PT  - JOURNAL ARTICLE
AU  - Fritts, Ryan K
AU  - Bird, Jordan T
AU  - Behringer, Megan G
AU  - Lipzen, Anna
AU  - Martin, Joel
AU  - Lynch, Michael
AU  - McKinlay, James B
TI  - Enhanced nutrient uptake is sufficient to drive emergent cross-feeding between bacteria in a synthetic community
AID  - 10.1101/770727
DP  - 2020 Jan 01
TA  - bioRxiv
PG  - 770727
4099  - http://biorxiv.org/content/early/2020/04/04/770727.short
4100  - http://biorxiv.org/content/early/2020/04/04/770727.full
AB  - Interactive microbial communities are ubiquitous, influencing biogeochemical cycles and host health. One widespread interaction is nutrient exchange, or cross-feeding, wherein metabolites are transferred between microbes. Some cross-fed metabolites, such as vitamins, amino acids, and ammonium (NH4+), are communally valuable and impose a cost on the producer. The mechanisms that enforce cross-feeding of communally valuable metabolites are not fully understood. Previously we engineered mutualistic cross-feeding between N2-fixing Rhodopseudomonas palustris and fermentative Escherichia coli. Engineered R. palustris excreted essential nitrogen as NH4+ to E. coli while E. coli excreted essential carbon as fermentation products to R. palustris. Here, we enriched for nascent cross-feeding in cocultures with wild-type R. palustris, not known to excrete NH4+. Emergent NH4+ cross-feeding was driven by adaptation of E. coli alone. A missense mutation in E. coli NtrC, a regulator of nitrogen scavenging, resulted in constitutive activation of an NH4+ transporter. This activity likely allowed E. coli to subsist on the small amount of leaked NH4+ and better reciprocate through elevated excretion of organic acids from a larger E. coli population. Our results indicate that enhanced nutrient uptake by recipients, rather than increased excretion by producers, is an underappreciated yet possibly prevalent mechanism by which cross-feeding can emerge.