a novel xylose isomerase nucleotide sequence obtained from a bovine rumen fluid metagenomic library and also provides the amino acid sequence encoded by the nucleotide sequence , and a vector and a transformant containing the nucleotide sequence . when the xylose isomerase is expressed , a host cell is endowed with the capability of converting xylose into xylulose , and the xylulose is further metabolized by the host cell . therefore , the host cell can take the xylose as a carbon source for growth . the xylose isomerase from a new source is expressed with high activity in saccharomyces cerevisiae and is a mesophilic enzyme with optimal temperature of 60 ° c .