Isolation and identification of extracts of Eichhornia crassipes and their allelopathic effects on algae

The Allelopathic Activity of Extracts and Isolated from Spirulina platensis

We determined the allelopathic effects of crude organic (hexane, ethyl acetate, and methanol) extracts of the cyanobacterial Spirulina platensis on barnyardgrass (Echinochloa crus-galli (L.) Beauv.) and Chinese amaranth (Amaranthus tricolor L.). The crude ethyl acetate extract showed the highest inhibitory activity and was subsequently fractionated by column chromatography into 23 fractions based on thin-layer chromatography band pattern similarities. Four concentrations (2000, 1000, 500, and 250 ppm) of each fraction were tested for their allelopathic activity. Fractions E6 and E13 exhibited the most significant inhibitory effects against Chinese amaranth. The constituents of the highly active E6F3-E6F5 fractions determined by GC-MS, chromatography, and spectroscopy included the fatty acids, γ-linolenic acid 15, oleic acid 12, and predominantly palmitic acid 7; minor constituents included 2-ethyl-3-methylmaleimide 9 and C₁₁ norisoprenoids (dihydroactinidiolide 10 and 4-oxo-β-ionone 13). Isolation of E13 fraction by column chromatography revealed four C₁₃ norisoprenoids: 3-hydroxy-β-ionone 17, 3-hydroxy-5α,6α-epoxy-β-ionone 18, 3-hydroxy-5β,6β-epoxy-β-ionone 19, and loliolide 20. Their structures were elucidated by NMR spectroscopy. All six isolated norisoprenoids inhibited seed germination and seedling growth of Chinese amaranth at concentrations of 250–1000 ppm. Allelochemicals from S. platensis could be utilized in the development of novel bioactive herbicides.

Eichhornia crassipes (Mart.) Solms: A Comprehensive Review of Its Chemical Composition, Traditional Use, and Value-Added Products

Eichhornia crassipes (Mart.) Solms, commonly known as water hyacinth, is one of the world’s most invasive aquatic plants of the Pontederiaceae family occurring in tropical and subtropical regions of the world. Although, E. crassipes causes significant ecological and socioeconomic issues such as a high loss in water resources, it has multipurpose applications since it is famous for many industrial applications such as bioenergy, biofertilizer production, wastewater treatment (absorption of heavy metals), and animal feed. Furthermore, E. crassipes is rich in diverse bioactive secondary metabolites including sterols, alkaloids, phenolics, flavonoids, tannins, and saponins. These secondary metabolites are well known for a wide array of therapeutic properties. The findings of this review suggest that extracts and some isolated compounds from E. crassipes possess some pharmacological activities including anticancer, antioxidant, anti-inflammatory, antimicrobial, skin whitening, neuroprotective, and hepatoprotective activities, among other biological activities such as allelopathic, larvicidal, and insecticidal activities. The present review comprehensively summarizes the chemical composition of E. crassipes, reported to date, along with its traditional uses and pharmacological and biological activities.

Interactions between elevated CO2 levels and floating aquatic plants on the alteration of bacterial function in carbon assimilation and decomposition in eutrophic waters

