Abstract: Genetically modified gram-negative bacteria, in particular E. coli, that are oversensitive to lysis. These bacteria are therefore useful to improve the yield of nucleic acid extraction, preferably extra-genomic nucleic acid extraction (e.g. plasmid), and/or the yield of a polypeptide, preferably encoded by an extra-genomic nucleic acid. In practice, the strains of E. coli are engineered with a combination of at least 2 mutated genes altering the envelop integrity. More particularly, at least one mutated gene is ompA and at least one mutated gene is a gene involved in Lpp functionality, such as, e.g., the lpp gene, the ybiS gene, the ycfS gene and the erfK gene. These combinations also include mutations in genes that are homologue to the ompA gene, and/or the lpp gene.