Horizontally acquired divergent O-antigen contributes to escape from cross-immunity in the classical bordetellae

Abstract

BackgroundHorizontal gene transfer (HGT) allows for rapid spread of genetic material between species, increasing genetic and phenotypic diversity. Although HGT contributes to adaptation and is widespread in many bacteria, others show little HGT. This study builds on previous work to analyze the evolutionary mechanisms contributing to variation within the locus encoding a prominent antigen of the classical bordetellae.ResultsWe observed amongst classical bordetellae discrete regions of the lipopolysaccharide O-antigen locus with higher sequence diversity than the genome average. Regions of this locus had less than 50% sequence similarity, low dN/dS ratios and lower GC content compared to the genome average. Additionally, phylogenetic tree topologies based on genome-wide SNPs were incongruent with those based on genes within these variable regions, suggesting portions of the O-antigen locus may have been horizontally transferred. Furthermore, several predicted recombination breakpoints correspond with the ends of these variable regions. To examine the evolutionary forces that might have selected for this rare example of HGT in bordetellae, we compared in vitro and in vivo phenotypes associated with different O-antigen types. Antibodies against O1- and O2-serotypes were poorly cross-reactive, and did not efficiently kill or mediate clearance of alternative O-type bacteria, while a distinct and poorly immunogenic O-antigen offered no protection against colonization.ConclusionsThis study suggests that O-antigen variation was introduced to the classical bordetellae via HGT through recombination. Additionally, genetic variation may be maintained within the O-antigen locus because it can provide escape from immunity to different O-antigen types, potentially allowing for the circulation of different Bordetella strains within the same host population.

Variation in the Frequency and Extent of Hybridization between Leucosceptrum japonicum and L. stellipilum (Lamiaceae) in the Central Japanese Mainland

“…They may also have been associated with hybridization at the margin of the range of previously geographical isolated species [95–98]. One possible scenario to account for the formation of the contact zone between L .…”

Bordetella pertussisand pertactin-deficient clinical isolates: lessons for pertussis vaccines

“…It is composed of a hydrophobic moiety called lipid A (encoded by the lpx locus in Bordetella), an oligosaccharide core and a long serospecific polysaccharide called the O antigen [38]. B. pertussis lacks the wbm operon [39] and does not produce this O antigen [40], hence the name LOS rather than LPS.…”

Modifications of Bordetella bronchiseptica core lipopolysaccharide influence immune response without affecting protective activity

“…14 Hester and co-workers suggested that horizontally acquired divergent O-antigen contributes to escape from cross-immunity in the classical Bordetellae. 15 Dispersal position of these genes may suggest a possible source of LPS structure diversity between different Bordetella circulating strains. However, when other available genomes were analyzed, those genes were in the same relative position suggesting that glycosyltransferase genes are part of the core rather than accessory genome.…”