Multiple Pathways Impact Swarming Motility ofPseudomonas fluorescensPf0-1

Abstract

AbstractSwarming motility in pseudomonads typically requires both a functional flagellum and production/secretion of a biosurfactant. Published work has shown that the wild-typePseudomonas fluorescensPf0-1 is swarming-deficient due to a point mutation in thegacAgene, which until recently, was thought to inactivate rather than attenuate the Gac/Rsm pathway. As a result, little is known about the underlying mechanisms that regulate swarming motility byP. fluorescensPf0-1. Here, we demonstrate that a ΔrsmAΔrsmEΔrsmImutant, which phenotypically mimics Gac/Rsm pathway overstimulation, is proficient at swarming motility. RsmA and RsmE appear to play a key role in this regulation. Transposon mutagenesis of the ΔrsmAΔrsmEΔrsmImutant identified multiple factors that impact swarming motility, including pathways involved in flagellar synthesis and biosurfactant production/secretion. We find that loss of genes linked to biosurfactant Gacamide A biosynthesis or secretion impact swarming motility, as does loss of the alternative sigma factor FliA, which results in a defect in flagellar function. Collectively, these findings provide evidence thatP. fluorescensPf0-1 can swarm if the Gac/Rsm pathway is activated, highlight the regulatory complexity of swarming motility in this strain, and demonstrate that the cyclic lipopeptide Gacamide A is utilized as a biosurfactant for swarming motility.ImportanceSwarming motility is a coordinated process that allows communities of bacteria to collectively move across a surface. ForP. fluorescensPf0-1, this phenotype is notably absent in the parental strain and to date little is known about the regulation of swarming in this strain. Here, we identify RsmA and RsmE as key repressors of swarming motility via modulating the levels of biosurfactant production/secretion. Via transposon mutagenesis and subsequent genetic analyses, we further identify potential regulatory mechanisms of swarming motility and link Gacamide A biosynthesis and transport machinery to swarming motility.