupts microbiota-gut-brain axis function and is associated with altered tryptophan metabolism, impaired gut barrier function, and disrupted diurnal rhythms. However, little is known about the effects of acute stress on the gut and how it is influenced by diurnal physiology. Here, we used germ-free and antibiotic-depleted mice to understand how microbiota-dependent oscillations in tryptophan metabolism would alter gut barrier function at baseline and in response to an acute stressor. Cecal metabolomics identified tryptophan metabolism as most responsive to a 15-min acute stressor, while shotgun metagenomics revealed that most bacterial species exhibiting rhythmicity metabolize tryptophan. Our findings highlight that the gastrointestinal response to acute stress is dependent on the time of day and the microbiome, with a signature of stress-induced functional alterations in the ileum and altered tryptophan metabolism in the colon.

The impact of acute and chronic stress on gastrointestinal physiology and function: a microbiota-gut-brain axis perspective

The physiological consequences of stress often manifest in the gastrointestinal tract. Traumatic or chronic stress is associated with widespread maladaptive changes throughout the gut, although comparatively little is known about the effects of acute stress. Furthermore, these stress-induced changes in the gut may increase susceptibility to gastrointestinal disorders and infection, and impact critical features of the neural and behavioural consequences of the stress response by impairing gut-brain axis communication. Understanding the mechanisms behind changes in enteric nervous system circuitry, visceral sensitivity, gut barrier function, permeability, and the gut microbiota following stress is an important research objective with pathophysiological implications in both neurogastroenterology and psychiatry. Moreover, the gut microbiota has emerged as a key aspect of physiology sensitive to the effects of stress. In this review, we focus on different aspects of the gastrointestinal tract including gut barrier function as well as the immune, humoral and neuronal elements involved in gut-brain communication. Furthermore, we discuss the evidence for a role of stress in gastrointestinal disorders. Existing gaps in the current literature are highlighted, and possible avenues for future research with an integrated physiological perspective have been suggested. A more complete understanding of the spatial and temporal dynamics of the integrated host and microbial response to different kinds of stressors in the gastrointestinal tract will enable full exploitation of the diagnostic and therapeutic potential in the fast-evolving field of host-microbiome interactions.

Detection of Bile Acids in Complex Matrices Using a Transcription Factor-Based Biosensor

Bile acids play an important role in digestion and human health, are found throughout the gastrointestinal tract, and are excreted in feces. Therefore, bile acids are promising biomarkers for monitoring health and detecting fecal contamination in water sources. Here, we engineered a bile acid sensor by expressing the transcription factor BreR, a TetR-like repressor from Vibrio cholorae, in Escherichia coli. The sensor was further optimized by screening a promoter library. To further characterize the BreR sensor and increase its utility, we moved expression to a cell-free expression (CFE) system, resulting in an approximately 3 orders of magnitude increase in deoxycholic acid sensitivity. We next optimized this sensor to detect bile acids in fecal water, wastewater, and serum and transferred the CFE sensor to a paper-based assay to enhance fieldability.

Evaluation of Human Performance Aiding Live Synthetically Engineered Bacteria in a Gut-on-a-Chip

Synbiotics are a new class of live therapeutics employing engineered genetic circuits. The rapid adoption of genetic editing tools has catalyzed the expansion of possible synbiotics, exceeding traditional testing paradigms in terms of both throughput and model complexity. Herein, we present a simplistic gut-chip model using common Caco2 and HT-29 cell lines to establish a dynamic human screening platform for a cortisol sensing tryptamine producing synbiotic for cognitive performance sustainment. The synbiotic, SYN, was engineered from the common probiotic E. coli Nissle 1917 strain. It had the ability to sense cortisol at physiological concentrations, resulting in the activation of a genetic circuit that produces tryptophan decarboxylase and converts bioavailable tryptophan to tryptamine. SYN was successfully cultivated within the gut-chip showing log-phase growth comparable to the wild-type strain. Tryptophan metabolism occurred quickly in the gut compartment when exposed to 5 μM cortisol, resulting in the complete conversion of bioavailable tryptophan into tryptamine. The flux of tryptophan and tryptamine from the gut to the vascular compartment of the chip was delayed by 12 h, as indicated by the detectable tryptamine in the vascular compartment. The gut-chip provided a stable environment to characterize the sensitivity of the cortisol sensor and dynamic range by altering cortisol and tryptophan dosimetry. Collectively, the human gut-chip provided human relevant apparent permeability to assess tryptophan and tryptamine metabolism, production, and transport, enabled host analyses of cellular viability and pro-inflammatory cytokine secretion, and succeeded in providing an efficacy test of a novel synbiotic. Organ-on-a-chip technology holds promise in aiding traditional therapeutic pipelines to more rapidly down select high potential compounds that reduce the failure rate and accelerate the opportunity for clinical intervention.

