Effects Of Model Marine Synechococcus-virus Interactions On DOM Components And Bacterial Community

Marine picocyanobacteria are major primary producers on the earth.Synechococcus,one of the representative picocyanobacteria groups,is widely distributed in the global ocean.The carbon fixed by Synechococcus enters the microbial loop in the form of dissolved organic matter(DOM)through cell excretion and viral lysis,which plays an important role in the carbon cycle.Viruses are the most abundant biological entities in the ocean,and Synechococcus virus is one of the important constituents.virocell is formed after virus infecting host cells.And then the viruses would reprogramme virocell’s metabolism,lyse the cells,even regulate host abundance and community composition,and finally accelerate the biogeochemical cycle in the ocean.However,it is unknown how viruses redirect the virocell’s metabolism,alter the produced DOM composition,and impact the co-occurring bacterial community.In this study,two Synechococcus-virus models were constructed to reveal the influence and contribution of Synechococcus-virus interaction to marine DOM pool.The viral regulation on host metabolism was analyzed through transcriptomics,and the effects of Synechococcusvirus interactions at different stages on DOM components were analyzed through FT-ICR-MS,and the impacts of phage-host interactions imposed on the co-occurring heterotrophic bacterial communities were explored.The main results of this study are:The podovirus S-CBP1 and the myovirus S-CREM1 are typical representatives of T7-like and T4-like cyanophages.The latent periods of S-CBP1 and S-CREM1 are 7～8 h and 10～12 h.The S-CBP1 and S-CREM1 share some AMGs,such as genes involved in photosynthesis genes(speD,hli and psbA)and phosphorus acquisition(mazG).In addition,S-CBP1 encodes an nblA involved in nitrogen transformation,while S-CREM1 encodes related a CP12 involved in carbon metabolism and a phoH involved in phosphorus acquisition.Moreover,S-CREM1 encodes more regulatory genes than S-CBP1,such as 3 antitoxin genes.Both S-CBP1 and S-CREM1 can effectively infect the host and take over the transcriptional resources in virocell,but they have different ways to control the transcriptional resources.S-CBP1 tends to control the transcriptional resources by the virus itself,while SCREM1 tends to regulate the transcriptional resources together with the host.There are both similarities and differences in host metabolism regulation between the two cyanophages.The two cyanophages both inhibit more metabolic processes than they promote,and reshape the same metabolic processes such as substance synthesis and degradation,substance transport and energy acquisition in the virocell.Specifically,both cyanophages up-regulate the expression of aromatic compound degradation genes,reshape the nitrogen metabolism process,promote the de novo pyrimidine and purine synthesis.inhibit Calvin cycle and glycolysis pathway,and promote pentose phosphate pathway.However.due to the difference of gene composition.SCBP1 and S-CREM1 have different effects on the virocell metabolism.In the remodeling process of carbon metabolism,the S-CBP1 can reduce the expression of a large number of Calvin cycle-related genes to inhibit Calvin cycle,while the S-CREM1 uses its encoded CP12 to inhibit Calvin cycle.In the remodeling process of nitrogen metabolism,S-CBP1 inhibits virocell’s nitrogen metabolism and transforms nitrogen source by expressing its encoded nblA,while S-CREM1 promotes nitrogen assimilation to obtain more nitrogen.S-CBPI and S-CREM1 both reduced the diversity of DOM released by virocell,and enhanced the biological activity of DOM by reducing the proportion of aromatic compounds and increasing the proportion of aliphatic compounds.The decrease of aromatic compounds may be related to the up-regulation of aromatic compound degradation genes.The cyanophages increased the number of DOM components with high biological activity by 4.1-5.1%and the intensity by 7.9～13.3%in their latent period.Since 1～5%of the marine Synechococcus cells are infected by viruses.the enhancement of DOM biological activity may play an important role in promoting the marine carbon cycle.During the lysis,the viral effects on DOM diversity and biological activity are phage specific.However,compared with latent period,DOM diversity of each cyanophage is higher during lysis.In addition,the DOM both in the control and treatment groups are enriched with N-and S-containing components,which indicates that Synechococcus DOM is an important source of N and S in the ocean.There is a complex correlation between the host differentially expressed genes and DOM molecules.The negative correlation is dominant,which may be related to the viral inhibition on host metabolism.The correlation in the podovirus-treatment is more complex,which may be related to the greater influence of podovirus on virocell metabolism.Genes in the two treatments have similarities in functional types,and these shared gene functions are related to carbohydrate metabolism,energy metabolism and transmembrane transport.The Synechococcus-cyanophage interactions impact the community composition of the co-occuring heterotrophic bacteria,especially in the lysis stage.The increase of DOM diversity has a more significant impact on heterotrophic bacterial community than the increase of DOM biological activity.There are complex correlations between the dominant groups of symbiotic bacteria and DOM molecules,among which Alphaproteobacteria and Bacteroidia are negatively correlated with DOM molecules,while Gammaproteobacteria is the opposite.