Oscillations of algal cell quota: Considering two-stage phosphate uptake kinetics.

Elucidating the mechanism of effect of phosphate (PO43-) uptake on the growth of algal cells helps understand the frequent outbreaks of algal blooms caused by eutrophication. In this study, we develop a comprehensive mathematical model that incorporates two stages of PO43- uptake and accounts for transport time delay. The model parameter values are determined by fitting experimental data of Prorocentrum donghaiense and the model is validated using experimental data of Karenia mikimotoi. The numerical results demonstrate that the model successfully captures the general characteristics of algal growth and PO43- uptake under PO43- sufficient conditions. Significantly, the experimental and mathematical findings suggest that the time delay associated with the transfer of PO43- from the surface-adsorbed PO43- (Ps) pool to the intracellular PO43- (Pi) pool may serve as a physiologically plausible mechanism leading to oscillations of algal cell quota. These results have important implications for resource managers, enabling them to predict and deepen their understanding of harmful algal blooms.

Nutrient Deficiency and an Algicidal Bacterium Improved the Lipid Profiles of a Novel Promising Oleaginous Dinoflagellate, Prorocentrum donghaiense, for Biodiesel Production.

The lipid production potentials of 8 microalgal species were investigated. Among these 8 species, the best strain was a dominant bloom-causing dinoflagellate, Prorocentrum donghaiense; this species had a lipid content of 49.32% ± 1.99% and exhibited a lipid productivity of 95.47 ± 0.99 mg liter-1 day-1, which was 2-fold higher than the corresponding values obtained for the oleaginous microalgae Nannochloropsis gaditana and Phaeodactylum tricornutum. P. donghaiense, which is enriched in C16:0 and C22:6, is appropriate for commercial docosahexaenoic acid (DHA) production. Nitrogen or phosphorus stress markedly induced lipid accumulation to levels surpassing 75% of the dry weight, increased the C18:0 and C17:1 contents, and decreased the C18:5 and C22:6 contents, and these effects resulted in decreases in the unsaturated fatty acid levels and changes in the lipid properties of P. donghaiense such that the species met the biodiesel specification standards. Compared with the results obtained under N-deficient conditions, the enhancement in the activity of alkaline phosphatase of P. donghaiense observed under P-deficient conditions partly alleviated the adverse effects on the photosynthetic system exerted by P deficiency to induce the production of more carbohydrates for lipogenesis. The supernatant of the algicidal bacterium Paracoccus sp. strain Y42 culture lysed P. donghaiense without decreasing its lipid content, which resulted in facilitation of the downstream oil extraction process and energy savings through the lysis of algal cells. The Y42 supernatant treatment improved the lipid profiles of algal cells by increasing their C16:0, C18:0, and C18:1 contents and decreasing their C18:5 and C22:6 contents, which is favorable for biodiesel production. IMPORTANCE This study demonstrates the high potential of Prorocentrum donghaiense, a dominant bloom-causing dinoflagellate, for lipid production. Compared with previously studied oleaginous microalgae, P. donghaiense exhibit greater potential for practical application due to its higher biomass and lipid contents. Nutrient deficiency and the algicidal bacterium Paracoccus sp. strain Y42 improved the suitability of the lipid profile of P. donghaiense for biodiesel production. Furthermore, Paracoccus sp. Y42 effectively lysed algal cells, which facilitates the downstream oil extraction process for biodiesel production and results in energy savings through the lysing of algal cells. This study provides a more promising candidate for the production of docosahexaenoic acid (DHA) for human nutritional products and of microalgal biofuel as well as a more cost-effective method for breaking algal cells. The high lipid productivity of P. donghaiense and algal cell lysis by algicidal bacteria contribute to reductions in the production cost of microalgal oil.

The potential of prodigiosin for control of Prorocentrum donghaiense blooms: Algicidal properties and acute toxicity to other marine organisms at various trophic levels.

