Phytochemicals and Allelopathy of Induced Water Hyacinth against Microcystis aeruginosa.

Induced water hyacinth with purple roots (PRWH) exerts a significant inhibitory effect on the growth of blue-green algae. Interestingly, its chemical constituents differ from those of wild-type water hyacinth and have not yet been reported. This study aimed to explore the chemical constituents of PRWH and its bioactive components serving as allelopathic agents against blue-green algae. Phytochemical investigation of the bioactive ethyl acetate fraction of a crude methanol extract from PRWH led to the isolation of 56 compounds, including 11 new phenylphenalene derivatives. The structures of these compounds were elucidated by comprehensive analyses through NMR, HRMS, and X-ray techniques. Bioactivity evaluation against Microcystis aeruginosa indicated that compounds 7, 12, 15, 37, 39, 45, and 47 potently inhibited blue-green algae growth.

Effects of fish feed addition scenarios with prometryn on Microcystis aeruginosa growth and water qualities.

The number of undesirable environmental impacts of fish feed has been reported widely. Although repeated fish feed exposures are more prospective to occur in water, previous studies were mostly conducted as a single exposure of fish feed. In order to fill these gaps, a 40 days incubator experiment was conducted to explore the effects of fish feed addition scenarios during the lag phase with prometryn on both Microcystis aeruginosa growth and concentrations of nutrients. The maximum algae densities in groups of single exposure were 6.0-26.2% and 8.8-74.4% higher than those in groups of double and triple exposures, respectively (P < 0.05). At the beginning of the experiment, concentrations of nutrients in groups with different feed exposure scenarios were significantly different. The pattern of nutrient limitation showed a transformation from phosphorus limitation to nitrogen limitation generally. Furthermore, the average inhibition rates of algae by prometryn in the case of a single fish feed exposure were 4.6-9.4% lower than those under double exposures, and 22.0-26.8% lower than those under triple exposures (P < 0.05). In addition, algae growth rates have been developed as a function of concentrations of consumed nutrients (R2 = 0.410-0.932). Based on the above results, we concluded that in terms of limiting algae growth multiple low-dosage additions of fish feed were considered as a better addition pattern. By optimizing feed addition scenarios, there is considerable potential to increase the environmental sustainability of aquaculture.

Proteomic mechanisms for the stimulatory effects of antibiotics on Microcystis aeruginosa during hydrogen peroxide treatment.

Application of low dosage of H2O2 at early stage of cyanobacterial life cycle is a promising route for cyanobacterial bloom mitigation, which could minimize adverse effects on non-target organisms. Besides, influence of co-existing contaminants on cyanobacterial bloom mitigation under combined pollution conditions remains unclear. This study assessed the influence of a mixture of four frequently detected antibiotics (tetracycline, sulfamethoxazole, ciprofloxacin and amoxicillin) during H2O2 treatment of Microcystis aeruginosa at early growth stage. H2O2 significantly (p < 0.05) inhibited growth rate, chlorophyll a content, Fv/Fm and rETRmax in a dose-dependent manner at low doses of 0.25-1 mg L-1, through downregulating proteins involved in cell division, cellular component organization, gene expression and photosynthesis. Although H2O2 increased microcystin content in each cyanobacterial cell through the upregulation of microcystin synthetases (mcyC and mcyF), total microcystin concentration in H2O2 treated groups was significantly (p < 0.05) reduced due to the decrease of cell density. Existence of 80 and 200 ng L-1 mixed antibiotics during H2O2 treatment facilitated the scavenging of ROS by antioxidant enzymes and significantly (p < 0.05) stimulated growth, photosynthesis, microcystin synthesis and microcystin release in H2O2 treated cells, through the upregulation of proteins involved in photosynthesis, oxidation-reduction process, biosynthesis, gene expression and transport. Mixed antibiotics increased the hazard of M. aeruginosa during H2O2 treatment, through the stimulation of microcystin synthesis and release at the proteomic level. Each target antibiotic should be controlled below 5 ng L-1 before the application of H2O2 for eliminating the interference of antibiotics on cyanobacterial bloom mitigation.

Amentoflavone, a novel cyanobacterial killing agent from Selaginella tamariscina.

