| Rice is the main food crop in our country.Bacterial leaf blight is a destructive bacterial disease in rice plantation,which produces tremendous threaten on economy and food safety in our country.Although resistance breeding,chemical and biological prevention have reduced the disease well,the efficiency of these strategies is unstable and the disease may break out unpredictably.Therefore,the new strategies are imperative to be found.At present,phage therapy has been well used in food processing,aquaculture,medical treatment and public health,agricultural disease,etc.Therefore,this research plans to discuss the feasibility to control bacterial leaf blight of rice with phage therapy.Xanthomonas oryzae pv.Oryzae(Xoo)is a pathogenic bacteria of bacterial leaf blight of rice.In this study,we used nine Xoo race including YN1,YN7,YN11,YN18,YN24,GD414,HEN11,FuJ,ScYc-b from different areas of China and type strain PX099A as target,to detect the Xoo phages in thirty-two soil samples from eleven areas of six provinces of China.We found that Xoo phages isolated are ubiquitous in soils and have different characteristics in different areas.The host range,electron morphology,structure protein profiles of the 15 purified Xoo phages showed these Xoo phages had high diversity,suggesting that there were abundant and various Xoo phages in China soils.The co-culture experiment in liquid media showed these Xoo phages had good control efficiency on ten different Xoo strains,and the control efficiency of mixed phages was better than single phage.This synergistic effect among different phages can be used as cocktail therapy to expand the host range and improve control efficiency.Meanwhile,these Xoo phages have good environment adaption under different temperature(4-50?)and pH(3-9)range.Moreover,the mixed Xoo phages showed good control efficiency against PXO99A in living rice.The pot experiment showed that the CFU of PXO99A decreased two magnitudes and the lesion length significant reduced after 14 days of infection in living rice which treated with mixed Xoo phages comparing with rice without any treatments.We further sequnced the whole genome of four unigue Xoo phages and have got the gemone sequnce of Xoo_sp2,Xoo_sp13,Xoo_sp14 and Xoo_sp15.Comparing with published genome of ten Xoo phage by spot analysis,we found that these two Xoo phages present new tpyes of Xoo phage.There are just 25.61%,17,96%,7.14%and 16.59%of functional genes respectively in Xoo_sp14 and Xoo_sp15 genome,indicating that there are many unknown function genes in these two Xoo phages.What's more,several unusual phage-encoded ORFs were found in these pahges,such as FtsK and modification methylase.The phylogenetic tree snalysis shows these genes are derived from bacterial genome,indicating highly frequent gene horizontal transferation has happened during the long co-evolution between phages and Xoo strain.Considering restriction enzyme is one of the mechanism when the host defense phage,and the discovery of abundant modification methylase in Xoo phages may be a special way of Xoo phages to defense its hosts.Our works reported four novel Xoo phages from China and declare that these phages could be used as an alternative environmental friendly biocontrol agent against rice BLB by using as cocktail phage therapy. |
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