The Gut Microbiome as a Regulator of the Neuroimmune Landscape

The gut microbiome influences many host physiologies, spanning gastrointestinal function, metabolism, immune homeostasis, neuroactivity, and behavior. Many microbial effects on the host are orchestrated by bidirectional interactions between the microbiome and immune system. Imbalances in this dialogue can lead to immune dysfunction and immune-mediated conditions in distal organs including the brain. Dysbiosis of the gut microbiome and dysregulated neuroimmune responses are common comorbidities of neurodevelopmental, neuropsychiatric, and neurological disorders, highlighting the importance of the gut microbiome–neuroimmune axis as a regulator of central nervous system homeostasis. In this review, we discuss recent evidence supporting a role for the gut microbiome in regulating the neuroimmune landscape in health and disease. Expected final online publication date for the Annual Review of Immunology, Volume 40 is April 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

A quantitative synthesis of soil microbial effects on plant species coexistence

Soil microorganisms play a major role in shaping plant diversity, not only through their direct effects as pathogens, mutualists, and decomposers, but also by altering interactions between plants. In particular, previous research has shown that the soil community often generates frequency-dependent feedback loops among plants that can either destabilize species interactions, or generate stabilizing niche differences that promote species coexistence. However, recent insights from modern coexistence theory have shown that microbial effects on plant coexistence depend not only on these stabilizing or destabilizing effects, but also on the degree to which they generate competitive fitness differences. While many previous experiments have generated the data necessary for evaluating microbially mediated fitness differences, these effects have rarely been quantified in the literature. Here we present a meta-analysis of data from 50 studies, which we used to quantify the microbially mediated (de)stabilization and fitness differences derived from a classic plant-soil feedback model. Across 518 pairwise comparisons, we found that soil microbes generated both stabilization (or destabilization) and fitness differences, but also that the microbially mediated fitness differences dominated. As a consequence, if plants are otherwise equivalent competitors, the balance of soil microbe-generated (de)stabilization and fitness differences drives species exclusion much more frequently than coexistence or priority effects. Our work shows that microbially mediated fitness differences are an important but overlooked effect of soil microbes on plant coexistence. This finding paves the way for a more complete understanding of the processes that maintain plant biodiversity.

Effect of exposure to antibiotics on the gut microbiome and biochemical indexes of pregnant women

IntroductionExposure to antibiotics (ABX) during pregnancy can have a systematic effect on both fetal and maternal health. Although previous biomonitoring studies have indicated the effects on children of extensive exposure to ABX, studies on pregnant women remain scarce. To explore the effect on pregnant women of environmental exposure to ABX through accidental ingestion and identify potential health risks, the present study investigated 122 pregnant women in East China between 2019 and 2020.Research design and methodsThe presence of six categories of ABX (quinolones, sulfonamides, lincosamides, tetracyclines, amide alcohol ABX, and β-lactams) in plasma samples taken from the pregnant women was investigated using an ABX kit and a time-resolved fluorescence immunoassay.ResultsAll six ABX were detected in the plasma, with a detection rate of 17.2%. It was discovered that the composition of intestinal flora in pregnant women exposed to ABX was different from that of pregnant women who had not been exposed to ABX. The intestinal flora of pregnant women exposed to ABX also changed at both the phylum and genus levels, and several genera almost disappeared. Furthermore, the metabolic levels of glucose and insulin and the alpha diversity of pregnant women exposed to ABX were higher than those of pregnant women not exposed to ABX.ConclusionPregnant women are potentially at higher risk of adverse microbial effects. Glucose metabolism and insulin levels were generally higher in pregnant women exposed to ABX than in unexposed women. Also, the composition and color of the gut microbiome changed.

Potential roles of 1,5-anhydro-d-fructose in modulating gut microbiome in mice

The gut microbiota has tremendous potential to affect the host’s health, in part by synthesizing vitamins and generating nutrients from food that is otherwise indigestible by the host. 1,5-Anhydro-d-fructose (1,5-AF) is a monosaccharide with a wide range of bioactive potentials, including anti-oxidant, anti-inflammatory, and anti-microbial effects. Based on its potential benefits and minimal toxicity, it is anticipated that 1,5-AF will be used as a dietary supplement to support general health. However, the effects of 1,5-AF on the gut microbiota are yet to be clarified. Here, using an unbiased metagenomic approach, we profiled the bacterial taxa and functional genes in the caecal microbiota of mice fed a diet containing either 2% 1,5-AF or a reference sweetener. Supplementation with 1,5-AF altered the composition of the gut microbiota, enriching the proportion of Faecalibacterium prausnitzii. 1,5-AF also altered the metabolomic profile of the gut microbiota, enriching genes associated with nicotinamide adenine dinucleotide biosynthesis. These findings support the potential benefits of 1,5-AF, but further studies are required to clarify the impact of 1,5-AF on health and disease.

