Algicidal Effect Research Articles

Isolation and characterization of the marine algicidal bacterium Pseudoalteromonas S1 against the harmful alga Akashiwo sanguinea

Akashiwo sanguinea is a notorious bloom-forming dinoflagellate, which adversely impacts environmental safety and public health. In this study, we successfully isolated a bacterium strain with potent algicidal effects against A. sanguinea. Both fatty acid profiling and 16S rDNA sequencing results suggested that this bacterium belongs to the genus Pseudoalteromonas, while the 16S rDNA homology analysis revealed that it is most similar to Pseudoalteromonas nigrifaciens strain 1350 (100 % similarity). The strain, namely S1, can lyse A. sanguinea in a low bacteria-to-algae ratio (50:1) in as short as 4 h. Interestingly, our results showed that this bacterium may exert its algicidal effect in both direct and indirect modes, which has seldom been reported in previous studies. This study represents the first report of Pseudoalteromonas having lytic activity against the red-tide-causing microalga A. sanguinea.

Bacteriological control by Raoultella sp. R11 on growth and toxins production of Microcystis aeruginosa

Microcystis aeruginosa is a cyanobacterium that can cause harmful algal blooms (HABs) in freshwater bodies. In this study, the bacterium Raoultella sp. R11 was evaluated for its ability to control the growth of M. aeruginosa. Algal growth, denitrification activity, and toxin production were measured in the presence of various concentrations of Raoultella sp. R11. The algicidal effects of Raoultella sp. R11 were studied by measuring the zeta potential (surface charge), the activity of superoxide dismutase (SOD), and the concentrations of chlorophyll-a, dissolved organic matter, and microcystin-LR in algal cultures. The results suggested that chlorophyll-a removal, which indicates algal death, was correlated with the dose of Raoultella sp. R11. The zeta potential and denitrification activity decreased in the presence of bacteria in a dose-dependent manner. SOD activity was correlated with the inoculation dosage of Raoultella sp. R11. Using a 30% (v/v) dose of bacterial culture, the removal efficiency of chlorophyll-a was as high as 94.28% after 6days. In addition, dissolved microbial metabolites and humic acid were detected in high quantities whereas low quantities of protein-like substances and fulvic acid were found. Furthermore, toxic microcystin-LR produced by the algae was eliminated at up to 92.21% efficiency. A high denitrification rate (1.57mg NO3--NL−1h−1) and chlorophyll-a removal efficiency (73.12%) were observed within 6days at an inoculation dosage of 20% (v/v) of bacterial culture. Our findings indicated that Raoultella sp. R11 has a high potential for applications in simultaneously controlling M. aeruginosa and facilitating denitrification in freshwater bodies.

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

To biochemically characterize synthetic peptides to control harmful algal blooms (HABs) that cause red tides in marine water ecosystems. 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. These synthetic peptides may prove promising for general marine ecosystem remediation where HABs have become widespread and resulted in serious economic loss.

Comparative genome analyses of novel Mangrovimonas-like strains isolated from estuarine mangrove sediments reveal xylan and arabinan utilization genes

To date, the genus Mangrovimonas consists of only one species, Mangrovimonas yunxiaonensis strain LY01 that is known to have algicidal effects against harmful algal blooms (HABs) of Alexandrium tamarense. In this study, the whole genome sequence of three Mangrovimonas-like strains, TPBH4T(=LMG 28913T,=JCM 30882T), ST2L12T(=LMG 28914T,=JCM 30880T) and ST2L15T(=LMG 28915T,=JCM 30881T) isolated from estuarine mangrove sediments in Perak, Malaysia were described. The sequenced genomes had a range of assembly size ranging from 3.56Mb to 4.15Mb which are significantly larger than that of M. yunxiaonensis LY01 (2.67Mb). Xylan, xylose, L-arabinan and L-arabinose utilization genes were found in the genome sequences of the three Mangrovimonas-like strains described in this study. In contrast, these carbohydrate metabolism genes were not found in the genome sequence of LY01. In addition, TPBH4T and ST2L12T show capability to degrade xylan using qualitative plate assay method.

