Harmful Cyanobacterial Blooms (HCBs): innovative green bioremediation process based on anti-cyanobacteria bioactive natural products.

Over the last decades, Harmful Cyanobacterial Blooms (HCBs) represent one of the most conspicuous hazards to human health in freshwater ecosystems, due to the uses of the water for drinking, recreation and aquaculture. Cyanobacteria are one of the main biological components in freshwater ecosystems and they may proliferate in nutrients rich ecosystems causing severe impacts at different levels. Therefore, several methods have been applied to control cyanobacterial proliferation, including physical, chemical and biological strategies. However, the application of those methods is generally not very efficient. Research on an eco-friendly alternative leading to the isolation of new bioactive compounds with strong impacts against harmful cyanobacteria is a need in the field of water environment protection. Thus, this paper aims to give an overview of harmful cyanobacterial blooms and reviews the state of the art of studying the activities of biological compounds obtained from plants, seaweeds and microorganisms in the cyanobacterial bloom control.

Effect of iron and phosphorus on the microalgae growth in co-culture.

Iron and phosphorus (P) are the important micro- and macro-nutrient for microalgae growth, respectively. However, the effect of iron and P on microalgae growth in co-culture associating with the formation of dominate algae has not been investigated before. In the current study, Anabaene flos-aquae, Chlorella vulgaris and Melosira sp. were co-cultivated under the addition of different initial iron and P to reveal the effect of iron and phosphorus on the growth of microalgae. The results showed that the mean growth rate of A. flos-aquae, C. vulgaris and Melosira was 0.270, 0.261 and 0.062, respectively, indicating that the A. flos-aquae and C. vulgaris algae are liable to be the dominant algae while the growth of Melosira was restrained when co-cultured. The ratio of Fe to P has a significant impact on the growth of microalgae and could be regarded as an indicator of algae growth. Microalgae showed a much more obvious uptake of iron compared to that of P. The information obtained in the current study was useful for the forecast of water quality and the control of microalgae bloom.

Eutrophication weakens stabilizing effects of diversity in natural grasslands.

Studies of experimental grassland communities have demonstrated that plant diversity can stabilize productivity through species asynchrony, in which decreases in the biomass of some species are compensated for by increases in others. However, it remains unknown whether these findings are relevant to natural ecosystems, especially those for which species diversity is threatened by anthropogenic global change. Here we analyse diversity-stability relationships from 41 grasslands on five continents and examine how these relationships are affected by chronic fertilization, one of the strongest drivers of species loss globally. Unmanipulated communities with more species had greater species asynchrony, resulting in more stable biomass production, generalizing a result from biodiversity experiments to real-world grasslands. However, fertilization weakened the positive effect of diversity on stability. Contrary to expectations, this was not due to species loss after eutrophication but rather to an increase in the temporal variation of productivity in combination with a decrease in species asynchrony in diverse communities. Our results demonstrate separate and synergistic effects of diversity and eutrophication on stability, emphasizing the need to understand how drivers of global change interactively affect the reliable provisioning of ecosystem services in real-world systems.

Herbivores and nutrients control grassland plant diversity via light limitation.

Human alterations to nutrient cycles and herbivore communities are affecting global biodiversity dramatically. Ecological theory predicts these changes should be strongly counteractive: nutrient addition drives plant species loss through intensified competition for light, whereas herbivores prevent competitive exclusion by increasing ground-level light, particularly in productive systems. Here we use experimental data spanning a globally relevant range of conditions to test the hypothesis that herbaceous plant species losses caused by eutrophication may be offset by increased light availability due to herbivory. This experiment, replicated in 40 grasslands on 6 continents, demonstrates that nutrients and herbivores can serve as counteracting forces to control local plant diversity through light limitation, independent of site productivity, soil nitrogen, herbivore type and climate. Nutrient addition consistently reduced local diversity through light limitation, and herbivory rescued diversity at sites where it alleviated light limitation. Thus, species loss from anthropogenic eutrophication can be ameliorated in grasslands where herbivory increases ground-level light.

A possible environmental-friendly removal of Microcystis aeruginosa by using pyroligneous acid.

