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)-ß-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)-ß-D-glucopyranosyl-glycerol on A. carterae and K. mikimotoi were determined.

Isolation of anti-algal substances from Cylindrotheca closterium and their inhibition activity on bloom-forming Prorocentrum donghaiense.

This paper studied the allelopathic effect of Cylindrotheca closterium on the growth of Prorocentrum donghaiense, the model of harmful algal blooms in aquatic environment, by the co-culture tests and bioassay-guided fraction methods. The growth of P. donghaiense in co-cultures was observably suppressed by C. closterium, and P. donghaiense biomass in C/P = 3: 1 group increased slowly with a low growth rate of 0.18 d-1 after 4 days. Petroleum ether (PE) extract derived from C. closterium filtrates was isolated by C18 column and the allelopathy of all isolated fractions for P. donghaiense was investigated. After 96 h cultivation, the inhibition ratio of PE-Ⅲ and PE-Ⅷ fractions on P. donghaiense could reach up to 70.2% and 64.3% at the concentration of 10-fold when compared to control, while the other fractions displayed relatively low inhibitory effects on P. donghaiense. PE-Ⅲ and PE-Ⅷ fractions also decreased the chlorophyll content and maximum quantum yield of photosystem II (Fv/Fm) of P. donghaiense cells. The activities of superoxide dismutase (SOD), one of antioxidant enzymes, reduced around 8.3% and 13.7% following exposure to 2-fold PE-Ⅲ and PE-Ⅷ, and was significantly decreased following higher exposure concentrations. After 96 h of 10-fold PE-Ⅲ and PE-Ⅷ treatments, Catalase (CAT) activity reduced to 44.86% and 46.42% of that observed in the control group. At the same time, a significant increase in malondialdehyde (MDA) contents was observed. These findings suggested that PE-Ⅲ and PE-Ⅷ fractions contained main allelochemicals and possibly acted as promising algistatic agents for emergency handling of P. donghaiense blooms.

Effects of CeO2 Nanoparticles on Microcystis aeruginosa Growth and Microcystin Production.

The interaction between metal oxide nanoparticles and toxin-producing cyanobacteria is relatively unknown. The present work exposed Microcystis sp.7806 to different concentrations of cerium oxide nanoparticles (CeO2 NPs) (1 mg/L, 10 mg/L and 50 mg/L), and evaluated the growth, photosynthetic activity, reactive oxygen species level, and the extra-(intra-) cellular microcystin-LR (MC-LR) contents. The particle size, zeta potential and cerium ions released into the medium were analyzed. Results showed 10 mg/L NP treatment promoted algae growth but slightly inhibited the photosynthetic yield of algae, and the 50 mg/L treatment reduced algae biomass. The algal cells remarkably responded to oxidative stress at higher concentrations (10 mg/L and 50 mg/L). CeO2 NPs largely increased the intracellular MC-LR content at 50 mg/L, and significantly reduced the extracellular MC-LR content at any concentration. This demonstrates CeO2 NPs may pose an ecological risk potential during harmful algal blooms by stimulating toxin production.

Stress of algicidal substances from a bacterium Exiguobacterium sp. h10 on Microcystis aeruginosa.

Microcystis aeruginosa is a cyanobacterial bloom-causing species and is considered a serious threat to human health and biological safety. In this study, the algicidal bacterium h10 showed high algicidal effects on M. aeruginosa 7820, and strain h10 was confirmed to belong to the genus Exiguobacterium, for which the name Exiguobacterium sp. h10 is proposed. Algicidal activity and mode analysis revealed that the supernatant, rather than the bacterial cells, was responsible for the algicidal activity, indicating that the algicidal mode of strain h10 is by indirect attack through the production of algicidal substances. Analysis of the algicidal substance characteristics showed a molecular weight of <1000 Da and that algicidal substances exhibit high thermal stability and pH instability, and the characteristic functional groups of the algicidal substance mainly included carbonyl, amino and hydroxyl groups. Under the effects of the algicidal substance, the cellular pigment content was significantly decreased, and the algal cell structure and morphology were seriously damaged. The results indicate that the algicidal bacterium Exiguobacterium sp. h10 could be a potential bio-agent for controlling cyanobacterial blooms of M. aeruginosa. SIGNIFICANCE AND IMPACT OF THE STUDY: In this study, the effects of algicidal substances from an algicidal bacterium Exiguobacterium sp. h10 on the toxic cyanobacterium, Microcystis aeruginosa 7820, were first investigated. The algicidal mode of action was confirmed as an indirect attack through the production of algicidal substances. The characteristics of the algicidal substance were determined, especially the functional groups analysis that confirmed the algicidal substances were glycolipid mixtures. With the stress of algicidal substances, the algal chlorophyll a synthesis, cell structure and morphology were seriously damaged. This study proved that algicidal bacteria are promising sources of potential cyanobacterial bloom-control, and provided good procedures for the identification and analysis of an algicidal bacterium and substances.

