Transcriptomic analysis of swarm motility phenotype of Salmonella enterica serovar Typhimurium mutant defective in periplasmic glucan synthesis

Movement of food-borne pathogens on moist surfaces enables them to migrate towards more favorable niches and facilitate their survival for extended periods of time. Salmonella enterica serovar Typhimurium mutants defective in OPG synthesis are unable to exhibit motility on moist surfaces (swarming) however their mobility in liquid (swim motility) remains unaffected. In order to understand the role of OPG in swarm motility, transcriptomic analysis was performed using cells growing on a moist agar surface.  In the opgGH-deletion mutant, lack of OPG significantly altered transcription of 1039 genes out of total 4712 genes (22%). Introduction of a plasmid borne copy of opgGH into the opgGH-deletion mutant restored normal expression of all but 30 genes, indicating a wide-range influence of OPG on gene expression under the swarm motility condition.  Major pathways that were differentially-expressed in opgGH mutants were motility, virulence and invasion, and genes related to the secondary messenger molecule, cyclic di-GMP.  These observations provide insights and help explain the pleiotropic nature of OPG mutants such as sub-optimal virulence and competitive organ colonization in mice, biofilm formation, and sensitivity towards detergent stress. The study comprised nine samples, three replicates for three strains of the organism.  It compared opgGH mutant Salmonella enterica subsp. enterica serovar Typhimurium str. SL1344 with the wild type parental strain and the opgGH mutant carrying a plasmid borne wild-type copy of opgGH genes with the wild type parental strain.