Prorocentrum donghaiense, a marine dinoflagellate, causes harmful algal blooms (HABs) characterised by the highest outbreak frequency and most extensive coverage among similar species in the East China Sea. Highly efficient and ecofriendly biocontrol strategies should be developed for HAB control. Prodigiosin is an efficient biological algicide that demonstrated strong algicidal activity towards P. donghaiense. However, the mechanism of its toxicity to P. donghaiense is unknown. These factors were investigated to evaluate potential use of prodigiosin for control of P. donghaiense blooms. Photosynthetic electron transport rate, maximum quantum yield and respiration rate of P. donghaiense decreased significantly upon exposure to prodigiosin, indicating that prodigiosin rapidly exerted adverse effects on the chloroplasts and mitochondria. Furthermore, a significant increase in dichlorofluorescein fluorescence intensity indicated an overproduction of reactive oxygen species (ROS). The antioxidant system of P. donghaiense scavenged ROS; however, an increase in malondialdehyde concentrations indicated that excessive ROS were still able to initiate lipid peroxidation. Thus, ROS production resulted in the formation of lipids with a reduced degree of unsaturation. Lipid peroxidation decreased lipid fluidity and rigidified the membrane system, causing serious functional destruction of the membrane. Flow cytometry analysis indicated that prodigiosin arrested the cell cycle of P. donghaiense. However, surviving algal cells were able to repair the damaged functions and resume the cell cycle after prodigiosin was removed by photodegradation. Otherwise, P. donghaiense cells lost their membrane integrity and died. To begin an evaluation of ecological safety of prodigiosin, we tested four marine organisms at various trophic levels. The results of these tests indicated that Chlorella vulgaris, Photobacterium phosphoreum, Artemia salina and Lateolabrax japonicus were less sensitive to prodigiosin than P. donghaiense. Toxicity to all five organisms declined after prodigiosin was exposed to sunlight for 6 h. Considering the toxic doses of prodigiosin to various organisms and its photodegradation characteristics, we suggest that prodigiosin has potential in controlling P. donghaiense blooms but should be applied at night, in small doses, with multiple applications.

Programmed cell death induced by modified clay in controlling Prorocentrum donghaiense bloom.

Modified clay (MC), an effective material used for the emergency elimination of algal blooms, can rapidly reduce the biomass of harmful algal blooms (HABs) via flocculation. After that, MC can still control bloom population through indirect effects such as oxidative stress, which was initially proposed to be related to programmed cell death (PCD) at molecular level. To further study the MC induced cell death in residual bloom organisms, especially identifying PCD process, we studied the physiological state of the residual Prorocentrum donghaiense. The experimental results showed that flocculation changed the physiological state of the residual cells, as evidenced by growth inhibition and increased reactive oxygen species production. Moreover, this research provides biochemical and ultrastructural evidence showing that MC induces PCD in P. donghaiense. Nuclear changes were observed, and increased caspase-like activity, externalization of phosphatidylserine and DNA fragmentation were detected in MC-treated groups and quantified. And the mitochondrial apoptosis pathway was activated in both MC-treated groups. Besides, the features of MC-induced PCD in a unicellular organism were summarized and its concentration dependent manner was proved. All our preliminary results elucidate the mechanism through which MC can further control HABs by inducing PCD and suggest a promising application of PCD in bloom control.

Alkaline phosphatase activities and regulation in three harmful Prorocentrum species from the coastal waters of the East China Sea.

Harmful blooms of Prorocentrum donghaiense occur annually in the phosphorus-scarce coastal waters of the East China Sea (ECS). The enzymatic activities of alkaline phosphatase (AP) and its regulation by external phosphorus were studied during a P. donghaiense bloom in this area. The AP characteristics of P. donghaiense was further compared with Prorocentrum minimum and Prorocentrum micans in monocultures with both bulk and single-cell enzyme-labeled fluorescence AP assays. Concentrations of dissolved inorganic phosphorus (DIP) varied between 0.04 and 0.73 µmol l-1, with more than half recording stations registering concentrations below 0.10 µmol l-1. Concentrations of dissolved organic phosphorus (DOP) were comparable or even higher than those of DIP. P. donghaiense suffered phosphorus stress and expressed abundant AP, especially when DIP was lower than 0.10 µmol l-1. The AP activities showed a negative correlation with DIP but a positive correlation with DOP. The AP activities were also regulated by internal phosphorus pool. The sharp increase in AP activities was observed until cellular phosphorus was exhausted. Most AP of P. donghaiense was located on the cell surface and some were released into the water with time. Compared with P. minimum and P. micans, P. donghaiense showed a higher AP affinity for organic phosphorus substrates, a more efficient and energy-saving AP expression quantity as a response to phosphorus deficiency. The unique AP characteristic of P. donghaiense suggests that it benefits from the efficient utilization of DOP, and outcompete other species in the phosphorus-scarce ECS.

