H2 generated by fermentation in the human gut microbiome influences metabolism and competitive fitness of gut butyrate producers, 2023, Campbell et al

Background
Hydrogen gas (H2) is a common product of carbohydrate fermentation in the human gut microbiome and its accumulation can modulate fermentation. Concentrations of colonic H2 vary between individuals, raising the possibility that H2 concentration may be an important factor differentiating individual microbiomes and their metabolites. Butyrate-producing bacteria (butyrogens) in the human gut usually produce some combination of butyrate, lactate, formate, acetate, and H2 in branched fermentation pathways to manage reducing power generated during the oxidation of glucose to acetate and carbon dioxide. We predicted that a high concentration of intestinal H2 would favor the production of butyrate, lactate, and formate by the butyrogens at the expense of acetate, H2, and CO2. Regulation of butyrate production in the human gut is of particular interest due to its role as a mediator of colonic health through anti-inflammatory and anti-carcinogenic properties.

Results
For butyrogens that contained a hydrogenase, growth under a high H2 atmosphere or in the presence of the hydrogenase inhibitor CO stimulated production of organic fermentation products that accommodate reducing power generated during glycolysis, specifically butyrate, lactate, and formate. Also as expected, production of fermentation products in cultures of Faecalibacterium prausnitzii strain A2-165, which does not contain a hydrogenase, was unaffected by H2 or CO. In a synthetic gut microbial community, addition of the H2-consuming human gut methanogen Methanobrevibacter smithii decreased butyrate production alongside H2 concentration. Consistent with this observation, M. smithii metabolic activity in a large human cohort was associated with decreased fecal butyrate, but only during consumption of a resistant starch dietary supplement, suggesting the effect may be most prominent when H2 production in the gut is especially high. Addition of M. smithii to the synthetic communities also facilitated the growth of E. rectale, resulting in decreased relative competitive fitness of F. prausnitzii.

Conclusions
H2 is a regulator of fermentation in the human gut microbiome. In particular, high H2 concentration stimulates production of the anti-inflammatory metabolite butyrate. By consuming H2, gut methanogenesis can decrease butyrate production. These shifts in butyrate production may also impact the competitive fitness of butyrate producers in the gut microbiome.

Open access, https://microbiomejournal.biomedcentral.com/articles/10.1186/s40168-023-01565-3

 

Haha it always cheers me up to see a study on the composition of farts.

 

Does this mean my massively methanogenic gut isn't just responsible for a good portion of climate change but also for my failure to recover from ME?

Joking aside, there've been findings of low butyrate in ME, e.g. here (try the tag 'butyrate' for more)

The usual advice is to increase consumption of resistant starch to feed the microbiome. Certain gut bacteria then turn the starch into H2 and other species in turn convert the H2 into butyrate and other goodies.

However, this study seems to suggest that if you're lumbered with a lot of Methanobrevibacter smithii then eating more resistant starch wouldn't work to increase butyrate. Instead the starch would just cause the M. smithii to make ever more methane and also lead to a vicious circle of "decreased relative competitive fitness of F. prausnitzii", which possibly is not a good thing if the findings elsewhere are true that F. prausnitzii (butyrate producers) are already low in ME.

Perplexingly the authors suggest trying hydrogen-rich water to escape this conundrum. Putting aside the fact that a cursory Internet search points to more hype than research behind hydrogen-rich water, why would H2 from hydrogen-rich water get turned into butyrate if H2 generated by the microbiome gets gobbled up by M. smithii to make methane?

[I've only read the abstract and the brief treatment section, plus skimmed the figures. There may be a sensible explanation somewhere else in the paper]

FWIW, I had a couple of breath tests for methane and both were off the scale high. Generally anything over 10 or 12ppm is considered too high and in this study even the most prolific methane producers only managed about 50ppm (Fig. 3). I came in at 150ppm at baseline and a post-challenge peak of 331ppm