Nitzschia Closterium Research Articles

Novel indole-based self-polishing environmentally friendly acrylic antifouling coatings

Marine biological pollution poses a significant threat to both marine activities and human biomedical applications. The pivotal solution lies in the development of environmentally friendly antifouling coatings. In this study, indole derivatives containing carbon-carbon double bond (specifically allyl 5-Cl/NO2-indole-carboxylate, abbreviated as ACIC/ANIC) were synthesized from 5-Cl/NO2-indole and incorporated into zinc acrylate resins via N-acylation reaction. The resulting mixture of zinc acrylate resin and polycaprolactone (PCL) was integrated into acrylic urethane lacquers (AUL), and the self-polishing and antifouling properties of these lacquers were comprehensively evaluated through antimicrobial experiments, algal inhibition studies, static simulations, and antifouling experiments conducted in marine environments. The findings demonstrate that these coatings not only exhibit effective self-polishing properties but also outperform pure zinc acrylate resins in terms of antifouling properties. Moreover, the incorporation of PCL prolongs the service life of the coatings. In specific, the coatings containing ANIC showcased impressive antimicrobial activity with antimicrobial rates of 92.79 % and 99.71 % against typical Gram-negative (E. coli) and Gram-positive (S. aureus) bacteria, respectively. Additionally, the algal inhibition rate against Nitzschia closterium and Phaeodactylum tricornutum reached 90.35 % and 79.74 %, respectively. In summary, ANIC emerges as an efficient and environmentally friendly coating material, offering a promising approach to address the economic and operational problems associated with marine bio-pollution.

Targeted cultivation of diatoms in mariculture wastewater by nutrient regulation and UV-C irradiation.

Mariculture wastewater poses environmental challenges due to pollution and eutrophication. Targeted cultivation of diatoms in wastewater can help alleviate these issues while generating beneficial algae biomass, however reliable operating methods are lacking. We proposed a novel method for treating mariculture wastewater that employed UV-C irradiation and nutrient regulation to achieve targeted diatom cultivation. This study first examined growth of four diatom species (Nitzschia closterium, Chaetoceros muelleri, Cyclotella atomus, and Conticribra weissflogii) in mariculture wastewater. C. muelleri and C. weissflogii demonstrated better adaptability compared to N. closterium and C. atomus. Additionally, the growth and nutrient utilization of C. muelleri were studied under varying concentrations of silicate, phosphate, ammonium, and trace elements in wastewater. Optimal growth was observed at 500 μmol/L silicate, 0.6 mg/L phosphate, and 4 mg/L ammonium. Ammonium proved to be a more effective nitrogen source than urea and nitrate in promoting growth at this low level. Surprisingly, trace element supplementation did not significantly impact growth. Finally, this study utilized UV-C irradiation as a pre-treatment method for wastewater prior to nutrient adjustment, significantly enhancing the growth of C. muelleri. Overall, this study provides guidance on regulating key nutrients and pre-treatment method to optimize diatom biomass production from mariculture wastewater. This approach not only addresses environmental challenges associated with mariculture but also contributes to sustainable aquaculture practices through the recovery of valuable aquatic resources.

Transparent amphiphilic silicone-based fouling-release coatings: Analyzing the effect on coating-fouling interfacial behavior

The amphiphilic antifouling coatings are effective for inhibiting fouling adhesion. Herein, the amphiphilic coatings were prepared by introducing polyether-modified polydimethylsiloxane (PE-PDMS). Uniform morphology, high transmittance, low surface roughness and amphiphilic property were obtained. PE-PDMS appearing as interspersed chains endowed the coating with amphiphilic characteristic. The artificial seawater promoted the migration of polyether to the surface. The protein adhesion force and quality were significantly reduced according to AFM-based colloidal probe technique and Quartz Crystal Microbalance with Dissipation, respectively. The coating exhibited antibacterial activity against Pseudoalteromonas xiamenensis (84.0%), Escherichia coli (69.2%) and Staphylococcus aureus (63.0%), respectively. 63.1% Halamphora. sp and 75.8% Nitzschia closterium f. had been inhibited, while the coatings possessed outstanding fouling release property with above 76.1% diatom detached after water exposure, proving that the amphiphilic parts weakened the adhesion of fouling. The mussel settlement assay confirmed that less adhesive plaques existed over the amphiphilic coatings. In addition, the expression for mussel adhesion proteins (mfp-5 and mfp-6) were significantly increased, demonstrating that amphiphilic polymers interfered with the adhesion response of the mussels. The effect on the interfacial behavior between fouling and coating is explored, providing a meaningful issue for the development of environmentally friendly antifouling coatings.

