The KL 24 gene cluster and a genomic island encoding a Wzy polymerase contribute genes needed for synthesis of the K 24 capsular polysaccharide by the multiply antibiotic resistant Acinetobacter baumannii isolate RCH 51

The whole-genome sequence of the multiply antibiotic resistant Acinetobacter baumannii isolate RCH51 belonging to sequence type ST103 (Institut Pasteur scheme) revealed that the set of genes at the capsule locus, KL24, includes four genes predicted to direct the synthesis of 3-acetamido-3,6-dideoxy-D-galactose (D-Fuc3NAc), and this sugar was found in the capsular polysaccharide (CPS). One of these genes, fdtE, encodes a novel bifunctional protein with an N-terminal FdtA 3,4-ketoisomerase domain and a C-terminal acetyltransferase domain. KL24 lacks a gene encoding a Wzy polymerase to link the oligosaccharide K units to form the CPS found associated with isolate RCH51, and a wzy gene was found in a small genomic island (GI) near the cpn60 gene. This GI is in precisely the same location as another GI carrying wzy and atr genes recently found in several A. baumannii isolates, but it does not otherwise resemble it. The CPS isolated from RCH51, studied by sugar analysis and 1D and 2D H and C NMR spectroscopy, revealed that the K unit has a branched pentasaccharide structure made up of Gal, GalNAc and GlcNAc residues with D-Fuc3NAc as a side branch, and the K units are linked via a b-D-GlcpNAc-(1fi3)-b-D-Galp linkage formed by the Wzy encoded by the GI. The functions of the glycosyltransferases encoded by KL24 were assigned to formation of specific bonds. A correspondence between the order of the genes in KL24 and other KL and the order of the linkages they form was noted, and this may be useful in future predictions of glycosyltransferase specificities. INTRODUCTION Capsular polysaccharide (CPS) that coats the surface of Acinetobacter baumannii cells has been shown to provide protection from phagocytosis, desiccation and some antibiotics [1, 2]. CPS is built up by joining multiple copies of a complex oligosaccharide known as a K unit, which consists of specific sugars linked in a specific order. In general, the genes required for CPS biosynthesis in A. baumannii are clustered at the K locus, which is located between conserved fkpA and lldP genes [3]. However, there are many different sets of genes known to occupy the K locus in different A. baumannii strains [3–8], and each distinct gene set is identified by a KL number. All KL include genes that support the synthesis of common sugars, glucose (Glc), galactose (Gal) and N-acetylglucosamine (GlcNAc), and most include a gene to convert GlcNAc into N-acetylgalactosamine (GalNAc). However, the central portion of some gene clusters (between genes gna and galU) includes different modules of genes that direct the synthesis of specific additional sugar components [3, 8, 9]. There are also differences in the number and identity of the genes for glycosyltransferases that Received 7 December 2016; Accepted 12 January 2017 Author affiliations: School of Molecular Bioscience, The University of Sydney, Sydney, Australia; Institute of Health and Biomedical Innovation, School of Biomedical Sciences, Faculty of Health, Queensland University of Technology, Brisbane, Australia; N. D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, Moscow, Russia; Higher Chemical College of the Russian Academy of Sciences, D. I. Mendeleev University of Chemical Technology of Russia, Moscow, Russia; M. M. Shemyakin and Y. A. Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow, Russia; Moscow Institute of Physics and Technology, Dolgoprudny, Moscow Region, Russia; State Research Center for Applied Microbiology and Biotechnology, Obolensk, Moscow Region, Russia; School of Life and Environmental Sciences, The University of Sydney, Sydney, Australia. *Correspondence: Johanna J. Kenyon, johanna.kenyon@qut.edu. au