Poster Presentation Australian Society for Microbiology Annual Scientific Meeting 2018

Acinetobacter baumannii K24 capsular polysaccharide requires a novel gene for sugar biosynthesis and a gene located outside of the K locus (#311)

Johanna J Kenyon 1 , Ruth M Hall 2
  1. Queensland University of Technology, Brisbane, QLD, Australia
  2. University Of Sydney, CAMPERDOWN, NSW, Australia

Capsular polysaccharide (CPS) is one of the primary virulence determinants for the important nosocomial pathogen, Acinetobacter baumannii; acting as an external barrier that protects the organism from antimicrobial compounds, the host immune response, and other external threats. This bacterial surface structure displays significant heterogeneity between different isolates in the species, and 125 different sets of genes have been found at the chromosomal K locus (KL) in an analysis of more than 1000 genome sequences. Our investigation into this genomic region in the multiply antibiotic resistant strain, RCH51, revealed a new gene cluster named KL24. The KL24 gene cluster resembled other A. baumannii gene clusters in that it contained genes for nucleotide-sugar biosynthesis, glycosyltransfer, capsule export, and capsule unit translocation (wzx), though a wzy gene for CPS unit polymerisation was not found. The K24 CPS structure was elucidated by NMR and found to contain D-galactose, N-acetyl-D-glucosamine, N-acetyl-D-galactosamine, and the rare sugar, 3-acetamido-3,6-dideoxy-D-galactose (D-Fuc3NAc). Three out of five genes for D-Fuc3NAc synthesis were found in KL24. However, an additional gene was found and predicted to encode a new bifunctional protein, FdtE, with a N-terminal 3,4-ketoisomerase domain and a C-terminal acetyltransferase domain, which would replace the activity of the other two proteins in the synthesis pathway. Investigation of the whole genome sequence of RCH51 further revealed a wzy gene in a small genomic island (GI) in the same location as a different GI carrying wzy found in several other A. baumannii isolates. Evidence was found that suggested the GI is likely mobile. Direct correlation of CPS gene cluster content and CPS structural data of these major antigenic structures in A. baumannii has proven to be a useful method to predict novel synthesis pathways and confirm the functions of proteins involved in CPS biosynthesis. This knowledge forms the foundations for future biochemical studies.