Cyanobacteria blooms are crucial environmental issues by threatening both aquatic ecosystem and human health. A biomass by-product with antimicrobial activity, pyroligneous acid (PA) was tested for its suitability for removal of the cyanobacteria Microcystis aeruginosa (M. aeruginosa) in this work. Results show that the removal efficiency could reach up to 90% in the presence of 0.45% of PA and the inhibition to M. aeruginosa growth could extend to at least 40 days. The removal mechanism was studied. Both organic acids and phenols are functional content in M. aeruginosa removal and acetic acid is the most important one. Zeta potential analysis and morphology study show that the damage of cells dominates the flocculation and sedimentation of M. aeruginosa under low PA concentration (<0.7%), and increasing PA (≥0.7%) resulted in a trend of zeta potential to zero, thus removing any "shield" and triggering flocculation. Finally, study on the phenols residual after M. aeruginosa treatment shows that it could be close to 0 in 70 h. Therefore, this work proposes a possible method for world-wide treatment of cyanobacteria bloom and a new way for further utilization of PA.

The Algicidal Bacterium Kordia algicida Shapes a Natural Plankton Community.

Plankton communities consist of complex microbial consortia that change over time. These fluctuations can be only partially explained by limiting resources. Biotic factors such as herbivores and pathogens also contribute to the control of algal blooms. Here we address the effects of algicidal bacteria on a natural plankton community in an indoor enclosure experiment. The algicidal bacteria, introduced into plankton taken directly from the North Sea during a diatom bloom, caused the rapid decline of the bloom-forming Chaetoceros socialis within only 1 day. The haptophyte Phaeocystis, in contrast, is resistant to the lytic bacteria and could benefit from the removal of the competitor, as indicated by an onset of a bloom in the treated enclosures. This cascading effect caused by the bacterial pathogen accelerated the succession of Phaeocystis, which bloomed with a delay of only several weeks in the in situ waters at Helgoland Roads in the North Sea. The algicidal bacteria can thus modulate the community within the limits of the abiotic and biotic conditions of the local environment. Implications of our findings for plankton ecosystem functioning are discussed.IMPORTANCE Plankton communities change on a seasonal basis in temperate systems, with distinct succession patterns; this is mainly due to algal species that have their optimal timing relative to environmental conditions. We know that bacterial populations are also instrumental in the decay and termination of phytoplankton blooms. Here, we describe algicidal bacteria as modulators of this important species succession. Upon treatment of a natural plankton consortium with an algicidal bacterium, we observed a strong shift in the phytoplankton community structure, compared to controls, resulting in formation of a succeeding Phaeocystis bloom. Blooms of this alga have a substantial impact on global biogeochemical and ecological cycles, as they are responsible for a substantial proportion of primary production during spring in the North Sea. We propose that one of the key factors influencing such community shifts may be algicidal bacteria.

Bioprospecting microalgae from natural algal bloom for sustainable biomass and biodiesel production.

Natural algal bloom consists of promising algal species which could be a feasible option for the source of bulk biomass and biodiesel production. It has been found in five natural fresh water algal blooms (Uttar Pradesh, India), containing high nitrogen (N) (4.6 ± 0.32 mg/L) and phosphorus (P) (4.12 ± 0.29 mg/L) concentration during spring (23.9-25.9 °C) and summer season (32.0-35.0 °C). Among the isolated algae from naturally occurring bloom, Chlorella sorokiniana MKP01 exhibited highest biomass (1.02 ± 0.02 g/L) and lipid content (174.1 ± 9.6 mg/L) in untreated tap water and urea/single super phosphate (SSP) in the ratio (2:1). The biodiesel quality was assessed and found to be with the Indian and international standards. Algal bloom was artificially developed in the open pond containing 10,000 l tap water supplemented with Urea/SSP (2:1) for a consistent supply of bulk biomass, yielded 8 kg of total biomass and lipid 1.3 kg.

Inhibition of Scenedesmus quadricauda on Microcystis flos-aquae.

Allelopathy by hydrophytes can be utilized to control algal blooms. This study was conducted to investigate the allelopathic effect (inhibition) of Scenedesmus quadricauda on Microcystis flos-aquae. When M. flos-aquae was co-cultured with S. quadricauda, the secretion of high-MW biopolymer by M. flos-aquae was inhibited by S. quadricauda. We further identified the allelochemicals and found that 4-tert-butylpyrocatechol (TBC) was the main active ingredient that could inhibit the growth of M. flos-aquae. When the dose of TBC was larger than 0.2 mg/L, almost all of the M. flos-aquae died. Additionally, TBC was found to suppress the growth of M. flos-aquae by disturbing the synthesis and secretion of proteins and polysaccharides and harming the chlorophyll to affect the light harvesting of algal cells. Therefore, TBC has the potential for use as a potential and promising algaecide to restrain the biomass of M. flos-aquae.

Algicidal characterization and mechanism of Bacillus licheniformis Sp34 against Microcystis aeruginosa in Dianchi Lake.