Effects of multiwalled carbon nanotubes on the dissolved organic matter released by Prorocentrum donghaiense: Results of spectroscopic studies.

Many reports have investigated the effects of carbon nanotubes (CNTs) on the properties of terrestrial dissolved organic matter (DOM), which could significantly altered its binding affinity for contaminants. However, the effects of CNTs on algogenic DOM are largely unknown. To address this issue, the properties of algogenic DOM released by Prorocentrum donghaiense (P. donghaiense-DOM) under the stress from 0.1 to 10.0 mg/L graphitized multiwalled CNTs were nondestructively characterized by the use of UV-visible absorption and fluorescence excitation-emission matrices with parallel factor analysis. The results showed that the changes in the properties of P. donghaiense-DOM were highly dependent on the CNTs concentration. The properties of P. donghaiense-DOM under 0.1 mg/L CNTs treatment showed no obvious differences compared to the control. The addition of 0.5-10.0 mg/L CNTs changed the release pathways of P. donghaiense-DOM, resulting in significant alterations to the properties of P. donghaiense-DOM. The aromaticity, molecular weight, protein-like and humic-like components were enhanced under stress from 0.5 to 1.0 mg/L CNTs on day 4, which can be ascribed to the overproduction of extracellular DOM (EDOM) that occurred in response to the significant increase in intracellular ROS levels. CNTs at 5.0 and 10.0 mg/L significantly induced membrane damage to P. donghaiense on day 4, which led to the leakage of intracellular DOM (IDOM) and then increased the molecular weight and protein-like components but decreased the aromaticity and humic-like components. After the P. donghaiense recovered to its normal growth under 0.5-10.0 mg/L CNTs treatments, the changes in the properties of P. donghaiense-DOM were attributed to the release pathways of P. donghaiense-DOM that were governed by the production of EDOM and the leakage of IDOM in the stationary and declining phases, respectively.

Algicidal Activity of Novel Marine Bacterium Paracoccus sp. Strain Y42 against a Harmful Algal-Bloom-Causing Dinoflagellate, Prorocentrum donghaiense.

Prorocentrum donghaiense blooms occur frequently in the Yangtze River estuary and the adjacent East China Sea. These blooms have damaged marine ecosystems and caused enormous economic losses over the past 2 decades. Thus, highly efficient, low-cost, ecofriendly approaches must be developed to control P. donghaiense blooms. In this study, a bacterial strain (strain Y42) was identified as Paracoccus sp. and was used to lyse P. donghaiense The supernatant of the strain Y42 culture was able to lyse P. donghaiense, and the algicidal activity of this Y42 supernatant was stable with different temperatures and durations of light exposure and over a wide pH range. In addition to P. donghaiense, Y42 showed high algicidal activity against Alexandrium minutum, Scrippsiella trochoidea, and Skeletonema costatum, suggesting that it targets primarily Pyrrophyta. To clarify the algicidal effects of Y42, we assessed algal lysis and determined the chlorophyll a contents, photosynthetic activity, and malondialdehyde contents of P. donghaiense after exposure to the Y42 supernatant. Scanning electron microscopy and transmission electron microscopy analyses showed that the Y42 supernatant disrupted membrane integrity and caused algal cell breakage at the megacytic zone. Photosynthetic pigment loss and significant declines in both photosynthetic efficiency and the electron transport rate indicated that the Y42 supernatant damaged the photosynthetic system of P. donghaiense Malondialdehyde overproduction indicated that the Y42 supernatant caused lipid peroxidation and oxidative damage to membrane systems in the algal cell, ultimately leading to death. The findings of this study reveal the potential of Y42 to remove algal cells from P. donghaiense blooms.IMPORTANCEP. donghaiense is one of the most common dinoflagellate species that form harmful algal blooms, which frequently cause serious ecological pollution and pose health hazards to humans and other animals. Screening for bacteria with high algicidal activity against P. donghaiense and studying their algicidal processes and characteristics will contribute to an understanding of their algicidal effects and provide a theoretical basis for preventing algal blooms and reducing their harm to the environment. This study reports the algicidal activity and characteristics of Paracoccus against P. donghaiense The stability of the algicidal activity of Paracoccus in different environments (including different temperature, pH, and sunlight conditions) indicates its potential for use in the control of P. donghaiense blooms.

