Strengthen or Weaken: Evolutionary Directions of Cross-Feeding After Formation

Interactions between species and the evolution of strains are important biotic factors determining the microbial community dynamics, with these two processes being deeply intertwined. Cross-feeding is a prevailing mutualistic interaction in natural microbial communities in which metabolites secreted by one microbe can be utilised by another. Constructing synthetic microbial consortia based on cross-feeding is a promising strategy for bioremediation and bioproduction. But how to improve the performance and the stability of consortia remains a challenge. This review discusses the features of two opposite evolutionary directions of cross-feeding consortia over time, providing insights into the factors affecting the evolutionary process. While coevolving, cross-feeding may strengthen with stronger metabolic coupling, deeper growth dependence, and/or deeper evolutionary dependence; then the consortia become reinforced. Conversely, unsuitable environmental conditions can lead to the direct collapse of the cross-feeding consortia due to metabolic decoupling, partner extinction, or cheater dominance. The loss of the fitness advantage and the constraints on the evolutionary ability can also lead to the weakening of cross-feeding. Cross-feeding partners can affect the evolution of focal strains from different aspects, such as niche space, selective pressure, horizontal gene transfer, and evolutionary rate. Analysing cross-feeding from an evolutionary perspective will advance our understanding of microbial community dynamics and enable rational designs of efficient and stable synthetic microbial consortia.