Genetic Diversity as Consequence of a Microaerobic and Neutrophilic Lifestyle

Abstract

As a neutrophilic bacterium, Helicobacter pylori is growth deficient under extreme acidic conditions. The gastric pathogen is equipped with an acid survival kit, regulating urease activity by a pH-gated urea channel, opening below pH 6.5. After overcoming acid stress, the bacterium’s multiplication site is situated at the gastric mucosa with near neutral pH. The pathogen exhibits exceptional genetic variability, mainly due to its capability of natural transformation, termed competence. Using single cell analysis, we show here that competence is highly regulated in H. pylori. DNA uptake complex activity was reversibly shut down below pH 6.5. pH values above 6.5 opened a competence window, in which competence development was triggered by the combination of pH increase and oxidative stress. In contrast, addition of sublethal concentrations of the DNA-damaging agents ciprofloxacin or mitomycin C did not trigger competence development under our conditions. An oxygen-sensitive mutant lacking superoxide dismutase (sodB) displayed a higher competent fraction of cells than the wild type under comparable conditions. In addition, the sodB mutant was dependent on adenine for growth in broth and turned into non-cultivable coccoid forms in its absence, indicating that adenine had radical quenching capacity. Quantification of periplasmically located DNA in competent wild type cells revealed outstanding median imported DNA amounts of around 350 kb per cell within 10 min of import, with maximally a chromosomal equivalent (1.6 Mb) in individual cells, far exceeding previous amounts detected in other Gram-negative bacteria. We conclude that the pathogen’s high genetic diversity is a consequence of its enormous DNA uptake capacity, triggered by intrinsic and extrinsic oxidative stress once a neutral pH at the site of chronic host colonization allows competence development.

Following transforming DNA in Helicobacter pylori from uptake to expression

“…Indeed, since in most cases (92%) both daughter cells will display the fluorescent marker, integration is likely to occur before the replication of the locus. We cannot however rule out the possibility that, having incorporated large amounts of tDNA (Kruger et al ., ), two independent recombination events might have occurred. For the studies presented here the site of GFP insertion at the ureA locus ( hp0073 ) is relatively close to the origin of replication of the chromosome (Donczew et al ., ).…”

“…New microscopy approaches are emerging to better comprehend the mechanisms involved in the process of transformation. In recent times, several studies revealed the formation of tDNA foci on the surface of competent bacteria (Stingl et al, 2010;Berge et al, 2013;Gangel et al, 2014;Hahn et al, 2015;Kruger et al, 2016). Only one group followed by microscopy the tDNA passage into the cytoplasm .…”

The use of stool specimens reveals Helicobacter pylori strain diversity in a cohort of adolescents and their family members in a developed country

“…The estimated mutation rate suggested a mutation burst during the acute infection phase that is over 10 times faster than the mutation rate during chronic infection, and orders of magnitude faster than mutation rates in any other bacteria ( Linz et al, 2014 ). Tracking of fluorescent DNA in competent bacteria has shown that H. pylori has the capacity to take up large quantities of DNA ( Kruger et al, 2016 ) and natural competence has been shown to promote chronic infection in a murine model of infection ( Dorer et al, 2013 ). The presence of multiple strains combined with natural competence may enable H. pylori to adapt to different environmental conditions in the stomachs of individuals.…”

DNA Transfer and Toll-like Receptor Modulation by Helicobacter pylori

“…Based on its homology to the archetypal T4SS of A. tumefaciens , a two-step DNA uptake model has been proposed (Stingl et al 2010). The ComB T4SS facilitates double-stranded DNA uptake into the periplasm, and a second, ComEC system is then utilized to incorporate the periplasmic DNA across the cytoplasmic membrane and into the host cell (Stingl et al 2010; Kruger et al 2016). …”