Meeting report of the sixth annual tri-service microbiome consortium symposium

The Tri-Service Microbiome Consortium (TSMC) was founded to enhance collaboration, coordination, and communication of microbiome research among DoD organizations and to facilitate resource, material and information sharing amongst consortium members, which includes collaborators in academia and industry. The 6th Annual TSMC Symposium was a hybrid meeting held in Fairlee, Vermont on 27-28 September 2022 with presentations and discussions centered on microbiome-related topics within seven broad thematic areas: (1) Human Microbiomes: Stress Response; (2) Microbiome Analysis & Surveillance; (3) Human Microbiomes Enablers & Engineering; (4) Human Microbiomes: Countermeasures; (5) Human Microbiomes Discovery - Earth & Space; (6) Environmental Micro & Myco-biome; and (7) Environmental Microbiome Analysis & Engineering. Collectively, the symposium provided an update on the scope of current DoD microbiome research efforts, highlighted innovative research being done in academia and industry that can be leveraged by the DoD, and fostered collaborative opportunities. This report summarizes the activities and outcomes from the 6th annual TSMC symposium.

Current advances in microbiome sciences within the US Department of Defense: part 2 - enabling technologies and environmental microbiomes

Microbiomes involve complex microbial communities wherein the micro-organisms interact with one another as well as their associated hosts or environmental niches. Much of the characterisation of these communities and the associations have been achieved through 'omics' technologies, such as metagenomics, metaproteomics and metametabolomics, and model systems. Recent research in host-associated microbiomes has been aimed at understanding the role microbes may play in host fitness or conversely how host activities/conditions may perturb the microbial community, which can further affect host health. These studies have led to the investigation of detection, intervention or modulation methods, which may serve to provide benefits to the host and advance our understanding of microbiome associations. With the clear implications on human health and disease, the US Department of Defense (DoD) has made microbiome research a priority, with the founding of the Tri-Service Microbiome Consortium (TSMC) to enhance collaboration, coordination,and communication of microbiome research among DoD organisations and partners in academia and industry. DoD microbiome research focuses mainly on the following themes: (1) human health and performance, (2) environmental microbiomes and (3) enabling technologies. This review provides an update of current DoD microbiome research efforts centred on enabling technologies and environmental microbiomes and highlights innovative research being done in academia and industry that can be leveraged by the DoD. These topics were also communicated and further discussed in the Fifth Annual TSMC Symposium. This paper forms part of the special issue of BMJ Military Health dedicated to personalised digital technology for mental health in the Armed Forces.

Current advances in microbiome sciences within the US Department of Defense-part 1: microbiomes for human health and performance

Microbiomes involve complex microbial communities where the microorganisms interact with one another as well as their associated hosts or environmental niches. The characterisation of these communities and associations have largely been achieved through 'omics' technologies, such as metagenomics, metaproteomics and metametabolomics, and model systems. Recent research in host-associated microbiomes have been aimed at understanding the roles microbes may play in host fitness or conversely how host activities/conditions may perturb the microbial community, which can further affect host health. These studies have led to the investigation of detection, intervention or modulation methods, which may serve to provide benefits to the host and advance our understanding of microbiome associations. With the clear implications on human health and disease, the US Department of Defense (DoD) has made microbiome research a priority, with the founding of the Tri-Service Microbiome Consortium (TSMC) to enhance collaboration, coordination and communication of microbiome research among DoD organisations and partners in academia and industry. DoD microbiome research focuses mainly on the following themes: (1) Human health and performance; (2) Environmental microbiomes; and (3) Enabling technologies. This review provides an update of current DoD microbiome research efforts centred on human health and performance and highlights innovative research being done in academia and industry that can be leveraged by the DoD. These topics were also communicated and further discussed during the fifth Annual TSMC Symposium. This paper forms part of the special issue of BMJ Military Health dedicated to Personalised Digital Technology for Mental Health in the Armed Forces.