Dynamic migration mechanism of borneol synergistic polyethylene glycol for the construction of silicon-acrylate antifouling coating

Silicone-based coatings are vulnerable to marine fouling organisms in static environments, which seriously hampers its practical application. Here, an amphiphilic acrylate polymer is designed by hydrophilic polyethylene glycol and antibacterial borneol, which is introduced into polydimethylsiloxane (PDMS) by covalent linking to prepare antifouling coatings. XPS and CA tests prove that amphiphilic acrylate polymer can migrate to coating surface in the marine environment to maximize antifouling properties. Mytilus edulis foot protein adhesion test find it can weaken interface force between Mefp-3 and surface. Laboratory antifouling performance evaluations confirm that the coatings are effective against the adhesion of bacteria (86.72 % reduction for E. coli), diatoms (87.76 % reduction for Nitzschia closterium). The good antifouling properties of coatings are ascribed to the synergistic effect among unique bicyclic monoterpene structure of natural non-toxic borneol and amphiphilic acrylate polymer on surface of coatings. Moreover, the coating is less harmful to the marine ecological balance than traditional coatings containing toxic biocides due to the introduction of natural non-toxic borneol. This work contributes new insights in the exploration of environmentally friendly coating with excellent static antifouling performance.

Study on Calibration Method for the Count of Living Algal Cells Detection Based on Variable Fluorescence in Ballast Water.

In the monitoring the discharge of ballast water, the count of living algal cells is of utmost significant. Variable fluorescence, denoted as Fv, stands as an optimal parameter for photosynthetic fluorescence, efficiently charactering the living algal cells count, unaffected by the ballast waters' complex background fluorescence environment. This study deeply investigates the quantitative relationship between Fv and the count of living algal cells. Observations indicate that single cell fluorescence yield (abbreviated as SCF) varies significantly across different algae species, leading to considerable errors in quantifying living algal cell count in ballast water with unknown components using the calibration relationship between Fv and the cell count. Thus, correcting SCF prior to calibration becomes necessary. The paper proposes an innovative SCF correction method based on cell cross-sectional area and an eμ factor (where μ is the expected value of the functional absorption cross-section of PSII) This method mitigates the influence of cell size and species differences on quantifying the living algal cell count. Correction operation trials revealed that dividing the SCF measurement by cell cross-sectional area and multiplying by eμ enhanced the correction effect. Comparative experiments demonstrated marked improvement: Relative errors (REs) for Chlorella pyrenoidosa and Chlorella marine, both belonging to the Chlorophyta group, fell from 92.1% and 90.6% to 37.2% and 9.5% respectively post-correction. Similarly, REs for Thalassiosira weissflogii and Nitzschia closterium minutissima, from the Bacillariophyta group, decreased from 74.7% and 68.1% to 14.3% and 19.1% respectively. The RE of Peridinium from the Pyrrophyta group dropped from 28.4% to 12.1%. The results underscore the effectiveness of cell cross-sectional area and eμ in correcting SCF, thus offering a novel correction method for swift and precise measurement of living algal cell count in ballast water, based on variable fluorescence.

Spray-Drying Hydrophobic Cellulose Nanocrystal Coatings with Degradable Biocide Release for Marine Antifouling.

