Viral Lysis Of Synechococcus Contributed To Marine Dissolved Organic Matter Pool

Marine Synechococcus,one of the major picocyanobacterial groups,are abundant and widely distributed in world's ocean.Synechococcus contribute highly to marine primary production and play important roles in diverse oceanic ecosystems.Viruses are the most abundant life entities in the ocean,which are the major players in marine ecosystem and biogeochemical cycles.Viruses induced major mortality of Synechococcus.Viral-lysis of Synechococcus released dissolved organic matter(DOM)and particulate organic matter(POM)from Synechococcus.This pathway short-cut the material transfer via food wed and directly released organic matter from primary producer into environment,contributing to the dissolved organic carbon(DOC)pool.Synechococcus are prokaryotic photosynthetic microbes,the unique cellular structure made them different from bacteria or eukaryotic phytoplankton.The cell lysate and metabolites from Synechococcus via viral infection should have novel properties which essential to marine DOM reservoir,however,the characterization of viral-induced DOM from Synechococcus(Synechococcus vDOM)remains elusive.This study focused on marine Synechococcus and their viruses,especially viral-lysis process and impact on Synechococcus.Based on culture experiments with model strains,we try to describe the chemical composition and physical properties of Synechococcus vDOM,unveiling the mystery of marine DOM diversity and sources.We try to tracking the fate of Synechococcus vDOM and the responses of bacterial community with the dark incubation experiment.Thus,we can further understand the importance of marine Synechococcus and their viruses in marine ecosystem and global biogeochemical cycles.Progress was made as following:1.We isolated and purified Synechococcus strains and viral strains from coastal sea water,set up viral-host model systems for the following study.Synechococcus isolations were identified with phylogenetic analysis.Draft genome analysis of three of the isolations revealed the coastal environmental adaptation of the Synechococcus strains.One of the viral isolations were identified as a T4-like myovirus based on draft genome analysis.2.We showed that cultured Synechococcus released FDOM during viral-lysis process,that closely matched the typical fluorescent signals found in oceanic environments.Synechococcus FDOM also shows comparable apparent fluorescent quantum yields and undergoes similar photo-degradation behavior when compared with deep-ocean FDOM,further strengthening the similarity between them.Ultrahigh-resolution mass spectrometry(MS)and nuclear magnetic resonance spectroscopy reveal abundant nitrogen-containing compounds in Synechococcus vDOM,which may originate from degradation products of the fluorescent phycobilin pigments.Given the importance of Synechococcus in the global carbon cycle,the results indicate that are Synechococcus likely to be important sources of marine autochthonous FDOM,viral-lysis catalyzed the release process of the specific DOM components into enviroment.3.Addition of Synechococcus vDOM increased the diversity of DOM chemical composition.The abundant nitrogen components introduced by vDOM were largely degraded during the 90 days' incubation experiment,however,several specific DOM molucules which already exsited in the coastal sea water were accumulated.Upon the addition of vDOM,bacterial abundance increased sharply and bacterial community enriched dramatically,reflected by the changed bacterial composition and increased biodiversity indices.The network analysis was applied to link the degradation behavior of chemical species with bacterial species.Certain bacterial OTUs form specific relationship with particular vDOM components.Viral-induced DOM production from Synechococcus supplied the chemical diversity of marine DOM and supported the biodiversity of marine bacterial community.4.To understand the flux and contribution of Synechococcus vDOM to the marine DOM reservoir,we furthur conducted the modified dilution assay to estimate the viral-induced mortality of Synechococcus.However,the results proved the application limitation of this method on Synechococcus.