Isolation And Characterization Of A Novel Cyanophage Infecting Synechococcus Sp.strain CB0101

In different ecological environments,different cyanobacterial groups occupy different ecological niches depending on their unique adaptation mechanisms and abilities.As a picoplankton in Cyanophyta,Synechococcus is widely distributed in the global marine waters and has rich ecology,species and genetic diversity.It is generally believed that Synechococcus plays an important role in the fixation of carbon dioxide and the contribution of the total primary productivity of the biosphere.Cyanobacterial viruses,also known as cyanophages,regulate the abundance and community structure of cyanobacteria by infecting host cells,and mediate horizontal gene transfer between hosts.Meanwhile,as an important factor leading to the lysis of the cyanobacteria,cyanophages regulate the population density and community structure of the cyanobacteria in the aquatic ecosystem by infecting and lysing host cells,and subsequently affect the energy flow and material cycle of the ecosystem.In this study,we have successfully isolated and characterized a virus from Shenzhen Bay,Shenzhen,Guangdong Province,using Synechococcus sp.strain CB0101 as the host algae.The phage belongs to the family Myoviridae and is named S-SBM1 according to the current naming rules.The host range test analysis showed that among all of cyanobacteria(Chroococcus,Microcystis,Prochlorococcus and other Synechococcus in different salinities)examined,the phage infects the strain CB0101 exclusively,suggesting that the phage S-SBM1 has a high specificity against Synechococcus sp.strain CB0101.The negative-staining images taken by transmission electron microscopy(TEM)showed that the S-SBM1 is a T4-like phage.Its head is icosahedral-shaped,with a diameter of 75-80 nm.The retractable rigid tail is columnar-shaped,with a diameter of about 25 nm and a length of 70-90 nm.The head and tail are connected via a neck,while the baseplate is connected to the end of the tail.The complete genome of the novel cyanophage S-SBM1 is a linear double-stranded DNA,with a total length of 177,834 bp and a GC content of 43.31%.The annotation of S-SBM1 genome resulted in the prediction of 239 open reading frames(ORFs)and six transporting RNA(tRNA)genes.These include many auxiliary metabolic genes(AMGs),such as genes encoding cobS,CP12 family proteins,heat shock protein HSP,mazG,phoH,psbA,2OG-Fe(II)oxygenase and so on.Previous studies have shown that these genes can affect cell metabolism after infection,and provide energy and materials for the DNA replication and multiplication of phages.In addition,43 proteins,including 28 structural proteins,four DNA replication-related proteins,two proteins involved in DNA metabolism and repair,and one protein involved in phage packaging,were identified by high-throughput proteomic mass spectrometry.The results of this study have expanded our knowledge of cyanophages,and may aid in the deeper understanding of the interaction between cyanophages and their host cyanobacteria.In addition,the relevant omics data will help us to recognize the genetic potential of phages and to understand how phytoplankton viruses affect the evolution and survival of cyanobacteria.