Microcystis aeruginosa blooms are a worldwide serious environmental problem and bloom control with bacteria is promising. In this study, a Bacillus licheniformis strain Sp34 with potent algicidal and inhibitory effects on the microcystins synthesis against fast-growing M. aeruginosa was isolated from Dianchi Lake. Sp34 killed the bloom-causing algal strain M. aeruginosa DCM4 of Dianchi Lake with an initial Chlorophyll-a concentration of 2.0 mg/L at a cell density of no less than 1.35 × 105 CFU/ml. It can also efficiently kill some other harmful algal species, such as M. wesenbergii and Phormidium sp. The algicidal activity of Sp34 relied on the release of algicidal substances, which had good heat (-20°C to 121°C) and acid-base (pH 3-11) resistance. In addition, the high algicidal activity depended on the good growth of algae indicated by the significantly positive correlations between algal growth and algicidal ratio (p < .001). The algicidal effect of Sp34 involved causing oxidative stress, lipid peroxidation, and morphological injury of algal cells, along with DNA damage and dysfunction of DNA-repair function, weakening the photosynthesis system, and inhibiting microcystin synthesis. In general, Sp34 can kill fast-growing M. aeruginosa and inhibit algal microcystin synthesis efficiently, so, it is a promising biocontrol agent to mitigate cyanobacterial blooms.

Effects and control of metal nutrients and species on Microcystis aeruginosa growth and bloom.

The effects and control of typical metal nutrients, copper, iron, and zinc, on the growth and bloom of Microcystis aeruginosa were investigated with a series of flask-shaking tests. The optimal concentrations of copper, iron, and zinc for algal growth were 0.001, 3-12, and 0.05 mg/L, respectively. The order of toxicity to the alga was Cu > Zn > Fe. The effects of the species, for a trace metal at the same concentrations, on the growth of M. aeruginosa were relatively remarkable. Ionic and complexation species induced more algal growth than the carbonate and sulfide-bound species. Changes in copper concentration and iron species were adopted to adjust and control the bloom of M. aeruginosa. Increases in copper concentrations significantly suppressed the M. aeruginosa bloom. The growth rate of M. aeruginosa slowed significantly when ionic iron was replaced with sulfide-bound iron, and the control of bloom was remarkable. PRACTITIONER POINTS: Using trace metal nutrient species and concentration to regulate and control algal growth and bloom may pave another way for the management of cyanobacterial bloom.

Nutrient limitation and enzymolysis of phosphorus in Meiliang Bay, Lake Taihu, during algal blooms.

In this study, algal growth potential tests were performed in water samples collected from six sampling sites in Meiliang Bay, Lake Taihu. The potential release of soluble reactive phosphorus (SRP) by enzymatic hydrolysis of enzymatically hydrolyzable phosphorus (EHP) was simultaneously evaluated. Results show that all studied regions were in highly eutrophic states, with additional nitrogen (N) or phosphorus (P) inputs, inducing negligible further increase in algal growth. EHP in water could be rapidly transformed into SRP, further supporting the proliferation of algal blooms. The shortest EHP mineralization time was calculated as 69 minutes; therefore, limiting specific nutrient inputs alone in extremely eutrophic lakes can have a limited effect on suppressing the proliferation of algal blooms. Methods to establish a suitable environmental fate for excessive nitrogen and phosphorus nutrients may be more effective and provide more significant results. PRACTITIONER POINTS: N and P were no longer serving as the limiting factors in Meiliang Bay. Enzymatically hydrolysable phosphorus could be hydrolyzed into soluble reactive phosphorus in a very short period during algal blooms. Both enzymatically hydrolysable phosphorus and soluble reactive phosphorus are required to be curbed in practical eutrophication control.

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.

Seasonal dependency of controlling factors on the phytoplankton production in Taihu Lake, China.

