Lopez, J. G. | Search bioRxiv

bioRxiv2022

Gut bacterial nutrient preferences quantified in vivo

Great progress has been made in understanding gut microbiomes products and their effects on health and disease. Less attention, however, has been given to the inputs that gut bacteria consume. Here we quantitatively examine inputs and outputs of the mouse gut microbiome, using isotope tracing. The main input to microbial carbohydrate fermentation is dietary fiber, and to branched-chain fatty acids and aromatic metabolites is dietary protein. In addition, circulating host lactate, 3-hydroxybutyrate and urea (but not glucose or amino acids) feed the gut microbiome. To determine nutrient preferences across bacteria, we traced into genus-specific bacterial protein sequences. We find systematic differences in nutrient use: Most genera in the phylum Firmicutes prefer dietary protein, Bacteroides dietary fiber, and Akkermansia circulating host lactate. Such preferences correlate with microbiome composition changes in response to dietary modifications. Thus, diet shapes the microbiome by promoting the growth of bacteria that preferentially use the ingested nutrients.

molecular biology↗

bioRxiv2021

Noisy metabolism can drive the evolution of microbial cross-feeding

Cross-feeding, the exchange of nutrients between organisms, is ubiquitous in microbial communities. Despite its importance in natural and engineered microbial systems, our understanding of how cross-feeding arises is incomplete, with existing theories limited to specific scenarios. Here, we introduce a novel theory for the evolution of cross-feeding, which we term noise-averaging cooperation (NAC). NAC is based on the idea that, due to their small size, bacteria are prone to noisy regulation of metabolism which limits their growth rate. To compensate, related bacteria can share metabolites with each other to "average out" noise and improve their collective growth. This metabolite sharing among kin then allows for the evolution of metabolic interdependencies via gene deletions (this can be viewed as a generalization of the Black Queen Hypothesis). We first characterize NAC in a simple model of cell metabolism, showing that metabolite leakage can in principle substantially increase growth rate in a community context. Next, we develop a generalized framework for estimating the potential benefits of NAC among real bacteria. Using single-cell protein abundance data, we predict that bacteria suffer from substantial noise-driven growth inefficiencies, and may therefore benefit from NAC. Finally, we review existing evidence for NAC and outline potential experimental approaches to detect NAC in microbial communities.

microbiology↗