Description

No matter in conventional genetic engineering or synthetic biology, we transfect the chassis bacteria, such as Escherichia coli and Bacillus thuringiensis, with the vector where the target gene is inserted and then get the engineering bacteria. But here comes two problems. The first one, when we use the engineered bacteria outside the laboratory that the horizontal gene transfer (HGT) of the extern gene between the engineered bacteria and other wild species may cause uncertain danger or even biohazard. And the second one, we have difficulty maintaining a high copy number of the vectors (which is also called Plasmid Addiction) between different generations and gaining the genetic stability of the engineered bacteria.And thus one of the targets of the project is to construct a new system of geneguard which will has two functions: 1. preventing the HGT between engineered bacteria and wild type, the HGT will cause the new host to die and insure the biosafety 2. maintaining a high copy number of the vectors in host bacteria, which can improved the stability of the engineered bacteria.

Background

Horizontal gene transfer (HGT): It refers to the transfer of genetic material that happens independently of reproduction. In bacteria, there are several mechanisms for HGT: transformation, transduction, bacterial conjugation, and gene transfer agents. The target of the geneguard is to prevent its happening.

Plasmid Addiction: In almost all microbe systems, the low copy number of the plasmids (or other vectors) may cause the loss of the target gene and the genetic instability of the engineered bacteria. The system of the plasmid addition contains a pair of stable toxin and an unstable antidote. When the plasmid is missing, the unstable antidote is decomposed by the enzyme, and the toxin causes the plasmid-missing bacteria to die.