Yeast strains for the production of xylitol

A modified non-pathogenic yeast strain, said yeast strain being modified such that metabolism of xylitol is reduced or eliminated and said strain therefore has a genetically reduced ability for using xylose as a sole carbon source as compared to the corresponding unmodified yeast strain, said yeast strain being selected from the group consisting of the species Candida, Hansenula, Kluyveromyces, and Pichia, wherein said modified strain is capable of producing and accumulating xylitol in the growth medium when said modified yeast strain is growing on xylose, and wherein said xylitol that is produced is 35%-68.5% of the xylose that is consumed.

A modified non-pathogenic yeast strain, being modified such that metabolism of xylitol is reduced or eliminated and said strain therefore has a genetically reduced ability for using xylose as a sole carbon source as compared to the corresponding unmodified yeast strain, said modified strain being produced by a method comprising:

• (a) selecting a non-pathogenic yeast strain that can synthesize and metabolize xylitol, said yeast strain being selected from the group consisting of the species Candida, Hansenula, Kluyveromyces, and Pichia and said yeast strain being genetically capable of using xylose as a sole carbon source for growth;
• (b) modifying said yeast strain of part (a), such that metabolism of said xylitol is reduced or eliminated and said yeast strain therefore has a genetically reduced ability for using xylose as a sole carbon source for growth after said modifying;
• (c) selecting the desired modified yeast strain based upon an increased ability of said modified strain to produce xylitol when compared to the strain of part (a), wherein said modified strain is capable of producing and accumulating xylitol in the growth medium when said modified yeast strain is growing on xylose, and wherein said xylitol that is produced is 35%-68.5% of the xylose that is consumed.

Culture medium from the culture of a modified non-pathogenic yeast strain in xylose-containing medium, said yeast strain being modified such that metabolism of xylitol is reduced or eliminated and said strain therefore has a genetically reduced ability for using xylose as a sole carbon source as compared to the corresponding unmodified yeast strain, said yeast strain being selected from the group consisting of the species Candida, Hansenula, Kluyveromyces, and Pichia, wherein said modified strain is capable of producing and accumulating xylitol in said medium when said modified yeast strain is growing on xylose, wherein said medium comprises the xylitol that was secreted into said medium during said culture of said modified yeast strain in said medium, and wherein said xylitol that is produced is 35%-68.5% of the xylose that is consumed.

A modified non-pathogenic yeast strain, said yeast strain being modified such that metabolism of xylitol is reduced or eliminated and said strain therefore has a genetically reduced ability for using xylose as a sole carbon source as compared to the corresponding unmodified yeast strain, wherein said yeast strain is selected from the species Kluyveromyces, and wherein said modified strain is capable of producing and accumulating xylitol in the growth medium when said modified yeast strain is growing on xylose.

Culture medium from the culture of a modified non-pathogenic yeast strain in xylose-containing medium, said yeast strain being modified such that metabolism of xylitol is reduced or eliminated and said strain therefore has a genetically reduced ability for using xylose as a sole carbon source as compared to the corresponding unmodified yeast strain, wherein said yeast strain is selected from the species Kluyveromyces, wherein said modified strain is capable of producing and accumulating xylitol in said medium when said modified yeast strain is growing on xylose, and wherein said medium comprises the xylitol that was secreted into said medium during said culture of said modified yeast strain in said medium.