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

UNLABELLED: Competition for resources is one of the major drivers for evolution and retention of new traits in microbial communities. Quorum sensing-dependent traits of the opportunistic human pathogen Pseudomonas aeruginosa allow it to survive and thrive in the presence of other microbes. Here, we report a unique mechanism that P. aeruginosa employs specifically against Klebsiella pneumoniae to displace it on solid surfaces. Interestingly, P. aeruginosa employs neither proteases nor toxic secondary metabolites against K. pneumoniae. Rhamnolipid biosurfactant under the control of the RhlR quorum sensing system appears to be the primary factor required to displace Klebsiella effectively. Under conditions of iron limitation, both bacteria produce iron-scavenging molecules, while P. aeruginosa also produces rhamnolipid biosurfactant, allowing it to push Klebsiella cells away from the substratum. Our study describes a unique quorum and iron-responsive mechanism in P. aeruginosa to support its own growth during resource competition on a solid surface.

IMPORTANCE

Competition is common among organisms in nature. Bacteria have been known to deal with their neighbors using toxins and enzymes that kill or disable the latter. Here, we describe a simple, detergent-mediated mechanism that a common bacterium employs against its neighbor to push them away. This only happens in a time of scarcity of iron, an element essential for life, big and small.