Lactic acid bacteria with sweetening properties and uses thereof

1. A lactose-positive, galactose-negative, Streptococcus thermophilus strain, wherein:

the lactose-positive, galactose-negative, Streptococcus thermophilus strain has a mutation in the glcK gene;

the strain exhibits glucokinase activity, and the exhibited glucokinase activity is between 200 and 1500 U/g of total protein extract, as assayed by test A; and

the strain exhibits a ratio of beta-galactosidase activity as assayed by test D over glucokinase activity as assayed by test E of at least 4×10 −6 .

2. The lactose-positive, galactose-negative, Streptococcus thermophilus strain according to claim 1 , wherein the glucokinase activity in said strain is between 300 and 1200 U/g of total protein extract, as assayed by test A.

3. The lactose-positive, galactose-negative, Streptococcus thermophilus strain according to claim 1 , wherein the glucokinase activity in said strain is between 10 and 50% of the glucokinase activity of the DGCC7710 strain (deposited at the DSMZ under accession number DSM28255 on Jan. 14, 2014), when both are assayed by test A.

4. The lactose-positive, galactose-negative, Streptococcus thermophilus strain according to claim 1 , wherein:

the strain exhibits a glucokinase maximum forward velocity (Vmax); and

the exhibited glucokinase Vmax is

defined by one or two of these parameters:

the glucokinase Vmax in said strain is between 300 and 1200 U/g, as assayed by test C;

the glucokinase Vmax in said strain is between 10 and 50% of the glucokinase Vmax of the DGCC7710 strain (deposited at the DSMZ under accession number DSM28255 on Jan. 14, 2014), when both are assayed by test C.

5. The lactose-positive, galactose-negative, Streptococcus thermophilus strain according to claim 1 , wherein the mutated glcK gene codes for a glucokinase having an amino acid at its position 275 which is a lysine.

6. The lactose-positive, galactose-negative, Streptococcus thermophilus strain according to claim 1 , which is further mutated in the ccpA gene.

7. The lactose-positive, galactose-negative, Streptococcus thermophilus strain according to claim 6 , wherein the sequence of said mutated ccpA gene is as defined in SEQ ID NO:71.

8. The lactose-positive, galactose-negative, Streptococcus thermophilus strain according to claim 1 , which is further mutated in the manL gene encoding a protein of the mannose-glucose-specific PTS.

9. The lactose-positive, galactose-negative, Streptococcus thermophilus strain according to claim 8 , wherein the mutated manL gene encoding a protein of the mannose-glucose-specific PTS codes for a protein having the sequence of the IIAB Man 305 protein of SEQ ID NO:156.

10. The lactose-positive, galactose-negative, Streptococcus thermophilus strain according to claim 1 , wherein the Streptococcus thermophilus strain is characterized such that a milk fermented with said Streptococcus thermophilus strain in accordance with test B achieves a glucose concentration of at least 8 mM.

11. The lactose-positive, galactose-negative, Streptococcus thermophilus strain according to claim 1 , which is further:

a) mutated in the lacZ gene encoding a beta-galactosidase such that the lactose hydrolysis activity of said beta-galactosidase is increased, or

b) mutated in the ptsH gene encoding HPr.

12. A composition, wherein the composition comprises:

a lactose-positive, galactose-negative, Streptococcus thermophilus strain according to claim 1 ; and

one or more strain(s) selected from the group consisting of a strain of the Lactobacillus genus, a strain of the Lactococcus genus, and a strain of the Bifidobacterium genus.

13. A method for manufacturing a fermented product, wherein the method comprises:

inoculating a substrate with the lactose-positive, galactose-negative, Streptococcus thermophilus strain according to claim 1 , and

fermenting said inoculated substrate.

14. A method according to claim 13 , wherein:

the fermented product comprises a fermented dairy product, and

the substrate comprises a milk substrate.