Toroidal displacement of Klebsiella pneumoniae by Pseudomonas aeruginosa is a unique mechanism to avoid competition for iron

Abstract

Competition for resources is one of the major drivers for evolution and retention of new traits in microbial communities. Quorum-dependent traits of opportunistic human pathogen Pseudomonas aeruginosa allow it to survive and thrive in nature. Here, we report a unique surfactant-driven pushing mechanism that P. aeruginosa employs specifically against Klebsiella pneumoniae. The pushing is accomplished in a manner that is dependent on nutrient limitation and quorum sensing. We find that P. aeruginosa employs neither proteases nor toxic secondary metabolites against K. pneumoniae. Rhamnolipid biosurfactant appears to be the only factor required to displace Klebsiella effectively. Both rhamnolipid production and the pushing ability of P. aeruginosa are suppressed by iron supplementation. We show that both these bacteria produce several siderophores in minimal medium and rapidly deplete iron. Under these conditions, P. aeruginosa pushes Klebsiella away from the substratum using rhamnolipid, reducing the competition for iron. Our study describes a unique quorum and iron-responsive mechanism in P. aeruginosa to support its own growth during resource competition.