Algicidal effects and denitrification activities of Acinetobacter sp. J25 against Microcystis aeruginosa

Harmful algal blooms (HABs) could be deemed hazardous materials in aquatic environment. Microcystis aeruginosa is a toxic HAB causing alga, which causes serious economic losses and health problems. In this study, a strain J25 with the high algicidal activity isolated from an eutrophic Qu Jiang Lake, was identified as Acinetobacter sp. based on its morphological features and phylogenetic analysis by sequencing of 16S rDNA. Its algae-lysing characteristics on M. aeruginosa, was tested under the different conditions. The results showed that the strain J25 had good tolerance of acid and alkali, and full illumination played a positive role in the algae removal. Furthermore, this was the first report about the relationship between algicidal and denitrification activities. The maximum denitrification rate (1.62mg NO3−–NL−1h−1) was observed within 6 days at 15% of inoculum.

Algicidal effect of chitosan according to various molecular-weight against green-tide

Event Abstract Back to Event Algicidal effect of chitosan according to various molecular-weight against green-tide Jae-Woon Nah1, Changyong Choi1, Soo-Kyung Choi1, Hyun-Su Lee1, Sun-Ju Choi1, Sung-Cho Kim2 and Gyeong-Won Jeong1 1 Sunchon National University, Department of Polymer Science and Engineering, Korea 2 Sunchon National University, Department of Mechanical Engineering, Korea Introduction: Harmful algal blooms (HABs) commonly cause mass mortalities of fish, shellfish, and other freshwater life due to toxin production and depletion of oxygen. Repeated and widespread HABs can drastically change freshwater ecologies. Furthermore, ingestion of freshwater-foods with algal toxins can lead to illness and death in humans and animals, and exposure to aerosolized toxins from contaminated water causes respiratory problems in humans[1]. For these reasons, it is important to develop materials and methods to prevent or control HABs in freshwater environments, aquaculture industry, and human health. Chitosan was recently used to convert sand into effective flocculants for mitigation of HABs in marine and freshwater systems and soil/clay flocculation. However, there have been no reports of the use of chitosan alone for removing and controlling HAB[2]. We investigated the selective algicidal effect of Chitosan with various molecular weight against green-tide. Furthermore, the mode of algicidal action, molecular weight range, selective killing for harmful green-tide, non-cytotoxic effects, and recovered survival of freshwater in the presence of an artificial green-tide were demonstrated. Experimental Methods: Chitosan solution was prepared by using lactic acid as a solvent. 5 units of chitosanase originated from Bacilllus pumilus BN-262 was added to 100 mL of the said 5% chitosan solution (pH 5.0 ~ 5.5), followed by enzyme reaction at 40 ℃ for 36 hours. Upon completion of the reaction, the mixture was filtered by using a 1 μm pre-filter and then filtered again by using a hollow filter. The obtained filtrate was concentrated by using the nanofilter system, followed by sterilization and drying with an air spray dryer. As a result, chitosan polysaccharide was obtained. The cytotoxicity of chitosan was evaluated using an MTT assay in L929 cell lines. In addition, anti-green algae activity using various molecular weight chitosan was confrimed by inhibitory concentration (IC50). Results and Discussion: Cytotoxicity of chitosan was confirmed by MTT assay. The results showed that cell viability of high molecular chitosan (780kDa) and low molecular chitosan (10kDa) was measured above 70% and mentioned harmless materials. To confirm algicidal activity of chitosan with various molecular weight, we investigated by inhibitory concentration (IC50). The results showed that algicidal activity of chitosan (Mw:780 kDa) against microcystis, anabaena, and chlorella was indicated such as 0.012g/L, 0.024 g/L and 0.012 g/L, respectively. In addition, algicidal activity in case of chitosan (Mw: 10 kDa) was indicated such as 0.39 g/L, 0.097 g/L, and 0.049 g/L, respectively. These results mean that algicidal effect of high molecular weight chitosan was better than low molecular chitosan. For these reason, chitosan free-amine of positive charge was affected to membrane with negative charge of green-tide. Moreover, free-amine of high molecular weight chitosan was existed more than low molecular weight chitosan. Therefore, chitosan has a potential ability of control without cytotoxicity at green-tide. Conclusion: In this study, we prepared chitosan for removed green-tide. The cytotoxicity of prepared chitosan was not indicated. In addition, algicidal activity of chitosan was confirmed by inhibitory concentration (IC50). Theses results suggest that chitosan can be utilize as material of protecting freshwater ecology from green-tide. This work was supported by National Research Foundation of Korea (NRF) grant funded by the Ministry of Science, ICT & Future Planning. (No. NRF-2014R1A2A1A10053027).

