Red Tide Microalgae Research Articles

Purification and Screening of the Antialgal Activity of Seaweed Extracts and a New Glycolipid Derivative against Two Ichthyotoxic Red Tide Microalgae Amphidinium carterae and Karenia mikimotoi.

Ichthyotoxic red tide is a problem that the world is facing and needs to solve. The use of antialgal compounds from marine macroalgae to suppress ichthyotoxic red tide is considered a promising biological control method. Antialgal substances were screened and isolated from Bangia fusco-purpurea, Gelidium amansii, Gloiopeltis furcate, Hizikia fusifarme, Laminaria japonica, Palmaria palmata, and Sargassum sp. to obtain new materials for the development of algaecides against ichthyotoxic red tide microalgae using bioactivity-guided isolation methods. The fractions of seven macroalgae exhibited selective inhibitory activities against Amphidinium carterae and Karenia mikimotoi, of which the ethyl acetate fractions had the strongest and broadest antialgal activities for the two tested red tide microalgae. Their inhibitory effects on A. carterae and K. mikimotoi were even stronger than that of potassium dichromate, such as ethyl acetate fractions of B. purpurea, H. fusifarme, and Sargassum sp. Thin-layer chromatography and ultraviolet spectroscopy were further carried out to screen the ethyl acetate fraction of Sargassum sp. Finally, a new glycolipid derivative, 2-O-eicosanoyl-3-O-(6-amino-6-deoxy)-β-D-glucopyranosyl-glycerol, was isolated and identified from Sargassum sp., and it was isolated for the first time from marine macroalgae. The significant antialgal effects of 2-O-eicosanoyl-3-O-(6-amino-6-deoxy)-β-D-glucopyranosyl-glycerol on A. carterae and K. mikimotoi were determined.

Yessotoxin production and aerosolization during the unprecedented red tide of 2020 in southern California

An April–May 2020 bloom of the red tide microalga Lingulodinium polyedra developed to an unprecedented size, extending from northern Baja California to the Santa Barbara Channel. The L. polyedra strain is native to coastal California and is known to produce low levels of a toxic di-sulfated polyether named yessotoxin (YTX). In order to assess the evolution of the YTX content throughout the bloom and its transfer to water and aerosols, the concentration of YTX analogs was measured in the particulate and the dissolved organic matter of the sea surface water as well as in onshore sea spray aerosols. The YTX cell content was characteristic of Californian strains of L. polyedra. A lower production of YTX analogs by the cells at the peak of the bloom was detected, yielding total YTX content (particulate + dissolved) ranging from below the detection limit to 6.89 ng L−1 at that time. Yessotoxin and homo-yessotoxin were detected in sea spray aerosol measured onshore (from below detection limit to 20.67 ± 8.37 pg m−3), constituting the first detection of YTX analogs in coastal aerosols. The aerosolized YTX did not correlate with the seawater content but rather with westerly winds and higher tides. The presence of YTX in aerosols motivates further investigation into potential correlations with adverse effects in humans.

Metabolites and metabolic pathways associated with allelochemical effects of linoleic acid on Karenia mikimotoi

Linoleic acid (LA) shows great potential in inhibiting the growth of multiple red tide microalgae by disturbing algal physio-biochemical processes. However, our knowledge on the mechanisms of algal mortality at metabolic level remains limited. Herein, the response of K. mikimotoi to LA was evaluated using metabolomics, stable isotope techniques (SIT), and physiological indicators. Results showed that 100 μg/L LA promoted the growth of K. mikimotoi, which was significantly inhibited by 500 μg/L LA, along with a significant reduction of photosynthetic pigments and a significant increase of reactive oxygen species (ROS). SIT showed that LA entered algal cells, and 56 isotopologues involved in ferroptosis, carotenoid biosynthesis, and porphyrin metabolism were identified. Non-targeted metabolomics identified 90 and 111 differential metabolites (DEMs) belonging to 11 metabolic pathways under the 500 μg/L and 100 μg/L LA exposure, respectively. Among them, 34 DEMs were detected by SIT. Metabolic pathway analysis showed that 500 μg/L LA significantly promoted ferroptosis, and significantly inhibited carotenoid biosynthesis, porphyrin metabolism, sphingolipid metabolism, and lipopolysaccharide biosynthesis, presenting changes opposite to those observed in 100 μg/L LA-treated K. mikimotoi. Overall, this study revealed the metabolic response of K. mikimotoi to LA, enriching our understanding on the allelochemical mechanism of LA on K. mikimotoi.

