Reductive acetogenesis in the hindgut and attempts to its induction in therumen - A review

Hindgut fermentation differs from rumen fermentation by a. lower methane pr oduction and the presence of reductive acetogenesis (RA). Moreover, it has been. shown that with ageing RA is replaced completely (rumen) or-partially (hindgut) by methanogenesis (M). In some animals, as well as ill, humans, the importance of M has been related to a genetic predisposition, although from results obtained with rabbit caecal contents, this remains questionabl e. Former results suggested the importance of easily fermentable substrate for RA, more specific recent data suggest a promoting effect for homoacetog enic growth. In a second part of the paper attempts to induce RA ill the rumen are revie wed. Neither addition of free amino acids, mucins, hydrogenotrophic substra tes or bile salts were able to stimulate RA during batch incubations with r umen contents, even after selective inhibition of M. Only the introduction of a reductive strain Peptostreptococcus productus after selective inhibiti on of M by 2-BES or addition of a bacteriocin like inhibitor of M (Lactobac illus plantarun 80), resulted ill induction Of RA in short and long term in vitro incubations with rumen contents. However, in vivo reduction of M in the sheep rumen was riot accompanied by RA and, methane production recovere d after a short period.