Gram-positive bacteria of the species

1 . A gram-positive bacterium of the species Streptococcus thermophilus or Lactococcus lactis , wherein the gram-positive bacterium has been modified to decrease or abolish expression or activity of a surface protease by mutagenesis and to have increased production of a heterologous protein of interest as compared to an otherwise identical gram-positive bacterium that has not been modified to decrease or abolish expression or activity of the surface protease,

wherein the surface protease comprises an amino acid sequence having at least 80% sequence identity with the sequence of SEQ ID NO: 1, and

wherein SEQ ID NO: 1 is defined as follows:

I-A-G-T-G-T-I-E-X1-D-G-X2-X3-G-X4-I-G-G-X5-X6-X7-K

wherein

X1 is histidine (H) or lysine (K);

X2 is serine(S), alanine (A) or threonine (T);

X3 is isoleucine (I), leucine (L) or valine (V);

X4 is aspartic acid (D) or glutamine (Q);

X5 is alanine (A) or valine (V);

X6 is aspartic acid (D) or tyrosine (Y); and

X7 is lysine (K) or leucine (L).

2 . The bacterium of to claim 1 , wherein the gram-positive bacterium is of the species Streptococcus thermophilus and, wherein the surface protease comprises an amino acid sequence having at least 70% sequence identity with the sequence of SEQ ID NO: 2 when the sequences are aligned along their entire length.

3 . The bacterium of claim 2 , wherein the gram-positive bacterium has been further modified to decrease or abolish expression and/or activity of at least one other surface protease by mutagenesis as compared to an otherwise identical gram-positive bacterium that has not been modified to decrease or abolish expression or activity of the at least one other surface protease, wherein the at least one other surface protease has:

(i) an amino acid sequence having at least 70% sequence identity with the sequence of SEQ ID NO: 8; or

(ii) an amino acid sequence having at least 70% sequence identity with the sequence of SEQ ID NO: 9.

4 . The bacterium of claim 2 , wherein the gram-positive bacterium has been further modified to decrease or abolish expression and/or activity of at least first and second other surface proteases by mutagenesis as compared to an otherwise identical gram-positive bacterium that has not been modified to decrease or abolish expression or activity of the at least first and second other surface proteases,

(i) wherein the first other surface protease has an amino acid sequence having at least 70% sequence identity with the sequence of SEQ ID NO: 8; and

(ii) wherein the second other surface protease has an amino acid sequence having at least 70% sequence identity with the sequence of SEQ ID NO: 9.

5 . The bacterium of claim 1 , wherein the gram-positive bacterium is of the species Lactococcus lactis and, wherein the surface protease comprises an amino acid sequence having at least 70% sequence identity with the sequence of SEQ ID NO: 3 or with the sequence of SEQ ID NO: 4 when the sequences are aligned over their entire length.

6 . The bacterium of claim 5 , wherein the gram-positive bacterium has been further modified to decrease or abolish expression and/or activity of at least one other surface protease by mutagenesis as compared to an otherwise identical gram-positive bacterium that has not been modified to decrease or abolish expression or activity of the at least one other surface protease, wherein the at least one other surface protease has:

(i) an amino acid sequence having at least 70% sequence identity with the sequence of SEQ ID NO: 10; or

(ii) an amino acid sequence having at least 70% sequence identity with the sequence of SEQ ID NO: 11.

7 . The bacterium of claim 5 , wherein the gram-positive bacterium has been further modified by mutagenesis to decrease or abolish expression and/or activity of at least first and second other surface proteases as compared to an otherwise identical gram-positive bacterium that has not been modified to decrease or abolish expression or activity of the at least first and second other surface proteases,

(i) wherein the first other surface protease has an amino acid sequence having at least 70% sequence identity with the sequence of SEQ ID NO: 10; and

(ii) wherein the second other surface protease has an amino acid sequence having at least 70% sequence identity with the sequence of SEQ ID NO: 11.

8 . The bacterium of claim 1 , wherein the gram-positive bacterium comprises an expression vector containing a DNA fragment encoding the heterologous protein of interest or a DNA fragment encoding the heterologous protein of interest inserted in its chromosome.

9 . A method for producing a heterologous protein of interest, the method comprising culturing the gram-positive bacterium of claim 8 to produce the heterologous protein of interest.