Nto pPIC3.5K by BamH I and Not I sites 1516647 to generate plasmid pPIC3.5K-CalBSP. About 5 mg of plasmid DNA linearized by Sac I was mixed with 80 mL of competent cells, and then it was transformed into Pichia cells by electroporation conducted on Gene Pulser (Bio-rad, Richmond, CA) according to the manufacturer’s instruction for S. cerevisiae to generate stable P. pastoris transformants via homologous recombination at the AOX1 locus between the transforming DNA and regions of homology within the Pichia genome. Positive clones were initially selected on MD medium (1.34 yeast nitrogen base, 461025 biotin, 2 dextrose) plates and then confirmed by colony PCR.Full-length CALB Gene and a-factor Signal Peptide AssemblyThe native and codon-optimized CALB genes were synthesized by a two-step gene synthesis strategy that combined an assembly PCR and an overlap extension PCR (AOE) [25]. In the first step, the oligonucleotides were separately assembled into fragments F1 and F2 by assembly PCR (A-PCR). This amplification was carried out in a 50-mL reaction system DprE1-IN-2 containing 200 mM of dNTPs, 0.1 mM of each oligonucleotide, 1.5 mM MgCl2 and 1 U of Pfu Turbo DNA polymerase (Stratagene, La Jolla, CA). The A-PCR were performed using the following cycle conditions: pre-denaturation at 94uC for 2 min; 30 cycles at a melting temperature of 94uC for 30 sec, an annealing temperature of 52uC for 30 sec and an extension temperature of 72uC for 1 min; Finally, an extra extension step of 72uC for 6 min. The amplicons were used as the templates in another round of PCR using two outer primers. The amplification was performed in a 50-mL reaction system containing 3 mL of A-PCR mixture, 200 mM of dNTPs, 1 mM of each primer, 1.25 mM of MgCl2 and 1 U of Pfu DNA polymerase. PCR products of F1 and F2 fragments were 1:50 diluted and then subjected to the overlap extension PCR (OE-PCR) with the outer primers containing the restriction digestion sites (Table S6 and S7). A 50-mL reaction contained 200 mM of dNTPs, 0.1 mM of each primer and 1 U Pfu DNA polymerase. Briefly, following a pre-denaturation step at 94uC for 2 min, amplification was carried out with 30 cycles at a melting temperature of 94uC for 30 sec, an annealing temperature of 52uC for 30 sec and an extension temperature of 72uC for 1 min. Finally, an extra extension step of 72uC for 5 min was followed. Subsequently, the PCR products were subjected to dA Dimethylenastron tailing and cloned into pMD18-T vector (Takara, Dalian, China).Three positive clones were selected and the insertion fragments were sequenced to confirm the synthesis accuracy. The a-factor signal peptide (279 bp) was synthesized by a single-step A-PCR using the same procedure mentioned above.FermentationA single colony of transformants was selected and inoculated into 50 mL BMGY (1 yeast extract, 2 peptone, 100 mM potassium phosphate buffer with pH 6.0, 1.34 yeast nitrogen base, 461025 biotin, 1 glycerol) medium in flask, and cultured at 28uC in a shaking incubator (250 
rpm) until an OD600 of 3.0 was obtained. The cells then were harvested and transferred into 50 mL BMMY (1 yeast extract, 2 peptone, 100 mM potassium phosphate buffer pH 6.0, 1.34 yeast nitrogen base, 461025 biotin, and 0.5 methanol) medium for the methanolinducible expression for another 4 days. Methanol at a final concentration of 0.5 was added every 24 h to induce the lipase expression, and the lipase activity was checked at intervals. A total of eight types of constructed transformant.Nto pPIC3.5K by BamH I and Not I sites 1516647 to generate plasmid pPIC3.5K-CalBSP. About 5 mg of plasmid DNA linearized by Sac I was mixed with 80 mL of competent cells, and then it was transformed into Pichia cells by electroporation conducted on Gene Pulser (Bio-rad, Richmond, CA) according to the manufacturer’s instruction for S. cerevisiae to generate stable P. pastoris transformants via homologous recombination at the AOX1 locus between the transforming DNA and regions of homology within the Pichia genome. Positive clones were initially selected on MD medium (1.34 yeast nitrogen base, 461025 biotin, 2 dextrose) plates and then confirmed by colony PCR.Full-length CALB Gene and a-factor Signal Peptide AssemblyThe native and codon-optimized CALB genes were synthesized by a two-step gene synthesis strategy that combined an assembly PCR and an overlap extension PCR (AOE) [25]. In the first step, the oligonucleotides were separately assembled into fragments F1 and F2 by assembly PCR 
(A-PCR). This amplification was carried out in a 50-mL reaction system containing 200 mM of dNTPs, 0.1 mM of each oligonucleotide, 1.5 mM MgCl2 and 1 U of Pfu Turbo DNA polymerase (Stratagene, La Jolla, CA). The A-PCR were performed using the following cycle conditions: pre-denaturation at 94uC for 2 min; 30 cycles at a melting temperature of 94uC for 30 sec, an annealing temperature of 52uC for 30 sec and an extension temperature of 72uC for 1 min; Finally, an extra extension step of 72uC for 6 min. The amplicons were used as the templates in another round of PCR using two outer primers. The amplification was performed in a 50-mL reaction system containing 3 mL of A-PCR mixture, 200 mM of dNTPs, 1 mM of each primer, 1.25 mM of MgCl2 and 1 U of Pfu DNA polymerase. PCR products of F1 and F2 fragments were 1:50 diluted and then subjected to the overlap extension PCR (OE-PCR) with the outer primers containing the restriction digestion sites (Table S6 and S7). A 50-mL reaction contained 200 mM of dNTPs, 0.1 mM of each primer and 1 U Pfu DNA polymerase. Briefly, following a pre-denaturation step at 94uC for 2 min, amplification was carried out with 30 cycles at a melting temperature of 94uC for 30 sec, an annealing temperature of 52uC for 30 sec and an extension temperature of 72uC for 1 min. Finally, an extra extension step of 72uC for 5 min was followed. Subsequently, the PCR products were subjected to dA tailing and cloned into pMD18-T vector (Takara, Dalian, China).Three positive clones were selected and the insertion fragments were sequenced to confirm the synthesis accuracy. The a-factor signal peptide (279 bp) was synthesized by a single-step A-PCR using the same procedure mentioned above.FermentationA single colony of transformants was selected and inoculated into 50 mL BMGY (1 yeast extract, 2 peptone, 100 mM potassium phosphate buffer with pH 6.0, 1.34 yeast nitrogen base, 461025 biotin, 1 glycerol) medium in flask, and cultured at 28uC in a shaking incubator (250 rpm) until an OD600 of 3.0 was obtained. The cells then were harvested and transferred into 50 mL BMMY (1 yeast extract, 2 peptone, 100 mM potassium phosphate buffer pH 6.0, 1.34 yeast nitrogen base, 461025 biotin, and 0.5 methanol) medium for the methanolinducible expression for another 4 days. Methanol at a final concentration of 0.5 was added every 24 h to induce the lipase expression, and the lipase activity was checked at intervals. A total of eight types of constructed transformant.