Study On The Use Of Bacteriophage For The Control Of Streptomyces Scab During Potato Storage

Potato scab disease is caused by the infection of Streptomyces scab.The epidermis of potato pieces will appear rusty,dark brown or black bumps.During the potato storage period,Streptomyces scab will spread from the diseased potato and cause other potatoes to be infected,and the diseased potato will also carry toxins,which is harmful to the human body.As a green and natural new bacteriostatic agent,bacteriophages can effectively prevent the spread of pollution by Streptomyces scab.This study used Streptomyces scab as the host,isolated two bacteriophages from diseased potatoes,and then studied the biological characteristics,genomics,and prevention and control of the bacteriophages during the storage period.This is the prevention and treatment of bacteriophage biological agents in the food field.And the application has laid the foundation.The main content and results are as follows :(1)Isolation of Streptomyces scab phageIn the early stage of the research of common scab 34 strains of Streptomycesbacteria to host,diseased potato as samples,using drip method and flat coating method to isolate two virulent phage strains,named ? S1 and ? S2.(2)Analysis of biological characteristics of Streptomyces scab phageThe biological characteristics of the two strains of phages were studied.It was found that they were phages with wide host spectrum and strong cleavage ability.Observed under transmission electron microscope,?S1 capsid protein of the head is about 66 nm±5nm in diameter,is the contraction of the tail,tail length of about 129±7 nm,which can determine the phage as part of the phage with tail,long tail phage families.The head diameter of the ?S2 protein shell is about 64±7 nm,and the non-shrinkage end length is about 196±8 nm,and it is judged that the phage belongs to long tail phage.The optimal multiplicity of infection for phage?S1,?S2 was 0.01,0.1.The growth curve of phage?S1 an ?S2 showed that the incubation period was 20 min,but the ?S1 burst period was about 50 min.,the ?S2 burst period was about 60 min.The temperature stability test showed that the bacteriophage ?S1 and ?S2 have the highest activity at 30°C,while the bacteriophage ?S1 is inactivated at a high temperature of 80°C,and ?S2 is inactivated at90°C.In the acid-base tolerance test,when p H<2 or p H>10,the survival rate of phage?S1 and ?S2 dropped sharply.(3)The genomic study of Streptomyces scab phagePhage ?S2 genome sequencing results show its genome length of 36789 bp,GC content of 66.23.46 CDS were located on the positive strand,2 CDS were located on the negative strand,44 had putative functions,and the remaining four were unknown coding sequences.Further analysis showed that the structure of phage ?S2 gene modules and phage Sphi SASD1 sequence of gene has a certain degree of conservatism,and through the homology comparison analysis,phage ?S2 and Streptomyces phage Sphi SASD1 highest homology,genetic relationship of the two recently.(4)Experiments on bacteriophage control of susceptible potatoesTake two healthy potatoes with a smooth surface and at the same growth period,and punch three holes with the same area respectively.The first hole is injected with the bacteria liquid,the second hole was not treated,and the third hole was injected with the bacteria liquid and then the phage was added.Observe the lesions and necrosis of the potato flesh in the potato aperture after 1d,3d,and 5d.The results are as follows: the first small hole of the two potatoes was found to have severe necrosis,and the potato flesh was dark brown;there was no necrosis of the potato flesh found in the third small hole,and the color was light brown;the second small hole was not treated.The color was slightly oxidized and was light brown.The experimental results show that the bacteriophage can kill the injected scab pathogens and effectively prevent potato scab infection.(5)Experiment on reducing the toxin Thaxtomin A in sick potatoesDetecting the content of Thaxtomin A in scabs at different depths found that the toxin content at 0.5 cm under the potato skin was higher than the toxin content at 1 cm under the skin.After spraying the phage preparation,the content was measured.The toxin content at 1cm was reduced by 0.159mg/g and 0.075mg/g respectively.Phage control experiments show that phage ?S2 can reduce the toxin content of Thaxtomin A in potatoes,and effectively prevent the contamination of Streptomyces scab and the spread of toxins.