Metagenomic systems biology of the human gut microbiome reveals topological shifts associated with obesity and inflammatory bowel disease

TLDR

The human microbiome is essential for host physiology, yet disease‑associated compositional variation is poorly understood in terms of its impact on community structure and host interactions. This study introduces a metagenomic systems biology framework that integrates metagenomic data with in silico metabolic network analysis to investigate microbiome organization. Using fecal metagenomes from 124 unrelated individuals, six monozygotic twin pairs and their mothers, the authors constructed community‑level metabolic networks and mapped gene abundance variations onto network topology. They found that genes associated with obesity or IBD occupy peripheral, input‑enriched positions, that obese microbiomes are less modular—suggesting adaptation to low‑diversity environments—and that these topological shifts correlate with species composition, providing a foundation for linking microbiome organization to human health.

Abstract

The human microbiome plays a key role in a wide range of host-related processes and has a profound effect on human health. Comparative analyses of the human microbiome have revealed substantial variation in species and gene composition associated with a variety of disease states but may fall short of providing a comprehensive understanding of the impact of this variation on the community and on the host. Here, we introduce a metagenomic systems biology computational framework, integrating metagenomic data with an in silico systems-level analysis of metabolic networks. Focusing on the gut microbiome, we analyze fecal metagenomic data from 124 unrelated individuals, as well as six monozygotic twin pairs and their mothers, and generate community-level metabolic networks of the microbiome. Placing variations in gene abundance in the context of these networks, we identify both gene-level and network-level topological differences associated with obesity and inflammatory bowel disease (IBD). We show that genes associated with either of these host states tend to be located at the periphery of the metabolic network and are enriched for topologically derived metabolic “inputs.” These findings may indicate that lean and obese microbiomes differ primarily in their interface with the host and in the way they interact with host metabolism. We further demonstrate that obese microbiomes are less modular, a hallmark of adaptation to low-diversity environments. We additionally link these topological variations to community species composition. The system-level approach presented here lays the foundation for a unique framework for studying the human microbiome, its organization, and its impact on human health.