Response mechanism of overexpress LBA0625 in Lactococcus lactis NZ9000 at freeze-drying process revealed by transcriptomic analysis

Background: Uridine diphosphate glucose pyrophosphorylase (UGPase) is an important cytosolic enzyme in polysaccharide synthesis, which plays an important role in the growth and development of bacteria. However, the regulatory mechanisms of UGPase in freeze-drying resistance are still unclear. Results: In this work, the LBA0625 gene of Lactobacillus acidophilus ATCC4356 which is able to induct of the production of UGPase-0625 were overexpressed in Lactococcus lactis NZ9000. And the physiological changes and transcriptomics of the strains were analyzed to determine possible survival mechanisms. The results showed that LBA0625 overexpression significantly enhanced survival rate from 57.14 % to 79.29% and increased UGPase activity by 48.35%, which indicating that there has a positive relationship between stress tolerance and LBA0625 overexpression. Transcriptome analysis showed that there were total 441 differentially expressed genes (DEGs) after LBA0625 overexpression, including 433 upregulated DEGs and 8 downregulated DEGs. Many of the upregulated DEGs are related to oxidative phosphorylation and exopolysaccharide to facilitate L. lactis NZ9000 biochemical reactions, eventually enhanced freeze-drying resistance. Conclusions: The results of this study suggested the mechanisms involved in overexpression of LBA0625 in L. lactis NZ9000 and would construct in the field of stress-resistant to lactic acid bacteria.