Synthetic biology: From the first synthetic cell to see its current situation and future development

Zhang, LiuYan; Chang, SuHua; Wang, Jing

(ii) Minimal genome. Newly designed/re-designed bio-modules need to be loaded into a proper vector (chassis) to express and function. An ideal chassis is supposed to have a simplified but robust genome, i.e. "minimal genome", to reduce background noise and complexity, and to improve predictability and controllability of the new system. A minimal genome is a collection of essential gene contents which has the ability to sustain normal cellular life under ideal conditions, that is, in the presence of a full complement of essential nutrients and in the absence of environmental stress [8] . So the key question for minimal genome research is to identify the essentiality of genes. Usually there are two strategies [9] to get a minimal genome: the top-down strategy which aims to delete the non-essential segments from existing natural genomes, and the bottom-up strategy which obtains a minimal genome by de novo synthesis and assembly of essential genes. It should be noted that here the "minimal genome" is not an absolute concept but a relative concept in comparison to natural genomes. Usually the living condition and research objective help define the boundary of a minimal genome [10] . It is hard to get a universal chassis suitable for different research or application purposes. With more microbial genomes being sequenced, the rich database of genome sequences, as well as the rapid development of DNA sequencing and synthesis techniques, provide strong foundations for the construction of minimal genomes.