Submitted to: Molecular Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/15/2003
Publication Date: 4/1/2004
Citation: Qingfeng, W., Frye, J.G., Mcclelland, M., Harshey, R.M. 2004. Gene expression patterns during swarming in salmonella typhimurium: genes specific to surface growth and putative new motility and pathogenicity genes. Molecular Microbiology. 52(1):169-187. Interpretive Summary: One of the characteristics of Salmonella that make it a persistent contaminant of food processing and preparation surfaces is its ability to swarm on surfaces and form biofilms. Swarming is a poorly understood form of surface motility which shares features with biofilm formation and host invasion. To investigate this, global gene expression profiles of Salmonella typhimurium were determined by DNA microarray over an 8hr time course during swarming. These were compared to a similar time course of growth in liquid media and on hard agar where the bacteria cannot swarm. Cluster analysis of expression patterns identified dozens of new genes and pathways involved in motility and virulence, increasing our understanding of swarming and pathogenesis. These pathways can be targeted by investigators for inhibition with chemicals or coatings to prevent swarming and biofilm formation on surfaces. Prevention of processing surface contamination would have a beneficial impact on food safety and human health.
Technical Abstract: Swarming is a specialized form of surface motility displayed by several flagellated bacterial genera, which shares features with other surface phenomenon such as biofilm formation and host invasion. Swarmer cells are generally more flagellated and longer than vegetative cells of the same species propagatedin liquid media, and move within an encasement of polysaccharide ‘slime’. Signals and signaling pathways controlling swarm cell differentiation are largely unknown. In order to test whether there is a genetic program specific to swarming, we have determined global gene expression profiles of Salmonella typhimurium over an 8 h time course during swarming, and compared the microarray data with a similar time course of growth in liquid media as well as on harder agar where the bacteria do not swarm. Our data show that bacteria growing on the surface of agar have a markedly different physiology from those in broth, as judged by differential regulation of nearly one-third of the functional genome. The large number of genes showing surface-specific up regulation included those for lipopolysaccharide synthesis, iron metabolism and type III secretion. Although swarming-specific induction of flagellar gene expression was not generally apparent, genes for iron metabolism were strongly induced specifically on swarm agar. Surface-dependent regulation of many virulence genes suggests that growth on an agar surface could serve as a model for gene expression during the initial stages of host infection. Based on cluster analysis of distinctive expression patterns, we report here the identification of putative new genes involved in motility and virulence.