Fibrobacteres

Fibrobacteres is a phylum of bacteria best known for its members’ capacity to degrade cellulose. The most thoroughly studied species is Fibrobacter succinogenes, isolated from the rumen of ruminant animals. Members of this phylum have been found in the digestive tracts of herbivores and in anaerobic environments such as soils and sediments.

Morphology and physiology: Fibrobacteres are generally Gram-negative, non-spore-forming, obligately anaerobic bacteria. They are typically slender, rod-shaped cells. They possess a repertoire of extracellular cellulases and other carbohydrate-active enzymes that enable efficient breakdown of crystalline cellulose. Fermentation of the resulting sugars yields mainly succinate, with acetate and formate as additional products.

Ecology and role: In the rumen and similar environments, Fibrobacteres contribute significantly to plant fiber digestion, enabling the host to access energy from cellulose. They often participate in synergistic interactions with other cellulolytic and fermentative microbes, contributing to the overall fermentation ecosystem. Their environmental presence reflects niches where plant-derived cellulose is abundant and oxygen is limited.

Taxonomy and genetics: Fibrobacteres constitute a relatively small and evolving phylum within the bacterial tree of life. Taxonomic placement places Fibrobacteres with the class Fibrobacteria, order Fibrobacterales, and family Fibrobacteraceae, including the genus Fibrobacter. Beyond cultivated species, many environmental lineages are known only from 16S rRNA gene sequences. The genome of Fibrobacter succinogenes has been sequenced, revealing numerous cellulolytic enzymes and transport systems relevant to cellulose utilization.