2.1. Bacterial Strains and Plasmids

E. coli JM109 (Promega) was used as host for cloning and expression of genes in a pHsh vector constructed by this laboratory (Shine E Biotech, Nanjing, China). E. coli cells were routinely grown aerobically in Luria–Bertani (LB) medium at 30 °C, and 100 μg/mL ampicillin was added to the LB medium for selective cultures. The plasmids pHsh-1655, pHsh-1756, and pHsh-0257 were constructed previously [27].