Tracing long-distance electron transfer and cable bacteria in freshwater sediments by agar pillar gradient columns.

Cable bacteria (CB) perform electrogenic sulfur oxidation (e-SOx) by spatially separating redox half reactions over centimetre distances. For freshwater systems, the ecology of CB is not yet well understood, partly because they proved difficult to cultivate. This study introduces a new 'agar pillar' approach to selectively enrich and investigate CB populations. Within sediment columns, a central agar pillar is embedded, providing a sediment-free gradient system in equilibrium with the surrounding sediment. We incubated freshwater sediments from a streambed, a sulfidic lake and a hydrocarbon-polluted aquifer in such agar pillar columns. Microprofiling revealed typical patterns of e-SOx, such as the development of a suboxic zone and the establishment of electric potentials. The bacterial communities in the sediments and agar pillars were analysed over depth by PacBio near-full-length 16S rRNA gene amplicon sequencing, allowing for a precise phylogenetic placement of taxa detected. The selective niche of the agar pillar was preferentially colonized by CB related to Candidatus Electronema for surface water sediments, including several potentially novel species, but not for putative groundwater CB affiliated with Desulfurivibrio spp. The presence of CB was seemingly linked to co-enriched fermenters, hinting at a possible role of e-SOx populations as an electron sink for heterotrophic microbes. These findings add to our current understanding of the diversity and ecology of CB in freshwater systems, and to a discrimination of CB from surface and groundwater sediments. The agar pillar approach provides a new strategy that may facilitate the cultivation of redox gradient-dependent microorganisms, including previously unrecognized CB populations.

Helicobacter pylori γ-glutamyl transferase contributes to colonization and differential recruitment of T cells during persistence.

Helicobacter pylori γ-glutamyl transferase (gGT) is a key bacterial virulence factor that is not only important for bacterial gastric colonization but also related to the development of gastric pathology. Despite accumulating evidence for pathogenic and immunologic functions of H. pylori gGT, it is still unclear how it supports gastric colonization and how its specific effects on the host's innate and adaptive immune responses contribute to colonization and pathology. We have compared mice showing similar bacterial load after infection with gGT-proficient or gGT-deficient H. pylori to analyse the specific role of the enzyme during infection. Our data indicate that H. pylori gGT supports initial colonization. Nevertheless, bacteria lacking gGT can still colonize and persist. We observed that the presence of gGT during infection favoured a proinflammatory innate and adaptive immune response. Notably, H. pylori gGT activity was linked to increased levels of IFNγ, which were attributed to a differential recruitment of CD8+ T cells to the stomach. Our data support an essential role for H. pylori gGT in gastric colonization and further suggest that gGT favours infiltration of CD8+ cells to the gastric mucosa, which might play an important and yet overlooked role in the pathogenesis of H. pylori.

Identification of a High-Affinity Pyruvate Receptor in Escherichia coli.

Two-component systems are crucial for signal perception and modulation of bacterial behavior. Nevertheless, to date, very few ligands have been identified that directly interact with histidine kinases. The histidine kinase/response regulator system YehU/YehT of Escherichia coli is part of a nutrient-sensing network. Here we demonstrate that this system senses the onset of nutrient limitation in amino acid rich media and responds to extracellular pyruvate. Binding of radiolabeled pyruvate was found for full-length YehU in right-side-out membrane vesicles as well as for a truncated, membrane-integrated variant, confirming that YehU is a high-affinity receptor for extracellular pyruvate. Therefore we propose to rename YehU/YehT as BtsS/BtsR, after "Brenztraubensäure", the name given to pyruvic acid when it was first synthesized. The function of BtsS/BtsR was also assessed in a clinically relevant uropathogenic E. coli strain. Quantitative transcriptional analysis revealed BtsS/BtsR importance during acute and chronic urinary-tract infections.