在乳酸乳球菌中表达外源谷氨酰胺转胺酶显著改善宿主菌好氧生长性能

为改善乳酸乳球菌的生长性能,以轮枝链霉菌染色体DNA为模板,扩增得到编码谷氨酰胺转胺酶成熟酶的基因mtg,将其克隆到质粒pNZ8148中,电转化乳酸乳球菌NZ9000,获得乳酸乳球菌NZ9000(pFL001)(重组菌)。在不控制pH条件下,重组菌的胞外pH显著高于对照菌NZ9000(pNZ8148);前者的最高生物量可达4.13gL,而后者只有0.34gL。在控制pH为6.5±0.1的条件下,重组菌最高生物量为4.73gL,对葡萄糖的菌体最高平均得率为71.1gmol,而相同条件下对照菌最高生物量为2.6gL,对葡萄糖的菌体最高平均得率为27.3gmol。由此表明,重组菌与对照菌相比,好氧生长性能得到显著改善。可能的原因是mtg的活性表达升高了重组菌的胞内pH,原先用于泵出胞内H 所需的部分能量可能因此得到节省,这样相应增加了用于细胞生长的能量。

Influence of expression of transglutaminase on the growth of Lactococcus lactis

To improve the aerobic growth performance of Lactococcus lactis subsp. cremoris NZ9000, the gene mtg encoding the mature microbial transglutaminase was amplified from the chromosomal DNA of Streptoverticillium mobaraense and then cloned into the nisin-inducible expression vector pNZ8148. The resulting plasmid pFL001 was transformed into strain NZ9000 by electroporation. Compared with strain NZ9000 harboring pNZ8148 (the control strain), strain NZ9000 harboring pFL001 (the recombinant strain) had a remarkably improved aerobic growth performance. When grown aerobically under non-pH-controlled conditions, the maximal biomass of the recombinant strain reached 4.13 g/L, which was 11-fold higher than the growth of the control strain (0.34 g/L). When grown aerobically with the pH controlled at 6.5 +/- 0.1, the maximal biomass of the recombinant strain reached 4.73 g/L, which was an 80% increase compared with the growth of the control strain. In addition, the efficiency of biomass synthesis relative to glucose consumption (Y(x/s)) of the recombinant strain, 71.7 g of biomass per mol of glucose, was 1.6-fold higher than that of the control strain. The significantly improved growth performance of the recombinant strain might be attributed to the expression of mtg in the recombinant strain, which might increase intracellular pH and save part of the energy(ATP) that was originally used for pumping the cytoplasmic H+, and as a consequence, the energy used for growth increased accordingly.