Transcriptome analysis of the bloom-forming dinoflagellate Prorocentrum donghaiense exposed to Ginkgo biloba leaf extract, with an emphasis on photosynthesis.

Ginkgo biloba leaf extract (GBE) can effectively treat bloom-forming freshwater algae. However, there is limited information about the underlying suppression mechanism of the marine bloom-forming Prorocentrum donghaiense-the most dominant algal bloom species in the East China Sea. We investigated the effect of GBE on P. donghaiense in terms of its response to photosynthesis at the molecular/omic level. In total, 93,743 unigenes were annotated using six functional databases. Furthermore, 67,203 differentially expressed genes (DEGs) were identified in algae treated with 1.8 g∙L-1 GBE. Among these DEGs, we identified the genes involved in photosynthesis. PsbA, PsbB and PsbD in photosystem II, PsaA in photosystem I, and PetB and PetD in the cytochrome b6/f complex were downregulated. Other related genes, such as PsaC, PsaE, and PsaF in photosystem I; PetA in the cytochrome b6/f complex; and atpA, atpD, atpH, atpG, and atpE in the F-type H+-ATPase were upregulated. These results suggest that the structure and activity of the complexes were destroyed by GBE, thereby inhibiting the electron flow between the primary and secondary quinone electron acceptors, primary quinone electron acceptor, and oxygen-evolving complex in the PSII complex, and interrupting the electron flow between PSII and PSI, ultimately leading to a decline in algal cell photosynthesis. These findings provide a basis for understanding the molecular mechanisms underlying P. donghaiense exposure to GBE and a theoretical basis for the prevention and control of harmful algal blooms.

Allelochemicals of Alexandrium tamarense and its algicidal mechanism for Prorocentrum donghaiense and Heterosigma akashiwo.

The effects of culture filtrate of Alexandrium tamarense on Prorocentrum donghaiense and Heterosigma akashiwo were investigated, including determination of algal density, photosynthesis, intracellular enzyme content and activity. The filtrate of A. tamarense had a stronger inhibitory effect on P. donghaiense than H. akashiwo, and the inhibitory effect decreased with higher temperature treatment of the filtrate. Instantaneous fluorescence (Ft) and maximum quantum yield of photosystem II (Fv/Fm) values of both kinds of target algae were reduced as exposed to the filtrate of A. tamarense, which proved that allelopathy could inhibit the normal operation of photosynthetic system. The increase of Malondialdehyde (MDA) content of the two kinds of target algae indicated that the cell membrane was seriously damaged by allelochemicals released by A. tamarense. The different responses of Superoxide Dismutase (SOD) and Catalase (CAT) activity in two kinds of target algae demonstrated the complexity and diversity of allelopathic mechanism. The filtrate of A. tamarense also influenced the metabolic function (ATPases) of P. donghaiense and H. akashiwo, and the influence on P. donghaiense was greater. Liquid-liquid extraction was used to extract and isolate allelochemicals from the filtrate of A. tamarense. It was found that only component I with molecular weight of 424.2573 and 434.2857 could inhibit the growth of P. donghaiense by HPLC-MS.

Exploring the Biosynthetic Possibilities of Hydroxylated Polybrominated Diphenyl Ethers from Bromophenols in Prorocentrum donghaiense: Implications for Bioremediation.