Algicidal Activity of Bacillamide Alkaloids and Their Analogues against Marine and Freshwater Harmful Algae.

Harmful algal blooms have become a great challenge to global aquatic ecosystems over the past decades. Given their low toxicity, high selectivity, and environment-friendly properties, the use of natural products and their analogues as algicides has proven to be particularly efficient. In the present study, algicidal activity of naturally occurring bacillamides A-C, alkaloid (1), and neobacillamide A, as well as their synthetic analogues were investigated intensively. Bioassay results showed that, relative to natural bacillamide alkaloids, aniline-derived analogue (10d) exhibited higher algicidal potential against three freshwater harmful algae Mycrocyctis aeruginosa, Scenedesmus obliquus, and Chlorella pyrenoidosa, suggesting that it could be used as a promising lead compound to develop novel algicide for controlling harmful algal blooms.

Improvement of cyanobacterial-killing biologically derived substances (BDSs) using an ecologically safe and cost-effective naphthoquinone derivative.

In previous studies, naphthoquinone (NQ) compounds have been shown to be effective, selective, and ecologically safe algicides for controlling harmful algal blooming species (HABs) or winter bloom species, such as Stephanodiscus hantzschii. However, there are no reports on NQ-based algicides for use with cyanobacterial blooming species. In this study, we developed 31 NQ compounds to investigate algicides for mitigating cyanobacterial blooms. In addition, to better apply these compounds in the field, we reduced the number of production steps to develop a cost-effective algicide. In preliminary testing, we screened NQ compounds that showed the best algicidal activity on target cyanobacteria, including Aphanizomenon, Dolichospermum, Microcystis, Oscillatoria, and Nostoc species. The compound NQ 2-0 showed the highest algicidal activity (90%) at a low concentration (≥1µM) on target algae. These were very limiting algicidal effects of 1µM NQ 2-0 observed against non-target algae, such as diatoms (Stephanodiscus hantzschii, Cyclotella meneghiniana, Synedra acus, and Aulacoseira granulata) or green algae (Cosmarium bioculatum and Scenedesmus quadricauda), and the effect did not exceed 15-25% (except against S. quadricauda). NQ 2-0 (1µM) showed no eco-toxicity, as represented by the survival rates of Pseudokirchneriella subcapitata (100%), Daphnia magna (100%), and Danio rerio (100%). Additionally, a chronic eco-toxicity assessment showed no toxicity toward the survival, growth or reproduction of D. magna. Moreover, NQ 2-0 quickly dissipated from field water samples and had a half-life of approximately 3.2 days. These results suggest that NQ 2-0 could be a selective and ecologically safe algicide to mitigate harmful cyanobacterial blooms.

Transcriptomic profiles reveal the genome-wide responses of the harmful dinoflagellate Cochlodinium polykrikoides when exposed to the algicide copper sulfate.

