Genomic Differences between Fibrobacter succinogenes S85 and Fibrobacter intestinalis DR7, Identified by Suppression Subtractive Hybridization

Fibrobacter is a highly cellulolytic genus commonly found in the rumen of ruminant animals and cecum of monogastric animals. In this study, suppression subtractive hybridization was used to identify the genes present inFibrobacter succinogenes S85 but absent fromF. intestinalis DR7. A total of 1,082 subtractive clones were picked, plasmids were purified, and inserts were sequenced, and the clones lacking homology toF. intestinalis were confirmed by Southern hybridization. By comparison of the sequences of the clones to one another and to those of theF. succinogenes genome, 802 sequences or 955 putative genes, comprising approximately 409 kb ofF. succinogenes genomic DNA, were identified that lack similarity to those ofF. intestinalis chromosomal DNA. The functional groups of genes, including those involved in cell envelope structure and function, energy metabolism, and transport and binding, had the largest number of genes specific toF. succinogenes . Low-stringency Southern hybridization showed that at least 37 glycoside hydrolases are shared by both species. A cluster of genes responsible for heme, porphyrin, and cobalamin biosynthesis inF. succinogenes S85 was either missing from or not functional inF. intestinalis DR7, which explains the requirement of vitamin B12 for the growth of theF. intestinalis species. Two gene clusters encoding NADH-ubiquinone oxidoreductase subunits probably shared byFibrobacter genera appear to have an important role in energy metabolism.