With increasing awareness about the ecological environment, increased attention has been paid to the application of eco-friendly materials in the field of marine antifouling. In this work, a novel coating having good mechanical strength and static marine antifouling characteristics was fabricated using cellulose nanocrystals (CNCs) as the skeleton material, with in situ growth of SiO2 as the basic superhydrophobic material and introducing hexadecyl trimethyl ammonium bromide (CTAB) and 4-bromo2-(4-chlorophenyl)-5-(trifluoromethyl)-1H-pyrrole-3-carbonitrile (Econea) into the coating. Due to the high strength and rod structure of CNCs, the coating maintained super-hydrophobicity after 50 cycles of abrasion tests. Moreover, the addition of CTAB during the synthesis of SiO2 led to the hydrolysis and polycondensation of tetraethyl orthosilicate at the micellar interface. Econea was fully mixed with SiO2 nanoparticles, thus slowing down the rate of release of Econea. Meanwhile, the adhesion between the coating and the substrate reached 1.9 MPa, which can meet the application requirements for marine environments. The bioassay using bacteria (Escherichia coli) and diatoms (Nitzschia closterium) showed that the rate of inhibition of the coating on bacteria and diatoms could reach 99 and 90%, respectively, after immersion in artificial seawater for 28 days. This research provides a facile and promising fabricating solution of an eco-friendly CNC-based coating having strong antifouling characteristics suitable for marine environments.

Preparation and properties of composite amphiphilic hydrogel anti-fouling materials

Amphiphilic hydrogel/organic substrate interfaces are commonly generated with a hydrophobic layer, which enhances underwater adhesion of the hydrogel via aggregation and assembly of the oleophilic structural units in the amphiphilic hydrogel. However, water absorption is considerably weakened by the hydrophobic interactions, which inhibits the formation of a stable hydration layer at the hydrogel/aqueous interface and leads to degradation of the anti-fouling ability of the amphiphilic hydrogel. Herein, composite amphiphilic hydrogel anti-fouling materials were prepared by mixing an amphiphilic hydrogel prepolymer and the pure aqueous structural units of a hydrogel prepolymer. In particular, adhesion of the hydrogels was strengthened by the oleophilic structural units of the amphiphilic hydrogel, and the hydrophilic structural units of the pure aqueous hydrogel formed a stable hydration layer at the hydrogel/aqueous interface; thus, the anti-fouling performance was strongly enhanced. As a result, superior adhesion of the composite amphiphilic hydrogel was maintained, and its resistance to shedding was clearly manifested in the experimental results obtained after immersion in static seawater (60 d) and rotating seawater (30 d); additionally, the water absorption capacity and anti-fouling effect were significantly better than those of the control amphiphilic hydrogel materials, e.g., the water uptake rate of the composite hydrogel BSH60T (S% = 324.2 %) was 6.7 times higher than that of the amphiphilic polymer hydrogel BS60T (S% = 48.3 %). Both proteins and Nitzschia closterium f. minutissima were very weakly attached to the surface of the composite amphiphilic hydrogel, and excellent anti-fouling performance was observed for the test panels in practical marine environments. This study provides a creative approach to optimizing the adhesion and anti-fouling properties of the hydrogel anti-fouling materials.

Unravelling Nutrients and Carbon Interactions in an Urban Coastal Water during Algal Bloom Period in Zhanjiang Bay, China