In this study, 44 profiles of gross primary productivity (GPP) and sunlight, along with water temperature, Chlorophyll-a (Chla) and nutrients, were observed in Meiliang Bay of Taihu Lake, China, in the spring, summer, and fall seasons. Effects of water temperature, light, and nutrient concentration were examined in relation to the GPP-unit-Chla (GPP of algae per Chla). The results showed that the optimum temperature for the GPP of phytoplankton was 27.9°C, the optimal PNA-unit-Chla (photon number absorbed by phytoplankton per Chla) was 0.25 (mol), and the HSCN-unit-Chla and HSCP-unit-Chla (half-saturation constants of nitrogen and phosphorus of algae per Chla) were 0.005 (mg/L) and 0.0004 (mg/L), respectively. The seasonal dependency of the effect of different factors on the GPP was analyzed. Compared with temperature and nutrients, light was found to be the most important factor affecting the GPP during the three seasons. The effect of temperature and nutrients on the GPP of phytoplankton has obvious seasonal change. In spring, temperature was the secondary factor affecting the GPP of phytoplankton, and the effect of nutrients may be negligible in the eutrophic lake on account of temperature limit, which showed that the GPP of algae was only affected by the physical process. In summer and fall, temperature didn't affect the GPP of algae, and the presence of nutrients was the secondary factor affecting the GPP of phytoplankton. From summer to fall, effect of phosphorus was weakened and effect of nitrogen was enhanced.

Seaweed Bioactive Compounds against Pathogens and Microalgae: Potential Uses on Pharmacology and Harmful Algae Bloom Control.

Cyanobacteria are found globally due to their adaptation to various environments. The occurrence of cyanobacterial blooms is not a new phenomenon. The bloom-forming and toxin-producing species have been a persistent nuisance all over the world over the last decades. Evidence suggests that this trend might be attributed to a complex interplay of direct and indirect anthropogenic influences. To control cyanobacterial blooms, various strategies, including physical, chemical, and biological methods have been proposed. Nevertheless, the use of those strategies is usually not effective. The isolation of natural compounds from many aquatic and terrestrial plants and seaweeds has become an alternative approach for controlling harmful algae in aquatic systems. Seaweeds have received attention from scientists because of their bioactive compounds with antibacterial, antifungal, anti-microalgae, and antioxidant properties. The undesirable effects of cyanobacteria proliferations and potential control methods are here reviewed, focusing on the use of potent bioactive compounds, isolated from seaweeds, against microalgae and cyanobacteria growth.

How do toxic metals affect harmful cyanobacteria? An integrative study with a toxigenic strain of Microcystis aeruginosa exposed to nickel stress.

Nickel (Ni) is an essential metal for some organisms, but also a common toxic pollutant released into the water. Toxicity of Ni has not been completely established for cyanobacteria; for this reason, we evaluated the effect of sub-inhibitory Ni concentrations on a toxigenic strain of Microcystis aeruginosa and on microcystins production. Population growth, photosynthetic pigments concentration, biomarkers, including antioxidant enzymes (catalase [CAT], glutathione peroxidase [GPx], and superoxide dismutase [SOD]), as well as macromolecules (proteins, carbohydrates and lipids) were quantified; SEM and TEM observations were also performed. Population growth was affected starting at 3µgL(-1), and at 24µgL(-1) growth was completely inhibited; the 96-h Ni(2+) IC50 was 3.7µgL(-1). Ni exposure increased pigments concentration, augmented all the macromolecules, and increased activities of CAT and GPx; alterations on the internal cell structure were also observed. The integrated biomarker response revealed that Ni(2+) augmented the antioxidant response and the macromolecules content. Ni stress also increased microcystins production. M. aeruginosa was affected by Ni at very low concentrations, even lower than those established as safe limit to protect aquatic biota. Aside from the toxic effects produced in this cyanobacterium, stimulation to produce toxins could potentiate the environmental risks associated with water pollution and eutrophication.

Modeling the impact of awareness on the mitigation of algal bloom in a lake.

The proliferation of algal bloom in water bodies due to the enhanced concentration of nutrient inflow is becoming a global issue. A prime reason behind this aquatic catastrophe is agricultural runoff, which carries a large amount of nutrients that make the lakes more fertile and cause algal blooms. The only solution to this problem is curtailing the nutrient loading through agricultural runoff. This could be achieved by raising awareness among farmers to minimize the use of fertilizers in their farms. In view of this, in this paper, we propose a mathematical model to study the effect of awareness among the farmers of the mitigation of algal bloom in a lake. The growth rate of awareness among the farmers is assumed to be proportional to the density of algae in the lake. It is further assumed that the presence of awareness among the farmers reduces the inflow rate of nutrients through agricultural runoff and helps to remove the detritus by cleaning the bottom of the lake. The results evoke that raising awareness among farmers may be a plausible factor for the mitigation of algal bloom in the lake. Numerical simulations identify the most critical parameters that influence the blooms and provide indications to possibly mitigate it.

Lake eutrophication and its implications for organic carbon sequestration in Europe.