Exploring Changes in the Host Gut Microbiota During a Controlled Human Infection Model for Campylobacter jejuni

Campylobacter jejuni infection is a leading cause of foodborne disease, common to children, adult travelers, and military populations in low- to middle-income countries. In the absence of a licensed vaccine, efforts to evaluate prophylactic agents are underway. The prophylactic efficacy of a twice-daily, 550 mg dose of the antibiotic rifaximin demonstrated no efficacy against campylobacteriosis in a controlled human infection model (CHIM); however, samples from the CHIM study were utilized to assess how the human gut microbiome responds to C. jejuni infection, and if a ‘protective’ microbiota exists in study participants not developing campylobacteriosis. Statistically significant, but minor, differences in study participant beta diversity were identified during the challenge period (p = 0.002, R² = 0.042), but no significant differences were otherwise observed. Pre-challenge alpha diversity was elevated in study participants who did not develop campylobacteriosis compared to those who did (p < 0.001), but alpha diversity declined in all study participants from the pre-challenge period to post-discharge. Our work provides insight into gut microbiome shifts observed during a C. jejuni CHIM and following antibiotic treatment. This study utilized a high dose of 1.7 x 10⁵ colony-forming units of C. jejuni; future work could include CHIM studies performed with inocula more closely mimicking natural exposure as well as field studies involving naturally-occurring enteric infections.

Meeting report of the fourth annual Tri-Service Microbiome Consortium symposium

The Tri-Service Microbiome Consortium (TSMC) was founded to enhance collaboration, coordination, and communication of microbiome research among U.S. Department of Defense (DoD) organizations. The annual TSMC symposium is designed to enable information sharing between DoD scientists and leaders in the field of microbiome science, thereby keeping DoD consortium members informed of the latest advances within the microbiome community and facilitating the development of new collaborative research opportunities. The 2020 annual symposium was held virtually on 24-25 September 2020. Presentations and discussions centered on microbiome-related topics within four broad thematic areas: (1) Enabling Technologies; (2) Microbiome for Health and Performance; (3) Environmental Microbiome; and (4) Microbiome Analysis and Discovery. This report summarizes the presentations and outcomes of the 4th annual TSMC symposium.

In vitro fermentation test bed for evaluation of engineered probiotics in polymicrobial communities

In vitro fermentation systems offer significant opportunity for deconvoluting complex metabolic dynamics within polymicrobial communities, particularly those associated with the human gut microbiome. In vitro gut models have broad experimental capacity allowing rapid evaluation of multiple parameters, generating knowledge to inform design of subsequent in vivo studies. Here, our method describes an in vitro fermentation test bed to provide a physiologically-relevant assessment of engineered probiotics circuit design functions. Typically, engineered probiotics are evaluated under pristine, mono- or co-culture conditions and transitioned directly into animal or human studies, commonly resulting in a loss of desired function when introduced to complex gut communities. Our method encompasses a systematic workflow entailing fermentation, molecular and functional characterization, and statistical analyses to validate an engineered probiotic’s persistence, plasmid stability and reporter response. To demonstrate the workflow, simplified polymicrobial communities of human gut microbial commensals were utilized to investigate the probiotic Escherichia coli Nissle 1917 engineered to produce a fluorescent reporter protein. Commensals were assembled with increasing complexity to produce a mock community based on nutrient utilization. The method assesses engineered probiotic persistence in a competitive growth environment, reporter production and function, effect of engineering on organism growth and influence on commensal composition. The in vitro test bed represents a new element within the Design-Build-Test-Learn paradigm, providing physiologically-relevant feedback for circuit re-design and experimental validation for transition of engineered probiotics to higher fidelity animal or human studies.

A Pilot Study of the Effect of Deployment on the Gut Microbiome and Traveler's Diarrhea Susceptibility

Traveler's diarrhea (TD) is a recurrent and significant issue for many travelers including the military. While many known enteric pathogens exist that are causative agents of diarrhea, our gut microbiome may also play a role in TD susceptibility. To this end, we conducted a pilot study of the microbiome of warfighters prior to- and after deployment overseas to identify marker taxa relevant to TD. This initial study utilized full-length 16S rRNA gene sequencing to provide additional taxonomic resolution toward identifying predictive taxa.16S rRNA analyses of pre- and post-deployment fecal samples identified multiple marker taxa as significantly differentially abundant in subjects that reported diarrhea, including Weissella, Butyrivibrio, Corynebacterium, uncultivated Erysipelotrichaceae, Jeotgallibaca, unclassified Ktedonobacteriaceae, Leptolinea, and uncultivated Ruminiococcaceae. The ability to identify TD risk prior to travel will inform prevention and mitigation strategies to influence diarrhea susceptibility while traveling.