BACKGROUND: Harmful algal blooms (HABs) caused by the dinoflagellate Cochlodinium polykrikoides lead to severe environmental impacts in oceans worldwide followed by huge economic losses. Algicide agent copper sulfate (CuSO4) is regard as an economical and effective agent for HABs mitigation; its biochemical and physiological effects were revealed in C. polykrikoides. However, molecular mechanisms of CuSO4 effect on the C. polykrikoides, even other HAB species, have not been investigated. The present study investigated the transcriptional response of C. polykrikoides against CuSO4 treatments, with the aim of providing certain molecular mechanism of CuSO4 effect on the C. polykrikoides blooms. RESULTS: RNA-seq generated 173 million reads, which were further assembled to 191,212 contigs. 43.3 %, 33.9 %, and 15.6 % of contigs were annotated with NCBI NR, GO, and KEGG database, respectively. Transcriptomic analysis revealed 20.6 % differential expressed contigs, which grouped into 8 clusters according to K-means clustering analysis, responding to CuSO4; 848 contigs were up-regulated and 746 contigs were down-regulated more than 2-fold changes from 12 h to 48 h exposure. KEGG pathway analysis of eukaryotic homologous genes revealed the differentially expressed genes (DEGs) were involved in diverse pathway; amongst, the genes involved in the translation, spliceosome, and/or signal transduction genes were highly regulated. Most of photosystem related genes were down-regulated and most of mitochondria related genes were up-regulated. In addition, the genes involved in the copper ion binding or transporting and antioxidant systems were identified. Measurement of chlorophyll fluorescence showed that photosynthesis was significantly inhibited by CuSO4 exposure. CONCLUSIONS: This study reported the first transcriptome of the C. polykrikoides. The widely differential expressed photosystem genes suggested photosynthetic machinery were severely affected, and may further contribute to the cell death. Furthermore, gene translation and transcription processes may be disrupted, inhibiting cell growth and proliferation, and possibly accelerating cell death. However, antioxidant systems resistant to CuSO4 caused stress; mitochondrion may compensate for photosynthesis efficiency decreasing caused energy deficiency. In addition, various signal transduction pathways may be involved in the CuSO4 induced regulation network in the C. polykrikoides. These data provide the potential transcriptomic mechanism to explain the algicide CuSO4 effect on the harmful dinoflagellate C. polykrikoides.

Algicidal Activity of Streptomyces eurocidicus JXJ-0089 Metabolites and Their Effects on Microcystis Physiology.

UNLABELLED: Copper sulfate (CuSO4) has been widely used as an algicide to control harmful cyanobacterial blooms (CyanoHABs) in freshwater lakes. However, there are increasing concerns about this application, due mainly to the general toxicity of CuSO4 to other aquatic species and its long-term persistence in the environment. This study reported the isolation and characterization of two natural algicidal compounds, i.e., tryptamine and tryptoline, from Streptomyces eurocidicus JXJ-0089. At a concentration of 5 µg/ml, both compounds showed higher algicidal efficiencies than CuSO4 on Microcystis sp. FACHB-905 and some other harmful cyanobacterial strains. Tryptamine and tryptoline treatments induced a degradation of chlorophyll and cell walls of cyanobacteria. These two compounds also significantly increased the intracellular oxidant content, i.e., superoxide anion radical (O2 (-)) and malondialdehyde (MDA), but reduced the activity of intracellular reductants, i.e., superoxide dismutase (SOD), of cyanobacteria. Moreover, tryptamine and tryptoline treatments significantly altered the internal and external contents of microcystin-LR (MC-LR), a common cyanotoxin. Like CuSO4, tryptamine and tryptoline led to releases of intracellular MC-LR from Microcystis, but with lower rates than CuSO4 Tryptamine and tryptoline (5 µg/ml) in cyanobacterial cultures were completely degraded within 8 days, while CuSO4 persisted for months. Overall, our results suggest that tryptamine and tryptoline could potentially serve as more efficient and environmentally friendly alternative algicides than CuSO4 in controlling harmful cyanobacterial blooms. IMPORTANCE: Cyanobacterial harmful algal blooms (CyanoHABs) in aquatic environments have become a worldwide problem. Numerous efforts have been made to seek means to prevent, control, and mitigate CyanoHABs. Copper sulfate (CuSO4), was once a common algicide to treat and control CyanoHABs. However, its application has become limited due to concerns about its general toxicity to other aquatic species and its long-term persistence in the environment. There is a great need for algicides with higher specificity and low environmental impacts. This study reports the isolation and characterization of two natural algicidal compounds from a streptomycete strain, Streptomyces eurocidicus JXJ-0089. Our results suggest that the identified algicides could potentially serve as more efficient and environmentally friendly alternative algicides than CuSO4 in controlling harmful cyanobacterial blooms.

