Quantum changes in Helicobacter pylori gene expression accompany host-adaptation

Abstract

Helicobacter pylori is a highly successful gastric pathogen. High genomic plasticity allows its adaptation to changing host environments. Complete genomes of H. pylori clinical isolate UM032 and its mice-adapted serial derivatives 298 and 299, generated using both PacBio RS and Illumina MiSeq sequencing technologies, were compared to identify novel elements responsible for host-adaptation. The acquisition of a jhp0562-like allele, which encodes for a galactosyltransferase, was identified in the mice-adapted strains. Our analysis implies a new β-1,4-galactosyltransferase role for this enzyme, essential for Ley antigen expression. Intragenomic recombination between babA and babB genes was also observed. Further, we expanded on the list of candidate genes whose expression patterns have been mediated by upstream homopolymer-length alterations to facilitate host adaption. Importantly, greater than four-fold reduction of mRNA levels was demonstrated in five genes. Among the down-regulated genes, three encode for outer membrane proteins, including BabA, BabB and HopD. As expected, a substantial reduction in BabA protein abundance was detected in mice-adapted strains 298 and 299 via Western analysis. Our results suggest that the expression of Ley antigen and reduced outer membrane protein expressions may facilitate H. pylori colonisation of mouse gastric epithelium.

Keywords: BabA; Helicobacter pylori; Lewis antigen; expression; host adaptation.

Figure 1

Whole-genome alignment of H. pylori strains UM032, 298 and 299 using Mauve indicates no genome shuffling. Insertions are visualised as gaps in the alignment.

Figure 2

Duplicate sequences in UM032, 298 and 299 complete genomes. The ' character indicates the erroneous overlaps at each end of the original published contig.

Figure 3

Recombination between babA and babB sequences.

Figure 4

Immunoblot analysis of H. pylori strains UM032, 298 and 299 whole cell lysates with anti-Le^y and anti-Le^b antibodies.

Figure 5

A schematic diagram of type I and type II Lewis antigen biosynthesis pathways in H. pylori strain UM032. GlcNAc, N-acetylglucosamine; LacNAc, N-acetyl-D-lactosamine.

Figure 6

Protein structure modelling comparing both UA948FucT and UM032_1086. The catalytic sites accounting for interaction with the donor substrate, GDP-fucose, are highlighted.

Figure 7

Real-time quantitation of genes identified with modified intergenic homopolymer-length. Data are expressed as fold change relative to strain UM032. The symbol * indicates statistical significance where p<0.05.

Figure 8

Western immunodetection of BabA in H. pylori strains UM032, 298 and 299. G27 and 26695 served as the positive and negative controls, respectively, in this assay.

Figure 9

Western immunodetection of UreB in H. pylori strains UM032, 298 and 299.