Bromophenols has been proven to synthesize hydroxylated polybrominated diphenyl ethers (OH-PBDEs), which may pose additional environmental and health risks in the process of bioremediation. In this study, the removal of 2,4-dibromophenol (2,4-DBP) and 2,4,6-tribromophenol (2,4,6-TBP) and the biosynthetic of OH-PBDEs by Prorocentrum donghaiense were explored. The removal efficiencies of 2,4-DBP and 2,4,6-TBP ranged from 32.71% to 76.89% and 31.15% to 78.12%, respectively. Low concentrations of 2,4-DBP stimulated algal growth, while high concentrations were inhibitory. Furthermore, exposure to 10.00 mg L-1 2,4-DBP resulted in the detection of 2'-hydroxy-2,3',4,5'-tetrabromodiphenyl ether (2'-OH-BDE-68) within P. donghaiense. In contrast, increasing concentrations of 2,4,6-TBP considerably inhibited P. donghaiense growth, with 4'-hydroxy-2,3',4,5',6-pentabromodiphenyl ether (4'-OH-BDE-121) detected within P. donghaiense under 5.00 mg L-1 2,4,6-TBP. Metabolomic analysis further revealed that the synthesized OH-PBDEs exhibited higher toxicity than their precursors and identified the oxidative coupling as a key biosynthetic mechanism. These findings confirm the capacity of P. donghaiense to remove bromophenols and biosynthesize OH-PBDEs from bromophenols, offering valuable insights into formulating algal bioremediation to mitigate bromophenol contamination.

Effect of dissolved organic nutrients on the bloom of Prorocentrum donghaiense in the East China Sea coastal waters.

Prorocentrum donghaiense blooms occur annually in the East China Sea coastal waters, degrading ecosystem functions and impeding economic development. Dissolved organic nitrogen and phosphorus (DON and DOP) are the main components in the marine nutrient pools and are closely related to harmful algal blooms. From April to June 2019, a survey was conducted along the East China Sea coast (Sansha and Lianjiang counties) to investigate the relationship between dissolved organic nutrients and P. donghaiense bloom. Our findings showed that dinoflagellates dominated the phytoplankton community, and dissolved organic nutrients were the major factors influencing community structure during the P. donghaiense bloom. Redundancy analysis indicated that P. donghaiense abundance was primarily affected by DON in the Sansha area while it was primarily affected by DON and DOP in the Lianjiang area. Correlation analysis also confirmed a strong positive correlation between dissolved organic nutrients and P. donghaiense abundance both in the Sansha and Lianjiang coastal areas (p < 0.001). Furthermore, a culture experiment was carried out during the bloom to further investigate the effect of dissolved organic nutrients on the phytoplankton community structure. After 10 days of culture, dinoflagellates' relative abundance decreased from 97.1% to 28.2% in the inorganic treatment, whereas dinoflagellates continued to dominate the phytoplankton community in the organic treatment (76.9%). As a result, we propose that dissolved organic nutrients are responsible for the P. donghaiense bloom outbreak and promote the phytoplankton community shift from diatoms to dinoflagellates.

Easy detection of Prorocentrum donghaiense by polymerase chain reaction-nucleic acid chromatography strip.

In recent years, Prorocentrum donghaiense, as a dominant species, has ranked first in terms of cumulative number and area of algal blooms in the East China Sea. In this study, the D1-D2 region of the large ribosomal subunit of P. donghaiense was used as the target gene, and specific primers DH-FP/DH-RP were designed according to the species-specific region of the target gene. An easy, sensitive and visual detection method refered to as polymerase chain reaction-nucleic acid chromatography strip (PCR-NACS) was established for P. donghaiense. The optimized parameters of the PCR amplification system are as follows: primer concentration, 0.15 µM; annealing temperature, 62 °C; and Mg2+ concentration, 1.5 mM. The specificity test showed that PCR-NACS was exlusively specific for the detection of the target algae. The sensitivity test show that the lowest detection limit (LDL) of PCR-NACS was 2.7 × 10-2 ng·µL-1 for genomic DNA and 3.58 × 102 copies·µL-1 for plasmid DNA, respectively. The tests using both genomic DNA and plasmid DNA as templates showed that the sensitivity of PCR-NACS was 10 times higher than that of ordinary PCR. The stability test showed that the interfering algal species did not affect the detection of the target algae by PCR-NACS. In addition, the test with simulated natural samples containing target algae showed that the LDL of PCR-NACS could reach 1.27 × 101 cells·mL-1. In summary, the PCR-NACS established in this study may provide a new method for easy identification of P. donghaiense in natural water samples.

