124W Poster - Evolutionary Genetics
Wednesday June 08, 8:30 PM - 9:15 PM

Authors:
Doran Goldman ¹; Katherine Xue ¹; Rashi Jeeda ²; Benjamin Good ¹; Dmitri Petrov ¹; Kerwyn Huang ¹; David Relman ¹

Affiliations:
1) Stanford University; 2) California Institute of Technology

Keywords:
Experimental evolution

The human gut microbiome remains remarkably diverse and stable over the course of adult life, despite constant exposure to new microbes from the environment. Various ecological factors and evolutionary processes may affect the likelihood that new strains successfully colonize an established community—for instance, an introduced strain might directly compete with a resident strain in a resource-limited environment, or it might adapt to utilize alternative resources in a resource-rich environment. However, it remains unclear to what extent each of these strategies plays a role in microbiome stability. The neutral theory of community ecology provides a highly simplified model for colonization in which the relative abundance of a newly introduced species is proportional to its inoculation dose. To test the predictions of neutral theory, we derived in vitro microbial communities from human stool samples and performed community coalescence experiments in which we systematically mixed eight pairs of communities at ratios ranging from 1:1000 to 1000:1. Neutral theory predicts that the relative abundance of a taxon will increase linearly with its inoculation dose, and that species diversity will be higher when communities are mixed at more even ratios, as more species persist at relative abundances above the sequencing limit of detection. In preliminary analyses, we observed that species diversity in the community mixtures often remained at levels similar to the parent communities regardless of mixture ratio, suggesting that diversity may be limited by resource competition even when many species are initially present in the community mixtures. While the relative abundances of some taxa increased with inoculation dose, as predicted by neutral theory, several species were also able to persist stably at relative abundances several times higher than predicted by their inoculation dose, indicating that these taxa may colonize by adapting to consume underutilized resources or engaging in mutualistic interactions with other species. Our results highlight the importance of both inoculation dose and other ecological and evolutionary processes in determining colonization success. These analyses will provide important insight into the ecological and evolutionary factors that promote colonization in gut microbial communities.