Fibrobacter succinogenes 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 only two cultivated 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 of F. succinogenes, we sequenced the genome of the type strain S85 to completion. A total of 3,085 open reading frames were predicted from its 3.84 Mbp genome. Analysis of sequences predicted to encode for carbohydrate-degrading enzymes revealed an unusually high number of genes that were classified into 49 different families of glycoside hydrolases, carbohydrate binding modules (CBMs), carbohydrate esterases, and polysaccharide lyases. Of the 31 identified cellulases, none contain CBMs in families 1, 2, and 3, typically associated with crystalline cellulose degradation. Polysaccharide hydrolysis and utilization assays showed that F. succinogenes was able to hydrolyze a number of polysaccharides, but could only utilize the hydrolytic products of cellulose. This suggests that F. succinogenes uses its array of hemicellulose-degrading enzymes to remove hemicelluloses to gain access to cellulose. This is reflected in its genome, as F. succinogenes lacks many of the genes necessary to transport and metabolize the hydrolytic products of non-cellulose polysaccharides. The F. succinogenes genome reveals a bacterium that specializes in cellulose as its sole energy source, and provides insight into a novel strategy for cellulose degradation.

Ruminococcus albus 7 is a highly cellulolytic ruminal bacterium that is a member of the phylum Firmicutes . Here, we describe the complete genome of this microbe. This genome will be useful for rumen microbiology and cellulosome biology and in biofuel production, as one of its major fermentation products is ethanol.

Fibrobacter succinogenes is a cellulolytic bacterium that degrades plant cell wall biomass in ruminant animals and is among the most rapidly fibrolytic of all mesophilic bacteria. The complete genome sequence of Fisuc was completed by the DOE Joint Genome Institute in late 2009. Using new expression tools developed at Lucigen and C5-6 Technologies and a multi-substrate screen, 5,760 random shotgun expression clones were screened for biomass-degrading enzymes, representing 2× genome expression coverage. From the screen, 169 positive hits were recorded and 33 were unambiguously identified by sequence analysis of the inserts as belonging to CAZy family genes. Eliminating duplicates, 24 unique CAZy genes were found by functional screening. Several previously uncharacterized enzymes were discovered using this approach and a number of potentially mis-annotated enzymes were functionally characterized. To complement this approach, a high-throughput system was developed to clone and express all the annotated glycosyl hydrolases and carbohydrate esterases in the genome. Using this method, six previously described and five novel CAZy enzymes were cloned, expressed, and purified in milligram quantities.