**4.1 The DY380** *E. coli* **strain**

The DY380 *E. coli* strain offers a highly efficient homologous recombination system for chromosome engineering by enabling efficient recombination of homologous sequences as short as 40-bp (Yu et al., 2000). A defective lambda prophage supplies the function that protects and recombines linear DNA. In addition, the system is strictly regulated by a temperature-sensitive lambda repressor. This allows homologous recombination between two sequences to be transiently induced by activating the prophage through incubation at 42°C for 15 minutes.
