The microbiota-gut-brain axis: neurobehavioral correlates, health and sociality

Complete Genome Sequence of Bifidobacterium longum GT15: Unique Genes for Russian Strains

In this study, we report the first completely annotated genome sequence of the Russian-origin Bifidobacterium longum subsp. longum strain GT15. We discovered 35 unique genes (UGs) which were detected from only the B. longum GT15 genome and were absent from other B. longum strain genomes (not of Russian origin).

Friends with social benefits: host-microbe interactions as a driver of brain evolution and development?

The tight association of the human body with trillions of colonizing microbes that we observe today is the result of a long evolutionary history. Only very recently have we started to understand how this symbiosis also affects brain function and behavior. In this hypothesis and theory article, we propose how host-microbe associations potentially influenced mammalian brain evolution and development. In particular, we explore the integration of human brain development with evolution, symbiosis, and RNA biology, which together represent a “social triangle” that drives human social behavior and cognition. We argue that, in order to understand how inter-kingdom communication can affect brain adaptation and plasticity, it is inevitable to consider epigenetic mechanisms as important mediators of genome-microbiome interactions on an individual as well as a transgenerational time scale. Finally, we unite these interpretations with the hologenome theory of evolution. Taken together, we propose a tighter integration of neuroscience fields with host-associated microbiology by taking an evolutionary perspective.

A deregulated intestinal cell cycle program disrupts tissue homeostasis without affecting longevity in Drosophila

Recent studies illuminate a complex relationship between the control of stem cell division and intestinal tissue organization in the model system Drosophila melanogaster. Host and microbial signals drive intestinal proliferation to maintain an effective epithelial barrier. Although it is widely assumed that proliferation induces dysplasia and shortens the life span of the host, the phenotypic consequences of deregulated intestinal proliferation for an otherwise healthy host remain unexplored. To address this question, we genetically isolated and manipulated the cell cycle programs of adult stem cells and enterocytes. Our studies revealed that cell cycle alterations led to extensive cell death and morphological disruptions. Despite the extensive tissue damage, we did not observe an impact on longevity, suggesting a remarkable degree of plasticity in intestinal function.

An insight into the gastrointestinal component of fibromyalgia: clinical manifestations and potential underlying mechanisms

Fibromyalgia syndrome is characterized by chronic generalized pain accompanied by a broad symptomatologic spectrum. Besides chronic fatigue, sleep disturbances, headaches and cognitive dysfunction that are extensively described in the literature, a considerable proportion of patients with fibromyalgia experience gastrointestinal symptoms that are commonly overlooked in the studies that are not specifically dedicated to evaluate these manifestations. Nevertheless, various attempts were undertaken to explore the gastrointestinal dimension of fibromyalgia. Several studies have demonstrated an elevated comorbidity of irritable bowel syndrome (IBS) among patients with fibromyalgia. Other studies have investigated the frequency of presentation of gastrointestinal symptoms in fibromyalgia in a nonspecific approach describing several gastrointestinal complaints frequently reported by these patients such as abdominal pain, dyspepsia and bowel changes, among others. Several underlying mechanisms that require further investigation could serve as potential explanatory hypotheses for the appearance of such manifestations. These include sensitivity to dietary constituents such as gluten, lactose or FODMAPs or alterations in the brain-gut axis as a result of small intestinal bacterial overgrowth or subclinical enteric infections such as giardiasis. The gastrointestinal component of fibromyalgia constitutes a relevant element of the multidisciplinary pathophysiologic mechanisms underlying fibromyalgia that need to be unveiled, as this would contribute to the adequate designation of relevant treatment alternatives corresponding to these manifestations.

