[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.