Transcriptomic analysis provides insights into the algicidal mechanism of cocamidopropyl betaine against the red tide microalgae Skeletonema costatum

This study investigated the effect of the surfactant cocamidopropyl betaine (CAB) on the growth of red tide microalgae Skeletonema costatum. It was found that CAB caused cell lysis in a time- and dose-dependent manner and significantly inhibited the growth of S. costatum. Additionally, the transcriptomic approach was coupled with physiological analysis to elucidate the inhibitory mechanism of CAB on S. costatum. Among the 30726 genes identified, 17720 and 20583 genes were differentially expressed after treatment for 3 h and 6 h, respectively, which revealed that CAB redirected metabolic pathways, of which the expressions of genes related to the proteasome, ABC transporters, and amino acid-related metabolism were significantly upregulated, while genes involved in photosynthesis, biofilm and cell wall synthesis, mitogen-activated protein kinase (MAPK) cascades and antioxidant system were downregulated. The results above corresponded to the decreasing antioxidant enzymes activities, protein and photosynthetic pigments contents, as well as the increasing malondialdehyde (MDA) content. Our study presented herein shed light on the algicidal mechanism of CAB at the transcriptome level and was useful to red tide control, and marine environmental protection.

Are there environmental benefits derived from coastal aquaculture of Sargassum fusiforme?

Seaweed farming may alleviate coastal eutrophication and acidification, and contribute to the coastal ecosystems. Sargassum fusiforme has nutritional and medicinal benefits, and its cultivation in China has expanded in recent years. However, the environmental benefits of coastal S. fusiforme farming to the surface seawater remain unclear. In this study, we compared cultured and non-cultured areas, during the culture and non-culture seasons, in the main S. fusiforme coastal growing area of China. The results showed that S. fusiforme farming slightly increased the dissolved oxygen content and pH of surface seawater but decreased the nutrient content and chemical oxygen demand. Furthermore, the eutrophication level of seawater decreased by 36% on average. In the later stage of cultivation, with large S. fusiforme biomass, the eutrophication level of the surface seawater decreased by >50%. In addition, S. fusiforme farming increased the phytoplankton biomass and diversity index, and in conjunction with environmental factors, altered the phytoplankton community structure. After the harvest of S. fusiforme, the dominant phytoplankton mostly comprised red tide microalgae, and their abundance was relatively large. Experiments and harvest evaluations showed that S. fusiforme cultivation removed 8082 t of carbon, 642 t of nitrogen, and 61 t of phosphorus from coastal China during one culture period. This study showed that large-scale cultivation of S. fusiforme can slightly improve coastal surface seawater quality by removing nutrients, alleviating eutrophication, and actively altering phytoplankton community structure. These environmental benefits may play an important role in maintaining the health of coastal ecosystems.

Development of environmentally friendly biological algicide and biochemical analysis of inhibitory effect of diatom Skeletonema costatum

Skeletonema costatum is a diatom widely distributed in red tide microalgae blooms and as one of the main algae causing harmful algal blooms, because of their rapid reproduction and production of toxic and harmful substances, often play a negative role in aquatic ecosystems, and human health and wellbeing. Bacillomycin D is a nonribosomal cyclic antifungal lipopeptide in the iturins family. In this study, Bacillomycin D was tested for its ability to inhibit the growth of S. costatum. The EC50 24h of Bacillomycin D on S. costatum was 24.70 µg/mL. The chlorophyll fluorescence parameters Fv/Fm, Fv/Fo, and yield of the diatoms decreased significantly with increasing concentrations of Bacillomycin D. Study of the mechanism showed that Bacillomycin D induced cell death by changing cell membrane permeability, promoting the release of cellular contents. In this study, transcriptomic analysis showed Bacillomycin D significantly inhibited the photosynthesis and metabolism of S. costatum. These findings investigated the inhibitory effect of Bacillomycin D on the growth of S. costatum and provided a theoretical foundation for the development of new environmentally friendly biological algicide.