Nutrients and carbon play important roles in algal bloom and development. However, nutrients and carbon interactions in the period of the spring algal bloom are not well understood. The aim of this study is to explore the nutrients and carbon interactions in the period of the spring algal bloom covering an urban Jinsha Bay (JSB) coastal water in Zhanjiang Bay (South China Sea) using in situ multidiscipline observation. The results showed that the average concentration of total nitrogen (TN), total phosphorus (TP), and dissolved silicon (DSi) was 97.79 ± 26.31 μmol/L, 12.84 ± 4.48 μmol/L, and 16.29 ± 4.00 μmol/L in coastal water, respectively. Moreover, the average concentration of total dissolved carbon (TDC), dissolved inorganic carbon (DIC) and organic carbon (DOC) in JSB was 2187.43 ± 195.92 μmol/L, 1516.25 ± 133.24 μmol/L, and 671.13 ± 150.81 μmol/L, respectively. Furthermore, the main dominant species were Phaeocystis globosa and Nitzschia closterium during the spring algal bloom. Additionally, the correlation analysis showed salinity (S) was significantly negatively correlated with nutrients, indicating that nutrients derived from land-based sources sustained spring algal bloom development. However, as the major fraction of TDC, DIC was significantly positively correlated with S, which was mainly derived from marine sources. Besides, the algal density showed a significant positive correlation with temperature (T) (p < 0.001) and dissolved oxygen (DO) (p < 0.001), but a significant negative correlation with DIC (p < 0.05), suggesting that spring algal blooms may be simulated by water T increase, and then large amounts of DIC and nutrients were adsorbed, accompanying DO release through photosynthesis in coastal water. This study revealed nutrients and carbon interactions in the spring algal bloom of urban eutrophic coastal water, which has implications for understanding the nutrients and carbon biogeochemical cycle and algal bloom mitigation under climate change and anthropogenic pressures in the future.

In situ preparation of spindle calcium carbonate-chitosan/poly (vinyl alcohol) anti-biofouling hydrogels inspired by shellfish

Hydrogels have received intensive interest in the marine environment due to their excellent anti-biofouling properties. In this work, a series of spindle CaCO3-Chitosan/poly (vinyl alcohol) (SCC/PVA) hydrogels were in situ prepared inspired by the good mechanical self-cleaning and properties of seashell. The morphologies, structure and components of the prepared hydrogels were studied by SEM, FTIR spectra, XRD, TGA, and TEM. The anti-biofouling properties of the prepared hydrogels against protein, bacteria and algae were evaluated by ultrahigh-resolution fluorescence microscopy. Results indicated that chitosan can affect the growth process of CaCO3 leading to the formation of a hollow spindle structure of CaCO3. The prepared SCC/PVA hydrogels have excellent underwater superoleophobicity properties. SCC/PVA-3 hydrogel has the best superoleophobicity property with an underwater contact angle of 167.5°. The compressive strength of SCC/PVA-3 hydrogel is 25 MPa, which is attributed to the doping of SCC. Compared to PVA hydrogel, the settlement of the Navicula, Nitzschia Closterium on the surface of SCC/PVA-3 hydrogels sample decreased by approximately 94 % and 88 %, respectively. The SCC/PVA hydrogels have some antibacterial ability against E. coli. SCC/PVA-3 hydrogel can effectively inhibit the adhesion of elegans with a test time of 180 days in the South China Sea.

Altering autotrophic carbon metabolism of Nitzschia closterium to mixotrophic mode for high-value product improvement

An adaptive laboratory evolution (ALE) strategy was designed to evolve autotrophic Nitzschia closterium to mixotrophic growth for high productivity of essential amino acid (EAA), eicosapentaenoic acid (EPA) and fucoxanthin. The N. closterium growth was limited under glucose initially, but a red light emitting diode was innovatively applied to modify carbon metabolism and obtain mixotrophic strain of N. closterium GM. The N. closterium GM biomass concentration was improved by 65.07% comparing with wild type, but exhibited weak photosynthesis and strong glucose metabolism. At carbon metabolism levels, ALE promoted NADPH oxidase activity and induced protein degradation to lipid biosynthesis by elevating acetyl-CoA and pyruvate contents. It also improved carbon flux to TCA cycle, and elevated contents of glucose-6-phosphate, fructose-6-phosphate, glyceraldehyde-3-phosphate for providing sufficient ATP and NADPH. Productivities of EPA, EAA and fucoxanthin were increased by 41.0%, 18.8% and 20.4%, respectively. This ALE strategy was promising in microalgal production of high-value products.

