Although we have gained insight into the biological and biochemical effects of natural sunlight exposure on prokaryotes, little is known about sunlight exposure on natural virus communities. To ...address this question, an investigation of the effects of sunlight and dark treatments on viral communities, viral production and decay rates in Kenting coastal waters was conducted. The average rate of net viral production in the sunlight and dark treatment was 0.010 and 0.018 × 10
6
viruses mL
–1
h
− 1
, respectively. Furthermore, averaged value for viral decay in the sunlight treatment was 0.016 × 10
6
viruses mL
− 1
h
− 1
, a significant decrease (ca. 60%=((0.83 − 0.33)/(0.83 × 100%)) was observed in sunlight conditions, whereas no significant changes occurred in dark conditions. The gross viral production under sunlight conditions was slightly higher, however, non-significantly higher than that in the dark treatment. As a result, we suggest that sunlight damages a large portion of the natural viral community, affecting the role viruses play in food webs.
There is no doubt that seagrass beds constitute one of the most productive ecosystems in shallow coastal waters. Despite this, picoplankton in seagrass ecosystems has received relatively little ...attention. The purpose of this study was to compare picoplankton growth and mortality rates between seagrass and unvegetated habitats using chamber incubations. We tested two main hypotheses: (i) incubation with seagrass would result in higher bacterial growth rates due to increased DOM release from seagrass photosynthesis, and (ii) Synechococcus spp. would be lower in the presence of seagrass due to competition for inorganic nutrients. Bacterial growth rates were higher in seagrass chambers (2.44 d–1) than in non-seagrass chambers (2.31 d−1), respectively, suggesting that organic carbon coming from the seagrass community may support bacterial production. Furthermore, the growth rate of Synechococcus spp. was significantly lower in the seagrass treatment than in the non-seagrass treatment, likely reflecting nutrient competition with the seagrass. Small-scale chambers proved to be a useful tool for studying the factors controlling spatial and temporal patterns of picoplankton across different habitats. Furthermore, future studies should examine picoplankton growth over a wider range of spatial scales in seagrass beds and adjacent unvegetated sediment.
Nanoflagellate grazing and viral lysis are the two main causes of mortality losses of marine bacterioplankton. Deciphering the mortality losses across the water column helps us understand their ...ecological and biogeochemical consequences. In this study, we implemented the two-point modified dilution method consisting of treatment of undiluted and 25% nanoflagellates and/or virus density at the surface (3 m), deep chlorophyll maximum (DCM), and the mesopelagic zone (300 m and 500 m deep) in the subtropical northwestern Pacific Ocean in summer. We found that the bacterial per capita growth (2.3 ± 0.6 d−1) and production (12.4 ± 6.9 μgC L−1 d−1) were significantly higher at the DCM layer than at the mesopelagic zone, possibly because of tight bacteria-phytoplankton coupling and trophic interactions between bacteria, nanoflagellates, and viruses. Further, we found that ∼70% of the bacterial mortality loss can be attributed to nanoflagellate grazing in the DCM layer, while most of the mortality loss in the surface and the mesopelagic zone can be attributed to viral lysis. We argue that while bacterial production is more efficiently transferred to higher trophic levels at the DCM layer, it is predominately recycled in the viral loop on the surface and the mesopelagic zone. Our results reveal the vertical variation of bacterial growth, production, mortality loss to nanoflagellate grazing, and viral lysis, from which we could deduct their depth-dependent impacts on carbon flux in the water column. Our study facilitates the understanding of the impacts of nanoflagellates and viruses on bacterioplankton and the bacteria-mediated biogeochemical cycling.
•In the north Pacific, bacterial growth is higher at the deep chlorophyll a maximum layer in summer.•Bacterial mortality caused by nanoflagellate outweighs viral lysis in the eutrophic zone.•Virus induced mortality is the main mortality cause in the mesopelagic zone.•Impacts of nanoflagellates and viruses on bacterial production are depth-dependent.
In mesoscale eddies, the chemical properties and biological composition are different from those in the surrounding water due to their unique physical processes. The mechanism of physical–biological ...coupling in warm-core eddies is unclear, especially because no studies have examined the effects of environmental factors on bacteria and viruses. The purpose of the present study was to examine the influence of an anticyclonic warm eddy on the relationship between bacterial and viral abundances, as well as viral activity (viral production), at different depths. At the core of the warm eddy, the bacterial abundance (0.48 to 2.82 × 105 cells mL−1) fluctuated less than that outside the eddy (1.12 to 7.03 × 105 cells mL−1). In particular, there was a four-fold higher viral–bacterial abundance ratio (VBR) estimated within the eddy, below the layer of the deep chlorophyll maximum, than outside the eddy. An anticyclonic warm eddy with downwelling at its center may contribute to viruses being transmitted directly into the deep ocean through adsorption on particulate organic matter while sinking. Overall, our findings provide valuable insights into the interaction between bacterial and viral abundances and their ecological mechanisms within a warm eddy.