Ecotoxicology of Polymetallic Nodule Seabed Mining: The Effects of Cobalt and Nickel on Phytoplankton Growth and Pigment Concentration.

In order to improve the understanding of the environmental impacts of polymetallic nodule mining, ecotoxicological studies were conducted on the growth of model phytoplankton species Skeletonema costatum and Prorocentrum donghaiense using cobalt and nickel. This study evaluated various physiological and ecological indicators, such as cell proliferation, chlorophyll a, pigments, total protein, and antioxidant enzyme markers. The results show that the introduction of low amounts of cobalt or nickel increased the growth rate of phytoplankton. The phytoplankton benefited from low concentrations of cobalt and nickel stress. The increased protein levels and decreased activity of antioxidant enzymes considerably impacted physiological responses during the promotion of cell abundance. High concentrations of cobalt or nickel resulted in decreased light-absorbing pigments, increased photoprotective pigments, an inactive chlorophyll content, decreased total proteins, and maximal antioxidant enzyme activity in phytoplankton. Throughout the experiment, both the phytoplankton protein and enzyme activity declined with prolonged stress, and the cells underwent age-induced damage. Thus, seabed mining's repercussions on phytoplankton could result in both short-term growth promotion and long-term damage. These consequences depend on the impurity concentrations infiltrating the water, their duration, and the organism's physiological responses.

[Effects of Polyethylene Microplastics on Growth and Halocarbon Release of Marine Microalgae].

Volatile halocarbons (VHCs) are important trace greenhouse gases and ozone-destroying substances and play an important role in global climate change. As an important producer of VHCs, the release of VHCs by marine microalgae is affected by marine environmental factors. Microplastics are an important pollutant in the ocean; however, there are few studies on VHCs release from marine microalgae under the influence of microplastics. This study aimed to explore the effects of different concentrations of polyethylene (PE) microplastics on the growth, photosynthesis, oxidative stress, and release of VHCs by diatoms and dinoflagellates by measuring the density of algae, maximum photoquantum efficiency (Fv/Fm), reactive oxygen species (ROS), and concentration of VHCs. The results revealed that PE microplastics mainly inhibited the growth of Nitzschia closterium f. minutissima and promoted the growth of Prorocentrum donghaiense. The addition of 50 µm PE microplastics had a shielding effect on the growth of the two microalgae, resulting in the inhibition of Fv/Fm of two kinds of microalgae, and the inhibition effect of PE microplastics on P. donghaiense was more significant. Compared with that in the control group, PE microplastic stress stimulated the increase in ROS production in algal cells, which caused an oxidative stress response in these microalgae, thereby promoting the release of three types of volatile brominated halocarbons.

Establishment of a multiplex polymerase chain reaction detection assay for three common harmful microalgae in the East China Sea.

It is urgent to develop techniques that can simultaneously detect multiple microalgae, due to the diversity of harmful algal blooms (HABs)-forming algal species. The target algae species in this study are Heterosigma akashiwo, Prorocentrum donghaiense and Karenia mikimotoi. These algae are the dominant species that cause HABs in the East China Sea, and the multiple detection technique focusing on these three algae is not common. Therefore, this study established a multiplex polymerase chain reaction(mPCR) to diagnose the three algae, which is simple and low cost. First, the corresponding specific primers were designed based on the D1-D2 region of the large subunit (LSU) ribosomal DNA sequence. Then, mPCR was established and the reaction conditions were optimized. And the specificity, sensitivity, and stability of mPCR were evaluated. The result of specificity test showed that the established mPCR had good specificity for the target microalgae and did not cross-react with eighteen non-target microalgae. The sensitivity of experiment was 3.3 × 10-1 ng µL-1, and the established mPCR was not affected by the interfering microalgae. Moreover, the practicability evaluation of mPCR by using the simulated natural water samples showed that the detection limit of target microalgae was 100 cells mL-1, which could meet the demand for early warning of HABs. In summary, the established mPCR is characterized by strong specificity, good stability, and multiple analysis to detect H. akashiwo, P. donghaiense, and K. mikimotoi.