Gut-brain axis serotonergic responses to acute stress exposure are microbiome-dependent

BACKGROUND

Understanding the mechanisms underpinning the response to acute stress is critical for determining how this can be modulated in both health and disease and across sexes. Stress can markedly alter the microbiome and gut-brain axis signaling with the serotonergic system being particularly sensitive to acute stress. As the impact of acute stress on regional serotonergic dynamics in the gut-brain axis and the contribution of the microbiome to this are poorly appreciated, we used microbiota-deficient mice to assess whether the serotonergic response to acute stress exposure is microbiome dependent.

METHODS

Adult male and female conventional, germ-free, and colonized germ-free mice underwent a single acute stressor and samples were harvested immediately or 45 minutes following stress. Serotonin and related metabolites and serotonergic gene expression were determined.

KEY RESULTS

Our data clearly show the microbiota influenced gastrointestinal serotonergic response to acute stress in a sex- and region-dependent manner. Male-specific poststress increases in colonic serotonin were absent in germ-free mice but normalized following colonization. mRNA serotonergic gene expression was differentially expressed in colon and ileum of germ-free mice on a sex-dependent basis. Within the frontal cortex, absence of the microbiome altered basal serotonin, its main metabolite 5-hydroxyindoleacetic acid, and prevented stress-induced increases in serotonin turnover.

CONCLUSIONS AND INFERENCES

The gut microbiome influences the set points of the brain and gastrointestinal serotonergic systems and affected their response to acute stress in a sex- and region-dependent manner.

Epidemiology and associated microbiota changes in deployed military personnel at high risk of traveler's diarrhea

Travelers’ diarrhea (TD) is the most prevalent illness encountered by deployed military personnel and has a major impact on military operations, from reduced job performance to lost duty days. Frequently, the etiology of TD is unknown and, with underreporting of cases, it is difficult to accurately assess its impact. An increasing number of ailments include an altered or aberrant gut microbiome. To better understand the relationships between long-term deployments and TD, we studied military personnel during two nine-month deployment cycles in 2015–2016 to Honduras. To collect data on the prevalence of diarrhea and impact on duty, a total of 1173 personnel completed questionnaires at the end of their deployment. 56.7% reported reduced performance and 21.1% reported lost duty days. We conducted a passive surveillance study of all cases of diarrhea reporting to the medical unit with 152 total cases and a similar pattern of etiology. Enteroaggregative E. coli (EAEC, 52/152), enterotoxigenic E. coli (ETEC, 50/152), and enteropathogenic E. coli (EPEC, 35/152) were the most prevalent pathogens detected. An active longitudinal surveillance of 67 subjects also identified diarrheagenic E. coli as the primary etiology (7/16 EPEC, 7/16 EAEC, and 6/16 ETEC). Eleven subjects were recruited into a nested longitudinal substudy to examine gut microbiome changes associated with deployment. A 16S rRNA amplicon survey of fecal samples showed differentially abundant baseline taxa for subjects who contracted TD versus those who did not, as well as detection of taxa positively associated with self-reported gastrointestinal distress. Disrupted microbiota was also qualitatively observable for weeks preceding and following the incidents of TD. These findings illustrate the complex etiology of diarrhea amongst military personnel in deployed settings and its impacts on job performance. Potential factors of resistance or susceptibility can provide a foundation for future clinical trials to evaluate prevention and treatment strategies.