A seagrass meadow is one of the most important ecosystems around the world, both economically and ecologically. An important feature of this ecosystem is the presence of large coastal seagrass beds, ...which dominate the primary production and contribute to the secondary productivity of the ecosystem. The microbial loop (consuming bacterial biomass by grazers and using seagrass-derived detritus by bacteria) may be an important mechanism for transferring seagrass-derived organic matter to aquatic food chains. The goal of this study is to gain a better understanding of how bacterial growth and mortality (grazing and viral lysis rates) differ in unvegetated meadow habitats and seagrass habitats. According to this study, DOC levels were higher in seagrass habitats (1685 g L−1) than in unvegetated water surroundings. The instantaneous growth rate of bacteria in seagrass habitats was 2.05 d−1, higher than that of unvegetated water. In a seagrass environment during the summer, we have found that viral lysis and grazing both result in similar mortality rates of bacteria during the summer season. It has been found, however, that bacterial production is controlled by the availability of resources (bottom-up control) in adjacent unvegetated waters, and is thus cycled internally within the bacteria–virus–DOC loop within those waters.
Viral production (VP) and bacterial mortality by viral lysis critically influence the production and mortality of aquatic bacteria. Although bacterial production, mortality by viral lysis, and viral ...density have been found to exhibit diel variations, the diel change in viral production has rarely been investigated. In this study, we conducted two diel dilution incubation experiments in a semi-enclosed, nutrient-rich coastal region in northeastern Taiwan to estimate the diel viral production and the mortality by viral lysis. We also compared two methods (linear regression between viral density and time versus arithmetic mean of VP during incubation) of estimating viral production. We found that viral production estimated by linear regression and bacterial mortality by viral lysis were higher during the daytime than during the nighttime. A possible explanation for the high viral production at daytime is that the bacterial community was composed of cell types with higher burst sizes at daytime. We further argued that the classical linear regression method can be used only when viral density significantly linearly increases with time, which does not always occur in dilution incubations. This study offered observations of diel variation in viral dynamics and discussed the methods estimating viral production in a marine environment.
In spite of the fact that the interactions between environmental parameters and prokaryotic and viral abundance have been explored in various aquatic environments, only a few independent estimates of ...viral production and decay in the estuarine region have been explored. In this study, data were analyzed for viral and prokaryotic abundance, viral production, and viral decay in a subtropical Danshui estuary in summer 2021. Prokaryotic abundance varied from 2.4 ± 0.6 × 105 to 12 ± 2.3 × 105 cells mL−1, and viral abundance ranged from 2.3 ± 0.9 × 105 to 6.9 ± 1.3 × 105 viruses mL−1 during the study period. Viral abundance was significantly correlated with prokaryotic abundance and chlorophyll a concentration. Furthermore, studies of changes in viral to prokaryotic abundance ratio (VPR) ranged from 0.42 ± 0.11 to 2.0 ± 0.25. Viral decay values were 2.1 ± 0.5 and 2.1 ± 0.3 × 104 virus mL−1h−1, and non-significant differences were observed between the inner estuary and coastal water region. Viral decay almost balanced gross viral production in this study. The dilution experiments revealed non-significant net viral production in July; thus, a lower VPR might be explained in this estuarine environment.
Viral dynamics are the result of the balance between the rates of viral production and decay. Here, we have carried out independent measurements of viral production and decay rates in different ...depths of the southern East China Sea in summer (August and October 2021). In this study, the prevalence of viral abundance at the surface waters (14.2~27.6 × 105 viruses mL−1) was significantly higher than the bottom of the euphotic zone (2.9~12.6 × 105 viruses mL−1). As for viruses to bacteria ratio (VBR) values, we found a wide variability both at the surface (1.4 to 3.2) and bottom of the euphotic zone (2.1 to 16.2). The results of our study showed that at all stations examined, in the southern East China Sea, the values of gross viral production (GVP) were significantly higher in the sunlit surfaces compared to the bottom of the euphotic zone. In particular, our analysis indicates that no significant viral decay rates (VD) were observed in some regions at the bottom of the euphotic zone. Here, we also provide a budget for viral abundance and net viral production in different regions in the southern East China Sea. The GVP or VD is not applicable in our case to explain VBR is high at bottom of the euphotic zone. The mechanisms underlying VBR uncoupling, viral production, and viral loss in marine systems are still being investigated.
There is no doubt that seagrass beds constitute one of the most productive ecosystems in shallow coastal waters. Despite this, picoplankton in seagrass ecosystems has received relatively little ...attention. The purpose of this study was to compare picoplankton growth and mortality rates between seagrass and unvegetated habitats using chamber incubations. We tested two main hypotheses: (i) incubation with seagrass would result in higher bacterial growth rates due to increased DOM release from seagrass photosynthesis, and (ii) Synechococcus spp. would be lower in the presence of seagrass due to competition for inorganic nutrients. Bacterial growth rates were higher in seagrass chambers (2.44 dsup.–1) than in non-seagrass chambers (2.31 dsup.−1), respectively, suggesting that organic carbon coming from the seagrass community may support bacterial production. Furthermore, the growth rate of Synechococcus spp. was significantly lower in the seagrass treatment than in the non-seagrass treatment, likely reflecting nutrient competition with the seagrass. Small-scale chambers proved to be a useful tool for studying the factors controlling spatial and temporal patterns of picoplankton across different habitats. Furthermore, future studies should examine picoplankton growth over a wider range of spatial scales in seagrass beds and adjacent unvegetated sediment.
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