Effects Of Ocean Acidification On Viral Ecological Characteristics

As the most abundant biological agents in the ocean,viruses are considered to be the major ecological,evolutionary and biogeochemical drivers in marine environment.Via viral infection and lysis,a large number of dissolved organic matters will be released into seawater,thus changing the nutrient and energy cycles of the marine food web.The microbial mortality induced by viruses makes viruses to be powerful agents for controlling the community composition.Meanwhile,viruses are also able to influence the physiological and ecological characteristics of host cells through viral infection and lysis,and play an important role in regulating hosts' diversity,metabolic activity and ecological processes.Ocean acidification,which was induced by increasing anthropogenic carbon dioxide,is modifying marine ecosystem structure and function and has the potential to alter the cycling of carbon and nutrients in the ocean surface.Ocean acidification may have direct and indirect consequences on marine viruses,including the changes of chemical environments,biogeochemical cycles,community compositions and heterotrophic/autotrophic metabolism.The thesis is based on the ecological function of marine viruses and their biogeochemical effects in marine ecosystem.In order to give a new insight into the role of virus in the future marine environments,we combined the studies of virioplankton in the field and the studies of virus-host model system in laboratory and investigated the responses of viral ecological characteristics(such as viral production,viral decay and life strategies)and virus-host interactions to ocean acidification.The results of this thesis can be summarized as follows:1.For a better understanding of the viral dynamics in the context of global climate change,we investigated the effects of elevated CO2(780?atm)on lytic viral production,lysogenic viral production and decay in the western Pacific Ocean and the South China Sea,and the contrast between light and darkness was set up here.We found that elevated CO2 stimulated lytic viral production in light compared with the ambient air,but no significant effect was found in dark,indicating that ocean acidification and light enhanced lytic viral production synergistically.Meanwhile,lysogenic viral production was not affected by elevated CO2 in both light and dark conditions,indicating that viral strategies were not changed by ocean acidification.In addition,no significant difference was found on viral decay between high CO2 concentration and control.However,viral decay was always higher in light contrast to darkness.In this study,light tend to be an important contributing factor for viral decay while elevated CO2 played a relatively minor role in viral decay.Our results indicated that extracellular viruses would be stable in acidified ocean and ocean acidification may stimulate lytic viral production via affecting the hosts or virus-host interactions.2.Direct responses of viruses of heterotrophic bacteria to ocean acidification were investigated under laboratory incubation,here we chose the roseophages R2C(podophage)and R4C(siphophage)to investigate the effects of elevated CO2(ambient air,780?atm,1,050?atm and 2,000?atm)on viral abundance,infectivities and infection cycles.The abundance of two phages remained consistent with different CO2 concentrations,indicating that elevated CO2 did not directly affect the population size of phages.The infectivity of phage R2C was higher in 2,000?atm CO2 than those in other CO2 concentrations,while no significant difference was showed for phage R4C in all CO2 concentrations,indicating that no direct consequence of ranged ocean acidification was found on the infectivities of most viruses of heterotrophic bacteria.In addition,elevated CO2 showed no direct effects on the latent period and?V/?B of phage R4C,indicating that ocean acidification did not change the infection cycle of virus of heterotrophic bacteria.Our results suggested that heterotrophic bacteriophages were quite stable in ranged ocean acidification in absence of other factors.3.To gain new insight into the response of virus of heterotrophic bacteria to ocean acidification,we investigated the effects of extracellular proteases on the abundance,infectivity and infection cycle of roseophage R4C under different CO2 concentrations(ambient air,780?atm and 1,050?atm)by setting up treatments with/without proteinase inhibitors.Lower abundance was found in the groups without proteinase inhibitors and no significant difference was found under different CO2 concentrations in both treatments(with/without proteinase inhibitors).The results verified that extracellular protease play an important role in viral decay.However,the abundance and infectivity of phage R4C in both treatments with and without proteinase inhibitors were decreased during incubation and the infectivity of phage R4C was decreased by elevated CO2 concentration.It implied that some heat labile and high molecular weight dissolved materials appeared responsible for the decay of phage R4C.Furthermore,elevated CO2 would decrease the infectivity of phage R4C combined with heat labile and high molecular weight dissolved materials.Compared with treatments without proteinase inhibitors,a lower infectivity was found in treatments with protease inhibitors.And the proteinase inhibitors were also suggested to be a pressor on the infectivity of phage R4C.In addition,elevated CO2 showed no significant effect on viral infection cycle in both treatments with and without proteinase inhibitors.Our results suggested a complex synthesis effect on viral infectivity in marine systems.4.We investigated the growth rate,Chlorophyll a content,fluorescence parameters(Fv'/Fm`,a,rETRmax and Ik)and carbonate fixation efficiency of Synechococcus CB0101 under different CO2 concentration levels(ambient air and 780?atm).The results showed that elevated C02 stimulated the Chlorophyll a content,rETRmax and Ik of Synechococcus CB0101 before adding cyanophage P1 while carbon fixation show no significant difference between high CO2 concentration and control.The results indicated that elevated CO2 could stimulate the light use efficiency of Synechococcus CBO101 and possibly enhance the absorption of light.However,elevated CO2 may enhance the consumption of matter and energy.Therefore,elevated CO2 is likely to promote the metabolism of Synechococcus CB0101.The Chlorophyll a content of Synechococcus CB0101 was increased by viral infection in both C02 concentrations while the fluorescence parameters(Fv'/Fm',?,rETRmax and Ik)were significantly decreased.During the infection,carbon fixation was increased in both CO2 concentrations and no significant difference was found between high C02 concentration and control.However,the Chlorophyll a content of Synechococcus CB0101 may increase the absorption of light while light energy conversion efficiency was declined.Moreover,the parameters of Ik and AV/AB were higher in high C02 concentrations after adding cyanophage P1.Overall,ocean acidification may affect the metabolism of Synechococcus and the interactions of Synechococcus and its cyanophage,which would contribute to viral produciton.