Effect of the Extracts of Sargassum fusiforme on Red Tide Microalgae in East China Sea

This study examined the effects of extracts of hijiki (Sargassum fusiforme) on the growth and physiology of three species of red tide microalgae (Prorocentrum donghaiensis, Skeletonema costatum, and Heterosigma akashiwo) that commonly grow in the East China Sea. The red tide algae were cultivated with the hijiki extracts at different concentrations to investigate the effects of the extracts on cells growth, chlorophyll a content, maximum quantum yield of PSII (Fv/Fm), the activities of four oxidoreductases including peroxidase (SOD), glutathione S-transferase (GST), glutathione peroxidase (GSH-Px), glutathione reductase (GR), and the level of the membrane lipid peroxidation product, malondialdehyde (MDA). The sensitivity of red tide algae to the extracts varied among the strains, with P. donghaiensis being the most sensitive, followed by S. costatum, and then H. akashiwo. Furthermore, the extracts had a rapid lethal effect on P. donghaiensis at over 1.6 g/L and on S. costatum and P. donghaiensis at over 8 g/L. From that concentration, increasing amounts of the extracts in cultures of S. costatum promoted a reduction in Chla contents and Fv/Fm values. In addition, the oxidoreductase activity of S. costatum was reduced at 4 and 6 g/L, as shown by the reduced activity of SOD, GR, GSH-Px, GST and MDA content in the cells. The results presented herein will be useful to the development and utilization of hijiki on red tide control, and marine environmental protection.

Effects of Polystyrene Microplastics on Growth and Toxin Production of Alexandrium pacificum.

Microplastics (MP) widely distributed in aquatic environments have adverse effects on aquatic organisms. Currently, the impact of MP on toxigenic red tide microalgae is poorly understood. In this study, the strain of Alexandrium pacificum ATHK, typically producing paralytic shellfish toxins (PST), was selected as the target. Effects of 1 and 0.1 μm polystyrene MP with three concentration gradients (5 mg L−1, 25 mg L−1 and 100 mg L−1) on the growth, chlorophyll a (Chl a), photosynthetic activity (Fv/Fm) and PST production of ATHK were explored. Results showed that the high concentration (100 mg L−1) of 1 μm and 0.1 μm MP significantly inhibited the growth of ATHK, and the inhibition depended on the size and concentration of MP. Contents of Chl a showed an increase with various degrees after MP exposure in all cases. The photosynthesis indicator Fv/Fm of ATHK was significantly inhibited in the first 11 days, then gradually returned to the level of control group at day 13, and finally was gradually inhibited in the 1 μm MP treatments, and promotion or inhibition to some degree also occurred at different periods after exposure to 0.1 μm MP. Overall, both particle sizes of MP at 5 and 25 mg L−1 had no significant effect on cell toxin quota, and the high concentration 100 mg L−1 significantly promoted the PST biosynthesis on the day 7, 11 and 15. No significant difference occurred in the cell toxin quota and the total toxin content in all treatments at the end of the experiment (day 21). All MP treatments did not change the toxin profiles of ATHK, nor did the relative molar percentage of main PST components. The growth of ATHK, Chl a content, Fv/Fm and toxin production were not affected by MP shading. This is the first report on the effects of MP on the PST-producing microalgae, which will improve the understanding of the adverse impact of MP on the growth and toxin production of A. pacificum.

Bacterial Community Composition and Chromophoric Dissolved Organic Matter Differs with Culture Time of Skeletonema dohrnii

Skeletonema dohrnii is a common red tide microalgae occurring in the coastal waters and throughout the world. The associated heterotrophic or autotrophic bacteria play vital roles in regulating algal growth, production, and physiology. In this study, we investigated the detailed bacterial community structure associated with the growth of S. dohrnii’s using high-throughput sequencing-based on 16S rDNA. Our results demonstrated that Bacteroidetes (48.04%) and Proteobacteria (40.66%) in all samples accounted for the majority of bacterial populations. There was a significant linear regression relationship between the abundance of bacterial phyla and culture time. Notable shifts in bacterial community composition were observed during algal growth: Flavobacteriales accounted for the vast majority of sequences at the order level. Furthermore, the relative abundance of Rhodobacterales was gradually reduced during the whole growth process of S. dohrnii (0–12 days). However, beyond that, the relative abundance of Marinobacter was slowly increasing. It is noteworthy that five fluorophores (Peaks T1, T2, I, M, and A) were detected during the growth stage of S. dohrnii. The characteristic indexes (fluorescence index, humification index, and biological index) of chromophoric dissolved organic matter (CDOM) also varied with the culture time. In addition, the taxa of bacteria had certain effects on CDOM and they were inextricably linked to each other.