First Evidence of Altererythrobacter sp. LY02 with Indirect Algicidal Activity on the Toxic Dinoflagellate, Alexandrium tamarense.

Alexandrium tamarense is a toxic harmful algal blooms (HABs) causing species, which poses great threat to human health and marine economy. In this study, we isolated an algicidal bacterium Altererythrobacter sp. LY02 towards to A. tamarense and later investigated the algicidal activity, algicidal mode, characteristics of algicidal active substance and algicidal procedure. The results indicated that the cell-free filtrate of strain LY02 showed high algicidal effect on algal growth, however, bacterial cells almost lost algicidal activity. The algicidal active substance was temperature- and pH-stability, and its molecular weight was less than 1000 Da, and was a non-proteinaceous material or non-polysaccharide, mid-polar substance. Under the algicidal effect of active substance, the morphology and structure of A. tamarense cells were seriously damaged as well as organelles. Our study confirmed that the algicidal active substance could be used as an excellent bio-agent for controlling HABs caused by A. tamarense.

Algicidal effect of hybrid peptides as potential inhibitors of harmful algal blooms.

OBJECTIVES: To biochemically characterize synthetic peptides to control harmful algal blooms (HABs) that cause red tides in marine water ecosystems. RESULTS: We present an analysis of several short synthetic peptides and their efficacy as algicidal agents. By altering the amino acid composition of the peptides we addressed the mode of algicidal action and determine the optimal balance of cationic and hydrophobic content for killing. In a controlled setting, these synthetic peptides disrupted both plasma and chloroplast membranes of several species known to result in HABs. This disruption was a direct result of the hydrophobic and cationic content of the peptide. Furthermore, by using an anti-HAB bioassay in scallops, we determined that these peptides were algicidal without being cytotoxic to other marine organisms. CONCLUSIONS: These synthetic peptides may prove promising for general marine ecosystem remediation where HABs have become widespread and resulted in serious economic loss.

Removal of Two Species of Harmful Algae Using Gramine Modified Montmorillonite.

A series of gramine modified montmorillonites (gramine-MMTs) were prepared and characterized by thermogravimetric analysis, X-ray diffraction and zeta potential measurements. These modified clays with various amounts of gramine all exhibited higher removal efficiencies of both Chattonella marina and Alexandrium tamarense than did natural clay. With the augmentation of gramine content in the modified clays, the removal efficiency increased. The 24 h LC50 values of gramine-MMT with 12.68 % of gramine on C. marina and A. tamarense were 9.16 and 10.21 mg L(-1), respectively. These data suggest gramine-MMT might be a promising material to remediate harmful algal blooms.

Growth inhibition and oxidative damage of Microcystis aeruginosa induced by crude extract of Sagittaria trifolia tubers.

Aquatic macrophytes are considered to be promising in controlling harmful cyanobacterial blooms. In this research, an aqueous extract of Sagittaria trifolia tubers was prepared to study its inhibitory effect on Microcystis aeruginosa in the laboratory. Several physiological indices of M. aeruginosa, in response to the environmental stress, were analyzed. Results showed that S. trifolia tuber aqueous extract significantly inhibited the growth of M. aeruginosa in a concentration-dependent way. The highest inhibition rate reached 90% after 6 day treatment. The Chlorophyll-a concentration of M. aeruginosa cells decreased from 343.1 to 314.2µg/L in the treatment group. The activities of superoxide dismutase and peroxidase and the content of reduced glutathione in M. aeruginosa cells initially increased as a response to the oxidative stress posed by S. trifolia tuber aqueous extract, but then decreased as time prolonged. The lipid peroxidation damage of the cyanobacterial cell membranes was reflected by the malondialdehyde level, which was notably higher in the treatment group compared with the controls. It was concluded that the oxidative damage of M. aeruginosa induced by S. trifolia tuber aqueous extract might be one of the mechanisms for the inhibitory effects.

Construction of target-specific virus-like particles for the delivery of algicidal compounds to harmful algae.

