Herbicides have been increasingly used worldwide and a large amount of herbicide residue eventually enters the ocean via groundwater or surface run-off every year. However, the global coastal ...pollution status of herbicides and their negative impact on marine life (especially phytoplankton) in natural environmental concentrations are poorly understood except for few special environments (e.g. the Great Barrier Reef, Australia). Our field investigation of the distribution of ten triazine herbicides in the Bohai Sea and the Yellow Sea of China revealed that the concentrations of triazine herbicides exceeded the “No Observed Effect Concentrations” for phytoplankton. Their total concentrations could be as high as 6.61 nmol L−1. Based on the concentration addition model, the toxicity of herbicide homologues is usually cumulative, and the combined toxicity of these ten triazine herbicides could cause 13.2% inhibition on the chlorophyll a fluorescence intensity of a representative diatom species Phaeodactylum tricornutum Pt-1, which corresponds roughly to the toxicity of atrazine in an equivalent concentration of 14.08 nmol L−1. Atrazine in this equivalent-effect concentration could greatly inhibit the growth of cells, the maximum quantum efficiency of photosystem II (Fv/Fm), and nutrient absorption of Phaeodactylum tricornutum Pt-1. Transcriptome analysis revealed that multiple metabolic pathways (Calvin cycle, tricarboxylic acid (TCA) cycle, glycolysis/gluconeogenesis, etc.) related with photosynthesis and carbon metabolism were greatly disturbed, which might ultimately influence the primary productivity of coastal waters. Moreover, with the values of its bioaccumulation factor ranging from 69.6 to 118.9, atrazine was found to be accumulated in algal cells, which indicates that herbicide pollution might eventually affect the marine food web and even threaten the seafood safety of human beings.
Abbreviations: CAGR, Compound annual growth rate (%); PS I/II, photosystem I/II; N, NO3-N, NO2-N, and NH4-N; P, PO4-P; Si, SiO4-Si. Data on global herbicide usage in this figure are from the databases of the Food and Agriculture Organization of the United Nations (http://www.fao.org/statistics/databases/en/) and the following references (Gu and Wang, 2016; Archbold and Nosarzewski, 2018; GlobeNewswire, 2017). Display omitted
•Total concentration of 10 triazine herbicides in coastal waters reached risk levels.•Triazine herbicides at environmental concentrations showed toxic effects on diatom.•Atrazine can be highly accumulated in algal cells.•The photosynthesis and carbon metabolism of diatom were significantly disturbed.•Coastal pollution of herbicide is a growing threat to primary productivity.
Picocyanobacteria make up half of the ocean's primary production, and they are subjected to frequent viral infection. Viral lysis of picocyanobacteria is a major driving force converting biologically ...fixed carbon into dissolved organic carbon (DOC). Viral-induced dissolved organic matter (vDOM) released from picocyanobacteria provides complex organic matter to bacterioplankton in the marine ecosystem. In order to understand how picocyanobacterial vDOM are transformed by bacteria and the impact of this process on bacterial community structure, viral lysate of picocyanobacteria was incubated with coastal seawater for 90 days. The transformation of vDOM was analyzed by ultrahigh-resolution mass spectrometry and the shift of bacterial populations analyzed using high-throughput sequencing technology. Addition of picocyanobacterial vDOM introduced abundant nitrogen components into the coastal water, which were largely degraded during the 90 days' incubation period. However, some DOM signatures were accumulated and the total assigned formulae number increased over time. In contrast to the control (no addition of vDOM), bacterial community enriched with vDOM changed markedly with increased biodiversity indices. The network analysis showed that key bacterial species formed complex relationship with vDOM components, suggesting the potential correspondence between bacterial populations and DOM molecules. We demonstrate that coastal bacterioplankton are able to quickly utilize and transform lysis products of picocyanobacteria, meanwhile, bacterial community varies with changing chemodiverisity of DOM. vDOM released from picocyanobacteria generated a complex labile DOM pool, which was converted to a rather stable DOM pool after microbial processing in the time frame of days to weeks.
