The proposed mechanism by P
limitation can upregulate secondary metabolism in Serratia 39006. In response to Pi limitation (or pstS mutation), PhoR activates PhoB by phosphorylation. Active PhoB can then activate transcription of smaI, pigA and rap (indicated using solid arrows). Upregulation of smaI results in activation of the QS regulated genes (pigA, carA and rap), via AHL mediated SmaR derepression (indicated using dashed arrows). Rap then further activates carA and pigA expression (indicated using solid arrows). This results in upregulation of Pig and Car production.