Marine Diatom Research Articles

A highly efficient adsorbent adapting to low pH condition for Pb(II) sequestration from aqueous solution − marine diatom: Laboratory and pilot scale tests

Highly efficient, economically feasible and environmentally friendly adsorbents have been a research hotspot for heavy metal sequestration. In the present study, dried marine diatom biomass (mainly composed of Chaetoceros sp.), which possessed high suface area and cumulative pore volume of 5.72 m2/g and 0.028 cm3/g, respectivly, were used to adsorb Pb(II) from aqueous solution. The immoblized marine diatom beads and an adsorption reactor filled with the beads were further investigated for continuous Pb(II) removal. The removal efficiency was evaluated as a function of contact time, initial concentration, pH and co-existing cations. Results indicated that the dried diatom biomass and the immobilized diatom beads effectively adsorbed Pb(II) under pH > 3.0 and pH > 4 0.0 conditions, respectively. The optimal conditions for the immobilized diatom beads preparation were: diatom powder dosage of 5.0 g / 100 mL sodium alginate solution, sodium alginate concentration of 20 g/L, CaCl2 concentration of 2 %, and cross linking time of 1 h. The Pb(II) adsorption on the marine diatom biomass and the immobilized beads were both well described by pseudo-second-order kinetic and Langmuir model. The maximumPb(II) adsorption capacities of the immobilized beads were 919.1 mg/g, which were much higher than that of the most of adsorbents reported elsewhere. Adsorption mechanism analysis demonstrated that Pb(II) was adsorbed onto the diatom biomass mainly through interaction with nitrogen bonds (mainly with pyrrolic nitrogen) and carboxylic groups, and ion exchange with light metals and hydrogen ions in quaternary nitrogen bonds. The diatom beads were used as adsorbents in a continuous Pb(II) treatment reactor, and the Pb(II) removal efficiency of the reactor reached to almost 100 % from the initial concentration of Pb(II) = 50 mg/L.

Performance characteristics of marine diatoms Cylindrotheca sp. and Trieres chinensis under nutrient limitation and their potency as feedstock for biodiesel production

Microalgae-derived biodiesel is commonly studied and recently gained attention as a possible substitute feedstock for production of biodiesel. In this study, the potential of marine diatoms, Cylindrotheca sp. (FPU 0031) and T. chinensis (FPU 0030), for production of biodiesel was evaluated by investigating the effect of nutrient limitation (100, 75, 50, and 25 % Roschin medium) on growth behavior response, lipid productivity, and FAME profiles of the diatom strains. The total lipid yield increased under nutrient-limited culture condition. When the concentration of the nutrient was restricted to 50 %, the average lipid yield of Cylindrotheca sp. and T. chinensis were 19.32 and 21.72 % with lipid productivity of 73.46 and 68.19 mg L−1 day−1, respectively. Nutrient limitation resulted in a decrease in biomass yield and an increase in the lipid yield of the diatom strains. The properties of biodiesel generated by the two diatoms were assessed based on FAME profiles using empirical equations. Results showed that Cylindrotheca sp. and T. chinensis conforms to the biodiesel standards specifications set by EN 14214 and ASTM D6751. The predicted properties of biodiesel observed for Cylindrotheca sp. and T. chinensis were both ideal, e.g. good cold filter plugging points (−6.94 °C and − 2.16 °C), cetane numbers (65.57 and 75.29), cloud points (1.81 °C and 7.75 °C), pour points (1.60 °C and − 4.86 °C), and low kinematic viscosities (2.89 and 2.16 mm2 s−1), respectively. Thus, suggesting the potential use of these diatoms as feedstock for producing biodiesel with high-grade fuel characteristics.