Antagonistic and synergistic effects of warming and microplastics on microalgae: Case study of the red tide species Prorocentrum donghaiense.

Bibliometric network analysis has revealed that the widespread distribution of microplastics (MPs) has detrimental effects on marine organisms; however, the combined effects of MPs and climate change (e.g., warming) is not well understood. In this study, Prorocentrum donghaiense, a typical red tide species in the East China Sea, was exposed to different MP concentrations (0, 1, 5, and 10 mg L-1) and temperatures (16, 22, and 28 °C) for 7 days to investigate the combined effects of MPs and simulated ocean warming by measuring different physiological parameters, such as cell growth, pigment contents (chlorophyll a and carotenoid), relative electron transfer rate (rETR), reactive oxygen species (ROS), superoxide dismutase (SOD), malondialdehyde (MDA), and adenosine triphosphate (ATP). The results demonstrated that MPs significantly decreased cell growth, pigment contents, and rETRmax, but increased the MDA, ROS, and SOD levels for all MP treatments at low temperature (16 °C). However, high temperatures (22 and 28 °C) increased the pigment contents and rETRmax, but decreased the SOD and MDA levels. Positive and negative effects of high temperatures (22 or 28 °C) were observed at low (1 and 5 mg L-1) and high MP (10 mg L-1) concentrations, respectively, indicating the antagonistic and synergistic effects of combined warming and MP pollution. These results imply that the effects of MPs on microalgae will likely not be substantial in future warming scenarios if MP concentrations are controlled at a certain level. These findings expand the current knowledge of microalgae in response to increasing MP pollution in future warming scenarios.

An overview of Prorocentrum donghaiense blooms in China: Species identification, occurrences, ecological consequences, and factors regulating prevalence.

Prorocentrum donghaiense Lu (also identified as Prorocentrum shikokuense Hada and Prorocentrum obtusidens Schiller) is a bloom-forming dinoflagellate species distributed worldwide. Blooms of P. donghaiense occur annually in adjacent waters of the East China Sea (ECS), especially in the waters near the Changjiang River Estuary. Blooms of this species have also been reported in nearby Japanese and Korean waters. There has been an apparent bloom-forming species succession pattern in the ECS since 2000, with diatom blooms in the early spring, shifting to long-lasting and large-scale dinoflagellate blooms dominated by P. donghaiense during the spring, and finally ended by diatom and/or Noctiluca scintillans blooms in summer. These bloom succession patterns were closely correlated with changes in environmental factors, such as temperature increase and anthropogenic eutrophication. Decreasing silicate by the construction of the Three Gorges Dam and increasing dissolved inorganic nitrogen flux were mainly influenced by high intensity human activities in the Changjiang River watershed, resulting in low Si/N ratio and high N/P ratios, possibly accelerating outbreak of P. donghaiense blooms. Phosphorous deficiency might be the most critical factor controlling the succession of microalgal blooms from diatoms to dinoflagellates. Prorocentrum donghaiense is a nontoxic species, but it can disrupt marine ecosystem by decreasing phytoplankton biodiversity and changing the structure of the food chain. Prorocentrum donghaiense blooms in the ECS have been intensively studied during the last two decades. Several possible mechanisms that contribute or trigger the annual blooms of this species have been proposed, but further research is required particularly on the aspect of nutrient budget, ecosystem impacts, as well as social-economic impact assessment.

Inhibitory effects of Prorocentrum donghaiense allelochemicals on Sargassum fusiformis zygotes probed by JIP-test based on fast chlorophyll fluorescence kinetics.

