Nucleotide sequence and expression of UDP-glucose dehydrogenase gene required for the synthesis of xanthan gum in Xanthomonas campestris.

ABSTRACT

Xanthomonas campestris pv. campestris, producing large amounts of exopolysaccharide xanthan gum, has a mucoid phenotype. Strain SD7 was a non-mucoid mutant deficient in UDP-glucose dehydrogenase. A DNA fragment able to complement the mutation of SD7 was cloned from the parental wild-type strain Xc11. Sequence analysis of the region required for the complementation revealed an open reading frame which could encode a polypeptide of 445 amino acids with a calculated molecular weight of 48,432, a size similar to that of the product produced by maxicell. The amino acid sequence had significant homology to that of the GDP-mannose dehydrogenase from Pseudomonas aeruginosa.