Origins and nature of large explosive eruptions in the lower East Rift Zone of Kīlauea volcano, Hawaii: Insights from ash characterization and geochemistry

Several powerful explosive eruptions have taken place in the populated lower East Rift Zone of Kīlauea within the past ∼750 years. These have created distinctive landforms, including a tephra rim enclosing Puʻulena Crater immediately south of the Puna Geothermal Venture power station, a tuff cone at Kapoho Crater near the eastern cape of the Island of Hawaiʻi, and a set of littoral cones, the Sand Hill in Nānāwale, where the 1840 lava flow poured into the ocean. Kapoho Crater tuff cone is the largest of these recent pyroclastic features. Mineral, glass, and melt inclusion analyses of tuff cone ash and later fissure-related scoriaceous materials also found within the crater indicate slightly evolved basaltic magmas (1120–1130 °C) that are compositionally similar to parts of the effusive lower East Rift Zone eruptions in 1955 and 2018. Tuff cone magmas were stored at depths of ∼2.5–3.5 km and had pre-eruptive volatile contents (0.5–0.8 wt% H2O, 280–340 ppm CO2, 1400–1800 ppm S) similar to other Kīlauea eruptions (e.g., 1959, 1960), suggesting that internal magma properties were unlikely to account for the unusual explosiveness of this eruption. Tephra componentry, grain-size analyses, and field observations confirm that the cone grew during a phreatomagmatic eruption mostly of vitric ash, probably where a fissure opened across the coastline or shallow ocean floor nearby. Supporting this hypothesis is the identification of at least two genera of marine diatoms within tuff cone strata. Sand Hill littoral cone ash is also vitric like that of Kapoho Crater, but distinctly coarser with abundant fluidal ejecta represented. In contrast, the Puʻulena Crater eruption deposited lithic ash and related blocks with minor juvenile magmatic contribution; a phreatomagmatic eruption that was dominantly phreatic. Differences in eruption styles are related to unique mechanics that tephra analyses help us interpret. While powerful explosive eruptions in the lower East Rift Zone are rare, they present a definite future hazard for inhabitants in this part of Hawaii.

Combined effect of light and glyphosate herbicide on growth rate of marine diatom algae.

The effect of glyphosate herbicide at concentrations of 25, 100, 150 and 200 μg.L-1 on growth characteristics of diatoms C. caspia and T. weissflogii under accumulative growth conditions was investigated. Increasing herbicide concentration in the medium resulted in growth suppression of both species and decreased the final abundance of the cultures in the stationary growth phase. The calculated concentrations of herbicide EC10 and EC50 (10 and 90 μg.L-1 for C. caspia and 7 and 25 μg·L-1 for T. weissflogii, respectively) led to a 10 and 50% reduction in the abundance of the studied cultures relative to the control, are ecologically significant and correspond to the values recorded in aquatic areas. The combined effect of light (in the range of 20-250 µE.m-2.s-1) and glyphosate (calculated concentrations of EC10 and EC50) on the growth characteristics of microalgae was evaluated. An increase in algal sensitivity to light was observed with glyphosate exposure. In both species, the increase in the concentration of glyphosate in the medium led to a decrease in the initial angle of slope of the light curve of growth under conditions of light limitation, a reduction in the value of light saturation of growth, narrowing of the boundaries of the light optimum and an increase in the degree of light inhibition. It is shown that the effect of the combined action of light and glyphosate exceeds the sum of the effects of each factor. This fact should be taken into account in ecotoxicological monitoring when assessing the risks of glyphosate ingress into aquatic ecosystems. An increase in glyphosate concentration in water during periods with high values of solar insolation is potentially dangerous due to a decrease in the photosynthetic activity of algae and a reduction in diatom algae abundance.

Development of an artificial propagation and breeding method for the beehorn snail (Clithon diadema)

