title: A third mode of surface-associated growth: immobilization of Salmonella enterica serovar Typhimurium modulates the RpoS-directed transcriptional programme.
abstract: Although the growth of bacteria has been studied for more than a century, it is only in recent decades that surface-associated growth has received attention. In addition to the well-characterized biofilm and swarming lifestyles, bacteria can also develop as micro-colonies supported by structured environments in both food products and the GI tract. This immobilized mode of growth has not been widely studied. To develop our understanding of the effects of immobilization upon a food-borne bacterial pathogen, we used the IFR Gel Cassette model. The transcriptional programme and metabolomic profile of Salmonella enterica serovar Typhimurium ST4/74 were compared during planktonic and immobilized growth, and a number of immobilization-specific characteristics were identified. Immobilized S.Typhimurium did not express motility and chemotaxis genes, and electron microscopy revealed the absence of flagella. The expression of RpoS-dependent genes and the level of RpoS protein were increased in immobilized bacteria, compared with planktonic growth. Immobilized growth prevented the induction of SPI1, SPI4 and SPI5 gene expression, likely mediated by the FliZ transcriptional regulator. Using an epithelial cell-based assay, we showed that immobilized S.Typhimurium was significantly less invasive than planktonic bacteria, and we suggest that S.Typhimurium grown in immobilized environments are less virulent than planktonic bacteria. Our findings identify immobilization as a third type of surface-associated growth that is distinct from the biofilm and swarming lifestyles of Salmonella.
authors.affiliation: Institute of Food Research, Norwich Research Park, Norwich, NR4 7UA, UK.
authors.forename: Gitte M
authors.initials: GM
authors.lastname: Knudsen
authors.forename: Maj-Britt
authors.initials: MB
authors.lastname: Nielsen
authors.forename: Terri
authors.initials: T
authors.lastname: Grassby
authors.forename: Vittoria
authors.initials: V
authors.lastname: Danino-Appleton
authors.forename: Line E
authors.initials: LE
authors.lastname: Thomsen
authors.forename: Ian J
authors.initials: IJ
authors.lastname: Colquhoun
authors.forename: Tim F
authors.initials: TF
authors.lastname: Brocklehurst
authors.forename: John E
authors.initials: JE
authors.lastname: Olsen
authors.forename: Jay C D
authors.initials: JC
authors.lastname: Hinton
mesh_terms: D000332:Aerobiosis; D000693:Anaerobiosis; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D018441:Biofilms; D004847:Epithelial Cells / Q000382:microbiology; D005407:Flagella / Q000235:genetics / Q000378:metabolism; D015964:Gene Expression Regulation, Bacterial; D012480:Salmonella Infections / Q000382:microbiology; D012486:Salmonella typhimurium / Q000235:genetics* / Q000254:growth & development* / Q000378:metabolism / Q000472:pathogenicity; D012808:Sigma Factor / Q000235:genetics* / Q000378:metabolism; D059467:Transcriptome
chemical_list: D001426:Bacterial Proteins; D012808:Sigma Factor; C069567:sigma factor KatF protein, Bacteria