Isolation And Characterization Of Synechococcus-Cyanophage Systems And Prochlorococcus From East China Sea

Two marine Synechococcus sp. strains and their cyanophages, four marine Prochlorococcus sp. strains were isolated from the coastal sample waters of East China Sea during August 2011. All the cultures isolates of marine Synechococcus and Prochlorococcus could utilize both NH4+and NO3-, occasionally at different growth rates. The in vivo absorption spectra indicate that these Synechococcus spp. absorbs light efficiently in the blue region, with high PUB/PEB ratios and the Ch1 b/a ratios of these Prochlorococcus were higher than 0.95, which was similar to most known Prochlorococcus strains. Based on their 16S rDNA、ITS and psbA gene sequences, the two Synechococcus strains were very similar to those members of clade III of the marine cluster A(MC-A) group, and the four Prochlorococcus strains were very similar to those members of High-B/A Prochlrococcus clade Ⅳ. The phylogenetic trees of 16S rDNA、 ITS、psbA sequences showed that the two coastal Synechococcus strains always clustered together; and the phylogenetic tree of 16S rDNA sequences showed that the Prochlrococcus strains selected from same N sources during isolation were closely related.Two new cyanophages infecting the above mentioned MC-A Synechococcus strains had been isolated from the same sampling locations, and the stable systems of Synechococcus-Cyanophage were established. The two Synechococcus caynophages SS-2 and SJ-2 were isolated and purified via the methods of the sucrose density gradient centrifugation and Most Probable Number. Transmission electron micrography of negative-stained specimens revealed that the cyanophage isolate SS-2 has an isometric head with a diameter of 65 nm and a long flexible tail 210 nm in length, and the cyanophage isolate SJ-2 has an isometric head with a diameter of 68 nm and a long flexible tail 280 nm in length. Both of the two Synechococcus cyanophages are specific to their hosts, the cyanophage SS-2 could infect marine Synechococcus strains SS01 and SJ01, which are closely related; the cyanophage SJ-2 could only infect marine Synechococcus strain SJ01. The genomes of the two Synehcococcus cyanophages were smaller than 23kb, and the genomes of SJ-2 were smaller than SS-2. Moreover, the two cyanophages DNA could not be digested with the restriction enzymes HindⅢ、 BamHI、 EcoRI, and the genomic DNA could not be amplified with the specific primers of g20、 psbA、DNApol genes. This is consistent with the characteristics of reported Synechococcus siphoviruses, but differentiated from any known Synechococcus myoviruses and podoviruses.