However, at the time of protein harvest in this study (16 hours post inoculation), its overall abundance in unadapted cultures was extremely low (when compared to that within adapted cultures) and, in all probability, under the detection limit for silver staining. PA exposure has been correlated with de novo protein synthesis [5]; therefore, the observed

increase in abundance of ribosomal proteins in this study is not surprising. Specifically, this study establishes a direct link between PA exposure and the overexpression of ribosomal proteins. The 50 S ribosomal proteins RplE and RplF (both components of the spc operon) have not been studied in abundance in Salmonella. However, it is known that the synthesis of ribosomal proteins fluctuates in accordance to the cell’s environment [35]. RplE was discovered to be crucial for cell viability 3-deazaneplanocin A in E. coli [20]. Knockout mutants lacking this gene were unable to compensate

for the loss in vitro and its absence ultimately proved to be lethal. It is quite possible that RplE may play a similar role in S. Enteritidis; however, this hypothesis Selleckchem Bafilomycin A1 has yet to be tested in Salmonella. It is certain the abundance of these ribosomal proteins in PA adapted cultures serves a purpose; however, this and other hypotheses must be tested to gain insight into their role in PA adapted cultures before further speculation can be made. Of the five proteins overexpressed in PA adapted

cultures, Dps and CpxR are those normally associated with virulence and pathogenesis in Salmonella and other enteropathogenic bacteria [28, 36]. Interestingly, these are also the only two proteins over-expressed at the mRNA level as well. The fact that RplE, RplF, and SodA were either suppressed (sodA and rplF) or unaffected (rplE) at the transcriptional level, yet overexpressed at the translational level is not highly unusual. In fact, studies comparing mRNA and protein abundances has demonstrated that, in general, the amount of mRNA levels in a cell at a given instance shows no correlation with the amount of protein that is produced by the cell [37, 38]. A potential mechanism for regulation of Dps in response to prolonged PA exposure may stem Phosphoprotein phosphatase from the fact that this protein is translationally regulated by the RNA-binding protein Hfq during stationary phase [38] and that expression of Dps is reduced in an Hfq deletion mutant during this time. (Expression of RplF is also reduced in an Hfq mutant; however, this expression pattern is specific to growth in acidified minimal medium.) PA exposure may increase the expression of Hfq during stationary phase and ultimately result in increased translation of Dps. Additionally, an interesting aspect with regards to RplE expression during stationary phase and Hfq-dependent regulation can be pointed out.