Harmful cyanobacterial bloom (HCB) by Microcystis aeruginosa is increasingly becoming a serious concern to the environment and human health alike. Currently, many physical, chemical, and biological controls are underway to eliminate HCB, but natural chemicals are rarely used. To find a control agent with low environmental toxicity and high potential for practical use, 60 plant extracts were screened. Only Selaginella tamariscina extract killed all four Microcystis aeruginosa strains, but not the other tested bacteria. Chloroform fraction of S. tamariscina extract (CSE) showed the highest killing activity. The effects of CSE on M. aeruginosa were monitored using differential interference contrast microscopy and flow-cytometry analysis, scanning electron microscopy, and transmission electron microscopy. The images showed that CSE-treated cells were abnormally altered, with damaged cell membranes, peptidoglycan layers, and cytoplasm. Quadrupole time-of-flight liquid chromatography-mass spectrometry was used to identify amentoflavone as a major active compound. Pure amentoflavone, even at low concentrations showed a powerful killing effect on M. aeruginosa, but not on other non-cyanobacteria. Overall, in this study, we have highlighted the potentials of S. tamariscina extracts and amentoflavone as selective HCB control agents.

Role of divalent metals Cu2+ and Zn2+ in Microcystis aeruginosa proliferation and production of toxic microcystins.

Cu2+ and Zn2+, two ubiquitous metals in water environments, can widely trigger algae blooms at favourable environmental conditions. This paper elucidates the roles of Cu2+ and Zn2+ in the proliferation of Microcystis aeruginosa (M. aeruginosa) and synthesis of Microcystins (MCs). Findings indicate significant influences of increasing Cu2+ and Zn2+ concentrations on cell proliferation at limited available phosphorus concentrations of less than 0.1 mg/L. By contrast, Cu2+ and Zn2+ notably affected MCs production at all the inoculated phosphorus concentrations. The critical concentrations of 1 µg/L and 5 µg/L for Cu2+ and Zn2+, respectively, are determined to trigger rapid cell proliferation and MCs production. Furthermore, the impacts of Cu2+ and Zn2+ on nitrogen absorption and, subsequently, on amino acids (AAs) formation in cells, is likely key in MCs synthesis. The two AAs Alanine (Ala) and glutamic acid (Glu) demonstrate the most notable variations with the concentrations of Cu2+ & Zn2+.

Comparative physiological tolerance of unicellular and colonial Microcystis aeruginosa to extract from Acorus calamus rhizome.

Microcystis blooms and their associated microcystins pose a significant health risk to humans. Microcystis normally occurs as colonies in eutrophic water bodies, and its physiological tolerance to algaecides is dissimilar to that of unicellular forms. However, the differences of physiological response to algaecides between unicellular and colonial Microcystis have been poorly explored. The current study investigated the effects of hexane extract of Acorus calamus rhizome (HEACR) on the physiological and photosynthetic mechanisms of unicellular and colonial M. aeruginosa in the laboratory. We analyzed the cell density, reactive oxygen species (ROS) level, malonaldehyde (MDA) content, photosynthetic pigments, capsular polysaccharide (CPS), and photosystem (PS II) parameters of the two morphological forms of Microcystis. Our results show that HEACR suppresses the growth of both unicellular and colonial M. aeruginosa, increases the intracellular ROS level and cause lipid peroxidation, as well as exerting a detrimental effect on chlorophyll a (chl a) content and photosynthetic efficiency. Almost 100% inhibition was observed for unicellular and colonial M. aeruginosa after 3 d exposure to 50 and 100 mg L-1 HEACR, respectively. The ROS level increase, MDA accumulation, the chl a decrease and carotenoid increase in unicellular M. aeruginosa were all more obvious than that in colonial cells. The fall in photosynthetic efficiency of unicellular M. aeruginosa were also more significant than that of colonial cells. After 3d exposure, the maximum quantum yield of PS II photochemistry (Fv/Fm), effective quantum yield of PS II photochemistry (Fv'/Fm') and effective quantum yield of photochemical energy conversion in PS II (YII) of unicellular M. aeruginosa was almost totally inhibited by 20 mg L-1 HEACR, while the Fv/Fm, Fv'/Fm' and YII of colonial M. aeruginosa decreased by 43%, 26% and 66% for 100 mg L-1 of HEACR, respectively. Comparing the two morphological forms of Microcystis, colonies show a greater increase in CPS level to more effectively resist the stress of HEACR and to mitigate ROS generation thereby better defending against oxidative damage. Furthermore, colonial M. aeruginosa shows better photoprotection ability than the unicellular form when exposed to HEACR. The colonies also sustain their maximum electron transport rate, increase their tolerance to strong light, and maintain a higher ability to disperse excess energy. These results demonstrated that HEACR can significantly interfere with the growth and physiological processes of both unicellular and colonial M. aeruginosa, but that colonial M. aeruginosa has a greater ability to adjust physiological tolerance to resist the stresses of HEACR.

