Role of dietary sulphate in the regulation of methanogenesis in the human large intestine.

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Abstract
Hydrogen produced during colonic fermentation may be excreted, or removed by H2 consuming bacteria such as methanogenic and sulphate reducing bacteria. In vitro, sulphate reducing bacteria compete with methanogenic bacteria for hydrogen when sulphate is present. In this study the hypothesis that sulphate in the diet could alter CH4 production in vivo has been tested. Six methane excreting volunteers were fed a low sulphate diet (1.6 mmol/d) for 34 days with the addition of 15 mmol sodium sulphate from days 11-20. Breath methane was measured and viable counts and metabolic activities of methanogenic bacteria and sulphate reducing bacteria determined in faeces. Whole gut transit time and daily stool weight were also measured. When sulphate was added to the diet, breath methane excretion decreased in three of the subjects while faecal sulphate reduction rates rose from 7.5 (0.5) to 20.3 (4.3) nmol SO4 reduced/h/g faeces. Sulphate reducing bacteria, which were not detected during the control diet, were found and viable counts of methanogenic bacteria fell from 10(7)-10(9)/g faeces to 10(6)/g. Methanogenic counts and breath CH4 recovered after sulphate addition was stopped. No change was found in the other three subjects. Faecal weights and transit times were not different between study periods. It is concluded that methanogenesis is regulated by dietary sulphate if sulphate reducing bacteria are present. Dietary sulphate may allow growth of sulphate reducing bacteria which inhibit the growth of methanogenic bacteria. This may explain the absence of CH4 in the breath of many people in western populations.