The dynamics of a family's gut microbiota reveal variations on a theme.

BACKGROUND: It is clear that the structure and function of the human microbiota has significant impact on maintenance of health and yet the factors that give rise to an adult microbiota are poorly understood. A combination of genetics, diet, environment, and life history are all thought to impact the development of the gut microbiome. Here we study a chronosequence of the gut microbiota found in eight individuals from a family consisting of two parents and six children ranging in age from two months to ten years old. RESULTS: Using 16S rRNA gene and metagenomic shotgun sequence data, it was possible to distinguish the family from a cohort of normal individuals living in the same geographic region and to differentiate each family member. Interestingly, there was a significant core membership to the family members' microbiota where the abundance of this core accounted for the differences between individuals. It was clear that the introduction of solids represents a significant transition in the development of a mature microbiota. This transition was associated with increased diversity, decreased stability, and the colonization of significant abundances of Bacteroidetes and Clostridiales. Although the children and mother shared essentially the identical diet and environment, the children's microbiotas were not significantly more similar to their mother than they were to their father. CONCLUSIONS: This analysis underscores the complex interactions that give rise to a personalized microbiota and suggests the value of studying families as a surrogate for longitudinal studies.

The gut microbiome modulates colon tumorigenesis.

UNLABELLED: Recent studies have shown that individuals with colorectal cancer have an altered gut microbiome compared to healthy controls. It remains unclear whether these differences are a response to tumorigenesis or actively drive tumorigenesis. To determine the role of the gut microbiome in the development of colorectal cancer, we characterized the gut microbiome in a murine model of inflammation-associated colorectal cancer that mirrors what is seen in humans. We followed the development of an abnormal microbial community structure associated with inflammation and tumorigenesis in the colon. Tumor-bearing mice showed enrichment in operational taxonomic units (OTUs) affiliated with members of the Bacteroides, Odoribacter, and Akkermansia genera and decreases in OTUs affiliated with members of the Prevotellaceae and Porphyromonadaceae families. Conventionalization of germfree mice with microbiota from tumor-bearing mice significantly increased tumorigenesis in the colon compared to that for animals colonized with a healthy gut microbiome from untreated mice. Furthermore, at the end of the model, germfree mice colonized with microbiota from tumor-bearing mice harbored a higher relative abundance of populations associated with tumor formation in conventional animals. Manipulation of the gut microbiome with antibiotics resulted in a dramatic decrease in both the number and size of tumors. Our results demonstrate that changes in the gut microbiome associated with inflammation and tumorigenesis directly contribute to tumorigenesis and suggest that interventions affecting the composition of the microbiome may be a strategy to prevent the development of colon cancer. IMPORTANCE: The trillions of bacteria that live in the gut, known collectively as the gut microbiome, are important for normal functioning of the intestine. There is now growing evidence that disruptive changes in the gut microbiome are strongly associated with the development colorectal cancer. However, how the gut microbiome changes with time during tumorigenesis and whether these changes directly contribute to disease have not been determined. We demonstrate using a mouse model of inflammation-driven colon cancer that there are dramatic, continual alterations in the microbiome during the development of tumors, which are directly responsible for tumor development. Our results suggest that interventions that target these changes in the microbiome may be an effective strategy for preventing the development of colorectal cancer.

Stabilization of the murine gut microbiome following weaning.

Ecologists hypothesize that community structure and stability affect productivity, sensitivity to invasion and extinction, and resilience and resistance to perturbations. Viewed in the context of the gut microbiome, the stability of the gut community is important for understanding the effects of antibiotics, diet change and other perturbations on host health and colonization resistance. Here we describe the dynamics of a self-contained community, the murine gut microbiome. Using 16S rRNA gene sequencing of fecal samples collected daily from individual mice, we characterized the community membership and structure to determine whether there were significant changes in the gut community during the first year of life. Based on analysis of molecular variance, we observed two community states. The first was observed in the 10 days following weaning and the second was observed by 15 days following weaning. Interestingly, these two states had the same bacterial populations, but those populations had different relative abundances in the two states. By calculating the root mean squared distances between samples collected in the early and late states for each mouse, we observed that the late state was more stable than the early state. This increase in stability was not correlated with increased taxonomic richness, taxonomic diversity, or phylogenetic diversity. In the absence of an experimentally induced perturbation, the second community state was relatively constant through 364 days post weaning. These results suggest a high degree of stability in the microbiome once the community reached the second state.