Several natural products isolated from a red alga Gracilaria lemaneiformis and its evaluation of antialgal activity against six common red tide microalgae.

The ethanol extracts of Gracilaria lemaneiformis that have inhibitory effects on Karenia mikimotoi and Skeletonema costatum were separated by liquid-liquid extraction using different polar solvents into five fractions with antialgal activities (petroleum ether, chloroform, ethyl acetate, n-butanol, and water-soluble fractions). These fractions were chromatographed on silica gel to give, after repeated preparative thin-layer chromatography (PTLC) purification processes, 1-β-D-ribofuranosyluracil (1), 3-hydroxymethyl-pyrrolopiperazine-2,5-dione (2), benzene-1,2-propanoic acid (3), 1-O-palmitoyl-2-O-palmitoleoyl-3-O-β-D-galactopyranosyl glycerol (4), 7-oxabicyclo[4.1.0]-heptan-3-ol (5), linoleic acid (6), 3,4-dimethoxy-6-(methoxymethyl)-tetrahydro-2H-pyran-2,5-diol (7), and 3,7,11,16-tetramethyl -2-heptadecen-1-ol (8). Five of them, natural products 1, 2, 5, 7, and 8, were isolated from Gracilaria lemaneiformis for the first time, and three natural products (3, 5, and 8) were isolated from marine macroalgae for the first time. Among them, natural products (1, 2, 3, 4, and 6) showed the most obvious inhibition activities to the growth of Karenia mikimotoi and Skeletonema costatum at the concentration of 80 μg/mL. Therefore, antialgal activities of these five natural products against Amphidinium carterae, Heterosigma akashiwo, Karenia mikimotoi, Phaeocystis globosa, Prorocentrum donghaiense, and Skeletonema costatum were further tested at different concentrations (0.4, 2, 10, and 50 μg/mL). This was the first report of antialgal activities of five natural products (1, 2, 3, 4, and 6) to these six red tide microalgae. They showed significantly selective antialgal activities against all tested red tide microalgae. At the concentration of 50 μg/mL, the growth of Amphidinium carterae, Heterosigma akashiwo, Karenia mikimotoi, and Phaeocystis globosa was obviously inhibited; for Karenia mikimotoi, natural products 1, 2, and 6 have significant antialgal activities; the growth inhibition of Skeletonema costatum that was exposed to natural products 1, 3, and 4 was remarkable. Furthermore, by analyzing and comparing EC50-96 h values, it has been determined that natural product 3 (natural product 4) showed the superior application potential than potassium dichromate and some reported natural products (such as gossonorol isolated from Porphyra yezoensis, trehalose purified from Ulva pertusa) as a characteristic antialgal agent against Amphidinium carterae (Phaeocystis globosa). In addition, natural products 1 and 3 also showed good superiority than some reported natural products in inhibiting Skeletonema costatum; however, it was a pity that they were inferior to potassium dichromate in the inhibiting this red tide microalgae. Taken together, it is not hard to conclude that Gracilaria lemaneiformis was a good source of natural products with antialgal activities against some red tide microalgae.

Bioactivities of algicidal C18 hydroxy unsaturated fatty acid isolated from the red alga Tricleocarpa jejuensis and its synthesized propargylic derivative

(±)-(E)-12-hydroxyoctadec-10-enoic acid (compound A) was isolated from the red alga Tricleocarpa jejuensis in our previous study as a potent algicidal compound against red tide microalga Chattonella antiqua (Ochrophyta, Raphidophyceae). Interestingly, its propargylic derivative, 12-hydroxyoctadec-10-ynoic acid (compound B), which was obtained as a synthetic intermediate of compound A, showed an even more extensive algicidal activity. In this study, the effects of compound A and B on the major causative species of harmful algal blooms (HABs) such as Chattonella marina (Ochrophyta, Raphidophyceae), Heterocapsa circularisquama, and Karenia mikimotoi (Miozoa, Dinophyceae) in addition to C. antiqua were investigated. Both compounds exhibited toxic effects on these red tide flagellates in a concentration dependent manner with LC50 < 10 μg/mL, and the activities of compound B were much stronger than compound A. Zooplankton rotifer (Brachionys plicatilis) was relatively resistant to the compounds, and the lethal effects of H. circularisquama and K. mikimotoi on rotifers were reduced in the presence of compound A and B, suggesting their potential usage in the mitigation strategy for HABs. Consistent with the toxicities on the HAB species, compound B showed stronger cytotoxicity on HeLa, XC, and U937 cells than A. Since compound B but not compound A showed haemolytic activity on rabbit erythrocytes, specific action of compound B on cell membrane may be responsible for the potent cytotoxicity. Furthermore, compound B exhibited higher antibacterial effect on Staphylococcus aureus than compound A, while both were not effective on Enchiridia coli. Our results suggest that compound A and B are promising multifunctional candidates with potential to develop not only as anti-red tide microalgae but also as tumor cell-killing and antibacterial agents. This is the first report indicating that replacing a double bond in the hydroxy unsaturated fatty acid with a triple bond results in much augmentation of the bioactivities.