Elevated atmospheric CO₂ concentration (eCO₂) may have different effects on the bacterial community with regard to C assimilation and decomposition in eutrophic waters compared to that in fresh waters with intermediate levels of nutrients and oceans. Aquatic plant growth under eCO₂ could further modify microbial activities associated with the C cycle in eutrophic waters. Therefore, there is an urgent need to further study how eCO₂ and its interactions with the growth of aquatic plants affect the composition and function of the bacterial community involved in mediating the C cycle in eutrophic waters. Accordingly, we designed a microcosm experiment to investigate the effects of ambient and high CO₂ concentrations on bacterial community composition and function in eutrophic waters with and without the growth of Eichhornia crassipes (Mart.) Solms. The results from 16S rRNA gene sequencing, function prediction, and q-PCR showed that eCO₂ significantly increased the abundance of bacterial and functional genes involved in CO₂ assimilation (photosynthetic bacteria; cbbL IA & IC, cbbL ID, cbbM, pufM) and C decomposition (Acidimicrobiia, Thermoleophilia, Gaiellales; ChiA), illustrating the functional enrichment with photoautotrophy, hydrocarbon degradation, cellulolysis, and aromatic hydrocarbon degradation. However, eCO₂ decreased the abundance of some chemoautotrophic bacteria, including nitrifying bacteria (Nitrospirae, Nitrosomonadaceae). In contrast, the cultivation of E. crassipes decreased the abundance of photosynthetic bacteria but increased the abundance of bacteria involved in complex C decomposition associated with root exudates and degradation, e.g. Fibrobacteres, Sphingobacteriales, Sphingomonadales, and Rhizobiales. eCO₂ and growth of E. crassipes had opposite effects on algal density in eutrophic waters, creating interactive effects that further decreased the diversity of the bacterial community and abundance of some CO₂-assimilating bacteria with nitrifying characteristics (Nitrosomonadaceae) and some C-degrading bacteria (Fibrobacteres) with denitrifying properties (Flavobacteriaceae, Sphingomonadaceae, and Gemmobacter). Therefore, the interactions between aquatic plants and the bacterial community in eutrophic waters under eCO₂ would be beneficial to the environment and help alleviate the greenhouse effect.

Contrasting impact of elevated atmospheric CO2 on nitrogen cycle in eutrophic water with or without Eichhornia crassipes (Mart.) Solms

The elevation of atmospheric CO₂ is an inevitable trend that would lead to significant impact on the interrelated carbon and nitrogen cycles through microbial activities in the aquatic ecosystem. Eutrophication has become a common trophic state of inland waters throughout the world, but how the elevated CO₂ affects N cycles in such eutrophic water with algal bloom, and how vegetative restoration helps to mitigate N₂O emission remains unknown. We conducted the experiments to investigate the effects of ambient and elevated atmospheric CO₂ (a[CO₂], e[CO₂]; 400, 800 μmol﹒mol^-1) with and without the floating aquatic plant, Eichhornia crassipes (Mart.) Solms, on N-transformation in eutrophic water using the ¹⁵N tracer method. The nitrification could be slightly inhibited by e[CO₂], due mainly to the competition for dissolved inorganic carbon between algae and nitrifiers. The e[CO₂] promoted denitrification and N₂O emissions from eutrophic water without growth of plants, leading to aggravation of greenhouse effect and forming a vicious cycle. However, growth of the aquatic plant, Eichhornia crassipes, slightly promoted nitrification, but reduced N₂O emissions from eutrophic water under e[CO₂] conditions, thereby attenuating the negative effect of e[CO₂] on N₂O emissions. In the experiment, the N transformation was influenced by many factors such as pH, DO and algae density, except e[CO₂] and plant presence. The pH could be regulated through diurnal photosynthesis and respiration of algae and mitigated the acidification of water caused by e[CO₂], leading to an appropriate pH range for both nitrifying and denitrifying microbes. Algal respiration at night could consume DO and enhance abundance of denitrifying functional genes (nirK, nosZ) in water, which was also supposed to be a critical factor affecting denitrification and N₂O emissions. This study clarifies how the greenhouse effect caused by e[CO₂] mediates N biogeochemical cycle in the aquatic ecosystem, and how vegetative restoration mitigates greenhouse gas emission.

Effect of propionamide on the growth of Microcystis flos-aquae colonies and the underlying physiological mechanisms

