| Glyceroglycolipids had antibacterial,antitumor,antiviral and other biological activity,which were widely used in food,cosmetics and biomedical industry.Although glyceroglycolipids have strong antibacterial activity,few or no literatures reported the inhibiting mechanism of glyceroglycolipids against bacterial now.The aim of study is to synthesize and separate monolauroyl-galactosylglycerol and investigate antimicrobial activity and mechanism of monolauroyl-galactosylglycerol.The main contents are described as follows:1.Study on the antibacterial and stability of monolauroyl-galactosylglycerol.Though using hole method for testing antibacterial of monolauroyl-galactosylglycerol against five bacterial and three fungi from food.The minimum inhibitory concentration(MIC)were determined by doubling dilution method.Plate dilution method and microbial turbidimetric method were studied the antimicrobial stability and laging of monolauroyl-galactosylglycerol.The results show that monolauroyl-galactosylglycerol could inhibit Escherichia coli,Pseudomouas fluorescens,Bacillus subtilis,Bacillus cereus and StapHylococcus aureus,but the material had little or no effect on the growth of Aspergillus niger,Aspergillus flavus and Saccharomyces cerevisiae.The MIC of monolauroyl-galactosylglycerol against Pseudomouas fluorescens was 0.078 mg/mL,the MIC of the material against other texted bacterial and fungi were 0.156 mg/mL.Under the condition of pH5-8,the antibacterial activity of monolauroyl-galactosylglycerol was stable.Temperature and ultra violet irradiation showed little effect on the antimicrobial activity of monolauroyl-galactosylglycerol.With salt concentration increasing,the antimicrobial activity of monolauroyl-galactosylglycerol decreased significantly.These results may be related to the srructure of monolauroyl-galactosylglycerol.Monolauroyl-galactosylglycerol is a kind of nonionic surface agents,the main features of biological surfactant are acidproof,heat resisting,Ionic stength resistance,low toxicity and biodegradability.The antimicrobial laging of monolauroyl-galactosylglycerol on Bacillus cereus was better than that of Escherichia coli.The antibacterial rate of monolauroyl-galactosylglycerol for Bacillus cereus almost remain at 100%within 36 h.However,with the time,the antibacterial rate of Escherichia coli and Bacillus cereus appeared a decreasing trend.The results may be associated with the enzyme system of Escherichia coli and Bacillus cereus effect on the degradation of monolauroyl-galactosylglycerol.2.Effects of monolauroyl-galactosylglycerol on cell membrane of bacteria.Escherichia coli and Bacillus cereus were used as indicator bacteria to investigate the antimicrobial mechanism of monolauroyl-galactosylglycerol.Though using the growth curves for testing the effect of monolauroyl-galactosylglycerol on the growth of bacteria.Spectrophotometry was used to measure the effect of monolauroyl-galactosylglycerol on the permeability of the cell wall,the leakage of intracellular macromolecules.Scanning electron microscope and transmission electron microscope were used to observe the bacterial ultrastructure which were affected by monolauroyl-galactosylglycerol.The results show that monolauroyl-galactosylglycerol could hinder the growth of Escherichia coli and Bacillus cereus in the extended period or the logarithmic phase of growth,thereby both texted bacterial cells could not reach the peak of normal growth.Monolauroyl-galactosylglycerol will damage the structure of the cell wall and the cell membrane,then changing the cell membrane permeability to result in the release of some cellular components such as proteins and nucleicacids,thereby disturbing the cellular metabolism.And the effect of monolauroyl-galactosylglycerol on the cell membrane was related to the concentration of monolauroyl-galactosylglycerol.The degree of fluorescence intensity decreased with the addition of the concentration of monolauroyl-galactosylglycerol.Moreover,monolauroyl-galactosylglycerol treatment results in the damage to Escherichia coli and Bacillus cereus.The texted cells of both texted bacterial cells appeared adhesion and aggregation of damaged cells or cellular debris.3.Effects of monolauroyl-galactosylglycerol on the genomes and protein synthesis of bacteria.Escherichia coli and Bacillus cereus were used as indicator bacteria to investigate the antimicrobial mechanism of monolauroyl-galactosylglycerol.Spectrophotometry was used to measure the effect of bacterial metabolism of the material.The effect of monolauroyl-galactosylglycerol on the conformation of membrane protein was determined by fluorescence analysis.The both texted bacteial cells were as research object for observing the quantity of DNA and the expression of protein with effect of monolauroyl-galactosylglycerol by agarose gel electrophoresis and sodium dodecyl sulphate polyacrylamide gel electrophoresis(SDS-PAGE).The results show that IV monolauroyl-galactosylglycerol could inhibit the metabolic activity of Escherichia coli and Bacillus cereus.The degree of intensity of inhibitory action with the addition of the concentration of the substance.It may be that the cell wall and the cell membrane of treated bacterial cells were damaged,many pits and gaps appeared in the images,the cells lost their protective barrier so that a large number of intracellular organic matter had lesked out,then these variation will disturb the normal bacterial cell metabolism and kill the bacteria.The results of agarose gel electrophoresis show that monolauroyl-galactosylglycerol not only could destroy the structure of DNA,but also interfere the synthesis of DNA.The aminoacid residue on cell membrane was quenched by monolauroyl-galactosylglycerol,and the fluorescence intensity was decreased.The photographs of SDS-PAGE suggest that the effect of monolauroyl-galactosylglycerol on the protein expression of Escherichia coli and Bacillus cereus are not obvious,it may be able to inhibit some synthesis of bacteria intracellular protein,or resulted in the leakage of proteins from bacterial cells.In short,the antimicrobial mechanism of monolauroyl-galactosylglycerol will be studied using the knowledge of lectron microscopy and biochemistry.All the results demonstrated that the antimicrobial effect of monolauroyl-galactosylglycerol is not just attributable to a unique pathway,this involve a series of process.The study found that the cell wall and the cell membrane of bacteria are important target of monolauroyl-galactosylglycerol.The substance not only involved intercellular reaction,but may also enter into the organism cell when both texted bacterial were treated with monolauroyl-galactosylglycerol.Moreover,the material could damage the structure of the cell wall and the cell membrane,then changing the cell membrane permeability to result in the release of some cellular components such as proteins and nucleicacids,thereby disturbing the cellular metabolism.Even after this,the mechanism of bacterial cells damage might be that monolauroyl-galactosylglycerol interfered synthesis of bacterial cell proteins and DNA or induced aggregation of bacterial proteins.These all changes could effect the cell growth and finally result in death. |
