干酪乳杆菌基因组改组菌株耐酸性表征

本实验对干酪乳杆菌基因组改组菌株的耐酸性进行了研究，结果表明，冷冻( － 80℃)和临界pH 值(pH3.2)对干酪乳杆菌基因组改组菌株影响不显著，HCl 和游离乳酸对该菌株生长有一定影响，游离乳酸影响更大。在pH5.0 条件下发酵60h，干酪乳杆菌改组菌株获得的菌体干重为6.34g/L，乳酸产量为87.6g/L，比原始菌株耐酸性有显著提高。

Characterization of Acid Tolerance of Genome-shuffled Strain of Lactobacillus casei rhamnosus

The acid tolerance of four strains of genome-shuffled Lactobacillus casei rhamnosus (Lc-F31, Lc-F32, Lc-F33 and Lc-F34) was characterized. The results showed after 3 passagings the viable numbers of these strains of genome-shuffled Lactobacillus casei which were spreaded on YE agar plate at pH 3.8 and 4.0 are similar. The acid tolerance of strain Lc-F34 in MRS liquidmedium at pH 3.2 is more significant compared with the original strain. The strain Lc-F31, Lc-F32, Lc-F33 and Lc- F34 still have good genetic stability after 20 passaging. Free lactic acid has more significant effect on growth of Lc-F34 than HCl in the shake-flask fermentation culture (YE medium) at differernt pHs. The batch fermentation of strain Lc-F34 was carried out in 5-L fermenter containing 3-L YE medium at the fixed pH 5.0 throughout the process. It was found that after 60-h fermentation, the produced lactate concentration of strain Lc-F34 is up to 87.6 g/L with the cell dry weight of 6.34 g/L.