One of the cellulase producers that is vital to propionate production but does not make propionate itself is Fibrobacter succinogenes.

It breaks down cellulose to glucose and uses that glucose as a growth substrate to generate ATP by substrate level phosphorylation.

In addition it makes acetate and succinate as end products of its own fermentation pathways. Acetate is used by the host ruminant and succinate is a growth substrate for some propionate producers.

The production of acetate and succinate together occurs in a coupled sequence of redox reactions where succinate production is geared to acetate production enabling a higher yield of ATP to be generated per mol of glucose used.

The fermentation process of Fibrobacter succinogenes is shown by the following pictures:

1. An overview of the production of acetate and succinate via two separate but linked reaction sequences. This involves the oxidation of pyruvate coupled to the reduction of fumarate.

2. Details of acetate production associated with ATP generation.

3. Details of succinate production with NAD regeneration and ATP production.


 
 

The succinate produced is released into the growth medium and is a growth substrate for bacterial species like Selenomonas and Veillonella which use it to make propionate.

The acetate produced by Fibrobacter is used by the host ruminant.

Acetate is always the most abundant Volatile Fatty Acid produced in the reticulo-rumen of all species on all diets at all times in normal health.