@entity1030 with @entity796 is a common and serious problem in @entity1 with @entity1577 ( @entity1577 ). The @entity796 isolates from these @entity1 typically have a mucoid colony morphology due to overproduction of the exopolysaccharide alginate, which contributes to the persistence of the organisms in the @entity1577 lung. Most of the alginate biosynthetic genes are clustered in the algD operon, located at 34 min on the chromosome. Alginate biosynthesis begins with the formation of an activated monomer, @entity3006 - @entity70143 , which is known to occur via the products of the algA, algC, and algD genes. @entity70144 forms in the periplasm, but the gene products involved in @entity70143 translocation across the inner membrane and its polymerization are not known. One locus of the operon which remained uncharacterized was a new gene called algK between alg44 and algE. We sequenced algK from the mucoid @entity1577 isolate FRD1 and expressed it in @entity526 , which revealed a polypeptide of the predicted size (52 kDa). The sequence of AlgK showed an apparent signal peptide characteristic of a lipoprotein. AlgK-PhoA fusion proteins were constructed and shown to be active, indicating that AlgK has a periplasmic subcellular localization. To test the phenotype of an AlgK-mutant, the algK coding sequence was replaced with a nonpolar @entity801 resistance cassette to avoid polar effects on genes downstream of algK that are essential for polymer formation. The algKdelta mutant was nonmucoid, demonstrating that AlgK was required for alginate production. Also, AlgK- mutants demonstrated a small-colony phenotype on L agar, suggesting that the loss of AlgK also caused a growth defect. The mutant phenotypes were complemented by a plasmid expressing algK in trans. When the algKdelta mutation was placed in an algJ::Tn501 background, where algA was not expressed due to polar transposon effects, the growth defect was not observed. AlgK- mutants appeared to accumulate a toxic extracellular product, and we hypothesized that this could be an unpolymerized alginate precursor. High levels of low-molecular-weight @entity13275 were produced by the AlgK- mutant. When AlgK- culture supernatants were subjected to dialysis, high levels of @entity11594 diffused out of the dialysis sac, and no uronic acids were detectable after extensive dialysis. In contrast, the mucoid wild-type strain produced only polymerized uronic acids (i.e., alginate), whereas the algKdelta algJ::Tn501 mutant produced no uronic acids. Thus, the alginate pathway in an AlgK- mutant was blocked after transport but at a step before polymerization, suggesting that AlgK plays an important role in the polymerization of @entity70143 to alginate.

Deletion of algK in mucoid @entity796 blocks alginate polymer formation and results in XXXX secretion.

@entity1 :: ('9606', 'Species') :: ['patients'] @entity801 :: ('MESH:D005839', 'Chemical') :: ['gentamicin'] @entity13275 :: ('CHEBI:27252', 'Chemical') :: ['uronic acid'] @entity796 :: ('287', 'Species') :: ['Pseudomonas aeruginosa', 'P. aeruginosa'] @entity11594 :: ('MESH:D014574', 'Chemical') :: ['uronic acids'] @entity3006 :: ('MESH:D006153', 'Chemical') :: ['GDP'] @entity70143 :: ('CHEBI:33821', 'Chemical') :: ['mannuronate'] @entity70144 :: ('CHEBI:27763', 'Chemical') :: ['Polymannuronate'] @entity1030 :: ('MESH:D029424', 'Disease') :: ['Chronic pulmonary infection'] @entity1577 :: ('MESH:D003550', 'Disease') :: ['CF', 'cystic fibrosis'] @entity526 :: ('562', 'Species') :: ['Escherichia coli']
@entity13275 :: (CHEBI:27252,Chemical) :: ['uronic acid']