Harmful algal blooms (HABs) can lead to substantial socio-economic losses and extensive damage to aquatic ecosystems, drinking water sources and human health. Common algicidal techniques, including ozonation, ultrasonic treatment and dispersion of algae-killing chemicals, are unsatisfactory both economically and ecologically. This study therefore presents a novel alternative strategy for the efficient control of deleterious algae via the use of host-specific virus-like particles (VLPs) combined with chemically synthesized algicidal compounds. The capsid protein of HcRNAV34, a single-stranded RNA virus that infects the toxic dinoflagellate, Heterocapsa circularisquama, was expressed in and purified from Escherichia coli and then self-assembled into VLPs in vitro. Next, the algicidal compound, thiazolidinedione 49 (TD49), was encapsidated into HcRNAV34 VLPs for specific delivery to H. circularisquama. Consequently, HcRNAV34 VLPs demonstrated the same host selectivity as naturally occurring HcRNAV34 virions, while TD49-encapsidated VLPs showed a more potent target-specific algicidal effect than TD49 alone. These results indicate that target-specific VLPs for the delivery of cytotoxic compounds to nuisance algae might provide a safe, environmentally friendly approach for the management of HABs in aquatic ecosystems.

Responses of Lyngbya wollei to algaecide exposures and a risk characterization associated with their use.

To make informed decisions regarding management of noxious algal growths, water resource managers require information on responses of target and non-target species to algaecide exposures. Periodic treatments of Phycomycin®-SCP (sodium carbonate peroxyhydrate) followed by Algimycin®-PWF (gluconate and citrate chelated copper) to control Lyngbya wollei growths for ten years provided an opportunity for a risk evaluation of treated coves in Lay Lake, AL. Abiotic sediment characteristics (acid soluble copper concentrations, acid volatile sulfides, percent organic matter and cation exchange capacity) and survival of Hyalella azteca and Chironomus dilutus were measured in sediment samples from treated and untreated coves to assess the bioavailability of potential copper-residuals. In laboratory studies to seek a more effective approach for managing the growth of Lyngbya, six algaecide treatments consisting of combinations of copper-based algaecides (Cutrine®-Ultra, Clearigate® and Algimycin®- PWF), a hydrogen peroxide based algaecide (Phycomycin®-SCP) and an adjuvant (Cide-Kick II) were assessed for efficacy in controlling L. wollei sampled from Lay Lake. The most efficient algaecide treatment was determined based on post-treatment algal wet weight and visual observations of responses to exposures. To estimate the margin of safety for non-target organisms, Pimephales promelas was exposed to the most efficacious treatment and a treatment of Phycomycin®-SCP followed by Algimycin®-PWF. Results from sediment experiments demonstrated that there were no measureable copper residuals and no adverse effects on H. azteca and C. dilutus from sediments following ten years of copper-based algaecide treatments. Based on the laboratory results, a treatment of Phycomycin®-SCP at 10.1 mg H2O2/L followed by Cide-Kick II at 0.2 mg/L and Algimycin®- PWF at 0.26 mg Cu/L could control the growth of Lyngbya wollei from Lay Lake, AL and enhance the margin of safety for non-target species (e.g. P. promelas).

Affinity and efficacy of copper following an algicide exposure: application of the critical burden concept for Lyngbya wollei control in Lay Lake, AL.

Accurate predictions of nuisance algae responses to algicide exposures are needed to guide management decisions. Copper sorption and responses of Lyngbya wollei (Farlow ex Gomont) Speziale and Dyck were measured in the laboratory and two areas in Lay Lake (AL, USA) to treatments of Captain(®) XTR (SePRO Corporation; chelated copper algicide) and a sequential treatment of GreenClean(®) Liquid (BioSafe Systems, LLC; peroxygen algicide) combined with Hydrothol(®) 191 (United Phosphorus, Inc.; endothall algicide) followed by Captain XTR. Measured filament viability in laboratory exposures predicted Captain XTR alone could control L. wollei in Lay Lake, with 2 mg Cu/g algae EC75. This produced a targeted field treatment of 9.7 kg Cu/ha which was divided into three applications of 0.3 mg Cu/L as Captain XTR in the treatment areas. Laboratory and field experiments indicated treatments of Captain XTR alone and the combination treatment resulted in comparable copper sorption and responses of L. wollei. Copper adsorbed greater to L. wollei in laboratory experiments than in the treated areas of Lay Lake with comparable exposures (2 mg Cu/g L. wollei). However, responses and infused copper were similar and correlated in laboratory experiments and treated areas of Lay Lake indicating infused copper is critical for governing toxicity. Laboratory exposures as mg Cu/g algae accurately predicted the necessary algicide exposure required to attain the critical burden of infused copper and elicit desired responses of L. wollei in treated areas of Lay Lake.