Reducing the formation and growth of Microcystis colonies is an important prerequisite for the effective prevention and treatment of cyanobacterial blooms. Microcystis flos-aquae colonies was selected to investigate the potential of propionamide for use in controlling cyanobacterial blooms. Propionamide, one of the major allelochemicals in the root exudates of E. crassipes, was tested using different concentrations (0, 0.2, 1, and 2mgL^-1) and dosing methods (one-time addition, semi-continuous addition, and continuous addition) to assess its effect on the growth of M. flos-aquae colonies. The results showed that in the presence of different concentrations of propionamide, the growth of M. flos-aquae colonies followed a logistic growth model, with a higher degree of fit at lower propionamide concentrations. With the semi-continuous addition of 2mgL^-1 propionamide, the growth of M. flos-aquae colonies was markedly inhibited; the relative inhibition ratio of algal cells reached >90% at day 7 of co-culture, and the colonial form gradually disintegrated, transforming mainly into unicellular and bicellular forms and small colonies (average diameter<50μm). Following the semi-continuous addition of 2mgL^-1 propionamide, the exopolysaccharide content, the chlorophyll-a concentration, and the maximum photochemical efficiency of photosystem II (Fv/Fm) trended downward in M. flos-aquae colonies, whereas the relative expression of the microcystin (MC) biosynthetic genes, mcyA and mcyH, was upregulated overall. Importantly, the synthesis of intracellular microcystin-LR (MC-LR) was decreased after an initial increase, and the extracellular MC-LR concentration did not differ significantly from that in the control group (p>0.05). Moreover, an acute toxicity test showed that 2mgL^-1 propionamide was generally non-toxic to Daphnia magna. In conclusion, appropriate use of propionamide could effectively control the expansion of M. flos-aquae colonies without potential risks to the ecological safety of aquatic environments; therefore, propionamide can actually be used to regulate cyanobacterial blooms in natural waters.

Allelopathic Effects of Myriophyllum aquaticum on Two Cyanobacteria of Anabaena flos-aquae and Microcystis aeruginosa

Allelopathy has been proposed as a sustainable means to control undesired algal growth and to reduce blooms threatening freshwater systems worldwide. In this study, the allelopathic effects of Myriophyllum aquaticum and its exudate on two typical bloom-forming cyanobacteria, Microcystis aeruginosa and Anabaena flos-aquae, were investigated under laboratory conditions. The growth of the cyanobacteria was strongly inhibited by live M. aquaticum while the primary addition of M. Aquaticum exudates had a significant inhibitory effect on the growth of M. aeruginosa but not A. flos-aquae. The results suggested that the persistent release of allelochemicals from live M. aquaticum was needed to effectively constrain the growth of A. flos-aquae. Analysis of cyanobacterial physiological indexes indicated that M. aquaticum produced an inhibitory effect on SOD enzyme activity of A. flos-aquae, while it affected membrane lipid peroxidation in M. aeruginosa. The results show the potential of M. aquaticum to mitigate cyanobacterial blooms in coexistence systems.

Research Progress on the use of Plant Allelopathy in Agriculture and the Physiological and Ecological Mechanisms of Allelopathy

Allelopathy is a common biological phenomenon by which one organism produces biochemicals that influence the growth, survival, development, and reproduction of other organisms. These biochemicals are known as allelochemicals and have beneficial or detrimental effects on target organisms. Plant allelopathy is one of the modes of interaction between receptor and donor plants and may exert either positive effects (e.g., for agricultural management, such as weed control, crop protection, or crop re-establishment) or negative effects (e.g., autotoxicity, soil sickness, or biological invasion). To ensure sustainable agricultural development, it is important to exploit cultivation systems that take advantage of the stimulatory/inhibitory influence of allelopathic plants to regulate plant growth and development and to avoid allelopathic autotoxicity. Allelochemicals can potentially be used as growth regulators, herbicides, insecticides, and antimicrobial crop protection products. Here, we reviewed the plant allelopathy management practices applied in agriculture and the underlying allelopathic mechanisms described in the literature. The major points addressed are as follows: (1) Description of management practices related to allelopathy and allelochemicals in agriculture. (2) Discussion of the progress regarding the mode of action of allelochemicals and the physiological mechanisms of allelopathy, consisting of the influence on cell micro- and ultra-structure, cell division and elongation, membrane permeability, oxidative and antioxidant systems, growth regulation systems, respiration, enzyme synthesis and metabolism, photosynthesis, mineral ion uptake, protein and nucleic acid synthesis. (3) Evaluation of the effect of ecological mechanisms exerted by allelopathy on microorganisms and the ecological environment. (4) Discussion of existing problems and proposal for future research directions in this field to provide a useful reference for future studies on plant allelopathy.

