Submitted to: PLoS One
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/11/2011
Publication Date: 4/19/2011
Publication URL: naldc.nal.usda.gov/catalog/54924
Citation: Suen, G., Weimer, P.J., Stevenson, D.M., Aylward, F.O., Boyum, J., Deneke, J., Drinkwater, C., Ivanova, N., Mikhailova, N., Chertkov, O., Goodwin, L.A., Currie, C.R., Mead, D., Brumm, P.J. 2011. The complete genome sequence of Fibrobacter succinogenes S85 reveals a cellulolytic and metabolic specialist. PLoS One. 6(4):e18814. Interpretive Summary: We determined the complete DNA sequence of Fibrobacter succinogenes, one of the most active fiber-degrading bacteria in the rumen of the cow. Analysis of the data reveals that this bacterium has a highly unusual complement of genes reponsible its superior fiber-degrading capacity. This genetic information will provide scientists with new combinations of enzymes for use in industrial fermentations of plant biomass to fuels and chemicals.
Technical Abstract: Fibrobacter succinogenes S85 is an important member of the rumen microbial community that converts plant biomass into nutrients usable by its host. This bacterium, which is also one of two known species in its phylum, is an efficient and prolific degrader of cellulose. Specifically, it has a particularly high activity against crystalline cellulose that requires close physical contact with this substrate. However, unlike other known cellulolytic microbes, it does not degrade cellulose using a cellulosome or by producing high extracellular titers of cellulase enzymes. To better understand the biology and cellulolytic degrading machinery of F. succinogenes, we sequenced its genome to completion. A total of 3,085 open reading frames were predicted from its 3.84 Mbp genome, which consists of a single circular chromosome. Analysis of sequences encoding carbohydrate-degrading enzymes revealed an unusually high number of genes (114) that were classified into 46 different families of glycosyl hydrolases, carbohydrate binding modules (CBMs), carbohydrate esterases and polysaccharide lyases. Of the 30 identified cellulases, none contain CBMs in families 1, 2, and 3, which are typically associated with crystalline cellulose degradation. Polysaccharide hydrolysis and utilization assays showed that F. succinogenes was able to both hydrolyze a number of polysaccharides, but only able to metabolize the end products of cellulose. This suggests a model where F. succinogenes utilizes its array of carbohydrate-degrading enzymes to remove polysaccharides and gain access to cellulose. This is reflected in its genome, as F. succinogenes lacks many of the genes necessary to both transport and metabolize non-cellulose polysaccharides. This genome reveals a bacterium that specializes on cellulose as its sole input for carbohydrate metabolism, and provides insight into a novel strategy for cellulose degradation.