Fibrobacter Succinogenes

''Fibrobacter succinogenes'' is a cellulolytic bacterium species in the genus ''Fibrobacter''. It is present in the rumen of cattle. ''F. succinogenes'' is a gram negative, rod-shaped, obligate anaerobe that is a major contributor to cellulose digestion. Since its discovery in the 1950s, it has been studied for its role in herbivore digestion and cellulose fermentation, which can be utilized in biofuel production.

History

''Fibrobacter succinogenes'' was isolated in 1954 by M.P. Bryant and R.N. Doetsch from bovine rumen at the University of Maryland. They isolated 8 different strains – S23, S61, S85, S111, S121, C2, M13, and M34, all of which belonged to one species – ''Bacteroides succinogenes.'' This species would later be renamed ''Fibrobacter succinogenes.'' S85 would soon become a model strain for research, and it continues to be representative of wild type species.

Genome

The genome of ''F. succinogenes'' is 3.84 Megabasepairs and is predicted to consist of 3085 open reading frames. Many of these genes encode for carbohydrate binding molecules, glycoside hydrolases, and other enzymes. Thirty-one genes are identified as cellulases. The genome also encodes for a number of proteins capable of breaking down sugars, but it lacks the machinery to transport and use all the products except for those derived from cellulose.

Relationship to other bacteria

Phylogenetic studies based RpoC and Gyrase B protein sequences, indicate that ''Fibrobacter succinogenes'' is closely related to the species from the phyla ''Bacteroidetes'' and ''Chlorobi''. ''Fibrobacter succinogenes'' and the species from these two other phyla also branch in the same position based upon conserved signature indels in a number of important proteins. Lastly and most importantly, comparative genomic studies have identified two conserved signature indels (a 5-7 amino acid insert in the RpoC protein and a 13-16 amino acid insertion in serine hydroxymethyltransferase) and one signature protein (PG00081) that are uniquely shared by ''Fibrobacter succinogenes'' and all of the species from ''Bacteroidetes'' and ''Chlorobi'' phyla. All of these results provide compelling evidence that ''Fibrobacter succinogenes'' shared a common ancestor with ''Bacteroidetes'' and ''Chlorobi'' species exclusive of all other bacteria, and these species should be recognized as part of a single “FCB”superphylum.

Metabolism

''F. succinogenes'' utilizes an orthogonal lignocellulose metabolism making it an efficient degrader of cellulose. This unique metabolism differs form other model cellulose degraders like ''Clostridium thermocellum'' and '' Trichoderma reesei'' which use cellulosomes and cellulose secretion systems, respectively. Cell adhesion to their cellulosic substrate is suggested to play a role in efficiency which could explain why ''F. succinogenes'' is such an efficient degrader. ''Fibrobacter succinogenes'' forms characteristic grooves in crystalline cellulose, and is readily detached from its substrate during sample preparation.

''F. succinogenes'' main metabolic machinery is in the cell envelope or periplasmic space. Depending on the type available cellulose, this bacteria will make a different set of proteins and enzymes necessary to degrade each type. It's been found that the degradation enzymes covalently bind to the outer surface of the cell. These enzymes have carbohydrate binding molecules that improve degradation by bringing substrates closer to the active sites of degradation enzymes. ''F. succinogenes'' is capable of breaking down many sugars, but only so that it can gain better access to cellulose, it sole food source. When grown on cellulose, the cell down-regulates other surface sugars and proteins, but and up-regulation of surface lipids. This regulation of other surface elements favors the formation and use of cellulose degrading enzymes. Beta glucans are the substrate of choice in the rumen and the products after digestion include formate, acetate, and succinate.

No amino acids are required for growth, so NH4+ is the sole nitrogen source essential to protein production. PO4---, NH4+, Mg++, Ca++, K+, and Na+ are all essential for growth. ''F. succinogenes'' can use glucose, but grows best on cellulose in the absence of glucose.

Application to biofuels

Biofuel production currently relies on use of feedstocks that could also be used for food. Alternative sources of feedstocks are available, but expensive to use. Cellulose, hemi-cellulose and lignocellulose can be used as alternatives. Using these sources to make biofuel is a 2 step process – 1. saccharification 2. fermentation. Saccharification is a pre-treatment that creates viable sugars for fermentation and is the bottlenecking step due to being expensive and energy intensive. Current feedstocks, such as corn grain, can skip this step since they are high in starches and can be readily fermented.

Since ''Fibrobacter succinogenes'' is an efficient saccharifier of cellulose, it has a potential to be used in the biological degradation of cellulose for biofuel production.

See also

* Fssl, a restriction enzyme found in ''F. succinogenes''
* List of methanogens in digestive tract of ruminants

References

External links

''Fibrobacter_succinogenes''
at NCBI taxonomy browser
Type strain of ''Fibrobacter succinogenes'' at Bac''Dive'' – the Bacterial Diversity Metadatabase

{{Taxonbar, from=Q5446451

Gut flora bacteria
Ruminants
Bacteria described in 1988