Evaluation of Probiotics for Warfighter Health and Performance

The probiotic industry continues to grow in both usage and the diversity of products available. Scientific evidence supports clinical use of some probiotic strains for certain gastrointestinal indications. Although much less is known about the impact of probiotics in healthy populations, there is increasing consumer and scientific interest in using probiotics to promote physical and psychological health and performance. Military men and women are a unique healthy population that must maintain physical and psychological health in order to ensure mission success. In this narrative review, we examine the evidence regarding probiotics and candidate probiotics for physical and/or cognitive benefits in healthy adults within the context of potential applications for military personnel. The reviewed evidence suggests potential for certain strains to induce biophysiological changes that may offer physical and/or cognitive health and performance benefits in military populations. However, many knowledge gaps exist, effects on health and performance are generally not widespread among the strains examined, and beneficial findings are generally limited to single studies with small sample sizes. Multiple studies with the same strains and using similar endpoints are needed before definitive recommendations for use can be made. We conclude that, at present, there is not compelling scientific evidence to support the use of any particular probiotic(s) to promote physical or psychological performance in healthy military personnel. However, plausibility for physical and psychological health and performance benefits remains, and additional research is warranted. In particular, research in military cohorts would aid in assessing the value of probiotics for supporting physical and psychological health and performance under the unique demands required of these populations.

Meeting report of the third annual Tri-Service Microbiome Consortium symposium

The Tri-Service Microbiome Consortium (TSMC) was founded to enhance collaboration, coordination, and communication of microbiome research among U.S. Department of Defense (DoD) organizations and to facilitate resource, material and information sharing among consortium members. The 2019 annual symposium was held 22-24 October 2019 at Wright-Patterson Air Force Base in Dayton, OH. Presentations and discussions centered on microbiome-related topics within five broad thematic areas: 1) human microbiomes; 2) transitioning products into Warfighter solutions; 3) environmental microbiomes; 4) engineering microbiomes; and 5) microbiome simulation and characterization. Collectively, the symposium provided an update on the scope of current DoD microbiome research efforts, highlighted innovative research being done in academia and industry that can be leveraged by the DoD, and fostered collaborative opportunities. This report summarizes the presentations and outcomes of the 3rd annual TSMC symposium.

Phenotype diffusion and one health: A proposed framework for investigating the plurality of obesity epidemics across many species

We propose the idea of "phenotype diffusion," which is a rapid convergence of an observed trait in some human and animal populations. The words phenotype and diffusion both imply observations independent of mechanism as phenotypes are observed traits with multiple possible genetic mechanisms and diffusion is an observed state of being widely distributed. Recognizing shared changes in phenotype in multiple species does not by itself reveal a particular mechanism such as a shared exposure, shared adaptive need, particular stochastic process or a transmission pathway. Instead, identifying phenotype diffusion suggests the mechanism should be explored to help illuminate the ways human and animal health are connected and new opportunities for optimizing these links. Using the plurality of obesity epidemics across multiple species as a prototype for shared changes in phenotype, the goal of this review was to explore eco-evolutionary theories that could inform further investigation. First, evolutionary changes described by hologenome evolution, pawnobe evolution, transposable element (TE) thrust and the drifty gene hypothesis will be discussed within the context of the selection asymmetries among human and animal populations. Secondly, the ecology of common source exposures (bovine milk, xenohormesis and "obesogens"), niche evolution and the hygiene hypothesis will be summarized. Finally, we synthesize these considerations. For example, many agricultural breeds have been aggressively selected for weight gain, microbiota (e.g., adenovirus 36, toxoplasmosis) associated with (or infecting) these breeds cause experimental weight gain in other animals, and these same microbes are associated with human obesity. We propose applications of phenotype diffusion could include zoonotic biosurveillance, biocontainment, antibiotic stewardship and environmental priorities. The One Health field is focused on the connections between the health of humans, animals and the environment, and so identification of phenotype diffusion is highly relevant for practitioners (public health officials, physicians and veterinarians) in this field.

Amplifying Riboswitch Signal Output Using Cellular Wiring

If fieldable riboswitch-based biological sensors are to fulfill their potential, it is necessary to increase their signal output. Here we report a novel modular amplification system using a riboswitch to initiate signaling between a sensing strain and a reporter strain of E. coli. A quorum sensing signaling molecule biologically wires the sensing and reporter strains together. The amplification circuit increased the amount of fluorescence generated on ligand binding compared to when the riboswitch controlled fluorescence expression directly. This had the corollary effect of increasing the sensitivity of the system, and allowed riboswitch-based reporting in E. coli strains that did not produce a detectable output when the riboswitch directly controlled reporter expression. The amplification circuit also reduced the time required to detect a signal output. The modularity of this amplification system coupled with the achievable increases in output can advance the development of riboswitches and biological sensors.

