Deep-sea Vent Bacteria Provide Insight into Evolution of Ulcer-Causing Relatives

Genes responsible for virulence in certain pathogenic bacteria, including strains associated with stomach cancer and ulcers in humans, also allow related deep-sea vent bacteria to thrive in their environment, according to new research published by the Proceedings of the National Academy of Sciences.

Researchers sequenced the genomes of previously unidentified species of Sulfurovum and Nitratiruptor obtained from samples collected at a hydrothermal vent in the Iheya North field near Japan at a depth of 1000 meters. The bacteria, like many other deep-sea vent bacteria, are chemolithoautotropic-that is, they make their own food from carbon dioxide using energy from inorganic molecules. As vent communities occur at such great depths that they receive no sunlight and cannot support photosynthetic organisms, it is instead the chemolithoautotrophic bacteria which form the base of the ecosystem. Many of these bacteria, including the two species sequenced, belong to a group called the epsilon-proteobacteria. Curiously, the epsilon-proteobacteria also include a number of animal pathogens, such as Helicobacter pylori, which is associated with ulcers and stomach cancer in humans, and the food-borne, diarrhea-causing Campylobacter jejuni.

Analysis of the two new deep-sea vent bacteria genomes revealed that they possessed copies of genes considered important to virulence in the pathogenic epsilon-proteobacteria. Among them were a cluster of genes responsible for evasion of host immune systems in the pathogenic bacteria; the authors suggested that the genes arose in ancestral deep-sea vent bacteria symbiotic with invertebrates (as many modern vent epsilon-proteobacteria are today), and were pre-adaptive to the evolution of pathogenic epsilon-proteobacteria.