Effects of Two Potential Allelochemicals on the Photosystem II of Nitzschia closterium and Monostroma nitidum

In aquaculture, high-density seaweed farming brings higher economic benefits but also increases outbreaks of diatom felt. The effective control of diatom felt in high-density seaweed farming has always been a research hotspot. This study selected two potential allelochemicals 2-hydroxycinnamic acid and quinic acid to explore their effects on a diatom Nitzschia closterium and an economic seaweed Monostroma nitidum. The results showed that 2-hydroxycinnamic acid had better inhibitory effects than quinic acid on the growth, pigment content and photosynthetic efficiency of N. closterium. Their half-maximal inhibitory concentrations at 120 h (IC50–120 h) were 0.9000 and 1.278 mM, respectively. Additionally, these allelochemicals had limited inhibitory effects on the growth, pigment content and photosynthetic efficiency of M. nitidum before 24 h. To further explore the allelopathic effect of these chemicals, this study focused on the photosystem II energy fluxes of N. closterium. It was found that 3 mM 2-hydroxycinnamic acid could destroy the whole photosynthetic system by devastating the PSII reaction centre (RC) before 24 h; however, the same concentration of quinic acid could only down-regulate the electron transport efficiency by changing the effective antenna size of an active RC and downregulating the PSII reaction centre density. These experimental results are expected to provide a new strategy to control diatom felt blooms on the high-density seaweed farming areas.

Constructing micro-dynamic surface of boron-polyurethane with endurable anti-fouling properties

Self-polishing coatings (SPC) with renewable surfaces are widely used in the shipping industry and offshore installations to prevent unexpected costs and safety concerns from marine biofouling. However, self-polishing coatings still suffer from uncontrollable release of antifouling biocides which is called “initial burst and final decay” and poor mechanical properties. Herein, a series of controlled-release boron-polyurethane antifouling coatings (DBIT) were prepared with good mechanical properties and micro-dynamic surface. 2, 2-bis(hydroxymethyl)propionic acid (DMPA) and pyridine-diphenylborane (PDB) were used as reaction sites and antifouling functional side chain groups, respectively, which endowing the coatings with the controlled release ability and good performance. The results showed that the DBIT coatings had certain mechanical properties, up to an ultimate stress of 14.8 MPa. The DBIT75 coating could reduce 90.6 % settlement of Halamphora sp., 92.7 % settlement of Nitzschia closterium, and repel the settlement of mussels. More importantly, DBITx coatings displayed excellent antifouling performance for at least 4 months in the field test, which shows that the controlled-release polyurethane coatings provide a new choice for marine antifouling applications.

Dynamic multi-level microstructured antifouling surfaces by combining quaternary ammonium modified GO with self-polishing copolymers

Marine biological fouling is the undesirable accumulation on the surfaces of submerged objects and causes environmental and economic consequence to ships and marine facilities. However, traditional coatings achieve antifouling by releasing toxic heavy metal antifouling agents, causing ecological problems. And the static antifouling performance of self-polishing antifouling coating is not good. To overcome the shortcoming, a novel antifouling strategy to build a self-renewing multi-level microstructure on the coating surface was developed by dispersing GO-based quaternary polymer brushes in a self-polishing fluoro/silyl acrylate copolymer. Quaternized GO exhibits excellent dispersibility in the silyl-based acrylate copolymer. A dynamic self-renewing surface is realized for the coating via a self-polishing effect that exposes the filler inside the coating at the surface. The multi-level microstructure of the sharp edge of GO and quaternized “spear” structure destroys the cell wall of organisms. And a “water-shield” on amphoteric ion surface on quaternized GO inhibits adhesion of organisms. The antibacterial and anti-algae tests demonstrated the excellent antifouling effect of the coating at only 0.1% (mass) filler content, with anti-algae ratio against Nitzschia closterium (N. closterium), Phaeodactylum tricornutum (P. tricornutum) and Halamphora sp. of 83.7%, 52.4%, and 65.8%, respectively. The proposed preparation method is simple and potentially applicable to large-scale production for antifouling application.

Effects of Temperature on Transparent Exopolymer Particle Production and Organic Carbon Allocation of Four Marine Phytoplankton Species.