Beehorn snail (Clithon diadema), known for its vibrant colors, is threatened with extinction due to excessive field collection. Therefore, this study investigated the effects of different diets and salinity (0‰–35‰) on the gonadal development, capsule productivity, embryonic development, and larval survival and growth of C. diadema. Adult snails (shell length: 9.09 ± 0.87 mm) were fed diatoms, including pennate marine diatom (Nitzschia grossestriata), boat-shaped diatom algae (Navicula sp.) and Cylindrotheca sp., along with giant tiger prawn (Penaeus monodon) commercial feed, sea lettuce (Ulva lactuca), or Cladophora fascicularis, while snail larvae (shell length: 154.85 ± 6.03 μm) were fed Isochrysis galbana or Chaetoceros muelleri. The diatom group outperformed commercial feed and U. lactuca groups. The highest capsule productivity, yielding 79–82 capsules in 4 weeks, occurred at 15‰-20‰ salinity for diatom-fed adults. Embryos thrived at 0‰ but didn't hatch; hatching required salinities above 0‰, highlighting saline necessity. In addition, acute salinity changes (0‰ to 30‰) can deform embryo. Embryonic development at 15‰–20‰ salinity lasted 13.56–14.33 days with 100% larval hatching. However, larvae hatched at >20‰ salinity exhibit improved the percentage of survival without feeding (longer median lethal times). I. galbana-fed larvae survived 68 days with a 75% rate, outlasting C. muelleri-fed larvae which perished within 28 days. I. galbana-fed larvae, raised for 68 days at 25‰ salinity, showed 100% survival, 44.44% metamorphosis, and a 3.1 times growth increase. Metamorphosis rates were highest at 25‰ salinity with I. galbana, exceeding the 20‰ group by 3.2 times. Mucus of C. diadema boosts larval metamorphosis to 50.00%, 9 times higher than without inducers. Based on previous results, we developed an artificial propagation and breeding method for C. diadema. Artificially propagating C. diadema in large quantities could reduce the need for wild harvesting, thereby mitigating negative ecological impacts from excessive collection.

Evaluation of antioxidant and anti-inflammatory activity and identification of bioactive compound from the marine diatom, Odontella aurita extract

Increased production of reactive oxygen species (ROS) leads to oxidative stress, with its damaging effect extending to the mitochondria and plasma membrane. Further, prolonged inflammation can result in chronic disease development. The marine microdiatom Odontella aurita is recognized for its potential in food and pharmaceutical development. Moreover, it contains antioxidant and anti-inflammatory properties. However, studies regarding the efficacy of their varying extract forms and their underlying mechanisms remain scarce. Therefore, this study aims to explore the antioxidant and anti-inflammatory effects of Odontella aurita extracts obtained using various extraction methods (hot water, 70% ethanol, and chloroform:methanol (CM)). Among the three Odontella aurita extracts, the CM extract demonstrated superior efficacy in protecting RAW 264.7 cells from H2O2-induced cytotoxicity. It significantly lowered the levels of ROS and enhanced the expression of superoxide dismutase and glutathione peroxidase. Furthermore, the CM extract outperformed other extracts in inhibiting LPS-induced nitric oxide production, reducing mRNA levels in nitric oxide synthase, cyclooxygenase, and the proinflammatory cytokines interleukin IL-1β, IL-6, TNFα. Additionally, CM extract effectively suppressed the activation of NF-κB/IκBα and JAK2-STAT3 in LPS-induced RAW 264.7 cells. HPLC–UV analysis revealed a remarkable 33-fold higher fucoxanthin content in CM compared to the ethanol extract. GC–MS analysis identified elevated levels of cholest-5-en-3-ol, phytol, eicosapentaenoic acid methyl ester, methyl palmitate, palmitoleic acid methyl ester, and neophytadiene in the CM extract. These findings suggest that Odontella aurita CM extract is a promising antioxidant candidate for preventing or treating inflammatory diseases, consequently emphasizing its potential for further development.Graphical

Species richness and intraspecific variation interactively shape marine diatom community functioning

AbstractBiodiversity generally increases productivity in ecosystems; however, this is mediated by the specific functional traits that come with biodiversity loss or gain and how these traits interact with environmental conditions. Most biodiversity studies evaluate the effects of species richness alone, despite our increasing understanding that intraspecific diversity can have equally strong impacts. Here, we manipulate both species richness and intraspecific richness (i.e., number of distinct strains) in marine diatom communities to explicitly test the relative importance of species and strain richness for biomass and trait diversity in six distinct temperature/nutrient environments. We show that species and strain richness both have significant effects on biomass and growth rates, but more importantly, they interact with each other, indicating that cross‐species diversity effects depend on within‐species diversity and vice versa. This intertwined relationship thus calls for more integrative approaches quantifying the relative importance of distinct biodiversity components and environmental context on ecosystem functioning.

The genome sequences of the marine diatom Epithemia pelagica strain UHM3201 (Schvarcz, Stancheva & Steward, 2022) and its nitrogen-fixing, endosymbiotic cyanobacterium.

