Studies On The Diversity And Biological Characteristics Of Beauveria Bassiana Virus

Mycovirus is a virus that can infect fungi and replicate itself,and is widely distributed in higher and lower fungi.Beauveria bassiana is a common species of ascomycetes,and has been widely used for biological control of pests.Fifty strains of B.bassiana were selected for ds RNA extraction,and high-throughput sequencing technology and RLM-RACE were used for ds RNA sequencing and ds RNA cloning.Finally,virus-free strains were obtained by single spore isolation,and the biological traits and pathogenicity were studied.The results are showed followed:1)Fifty strains of B.bassiana were randomly selected for viruses screening with cellulose CF-11 ds RNA extraction.Among them,almost 30%(15 strains)contained ds RNA,this showed that fungal viruses infected B.bassiana ubiquitouly with higher diversity.2)dsRNA isolated from three strains were sequenced using high-throughput sequencing technology.The results showed that RCEF5853 contains four fungal viruses,namely Beauveria bassiana Partitivirus 3(Bb PV-3),Beauveria bassiana mycovirus ds RNA1(Bb ds R1),Beauveria bassiana Victorivirus1(Bb VV-1)and Beauveria bassiana Chrysovirus 1(BbCV1),respectively.Among them,Bb PV-3 and Bb ds R1 are novel viruses that have not been reported previously.Bb PV-3 is composed of two ds RNA fragments with sizes of 1856 bp and 1719 bp,encoding a RNA-dependent RNA polymerase(Rd RP)and a coat protein(CP),respectively.Bb ds R1 is also composed of two ds RNA fragments,each about 2kb in size,and encodes a Rd RP and a CP,respectively.The RCEF1446 strain contains three viruses,Beauveria bassiana mycovirus bipartitate 1(Bb BMV-1),Beauveria bassiana Victorivirus 1(Bb VV-1)and Beauveria bassiana polymycovirus 1(Bb Pm V-1),Bb BMV-1 is a novel virus that has never been reported.Bb BMV-1 is composed of two ds RNA fragments with sizes of 2026 bp and 1810 bp,which encode Rd RP and CP respectively.RCEF4054 contains only one polymycovirus,named Beauveria bassiana polymycovirus 4(Bb Pm V-4).This virus possess 8 ds RNA fragments.The largest fragment encodes a Rd RP,and the other fragments encode putative proteins.Among them,the complete sequences of Bb PV-3,Bb BMV-1 and Bb Pm V-4 were determined by RLM-RACE method to clone the 5 ’and 3’ ends of each ds RNA fragment.3)The virus-free strain of RCEF4054 was obtained by single spore isolation.The virus-free strains showed no significant difference in growth rate and colony morphology on SDAY,1/4SDAY and PDA compared to RCEF4054;But spore production decreased by 52.3%,and is more sensitive to SDS with relative inhibition rate increased 10%.The germination time of the virus-free is earlier,the GT50 of the virus strain is 12.6 h,and virus-free strain is 9.5 h.Virus-free strains are more sensitive to ultraviolet irradiation and heat shock treatment;The most interesting is the virus enhances the insecticidal ability of B.bassiana by increasing infection ability of wall.In summary,the three strains of B.bassiana contain eight fungal viruses in total,four of which are novel species,indicating that the viruses in B.bassiana at a high diversity.The Bb Pm V-4 could reduce the sporulation of B.bassiana,and increases tolerance to UV and heat,the most important is that virus enhances the ability of host to kill insects significantly.