title: Effect of nitrate on methane production and fermentation by slurries of human faecal bacteria.
abstract: Most probable number counts showed that denitrifying species were the numerically predominant NO3- reducing bacteria in the faeces of five methanogenic individuals [about 10(10) bacteria (g dry wt faeces)-1]. In faecal slurries, however, denitrification was a relatively minor route of NO3- dissimilation, since only about 3% of the NO3- was converted to gaseous products, with NO3- being mainly reduced to NO2- and NH4+. When KNO2 was added to the slurries, denitrification became quantitatively more significant with approximately 23% of the NO2- being lost as gaseous products. The addition of KNO3 (10 mM) to slurries containing either starch or casein significantly decreased H2 and CH4 production. The effect of NO3- on methanogenesis was twofold: firstly, H2 accumulation decreased due to diversion of electrons towards NO3-/NO2- reduction, and as a result of H2 being used as an electron donor for NO3- reduction, resulting in the removal of the methanogenic substrate; secondly, there was direct inhibition of methane-producing bacteria by NO3- and NO2-. In starch-containing slurries, acetate: butyrate molar ratios were increased when NO3- was added but this effect was not observed when casein replaced starch. These results show that the ability of NO3-/NO2- to act as an electron sink can significantly influence the major products of the human colonic fermentation.
authors.affiliation: MRC Dunn Clinical Nutrition Centre, Cambridge, UK.
authors.forename: C
authors.initials: C
authors.lastname: Allison
authors.forename: G T
authors.initials: GT
authors.lastname: Macfarlane
mesh_terms: D001419:Bacteria / Q000378:metabolism*; D005232:Fatty Acids, Volatile / Q000096:biosynthesis; D005243:Feces / Q000382:microbiology*; D005285:Fermentation; D006801:Humans; D006859:Hydrogen / Q000378:metabolism; D007422:Intestines / Q000382:microbiology*; D008697:Methane / Q000096:biosynthesis*; D009566:Nitrates / Q000378:metabolism / Q000494:pharmacology*; D009584:Nitrogen / Q000378:metabolism
chemical_list: D005232:Fatty Acids, Volatile; D009566:Nitrates; D006859:Hydrogen; D009584:Nitrogen; D008697:Methane