Effect of Phospholipase A₁ Auxiliary Protein PlaS of Serratia marcescens on the Cell Membrane of Host Bacteria and Its Subcellular Localization

To prove that the phospholipase A₁ accessory protein PlaS of Serratia marcescens has a significantly disruptive effect on the cell membrane of Escherichia coli BL21 (DE3) during heterologous expression, changes in cell membrane properties were explored, their effect on cell membrane fatty acids was identified by gas chromatography-mass spectrometry (GC-MS), and subcellular localization was observed by laser confocal microscopy. The results showed that after the heterologous expression of PlaS, the inner and outer membrane permeability of the host bacterium was significantly increased, and cell membrane fluidity and surface hydrophobicity were severely decreased, indicating loss of cell membrane functions; the saturation degree of fatty acids was decreased, that is, the relative contents of straight-chain saturated fatty acids and trans-monounsaturated fatty acids in fatty acids were reduced, and the relative contents of cis-monounsaturated fatty acids were increased. Moreover, membrane rigidity was enhanced, membrane fluidity was reduced, and the cell membrane components and structure were abnormal, so that the cells could be susceptible to death. Laser confocal microscopy showed that significant fluorescence was observed in the host cell membrane. In summary, the heterologous expression of the membrane protein PlaS in E. coli disrupts the structure and function of the host cell membrane and exhibits growth inhibition, which will provide support for further research on the mechanism of PlaS inhibition and its functional development.