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Infection and Immunity, November 2003, p. 6426-6434, Vol. 71, No. 11
0019-9567/03/$08.00+0     DOI: 10.1128/IAI.71.11.6426-6434.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Identification of a 3-Deoxy-D-manno-Octulosonic Acid Biosynthetic Operon in Moraxella catarrhalis and Analysis of a KdsA-Deficient Isogenic Mutant

Nicole R. Luke,1, Simon Allen,2 Bradford W. Gibson,2,3 and Anthony A. Campagnari1,4*

Department of MicrobiologyImmunology,1 Department of Medicine, State University of New York at Buffalo, Buffalo, New York 14214,4 The Buck Institute for Age Research, Novato, California 94945,2 Department of Pharmaceutical Chemistry, University of California, San Francisco, California 941433

Received 24 July 2003/ Accepted 13 August 2003

Lipooligosaccharide (LOS), a predominant surface-exposed component of the outer membrane, has been implicated as a virulence factor in the pathogenesis of Moraxella catarrhalis infections. However, the critical steps involved in the biosynthesis and assembly of M. catarrhalis LOS currently remain undefined. In this study, we used random transposon mutagenesis to identify a 3-deoxy-D-manno-octulosonic acid (KDO) biosynthetic operon in M. catarrhalis with the gene order pyrG-kdsA-eno. The lipid A-KDO molecule serves as the acceptor onto which a variety of glycosyl transferases sequentially add the core and branch oligosaccharide extensions for the LOS molecule. KdsA, the KDO-8-phosphate synthase, catalyzes the first step of KDO biosynthesis and is an essential enzyme in gram-negative enteric bacteria for maintenance of bacterial viability. We report the construction of an isogenic M. catarrhalis kdsA mutant in strain 7169 by allelic exchange. Our data indicate that an LOS molecule consisting only of lipid A and lacking KDO glycosylation is sufficient to sustain M. catarrhalis survival in vitro. In addition, comparative growth and susceptibility assays were performed to assess the sensitivity of 7169kdsA11 compared to that of the parental strain. The results of these studies demonstrate that the native LOS molecule is an important factor in maintaining the integrity of the outer membrane and suggest that LOS is a critical component involved in the ability of M. catarrhalis to resist the bactericidal activity of human sera.

* Corresponding author. Mailing address: Department of Microbiology, State University of New York at Buffalo, 140 Biomedical Research Bldg., 3435 Main St., Buffalo, NY 14214. Phone: (716) 829-2673. Fax: (716) 829-3889. E-mail: AAC{at}acsu.buffalo.edu.

Editor: D. L. Burns

Infection and Immunity, November 2003, p. 6426-6434, Vol. 71, No. 11
0019-9567/03/$08.00+0     DOI: 10.1128/IAI.71.11.6426-6434.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.



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