Pathophysiology of autism spectrum disorders: Revisiting gastrointestinal involvement and immune imbalance

Autism spectrum disorders (ASD) comprise a group of neurodevelopmental abnormalities that begin in early childhood and are characterized by impairment of social communication and behavioral problems including restricted interests and repetitive behaviors. Several genes have been implicated in the pathogenesis of ASD, most of them are involved in neuronal synaptogenesis. A number of environmental factors and associated conditions such as gastrointestinal (GI) abnormalities and immune imbalance have been linked to the pathophysiology of ASD. According to the March 2012 report released by United States Centers for Disease Control and Prevention, the prevalence of ASD has sharply increased during the recent years and one out of 88 children suffers now from ASD symptoms. Although there is a strong genetic base for the disease, several associated factors could have a direct link to the pathogenesis of ASD or act as modifiers of the genes thus aggravating the initial problem. Many children suffering from ASD have GI problems such as abdominal pain, chronic diarrhea, constipation, vomiting, gastroesophageal reflux, and intestinal infections. A number of studies focusing on the intestinal mucosa, its permeability, abnormal gut development, leaky gut, and other GI problem raised many questions but studies were somehow inconclusive and an expert panel of American Academy of Pediatrics has strongly recommended further investigation in these areas. GI tract has a direct connection with the immune system and an imbalanced immune response is usually seen in ASD children. Maternal infection or autoimmune diseases have been suspected. Activation of the immune system during early development may have deleterious effect on various organs including the nervous system. In this review we revisited briefly the GI and immune system abnormalities and neuropeptide imbalance and their role in the pathophysiology of ASD and discussed some future research directions.

The microbiome in early life: self-completion and microbiota protection as health priorities

This minireview considers the benefits of refocusing attention away from treating the patient as a mammalian human to managing the complete patient: a majority microbial superorganism. Under the "completed self" model for formation of the human-microbial superorganism, the single, most pivotal sign in distinguishing a life course of health versus that filled with disease is self-completion (i.e., seeding of the minority mammalian human by the majority microbial portion of the symbiont). From a disease prevention perspective, microbial seeding at birth and subsequent nurturing of the microbiota are significant steps to reduce the risk of both noncommunicable diseases (e.g., type 1 diabetes) and certain infectious diseases. Management of the microbiome during pregnancy, birth, and shortly thereafter appears to be the most significant critical window for healthy superorganism formation. However, the bolus for microbiota seeding at birth and the nurturing process are subject to environmental influences and disruption, such as exposure to toxic chemicals and drugs, infections, and other physical and psychological stressors. Additionally, childhood and adult corrective measures, such as fecal transplantation and administration of prebiotics and probiotics, while potentially useful, may have limitations that are yet to be fully defined. This minireview considers (1) basic features of management of the microbiome to facilitate self-completion, (2) protection of the microbiota from environmental hazards, and (3) the benefits of using a superorganism focus for health management beginning with pregnancy and extending throughout childhood and adult life.

SYNbiotics Easing Renal failure by improving Gut microbiologY (SYNERGY): a protocol of placebo-controlled randomised cross-over trial

BACKGROUND

Emerging evidence suggests modulating the microbiota in the large bowel of patients with chronic kidney disease (CKD) through pre- and/probiotic supplementation may inhibit the development of key nephrovascular toxins. To date, quality intervention trials investigating this novel treatment in CKD are lacking. The aim of SYNERGY is to assess the effectiveness of synbiotics (co-administration of pre- and probiotics) as a potential treatment targeting the synthesis of uremic toxins, specifically, indoxyl sulphate (IS) and p-cresyl sulphate (PCS).

METHODS/DESIGN

Thirty-seven patients with moderate to severe CKD (Stage IV and V, pre-dialysis) will be recruited to a double-blind, placebo-controlled, randomised cross-over trial. Patients will be provided with synbiotic therapy or placebo for 6 weeks, with a 4 week washout before cross-over. The primary outcome is serum IS, total and free (unbound) concentrations, measured using ultra-performance liquid chromatography. Secondary outcomes include serum PCS, total and free (unbound) concentrations; cardiovascular risk, measured by serum lipopolysaccharides, serum trimethylamine-N-oxide (TMAO) and inflammation and oxidative stress markers; kidney damage, measured by 24 hour proteinuria and albuminuria, estimated glomerular filtration rate and renal tubule damage (urinary kidney injury molecule-1); patients' self assessed quality of life; and gastrointestinal symptoms. In addition, the effects on the community structure of the stool microbiota will be explored in a subset of patients to validate the mechanistic rationale underpinning the synbiotic therapy.

