A new strain of Lactococcus lactis producing D-tagatose was isolated and identified.Its L-arabinose isomerase coding gene was cloned and expressed in Escherichia coli BL21(DE3).The optimal temperature and pH of the pu...A new strain of Lactococcus lactis producing D-tagatose was isolated and identified.Its L-arabinose isomerase coding gene was cloned and expressed in Escherichia coli BL21(DE3).The optimal temperature and pH of the purified enzyme were 50◦C and 8.0.To produce D-tagatose from lactose,β-D-galactosidases from Lc.Lactis,Lactiplantibacillus plantarum,and Streptococcus thermophilus were further incorporated into E.coli by two strategies.Theseβ-D-galactosidases were fused to L-arabinose isomerase coupled with a peptide linker(GGGGS)3.Meanwhile,they were co-expressed with L-arabinose isomerase using pETDuet-1 vector.Among these recombinant strains,the cell co-expressing L-arabinose isomerase and S.thermophilusβ-D-galactosidase showed maximal activity.SDS-PAGE results confirmed that exogenous enzymes had the maximum soluble expression level in this strain.At the optimal condition,the conversion rate of D-tagatose from 300 g/L lactose achieved to 42.4%,and the volumetric productivity reached 4.28 g/L/h at 15 h.This research established a highly efficient biotransformation system to produce D-tagatose from lactose.展开更多
基金supported by Natural Science Foundation of Shandong Province(ZR2021QC160)Key Research and Development Program of Shandong Province(2020CXGC010602)Science and Technology Support Plan for Young People in Colleges and Universities of Shandong Province(2020KJE005).
文摘A new strain of Lactococcus lactis producing D-tagatose was isolated and identified.Its L-arabinose isomerase coding gene was cloned and expressed in Escherichia coli BL21(DE3).The optimal temperature and pH of the purified enzyme were 50◦C and 8.0.To produce D-tagatose from lactose,β-D-galactosidases from Lc.Lactis,Lactiplantibacillus plantarum,and Streptococcus thermophilus were further incorporated into E.coli by two strategies.Theseβ-D-galactosidases were fused to L-arabinose isomerase coupled with a peptide linker(GGGGS)3.Meanwhile,they were co-expressed with L-arabinose isomerase using pETDuet-1 vector.Among these recombinant strains,the cell co-expressing L-arabinose isomerase and S.thermophilusβ-D-galactosidase showed maximal activity.SDS-PAGE results confirmed that exogenous enzymes had the maximum soluble expression level in this strain.At the optimal condition,the conversion rate of D-tagatose from 300 g/L lactose achieved to 42.4%,and the volumetric productivity reached 4.28 g/L/h at 15 h.This research established a highly efficient biotransformation system to produce D-tagatose from lactose.