Riboswitch-Based Reversible Dual Color Sensor

Riboswitches are RNA-based "sensors" that utilize chemically induced structural changes in the 5'-untranslated region of mRNA to regulate expression of downstream genes. Coupling a specific riboswitch with a reporter gene system translates chemical detection by the cell into a quantifiable reporter protein signal. For the majority of reporter gene systems, the readout signal is only expressed in the presence of the target analyte. This makes it difficult to determine the viability and localization of the uninduced biosensor when it is used for "real-word" applications. To address this problem, we developed a dual-color reporter comprising elements of the E. coli fimbriae phase variation system: recombinase FimE controlled by a synthetic riboswitch and an invertible DNA segment (fimS) containing a constitutively active promoter placed between two fluorescent protein genes. Without an analyte, the fluorescent reporter constitutively expressed green fluorescent protein (GFPa1). Addition of the analyte initiated translation of fimE causing unidirectional inversion of the fimS segment and constitutive expression of red fluorescent protein (mKate2). Thus, the sensor is always fluorescent, but its color is determined by detection of a specific analyte. We demonstrate that the recombinase-based dual-color reporter can be successfully applied to monitor the activation of a theophylline synthetic riboswitch that was used as our model system. To show the feasibility of the FimE recombinase-based system to serve as a reporter for monitoring activation of multiple synthetic riboswitches and, therefore, expand the applicability of the system, we tested a number of previously developed synthetic riboswitches responsive to different analytes. We show that the dual-color reporter system can be successfully used to monitor activation of M6 and M6″ riboswitches responsive to ammeline and pyrimido[4,5-d]pyrimidine-2,4-diamine, respectively, and a 2,4,6-trinitrotoluene-responsive riboswitch developed in this study. We also demonstrate that the system can be reversed by HbiF recombinase-mediated fimS inversion to the initial state of the fluorescent reporter, creating a resettable and reusable cell-based sensor.

Identifying the cellular mechanisms of symbiont-induced epithelial morphogenesis in the squid-Vibrio association

The symbiotic association between the Hawaiian bobtail squid Euprymna scolopes and the luminous marine bacterium Vibrio fischeri provides a unique opportunity to study epithelial morphogenesis. Shortly after hatching, the squid host harvests bacteria from the seawater using currents created by two elaborate fields of ciliated epithelia on the surface of the juvenile light organ. After light organ colonization, the symbiont population signals the gradual loss of the ciliated epithelia through apoptosis of the cells, which culminates in the complete regression of these tissues. Whereas aspects of this process have been studied at the morphological, biochemical, and molecular levels, no in-depth analysis of the cellular events has been reported. Here we describe the cellular structure of the epithelial field and present evidence that the symbiosis-induced regression occurs in two steps. Using confocal microscopic analyses, we observed an initial epithelial remodeling, which serves to disable the function of the harvesting apparatus, followed by a protracted regression involving actin rearrangements and epithelial cell extrusion. We identified a metal-dependent gelatinolytic activity in the symbiont-induced morphogenic epithelial fields, suggesting the involvement of Zn-dependent matrix metalloproteinase(s) (MMP) in light organ morphogenesis. These data show that the bacterial symbionts not only induce apoptosis of the field, but also change the form, function, and biochemistry of the cells as part of the morphogenic program.

Elucidation of small RNAs that activate transcription in bacteria

Small non-coding RNA (sRNA) control of gene expression has been shown to play a prominent role in genetic regulation. While the majority of identified bacterial sRNAs exert their control at the translational level, a few examples of bacterial sRNAs that inhibit transcription have also been identified. Using an engineered combinatorial RNA library, we have elucidated bacterial sRNAs that activate transcription of a target gene in E. coli to varying degrees. Mutation of the strongest activator modified its activation potential. Our results suggest that transcriptional activation of our target gene results from recruitment of the bacterial RNA polymerase complex to the promoter region. These data, coupled with the malleability of RNA, provide a context to define synthetic control of genes in bacteria at the transcriptional level.

