The Novel Property Of Heptapeptide Of Microcin C7 In Affecting The Cell Growth Of Escherichia Coli

There is an urgent need for new solutions and new antibiotics to overcome antibiotic resistance which has been becoming a widespread and serious menace to human and animal health.Microcin C7(McC),widely distributed in enterobacteria,is a promising and Trojan horse antibiotic against antibiotic resistance.Previous studies have demonstrated that the heptapeptide of McC(MR)has the capacity of inhibiting protein synthesis,but lacks the capacity for inhibiting microbial cell growth.Additionally,MR can protect Microcin C7 from degradation.However,in this study,we fully investigated the novel proverty of MR and its analogues on microbial cell growth in terms of cell viability,enzyme activity and cell membrane integrity.First,MR and its analogues of MR,f-MR,a-MR,MK,f-MK and a-MK were synthesized using a solid-phase peptide synthesis method.The synthesized peptides were purified by a semi-preparative high performance liquid chromatography and then identified by a mass spectrometry.The effects of MR,f-MR,a-MR and a-MK on the growth of Escherichia coli were investigated.The experimental results show that MR,f-MR,a-MR and a-MK can kill Escherichia coli at 5.34 mM,8 mM,6.47 mM and 6.72 mM,respectively.MR and a-MR kill Escherichia coli completely within 10 min at 2.67 mM and 4 mM,respectively.Even at the low concentration,the number of Escherichia coli is significantly reduced to about 36.77%.The presence of 0.1%BSA in the culture medium has not effect on the inhibitory activity of MR,f-MR,MR,MK,f-MK,a-MK.However,in the rich media MR,f-MR,a-MR,MK,f-MK and a-MK have no effect on the growth of Escherichia coli.Furthermore,the(3-galactosidase,6-phosphogluconate dehydrogenase,and respiratory chain dehydrogenase of Escherichia coli treated by MR,f-MR and a-MR at different concentrations were detected by determining the intracellular enzyme and constituent enzyme activity.The activitives of β-galactosidase,6-phosphate dehydrogenase and respiratory chain dehydrogenase are completely inhibited by MR,f-MR and a-MR at 5.34mM,8mM and 6.47mM,respectively.In contrast,the activities of all enzymes are increased with decreasing concentration of the peptides.Finally,the effects of MR,f-MR and a-MR on cell membrane integrity of Escherichia coli were further evaluated by β-galactosidase activity assay and scanning tunneling electron microscopy.Both P-galactosidase activity assay and electron microscopy assay indicate that the cell membrane of Escherichia coli remains integrity even in the presence of MR,f-MR and a-MR at the lethal concentration.