Innate responses to gut microbiota; critical assessment of the necessary experimental controls

Analysis of early childhood intestinal microbial dynamics in a continuous-flow bioreactor

BACKGROUND

The human gut microbiota is inoculated at birth and undergoes a process of assembly and diversification during the first few years of life. Studies in mice and humans have revealed associations between the early-life gut microbiome and future susceptibility to immune and metabolic diseases. To resolve microbe and host contributing factors to early-life development and to disease states requires experimental platforms that support reproducible, longitudinal, and high-content analyses.

RESULTS

Here, we deployed a continuous single-stage chemostat culture model of the human distal gut to study gut microbiota from 18- to 24-month-old children integrating both culture-dependent and -independent methods. Chemostat cultures recapitulated multiple aspects of the fecal microbial ecosystem enabling investigation of relationships between bacterial strains and metabolic function, as well as a resource from which we isolated and curated a diverse library of early life bacterial strains.

CONCLUSIONS

We report the reproducible, longitudinal dynamics of early-life bacterial communities cultured in an advanced model of the human gut providing an experimental approach and a characterized bacterial resource to support future investigations of the human gut microbiota in early childhood.

Sex-specific post-inflammatory dysbiosis mediates chronic visceral pain in colitis

BACKGROUND

Despite achieving endoscopic remission, over 20% of inflammatory bowel disease (IBD) patients experience chronic abdominal pain. Visceral pain and the microbiome exhibit sex-dependent interactions, while visceral pain in IBD shows a sex bias. Our aim was to evaluate whether post-inflammatory microbial perturbations contribute to visceral hypersensitivity in a sex-dependent manner.

METHODS

Males, cycling females, ovariectomized, and sham-operated females were given dextran sodium sulfate to induce colitis and allowed to recover. Germ-free recipients received sex-appropriate and cross-sex fecal microbial transplants (FMT) from post-inflammatory donor mice. Visceral sensitivity was assessed by recording visceromotor responses to colorectal distention. The composition of the microbiota was evaluated via 16S rRNA gene V4 amplicon sequencing, while the metabolome was assessed using targeted (short chain fatty acids - SCFA) and semi-targeted mass spectrometry.

RESULTS

Post-inflammatory cycling females developed visceral hyperalgesia when compared to males. This effect was reversed by ovariectomy. Both post-inflammatory males and females exhibited increased SCFA-producing species, but only males had elevated fecal SCFA content. FMT from post-inflammatory females transferred visceral hyperalgesia to both males and females, while FMT from post-inflammatory males could only transfer visceral hyperalgesia to males.

CONCLUSIONS

Female sex, hormonal status as well as the gut microbiota play a role in pain modulation. Our data highlight the importance of considering biological sex in the evaluation of visceral pain.

Aryl Hydrocarbon Receptor (AhR) Activation by 2,3,7,8-Tetrachlorodibenzo-p-Dioxin (TCDD) Dose-Dependently Shifts the Gut Microbiome Consistent with the Progression of Non-Alcoholic Fatty Liver Disease

Gut dysbiosis with disrupted enterohepatic bile acid metabolism is commonly associated with non-alcoholic fatty liver disease (NAFLD) and recapitulated in a NAFLD-phenotype elicited by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in mice. TCDD induces hepatic fat accumulation and increases levels of secondary bile acids, including taurolithocholic acid and deoxycholic acid (microbial modified bile acids involved in host bile acid regulation signaling pathways). To investigate the effects of TCDD on the gut microbiota, the cecum contents of male C57BL/6 mice orally gavaged with sesame oil vehicle or 0.3, 3, or 30 µg/kg TCDD were examined using shotgun metagenomic sequencing. Taxonomic analysis identified dose-dependent increases in Lactobacillus species (i.e., Lactobacillus reuteri). Increased species were also associated with dose-dependent increases in bile salt hydrolase sequences, responsible for deconjugation reactions in secondary bile acid metabolism. Increased L. reuteri levels were further associated with mevalonate-dependent isopentenyl diphosphate (IPP) biosynthesis and o-succinylbenzoate synthase, a menaquinone biosynthesis associated gene. Analysis of the gut microbiomes from cirrhosis patients identified an increased abundance of genes from the mevalonate-dependent IPP biosynthesis as well as several other menaquinone biosynthesis genes, including o-succinylbenzoate synthase. These results extend the association of lactobacilli with the AhR/intestinal axis in NAFLD progression and highlight the similarities between TCDD-elicited phenotypes in mice to human NAFLD.