Development of charged liposomal delivery system for enhanced algicidal effect of DP-92

Development of charged liposomal delivery system for enhanced algicidal effect of DP-92

Prevent the degradation of algicidal ability in Scenedesmus-lysing bacteria using optimized cryopreservation.

With the anthropogenic nutrient loading increasing, the frequency and impacts of harmful algal blooms (HABs) have intensified in recent years. To biocontrol HABs, many corresponding algal-lysing bacteria have been exploited successively. However, there are few studies on an effective algal-lysing culture collection to prevent cells from death and particularly the degradation of algicidal ability to their hosts. An optimized cryopreservation was developed and experiments on the validation of this method on preventing algicidal degradation and effects of this optimized cryopreservation on the survival rate of Scenedesmus-lysing bacterium, Enterobacter NP23, isolated from Scenedesmus sp. community, China, on the algicidal dynamic of Scenedesmus wuhanensis was investigated. The optimized cryoprotectant composition consists of 30.0 g/L gelatin, 48.5 g/L sucrose, and 28.4 g/L glycerol, respectively. Using this approach, the survival rate of NP23 cells can still maintain above 90 % and the algal-lysing rate only decline 4 % after the 18-month cryoprotection. Moreover, the 16 generations' passage experiment showed a significant (p < 0.05) genetic stability of algicidal capacity after 18 months. The growth dynamic of S. wuhanensis was investigated in a 5-L bioreactor during 132 h in the absence or presence of NP23. As a result, NP23 has a significant (p < 0.05) inhibition to S. wuhanensis growth when injected into algal culture in the exponential phase at 60th hour. In addition, S. wuhanensis culture initially with NP23 exhibited a slow growth, performing a prolonged lag phase without a clear stationary phase and then rapidly decreased. Our findings, combined with the capacity of preventing the degradation of algicidal ability collectively suggest that the use of this opitimized cryopreservation may be a promising strategy for maintaining algicidal cells.

Algicidal effects of free-amine water-soluble chitosan to marine harmful algal species

Harmful algal blooms (HABs) commonly cause significant damage to aquatic systems due to toxin production and depletion of oxygen. In this study, the low molecular weight water-soluble chitosan (LMWSC) was investigated as a new algicidal compound by first investigating the potential of LMWSC in selective combating HABs. The LMWSCs disrupted algal cell and chloroplast membranes within 1h against HABs, leading to efflux of the intracellular components. For co-cultivation of harmful and harmless algal, LMWSC selectively kill the harmful algal. Based on these results, LMWSC is a promising novel material for harmful algal bloom control.

Discovery of an algicidal compound from Brevibacterium sp. BS01 and its effect on a harmful algal bloom-causing species, Alexandrium tamarense.

Blooms of the dinoflagellate Alexandrium tamarense have become worldwide phenomena and have detrimental impacts on aquatic ecosystems and human health. In this study, a culture supernatant of the marine actinomycete BS01 exerted a strong algicidal effect on A. tamarense (ATGD98-006). The target algicide from BS01 was separated by adsorption chromatography and identified by MALDI-TOF-MS and NMR analysis. The results suggested that the purified algicidal component corresponded to a hydrophobic compound (2-isobutoxyphenyl)amine (C10H15NO) with a molecular weight of 165 Da, which exhibited a significant algicidal effect (64.5%) on A. tamarense. After incubation in 5 μg/mL of (2-isobutoxyphenyl)amine for 24 h, the algae lost mobility and sank to the bottom of the flasks, and 56.5% of the algae cells lost vitality at a concentration of 20 μg/mL (p < 0.01) despite having intact cell profiles. Morphological analysis revealed that the cell structure of A. tamarense was altered by (2-isobutoxyphenyl)amine resulting in cytoplasm degradation and the loss of organelle integrity. The images following propidium iodide staining suggested that the algal nucleus was also severely damaged and eventually degraded due to exposure to the algicidal compound. All of the results indicate that (2-isobutoxyphenyl)amine from the actinomycete might be a candidate for the control of bloom-forming A. tamarense.