Simple SummaryTEP is the bridge mediating DOC and POC conversion in the ocean, which is a key component of the marine carbon cycle. TEP accelerates the accumulation or deposition rate of organic carbon at the sea surface and promotes the short- and long-term sequestration of carbon, counteracting atmospheric CO2 increase and global warming. Temperature, as the main driving factor of carbon fixation during phytoplankton photosynthesis, is closely related to TEP production. However, little is known about the effects of temperature on TEP the production, DOC secretion, and carbon pool allocation of phytoplankton. This study analyzed the effect of temperature on the carbon pool allocation of phytoplankton and the significance of TEP in the marine carbon pool. Our results suggest that increased temperature affects carbon pool allocation in phytoplankton cells by promoting DOC exudation and extracellular TEP formation. This study provides an important basis for understanding the contribution of TEP to the allocation of POC and DOC and will benefit the prediction of phytoplankton TEP production and the marine carbon cycle under the background of global warming.Transparent exopolymer particles (TEP) are sticky polymeric substances that are commonly found in the periphery of microbial cells or colonies. They can naturally flocculate smaller suspended particles into larger aggregates and thus play a crucial role in the biological pump and the global carbon cycle. Phytoplankton are the major contributors to marine TEP production, whereas the way TEP production interacts with abiotic factors at the species level is generally unknown but critical for estimating carbon fluxes. In this study, the effects of temperature on TEP production and carbon allocation were studied in two representative diatom species (Nitzschia closterium and Chaetoceros affinis) and two model dinoflagellate species (Prorocentrum micans and Scrippisella trichoidea). The results showed that temperature had a significant impact on TEP production in all species. First, increased temperature promoted the TEP production of all four species. Second, elevated temperature affected the carbon pool allocation, with enhanced dissolved organic carbon (DOC) exudation in the form of TEP in all species. The TEP-C/DOC percentages of N. closterium and P. micans were 93.42 ± 5.88% and 82.03 ± 21.36% at the highest temperature (24 °C), respectively, which was approximately two to five times higher than those percentages at 16 °C. In contrast, TEP’s contribution to the POC pool is lower than that to the DOC pool, ranging from 6.74 ± 0.79% to 28.31 ± 1.79% for all species. Moreover, phytoplankton TEP production may be related to cellular size and physiology. The TEP content produced by the smallest N. closterium (218.96 ± 15.04 fg Xeq./μm3) was ~5 times higher compared to P. micans, S. trichoidea, or C. affinis. In conclusion, TEP production is temperature sensitive and species specific, which should be taken into consideration the regarding TEP-mediated oceanic carbon cycle, particularly in the context of global warming.

Surface morphology properties and antifouling activity of Bi2WO6/boron-grafted polyurethane composite coatings realized via multiple synergy

An inorganic–organic composite coating is an effective way to solve the issue of marine organism attachment and realize multi-element synergistic antifouling. Herein, Bi2WO6/boron-grafted polyurethane composite coatings (BWOB) composed of Bi2WO6 with three morphologies (nanosheet, flower and microsphere) and boron-grafted polyurethane (ITB) were successfully synthesized to achieve high-efficiency antifouling. Bi2WO6 nanoparticles were evenly distributed on the surface and inside the ITB to form micro/nanostructures. In the composite coatings doped with flower-shaped Bi2WO6, BWOB-5 showed excellent antibacterial and antidiatom adhesion properties, achieving 95.43% and 98.38% against Escherichia coli and Staphylococcus aureus, respectively, and 98.62% against Nitzschia closterium. In addition, the micro/nanostructure on the surface, the stable production of hydroxyl radicals (·OH) and superoxide radicals (·O2–) during photocatalysis, and the antifouling functional groups of the resin matrix in the BWOB composite coatings were all conducive to photocatalytic antifouling activity. More importantly, BWOB coatings exhibited excellent environmentally friendly properties. Therefore, BWOB coatings are expected to have potential application value in the field of photocatalytic sterilization and antifouling.