DISCUSSION

IS and PCS are two novel uremic toxins implicated in both cardiovascular disease (CVD) and progression of CKD. Preliminary studies indicate that synbiotic therapy maybe a promising strategy when considering a targeted, tolerable and cost-efficient therapy for lowering serum IS and PCS concentrations. This trial will provide high quality 'proof-of-concept' data to elucidate both the efficacy of synbiotic therapy for lowering the toxins and whether reductions in serum IS and PCS translate into clinical benefits. Considering the potential of pre- and probiotics to not only shift toxin levels, but to also impede CVD and CKD progression, SYNERGY will provide vital insight into the effectiveness of this innocuous nutritional therapy.

TRIAL REGISTRATION

Universal Trial Number: U1111-1142-4363. Australian New Zealand Clinical Trials Registry Number: ACTRN12613000493741, date registered: 2nd May 2013.

Midichlorians--the biomeme hypothesis: is there a microbial component to religious rituals?

Background

Cutting edge research of human microbiome diversity has led to the development of the microbiome-gut-brain axis concept, based on the idea that gut microbes may have an impact on the behavior of their human hosts. Many examples of behavior-altering parasites are known to affect members of the animal kingdom. Some prominent examples include Ophiocordyceps unilateralis (fungi), Toxoplasma gondii (protista), Wolbachia (bacteria), Glyptapanteles sp. (arthropoda), Spinochordodes tellinii (nematomorpha) and Dicrocoelium dendriticum (flat worm). These organisms belong to a very diverse set of taxonomic groups suggesting that the phenomena of parasitic host control might be more common in nature than currently established and possibly overlooked in humans.

Presentation of the hypothesis

Some microorganisms would gain an evolutionary advantage by encouraging human hosts to perform certain rituals that favor microbial transmission. We hypothesize that certain aspects of religious behavior observed in the human society could be influenced by microbial host control and that the transmission of some religious rituals could be regarded as the simultaneous transmission of both ideas (memes) and parasitic organisms.

Testing the hypothesis

We predict that next-generation microbiome sequencing of samples obtained from gut or brain tissues of control subjects and subjects with a history of voluntary active participation in certain religious rituals that promote microbial transmission will lead to the discovery of microbes, whose presence has a consistent and positive association with religious behavior. Our hypothesis also predicts a decline of participation in religious rituals in societies with improved sanitation.

Implications of the hypothesis

If proven true, our hypothesis may provide insights on the origin and pervasiveness of certain religious practices and provide an alternative explanation for recently published positive associations between parasite-stress and religiosity. The discovery of novel microorganisms that affect host behavior may improve our understanding of neurobiology and neurochemistry, while the diversity of such organisms may be of interest to evolutionary biologists and religious scholars.

Reviewers

This article was reviewed by Prof. Dan Graur, Dr. Rob Knight and Dr. Eugene Koonin

Diminished brain resilience syndrome: A modern day neurological pathology of increased susceptibility to mild brain trauma, concussion, and downstream neurodegeneration