Consumption of Butylated Starch Alleviates the Chronic Restraint Stress-Induced Neurobehavioral and Gut Barrier Deficits Through Reshaping the Gut Microbiota

The beneficial effect of short-chain fatty acids (SCFAs) on host health has been well recognized based on the booming knowledge from gut microbiome research. The role of SCFA in influencing psychological function is highlighted in recent years but has not been fully elucidated. In this study, the SCFA-acylated starches were used to accomplish a sizeable intestine-targeted release of the SCFAs, and the neurobehavioral, immunological, and microbial effects were further investigated. Acetylated-, butylated-, and isobutylated-starch could attenuate the depression-like behaviors and excessive corticosterone production in chronically stressed mice. Butylated- starch significantly reduced the colonic permeability via increasing the tight junction proteins (including ZO-1, Claudin, and Occludin) gene expression and reduced the level of the inflammatory cytokines (including IL-1β and IL-6). The butylated starch’s neurological and immunological benefits may be derived from the gut microbiome modifications, including normalizing the abundance of certain beneficial microbes (Odoribacter and Oscillibacter) and metabolomic pathways (Tryptophan synthesis and Inositol degradation). The present findings further validate the brain-beneficial effect of butyrate and offer novel guidance for developing novel food or dietary supplements for improving mental health.

Changes in Gut Microbiota Induced by Doxycycline Influence in Vascular Function and Development of Hypertension in DOCA-Salt Rats

Previous experiments in animals and humans show that shifts in microbiota and its metabolites are linked to hypertension. The present study investigates whether doxycycline (DOX, a broad-spectrum tetracycline antibiotic) improves dysbiosis, prevent cardiovascular pathology and attenuate hypertension in deoxycorticosterone acetate (DOCA)-salt rats, a renin-independent model of hypertension. Male Wistar rats were randomly assigned to three groups: control, DOCA-salt hypertensive rats, DOCA-salt treated with DOX for 4 weeks. DOX decreased systolic blood pressure, improving endothelial dysfunction and reducing aortic oxidative stress and inflammation. DOX decreased lactate-producing bacterial population and plasma lactate levels, improved gut barrier integrity, normalized endotoxemia, plasma noradrenaline levels and restored the Treg content in aorta. These data demonstrate that DOX through direct effects on gut microbiota and its non-microbial effects (anti-inflammatory and immunomodulatory) reduces endothelial dysfunction and the increase in blood pressure in this low-renin form of hypertension.

Anti-oxidant and Anti-microbial activities of 2’’, 4’’-thiazolidindione derivatives of 7-flavonols

Objective: The synthesized compounds of 2’’,4’’-thiazolidindione derivatives of 7-flavonols*, after characterization, aimed to be tested for their anti-oxidant and anti-microbial effects. Methods: i) Free radical scavenging actions tested by hydrogen peroxide- nitric oxide- and by alkaline DMSO- methods and ii) anti-microbial effects against various bacterial pathogens and against candida albicans by disc diffusion method. Results: Data were found to be dose dependent and IC50 value was 30-60 µg/ml and the results revealed that the dinitro-, trinitro- and acetyl, dinitro derivatives showed better and/or equipotent activity to that of the standard, ascorbic acid. The synthesized compounds exerted variable inhibitory activities at a concentration of 1μg /10μl /disc with inhibition zone ranging from 7-26 mm in diameter and a good antifungal activity against Candida albicans at the concentration of (1μg /10μl /disc) with inhibition of 10-24 mm. Klebsiella tribatta are more susceptible to the action of the formylated samples, giving high inhibition values comparing to the other organisms. Compounds Ie and Ih resulted to a higher activity index (AI>1); compounds Id, Ig and Ii showed an equal value (AI=1); whereas, Ia, Ib, Ic and If showed only a moderate activity (AI<1) compared to the standard, Amikacin. Conclusion: The findings confirmed that the synthetic compounds of 3-formyl, 7-flavonol derivatives have significant anti-oxidant and anti-microbial activities.

Microbial effects on plant phenology and fitness

Plant development and the timing of developmental events (phenology) are tightly coupled with plant fitness. A variety of internal and external factors determine the timing and fitness consequences of these life-history transitions. Microbes interact with plants throughout their life-history and impact host phenology. This review summarizes current mechanistic and theoretical knowledge surrounding microbially-driven changes in plant phenology. Overall, there are examples of microbes impacting every phenological transition. While most studies focused on flowering time, microbial effects remain important for host survival and fitness, across all phenological phases. Microbially-mediated changes in nutrient acquisition and phytohormone signaling can release plants from stressful conditions and alter plant stress responses inducing shifts in developmental events. The frequency and direction of phenological effects appear to be partly determined by the lifestyle and the underlying nature of a plant-microbe interaction (i.e. mutualist or pathogenic), in addition to the taxonomic group of the microbe (fungi vs. bacteria). Finally, we highlight biases, gaps in knowledge, and future directions. This biotic source of plasticity for plant adaptation will serve an important role in sustaining plant biodiversity and managing agriculture under the pressures of climate change.