The Differential Responses of Coastal Diatoms to Ocean Acidification and Warming: A Comparison Between Thalassiosira sp. and Nitzschia closterium f.minutissima.

Marine diatoms are one of the marine phytoplankton functional groups, with high species diversity, playing important roles in the marine food web and carbon sequestration. In order to evaluate the species-specific responses of coastal diatoms to the combined effects of future ocean acidification (OA) and warming on the coastal diatoms, we conducted a semi-continuous incubation on the large centric diatom Thalassiosira sp. (~30 μm) and small pennate diatom Nitzschia closterium f.minutissima (~15 μm). A full factorial combination of two temperature levels (15 and 20°C) and pCO2 (400 and 1,000 ppm) was examined. The results suggest that changes in temperature played a more important role in regulating the physiology of Thalassiosira sp. and N. closterium f.minutissima than CO2. For Thalassiosira sp., elevated temperature significantly reduced the cellular particulate organic carbon (POC), particulate organic nitrogen (PON), particulate organic phosphate (POP), biogenic silica (BSi), chlorophyll a (Chl a), and protein contents, and the C:N ratio. CO2 only had significant effects on the growth rate and the protein content. However, for the smaller pennate diatom N. closterium f.minutissima, the growth rate, POC production rate, and the C:P ratio significantly increased with an elevated temperature, whereas the cellular POP and BSi contents significantly decreased. CO2 had significant effects on the POC production rate, cellular BSi, POC, and PON contents, the C:P, Si:C, N:P, and Si:P ratios, and sinking rate. The interaction between OA and warming showed mostly antagonistic effects on the physiology of both species. Overall, by comparison between the two species, CO2 played a more significant role in regulating the growth rate and sinking rate of the large centric diatom Thalassiosira sp., whereas had more significant effects on the elemental compositions of the smaller pennate diatom N. closterium f.minutissima. These results suggest differential sensitivities of different diatom species with different sizes and morphology to the changes in CO2/temperature regimes and their interactions.

Mechanism of the allelopathic effect of macroalgae Gracilaria bailiniae on Nitzschia closterium

With the rapid development of the seaweed industry in China, the scale and production of its commercial seaweed are ranked among the most significant worldwide. Consequently, the control of algal blooms, especially fouling diatoms, during macroalgae industrialisation is an important issue. Many diatom bloom studies have focused on physical and chemical controls, with limited economic and eco-friendly biological controls reported. In our study, Gracilaria bailiniae fresh thalli and aqueous extract profoundly suppressed Nitzschia closterium growth (50% inhibition concentration of the fourth day (IC50–4 day) was 0.667 × 10−3 g·mL−1 and 3.889 × 10−3 g·mL−1, respectively). The cellular morphology changes of N. closterium exposed to the G. bailiniae aqueous extract were severe atrophies and plasmolysis and dissolution of endocellular structures. To explore more potential allelochemicals to control N. closterium, the intracellular compounds of G. bailiniae were detected and screened. Three organic acids (citrate, hydroxyethanesulfonic acid (HA) and taurine) had allelopathic potential against N. closterium. Our results showed that citrate and HA markedly suppressed N. closterium (IC50–4 day: 1.035 mM and 1.151 mM, respectively); however, taurine poorly suppressed N. closterium (IC50–4 day: 2.500 mM). Therefore, HA is one of the main allelopathic compounds in G. bailiniae. Further, the allelopathic mechanism of HA against the N. closterium photosynthetic system broke its photosynthetic apparatus (oxygen-evolving complex, reaction centres, the effective antenna size and the donor side of photosystem II) and hindered electron transport. The experimental results provide a new and eco-friendly strategy to control diatom blooms.