Effect of flavonoids isolated from Tridax procumbens on the growth and toxin production of Microcystis aeruginos.

The excessive proliferation of toxin producing cyanobacteria constitutes a significant health risk to the environment and humans. This is due to the contamination of potable water and accumulation of cyanotoxins in plant and animal tissues. As a means of controlling bloom forming cyanobacteria, secondary metabolites with pro-oxidative activities from plants are used to treat water bodies contaminated with cyanobacterial blooms and their associated toxins. The objective of the present study was to evaluate the mechanism of action of extract, fractions and isolated flavonoids of Tridax procumbens L. on Microcystis aeruginosa (Kützing) Kützing. by monitoring changes in growth, oxidative stress, antioxidant response, and cyanatoxin microcystins (MCs) production. The extract, fraction 3 and the isolated flavonoids significantly reduced the cell density of the cyanobacterium. Furthermore, the extract and fraction 3 increased the production of reactive oxygen species, induced lipid peroxidation, and altered antioxidant enzyme activities of M. aeruginosa. The total MCs content of the cyanobacterium was negatively affected by the presence of the extract, fractions and isolated flavonoids. The present study show that T. procumbens has secondary metabolites that are capable of interfering with the physiology and microcystins production of M. aeruginosa. These characteristics are promising for the control of this noxious cyanobacterium in aquatic ecosystems.

Allelopathically inhibitory effects of eucalyptus extracts on the growth of Microcystis aeruginosa.

Microcystis aeruginosa (M. aeruginosa), as the dominant algae in eutrophic water bodies, has caused a serious harm to the local eco-environment. A biological tool, employing allelopathic inhibitory of eucalyptus to control M. aeruginosa, has been receiving tremendous attention. This work presents the results of the allelopathic inhibitory effects of eucalyptus (Eucalyptus grandis × E.urophylla 'GLGU9') extracts of roots (ERE), stems (ESE), and leaves (ELE) on culture solutions of M. aeruginosa and its eco-physiological mechanism. The inhibitory effects of the extracts on the growth of M. aeruginosa varied greatly with ELE exhibiting the highest level of potency. Modes of action by which ELE inhibited M. aeruginosa growth were established. They involved reduction in photosynthesis, disruption of the cell membrane integrity, and inhibition of esterase activities of the cyanobacterial cells. However, ELE did not exhibit any gradients of toxicity towards zebrafish nor Washington grass plant. Species abundance and diversity in the systems remained likewise unaffected by ELE. The synergistic interaction between ELE and single-component allelochemicals (e.g., gallic acid and berberine) was ascribed to the increase in efficacy of allelochemicals in the various systems. The results of this study provide an underlying, novel, and attractive approach for controlling the growth of M. aeruginosa in aquatic environments.

Effects of Phosphorus on Interspecific Competition between two cell-size Cyanobacteria: Synechococcus sp. and Microcystis aeruginosa.