To test the hypothesis that different drivers shape the diversity and biogeography of the total and active bacterial community, we examined the bacterial community composition along two transects, ...one from the inner Pearl River estuary to the open waters of the South China Sea (SCS) and the other from the Luzon Strait to the SCS basin, using 454 pyrosequencing of the 16S rRNA and 16S rRNA gene (V1‐3 regions) and thereby characterizing the active and total bacterial community, respectively. The diversity and biogeographic patterns differed substantially between the active and total bacterial communities. Although the composition of both the total and active bacterial community was strongly correlated with environmental factors and weakly correlated with geographic distance, the active bacterial community displayed higher environmental sensitivity than the total community and particularly a greater distance effect largely caused by the active assemblage from deep waters. The 16S rRNA vs. rDNA relationships indicated that the active bacteria were low in relative abundance in the SCS. This might be due to a high competition between active bacterial taxa as indicated by our community network models. Based on these analyses, we speculate that high competition could cause some dispersal limitation of the active bacterial community resulting in a distinct distance‐decay relationship. Altogether, our results indicated that the biogeographic distribution of bacteria in the SCS is the result of both environmental control and distance decay.
Viruses are ubiquitous and cause significant mortality in marine bacterial and archaeal communities. Little is known about the role of viruses in the sub-seafloor biosphere, which hosts a large ...fraction of all microbes on Earth. We quantified and characterized viruses in sediments from the Baltic Sea. The results show that the Baltic Sea sub-seafloor biosphere harbors highly abundant viruses with densities up to 1.8 × 10
viruses cm
. High potential viral production down to 37 meters below seafloor in ca. 6000-years-old sediments and infected prokaryotic cells visible by transmission electron microscopy demonstrate active viral infection. Morphological and molecular data indicate that the highly diverse community of viruses includes both allochthonous input from the overlying seawater and autochthonous production. The detection of cyanophage-like sequences showed that viruses of phototrophic hosts may persist in marine sediments for thousands of years. Our results imply that viruses influence sub-seafloor microbial community dynamics and thereby affect biogeochemical processes in the sub-seafloor biosphere.
•The slope of AOU–FDOMH relationship is the proxy of RDOM production efficiency.•A global comparable oceanic AOU–FDOMH relationship dataset is obtained.•The general tendencies of the slope of ...AOU–FDOMH relationship were discussed.•Factors that may affect the AOU–FDOMH relationship are summarized.•Applicable at a global scale in future studies are proposed.
The mechanism behind the source/production of refractory dissolved organic matter (RDOM) in the ocean remains an enigma, but the biological origin of RDOM has now been recognized and conceptualized as the microbial carbon pump (MCP). Consequently, the development of a proxy for the efficiency of the MCP production of RDOM is desirable. It has widely been observed that marine humic-like fluorescent dissolved organic matter (FDOMH) is linearly correlated with apparent oxygen utilization (AOU), and hence it is promising for exploring this relationship. Here, we discuss whether the slope of the AOU–FDOMH correlation can be an indicator for evaluating the MCP efficiency in the dark ocean. We gathered all the peer-reviewed literature on AOU–FDOMH relationships and summarized the general results and factors that may affect this relationship. Finally, we propose to make the AOU–FDOMH relationship comparable and applicable at a global scale in future studies to better constrain sources and sinks of FDOMH and its link to heterotrophic microbial respiration, namely, the FDOM-based MCP efficiency.
Particle sinking is an important process in the ocean, influencing the biogeochemical cycle and driving the long-term preservation of carbon into the deep sea via the biological pump. However, as an ...important component of marine ecosystems, the role of viruses during sinking is still poorly understood. Therefore, we performed a series of transplantation experiments in the South China Sea to simulate environmental changes during sinking and investigate their effects on viral eco-dynamics and life strategy. Our study demonstrated increased viral production but decreased virus-mediated bacterial mortality after transplantation. A larger burst size and switch from the lysogenic to lytic strategy were shown to contribute to enhanced viral productivity. We provide experimental evidence that surface viral ecological characteristics changed dramatically after transplantation into deep-sea waters, indicating a potential importance of viruses during vertical sinking in the ocean. This effect probably provides positive feedback on the efficiency of the biological pump.