Exploration of the antioxidant system and photosynthetic system of a marine algicidal Bacillus and its effect on four harmful algal bloom species.

A novel marine bacterium, strain B1, initially showed 96.4% algicidal activity against Phaeocystis globosa. Under this situation, 3 other harmful algal species (Skeletonema costatum, Heterosigma akashiwo, and Prorocentrum donghaiense) were chosen to study the algicidal effects of strain B1, and the algicidal activities were 91.4%, 90.7%, and 90.6%, respectively. To explore the algicidal mechanism of strain B1 on these 4 harmful algal species, the characteristics of the antioxidant system and photosynthetic system were studied. Sensitivity to strain B1 supernatant, enzyme activity, and gene expression varied with algal species, while the algicidal patterns were similar. Strain B1 supernatant increased malondialdehyde contents; decreased chlorophyll a contents; changed total antioxidant and superoxide dismutase activity; and restrained psbA, psbD, and rbcL genes expression, which eventually resulted in the algal cells death. The algicidal procedure was observed using field emission scanning electron microscopy, which indicated that algal cells were lysed and cellular substances were released. These findings suggested that the antioxidant and photosynthetic system of these 4 algal species was destroyed under strain B1 supernatant stress. This is the first report to explore and compare the mechanism of a marine Bacillus against harmful algal bloom species of covered 4 phyla.

Allelopathic interactions between the HAB dinoflagellate Ostreopsis cf. ovata and macroalgae

Intense blooms of the toxic benthic dinoflagellate Ostreopsis cf. ovata have been a recurrent phenomenon along several Mediterranean coasts during summer in the last few years. These blooms are often associated with noxious effects on humans and deaths of benthic invertebrates. Previous studies carried out on the Conero Riviera (northern Adriatic Sea) highlighted that Ostreopsis abundances recorded on rocks were significantly higher than on the surface of seaweeds, suggesting that some allelopathic interactions might occur between Ostreopsis and macroalgal substrates. In this study we investigated under experimental conditions the interactions between O. cf. ovata and three of the most common macroalgae in this area: Dictyota dichotoma (brown alga), Rhodymenia pseudopalmata (red alga) and Ulva rigida (green alga). Three different experiments were set up: O. cf. ovata was grown (i) together with fresh macroalgal tissues, (ii) in media in which macroalgae were previously cultured, and (iii) in media with the addition of dry macroalgal powder at different concentrations. The results indicated that all the investigated seaweeds exerted negative effects toward the benthic dinoflagellate O. cf. ovata. D. dichotoma inhibited the growth of O. cf. ovata in all tested experimental conditions; U. rigida had inhibitory effect both in form of fresh thalli and dry powder but not as growth medium filtrate, suggesting that either Ulva does not release any allelopathic compound in the medium in absence of O. cf. ovata or the alleged released allelochemicals are rapidly degradable. Neither the fresh thalli of R. pseudopalmata or the filtrate of its culture medium showed any inhibitory effects, while a negative effect was only observed at high concentrations of dry thallus powder. With the exception of D. dichotoma co-culture experiment, a complete algicidal effect was never observed partly because O. cf. ovata produced a large amount of resting stages, which permitted its survival.

Synergistic algicidal effect and mechanism of two diketopiperazines produced by Chryseobacterium sp. strain GLY-1106 on the harmful bloom-forming Microcystis aeruginosa.

A potent algicidal bacterium isolated from Lake Taihu, Chryseobacterium sp. strain GLY-1106, produces two algicidal compounds: 1106-A (cyclo(4-OH-Pro-Leu)) and 1106-B (cyclo(Pro-Leu)). Both diketopiperazines showed strong algicidal activities against Microcystis aeruginosa, the dominant bloom-forming cyanobacterium in Lake Taihu. Interestingly, these two algicidal compounds functioned synergistically. Compared with individual treatment, combined treatment with cyclo(4-OH-Pro-Leu) and cyclo(Pro-Leu) significantly enhanced algicidal activity, accelerated the increase in intracellular reactive oxygen species (ROS) levels in M. aeruginosa, and further decreased the activities of antioxidases, effective quantum yield and maximal electron transport rate of M. aeruginosa. The results also showed that the algicidal characteristics of cyclo(4-OH-Pro-Leu) are distinct from those of cyclo(Pro-Leu). Cyclo(4-OH-Pro-Leu) mainly interrupted the flux of electron transport in the cyanobacterial photosynthetic system, whereas cyclo(Pro-Leu) mainly inhibited the activity of cyanobacterial intracellular antioxidases. A possible algicidal mechanism for the synergism between cyclo(4-OH-Pro-Leu) and cyclo(Pro-Leu) is proposed, which is in accordance with their distinct algicidal characteristics in individual and combined treatment. These findings suggest that synergism between algicidal compounds might be used as an effective strategy for the future control of Microcystis blooms.