Identification and molecular characterization of a complement C3 molecule in a lophotrochozoan, the Hawaiian bobtail squid Euprymna scolopes

Examination of the EST database of the light organ of the Hawaiian bobtail squid Euprymna scolopes revealed a sequence with similarity to complement C3. RACE yielded the full open reading frame of this protein. Analysis of the resultant sequence revealed that Es-C3 (E. scolopes-C3) has conserved residues and domains known to be critical for C3 function. The gene encoding C3 was expressed in all tissues tested, indicating that its expression is widely distributed throughout the animal's body. Immunocytochemistry using an antibody against Es-C3 revealed that the protein is produced principally in the apical surfaces of epithelial cells. The finding of the gene encoding C3 in this mollusk extends the occurrence of this molecule to the lophotrochozoans, demonstrating that complement genes occur in all major branches of the animal kingdom.

Characterization and role of p53 family members in the symbiont-induced morphogenesis of the Euprymna scolopes light organ

Within hours of hatching, the squid Euprymna scolopes forms a specific light organ symbiosis with the marine luminous bacterium Vibrio fischeri. Interactions with the symbiont result in the loss of a complex ciliated epithelium dedicated to promoting colonization of host tissue, and some or all of this loss is due to widespread, symbiont-induced apoptosis. Members of the p53 family, including p53, p63, and p73, are conserved across broad phyletic lines and p63 is thought to be the ancestral gene. These proteins have been shown to induce apoptosis and developmental morphogenesis. In this study, we characterized p63-like transcripts from mRNA isolated from the symbiotic tissues of E. scolopes and described their role in symbiont-induced morphogenesis. Using degenerate RT-PCR and RACE PCR, we identified two p63-like transcripts encoding proteins of 431 and 567 amino acids. These transcripts shared identical nucleotides where they overlapped, suggesting that they are splice variants of the same gene. Immunocytochemistry and Western blots using an antibody specific for E. scolopes suggested that the p53 family members are activated in cells of the symbiont-harvesting structures of the symbiotic light organ. We propose that once the symbiosis is initiated, a symbiont-induced signal activates p53 family members, inducing apoptosis and developmental morphogenesis of the light organ.

An annotated cDNA library of juvenile Euprymna scolopes with and without colonization by the symbiont Vibrio fischeri

BACKGROUND

Biologists are becoming increasingly aware that the interaction of animals, including humans, with their coevolved bacterial partners is essential for health. This growing awareness has been a driving force for the development of models for the study of beneficial animal-bacterial interactions. In the squid-vibrio model, symbiotic Vibrio fischeri induce dramatic developmental changes in the light organ of host Euprymna scolopes over the first hours to days of their partnership. We report here the creation of a juvenile light-organ specific EST database.

RESULTS

We generated eleven cDNA libraries from the light organ of E. scolopes at developmentally significant time points with and without colonization by V. fischeri. Single pass 3' sequencing efforts generated 42,564 expressed sequence tags (ESTs) of which 35,421 passed our quality criteria and were then clustered via the UIcluster program into 13,962 nonredundant sequences. The cDNA clones representing these nonredundant sequences were sequenced from the 5' end of the vector and 58% of these resulting sequences overlapped significantly with the associated 3' sequence to generate 8,067 contigs with an average sequence length of 1,065 bp. All sequences were annotated with BLASTX (E-value < -03) and Gene Ontology (GO).

CONCLUSION

Both the number of ESTs generated from each library and GO categorizations are reflective of the activity state of the light organ during these early stages of symbiosis. Future analyses of the sequences identified in these libraries promise to provide valuable information not only about pathways involved in colonization and early development of the squid light organ, but also about pathways conserved in response to bacterial colonization across the animal kingdom.

Identifying components of the NF-kappaB pathway in the beneficial Euprymna scolopes-Vibrio fischeri light organ symbiosis

The Toll/NF-kappaB pathway is a common, evolutionarily conserved innate immune pathway that modulates the responses of animal cells to microbe-associated molecular patterns (MAMPs). Because MAMPs have been implicated as critical elements in the signaling of symbiont-induced development, an expressed sequence tag library from the juvenile light organ of Euprymna scolopes was used to identify members of the Toll/NF-kappaB pathway. Full-length transcripts were identified by using 5' and 3' RACE PCR. Seven transcripts critical for MAMP-induced triggering of the Toll/NF-kappaB phosphorylation cascade have been identified, including receptors, signal transducers, and a transcription factor. Further investigations should elucidate the role of the Toll/NF-kappaB pathway in the initiation of the beneficial symbiosis between E. scolopes and Vibrio fischeri.