The number of sports-related concussions has been steadily rising in recent years. Diminished brain resilience syndrome is a term coined by the lead author to describe a particular physiological state of nutrient functional deficiency and disrupted homeostatic mechanisms leading to increased susceptibility to previously considered innocuous concussion. We discuss how modern day environmental toxicant exposure, along with major changes in our food supply and lifestyle practices, profoundly reduce the bioavailability of neuro-critical nutrients such that the normal processes of homeostatic balance and resilience are no longer functional. Their diminished capacity triggers physiological and biochemical 'work around' processes that result in undesirable downstream consequences. Exposure to certain environmental chemicals, particularly glyphosate, the active ingredient in the herbicide, Roundup(®), may disrupt the body's innate switching mechanism, which normally turns off the immune response to brain injury once danger has been removed. Deficiencies in serotonin, due to disruption of the shikimate pathway, may lead to impaired melatonin supply, which reduces the resiliency of the brain through reduced antioxidant capacity and alterations in the cerebrospinal fluid, reducing critical protective buffering mechanisms in impact trauma. Depletion of certain rare minerals, overuse of sunscreen and/or overprotection from sun exposure, as well as overindulgence in heavily processed, nutrient deficient foods, further compromise the brain's resilience. Modifications to lifestyle practices, if widely implemented, could significantly reduce this trend of neurological damage.

The effects of gut microbiota on CNS function in humans

The role of the gastrointestinal microbiota in human brain development and function is an area of increasing interest and research. Preclinical models suggest a role for the microbiota in broad aspects of human health, including mood, cognition, and chronic pain. Early human studies suggest that altering the microbiota with beneficial bacteria, or probiotics, can lead to changes in brain function, as well as subjective reports of mood. As the mechanisms of bidirectional communication between the brain and microbiota are better understood, it is expected that these pathways will be harnessed to provide novel methods to enhance health and treat disease.

Mechanisms of visceral pain in health and functional gastrointestinal disorders

Background and aims Chronic visceral pain is common both in patients with identifiable organic disease and also in those without any structural, biochemical or immunological abnormality such as in the functional gastrointestinal disorders (FGIDs). We aim to provide a contemporaneous summary of pathways involved in visceral nociception and how a variety of mechanisms may influence an individual's experience of visceral pain. Methods In this narrative review, we have brought together evidence through a detailed search of Medline in addition to using our experience and exposure to recent research developments from ourselves and other research groups. Results FGIDs are a heterogeneous group of disorders whose aetiology largely remains an enigma. The germane hypothesis for the genesis and maintenance of chronic visceral pain in FGIDs is the concept of visceral hypersensitivity. A number of peripheral and central mechanisms have been proposed to account for this epiphenomenon. In the periphery, inflammatory mediators activate and sensitize nociceptive afferent nerves by reducing their transduction thresholds and by inducing the expression and recruitment of hitherto silent nociceptors culminating in an increase in pain sensitivity at the site of injury known as primary hyperalgesia. Centrally, secondary hyperalgesia, defined as an increase in pain sensitivity in anatomically distinct sites, occurs at the level of the spinal dorsal horn. Moreover, the stress responsive physiological systems, genetic and psychological factors may modulate the experience of visceral pain. We also address some novel aetiological concepts in FGIDs, namely the gastrointestinal microbiota, connective tissue abnormalities and the gastrointestinal neuromuscular disorders. Firstly, the gastrointestinal microbiota is a diverse and dynamic ecosystem, that safeguards the host from external pathogens, aids in the metabolism of polysaccharides and lipids, modulates intestinal motility, in addition to modulating visceral perception. Secondly, connective tissue disorders, which traditionally have been considered to be confined largely to the musculoskeletal system, have an increasing evidence base demonstrating the presence of visceral manifestations. Since the sensorimotor apparatus of the GI tract is embedded within connective tissue it should not be surprising that such disorder may result in visceral pain and abnormal gut motility. Thirdly, gastrointestinal neuromuscular diseases refer to a heterogeneous group of disorders in which symptoms arise from impaired GI motor activity often manifesting as abnormal transit with or without radiological evidence of transient or persistent dilation of the viscera. Although a number of these are readily recognizable, such as achalasia or Hirschsprung's disease, the cause in a number of patients is not. An international working group has recently addressed this "gap", providing a comprehensive morphologically based diagnostic criteria. Conclusions/implications Although marked advances have been made in understanding the mechanisms that contribute to the development and maintenance of visceral pain, many interventions have failed to produce tangible improvement in patient outcomes. In the last part of this review we highlight an emerging approach that has allowed the definition and delineation of temporally stable visceral pain clusters, which may improve participant homogeneity in future studies, potentially facilitate stratification of treatment in FGID and lead to improvements in diagnostic criteria and outcomes.