We present the genome assembly of the pennate diatom Epithemia pelagica strain UHM3201 (Ochrophyta; Bacillariophyceae; Rhopalodiales; Rhopalodiaceae) and that of its cyanobacterial endosymbiont (Chroococcales: Aphanothecaceae). The genome sequence of the diatom is 60.3 megabases in span, and the cyanobacterial genome has a length of 2.48 megabases. Most of the diatom nuclear genome assembly is scaffolded into 15 chromosomal pseudomolecules. The organelle genomes have also been assembled, with the mitochondrial genome 40.08 kilobases and the plastid genome 130.75 kilobases in length. A number of other prokaryote MAGs were also assembled.

Metabolic engineering of omega-3 long chain polyunsaturated fatty acids in plants using different ∆6- and ∆5-desaturases co-expressed with LPCAT from the marine diatom Phaeodactylum tricornutum

Continuous research on obtaining an even more efficient production of very long-chain polyunsaturated fatty acids (VLC-PUFAs) in plants remains one of the main challenges of scientists working on plant lipids. Since crops are not able to produce these fatty acids due to the lack of necessary enzymes, genes encoding them must be introduced exogenously from native organisms producing VLC-PUFAs. In this study we reported, in tobacco leaves, the characterization of three distinct ∆6-desaturases from diatom Phaeodactylum tricornutum, fungi Rhizopus stolonifer and microalge Osterococcus tauri and two different ∆5-desaturases from P. tricornutum and single-celled saprotrophic eukaryotes Thraustochytrium sp. The in planta agroinfiltration of essential ∆6-desaturases, ∆6-elongases and ∆5-desaturases allowed for successful introduction of eicosapentaenoic acid (20:5∆5,8,11,14,17) biosynthesis pathway. However, despite the desired, targeted production of ω3-fatty acids we detected the presence of ω6-fatty acids, indicating and confirming previous results that all tested desaturases are not specifically restricted to neither ω3- nor ω6-pathway. Nevertheless, the additional co-expression of acyl-CoA:lysophosphatidylcholine acyltransferase (LPCAT) from Phaeodactylum tricornutum boosted the proportion of ω3-fatty acids in newly synthesized fatty acid pools. For the most promising genes combinations the EPA content reached at maximum 1.4% of total lipid content and 4.5% of all fatty acids accumulated in the TAG pool. Our results for the first time describe the role of LPCAT enzyme and its effectiveness in alleviating a bottleneck called ‘substrate dichotomy’ for improving the transgenic production of VLC-PUFAs in plants.

Managing municipal wastewater remediation employing alginate-immobilized marine diatoms and silver nanoparticles

Wastewater remediation has become a major environmental concern in recent years, which has led scientists to look for innovative sustainable solutions. Diatoms have emerged as a potentially effective solution for wastewater treatment, primarily because of their extraordinary ability to absorb nutrients and engage in metabolic processes. The present study aims to accomplish two goals, firstly, green synthesis of silver nanoparticles (AgNPs) utilizing marine diatoms Chaetoceros sp. and Thalassiosira sp. Secondly, encapsulation of diatoms within a Ca-alginate hydrogel bead developed via the gelation method thus introducing a novel way to assess their effectiveness in nutrient bioremediation from wastewater. The study reveals that Thalassiosira sp. mediated AgNPs are very effective in removing phosphate and nitrate, with 74% and 65% removal rates respectively. Conversely, Chaetoceros sp. mediated AgNPs significantly decreased chemical oxygen demand (COD) by 73%. Furthermore, Thalassiosira sp. encapsulated in Ca-alginate hydrogel beads demonstrated significant removal rates: 64% for nitrate, 91% for phosphate, and 78% for COD, respectively. Furthermore, the biochemical profiles of both diatom-entrapped alginate beads were remarkable, and the approach shows potential for effective and sustainable wastewater treatment methods, which can further be investigated for long-term performance, scalability, and environmental impact on sustainability.

