Lactic acid bacteria

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

at least one mutated gene encoding a protein of the mannose-glucose-specific phosphotransferase system (mannose-glucose-specific PTS), the glucose import activity of which is decreased or abolished, and

at least one mutated gene selected from the group consisting of:

a) a mutation in a glucokinase (glcK) gene such that the glucokinase activity of said strain is reduced but not null,

wherein the protein sequence of said glucokinase is a glcK variant sequence having at least 90% identity with SEQ ID NO:25 or SEQ ID NO:46,

wherein the amino acid of the glucokinase corresponding to position 275 of SEQ ID NO: 25 is not a glutamic acid, and/or the amino acid of the glucokinase corresponding to position 144 of SEQ ID NO:46 is not a glycine;

b) a mutation in a catabolite control protein A (ccpA) gene, wherein the sequence of said mutated ccpA gene is selected from the group consisting of:

i) a sequence comprising SEQ ID NO:71, and

ii) a ccpA variant sequence having at least 90% identity with SEQ ID NO:71; and

c) a combination thereof.

2. The lactose-positive, galactose-negative, Streptococcus thermophilus strain according to claim 1 , carrying a mutation in at least one gene encoding a protein of the mannose-glucose-specific PTS, the glucose import activity of which is decreased or abolished, and carrying a mutation in a glcK gene such that the glucokinase activity of said strain is reduced but not null,

wherein the protein sequence of said glucokinase is a glcK variant sequence having at least 90% identity with SEQ ID NO:25 or SEQ ID NO:46,

wherein the amino acid of the glucokinase corresponding to position 275 of SEQ ID NO: 25 is not a glutamic acid, and/or the amino acid of the glucokinase corresponding to position 144 of SEQ ID NO:46 is not a glycine.

3. The lactose-positive, galactose-negative, Streptococcus thermophilus strain according to claim 2 , wherein the protein sequence of said glucokinase is a glcK variant sequence having at least 90% similarity or identity with SEQ ID NO:25, wherein the amino acid of the glucokinase corresponding to position 275 of SEQ ID NO:25 is not a glutamic acid.

4. The lactose-positive, galactose-negative, Streptococcus thermophilus strain according to claim 2 , wherein the protein sequence of said glucokinase is a glcK variant sequence having at least 90% similarity or identity with SEQ ID NO:46, wherein the amino acid of said glucokinase corresponding to position 144 of SEQ ID NO:46 is not a glycine.

5. The lactose-positive, galactose-negative, Streptococcus thermophilus strain according to claim 2 , further carrying a mutation in the ccpA gene.

6. The lactose-positive, galactose-negative, Streptococcus thermophilus strain according to claim 1 , carrying a mutation in at least one gene encoding a protein of the mannose-glucose-specific PTS, the glucose import activity of which is decreased or abolished, and carrying a mutation in a catabolite control protein A (ccpA) gene,

wherein the sequence of said mutated ccpA gene is selected from the group consisting of:

i) a sequence comprising SEQ ID NO:71, and

ii) a ccpA variant sequence having at least 90% identity with SEQ ID NO:71.

7. The lactose-positive, galactose-negative, Streptococcus thermophilus strain according to claim 6 , wherein the ccpA gene comprises a mutation selected from the group consisting of:

a non-sense mutation located between the nucleotide 1 and the nucleotide 270 of the coding sequence of the ccpA gene, and

a mutation located in the first quarter of the coding sequence of the ccpA gene leading to a frameshift of the open reading frame of the ccpA gene.

8. The lactose-positive, galactose-negative, Streptococcus thermophilus strain according to claim 1 , wherein the at least one gene encoding a protein of the mannose-glucose-specific PTS is selected from the group consisting of the manL gene, the manM gene and the manN gene.

9. The lactose-positive, galactose-negative, Streptococcus thermophilus strain according to claim 1 , wherein the mutated gene encoding a protein of the recite—mannose-glucose-specific PTS, the glucose import activity of which is decreased or abolished, is selected from the group consisting of:

a) a Streptococcus thermophilus IIAB Man protein truncated in position 305 (IIAB Man 305 );

b) a Streptococcus thermophilus IIC Man protein truncated in position 208 (IIC Man 208 ); and

c) a Streptococcus thermophilus IID Man protein truncated in position 28 (IID Man 28 ).

10. The lactose-positive, galactose-negative, Streptococcus thermophilus strain according to claim 9 , wherein the protein sequence of said IIAB Man 305 protein is selected from the group consisting of:

a) a sequence as defined in SEQ ID NO:112; and

b) a IIAB Man variant sequence having at least 90% sequence similarity or identity with SEQ ID NO:112; wherein the protein sequence of said IIC Man 208 is selected from the group consisting of:

a) a sequence as defined in SEQ ID NO:158; and

b) a IIC Man variant sequence having at least 90% sequence similarity or identity with SEQ ID NO: 158;

wherein the protein sequence of said IID Man 28 protein is selected from the group consisting of:

a) a sequence as defined in SEQ ID NO:207; and

b) a IID Man variant sequence having at least 90% sequence similarity or identity with SEQ ID NO: 207.

11. A composition comprising at least one lactose-positive, galactose-negative, Streptococcus thermophilus strain according to claim 1 in combination with one or more strain(s) selected from the group consisting of a strain of the Lactobacillus genus, a strain of the Lactococcus genus, or a strain of the Bifidobacterium genus.

12. A method for manufacturing a fermented dairy product comprising:

inoculating a milk substrate with the lactose-positive, galactose-negative, Streptococcus thermophilus strain according to claim 1 or a composition comprising at least one lactose-positive, galactose-negative, Streptococcus thermophilus strain according to claim 1 ; and

fermenting said inoculated milk, to obtain a fermented dairy product.

13. A fermented dairy product comprising at least one lactose-positive, galactose-negative, Streptococcus thermophilus strain according to claim 1 .

14. The composition of claim 11 , wherein the strain of the Lactobacillus genus is Lactobacillus delbrueckii subsp bulgaricus strain.

15. The composition of claim 11 , wherein the strain of the Lactococcus genus is a Lactococcus lactis strain.