Fig. 2
Novel technologies reviewed in this paper. a Modified chemically inducible chromosomal evolution (CIChE). The CIChE DNA cassette contains a triclosan marker and target gene(s), flanked by homologous regions. By recA-mediated recombination between the leading homologous region in one DNA strand with the trailing homologous region in another strand, one daughter cell contains two copies of the cassette will be generated. This process can be repeated when recA is present. b Tunable switch. When no inducer was added, the expression of TetR controlled by PBAD promoter was repressed, leading to normal expression of aroK under the regulation of PLtetO1. When l-arabinose exists, PBAD promoter was induced and transcription of PLtetO1 promoter was partially repressed by expressed TetR, resulting to decreased expression of aroK. c When AHL is absent, the transcriptional regulator EsaRI70V binds to the PesaS promoter and transcription of aroK is activated. As the accumulation of AHL generated by AHL synthase EsaI, binding of EsaRI70V is disrupted eventually and the activity of PesaS promoter is inhibited. As the expression level of EsaI can be varied by promoter and/or RBS libraries, the transcription of aroK can be regulated at variable times and cell densities during the fermentation