Effect of increased CO2 on calcium homeostasis and signaling in a marine diatom

AbstractOcean acidification influences photosynthesis, respiration, and metabolism in marine diatoms, leading to changes in diatom growth performance and shifts in phytoplankton communities. Previous studies have demonstrated that increases in seawater CO2 concentrations affect the uptake of trace metals such as iron, zinc, copper, and cobalt by marine diatoms. However, the influence of increased CO2 on calcium, which plays a vital role as a secondary messenger in various signaling pathways within organisms, has received limited attention so far. This study examined the effect of increased CO2 on Ca homeostasis and signaling in the marine diatom Phaeodactylum tricornutum. While seawater acidification had little effect on the diatom's growth, it significantly changed cell properties (surface topography, adhesion, and surface potential). Elevated CO2 concentrations reduced calcium accumulation P. tricornutum and lowered the rise of cytosolic Ca2+ transients stimulated by toxic aldehyde, phosphorus supplement, and hypo‐osmotic stress. Our results suggest that a continuous rise in atmospheric CO2 may alter diatoms' response to environmental cues.

Widespread Production of Polyunsaturated Aldehydes by Benthic Diatoms of the North Pacific Ocean's Salish Sea.

Diatoms are key primary producers across marine, freshwater, and terrestrial ecosystems. They are responsible for photosynthesis and secondary production that, in part, support complex food webs. Diatoms can produce phytochemicals that have transtrophic ecological effects which increase their competitive fitness. Polyunsaturated aldehydes (PUAs) are one class of diatom-derived phytochemicals that are known to have allelopathic and anti-herbivory properties. The anti-herbivory capability of PUAs results from their negative effect on grazer fecundity. Since their discovery, research has focused on their production by pelagic marine diatoms, and their effects on copepod egg production, hatching success, and juvenile survival and development. Few investigations have explored PUA production by the prolific suite of benthic marine diatoms, despite their importance to coastal trophic systems. In this study, we tested eight species of benthic diatoms for the production of the bioactive PUAs 2,4-heptadienal, 2,4-octadienal, and 2,4-decadienal. Benthic diatom species were isolated from the Salish Sea, an inland sea within the North Pacific ecosystem. All species were found to be producers of at least two PUAs in detectable concentrations, with five species producing all three PUAs in quantifiable concentrations. Our results indicate that production of PUAs from Salish Sea benthic diatoms may be widespread, and thus these compounds may contribute to benthic coastal food web dynamics through heretofore unrecognized pathways. Future studies should expand the geographic scope of investigations into benthic diatom PUA production and explore the effects of benthic diatoms on benthic consumer fecundity.

Zeaxanthin epoxidase 3 Knockout Mutants of the Model Diatom Phaeodactylum tricornutum Enable Commercial Production of the Bioactive Carotenoid Diatoxanthin.

Carotenoids are pigments that have a range of functions in human health. The carotenoid diatoxanthin is suggested to have antioxidant, anti-inflammatory and chemo-preventive properties. Diatoxanthin is only produced by a few groups of microalgae, where it functions in photoprotection. Its large-scale production in microalgae is currently not feasible. In fact, rapid conversion into the inactive pigment diadinoxanthin is triggered when cells are removed from a high-intensity light source, which is the case during large-scale harvesting of microalgae biomass. Zeaxanthin epoxidase (ZEP) 2 and/or ZEP3 have been suggested to be responsible for the back-conversion of high-light accumulated diatoxanthin to diadinoxanthin in low-light in diatoms. Using CRISPR/Cas9 gene editing technology, we knocked out the ZEP2 and ZEP3 genes in the marine diatom Phaeodactylum tricornutum to investigate their role in the diadinoxanthin-diatoxanthin cycle and determine if one of the mutant strains could function as a diatoxanthin production line. Light-shift experiments proved that ZEP3 encodes the enzyme converting diatoxanthin to diadinoxanthin in low light. Loss of ZEP3 caused the high-light-accumulated diatoxanthin to be stable for several hours after the cultures had been returned to low light, suggesting that zep3 mutant strains could be suitable as commercial production lines of diatoxanthin.

Continuous selenite biotransformation and biofuel production by marine diatom in the presence of fulvic acid

In this study, the biochemical response of Phaeodactylum tricornutum to varying concentrations of inorganic selenium (Se) was investigated. It was observed that, when combined with fulvic acid, P. tricornutum exhibited enhanced uptake and biotransformation of inorganic Se, as well as increased microalgal lipid biosynthesis. Notably, when subjected to moderate (5 and 10 mg/L) and high (20 and 40 mg/L) concentrations of selenite under fulvic acid treatment, there was a discernible redirection of carbon flux towards lipogenesis and protein biosynthesis from carbohydrates. In addition, the key parameters of microalgae-based biofuels aligned with the necessary criteria outlined in biofuel regulations. Furthermore, the Se removal capabilities of P. tricornutum, assisted by fulvic acid, were coupled with the accumulation of substantial amounts of organic Se, specifically SeCys. These findings present a viable and successful approach to establish a microalgae-based system for Se uptake and biotransformation.