The eutrophication of lowland lakes in Europe by excess nitrogen (N) and phosphorus (P) is severe because of the long history of land-cover change and agricultural intensification. The ecological and socio-economic effects of eutrophication are well understood but its effect on organic carbon (OC) sequestration by lakes and its change overtime has not been determined. Here, we compile data from ~90 culturally impacted European lakes [~60% are eutrophic, Total P (TP) >30 µg P l(-1) ] and determine the extent to which OC burial rates have increased over the past 100-150 years. The average focussing corrected, OC accumulation rate (C ARFC ) for the period 1950-1990 was ~60 g C m(-2) yr(-1) , and for lakes with >100 µg TP l(-1) the average was ~100 g C m(-2) yr(-1) . The ratio of post-1950 to 1900-1950 C AR is low (~1.5) indicating that C accumulation rates have been high throughout the 20th century. Compared to background estimates of OC burial (~5-10 g C m(-2) yr(-1) ), contemporary rates have increased by at least four to fivefold. The statistical relationship between C ARFC and TP derived from this study (r(2) = 0.5) can be used to estimate OC burial at sites lacking estimates of sediment C-burial. The implications of eutrophication, diagenesis, lake morphometry and sediment focussing as controls of OC burial rates are considered. A conservative interpretation of the results of the this study suggests that lowland European meso- to eutrophic lakes with >30 µg TP l(-1) had OC burial rates in excess of 50 g C m(-2) yr(-1) over the past century, indicating that previous estimates of regional lake OC burial have seriously underestimated their contribution to European carbon sequestration. Enhanced OC burial by lakes is one positive side-effect of the otherwise negative impact of the anthropogenic disruption of nutrient cycles.

Differential effects of ocean acidification on carbon acquisition in two bloom-forming dinoflagellate species.

Dinoflagellates represent a cosmopolitan group of phytoplankton with the ability to form harmful algal blooms. Featuring a Ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO) with very low CO2 affinities, photosynthesis of this group may be particularly prone to carbon limitation and thus benefit from rising atmospheric CO2 partial pressure (pCO2) under ocean acidification (OA). Here, we investigated the consequences of OA on two bloom-forming dinoflagellate species, the calcareous Scrippsiella trochoidea and the toxic Alexandrium tamarense. Using dilute batch incubations, we assessed growth characteristics over a range of pCO2 (i.e. 180-1200 µatm). To understand the underlying physiology, several aspects of inorganic carbon acquisition were investigated by membrane-inlet mass spectrometry. Our results show that both species kept growth rates constant over the tested pCO2 range, but we observed a number of species-specific responses. For instance, biomass production and cell size decreased in S. trochoidea, while A. tamarense was not responsive to OA in these measures. In terms of oxygen fluxes, rates of photosynthesis and respiration remained unaltered in S. trochoidea whereas respiration increased in A. tamarense under OA. Both species featured efficient carbon concentrating mechanisms (CCMs) with a CO2-dependent contribution of HCO3(-) uptake. In S. trochoidea, the CCM was further facilitated by exceptionally high and CO2-independent carbonic anhydrase activity. Comparing both species, a general trade-off between maximum rates of photosynthesis and respective affinities is indicated. In conclusion, our results demonstrate effective CCMs in both species, yet very different strategies to adjust their carbon acquisition. This regulation in CCMs enables both species to maintain growth over a wide range of ecologically relevant pCO2 .

Toxic mechanisms of the antiviral drug arbidol on microalgae in algal bloom water at transcriptomic level.

Increasing antivirals in surface water caused by their excessive consumption pose serious threats to aquatic organisms. Our recent research found that the input of antiviral drug arbidol to algal bloom water can induce acute toxicity to the growth and metabolism of Microcystis aeruginosa, resulting in growth inhibition, as well as decrease in chlorophyll and ATP contents. However, the toxic mechanisms involved remained obscure, which were further investigated through transcriptomic analysis in this study. The results indicated that 885-1248 genes in algae were differentially expressed after exposure to 0.01-10.0 mg/L of arbidol, with the majority being down-regulated. Analysis of commonly down-regulated genes found that the cellular response to oxidative stress and damaged DNA bonding were affected, implying that the stress defense system and DNA repair function of algae might be damaged. The down-regulation of genes in porphyrin metabolism, photosynthesis, carbon fixation, glycolysis, tricarboxylic acid cycle, and oxidative phosphorylation might inhibit chlorophyll synthesis, photosynthesis, and ATP supply, thereby hindering the growth and metabolism of algae. Moreover, the down-regulation of genes related to nucleotide metabolism and DNA replication might influence the reproduction of algae. These findings provided effective strategies to elucidate toxic mechanisms of contaminants on algae in algal bloom water.