A Comprehensive Review of Secondary Metabolites with Antialgal Activity from Marine Macroalgae against Red Tide Microalgae

Sun, Y.; Dong, S.; Zhou, W.; Guo, L.; Guo, G., and Zhang, X., 2019. A comprehensive review of secondary metabolites with antialgal activity from marine macroalgae against red tide microalgae. In: Guido-Aldana, P.A. and Mulahasan, S. (eds.), Advances in Water Resources and Exploration. Journal of Coastal Research, Special Issue No. 93, pp. 475–488. Coconut Creek (Florida), ISSN 0749-0208.Red tide, mainly caused by the large-scale reproduction of microscopic algae, has virtually affected every coastal country or region in the whole world over the last several decades. In order to control and mitigate the proliferation and diffusion of red tide microalgae, there are many methods or strategies for fighting or inhibiting red tide microalgae species, these methods or strategies included mechanical, chemical, biological, genetic methods and others. Unfortunately, the use of these methods or strategies is usually ineffective. There are some evidences that the inhibition effect of marine macroalgae on the growth of red tide microalgae is mainly due to the release of bioactive molecules, which are mainly secondary metabolites. Thus, antialgal secondary metabolites, isolated marine macroalgae, have become an environmentally friendly alternative approach. And relevant researches of antialgal secondary metabolites in marine macroalgae, such as screen, isolation, identification and other research etc., have also become very important subjects to biological control of red tide microalgae. The inhibition effects of marine macroalgae on red tide microalgae are here reviewed, focusing on antialgal secondary metabolites, isolated from marine macroalgae, against red tide microalgae growth. Further, this paper describes isolation and EC50-96 h (half maximal effective concentration) or IC50-96 h (half maximal inhibitory concentration) for red tide microalgae of some antialgal secondary metabolites, including the recently discovered compounds. Finally, this review is the first to demonstrate that development relationships between macroalgae and red tide using CiteSpace, and cluster view of macroalgae and red tide is given for the first time. This work provides scientists in the field with the necessary information and the urgent need to isolate and identify screening antialgal secondary metabolites in different marine macroalgae. Also, analysis result, which obtained through CiteSpace, has pointed out that allelopathic interaction between marine macroalgae and red tide microalgae has been developed into a study area during the last twenty years.

RNA-Seq Analysis Reveals Genes Related to Photoreception, Nutrient Uptake, and Toxicity in a Noxious Red-Tide Raphidophyte Chattonella antiqua.

Aquaculture industries are under threat from noxious red tides, but harm can be mitigated by precautions such as early harvesting and restricting fish feeding to just before the outbreak of a red tide. Therefore, accurate techniques for forecasting red-tide outbreaks are strongly needed. Omics analyses have the potential to expand our understanding of the eco-physiology of these organisms at the molecular level, and to facilitate identification of molecular markers for forecasting their population dynamics and occurrence of damages to fisheries. Red tides of marine raphidophytes, especially Chattonella species, often extensively harm aquaculture industries in regions with a temperate climate around the world. A red tide of Chattonella tends to develop just after an input of nutrients along the coast. Chattonella displays diurnal vertical migration regulated by a weak blue light, so it photosynthesizes in the surface layer during the daytime and takes up nutrients in the bottom layer during the nighttime. Superoxide produced by Chattonella cells is a strong candidate for the cause of its toxicity to bacteria and fishes. Here we conducted mRNA-seq of Chattonella antiqua to identify genes with functions closely related to the dynamics of the noxious red tide, such as photosynthesis, photoreception, nutrient uptake, and superoxide production. The genes related to photosynthetic pigment biosynthesis and nutrient uptake had high similarity with those of model organisms of plants and algae and other red-tide microalgae. We identified orthologous genes of photoreceptors such as aureochrome (newly five genes), the cryptochrome/photolyase (CRY/PHR) family (6-4PHR, plant CRY or cyclobutane pyrimidine dimer [CPD] Class III, CPD Class II, and CRY-DASH), and phytochrome (four genes), which regulate various physiological processes such as flagellar motion and cell cycle in model organisms. Six orthologous genes of NADPH oxidase, which produces superoxide on the cell membrane, were found and divided into two types: one with 5–6 transmembrane domains and another with 11 transmembrane domains. The present study should open the way for analyzing the eco-physiological features of marine raphidophytes at the molecular level.