The macro- and microalgae have been found to inhibit the growth and photosynthesis of one another due to allelopathic interactions between them. Sargassum fusiformis is a common and commercially cultivated seaweed in coastal waters of the East China Sea (ECS) and usually encounters dense harmful algal blooms (HABs) formed by dinoflagellates during their sexual reproduction period. In the present study, the effects of Prorocentrum donghaiense lipophilic extracted allelochemicals on the growth and photosynthesis of S. fusiformis zygotes were probed by fast chlorophyll fluorescence rise kinetics and chlorophyll a transient analysis (JIP-test). It was found that exposure to the allelochemicals led to decreased chlorophyll a content and photosynthetic rates of the zygotes in comparison to the ones in the control. In addition, using the JIP-test, it was found that the inhibitory effects of allelochemicals on photosynthesis of the zygotes were mainly exerted on the electron transport within PSII. The decrease of photosynthetic parameters such as VJ, Mo, ϕPo, ϕo, ϕEo, PI, PTR, PET in the zygotes exposed to the allelochemicals all revealed that the obstruction of electron transport, and the dominant decrease in PET, both implied that inhibition on the dark reaction contributed to the highest photosynthetic reduction. In addition, some reaction centers (RCs) in the zygotes exposed to the allelocamicals were inactivated, which led to higher dissipation of excitation energy, as demonstrated by the significant enhancement of the photosynthetic parameter DIo/RC. All the results indicated that the lipophilic extracts contained the allelochemicals of P. donghaiense which could inhibit the growth and photosynthesis of S. fusiformis zygotes by damaging the electron acceptors and inactivating RCs, and finally block the electron transport.

Effects of Prorocentrum donghaiense bloom on zooplankton functional groups in the coastal waters of the East China Sea.

Blooms of the non-toxic dinoflagellate Prorocentrum donghaiense are common in the East China Sea; however, the in situ impacts of these blooms on zooplankton community functions have not yet been conducted in this area. Using functional trait-based methods, we found that P. donghaiense bloom significantly changed the zooplankton community structure and functions in the coastal water of the East China Sea. Zooplankton species richness and biodiversity increased after the bloom. Based on body length, feeding type, trophic group and reproductive mode, we categorized zooplankton into four functional groups and characterized their dynamics. Before and after the bloom, the zooplankton community was dominated by herbivorous- and free-spawner- lineages represented by copepods and tunicates, while during the bloom, the zooplankton community was dominated by carnivorous- and egg-brooding- lineages represented by small jellyfish, chaetognaths and copepods.

Effect and mechanism of the algicidal bacterium Sulfitobacter porphyrae ZFX1 on the mitigation of harmful algal blooms caused by Prorocentrum donghaiense.

Sulfitobacter porphyrae ZFX1, isolated from surface seawater of the East China Sea during a Prorocentrum donghaiense bloom recession, exhibits high algicidal activity against P. donghaiense. To evaluate the algicidal effect of ZFX1, the algicidal mode and stability were investigated. The results showed that ZFX1 indirectly attacked algae by secreting algicidal compounds, and the algicidal activity of the ZFX1 supernatant was insensitive to different temperatures, light intensities and pH values (pH 3-12). To explore the algicidal mechanism of the ZFX1 supernatant, its effects on the morphological and ultrastructural alterations, photosynthetic capacity, reactive oxygen species (ROS) and antioxidative system of P. donghaiense were investigated. Scanning and transmission electron microscopy revealed that the ZFX1 supernatant destroyed the algal cell membrane structure and caused intracellular leakage. The decrease in the chlorophyll a content and the marked declines in both the photosynthetic efficiency (Fv/Fm) and the electron transport rate (rETR) indicated that the ZFX1 supernatant could damage the photosynthetic system of P. donghaiense. The excessive production of ROS in algal cells demonstrated the oxidative damage triggered by the ZFX1 supernatant. Although the antioxidant defense system of P. donghaiense was activated to scavenge excessive ROS, lipid oxidation occurred. The fatty acid composition profile indicated that the ZFX1 supernatant markedly increased the contents of two saturated fatty acids and a monounsaturated fatty acid and decreased the proportion of two polyunsaturated fatty acids, which resulted in lipids with a lower degree of unsaturation (DU). The decline in the DU decreased the lipid fluidity and rigidified the membrane system, and these effects destroyed the function of the membrane system and ultimately resulted in algal cell death. Therefore, ZFX1 probably plays a key role in mitigating P. donghaiense bloom by inducing lipid oxidation, decreasing the DU of lipids and ultimately destroying the membrane systems of algal cells.