Bacterial host strain

An isolated recombinant gram-negative bacterial cell comprising:

• i) one or more of the following mutated protease genes:
• a) a mutated Tsp gene, wherein the mutated Tsp gene encodes a Tsp protein having reduced protease activity or is a knockout mutated Tsp gene;
• b) a mutated ptr gene, wherein the mutated ptr gene encodes a Protease III protein having reduced protease activity or is a knockout mutated ptr gene;
• and
• c) a mutated DegP gene encoding a DegP protein having chaperone activity and reduced protease activity;
• wherein the cell is isogenic to a wild-type bacterial cell except for the mutated Tsp gene and/or mutated ptr gene and/or mutated DegP gene and optionally a polynucleotide sequence encoding a protein of interest;
• or
• ii) one or more of the following mutated protease genes:
• a) a knockout mutated Tsp gene comprising a mutation to the gene start codon and/or one or more stop codons positioned downstream of the gene start codon and upstream of the gene stop codon;
• and/or
• b) a knockout mutated ptr gene comprising a mutation to the gene start codon and/or one or more stop codons positioned downstream of the gene start codon and upstream of the gene stop codon;
• and
• c) optionally a mutated DegP gene encoding a DegP protein having chaperone activity and reduced protease activity.