The following picture shows the process of fermentation occurring
in Megasphaera elsdenii. This bacterium:
absorbs glucose released from cellulose by cellulolytic organisms and oxidises
it to pyruvate using NAD as the oxidising agent.
generates ATP by substrate level phosphorylation as occurs in the erythrocyte.
produces propionate by further enzyme action in a sequence that also
regenerates oxidised NAD and so helps ensure the bacteria maintain a high
ratio of NAD to NADH .
Lactate can also be taken up from the growth environment and this further
ensures high production of the oxidizing agent needed for NAD regeneration.
The fermentation pattern of Megasphaera exhibits the following
is used to make glucose in the liver of the host ruminant.
pyruvate is used as an oxidising agent, performing the functions of electron
acceptor to enable glycolysis to coninue and so to allow continued ATP
generation by substrate level phosphorylation.
the two reactions labelled 2 on the previous diagram are linked by the
cycling of acetyl CoA and acetate. This saves on the use of ATP and enables
further dumping of reducing equivalents to generate propionate as the waste
end product organic acid.