Antialgal Activity of Glycoglycerolipids Derived from a Green Macroalgae Ulva prolifera on Six Species of Red Tide Microalgae

1-O-palmitoyl -3-O-β-D-galactopyranosyl glycerol, 1-O-octadecanoic acid-3-O-β-D-galactopyranosyl glycerol, and 1-O-palmitoyl-2-O-oleoyl-3-O-β-D-galactopyranosyl glycerol were isolated from Ulva prolifera for the first time in our previous research. There are growth inhibiton of these three glycoglycerolipids against six species of red tide microalgae (Amphidinium carterae, Heterosigma akashiwo, Karenia mikimotoi, Phaeocystis globosa, Prorocentrum donghaiense, and Skeletonema costatum) investigated. Results showed that they have selective antialgal activity against six species of red tide microalgae, and antialgal activities against test red tide microalgae obviously enhanced with the increase of concentration of glycoglycerolipids. Among them, 1-O-octadecanoic acid-3-O-β-D-galactopyranosyl glycerol and 1-O-palmitoyl-2-O-oleoyl-3-O-β-D-galactopyranosyl glycerol exhibited more extensive antialgal activities, and the growth of Phaeocystis globosa, Prorocentrum donghaiense, and Skeletonema costatum (or Karenia mikimotoi, and Skeletonema costatum) was inhibited by these two glycoglycerolipids. Further, EC50-96h values of these three glycoglycerolipids for six red tide microalgae were obtained for the first time. By analyzing and comparing EC50-96h values, it has been determined that 1-O-octadecanoic acid-3-O-β-D-galactopyranosyl glycerol and 1-O-palmitoyl-2-O-oleoyl-3-O-γ-D-galactopyranosyl glycerol showed the superior application potential than potassium dichromate as a characteristic antialgal agent against Phaeocystis globosa; More importantly, 1-O-octadecanoic acid-3-O-β-D-galactopyranosyl glycerol exhibited the superior application potential than potassium dichromate and other reported compounds as a characteristic antialgal agent against Prorocentrum donghaiense.

Algicidal activities of secondary metabolites of marine macroalgal-derived endophytic fungi

Red tide occurrs frequently and causes significant damage to the environment and human health. As a result, development of new efficient and environment friendly red-tide microalgae inhibitors has gained increasing attention in recent times. Algicolous endophytic fungi with unique habitats are promising sources for active agents owing to their abundant secondary metabolites and distinguished activities. In this study, the algicidal activities of 49 marine macroalgal-derived endophytic fungi against phytoplankton Alexandrium tamarense, Prorocentrum donghaiense, Heterosigma akashiwo, and Chattonella marina were examined using 96-well microplate. Four fungal strains, including Aspergillus wentii (pt-1), A. ustus (cf-42), and A. versicolor (dl-29, pt-20), exhibited potent algicidal activities. A total of 32 pure compounds isolated from these fungi were noted to possess different degrees of algicidal activities. Of those, 11 compounds comprising five anthraquinones, two terpenoids, and four steroids showed high 24-h inhibition rates for the four red tide algae, with EC 50(24 h) values ranging from 0.01 to 14.29 μg/mL. Among them, compound 1 (1,5-dihydroxy-3-methoxy-7-methylanthraquinone) presented the strongest activity against H. akashiwo, and could decrease its chlorophyll a (Chl a ) and superoxide dismutase contents and increase the soluble protein, malondialdehyde, and peroxidase contents. These results suggested that the identified anti-algal compound might inhibit the growth of red tide algae by weakening photosynthesis (reducing Chl a content), destroying cell membrane, and damaging the antioxidant system.