Pico-cyanobacteria and micro-cyanobacteria coexist ubiquitously in many lakes. Differences in cell size and abilities to utilize nutrients may influence their distribution patterns. In this study, Synechococcus sp. and Microcystis aeruginosa were chosen as pico- and micro-cyanobacteria, respectively. Gradient phosphorus treatments (0.002, 0.01, 0.05, and 0.25 mg P L-1) were designed in mono- and co-cultures. Growth curves were recorded and fitted by the Monod equation. Moreover, the interspecific competition was analyzed by the Lotka-Volterra model. When mono-cultured in lower P conditions (≤ 0.01 mg P L-1), Synechococcus sp. obtained much higher biomass than M. aeruginosa. But, M. aeruginosa grew faster than Synechococcus sp. in higher P groups (≥ 0.05 mg P L-1) (p < 0.05). Synechococcus sp. has abilities to thrive in low-phosphorus environments, whereas M. aeruginosa favored high-phosphorus conditions. In co-cultures, Synechococcus sp. strongly inhibited M. aeruginosa at each P treatment.

Physiological and biochemical responses of Microcystis aeruginosa to phosphine.

The frequent outbreaks of cyanobacteria bloom are often accompanied by the generation and release of reduced phosphorus species (e.g., phosphine), which raises interesting questions regarding their potential algae-related effects. To clarify the physiological and biochemical responses of cyanobacteria to phosphine, Microcystis aeruginosa was treated with different concentrations of phosphine. Net photosynthetic rate, total antioxidant capacity (T-AOC), catalase (CAT) activity, and the concentrations of chlorophyll a, carotenoid and total protein were investigated and scanning electron microscopy (SEM) was conducted to elucidate the physiological and biochemical responses of M. aeruginosa to phosphine. The results showed that phosphine was beneficial to the growth of algal cells after M. aeruginosa acclimatized to the treatment of phosphine, and treatment with 2.48 × 10-2 mg/L phosphine had a greater positive effect on the growth and reproduction of M. aeruginosa than 7.51 × 10-3 mg/L phosphine, in which most algal cells were smooth and flat on day 16. Treatment with the high concentration of phosphine (7.51 × 10-2 mg/L) for 16 d reduced T-AOC, CAT activity, net photosynthetic rate, and the concentrations of chlorophyll a, carotenoid and total protein of M. aeruginosa to the minimums, resulting in the lysis and death of M. aeruginosa cells, which indicates phosphine has a toxic effect on the growth of algal cells. However, the high concentration of phosphine (7.51 × 10-2 mg/L) had a greater positive effect on the growth of M. aeruginosa cells than the lower two (7.51 × 10-3 mg/L and 2.48 × 10-2 mg/L) from 3 d to 12 d. Our findings provide insight into how phosphine potentially affects the growth of M. aeruginosa cells and the important roles of elevated phosphine on the outbreak of cyanobacteria bloom.

Anticyanobacterial phenolic constituents from the aerial parts of Eupatorium fortunei Turcz.

Four thymol derivatives and two phenolic compounds were isolated from the aerial parts of Eupatorium fortunei. The new structures were elucidated to be 7,8,9-trihydroxythymol (1), and 8,10-didehydro-7,9-dihydroxythymol (2) by means of MS and NMR analysis. The known compounds were identified as 8,9,10-trihydroxythymol (3), 10-acetoxy-8,9-dihydroxythymol (4), o-coumaric acid (5) and 4-(2-hydroxyethyl)benzaldehyde (6). Compound 3 showed strongest inhibitory effect on the growth of Microcystis aeruginosa in comparison with CuSO4.

Combination of Logistic and modified Monod functions to study Microcystis aeruginosa growth stimulated by fish feed.

