Effect Of Acidic Substances On Biofilm Formation And Antibacterial Activity Of Acidovorax Citrulli

Bacterial fruit blotch（BFB）of melon is caused by Acidovorax citrulli（Ac）,which is a destructive disease in watermelon and cantaloupe production,and also an international quarantine disease.It causing significant losses to watermelon and cantaloupe industry.There are no effective measures to prevent BFB.The biofilm formed by pathogenic bacteria plays an important role in the pathogenesis of plants.Inhibition or reduction of biofilm formation will be a new strategy to control BFB.Object:To determine the effect of acid substances on A.citrulli biofilm formation,preliminary reveal the mechanism of acid substances on A.citrulli and its biofilm,and explore the relationship between biofilm formation and pathogenicity of A.citrulli,in order to provide theoretical basis for inhibiting biofilm formation and preventing BFB,Method:By microporous plate method and used crystal violet staining,the best external factors for the biofilm formation of A.citrulli were screened out,and the ability of A.citrulli biofilm formation in acidic environment was detected.Oxford cup method,microscopic observation,flagella staining,fluorescence quantitative detection and other methods were used to determine the influence of acid substances on A.citrulli growth,bacterial structure,biofilm formation and virulence related gene expression,to explore the antibacterial mechanism of acid substances on A.citrulli.In order to investigate the effects of acidic substances on the biofilm formation and pathogenicity of A.citrulli on cantaloupe leaves,the activities of A.citrulli cellulase and pectinase in acidic environment and the biofilm formation and pathogenicity of A.citrulli on cantaloupe leaves were measured.Results:The initial bacterial concentration was 1×10⁷cfu/m L,the inoculation amount was 1:10（bacterial liquid:culture medium）and the LB culture medium contained 10μg/m L Mg SO₄at 28°C for 24 h,which was most suitable for the biofilm formation of A.citrulli,but the biofilm formation of A.citrulli was inhibited in acidic environment.The inhibitory effect of organic acids on the growth of A.citrulli was more obvious than inorganic acids at the same p H.With the decrease of p H,the inhibitory effect of organic acids was remarkable,and the diameter of inhibition zone reached 32.67 mm after acetic acid treatment at p H 2.After acetic acid treatment,the flagella of A.citrulli fell off,the bacteria appeared pores and shrinkage deformation,and the complete cell morphology was not observed in the p H 2 treatment group.Acetic acid destroyed the stability of the cell membrane of A.citrulli,resulting in the leakage of nucleic acids and other substances in cells increased,and some bacteria died.At the same time,intracellular reactive oxygen content changes and the expression of some genes related to A.citrulli biofilm formation and pathogenicity decreased significantly.Under acidic conditions,the cellulase and pectinase activities produced by A.citrulli decreased.In addition,A.citrulli could form biofilm on cantaloupe leaves,after 7 days of inoculation,the inoculation concentration of about 1×10⁸cfu/m L of A.citrulli formed more biofilms on cantaloupe leaves,the diseased leaves were dyed with large area and dark color,and the disease was serious.The acetic acid at p H 4 could inhibit A.citrulli biofilm formation on the cantaloupe leaves and reduce the disease index of the disease.Conclusion:Acidic substances can inhibit the growth of A.citrulli,affect its biological characteristics such as cell structure,and inhibit the biofilm formation of A.citrulli.Using acetic acid solution to deal with A.citrulli biofilm can effectively reduce the incidence of cantaloupe seedlings.This study showed that acetic acid had a certain inhibitory effect on the biofilm formation and pathogenicity of A.citrulli,in order to use acidic substances to prevent BFB safely and effectively.