Bacilysin from Bacillus amyloliquefaciens FZB42 has specific bactericidal activity against harmful algal bloom species.

Harmful algal blooms, caused by massive and exceptional overgrowth of microalgae and cyanobacteria, are a serious environmental problem worldwide : In the present study, we looked for Bacillus strains with sufficiently strong anticyanobacterial activity to be used as biocontrol agents. Among 24 strains, Bacillus amyloliquefaciens FZB42 showed the strongest bactericidal activity against Microcystis aeruginosa, with a kill rate of 98.78%. The synthesis of the anticyanobacterial substance did not depend on Sfp, an enzyme that catalyzes a necessary processing step in the nonribosomal synthesis of lipopeptides and polyketides, but was associated with the aro gene cluster that is involved in the synthesis of the sfp-independent antibiotic bacilysin. Disruption of bacB, the gene in the cluster responsible for synthesizing bacilysin, or supplementation with the antagonist N-acetylglucosamine abolished the inhibitory effect, but this was restored when bacilysin synthesis was complemented. Bacilysin caused apparent changes in the algal cell wall and cell organelle membranes, and this resulted in cell lysis. Meanwhile, there was downregulated expression of glmS, psbA1, mcyB, and ftsZ-genes involved in peptidoglycan synthesis, photosynthesis, microcystin synthesis, and cell division, respectively. In addition, bacilysin suppressed the growth of other harmful algal species. In summary, bacilysin produced by B. amyloliquefaciens FZB42 has anticyanobacterial activity and thus could be developed as a biocontrol agent to mitigate the effects of harmful algal blooms.

Algicidal metabolites produced by Bacillus sp. strain B1 against Phaeocystis globosa.

The bloom of Phaeocystis globosa has broken out frequently in the coastal areas of China in recent years, which has led to substantial economic losses. This study shows that Bacillus sp. strain B1, which was previously identified by our group, is effective in regulating P. globosa by excreting active metabolites. Heat stability, pH stability and molecular weight range of the algicidal compounds from strain B1 were measured and the results demonstrated that the algicidal activities of these compounds were not affected by pH or temperature variation. The algicidal compounds extracted with methanol were isolated and purified by ODS-A column chromatography and HPLC. The algicidal compounds corresponding to peaks 2-5 eluted from HPLC were further analysed by quadrupole time-of-flight mass spectrometry (Q-TOF-MS). PeakView™ Software determined the compounds corresponding to peaks 2-5 to be L-histidine, o-tyrosine, N-acetylhistamine and urocanic acid on the basis of the accurate mass information, the isotopic pattern and MS-MS spectra. Furthermore, these compounds were also able to eliminate Skeletonema costatum, Prorocentrum donghaiense and Heterosigma akashiwo. This is the first report of bacteria-derived algicidal compounds being identified only by Q-TOF-MS and PeakView™ Software, and these compounds may be used as the constituents of algicides in the future.

The effects of three chemical algaecides on cell numbers and toxin content of the cyanobacteria Microcystis aeruginosa and Anabaenopsis sp.