The ecological health of aquaculture water is threatened by wasted fish feed and herbicides. In order to study the effect of prometryn and fish feed on Microcystis aeruginosa growth based on Monod and Logistic functions, four different concentrations of prometryn (0, 50, 100 and 200 µg L-1) and two different dosages of fish feed (0.075 g, 0.15 g; d < 0.85 mm) were added into the culture medium, and the fish feed was the source of nitrogen and phosphorus in the MII medium. Results showed that Microcystis aeruginosa growth can be fitted well by Logistic and modified Logistic functions with 0-200 µg L-1 prometryn (R2 = 0.981-0.998 and R2 = 0.989-0.999, respectively). With the same concentration of prometryn, the maximum algae density (Nmax) of Microcystis aeruginosa calculated by both Logistic and modified Logistic functions increased with increasing dosage of fish feed and with the same dosage of fish feed, Nmax declined with increasing concentrations of prometryn. Inhibition of prometryn on algae growth stimulated by fish feed is of double concentration-dependence, inhibition rates (I) are lower in 0.15 g fish feed medium than 0.75 g ones generally, implying that more nutrients can alleviate the stress caused by prometryn on algae. Derived formula for the specific growth rate, growth rate and inhibition rate using modified Logistic function agreed reasonably well with measured data. Jointly application of modified Monod and Logistic functions can better describe the relationship between specific growth rates and nutrients concentrations compared to combination of Monod and Logistic functions. In addition, equations for describing variations of nutrients concentrations (PO43--P and NH4+-N) with time were also derived based on both modified Monod and Logistic functions, which agree reasonably well with the measured data. In sum, the combination of modified Monod and Logistic functions provides a promising and robust method in studying algal growth stimulated by fish feed in incubator experiments.

Allelopathic Effects on Microcystis aeruginosa and Allelochemical Identification in the Cuture Solutions of Typical Artificial Floating-Bed Plants.

Cyperus alternifolius (C. alternifolius) and Canna generalis (C. generalis) are widely used as artificial floating-bed (AFB) plants for water pollution control. This study evaluated the release of anti-cyanobacterial allelochemicals from both plants in AFB systems. A series of cyanobacterial assays using pure culture solutions and extracts of culture solutions of C. alternifolius and C. generalis demonstrated allelopathic growth inhibition of a cyanobacterium M. aeruginosa. After 45 days of incubation by the culture solutions, both final inhibitory rates of M. aeruginosa were more than 99.6% compared with that of the control groups. GC/MS analyses indicated the presence of a total of 15 kinds of compounds, including fatty acids and phenolic compounds, in both plants' culture solutions, which are are anti-cyanobacterial. These findings provide a basis to apply artificial floating-bed plants for cyanobacterial inhibition using allelopathic effects.

Effects of aqueous extracts from the rhizome of Pontederia cordata on the growth and interspecific competition of two algal species.

Single and co-culture systems of Microcystis aeruginosa and Scenedesmus obliquus were prepared with different initial algal densities and treated with different concentrations of aqueous extracts from the rhizome of Pontederia cordata to study its inhibitory effect on algal growth and the competitive relationship between these two algal species. The results showed that aqueous extracts could inhibit the growth of M. aeruginosa and S. obliquus, and the inhibition rate of aqueous extracts on the growth of M. aeruginosa was always higher than that of S. obliquus. A Lotka-Volterra competition model revealed that these two algal species can co-exist without the addition of aqueous extracts, and S. obliquus exhibited a stronger ability to compete than that of M. aeruginosa. Meanwhile, the dominant algal species changed with the addition of aqueous extracts regardless of the initial ratios of the two algae. The species ratio of mixed cultures had a strong effect on the interspecific interaction between the two algae. The higher proportion of S. obliquus in the initial proportion of two algae, the stronger competitive ability of S. obliquus when compared with that of M. aeruginosa.

Phosphorus Influences the Interaction Between Toxigenic Microcystis and Chloramphenicol.

Microcystis growth and physiological responses to chloramphenicol (CAP)-stress were explored at different phosphorus (P) concentrations during 20-day exposure. Under CAP-stress, Microcystis exhibited (i) stronger total protein synthesis and antioxidant defenses at 5 mg/L P than 0.05-0.5 mg/L P in early test period (before day 8), and (ii) greater CAP-removal via biodegradation at 5 mg/L P in mid-late period. Due to above mechanisms, 5 mg/L P largely alleviated the inhibitory effect of CAP on Microcystis growth until test end, thus minimizing CAP toxicity to Microcystis, compared with 0.05-0.5 mg/L P. Moreover, microcystin-production and -release by Microcystis under CAP-stress were also P-dependent. These results suggested that under CAP-stress, although Microcystis growth was more inhibited at 0.05-0.5 mg/L P, higher microcystin-release and CAP residual at 0.05-0.5 mg/L P than at 5 mg/L P still caused eco-risks, which had important implication for risk assessment during Microcystis-dominated blooms and CAP pollution co-occurrence in different waters.

