A eukaryotic microbial cell comprising nucleotide sequences the expression of which confers to, or increases in the cell the ability to directly isomerise xylose into xylulose, wherein the nucleotide sequence encodes a polypeptide with xylose isomerase activity, wherein the amino acid sequence of the polypeptide: i) has at least 70% sequence identity with the amino acid sequence of at least one of SEQ ID NO's 1,2 and 35; ii) comprises xylose isomerise signature sequences VXW GREG[YSTA] at positions 187-195 and [LIVM]EPKPX P at positions and 232-239, wherein "X" can be any amino acid and wherein aminoacids in brackets indicate that one of the bracketed amino acids can be present at that position in the signature sequence; iii) comprises the conserved catalytic amino acid residues His-102, Asp-105, and Asp-340; and, iv) comprises one or more amino acid sequence elements selected from the group consisting of: (a) a methionine residue at position 91; (b) the amino acid sequence TGIKLL at positions 134-139; (c) a phenylalanine residue at position 230; (d) the amino acids phenylalanine and lysine at positions 264 and 265, respectively; (e) the amino acid sequence TLAGH at positions 274-278; (f) the amino acid sequence RYASF at positions 387-391; (g) a glycine residue at position 394; and, (h) an alanine residue at position 431; wherein the amino acid positions of ii), iii) and of the sequence elements (a) - (h) refer to positions in the reference amino acid sequence of SEQ ID NO: 3, and wherein the polypeptide does not comprise an amino acid sequence having more than 90% sequence identity with one of SEQ ID NO: 3-7. i) has at least 70% sequence identity with the amino acid sequence of at least one of SEQ ID NO's 1,2 and 35; ii) comprises xylose isomerise signature sequences VXW GREG[YSTA] at positions 187-195 and [LIVM]EPKPX P at positions and 232-239, wherein "X" can be any amino acid and wherein aminoacids in brackets indicate that one of the bracketed amino acids can be present at that position in the signature sequence; iii) comprises the conserved catalytic amino acid residues His-102, Asp-105, and Asp-340; and, iv) comprises one or more amino acid sequence elements selected from the group consisting of: (a) a methionine residue at position 91; (b) the amino acid sequence TGIKLL at positions 134-139; (c) a phenylalanine residue at position 230; (d) the amino acids phenylalanine and lysine at positions 264 and 265, respectively; (e) the amino acid sequence TLAGH at positions 274-278; (f) the amino acid sequence RYASF at positions 387-391; (g) a glycine residue at position 394; and, (h) an alanine residue at position 431; wherein the amino acid positions of ii), iii) and of the sequence elements (a) - (h) refer to positions in the reference amino acid sequence of SEQ ID NO: 3, and wherein the polypeptide does not comprise an amino acid sequence having more than 90% sequence identity with one of SEQ ID NO: 3-7. (a) a methionine residue at position 91; (b) the amino acid sequence TGIKLL at positions 134-139; (c) a phenylalanine residue at position 230; (d) the amino acids phenylalanine and lysine at positions 264 and 265, respectively; (e) the amino acid sequence TLAGH at positions 274-278; (f) the amino acid sequence RYASF at positions 387-391; (g) a glycine residue at position 394; and, (h) an alanine residue at position 431; wherein the amino acid positions of ii), iii) and of the sequence elements (a) - (h) refer to positions in the reference amino acid sequence of SEQ ID NO: 3, and wherein the polypeptide does not comprise an amino acid sequence having more than 90% sequence identity with one of SEQ ID NO: 3-7.