Diatom record the holocene marine facies deposition history in inner bay of Pearl River Estuary, South China

To understand the evolution of river mouth systems under natural and human being forces is a critical task in coastal and marine science studies. We present a new sedimentary record with diatom, grainsize analysis and radiocarbon age dating, recovered from a drilling core in an inner bay of the Pearl River Estuary, South China, in order to describe marine facies depositional history and to examine relative palaeoclimatic and palaeoenvrionmental changes during the Holocene. The occurrence of marine diatoms at ca. 9,000 cal. yr. BP provides marine facies starting point at this core profile in the shoal area, west of the Pearl River Estuary. Three fossil diatom units were distinguished following the early to late Holocene epoch division. The changed diatom bio-facies before and after ca. 8,200 cal. yr. BP, especially in coastal and neritic species relative abundances contrast, offers a diatom floral response to the "8.2 kyr" event. In middle Holocene, enhanced diatom absolute abundances of tropical open-sea water species and increased neritic species number and relative abundances, with more sand fractions, provide evidences of diatom bio-facies response to higher sea-level and strong hydrodynamic clearly. Following the regression, fossil diatom flora experienced a long-term decline after ca. 5,500 cal. yr. BP, until to ca. 1,400 cal. yr. BP. In the past ca. 1,400 years, there has been a clear increase in the absolute abundances and biodiversity of diatoms, along with a greater presence of coarse granularity fractions. This is a strong signal that human activities influenced local environmental change, combined with natural forces.An interesting phenomenon of higher sedimentation rate was observed in three periods as a millennial-scale pulse, at ca. 9,000–8,000 cal. yr. BP, ca. 6,500 - 5,500 cal. yr. BP, and ca. 1,000 - 0 cal. yr. BP. Meanwhile, two periods of lower sedimentation rate over longer time interval occurred during those pulses. Through regional correlation, this study presents a record of deposition after ca. 9,000 cal. yr. BP in Holocene marine facies, provide improved understanding of the west shoal evolution history in Pearl River Estuary, and natural and human being impact on diatom flora and coastal geo-environment in low latitude river mouth systems in Asian Monsoon realm.

Lead removal from the aqueous solution by extracellular polymeric substances produced by the marine diatom Navicula salinicola

ABSTRACT Microbial extracellular polymeric substances (EPS) have recently emerged as significant contributors in diverse biotechnological applications. Extracellular polymeric substances (EPS), produced by a Navicula salinicola strain, have been studied for potential applications in a specific heavy metal (lead (Pb II)) removal from wastewater. The optimisation of operational parameters, mainly pH, Pb and EPS concentrations, using the Box–Behnken design (BBD) was undertaken to enhance lead uptake. The higher Pb adsorption capacity reached 2211.029 mg/g. Hydroxyl, carbonyl, carboxyl, phosphoric, and sulfhydryl groups were identified quantitatively as potential sites for Pb adsorption. EPS exhibited a notable flocculation rate of 70.20% in kaolin clay at a concentration of 15 mg/L. They demonstrated an emulsifying activity greater than 88%, showcasing their versatile potential for both sedimentation processes and stabilising liquid–liquid systems. EPS could be excellent nonconventional renewable biopolymers for treating water and wastewater.

Temperature optima of a natural diatom population increases as global warming proceeds

AbstractStudies in laboratory-based experimental evolution have demonstrated that phytoplankton species can rapidly adapt to higher temperatures. However, adaptation processes and their pace remain largely unknown under natural conditions. Here, by comparing resurrected Skeletonema marinoi strains from the Baltic Sea during the past 60 years, we show that modern S. marinoi have increased their temperature optima by 1 °C. With the increasing ability to grow in higher temperatures, growth rates in cold water decreased. Modern S. marinoi modified their valve:girdle ratio under warmer temperatures, which probably increases nutrient uptake ability. This was supported by the upregulation of several genes related to nitrate metabolism in modern strains grown under high temperatures. Our approach using resurrected strains demonstrates the adaptation potential of naturally occurring marine diatoms to increasing temperatures as global warming proceeds and exemplifies a realistic pace of evolution, which is an order of magnitude slower than estimated by experimental evolution.