Antialgal compounds with antialgal activity against the common red tide microalgae from a green algae Ulva pertusa

Nine antialgal active compounds, (i.e. trehalose (1), twenty-two methyl carbonate (2), (-)-dihydromenisdaurilide (3), 3,7,11,15-tetramethyl-2-hexadecen-1-ol (4), isophytol (5), 8-hexadecenol (6), 17-hydroxyheptadecanoic acid (7), trans-asarone (8) and 2-amino-3-mercaptopropanoic acid (9)) were isolated from Ulva pertusa for the first time by sephadex LH-20 column chromatography, silica gel column chromatography and repeated preparative TLC. Except for compound 4, all compounds represented novel isolated molecules from marine macroalgae. Further, antialgal activities of these compounds against Amphidinium carterae, Heterosigma akashiwo, Karenia mikimitoi, Phaeocystis globosa, Prorocentrum donghaiense and Skeletonema costatum were investigated for the first time. Results showed these nine compounds have selectivity antialgal effects on all test red tide microalgae, and antialgal activities against red tide microalgae obviously enhanced with the increase of concentration of antialgal compounds. Based on this, EC50–96 h values of these nine compounds for six red tide microalgae were obtained for the first time. By analyzing and comparing EC50–96 h values, it has been determined that seven compounds (1, 3, 4, 6, 7, 8 and 9) showed the superior application potential than potassium dichromate or gossonorol and other six compounds as a characteristic antialgal agent against Heterosigma akashiwo, Karenia mikimitoi and Prorocentrum donghaiense. Overall this study has suggested that green algae Ulva pertusa is a new source of bioactive compounds with antialgal activity.

Sesquiterpenoids with antialgal activity against the common red tide microalgae from marine macroalga Porphyra yezoensis.

Previous studies showed that methanol extracts from Porphyra yezoensis significantly inhibited Karenia mikimitoi and Skeletonema costatum. Five sesquiterpenoids (1-5) were successfully isolated from this marine macroalga through a combination of silica gel column chromatography and repeated preparative thin-layer chromatography in this paper. Their structure was identified as gossonorol (1), 7,10-epoxy-ar-bisabol-11-ol (2), cyclonerodiol (3), cadinol, (4) and 4-cadinen-1-ol (5) on the basis of spectroscopic data. These sesquiterpenoids were isolated from Porphyra yezoensis for the first time, and cyclonerodiol (3) and cadinol (4) isolated from marine macroalgae for the first time. Further, a quantitative relationship between the inhibition of algal growth and the concentration of each antialgal sesquiterpenoid (gossonorol, 7,10-epoxy-ar-bisabol-11-ol and cyclonerodiol) was determined and important parameters, e.g., EC50-96h for future practical HAB control are to be obtained. Results showed that three sesquiterpenoids (1-3) had selective antialgal activity against the growth of red tide microalgae (Amphidinium carterae, Heterosigma akashiwo, Karenia mikimitoi, Phaeocystis globosa, Prorocentrum donghaiense, and Skeletonema costatum). More than two test red tide microalgae were significantly inhibited by these three sesquiterpenoids (1-3). Their antialgal activity against red tide microalgae has not been previously reported. Furthermore, EC50-96h of gossonorol (1) and 7,10-epoxy-ar-bisabol-11-ol (2) for specific test red microalgae were not only significantly less than 10μg/mL, but also were smaller than/or very close to those of potassium dichromate. Gossonorol (1) and 7,10-epoxy-ar-bisabol-11-ol (2) possessed good application potential than potassium dichromate as a characteristic antialgal agent against the specific harmful red tide microalgae (Heterosigma akashiwo, Phaeocystis globosa, and Prorocentrum donghaiense) (or Heterosigma akashiwo and Karenia mikimitoi).

