Figure 1

Overview of the devices used in this work. The gram-negative bacteria envelope consists in an inner membrane, an outer membrane and a peptidoglycan layer, which is linked to the outer membrane via oligopeptide (OP)-lipoprotein (LPP)-lipid (L) complexes and gives structural strength to the cell wall [25]. The lysis device is composed by a promoterless operon encoding a holin (gene t) and a lysozyme (gene e). When the operon is expressed, holin forms lesions in the inner membrane. Lysozyme can pass through these lesions, reaching and attacking the peptidoglycan layer, thus achieving cell lysis. In addition, the weak promoter BBa_J23116 constitutively expresses gene rI, encoding an antiholin, which inhibits the holin action caused by basal expression of the t-e operon (A). BBa_F2620 HSL-inducible input device is composed by a luxR expression cassette, driven by the tetR promoter, and the lux promoter, which is normally off. Its transcription can be induced by the LuxR transcription factor in presence of exogenously added HSL (B). BBa_K098995 heat-inducible input device is composed by a cIts expression cassette, driven by the BBa_J23114 constitutive promoter, and PR repressible promoter from lambda phage. cIts is a heat-sensitive repressor of PR: when temperature is 30°C the repressor tightly keeps the promoter in the off-state, while a temperature shift to 42°C can induce the transcription of PR (C). Plasmid maps of the promoterless lysis device pLC-T4Lys^-, the HSL-inducible lysis device pLC-T4LysHSL and the heat-inducible lysis device pLC-T4LysHeat, all of them in a low copy number vector (D).