겨울철 규조류 대발생 제어를 위한 Naphthoquinone 유도체 Nq 4-6의 적용 가능성

We conducted the algicidal activity screening tests using 10 L microcosm to investigate the possibility of the field application of naphthoquinone derivative Nq 4-6 compound as an algicide. We determined its application range to assess its algicidal effects on the phytoplankton and to evaluate the response of the planktonic community and the water environment to this chemical. From results of the microcosm experiments, Nq 4-6 compound showed high algicidal activity on the centric diatoms such as Stephanodiscus hantzschii and Cyclotella meneghiniana, but it had no effect on other phytoplankton. The abundance of S. hantzschii continuously increased in the control, but its cell density decreased 1 day after the Nq 4-6 treatment. In particular, Nq 4-6 showed algicidal activity of 94.4% against S. hantzschii 7 days after the treatment. The dominance index of phytoplankton community was lower in the treatment than in the control. The diversity index, richness index and evenness index of phytoplankton community was higher in the treatment. Environmental factors and biological factors did not show specific changes after the Nq 4-6 compound treatment. Therefore, the results of this study demonstrates that Nq 4-6 is an effective agent for the control of S. hantzschii blooms, and that the microcosm tests play a crucial role when assessing field application.

Isolation of an algicide from a marine bacterium and its effects against the toxic dinoflagellate Alexandrium catenella and other harmful algal bloom species.

The aim of this study was to isolate and identify bacteria demonstrating an algicidal effect against Alexandrium catenella and to determine the activity and range of any algicide discovered. The morphological and biochemical attributes of an algicidal bacterium, isolate YS-3, and analysis of its 16S rRNA gene sequence revealed it to be a member of the genus Brachybacterium. This organism, designated Brachybacterium sp. YS-3, showed the greatest effect against A. catenella cells of all bacteria isolated, and is assumed to produce secondary metabolites. When 10% solutions of culture filtrates from this strain were applied to A. catenella cultures, over 90% of cells were killed within 9 h. Bioassay-guided isolation of the algicide involved led to the purification and identification of an active compound. Based on physicochemical and spectroscopic data, including nuclear magnetic resonance and mass analyses, this compound was identified as 1-acetyl-β-carboline. This algicide showed significant activity against A. catenella and a wide range of harmful algal bloom (HAB)-forming species. Taken together, our results suggest that Brachybacterium sp. YS-3 and its algicide represent promising candidates for use in HAB control.

Allelopathic effects of Ailanthus altissima extracts on Microcystis aeruginosa growth, physiological changes and microcystins release

The use of allelochemicals has been proved an environmentally friendly and promising method to control harmful algal blooms. This study was conducted to explore the application potential of Ailanthus altissima (A. altissima) extracts in Microcystis aeruginosa (M. aeruginosa) control for the first time. Four treatments with A. altissima extractions (25mgL−1, 50mgL−1, 100mgL−1, and 200mgL−1 respectively) and a control group were built to investigate the effects of A. altissima on the growth, cellular microstructure and cell viability, physiological changes, and release of extracellular matters. Results showed that the cell density of M. aeruginosa was effectively inhibited by A. altissima extract, and the inhibition rates were dose-dependent within 5d. Especially for the treatment with 200mgL−1 of extract, the inhibitory rates remains above 90% after 5d exposure. In addition, A. altissima effectively decreased the amount of extracellular cyanotoxin microcystins and destroyed the photosynthesis-related structure of algae cell during the experimental period. The results demonstrated the A. altissima extracts can be used as an effective and safe algicide to control algal blooms. However, it must be noted that specific compounds responsible for algicidal effect should be isolated and identified to explore inhibition mechanism of A. altissima in future study.