Quorum sensing of microalgae associated marine Ponticoccus sp. PD-2 and its algicidal function regulation

Quorum sensing (QS) systems play important roles in regulating many physiological functions of microorganisms, such as biofilm formation, bioluminescence, and antibiotic production. One marine algicidal bacterium, Ponticoccus sp. PD-2, was isolated from the microalga Prorocentrum donghaiense, and its N-acyl-homoserine lactone (AHL)-mediated QS system was verified. In this study, we analyzed the AHLs profile of strain PD-2. Two AHLs, 3-oxo-C8-HSL and 3-oxo-C10-HSL, were detected using a biosensor overlay assay and GC–MS methods. Two complete AHL-QS systems (designated zlaI/R and zlbI/R) were identified in the genome of strain PD-2. When expressed in Escherichia coli, both zlaI and zlbI genes could each produce 3-oxo-C8-HSL and 3-oxo-C10-HSL. Algicidal activity was investigated by evaluating the inhibitory rate (IR) of microalgae growth by measuring the fluorescence of viable cells. We found that the metabolites of strain PD-2 had algicidal activity against its host P. donghaiense (IR 84.81%) and two other red tide microalgae, Phaeocystis globosa (IR 78.91%) and Alexandrium tamarense (IR 67.14%). β-cyclodextrin which binds to AHLs and inhibits the QS system reduced the algicidal activity more than 50%. This indicates that inhibiting the QS system may affect the algicidal metabolites production of strain PD-2. Our study indicated that a QS-regulated algicidal system may play a potential role in the process of red tides disintegration. QS might be a potential way to control red tides.

Isolation and purification of antialgal compounds from the red alga Gracilaria lemaneiformis for activity against common harmful red tide microalgae

Seven antialgal compounds (1-7) were successfully isolated from the red alga Gracilaria lemaneiformis through a combination of silica gel column chromatography and repeated preparative thin-layer chromatography. On the basis of the spectral data, the compounds were identified as gossonorol (1), 7,10-epoxy-ar-bisabol-11-ol (2), glycerol monopalmitate (3), stigmasterol (4), 15-hydroxymethyl-2, 6, 10, 18, 22, 26, 30-heptamethyl-14-methylene-17-hentriacontene (5), 4-hydroxyphenethyl alcohol (6), and margaric acid (7). These seven compounds were isolated from G. lemaneiformis for the first time, while the compounds 4, 6, and 7 were isolated from marine macroalgae for the first time. Furthermore, a quantitative relationship between the inhibition of algal growth and the concentration of each antialgal compound was determined and important parameters for future practical HAB control, e.g., EC50-96h, were also obtained. The results indicated that isolated compounds 1-7 possess selective antialgal activity against the growth of several red tide microalgae (including Amphidinium carterae, Heterosigma akashiwo, Karenia mikimitoi, Phaeocystis globsa, Prorocentrum donghaiense, and Skeletonema costatum). Their antialgal activity against test red tide microalgae has not been previously reported. Furthermore, the EC50-96h of one or more of the compounds towards the tested red microalgae was not only significantly less than 10μg/mL but also was smaller than that of the characteristic antialgal agent potassium dichromate. The study demonstrates that compounds 1-7 possess significant application potential as antialgal agents against several harmful red tide microalgae.

Antialgal and antilarval activities of bioactive compounds extracted from the marine dinoflagellate Amphidinium carterae

With the global ban on the application of organotin-based marine coatings by the International Maritime Organization, the development of environmentally friendly, low-toxic and nontoxic antifouling compounds for marine industries has become an urgent need. Marine microorganisms have been considered as a potential source of natural antifoulants. In this study, the antifouling potential of marine dinoflagellate Amphidinium carterae, the toxic and red-tide microalgae, was investigated. We performed a series of operations to extract the bioactive substances from Amphidinium carterae and tested their antialgal and antilarval activities. The crude extract of Amphidinium carterae showed significant antialgal activity and the EC50 value against Skeletonema costatum was 55.4 μg mL−1. After purification, the isolated bioactive substances (the organic extract C) exhibited much higher antialgal and antilarval activities with EC50 of 12.9 μg mL−1 against Skeletonema costatum and LC50 of 15.1 μg mL−1 against Amphibalanus amphitrite larvae. Subsequently, IR, Q-TOFMS, and GC-MS were utilized for the structural elucidation of the bioactive compounds, and a series of unsaturated and saturated 16- to 22-carbon fatty acids were detected. The data suggested the bioactive compounds isolated from Amphidinium carterae exhibited a significant inhibiting effect against the diatom Skeletonema costatum and Amphibalanus amphitrite larvae, and could be substitutes for persistent, toxic antifouling compounds.