FleN contributes to heterogeneous swimming at high temperatures in Pseudomonas syringae

Abstract

Motility is generally conserved among many animal and plant pathogens. Environmental conditions, however, significantly impact expression of the motile phenotype. In this study, we describe a novel heterogeneous motility phenotype in Pseudomonas syringae, where under normally suppressive incubation conditions (30{degrees}C) punctate colonies arise that are spatially isolated from the point of inoculation, giving rise to a motility pattern we term constellation swimming (CS). We demonstrate that this phenotype is reproducible, reversible, and dependent on a functioning flagellum. Mirroring the heterogeneous motility phenotype, we demonstrate the existence of a sub-population of cells under non-permissive conditions that express flagellin (fliC) at levels similar to cells incubated under permissive conditions using both quantitative single cell microscopy and flow cytometry. To understand the genetics underlying the CS phenotype, we selected for naturally arising mutants that exhibited a normal swimming phenotype at the warmer incubation temperature. Sequencing these mutants recovered several independent non-synonymous mutations within FleN (also known as FlhG) as well as mutations within the promoter region of FleQ, the master flagellum regulator in Pseudomonas. We further show that nutrient depletion is the likely underlying cause of CS, as reduced nutrients will stimulate both fliC expression and a normal swimming phenotype at 30 {degrees}C.