FIG 9.
Schematic showing the link between de novo pyrimidine synthesis, SCV, and alginate biosynthesis through sigma factors RpoN and AlgU competition for PalgD. (A) Disruption in the pyrimidine de novo biosynthetic pathway results in decreased levels of UMP. This causes an increase in RpoN that competes with AlgU to bind to the algD promoter (PalgD), thereby inhibiting alginate production. (B) The addition of free uracil to the medium causes the levels of UMP to increase through the salvage pathway and thereby decrease the levels of RpoN, which allows AlgU to bind to the algD promoter (PalgD); this results in alginate production. Moreover, overexpression of algU using pHERD20T and arabinose results in increased AlgU in the cell that outcompetes RpoN and results in alginate production.