title: Surface swarming motility by Pectobacterium atrosepticum is a latent phenotype that requires O antigen and is regulated by quorum sensing.
abstract: We describe a previously cryptic phenotype associated with the opportunistic phytopathogen Pectobacterium atrosepticum (Pca): surface swarming. We found that when Pca was spotted onto plates containing <0.5% (w/v) agar, the culture produced copious amounts of extracellular matrix material containing highly motile cells. Once produced, this 'slime layer' spread rapidly across the plate either as an advancing front or as tendrils. Transposon mutagenesis was used to identify mutants that were affected in swarming. Hypo-swarmer mutants mostly carried insertions in a horizontally acquired island (HAI5), which encodes a cluster of genes involved in O antigen biosynthesis. Hyper-swarmer mutants mostly carried insertions in hexY, a known antagonist of the class I flagellar master regulator, FlhD4C2. In addition, we found that the nucleoid protein, histone-like nuclear structuring protein 2 (H-NS2), also regulated swarming behaviour. A mutant in which hns2 was overexpressed displayed a hyper-swarming phenotype, whereas a mutant in which the hns2 ORF was inactivated had a hypo-swarming phenotype. Swarming was also regulated by quorum sensing (QS) and by the carbon source being utilized. We show, using a range of epistasis experiments, that optimal swarming requires both motility and O antigen biosynthesis, and that H-NS2 and QS both promote swarming through their effects on motility.
authors.affiliation: Department of Biochemistry, Tennis Court Road, Cambridge, CB2 1QW, UK.
authors.forename: Steven D
authors.initials: SD
authors.lastname: Bowden
authors.affiliation: Department of Biochemistry, Tennis Court Road, Cambridge, CB2 1QW, UK.
authors.forename: Nicola
authors.initials: N
authors.lastname: Hale
authors.affiliation: Department of Biochemistry, Tennis Court Road, Cambridge, CB2 1QW, UK.
authors.forename: Jade C S
authors.initials: JCS
authors.lastname: Chung
authors.affiliation: Department of Chemistry, Lensfield Road, Cambridge, CB2 1EW, UK.
authors.forename: James T
authors.initials: JT
authors.lastname: Hodgkinson
authors.affiliation: Department of Chemistry, Lensfield Road, Cambridge, CB2 1EW, UK.
authors.forename: David R
authors.initials: DR
authors.lastname: Spring
authors.affiliation: Department of Biochemistry, Tennis Court Road, Cambridge, CB2 1QW, UK.
authors.forename: Martin
authors.initials: M
authors.lastname: Welch
mesh_terms: D053898:Biosynthetic Pathways; D004251:DNA Transposable Elements; D016326:Extracellular Matrix Proteins / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D044404:Genomic Islands; D008124:Locomotion; D016254:Mutagenesis, Insertional; D019081:O Antigens / Q000096:biosynthesis*; D044043:Pectobacterium / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D011135:Polysaccharides, Bacterial / Q000378:metabolism; D053038:Quorum Sensing
chemical_list: D004251:DNA Transposable Elements; D016326:Extracellular Matrix Proteins; D019081:O Antigens; D011135:Polysaccharides, Bacterial