Effect of linoleic acid sustained-release microspheres on Microcystis aeruginosa antioxidant enzymes activity and microcystins production and release

The objective of this work was to identify the optimal dose range for good anti-algal effect of linoleic acid (LA) sustained-release microspheres and investigate their impact on the antioxidant enzymes (super oxide dismutase, Catalase and Peroxidase) activity changes of Microcystis aeruginosa, as well as the production and release of microcystins (MCs). Based on measured changes in algal cell density and inhibitory ratio (IR), the optimal dose of LA microspheres was 0.3 g L(-1) with over 90% of IR in this study. The Chlorophyll a content and antioxidant enzymes activity in the LA microspheres group decreased markedly until beyond the minimal detection limit after 16 d and 9 d, respectively. In addition, LA microspheres demonstrated no significant impact on the extracellular release of MCs during the culturing period. The amount of intracellular microcystin-LR (MC-LR) per 10(6) algal cells in LA microspheres group was highest among all groups during the whole experimental process. Under the sustained stress of LA released from LA microspheres, the LA microspheres could decrease the production and release of algal toxins. There was no increase in the total amount of MC-LR in the algal cell culture medium. These indicated that LA sustained-release microspheres represent a high degree of ecological safety and their practical applications for the treatment of water undergoing algal blooms need further study.

Algicidal effects of four Chinese herb extracts on bloom-forming Microcystis aeruginosa and Chlorella pyrenoidosa

Extracts from four Chinese herbs, Phellodendri chinensis cortex, Artemisia annua L., Scutellaria baicalensis G. and Citrus reticulate peel were tested for their algicidal effects on Microcystis aeruginosa and Chlorella pyrenoidosa. The results showed that M. aeruginosa was more susceptible than C. pyrenoidosa. The growth of M. aeruginosa was significantly inhibited (p < 0.05) by the four herb extracts. Among the four herbs, P. chinensis cortex and S. baicalensis had the greatest inhibitory effects on M. aeruginosa, followed by C reticulate peel and A. annua. The 50% effective concentrations (EC50) of S. baicalensis, P chinensis cortex, C. reticulate peel and A. annua were 0.87, 0.88, 5.27 and 1 1.16 gherb L-1, respectively. The growth of C. pyrenoidosa was moderately inhibited by the herb extracts individually. The EC5o concentrations for S. baicalensis, P. chinensis cortex, C. reticulate peel andA. annua were 8.67, 11.67, 12.81 and 12.44 g herb L-1', respectively. Extract from S. baicalensis displayed stronger algicidal effects on C. pyrenoidosa than the other three herbs, although no lethal effect on C. pyrenoidosa was observed during the cultivation period. Compared with corresponding individual extract at the same dosage, the binary mixtures of the four herb extracts enhanced the algicidal effects on M. aeruginosa. The maximum inhibitory rates of all binary mixtures of the four herb extracts were all above 92% during the 10-day incubation. The results demonstrate that Chinese herbs, such as P. chinensis cortex or S. baicalensis and their combinations, could offer an effective alternative for mitigating outbreaks of harmful algal blooms in water bodies.

Effects of allelochemical extracted from water lettuce (Pistia stratiotes Linn.) on the growth, microcystin production and release of Microcystis aeruginosa

This study explored the optimisation of a method of extracting allelochemicals from Pistia stratiotes Linn., identified the optimal dose range for the allelochemicals' anti-algal effect and investigated their impact on the growth of Microcystis aeruginosa, as well as the production and release of microcystin-LR (MC-LR). Based on measured changes in algal cell density and chlorophyll a (Chl-a) content, the allelochemicals were confirmed to have the strongest anti-algal effect with the lowest half-effect concentration of 65 mg L(-1) when they were extracted using ethyl acetate as the extraction solvent, 1:20 g mL(-1) as the extraction ratio and 1 h as the extraction time. The allelochemicals extracted from P. stratiotes using this optimal method exhibited the strongest inhibitory effect on the growth of algae when used within a dose range of 60-100 mg L(-1); the relative inhibitory ratio reached 50-90%, and Chl-a content reduced 50-75% in algae cell cultures within 3-7 days. In addition, the extracted allelochemical compounds demonstrated no significant impact on the extracellular release of MC-LR during the culturing period. The amount of intracellular MC-LR per 10(6) algal cells increased depending on the increasing dose of allelochemicals from P. stratiotes after 7 days of culturing and maintained stability after 16 days. There was no increase in the total amount of MC-LR in the algal cell culture medium. Therefore, the application of allelochemicals from P. stratiotes to inhibit M. aeruginosa has a high degree of ecological safety and can be adopted in practical applications for treating water subjected to algae blooms because the treatment can effectively inhibit the proliferation of algal cells without increasing the release of cyanotoxin.

