Salmonella regulatory networks that contribute to proliferation in tomato soft rots: mechanisms and food safety implications

The proposed project seeks to fill the gap of knowledge that exists in our understanding of how Salmonella persists and even thrives in non-traditional hosts, such as plants. Several studies documented mechanisms by which Salmonella attaches to plant surfaces and persists inside plant tissues. It is also clear that Salmonella engages in complex interactions with phytobacteria, and these interactions can surpress or promote growth of Salmonella on plant surfaces and inside plant tissues. However, mechanisms by which Salmonella interacts with phytobacteria, including Pectobacterium are much less understood. Because presence of phytopathogens was shown to be an important risk factor for produce safety in the retail environment, understanding mechanisms of these interactions will likely have direct impact on improving produce safety farm-to-fork.Objective 1. To define Salmonella metabolic pathways involved in persistence within soft rots.TN-seq revealed that genes involved in gluconeogenesis were critical to fitness within soft rot. Because orthologs of the global regulatory system GacS/GacA (BarA/SirA in Salmonella) are known to control the switch from glycolysis to gluconeogenesis, I will test the hypothesis that the sensor kinase BarA perceives a cue within the soft rot and triggers SirA-mediated changes in gene expression. Furthermore, I hypothesize that BarA/SirA Regulon is central to the fitness of Salmonella within soft rots.Objective 2. To characterize the contribution of a novel small regulatory sRNA-IV to the regulation of Salmonella genes involved in persistence within tomatoes and soft rots.The analysis of intragenic regions selected for in the TN-seq screen identified a number of novel putative regulatory elements. One of the intergenic regions appears to harbor sRNA-IV. I will test the hypothesis that sRNA-IV controls a regulon involved in fitness within plants and in soft rots. Intriguingly, barA was predicted as one of the sRNA-IV targets. If this bioinformatics pre-diction is supported by the experimental data, this will reveal a novel mechanism of regulation for a GacS/GacA ortholog, which potentially integrates signals perceived by the sensor kinase with other inputs such as sRNA which controls expression of barA.