| Penicillium expansum is a major pathogenic bacterium during post-harvest storage of apples,which causes Penicillium disease in many countries and causes huge economic losses to the apple industry.Patulin(PAT)is a secondary product produced by the metabolism of P.expansum,which cannot be effectively removed during product processing due to its water-solubility and heat/acid stability.It can also alter cell permeability,reduce cell activity,and induce oxidative stress and apoptosis in mammalian cells.Physical and chemical fungicides are commonly used to control P.expansum infestation in apples,but they have limitations in terms of cost,efficiency and safety factors.Biological control agents not only inhibit pathogens from infesting fruit and reduce economic losses,but also decrease the risks and costs associated with physical and chemical sterilization methods to remove toxins.Therefore,in this paper,an antagonistic bacterial strain with inhibitory effect on P.expansum was isolated by screening and identified by morphological and molecular biological methods.The active substances that inhibited P.expansum were investigated and the expression of related resistance genes was verified by molecular biology.The high-performance liquid chromatography(HPLC)technique was used to investigate the functional components of P.expansum that have a degrading effect on PAT and to study their degradation efficiency.The effects of antagonistic bacteria and their active substances on apples and juice were also investigated by examining the quality of treated apples and juice.The main findings of this paper are as follows(1)An antagonistic strain of bacteria(YL-RY0310)was isolated and screened from orchard soil,and its inhibitory effect on P.expansum was 62.57% and 77.44%,respectively,as verified by plate standoff and in vivo apple biocontrol experiments.It was identified as Bacillus mojavensis sp.by morphological observation and 16 S r RNA sequencing analysis.(2)The total DNA sequence of Bacillus subtilis YL-RY0310 was extracted,amplified by PCR with Bacillus lipopeptide-specific primers,and the sequence of lipopeptide-related resistance gene of YL-RY0310 was found by agarose gel electrophoresis analysis.It was verified by liquid shake flask culture antagonism assay that the cell-free fermentation broth of Bacillus mojavensis YL-RY0310 and its lipopeptide-like inhibitory substance extract could effectively inhibit the growth of P.expansum spores.Meanwhile,the Oxford cup assay further verified that the concentrated lipopeptide-like inhibitory substances could effectively inhibit the growth of P.expansum.(3)The fermentation broth of Bacillus mojavensis YL-RY0310 was treated with different treatments and the removal of PAT by antagonistic bacteria was investigated by liquid shake flask culture experiment.The degradation efficiency of intracellular enzyme of YL-RY0310 was 62.60% at 36 h of reaction time,and the degradation rate of extracellular enzyme on PAT increased with the extension of fermentation time of bacterial suspension,and the degradation effect on PAT was 56.94% at 96 h of fermentation.(4)By detecting the changes in the contents of apple quality indexes,it was found that Bacillus mojavensis YL-RY0310 had no significant effects on the contents of soluble sugar,vitamin C,titratable acid and total phenols in apples,and the soluble solids contents of apples treated with YL-RY0310 suspension were reduced,while there were no significant changes in the soluble solids contents of apples treated with the injection suspension.By examining the content changes of apple juice quality indexes,it was found that the intracellular enzymes of Bacillus mojavensis YL-RY0310 did not significantly reduce the contents of soluble sugars,vitamin C,titratable acids,total phenol and soluble solids in apple juice. |
PDF Full Text Request