The Cyanobacteria Prochlorococcus and Synechococcus account for a substantial fraction of marine primary production. Here, we present quantitative niche models for these lineages that assess present ...and future global abundances and distributions. These niche models are the result of neural network, nonparametric, and parametric analyses, and they rely on >35,000 discrete observations from all major ocean regions. The models assess cell abundance based on temperature and photosynthetically active radiation, but the individual responses to these environmental variables differ for each lineage. The models estimate global biogeographic patterns and seasonal variability of cell abundance, with maxima in the warm oligotrophic gyres of the Indian and the western Pacific Oceans and minima at higher latitudes. The annual mean global abundances of Prochlorococcus and Synechococcus are 2.9 ± 0.1 × 10 ²⁷ and 7.0 ± 0.3 × 10 ²⁶ cells, respectively. Using projections of sea surface temperature as a result of increased concentration of greenhouse gases at the end of the 21st century, our niche models projected increases in cell numbers of 29% and 14% for Prochlorococcus and Synechococcus , respectively. The changes are geographically uneven but include an increase in area. Thus, our global niche models suggest that oceanic microbial communities will experience complex changes as a result of projected future climate conditions. Because of the high abundances and contributions to primary production of Prochlorococcus and Synechococcus , these changes may have large impacts on ocean ecosystems and biogeochemical cycles.
Podoviruses are among the major viral groups that infect marine picocyanobacteria Prochlorococcus and Synechococcus. Here, we reported the genome sequences of five Synechococcus podoviruses isolated ...from the estuarine environment, and performed comparative genomic and phylogenomic analyses based on a total of 20 cyanopodovirus genomes. The genomes of all the known marine cyanopodoviruses are highly syntenic. A pan-genome of 349 clustered orthologous groups was determined, among which 15 were core genes. These core genes make up nearly half of each genome in length, reflecting the high level of genome conservation among this cyanophage type. The whole genome phylogenies based on concatenated core genes and gene content were highly consistent and confirmed the separation of two discrete marine cyanopodovirus clusters MPP-A and MPP-B. The genomes within cluster MPP-B grouped into subclusters mainly corresponding to Prochlorococcus or Synechococcus host types. Auxiliary metabolic genes tend to occur in a specific phylogenetic group of these cyanopodoviruses. All the MPP-B phages analyzed here encode the photosynthesis gene psbA, which are absent in all the MPP-A genomes thus far. Interestingly, all the MPP-B and two MPP-A Synechococcus podoviruses encode the thymidylate synthase gene thyX, while at the same genome locus all the MPP-B Prochlorococcus podoviruses encode the transaldolase gene talC. Both genes are hypothesized to have the potential to facilitate the biosynthesis of deoxynucleotide for phage replication. Inheritance of specific functional genes could be important to the evolution and ecological fitness of certain cyanophage genotypes. Our analyses demonstrate that cyanopodoviruses of estuarine and oceanic origins share a conserved core genome and suggest that accessory genes may be related to environmental adaptation.
Tangential flow filtration (TFF), which has been widely adopted to concentrate a diverse array of microbes from water, is a promising method of microbial separation or removal. However, it is ...essential to select an optimal membrane suitable for the specific filtration application. This study evaluated two different scales of TFF systems for concentrating and separating microbes (including bacteria and viruses) from contrasting marine waters. Among bacteria-size membranes, polyvinylidene difluoride (PVDF) membranes showed higher bacterial recovery, but lower viral permeation efficiencies than polyethersulfone (PES) membranes, regardless of environments and scales of TFF. Estuary samples showed significantly higher percentages of bacterial retention than nearshore and ocean samples. For virus-size membranes, a higher viral recovery and lower sorption was observed for regenerated cellulose membrane than PES membranes in the small-scale TFF. Similar viral recoveries were observed between PES membranes in the large-scale TFF, with higher viral concentrations being observed in estuary samples than in nearshore samples. Deep ocean samples showed the lowest recovery of viruses, which was consistent with observations of bacterial recovery. Synthetically, PVDF may be more suitable for the concentration of bacterial cells, while PES would be a better choice for the collection of viruses. When compared with the PES membrane, regenerated cellulose is better for viral concentration, while PES is recommended to obtain bacteria- and virus-free seawater.
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