However, other mechanisms also appear to play a role, facilitating the small increase in AHL production observed in response to Pi limitation despite the absence of a functional PstSCAB-PhoU system. Figure 8 A pstS mutant is largely HDAC inhibition unresponsive to P i limitation. (A) Pig and (B) AHL production was measured from a pstS mutant (ROP2) grown to early stationary phase in phosphate-limiting medium with (open bars) or without (solid bars) the addition of 5 mM KH2PO4. Discussion There are multiple studies

identifying environmental factors that effect Pig production in Serratia spp., including the effects of salt concentration, temperature, oxygen availability and multiple metal ion concentrations [27]. However, the molecular mechanism underlying most of these responses has not been elucidated. Here, we investigate the molecular mechanism by which Pi limitation affects secondary metabolism in the enteric bacteria Serratia 39006. It was previously shown that a pstS mutation in Serratia 39006 resulted in the upregulation of QS and secondary metabolism [29].

Here, we demonstrate that these effects are occurring via the PhoBR two-component system, since a secondary mutation in phoBR abolished the effects of a pstS mutation. In addition, we confirm that QS and secondary metabolism C188-9 are upregulated in response to Pi limitation, and that this is occurring primarily via the PstSCAB-PhoU transport system. We also demonstrate that expression of rap is upregulated in response to a pstS mutation. Rap is an activator of Pig and Car, and a repressor of surfactant production and swarming motility, in Serratia 39006 [19, 29]. Rap shares similarity with the SlyA/MarR-family global transcription factor,

RovA, which regulates genes required for host colonization in Yersinia spp. [32–34]. Therefore, our results indicate that three global transcriptional regulators, Rap, SmaR and PhoB, are involved in mediating the effects of Pi limitation Urocanase on secondary metabolism in Serratia 39006. A mutation of the pstSCAB-phoU genes resulted in a clear increase in Pig and AHL production, and a clear increase in pigA, smaI and rap transcription. However, following Pi limitation, the effects on secondary metabolism and gene expression were less dramatic. The degree of activation of Pig and AHL production, and pigA transcription, was approximately 35% lower following Pi limitation than the levels of activation observed in a pstS mutant. In addition, a clear increase in rap transcription was not observed following Pi limitation. It is possible that this reduced effect is due to the fact that a pstS mutant is constitutively mimicking extreme Pi limitation.