Antibacterial Activities And Mechanism Of Chitosan And Its Complex Against Several Bacterial Pathogen Of Horticultural Crops

Chitosan is a natural substance of broad-spectrum antibacterial activity. This experiment is to study the antibacterial activity and inhibition mechanism of two kinds of acid-soluble chitosan (chitosan A with deacetylation degree>85%and chitosan B with deacetylation degree>75%) on12pathogenic strains of Xanthomonas bacteria isolated from different geographical types of rape. The result turned out that both two kinds of acid-soluble chitosan inhibited the growth of pathogenic bacteria Xanthomonas significantly based on the OD600value of Xanthomonas bacteria suspension. The OD260value of Xanthomonas bacteria suspension treated with mentioned two kinds of acid-soluble chitosan increased, which showed increased leakage of DNA and RNA of test strains. The OD280value of Xanthomonas bacteria suspension with mentioned two kinds of acid-soluble chitosan decreased, which showed chitosan blocked the secretion of intracellular proteins of pathogenic strains of Xanthomonas bacteria with exception of chitosan A at0.1mg/mL for0.5h and at0.2mg/mL for2h.These results tell that chitosan has a complex interaction with bacterial cell membranes influenced by treatment duration, strain types, the types of chitosan and chitosan concentration. Chitosan treatment caused the concentration of bacterial protoplasts and morphology change of cell surface through TEM images. The cell membrane and cell wall of some strains of Xanthomonas bacteria severely distorted or even broken, while other strains were wrapped with a thick dense ribbon layer. Two different changes in cell morphology explained chitosan has different influences on DNA, RNA and protein release.Besides, scanning electron micrograph and biofilm formation testing showed that two kinds of chitosan can cause peeling of the biofilm. In summary, for disease-causing bacteria, chitosan plays an important role in antimicrobial mechanism by causing cell membrane and biofilm damage.Compositing chitosan with other substances can expand the field of applications of chitosan as well as improve the function of chitosan in a specific area. In this experiment, chitosan is composited with some substances of certain degree of antimicrobial activity. The result showed an effective inhibition to Acidovorax avenae subsp. citrulli, which caused bacterial fruit blotch under lower concentration. The treatment of combinition of0.1mg/mL chitosan with0.02%Glutaraldehyde,1mg/L CTAB,10mg/L DDAB,0.5mg/L ammonium chloride respectively inhibited the Acidovorax avenae subsp. citrulli with inhibitory rate higher than90%. The result showed that four chemicals with antibacterial activity mentioned above when combined with chitosan increased their antimicrobial activities under low concentration conditions, thus confirmed combined-inhibition as a co-efficient, low-power mode.