Biological Characteristics Of Two Chromohalobacter Beiierinckii Viruses

Viruses flourishing in hypersaline environments are called haloviruses,which can be classified into haloarchaeal viruses,halobacterial viruses and eukaryotic haloviruses based on their hosts.Interaction of viruses and hosts has tremendous impact on cellular and viral evolution,nutrient cycling.Besides the protozoa,haloviruses are the major cellular predators in hypersaline environments,indicating that the role of viruses is highly important in these ecosystems.This dissertation explores the biological characteristics of two halobacterial viruses(YPCBV-1,YPCBV-2)and their hosts(Chromohalobacter beijerinckii F3,CGMCC 1.9020),especially effects of the NaCl salinity on biological characteristics.Virus YPCBV-1 and its host Chromohalobacter beijerinckii F3 originate from Yipinglang salt mine in Yunnan province.CGMCC 1.9020 was purchased from China General Microbiological Culture Collection Center(CGMCC),it was isolated from pond water at East Minggang dam which located in Ninghai County,Zhejiang province.YPCBV-2 is the mutant virus of YPCBV-1,which is the several plaques caused by high titer YPCBV-1 infecting 1.9020.The mutation rate is 10-5-10-7.However,no plaques can be produced while YPCBV-2 infecting F3.Although most of biological properties of the two pairs of viruses and hosts are similar,they cannot cross infected,which reflects the diversity of microorganisms in nature and the excellent scientific research value.Moreover,the cross-adsorption assay shows that the position of the mutation could be a receptor with adsorption function.Biological properties of host strains F3 and 1.9020 are almost identical,both of them can live in salinity range from 2%to 25%,with an optimum concentration of 5%.Colonies appear slightly yellowish,opaque and circular with 1.2-2.0 mm in diameter on MLB plate.TEM shows that cell is rod-like with flagella,its dimensions are approximately 1.6-2.1 ?m × 0.5-0.6 ?m.Viruses can form semitransparent and vague plaques with 0.5-1.5 mm in diameter.TEM images show YPCBV-1 is sphere-like,with 20-56 nm in diameter,which brings challenges to classification and identification.Although YPCBV-1 is the most similar to the pleomorphic viruses which is extremely sensitive to chloroform,it is not sensitive to chloroform.This indicates that YPCBV-1 is probably a new type virus,but needs a further confirmation.Viruses are unstable in high temperature,they have narrow host range,the optimal multiplicity of infection(MOI)is 1.They can stable at pH 5-10,YPCBV-1 is apt to be tolerant acid environments,but YPCBV-1 favors alkaline environments.Latent period,lytic period and burst size of YPCBV-1 are influenced by NaCl concentration.Under 5%concentration,virus can lyse host with low efficiency.At the concentration of 15%,the burst size reaches a maximum of 25 viruses per bacterium.When NaCl concentration rises to 20%,latent and lytic period are prolonged distinctly.The adsorption rates of virus to host decreased with the increase of salinity from 8%to 30%.5%and 8%were optimum adsorption salt concentration for YPCBV-1 and YPCBV-2,resp tively.Two viruses can form plaques at the salinity range of 8-20%.Plaques formation of YPCBV-1 was much more sensitive to salinity than YPCBV-1's.In contrast with YPCBV-1,YPCBV-2 plaques formation is postponed for several hours.YPCBV-2 optimal infection salinity was 10%.As for YPCBV-1,amounts of virus progeny affected by salinity fluctuation before adsorption.YPCBV-1 is more likely to produce more progeny in a host with no salinity change.YPCBV-1 is unstable in water without salt,whose activity is dependent on the salt solution of NaCl or KCl,it can survive for a long time in NaCl or KCl solution with the range of from 1%to saturation,except the saturation salinity,the survival rates increased with the increase of salinity.Moreover,it also survives in 5-10%NaBr solution,1-10%CaCl2 solution,5-30%Salt water solution.In contrast with other salt solution,YPCBV-1 survival rates decreased with the increase of CaCl2 concentration.For YPCBV-2,the survival rate increased with the increase of NaCl salinity,it prefers water without salt to YPCBV-1.YPCBV-1 genome is dsDNA,it can be cut by restriction endonuclease EcoR I?Xho I.The cut segments can be inferred the genome is 30 Kbp in length.This paper poses on important significance to enrich the halovirus resources and provides materials for studying virus-host interaction.It also brings theoretical basis and method guidance for further development and utilization of haloviruses.