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J. Bacteriol. doi:10.1128/JB.01489-06
Copyright (c) 2006, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

A Second Galacturonic Acid Transferase is Required for Core Lipopolysaccharide Biosynthesis and Complete Capsule Association to the Cell Surface in Klebsiella pneumoniae

Departamento de Microbiología, Facultad de Biología, Universidad de Barcelona, Diagonal 645, 08071 Barcelona, Spain, Departamento de Microbiología y Parasitología Sanitarias, Facultad de Farmacia, Universidad de Barcelona, Av. Joan XXIII s/n, Barcelona 08028, Spain, and Dipartimento di Chimica Organica e Biochimica, Università Federico II di Napoli, Complesso Universitario Monte S. Angelo, Via Cintia 4, 80126 Napoli, Italy

^* To whom correspondence should be addressed. Email: jtomas{at}ub.edu.

	Abstract

The core lipopolysaccharide (LPS) of Klebsiella pneumoniae contains two galacturonic acid (GalA) residues but only one GalA transferase (WabG) has been identified. Data from chemical and structural analysis of LPS isolated from a wabO mutant show the absence of the inner core -GalA residue linked to L-glycero-D-manno-heptose III (L,D-Hep III). An in vitro assay demonstrates that the purified WabO is able to catalyze the transfer of GalA from UDP-GalA to acceptor LPS isolated from the wabO mutant, but not to LPS isolated from waaQ mutant (deficient in L,D-Hep III) . The absence of this inner core -GalA residue results in a decrease in virulence in a capsule dependent experimental mouse pneumonia model. In addition, this mutation leads to a strong reduction in cell bound capsule. Interestingly, a K66 Klebsiella strain (natural isolate) without a functional wabO gene shows reduced levels of cell bound capsule in comparison to other K66 strains. Thus, the WabO enzyme plays an important role in core LPS biosynthesis and determines the level of cell bound capsule in Klebsiella pneumoniae.