Different Substrate Preferences Help Closely Related Bacteria To Coexist in the Gut

Many factors shape the ability of different microbes to coexist in microbial communities. In the human gut, dietary and host-derived nutrients largely drive microbial community structure. How gut microbes with very similar nutrient profiles are able to coexist over time within the same host is not fully understood. Tuncil et al. (mBio 8:e01068-17, 2017, https://doi.org/10.1128/mBio.01068-17) explored glycan prioritization in two closely related human gut bacteria, Bacteroides ovatus and Bacteroides thetaiotaomicron, on complex glycan mixtures that both organisms can degrade. Determining depletion of the individual glycans over time in pure cultures and cocultures revealed that the bacteria seem to have hardwired differences in their preferences for different glycans which likely contribute to their stable coexistence. The researchers also established that gene expression changes of the corresponding polysaccharide utilization loci did not always mirror glycan depletion, which highlights that additional regulatory mechanisms must be present.