Allelopathic effects of gallic acid from Aegiceras corniculatum on Cyclotella caspia

High abundance of algae and eutrophication were observed in mangrove wetlands and these were estimated to be associated with root exudates of some specific mangrove plants to a certain extent. Root exudates form allelopathic effects from mangroves. The main secondary metabolites of Aegiceras corniculatum had been detected to be organic phenolic acids. Gallic acid had been isolated and identified from A. corniculatum. The half-maximal inhibitory concentration of gallic acid on alge Cyclotella caspia was tested as 15.46 mg/L. The effects on algal cell morphology were mainly shown as elongated cells, with no apparent cell inclusions, such as oil droplets, chloroplast. At a dose of 2 mg/L, gallic acid had a stimulative effect on the specific growth rate of algae on day 3. The contents of malondialdehyde, superoxide dismutase, soluble carbohydrates and chlorophyll a in algal cells showed an overall "low promotion and high suppression". Our results could provide preliminary and valuable reference on the complex influences of mangroves on microecology and microbial communities in the rhizosphere system.

Secondary Metabolites of Eichhornia crassipes (Waterhyacinth): A Review (1949 to 2011)

Eichhornia crassipes (Mart.) Solms (Waterhyacinth), an aquatic perennial herb present throughout the world, has a myriad of metabolites. Phenalenone compounds and sterols have been isolated from this plant. Extracts, as well as pure compounds isolated from this plant, have been demonstrated to possess pharmacological activities. An account of the phytochemistry, pharmacological activities and several applications of waterhyacinth are included in this review.

Inhibitory effects and mechanisms of Hydrilla verticillata (Linn.f.) Royle extracts on freshwater algae

To pursue an effective way to control freshwater algae, four extracts from a submerged macrophyte Hydrilla verticillata (Linn.f.) Royle were tested to study its inhibitory effects on Anabaena flos-aquae FACHB-245 and Chlorella pyrenoidosa Chick FACHB-9. Extract with the highest inhibiting ability was further studied in order to reveal the inhibitory mechanism. The results demonstrated that H. verticillata extracts inhibited the growth of A. flos-aquae and C. pyrenoidosa, and methanol extract had the highest inhibiting ability. The mechanism underlying the algal growth inhibition involves the superoxide anion radical generation that induces the damage of cell wall and release of intracellular components.

Allelopathic effects of water hyacinth [Eichhornia crassipes]

Eichhornia crassipes (Mart) Solms is an invasive weed known to out-compete native plants and negatively affect microbes including phytoplankton. The spread and population density of E. crassipes will be favored by global warming. The aim here was to identify compounds that underlie the effects on microbes. The entire plant of E. crassipes was collected from El Zomor canal, River Nile (Egypt), washed clean, then air dried. Plant tissue was extracted three times with methanol and fractionated by thin layer chromatography (TLC). The crude methanolic extract and five fractions from TLC (A-E) were tested for antimicrobial (bacteria and fungal) and anti-algal activities (green microalgae and cyanobacteria) using paper disc diffusion bioassay. The crude extract as well as all five TLC fractions exhibited antibacterial activities against both the gram positive bacteria; Bacillus subtilis and Streptococcus faecalis; and the gram negative bacteria; Escherichia coli and Staphylococcus aureus. Growth of Aspergillus flavus and Aspergillus niger were not inhibited by either E. crassipes crude extract nor its five fractions. In contrast, Candida albicans (yeast) was inhibited by all. Some antialgal activity of the crude extract and its fractions was manifest against the green microalgae; Chlorella vulgaris and Dictyochloropsis splendida as well as the cyanobacteria; Spirulina platensis and Nostoc piscinale. High antialgal activity was only recorded against Chlorella vulgaris. Identifications of the active antimicrobial and antialgal compounds of the crude extract as well as the five TLC fractions were carried out using gas chromatography combined with mass spectroscopy. The analyses showed the presence of an alkaloid (fraction A) and four phthalate derivatives (Fractions B-E) that exhibited the antimicrobial and antialgal activities.