Interactions between Microcystis aeruginosa and coexisting bisphenol A at different phosphorus levels.

Microcystis aeruginosa is known as the main contributor to cyanobacterial bloom, which is prevalent globally and degrades freshwater systems worldwide. The argument that the introduction of anthropogenic contaminants in fresh water stimulates cyanobacterial growth and microcystin production has attracted widespread attention. Bisphenol A (BPA), one of the most abundant endocrine-disrupting compounds, is often detected in various water bodies due to its notably high annual levels of production and use. Research on the combined effects of endocrine-disrupting compounds and environmental factors on cyanobacteria remains limited. To investigate the mechanism of interactions between contaminants and cyanobacteria at the cellular and proteomic levels, the growth rate, chlorophyll-a content, photosynthetic activities, microcystin-LR (MC-LR) production and release, reactive oxygen species (ROS) content, superoxide dismutase (SOD) activities, malondialdehyde (MDA) content, and proteome expression of M. aeruginosa under 1 µM BPA stress at a standard phosphorus level were investigated. The results showed that stress responses to BPA included increases in the growth rate, chlorophyll-a content, and Fv/Fm and rETRmax values under the low phosphorus condition. Responses involving ROS, SOD, and MDA indicated that phosphorus sufficiency and BPA caused oxidative stress in M. aeruginosa. Moreover, phosphorus sufficiency and BPA stimulated the production and release of MCs. Compared to levels in the non-BPA-treated group, exposure of M. aeruginosa to BPA caused 72 up-regulated proteins, which were primarily associated with photosynthesis, ribosome, fatty acid biosynthesis, glycolysis/glyconeogenesis, and carbon fixation in photosynthetic organisms. The 105 down-regulated proteins were related to quorum sensing, base excision repair, ABC transporters, longevity regulating and cell cycle-caulobacter, suggesting that the cytotoxicity of cyanobacterial cells induced by BPA was significantly increased. These findings provide insights into the molecular mechanism of the effects of BPA and phosphorus on M. aeruginosa, suggesting that coexisting pollutants may cause greater harm to and health risks in the environment.

Algicidal properties of extracts from Cinnamomum camphora fresh leaves and their main compounds.

Plant allelochemicals are considered as the source of effective, economic and friendly-environmental algaecides. To uncover the anti-algal activities of Cinnamomum camphora fresh leaves and their main algicidal agents, we investigated the inhibitory effects of water and methanol extracts from C. camphora fresh leaves on Microcystis aeruginosa and Chlamydomonas reinhardtii cell growth, analyzed the composition of the water and methanol extracts, and determined the main compounds in extracts on the growth of the two algae and their anti-algal mechanism from photosynthetic abilities. Water and methanol extracts from C. camphora fresh leaves can inhibit M. aeruginosa and C. reinhardtii cell growth, and methanol extracts showed stronger inhibitory effects, due to their more compounds and higher molar concentration. There were 23 compounds in the water extracts, mainly including terpenoids, esters, alcohols, and ketones. Compared to the water extracts, 9 new compounds were detected in the methanol extracts, and the molar concentration of total compounds in methanol extracts increased by 1.3 folds. Camphor, α-terpineol and linalool were 3 main compounds in the water and methanol extracts. Their mixture (1: 3: 6) and individual compound showed remarkable inhibition on M. aeruginosa and C. reinhardtii cell growth. The degradation of photosynthetic pigments and the reduction of maximum quantum yield of photosystem II (PSII) photochemistry, coefficient of photochemical quenching as well as apparent electron transport rate in C. reinhardtii cells aggravated gradually with increasing the concentration of the mixture and individual compound, while the non-photochemical dissipation of absorbed light energy increased gradually, which led to the decline of photosynthetic abilities. This indicated that camphor, α-terpineol and linalool were 3 main algicidal agents in C. camphora fresh leaf extracts, and they inhibited algal growth by inducing photosynthetic pigment degradation and declining PSII efficiency. Therefore, C. camphora fresh leaf extracts and their main components have potential utilization values as algaecides.

Inhibitory effects of extracts from Cinnamomum camphora fallen leaves on algae.

