Abstract:
Microbial communities from cow rumen are known for their ability to degrade diverse plant polymers at high rates. In this
work, we identified 15 hydrolases through an activity-centred metagenome analysis of a fibre-adherent microbial
community from dairy cow rumen. Among them, 7 glycosyl hydrolases (GHs) and 1 feruloyl esterase were successfully
cloned, expressed, purified and characterised. The most striking result was a protein of GH family 43 (GHF43), hereinafter
designated as R_09-02, which had characteristics very distinct from the other proteins in this family with mono-functional bxylosidase,
a-xylanase, a-L-arabinase and a-L-arabinofuranosidase activities. R_09-02 is the first multifunctional enzyme to
exhibit b-1,4 xylosidase, a-1,5 arabinofur(pyr)anosidase, b-1,4 lactase, a-1,6 raffinase, a-1,6 stachyase, b-galactosidase and a-
1,4 glucosidase activities. The R_09-02 protein appears to originate from the chromosome of a member of Clostridia, a class
of phylum Firmicutes, members of which are highly abundant in ruminal environment. The evolution of R_09-02 is
suggested to be driven from the xylose- and arabinose-specific activities, typical for GHF43 members, toward a broader
specificity to the glucose- and galactose-containing components of lignocellulose. The apparent capability of enzymes from
the GHF43 family to utilise xylose-, arabinose-, glucose- and galactose-containing oligosaccharides has thus far been
neglected by, or could not be predicted from, genome and metagenome sequencing data analyses. Taking into account the
abundance of GHF43-encoding gene sequences in the rumen (up to 7% of all GH-genes) and the multifunctional phenotype
herein described, our findings suggest that the ecological role of this GH family in the digestion of ligno-cellulosic matter
should be significantly reconsidered.
