초록
<P><B>Background</B></P><P>Bacteria in the genus <I>Ruminococcus</I> are ubiquitous members of the mammalian gastrointestinal tract. In particular, they are important in ruminants where they digest a wide range of plant cell wall polysaccharides. For example, <I>Ruminococcus albus</I> 7 is a primary cellulose degrader that produces acetate usable by its bovine host. Moreover, it is one of the few organisms that ferments cellulose to form ethanol at mesophilic temperatures <I>in vitro</I>. The mechanism of cellulose degradation by <I>R. albus</I> 7 is not well-defined and is thought to involve pilin-like proteins, unique carbohydrate-binding domains, a glycocalyx, and cellulosomes. Here, we used a combination of comparative genomics, fermentation analyses, and transcriptomics to further clarify the cellulolytic and fermentative potential of <I>R. albus</I> 7.</P><P><B>Results</B></P><P>A comparison of the <I>R. albus</I> 7 genome sequence against the genome sequences of related bacteria that either encode or do not encode cellulosomes revealed that <I>R. albus</I> 7 does not encode for most canonical cellulosomal components. Fermentation analysis of <I>R. albus</I> 7 revealed the ability to produce ethanol and acetate on a wide range of fibrous substrates <I>in vitro</I>. Global transcriptomic analysis of <I>R. albus</I> 7 grown at identical dilution rates on cellulose and cellobiose in a chemostat showed that this bacterium, when growing on cellulose, utilizes a carbohydrate-degrading strategy that involves increased transcription of the rare carbohydrate-binding module (CBM) family 37 domain and the tryptophan biosynthetic operon.</P><P><B>Conclusions</B></P><P>Our data suggest that <I>R. albus</I> 7 does not use canonical cellulosomal components to degrade cellulose, but rather up-regulates the expression of CBM37-containing enzymes and tryptophan biosynthesis. This study contributes to a revised model of carbohydrate degradation by this key member of the rumen ecosystem.</P><P><B>Electronic supplementary material</B></P><P>The online version of this article (doi:10.1186/1471-2164-15-1066) contains supplementary material, which is available to authorized users.</P>