Effects of chitosan, gallic acid, and algicide on the physiological and biochemical properties of Microcystis flos-aquae.

The effects of chitosan, gallic acid, and algicide chitosan-gallate on the activities of antioxidant enzymes, malonaldehyde (MDA) content, and photosynthetic activity of Microcystis flos-aquae were investigated to explore the physiological and biochemical mechanisms of algicides. Results demonstrated that chitosan did not significantly affect catalase (CAT) and superoxide dismutase (SOD) activities, MDA content, and photosynthetic activity in this alga. At 30mgL(-1), gallic acid, CAT, and SOD activities and MDA of M. flos-aquae cells showed maximums of 2.872 × 10(-10)mg·cell(-1)min(-1), 0.787 × 10(-8)U·cell(-1), and 0.626 × 10(-8)nmol·cell(-1), respectively. Photosynthetic organs in algal cells were severely damaged under the stress of high gallic acid concentrations, inducing blockage of photosynthetic electron transport and resulting in the inability to restore normal photosynthetic activity. CAT and SOD activities and MDA content with lower algicide concentration were significantly higher than the control group (p < 0.05) and, in higher algicide groups, significantly lower than the control (p < 0.05). Algicide releasing gallic acid in groups treated with 60, 90, and 130mg/L algicide was strong enough to cause severe damage to photosynthetic organs in these algal cells. The algicide suppression time was longer than that of directly added gallic acid.

살조물질과 황토를 이용한 적조생물 제어에 따른광합성 효율 및 전자전달율의 차이

유해 유독 적조생물의 대발생은 해양생물 건강성과 수산어족자원에 심각한 피해를 입힌다. 본 연구에서는 미세조류의 대발생을 억제하기 위해 개발된 Thiazolidione 유도체(TD49)와 현장에서 적조생물을 제어하기 위하여 살포되는 황토에 대한 살조능을 조사하였다. 아울러 적조생물 생사판별과 관련된 자가영양생물의 광합성에 영향을 미칠 수 있는 활성엽록소(activity Chl. a), 광합성효율(<TEX>$F_v/F_m$</TEX>), 전자 전달율(electron transport rate, ETR)등을 평가하였다. 대상적조생물은 유해조류 3종과 비유해 조류 1종을 선택하였으며, 유해조류는 침편모조류 Heterosigma akashiwo, Chattonella marina와 더불어 와편모조류 Heterocapsa circularisquama를 비교하였고, 비유해조류는 은편모조류 Rhodomonas salina에 대하여 평가하였다. 유해조류 3종은 살조물질(TD49)에 의하여 빠른 시간에 세포가 파괴되어 우수한 살조 효과(>80%)를 보인 반면, 황토에 관해서는 살조효율이 30%이하로 낮게 나타났다. 또한 TD49에 대한 유해조류 3종의 살조효율은 H. circularisquama> C. marina> H. akashiwo 순으로 높게 나타났으며, 광합성 효율 및 전자전달율 또한 극히 낮게 나타나, 광합성에 치명적인 영향을 미치는 것으로 사료되었다. 반면, 유해조류 3종에 관해서 황토에 대한 광합성 효율과 전자전달율은 대조군과 유의한 차이를 보이지 않았다(p>0.01). 비유해종 R. salina 은 대조군에 비하여 TD49와 황토의 살조 효과, 광합성효율 및 전자전달율의 차이는 명확하게 나타나지 않았고, 오히려 TD49물질에서 성장에 긍정적인 영향을 미치는 것을 확인하였다. 결과적으로 본 연구에서 TD49물질은 유해적조 생물을 선택적으로 제어 할 수 있으며, 현장 적용시 우수한 살조 효과를 가질 수 있을 것으로 판단된 반면, 황토는 적조생물 제어에 적합하지 않을 것으로 사료되었다. The development of worldwide harmful algal blooms(HAB) is a serious problem for public health and fisheries industries. To evaluate the algicidal impact on the HAB species, algicide thiazolidinedione derivative (TD49) and yellow clay were examined, which is focus on assess the algicidal effects and inhibition to photosynthesis of HAB species. To obtain the detailed information, we analyzed the viability of target species related to activity Chl. a, photosynthetic efficiency(<TEX>$F_v/F_m$</TEX>), and electron transport rate(ETR). Culture experiment was conducted to evaluate the algicidal effects of three harmful species(raphidophyceae Heterosigma akashiwo, Chattonella marina, and dinophyceae Heterocapsa circularisquama) and one non-harmful species (cryptophyceae Rhodomonas salina). Our experiments revealed that three HAB species were easily destroyed of the cell walls after TD49 dosing. Also, they had significantly reducing values of active Chl. a, <TEX>$F_v/F_m$</TEX>, and ETR, due to the damage of photosystem II by inter-cellular disturbance. As a result, the algicidal effect(%) for the three HABs were as follows, in the order of greatest to the least: H. circularisquama> C. marina> H. akashiwo. However, the algicidal effect for yellow clay remained to be <30% (p>0.01), implying that it may not have damaged the photosystem II. On the other hand, non-HAB R. salina was promoted at both TD49 and yellow clay treatments. Our results demonstrated that the TD49 is a good agent for the control of HABs H. akashiwo, C. marina, and H. circularisquama, whereas the yellow clay would not be suitable for the field application based on our experimental results.

