Relationships of capsular polysaccharides belonging to Campylobacter jejuni HS1 serotype complex

Abstract

The Campylobacter jejuni capsule type HS1 complex is one of the most common serotypes identified worldwide, and consists of strains typing as HS1, HS1/44, HS44 and HS1/8. The capsule structure of the HS1 type strain was shown previously to be composed of teichoic-acid like glycerol-galactosyl phosphate repeats [4-)-α-D-Galp-(1-2)-Gro-(1-P-] with non-stoichiometric fructose branches at the C2 and C3 of Gal and non-stoichiometric methyl phosphoramidate (MeOPN) modifications on the C3 of the fructose. Here, we demonstrate that the capsule of an HS1/44 strain is identical to that of the type strain of HS1, and the capsule of HS1/8 is also identical to HS1, except for an additional site of MeOPN modification at C6 of Gal. The DNA sequence of the capsule locus of an HS44 strain included an insertion of 10 genes, and the strain expressed two capsules, one identical to the HS1 type strain, but with no fructose branches, and another composed of heptoses and MeOPN. We also characterize a HS1 capsule biosynthesis gene, HS1.08, as a fructose transferase responsible for the attachment of the β-D-fructofuranoses residues at C2 and C3 of the Gal unit. In summary, the common component of all members of the HS1 complex is the teichoic-acid like backbone that is likely responsible for the observed sero-cross reactivity.

Fig 1. Structure of teichoic acid-like capsules among the HS1 complex.

Fig 2. Alignment of variable CPS loci from C. jejuni HS1 and HS44 Penner type strains.

Genes are color coded as follows: Navy blue, MeOPN biosynthesis and transferase; red, CPS transport and assembly; yellow, putative methyl transferase; purple, Heptose/deoxyheptose biosynthesis; blue, putative glycosyl transferase; green, sugar biosynthesis; brown, hypothetical.

Fig 3. NMR of Penner HS1 type strain native CPS and HS1/44 native CPS and defructosylated CPS.

(A) 1D ³¹P NMR spectra of C. jejuni Penner HS1 type strain CPS (top) and HS1/44 CPS (bottom) showing the teichoic-acid phosphate resonances (0.02–1.25 ppm) and the MeOPN-3-Fru resonances (14.25–14.85 ppm); (B) 2D ¹H-¹H COSY spectrum of defructosylated HS1/44 CPS; (C) 2D ¹H-¹³C HSQC spectrum of defructosylated HS1/44 CPS; (D) 2D ¹H-¹³C HMBC spectrum of defructosylated HS1/44 CPS.

Fig 4. NMR of HS1/44 CPS.

(A) 2D ¹H-¹³C HSQC spectrum of HS1/44 native CPS; (B) 2D ¹H-³¹P HMBC spectrum of HS1/44 native CPS.

Fig 5. Characterization of mutants in the HS1.08 gene.

A. Alcian blue stained 12.5% SDS PAGE of crude CPS preparations. Lane 1, Precision Plus protein standards; lane 2, HS1 wildtype; lane 3, HS1 1.08 mutant; lane 4, HS1 1.08 mutant complemented; B. ³¹P NMR of CPS from strain HS1 ΔHS1.08::cat showing the CPS devoid of MeOPN; C. ³¹P NMR spectrum of CPS from HS1 1.08 mutant complemented, showing the re-insertion of MeOPN in the CPS.; D. 1D ³¹P NMR of C. jejuni HS44 (strain 2871) CPS preparation; E. ¹H-³¹P HMBC NMR of defructosylated C. jejuni HS1 strain 3588.

Fig 6. Bacterial sensitivities to complement killing by Normal Human Serum (NHS) serum killing.

(A) C. jejuni HS1 strain and mutants, (B) C. jejuni HS44 strain and mutants.