Impact of dietary fiber on gut microbiota composition, function and gut-brain-modules in healthy adults - a systematic review protocol.

Background: The gut microbiota has been extensively implicated in health and disease. The functional outputs of the gut microbiota, such as microbial metabolites, are considered particularly important in this regard. Significant associations exist between alterations in the relative abundance of specific microbial taxa and mental health disorders. Dietary fiber has the potential to alter gut microbiota composition and function, modifying bacterial enzymatic function and the production of metabolites. As many taxa of microorganisms have enzymes capable of producing or degrading neurochemicals i.e. neuroactive gut brain modules, new predictive tools can be applied to existing datasets such as those harvested from dietary fiber interventions. We endeavor to perform a systematic review in order to identify studies reporting compositional gut microbiota alterations after interventions with dietary fiber in healthy individuals. We aim to also extract from the selected studies publicly available microbial genomic sequence datasets for reanalysis with a consistent bioinformatics pipeline, with the ultimate intention of identifying altered gut brain modules following dietary fiber interventions. Methods: Interventional trials and randomized controlled studies that are originally published, including cross-over and non-crossover design and involving healthy adult humans will be included. A systematic search of PubMed/MEDLINE and EMBASE, two electronic databases, will be completed. Discussion: Various types of dietary fiber have an impact on the gut microbiota composition, with some promoting the growth of particular taxa while others are reduced in relative abundance. Our search focuses on the impact of this food component on the microbiota of healthy individuals. Compositional gut microbial changes have been reported and our review will compile and update these observations after reanalysis of their datasets with a consistent bioinformatic pipeline. From this it may be possible to predict more detailed functional consequences in terms of neuroactive gut brain modules, of the compositional alterations in gut microbial taxa.

Probiotic Yeasts and Vibrio anguillarum Infection Modify the Microbiome of Zebrafish Larvae.

The host microbiome plays an essential role in health and disease. Microbiome modification by pathogens or probiotics has been poorly explored especially in the case of probiotic yeasts. Next-generation sequencing currently provides the best tools for their characterization. Debaryomyces hansenii 97 (D. hansenii 97) and Yarrowia lipolytica 242 (Y. lipolytica 242) are yeasts that protect wildtype zebrafish (Danio rerio) larvae against a Vibrio anguillarum (V. anguillarum) infection, increasing their survival rate. We investigate the effect of these microorganisms on the microbiome and neutrophil response (inflammation) in zebrafish larvae line Tg(Bacmpx:GFP) i114. We postulated that preinoculation of larvae with yeasts would attenuate the intestinal neutrophil response and prevent modification of the larval microbiome induced by the pathogen. Microbiome study was performed by sequencing the V3-V4 region of the 16S rRNA gene and prediction of metabolic pathways by Piphillin in conventionally raised larvae. Survival and the neutrophil response were both evaluated in conventional and germ-free conditions. V. anguillarum infection resulted in higher neutrophil number in the intestinal area compared to non-infected larvae in both conditions. In germ-free conditions, infected larvae pre-inoculated with yeasts showed fewer neutrophil numbers than infected larvae. In both conditions, only D. hansenii 97 increased the survival of infected larvae. Beta diversity of the microbiota was modified by V. anguillarum and both yeasts, compared to non-inoculated larvae. At 3 days post-infection, V. anguillarum modified the relative abundance of 10 genera, and pre-inoculation with D. hansenii 97 and Y. lipolytica 242 prevented the modification of 5 and 6 of these genera, respectively. Both yeasts prevent the increase of Ensifer and Vogesella identified as negative predictors for larval survival (accounting for 40 and 27 of the variance, respectively). In addition, yeast pre-inoculation prevents changes in some metabolic pathways altered by V. anguillarum's infection. These results suggest that both yeasts and V. anguillarum can shape the larval microbiota configuration in the early developmental stage of D. rerio. Moreover, modulation of key taxa or metabolic pathways of the larval microbiome by yeasts can be associated with the survival of infected larvae. This study contributes to the understanding of yeast-pathogen-microbiome interactions, although further studies are needed to elucidate the mechanisms involved.

Cultivable Yeast Microbiota from the Marine Fish Species Genypterus chilensis and Seriolella violacea.

Because of its outstanding biological and industrial importance, many efforts have been made to characterize the mycobiota of new environments and their biochemical and biotechnological potentials. Gut mycobiota can be a source of novel yeasts with the potential to be used as probiotics or have industrial applications. In this work, we characterized two as-yet unexplored yeast communities from the intestinal content of the cultured marine Chilean fishes Genypterus chilensis (G. chilensis) and Seriolella violacea (S. violacea). Yeasts were isolated through culture, identified by sequencing their ITS region, and characterized their enzymatic profile with API®ZYM. Rhodotorula mucilaginosa was identified in both fish species. For the first time, Candida palmioleophila, Candida pseudorugosa, Cystobasidium slooffiae, and a member of the Yamadazyma genus were also identified and described as part of the normal fish gut-microbiota. Furthermore, the diverse enzymatic profile exhibited by some of these isolates suggests that it may be possible to develop novel applications for them, such as new probiotics and other biotechnological applications.

The behavioral and neurochemical characterization of a Drosophila dysbindin mutant supports the contribution of serotonin to schizophrenia negative symptoms.

Mutations in the dystrobrevin binding protein 1 (DTNBP1) gene that encodes for the dysbindin-1 protein, are associated with a higher risk for schizophrenia. Interestingly, individuals carrying high-risk alleles in this gene have been associated with an increased incidence of negative symptoms for the disease, which include anhedonia, avolition and social withdrawal. Here we evaluated behavioral and neurochemical changes in a hypomorphic Drosophila mutant for the orthologue of human Dysbindin-1, dysb1. Mutant dysb1 flies exhibit altered social space parameters, suggesting asocial behavior, accompanied by reduced olfactory performance. Moreover, dysb1 mutant flies show poor performance in basal and startle-induced locomotor activity. We also report a reduction in serotonin brain levels and changes in the expression of the Drosophila serotonin transporter (dSERT) in dysb1 flies. Our data show that the serotonin-releasing amphetamine derivative 4-methylthioamphetamine (4-MTA) modulates social spacing and locomotion in control flies, suggesting that serotonergic circuits modulate these behaviors. 4-MTA was unable to modify the behavioral deficiencies in mutant flies, which is consistent with the idea that the efficiency of pharmacological agents acting at dSERT depends on functional serotonergic circuits. Thus, our data show that the dysb1 mutant exhibits behavioral deficits that mirror some aspects of the endophenotypes associated with the negative symptoms of schizophrenia. We argue that at least part of the behavioral aspects associated with these symptoms could be explained by a serotonergic deficit. The dysb1 mutant presents an opportunity to study the molecular underpinnings of schizophrenia negative symptoms and reveals new potential targets for treatment of the disease.