Effects Of D-Asp And Acetylation Modification On Lactococcus Lactis Peptidoglycan

Peptidoglycan(PG)is responsible for cell wall continuum and integrity,besides,it affects cell growth and division.The synthesis of PG is a dynamic process in which the synthase and hydrolase are coordinated.To explore the relationship between PG regulation and the growth as well as acid resistance of Lactococcus lactis F44,a series of studies on the synthesis and modifications of PG were performed.With the decrease of pH,the crosslinkage of PG reduced,indicating that PG structure altered at different pH.As one major component of PG,D-Asp plays an important role in PG synthesis.When analysis the intracellular Asp content found that D-Asp reduced,while,L-Asp increased with the decrease of pH.The fluctuations of Asp under different pH might affect the PG synthesis.Furthermore,the quantitative proteomics and in vitro enzymatic reaction analysis showed that pH values were tightly regulated the reversible racemization reaction of RacD,which altered the content of D-Asp.The results of enzymatic kinetics experiments and the synthesis of UDP-MurNAc-pentapeptide-D-Asp in vitro further demonstrated that pH affected the racemic catalytic activity to regulate D-Asp content,leading to altering PG structure.PG is usually modified with O-acetylation at MurNAc and N-deacetylation at GlcNAc in Lactococcus lactis F44.In this study,increasing the two modifications improved the integrity of cell wall by decreasing the susceptibility to PG hydrolases.The robust cell wall rendered strains more autolysis resistance and acid tolerance,leading to the increase of nisin yield in fed-batch fermentations.To our knowledge,the study was first to demonstrate that the enzyme activity of RacD was regulated by pH resulting in changing of intracellular D-Asp content,which affected the structure of PG.In addition,the modifications of PG affected the hydrolase activity to improve the integrity of PG,which increase the robustness of cells and nisin production,which could apply the mechanism to practice other valuable industrial products.