Optimizing Microalgae Diet, Temperature, and Salinity for Dwarf Surf Clam, Mulinia lateralis, Spat Culture

Dwarf surf clam, Mulinia lateralis, is widely considered as a model species for bivalves. The development of a standard culture system could greatly promote the production of high-quality individuals, yet information on the culture conditions for M. lateralis spat is still limited. This study aims to determine the suitable microalgae diet, temperature, and salinity for M. lateralis spat culture. The typically fed microalgae species, including Chlorella pyrenoidesa (Cp), Platymonas helgolandica (Ph), Dunaliella salina (Ds), Nitzschia closterium (Nc), and Chaetoceros muelleri (Cm), could be taken up by M. lateralis spat, and their filtration rates on Cp, Nc, and Cm were higher than those on Ds and Ph. For the entire spat culture, all diet trials showed similar survival percentages, while the mono-specific diet Cp exhibited the highest growth rate, suggesting that Cp was the optimal microalgae species for M. lateralis spat. Through simultaneously maximizing the growth and survival of spat, the optimal microalgae concentration and stocking density were 5 × 104 cells ml–1 and 400–600 individuals m–2 for 30–40-day-old spat as well as 1 × 105 cells ml–1 and 400–600 individuals m–2 for 40–50-day-old spat, respectively. In addition, the spat had higher growth rates and survival percentages at the temperature of 20–22°C and salinity of 22–25 ppt. The results of this study provide a basis for further culture of M. lateralis spat, and the optimized conditions will be of great significance for the construction of the standard culture system of M. lateralis.

Performance assessment of capsaicin derivatives containing amide groups used as active substances for antifouling coatings

The culprit of biofouling is the formation and reproduction of viable microbial biofilms. For many years, biofouling is a critical issue in marine pollution treatment and has drawn great attention. Herein, eight capsaicin (CAP) derivatives were prepared using aromatic hydrocarbons and amides as raw materials, thereinto, compounds A1, A2, A3, A4, and B1 has not been reported, being considered some new compounds. Meanwhile, the antifouling (AF) property of CAP derivatives were characterized for the first time. The inhibition rates of these CAP derivatives (20 μg·mL−1) against Escherichia coli and Staphylococcus aureus exceed 80% and 92%, respectively. The anti-algal activity of the CAP derivatives is time and concentration dependent. Compounds A3 and A4 exhibit excellent anti-algal activity (> 77.30% against Nitzschia closterium and > 82.50% against C. vulgaris), and their toxicity is lower than that of currently used antifoulants, such as TBT and SeaNine 211. Most importantly, AF coatings with CAP derivatives show excellent AF effects in marine environments for 180 days; moreover, as auxiliary AF agents, CAP derivatives further enhance the AF performance of cuprous oxide-containing coatings, which are widely used as antifoulants. The phenolic hydroxyl group, benzene ring, amide group and chlorine atom in the CAP derivatives are supposed to be the main active groups contributing to the AF performance. This study may provide a promising method to solve marine pollution.

RNA Interference by Ingested Dsrna-Expressing Bacteria to Study Porphyrin Pigmentation in Crassostrea gigas

Porphyrins are a widespread group of pigments in nature which are believed to contribute to shell colors in mollusks. Previous studies have provided candidate genes for porphyrin shell coloration, however, the linkage analysis between functional genes and porphyrin pigmentation remains unclear in mollusks. RNA interference is a powerful molecular tool for analyzing the loss of functions of genes in vivo and alter gene expression. In this study, we used unicellular alga Platymonas subcordiformis and Nitzschia closterium f. minutissima as vectors to feed oysters with Escherichia coli strain HT115 engineered to express double-stranded RNAs targeting specific genes involved in porphyrin synthesis. A strain of Crassostrea gigas with orange shell was used to target key haem pathway genes expression using the aforementioned approach. We show here that feeding the oysters with E. coli, containing dsRNA targeting pigmentation genes, can cause changes in the color of the newly deposited shell. For example, the RNAi knockdown of CgALAS and CgPBGD resulted in the loss of uroporphyrin pigmentation from the shell due to the accumulation of the pigment in the oyster’s mantle. The study probed the crucial role of ALAS and PBGD genes potential functions of uroporphyrin production and shell color pigmentation in C. gigas.