Algicidal effect of bacterial isolates of Pedobacter sp. against cyanobacterium Microcystis aeruginosa

The aim of this study was to isolate algicidal bacteria so as to control harmful cyanobacterium Microcystis aeruginosa (M. aeruginosa) blooms using biological methods. Nine bacterial strains were isolated to inhibit the growth of M. aeruginosa, among which the MaI11-5 bacterial strain exhibited remarkable algicidal activity against M. aeruginosa cells during the test. Based on the 16S rDNA analysis, the isolated MaI11-5 was identified as Pedobacter sp. through morphology and homology research. The results of cocultivation of the cyanobacteria with MaI11-5 algicidal isolates showed obvious algicidal activity against cyanobacterial cells. The algicidal effect of MaI11-5 exceeded 50% after two days, exceeded 70% after four days, and reached 80% after seven days. The observation results with a scanning electron microscope showed that the cyanobacterial cells aggregated and produced mucous-like substances when cocultivated with the algicidal bacteria. The results indicated that the MaI11-5 bacterial strain may possess a novel function for controlling harmful blooms and further studies will provide new insights into its role in water environment.

On the control of Microcystis aeruginosa and Synechococccus species using an algicidal bacterium, Stenotrophomonas F6, and its algicidal compounds cyclo-(Gly-Pro) and hydroquinone

Cyanobacterial blooms occur annually in Lake Taihu, causing large ecological and economic losses. As part of efforts to enhance the strategies explored to control cyanobacterial blooms, an algicidal bacterium, F6, was isolated from Lake Taihu and then identified as a Stenotrophomonas species by 16S rDNA sequence analysis. The results showed that Stenotrophomonas F6 exhibited strong algicidal activity against dominant cyanobacterial bloom-forming species in Lake Taihu, mainly via excretion of extracellular algicidal compounds. The algicidal compounds were subsequently extracted with ethyl acetate, purified by high-performance liquid chromatography (HPLC) and identified as cyclo-(Gly-Pro) and hydroquinone by gas chromatography–mass spectrometry (GC–MS) and 1H nuclear magnetic resonance (NMR) analysis. Cyclo-(Gly-Pro) exerted a strong algicidal effect against Microcystis aeruginosa 9110 with a 50 % effective concentration (EC50,24h) value of 5.9 mg L−1, but had no algicidal effect on Synechococcus sp. BN60. Hydroquinone showed stronger algicidal activity against both M. aeruginosa 9110 and Synechococcus sp. BN60, with EC50,24h values of 0.96 and 5.6 mg L−1, respectively. Through characterization of algicidal process, the algicidal activity of Stenotrophomonas F6 was found to be dependent on the concentration of algicidal compounds, and the secreted algicidal compounds could be detected only when the cell density of F6 was above a threshold of 2–4 × 108 CFU mL−1. Taken together, these results suggest that the algicidal bacterium F6 and its two algicidal compounds have the potential for use as bio-agents for controlling cyanobacterial blooms in Lake Taihu.