Hydrogen Fuels Cells in the Gut

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Science Translational Medicine  01 Jan 2014:
Vol. 6, Issue 217, pp. 217ec1
DOI: 10.1126/scitranslmed.3008236

As automakers warm to the virtues of hydrogen as an alternative fuel for cars, it is intriguing to realize that some bacteria have seen the value of hydrogen as fuel all along. Resident anaerobic bacteria in the colon release molecular hydrogen (H2) as a metabolic end-product of carbohydrate fermentation, creating an opportunity for other bacteria to scavenge the leftover H2 as a fuel for growth. Now, Maier and colleagues begin to identify mechanisms by which Salmonella Typhimurium (S. Tm) invades the colonic microbiota and replicates in the early stages of infection before inflammation-derived nutrients are available.

Using an unbiased competitive-infection screening approach, the authors found that S. Tm strains with mutations in genes that encode a membrane-bound hydrogenase complex—which is used to split H2 to provide electrons for the electron transport or respiratory chain—displayed a colonization defect in mice. To confirm this finding, they constructed a site-directed S. Tm mutant strain (S. Tmhyb) that lacked all structural genes for the hydrogenase complex and evaluated the fitness of this strain in vitro and in vivo. In vitro, the S. Tmhyb strain was outcompeted by wild-type S. Tm when H2 was available, but not in the absence of H2. In vivo, the S. Tmhyb strain showed a growth and colonization defect, relative to wild-type hydrogenase strains, in the early stages of infection (before any host inflammatory response) that disappeared in germ-free mice and with pretreatment by antibiotics or a competing H2 consumer.

This study provides insight into the mechanisms by which Salmonella and presumably other H2-consuming bacteria gain entry into the dense and competitive colonic ecosystem in the early stages of colonization before other established virulence factors come into play. Additional studies are needed to investigate the role of diet and interindividual differences in gut microbiota composition on H2 levels in the colon and the risk of Salmonella infection. Treatment with nonpathogenic H2-consuming bacteria is a potential strategy to decrease the risk of enteric infection.

L. Maier et al., Microbiota-derived hydrogen fuels Salmonella Typhimurium invasion of the gut ecosystem. Cell Host Microbe 14, 641–651 (2013). [Abstract]

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