An Economic Framework of Microbial Trade

Abstract

A large fraction of microbial life on earth exists in complex communities where metabolic exchange is vital. Microbes trade essential resources to promote their own growth in an analogous way to countries that exchange goods in modern economic markets. Inspired by these similarities, we developed a framework based on general equilibrium theory (GET) from economics to predict the population dynamics of trading microbial communities. Our biotic GET (BGET) model provides an a priori theory of the growth benefits of microbial trade, yielding several novel insights relevant to understanding microbial ecology and engineering synthetic communities. We find that the economic concept of comparative advantage is a necessary condition for mutualistic trade. Our model suggests that microbial communities can grow faster when species are unable to produce essential resources that are obtained through trade, thereby promoting metabolic specialization and increased intercellular exchange. Furthermore, we find that species engaged in trade exhibit a fundamental tradeoff between growth rate and relative population abundance, and that different environments that put greater pressure on group selection versus individual selection will promote varying strategies along this growth-abundance spectrum. We experimentally tested this tradeoff using a synthetic consortium of Escherichia coli cells and found the results match the predictions of the model. This framework provides a foundation to study natural and engineered microbial communities through a new lens based on economic theories developed over the past century.

Species dynamics and interactions via metabolically informed consumer-resource models

“…While we are using this as a model with both competition (e.g., shared resources) and facilitation (e.g., metabolic cross feeding) interactions, it also represents the natural cross-feeding interaction between lactate producing and lactate consuming bacteria found in human and animal digestive systems (Duncan et al, 2004). These metabolic cross-feeding interactions are common in microbial systems (Mee et al, 2014;Tasoff et al, 2015;Zelezniak et al, 2015) and have industrial applications (Jiao et al, 2012). As such, our model demonstrates how competition and facilitation mediate species dynamics and coexistence conditions and can be used to understand natural and engineered microbial systems.…”

Phase Transitions in Mutualistic Communities under Invasion

“…This type of symbiotic network is abundant in nature, appearing everywhere from auxotrophic bacteria [20,21] to nitrogen fixation in plant root microecosystems [22]. In particular, amino acid cross-feeding has been extensively characterized both theoretically and experimentally [23][24][25][26]. Fig.…”

Paradoxes in Leaky Microbial Trade

“…Microbes live in complex communities where goods such as metabolites are produced and exchanged [1,2,3,4]. As goods flow in and out of cells, a type of economy emerges [5,6]. In this economy, each organism faces decisions concerning which goods to produce and in what quantities [7].…”

“…In instances where each good produced is growth-limiting to the other organism, there is a positive feedback loop so each organism does best by producing as much of their good as possible so long as it does not interfere with other cell functions. One common result of these syntrophic exchanges is a synergy between organisms, where the combined community has enhanced growth relative to any isolated individual [6].…”