Toxic cyanobacteria blooms are a growing concern for public health and safety, due in part to the production of the hepatotoxin microcystin by certain species, including Microcystis aeruginosa. Management strategies for controlling cyanobacteria blooms include algaecide treatments, often with copper sulfate, and more recently oxidizers such as sodium percarbonate that produce hydrogen peroxide. This study assessed the effects of two copper-containing algaecides and one sodium percarbonate-containing algaecide on mitigating cell numbers and toxin content of cultured M. aeruginosa and summer (July) bloom samples of Anabaenopsis sp. in a brackish stormwater detention pond. Monitoring of the bloom revealed that Anabaenopsis sp. was associated with elevated levels of orthophosphate compared to nitrogen (dissolved inorganic nitrogen to phosphorus ratios were 0.19-1.80), and the bloom decline (September-October) was likely due to lower autumn water temperatures combined with potential grazing by the dinoflagellate Protoperidinium quinquecorne. Laboratory-based algaecide experiments included three dose levels, and cyanobacteria cell numbers and microcystin concentrations (particulate and dissolved) were evaluated over 7 d. Following exposure, copper-containing treatments generally had lower cell numbers than either sodium percarbonate-containing or control (no algaecide) treatments. Addition of algaecides did not reduce overall microcystin levels, and a release of toxin from the particulate to dissolved phase was observed in most treatments. These findings indicate that algaecide applications may visibly control cyanobacteria bloom densities, but not necessarily toxin concentrations, and have implications for public health and safety.

A novel thiazolidinedione derivative TD118 showing selective algicidal effects for red tide control.

Thiazolidinedione (TD) derivatives have been found to have an algicidal effect on harmful algal bloom microalgae. In this study, 75 TD derivatives were synthesized and analyzed for algicidal activity. Among these synthetic TDs, 18 TD derivatives showed specific algicidal activity on two strains belonging to the classes Raphidophyceae (Chattonella marina and Heterosigma akashiwo) and Dinophyceae (Cochlodinium polykrikoides). Two strains belonging to Bacillariophyceae (Navicula pelliculosa and Phaeodactylum EPV), one strain belonging to Dinophyceae (Amphidinium sp.), and a Eustigmatophycean microalga (Nannochloropsis oculata) showed less sensitivity to the TD derivatives than the other two phyla. The most reactive TD derivative, compound 2 (TD118), was selected and tested for morphological and physiological changes. TD118 effectively damaged the cell membrane of C. marina, H. akashiwo and C. polykrikoides. The O2 evolution and photosystem II efficiency (F(v)/F(m)) of C. marina, H. akashiwo and C. polykrikoides were also severely reduced by TD118 treatment. Amphidinium sp., N. pelliculosa, Phaeodactylum EPV and N. oculata showed less reduction of O2 evolution and the F(v)/F(m) by TD118. These results imply that the species-specific TD structure relationship may be due to structural and/or physiological differences among microalgal species.

Enhanced inhibitory efficiency against toxic bloom forming Raphidiopsis raciborskii by Streptomyces sp. HY through triple algicidal modes: Direct and indirect attacks combined with bioflocculation.

Raphidiopsis raciborskii (R. raciborskii) forms harmful cyanobacterial blooms globally, and poses a great threat to the safety of drinking water and public health. There is a great need to develop eco-friendly biological alternative measures to mitigate mass blooms of R. raciborskii. However, previous rare studies on algicidal microorganisms against R. raciborskii restricted this aim. Recently, an algicidal bacterium Streptomyces sp. HY (designated HY) was identified with flavones producing ability, and could remove up to 98.73 % of R. raciborskii biomass within 48 h by directly attacking the cyanobacterium and release of algicidal substances (i.e., flavonoids) with a inoculum ratio of 5 %. Algicidal rate of HY was enhanced by 88.05 %, 89.33 % under dark and light, and full-light conditions respectively, when compared with the dark condition. Its algicidal substances were stable in a broad range of temperature (-80-55 °C) and pH (3-11) conditions, and all treated groups exhibited ≈ 100 % algicidal rate at day 3. HY treatment disrupted the photosynthesis system and triggered serious oxidative stress resulting in severe morphological injury. Thereby, HY treatment significantly affected expression levels of several essential genes (i.e., psbA, psaB, rbcL, ftsZ, recA, grpE), and simultaneously inhibited the biosynthesis and release of cylindrospermopsin. Yet, HY treatment didn't show any toxicity to zebrafish test embryos. Such results indicate that HY is a promising algicidal candidate strain to control global R. raciborskii blooms, and holds great promises for an effective biological measure to sustain water safety.