UDP-glucose dehydrogenase Ugd in E. coli is activated by Gmd and RffD, is inhibited by CheY, and regulates swarming

The two most common mechanisms of polymyxin resistance in bacteria involve glycosylation of the outer membrane lipopolysaccharide (LPS) and production of the exocapsular polysaccharide, colanic acid (CA). UDP-glucose dehydrogenase, Ugd, is required for both CA biosynthesis and LPS modification. We here show that Ugd is activated by the GDP-mannose-4,6-dehydratase (Gmd, YefA, YefN), UDP-N-acetyl-D-mannosamine dehydrogenase (RffD, WecC), and ribonuclease HII (RnhB). The former two enzymes are involved in Lipid A and colanic acid biosyntheses, respectively, while RnhB cleaves RNA in RNA:DNA hybrids. Moreover, CheY inhibits the phosphorylated, activated form of Ugd (Ugd-P). Finally, Ugd is involved in the regulation of swarming, since a mutant has an increased swarming rate, while Ugd overproduction inhibits swarming. Two-hybrid bacterial assays reveal direct interaction of Ugd with RssB (an anti-RpoS factor) and CheY in vivo.