Genome and Methylome Adaptation of -Negative Helicobacter pylori during Experimental Human Infection.

Multiple studies have demonstrated rapid bacterial genome evolution during chronic infection with In contrast, little was known about genetic changes during the first stages of infection, when selective pressure is likely to be highest. Using single-molecule, real-time (SMRT) and Illumina sequencing technologies, we analyzed genome and methylome evolution during the first 10 weeks of infection by comparing the pathogenicity island (PAI)-negative challenge strain BCS 100 with pairs of reisolates from gastric antrum and corpus biopsy specimens of 10 human volunteers who had been infected with this strain as part of a vaccine trial. Most genetic changes detected in the reisolates affected genes with a surface-related role or a predicted function in peptide uptake. Apart from phenotypic changes of the bacterial envelope, a duplication of the catalase gene was observed in one reisolate, which resulted in higher catalase activity and improved survival under oxidative stress conditions. The methylomes also varied in some of the reisolates, mostly by activity switching of phase-variable methyltransferase (MTase) genes. The observed mutation spectrum was remarkable for a very high proportion of nonsynonymous mutations. Although the data showed substantial within-strain genome diversity in the challenge strain, most antrum and corpus reisolates from the same volunteers were highly similar to each other, indicating that the challenge infection represents a major selective bottleneck shaping the transmitted population. Our findings suggest rapid election of during early-phase infection providing adaptation to different individuals by common mechanisms of genetic and epigenetic alterations. Exceptional genetic diversity and variability are hallmarks of , but the biological role of this plasticity remains incompletely understood. Here, we had the rare opportunity to investigate the molecular evolution during the first weeks of infection by comparing the genomes and epigenomes of strain BCS 100 used to challenge human volunteers in a vaccine trial with those of bacteria reisolated from the volunteers 10 weeks after the challenge. The data provide molecular insights into the process of establishment of this highly versatile pathogen in 10 different human individual hosts, showing, for example, selection for changes in host-interaction molecules as well as changes in epigenetic methylation patterns. The data provide important clues to the early adaptation of to new host niches after transmission, which we believe is vital to understand its success as a chronic pathogen and develop more efficient treatments and vaccines.