The Genomics Analysis And Physiological Characterization Of Cyanophage Isolated From The Southern China Sea

Viruses are thought to affect the population dynamics,community structure,metabolic activity,and evolution of their hosts and then impact the microbial ecology and biogeochemical cycling in aquatic ecosystems.Cyanophages are important components of the marine viruses and contain many host-derived metabolic genes,which encompass many metabolic functions and enhance key steps of host meta'bolism to increase viral replication.The physiological,genomic,phylogenic and proteomic traits of cyanophages isolated from the Southern China Sea were investigated.The results of this thesis are:1.A cyanophage strain S-SCSM1 was isolated from the South China Sea,infecting both Synechococcus and Prochlorococcus strains.S-SCSM1 is a T4-like virus with unique genetic features.The genome of S-SCSM1 is 229.08 kb with a G+C content of 39.76%.A total of 293 ORFs,nine tRNA genes,and two ncRNA genes were predicted in the S-SCSM1 genome.Genes related to viral structure,DNA replication and metabolism were conserved as other T4-like cyanophages.Various auxiliary metabolic genes(AMGs)were predicted in the S-SCSM1 genome,including a mannose-6-phosphate isomerase gene(PMI)involved in carbon metabolism,a collection of novel lipopolysaccharide synthesis(LPS)genes,13 genes encoding 20G-Fe(?)superfamily proteins(20G)and two genes related to plasmid stability and lethal regulation.S-SCSM1 PMI represents the first instance of this gene that is found in cultured cyanophages and is phylogenetically divergent from those identified in cyanobacteria or bacteria.The multicopy and diverse 2OG genes in the S-SCSM1 genome indicate their importance and functions in reprograming host metabolism during infection.Two ncRNAs encoding cis-regulatory elements in the S-SCSM1 genome are thought to be associated with host metabolism and photosynthesis.Interestingly,the S-SCSM1 virion encapsidates six proteins that are possibly related to the host metabolic regulation.2.Ten Prochlorococcus phage all phylogenetically belong to A cluster T4-like cyanophage and 0430-25?1430-53 and 1430-57 may form a new clade in A cluster.Genome sizes of ten phage range from 119.11 kb to 224.18 kb and the G+C contents are within the scope of 35.03%-39.35%.These phages contain a large number of genes with unknown functions.Some interesting genes,which encode proteins responsible for viral attachment(hemagglutinin domain protein)and viral DNA protection from host restriction(anti-restriction protein)and heavy metal stress(retrovirus-related Pol polyprotein from transposon TNT 1-94),are found in Prochlorococcus phage genome.In addition,some new AMGs are also found,including NifU gene involved in synthesizing iron-sulfur metalloclusters required for nitrogen fixation,glycogen phosphorylase gene,cadherin gen e encoding protein for the development of cell polarization and toxin genes related to the synthesis of cytolytic exotoxin.The analysis of Prochlorococcus phage genomics revealed the diversity of viral genes.