For easy expression in E. coli, optimized gene of CALB and TLL
were synthesized. They were inserted into the corresponding
restriction enzyme sites of plasmid pRSFDuet to give recombinant
expression plasmid pRSFDuet-Calb and pRSFDuet-Tll, respectively.
CALB gene was also inserted into the corresponding restriction enzyme
sites of plasmid pRSFDuet-Tll to give recombinant co-expression
plasmid pRSFDuet-Calb-Tll. After transformation into E. coli BL
21 (DE3) and selection with kanamycin, E. coli (Calb/Tll) coexpressing
CALB and TLL with one plasmid (pRSFDuet-Calb-Tll)
and E. coli (Calb-Tll) co-expressing the two enzymes with two plasmids
(PETDuet-Calb and pRSFDuet-Tll) were obtained. In addition,
E. coli (Calb) expressing CALB and E. coli (Tll) expressing TLL were
also engineered for comparison.
All E. coli recombinant strains grew well in LB medium, and the
lipases were expressed by induction with 0.2 mM IPTG. After 4 h
induction, the cells were harvested at an OD600nm of 3.0 (Fig. S2).
The soluble cell-free extracts of these strains were analyzed by
SDS–PAGE. As shown in Fig. 2, both CALB and TLL were clearly
expressed in E. coli (Calb/Tll) with one plasmid as well as E. coli
(Calb-Tll) with two plasmids.