It's a gut feeling: how the gut microbiota affects the state of mind

Common human experience shows that stress and anxiety may modulate gut function. Such observations have been combined with an increasing evidence base that has culminated in the concept of the brain-gut axis. Nevertheless, it has not been until recently that the gut and its attendant components have been considered to influence higher cerebral function and behaviour per se. Moreover, the proposal that the gut and the bacteria contained therein (collectively referred to as the microbiota) can modulate mood and behaviours, has an increasing body of supporting evidence, albeit largely derived from animal studies. The gut microbiota is a dynamic and diverse ecosystem and forms a symbiotic relationship with the host. Herein we describe the components of the gut microbiota and mechanisms by which it can influence neural development, complex behaviours and nociception. Furthermore, we propose the novel concept of a 'state of gut' rather than a state of mind, particularly in relation to functional bowel disorders. Finally, we address the exciting possibility that the gut microbiota may offer a novel area of therapeutic intervention across a diverse array of both affective and gastrointestinal disorders.

The mucosal microbiome in shaping health and disease

More than 300 years after Antonie van Leeuwenhoek gave the first description of microbes that colonize human body surfaces, the re-discovery of this multifaceted microbial world within our bodies has challenged our principal view on microbes. Novel sequencing techniques provide a plethora of (meta)genomic data, which elucidate the unique properties of mircobiota in different subjects. Moreover, the variety of metabolic and immunologic interactions between the mircobiota and the host's epithelial surfaces has challenged the paradigm of a unidirectional interplay between a given pathogen and the host's immune defense. The newly discovered mechanisms that underlie the symbiosis between the host, specific colonizers, and the mircobiota as a whole indicate that this colonization is more than a friendly coexistence. In fact, it represents a complex ecosystem with implications for the human metabolic homeostasis and immune tolerance. The resilience of the mircobiota and the capability to maintain a well-established equilibrium between symbionts and potential pathogens seem to be determining factors in shaping health or disease.

Microbial genes, brain & behaviour - epigenetic regulation of the gut-brain axis

To date, there is rapidly increasing evidence for host-microbe interaction at virtually all levels of complexity, ranging from direct cell-to-cell communication to extensive systemic signalling, and involving various organs and organ systems, including the central nervous system. As such, the discovery that differential microbial composition is associated with alterations in behaviour and cognition has significantly contributed to establishing the microbiota-gut-brain axis as an extension of the well-accepted gut-brain axis concept. Many efforts have been focused on delineating a role for this axis in health and disease, ranging from stress-related disorders such as depression, anxiety and irritable bowel syndrome to neurodevelopmental disorders such as autism. There is also a growing appreciation of the role of epigenetic mechanisms in shaping brain and behaviour. However, the role of epigenetics in informing host-microbe interactions has received little attention to date. This is despite the fact that there are many plausible routes of interaction between epigenetic mechanisms and the host-microbiota dialogue. From this new perspective we put forward novel, yet testable, hypotheses. Firstly, we suggest that gut-microbial products can affect chromatin plasticity within their host's brain that in turn leads to changes in neuronal transcription and eventually alters host behaviour. Secondly, we argue that the microbiota is an important mediator of gene-environment interactions. Finally, we reason that the microbiota itself may be viewed as an epigenetic entity. In conclusion, the fields of (neuro)epigenetics and microbiology are converging at many levels and more interdisciplinary studies are necessary to unravel the full range of this interaction.