Amphiphilic Post‐Modification of Red Algae‐Derived Carrageenan Coatings for Balanced Marine Antifouling Applications

AbstractPolysaccharide coatings are of interest for marine antifouling applications because of their good marine antifouling properties and environmentally benign characteristics. However, the hydrophilic nature of polysaccharide coatings can lead to the adsorption of marine sediment, which can negatively impact their antifouling properties. Amphiphilic modification of polysaccharide coatings has been demonstrated to address these issues. In this study, we report a simple method for post‐modification of a sulfated polysaccharide carrageenan (CAR) coating to make it amphiphilic. A hydrophilic CAR coating is first formed on solid substrates, followed by grafting hydrophobic molecules onto the CAR‐coated surfaces through metal‐ion‐mediated coordinate bond formation. The resulting amphiphilic CAR coating effectively reduces both marine sediment (silt) adsorption and marine diatom adhesion, achieving a balanced marine antifouling performance.

Morphological and physiological responses of the cosmopolitan marine diatom Thalassiosira rotula to acidification

We investigated the effect of decreased pH on the morphology and nutrient physiology of the cosmopolitan marine diatom Thalassiosira rotula (CCMP3362) by acclimating unialgal cultures to two different CO2 gas concentrations under optimal light, temperature and nutrient conditions. At lower pH (higher CO2), T. rotula exhibited a reduction in cell diameter (7%), surface area (13%), and volume (20%), and an increase in surface area-to-volume ratio (7%). All measures of silicification in T. rotula, i.e., silica (SiO2) quota, rate of silicic acid (Si(OH)4) utilization, and elemental ratios of SiO2:C and SiO2:N, remained unchanged. Similarly, carbon (C) and nitrogen (N) quotas, ratios and utilization rates were mostly unaffected by pH. In contrast, the utilization rate of nitrate (ρNO3) was significantly lower at decreased pH when the rate was normalized by cell number instead of by cell volume. The changes in cell morphology found in this study under low pH were likely not large enough to significantly impact physiological processes and the role of this species in marine food webs and biogeochemical cycles. It is possible that the interactive effects of pH, temperature, light, and nutrient availability characteristic of different regions of the world ocean could result in stronger physiological and morphological responses in this widespread diatom. However, under constant optimal growth conditions, T. rotula was only mildly affected by changes in pH, and in particular the physiology and elemental stoichiometry of C, N and Si were not sensitive to acidification.

Marine benthic diatom Psammodictyon panduriforme (MACC 35) as a potent producer of long chain hydrocarbons and fatty acids of biofuel significance

Marine diatoms are promising feedstock for biofuel industries as a source of hydrocarbons and fatty acids. In the present study, eleven marine diatom isolates from the west coast of India were analysed for hydrocarbons and lipids. The comparative analyses indicated that Psammodictyon panduriforme (MACC 35), a diatom isolate from the water samples collected from 1000 m depth, with a hydrocarbon yield of 37.27 mg g−1 L−1 and 2.1 % of the total biomass of 0.56 gL−1 was a promising species followed by Biddulphia sp. (MACC 6) with hydrocarbon yield of 25.4 mg g−1 L−1 and 1.3 % of the total biomass of 0.48 g L−1. Hydrocarbon analyses by gas chromatography with high resolution mass spectrometry (GCMS) showed that the long chain hydrocarbons found in the majority of the marine diatoms were undecane 4,7 dimethyl, hexadecane, octadecane,3-ethyl-5-(2-ethyl-butyl), tetradecane, tetracosane, eicosane-2 methyl, heptacosaneand hexacosane. The fatty acid profile showed the presence of stearic acid, 9-octadecenoic acid, myristic acid, palmitic acid, and arachidic acid with excellent biodiesel properties. Hydrocarbons of high fuel quality can be produced by optimizing hydrocarbon production in the potent marine diatom Psammodictyon panduriforme and catalytic cracking of long chain hydrocarbons to short chain alkanes with high octane ratings.