Find in Library

<i>Lactobacillus acidophilus</i> NCFM is widely used in the fermentation industry; using it as a freeze-dried powder can greatly reduce the costs associated with packaging and transportation, and even prolong the storage period. Previously published research has reported that the expression of <i>galU</i> (EC: 2.7.7.9) is significantly increased as a result of freezing and drying. Herein, we aimed to explore how <i>galU</i> plays an important role in improving the resistance of <i>Lactobacillus acidophilus</i> NCFM to freeze-drying. For this study, <i>galU</i> was first knocked out and then re-expressed in <i>L. acidophilus</i> NCFM to functionally characterize its role in the pertinent metabolic pathways. The knockout strain Δ<i>galU</i> showed lactose/galactose deficiency and displayed irregular cell morphology, shortened cell length, thin and rough capsules, and abnormal cell division, and the progeny could not be separated. In the re-expression strain p<i>galU</i>, these inhibited pathways were restored; moreover, the p<i>galU</i> cells showed a strengthened cell wall and capsule, which enhanced their resistance to adverse environments. The p<i>galU</i> cells showed GalU activity that was 229% higher than that shown by the wild-type strain, and the freeze-drying survival rate was 84%, this being 4.7 times higher than that of the wild-type strain. To summarize, expression of the <i>galU</i> gene can significantly enhance gene expression in galactose metabolic pathway and make the strain form a stronger cell wall and cell capsule and enhance the resistance of the bacteria to an adverse external environment, to improve the freeze-drying survival rate of <i>L. acidophilus</i> NCFM.