Ecological Effects Of Marine Viral Lysis And Lysate

Marine viruses are the most abundant microorganism in the ocean and are the reservoir of most of the genetic diversity in the sea.As as major source of its host's mortality,virus could influence the abundance,production,respiration and diversity of its host,and are a major force behind marine biogeochemical cycles.In order to investigate the ecological effects of viral lysis and lysate,we isolated phages infecting Dinoroseobacter and Erythrobacter belonging to AAPB.The bioavailability of phage lysate was evaluated for marine bacterial communities of Xiamen coast.Moreover,the effects of virus upon bacterial populational metabolisms(e.g.,bacterial production and bacterial respiratorion)were investigated at the South China Sea.Then based on the Aquatron Tower system,the ecological role of virual lysis was explored during long-term incubation.The main results obtained in our studies were as followed:Twenty long-tailed phage species infecting Reosobacter and Erythrobacter were isolated and purified from coastal waters of Xiamen,Zhoushan,Pearl River estuary and Qingdao.The host range of phages infecting Reosobacter was relatively narrow,and the host ranges of phages infecting Erythrobacter were quite broad.Furthermore,phage vB_EliS-R6L,which infects Erythrobacter litoralis DSM8509 and was isolated from coastal waters of Xiamen,was selected for physiological and genomic analysis.Phage vB_EliS-R6L is the first virus that can infect marine bacteria belonging to the genus Erythrobacter.TEM micrographs revealed that it belongs to the siphovirus family,with an icosahedral capsid 75.9 ± 2.2 nm in diameter and a characteristically long tail of 165.6± 2.3 nm.The phage has a wide temperature and pH tolerance.With a 65.7-kb genome encoding 108 putative gene products,phage vB_EliS-R6L is novel among the cultured phage community and is largely different than all other known phages.Phage vB_EliS-R6L encodes five methylase proteins,suggesting the potential to overcome host resistance systems.Auxiliary metabolic genes in the phage genome were also annotated,such as those coding for an acyl carrier protein and phosphoadenosine phosphosulfate reductases.Metagenomic recruitment suggest that vB_EliS-R6L-like phages are widely distributed in the marine environment,especially in coastal waters.Based on the vB_DshP-R7L-Roseobacter Shibae DFL12T system,14C-glucose was used for tracing the flux of carbon during the process of phage lysis and the bioavailability of lysate.The results showed that the phage lysis could result in a huge mortality of its hosts,significantly reduced the bacterial respiratory(32.27%),and released 5.21 times more carbon.Based on the phage-host system,the bioavailability of lysate with different particle sizes was explored for the coastal bacterial community of Xiamen.The results showed that the the bacterial productions of the treatments appended with viral lyaste(both<0.3?m and 0.3-0.75?m component)were much higher than that of the cell exudates,suggesting that viral lysate was more labile than cell exudates.After the incubation for 65 days,86.69%of the 14C of<0.3?m viral lyaste was tranfered into inorganic carbon,and 50.98%of the 0.3-0.7 ?m lysate was tranfered,indicating that the labile level of<0.3?m lysate was higher than the 0.3-0.7?m one.In three stations in the South China Sea,four treatments with different virus concentrations,were established.Compared with the virus-inactivated ones,the presence of active virus with same concentration could increase the bacterial respiration by 38.20?81.99%,and inhibit bacterial production and bacterial growth efficiency.However,the impact of the virus upon the bacterial communities differed among the treatments with different concentrations of active viruses,suggesting that the relationship between the viruses and its hosts was complicated and maybe influenced by the virus concentration.The correlation analysis implied that the active virus tended to infect high fluorescence bacteria and likely change the bacterial lifestyle from r-to k-choice.In addition,compared to cell exudates,viral lysate(<100 kDa)was labile and could significantly stimulate the growth of bacterial communities.The ecological role of marine viral lysing was studied before and after the inoculation of algal fragments,with the Aquatron Tower container.The results showed that the addition of algal fragments promoted the increase of bacterial abundance,viral abundance,virus production and the fraction of lysated bacteria within 1 d.And after 2 d,the fraction of lysated bacteria decreased significantly,and the mean values after the inoculation was much lower than that before,suggesting the decreasing top-down control of virus upon bacteria.During the incubation,there was a slight acidification.The correlation analysis showed that acidification could promote the increase of bacterial abundance and the viral production,then the carbon flux of the lysing of bacterial cells by virus may increase.