Natural allelochemicals are considered as a source of algaecides. To uncover the anti-algal activity of Cinnamomum camphora fallen leaves and promote their usage as algaecides, the composition of their water and methanol extracts was analyzed, and the inhibitory effects of extracts on the growth of Microcystis aeruginosa and Chlamydomonas reinhardtii, and chlorophyll (Chl) content and photosynthetic abilities in C. reinhardtii were investigated. Twenty-five compounds were detected in the water extracts, mainly including terpenoids, esters, alcohols, and ketones. Compared to water extracts, there were more compounds and higher concentration in methanol extracts. Both water and methanol extracts inhibited the growth of the two algae, and 15 mg·ml-1 methanol extracts killed the algal cells after 48 h. The levels of Chl a and Chl b, as well as maximum quantum yield of photosystem II photochemistry (Fv/Fm) in C. reinhardtii cells reduced gradually with increasing the concentration of extracts, while the maximum quantum yield of non-photochemical de-excitation (φDO) increased gradually. At the same concentration, methanol extracts showed stronger inhibitory effects than water extracts, due to their higher number of compounds and higher concentration. Therefore, C. camphora fallen leaves have a potential value as an algaecide.

Effects of Dracontomelon duperreanum Leaf Litter on the Growth and Photosynthesis of Microcystis aeruginosa.

This study investigated the use of Dracontomelon duperreanum leaf litter extract (DDLLE) in inhibiting the growth and photosynthesis of the algae Microcystis aeruginosa. The goal of the study was to evaluate a potential solution for cyanobacterial bloom prevention. M. aeruginosa was exposed to extract concentrations from 0.4 to 2.0 g L-1. Chlorophyll-a (Chl-a) content and photosynthesis levels were assessed using pulse amplitude modulated fluorimetry phytoplankton analyzer. Results suggested that the extract could efficiently suppress M. aeruginosa growth. The content of Chl-a was only 19.0 µg L-1 and achieved 96.0% inhibition rate when exposed to 2.0 g L-1 on day 15. Growth rate in response to different extract concentrations were consistent with changes in the photosynthesis efficiency (alpha), maximal relative electron transport rate and maximal photochemical efficiency of photosystem II (F v /F m ). Furthermore, several kinds of volatile chemicals and their concentrations in DDLLE had been identified by GC-MS, which of them play major role to suppress the growth of M. aeruginosa should be further studied.

Effects of lanthanum on Microcystis aeruginosa: Attention to the changes in composition and content of cellular microcystins.

Algal blooms threaten human health and aquatic ecosystem through the production of microcystins (MCs) by toxic strains. The accumulation of rare earth elements (REEs) in water affects the growth and physiological activities of algae. However, whether or how REEs affect cellular microcystins (MCs) is largely unknown. In this study, the effects of lanthanum ion [La(III)], a type of REE, on the MCs in Microcystis aeruginosa were investigated, and the mechanism of the effect was analyzed using ecological stoichiometry. The different concentrations of La(III) were selected to correlate environmental pollution status. Low-dose La(III) (0.2, 2.0, and 4.0 µM) exposure increased the total content of MCs and the percentage contents of microcystin-YR (MC-YR) and microcystin-LW (MC-LW) and decreased the percentage content of microcystin-LR (MC-LR). High-dose La(III) (8.0, 20, 40, and 60 µM) exposure decreased the total content of the MCs, increased the percentage content of MC-LR, and decreased the percentage contents of MC-YR and MC-LW. The changes in the total MCs content were positively associated with the ratios of C:P and N:P in algal cells. The composition of MCs was dependent on the ratio of C:N in algal cells; for example, the percentage content of MC-LR decreased and the percentage content of MC-YR and MC-LW increased as the ratio of C:N in algal cells increased. In conclusion, La(III) could affect the content and composition of MCs via changes in the growth and chlorophyll-a content of Microcystis aeruginosa, and these effects depended on the ratios of C:P, N:P, and C:N in Microcystis aeruginosa. Such changes may influence the toxicity of Microcystis blooms. The results provides a new insight into the mechanism of REEs effects on algal toxins and provide references for evaluating environmental risks of REEs pollution in aquatic ecosystems.