Scenedesmus Quadricauda Research Articles

Treatment of real aquaculture wastewater from a fishery utilizing phytoremediation with microalgae

AbstractBACKGROUNDIn this study, five microalgal species (Chlorella vulgaris, Chlorococcum sp. GD, Parachlorella kessleri TY, Scenedesmus quadricauda, and Scenedesmus obliquus) were cultivated in batch mode to evaluate their respective potential for the treatment of real aquaculture wastewater from a fishery. Subsequently, the microalga with the best performance was cultivated with different initial inoculation concentrations to evaluate the effect of initial inoculation on pollutant removal efficiency.RESULTSWhen real aquaculture wastewater was inoculated with exogenous microalgae, the growth of both indigenous microalgae and bacteria was significantly inhibited. Pollutant removal was closely related to exogenous inoculation of microalgae. Parachlorella kessleri TY had high growth potential and pollutant removal capability in aquaculture wastewater, compared with the other four microalgae. When the wastewater was inoculated with low biomass concentrations of P. kessleri TY (50–100 mg L−1), it grew well and degraded most of the encountered pollutant. In particular, P. kessleri TY with 100 mg L−1 of inoculation concentration removed 94.4% of COD, 96.2% of ammonium, 99% of nitrite, 94.3% of nitrate, and 95.6% of phosphorus after 3 days of cultivation.CONCLUSIONSBoth the screening for microalgal species and the regulation of initial inoculation concentrations are promising approaches to enhance pollutant removal efficiency from real aquaculture wastewater. © 2018 Society of Chemical Industry

Draft genome sequence and detailed characterization of biofuel production by oleaginous microalga Scenedesmus quadricauda LWG002611

BackgroundDue to scarcity of fossil fuel, the importance of alternative energy sources is ever increasing. The oleaginous microalgae have demonstrated their potential as an alternative source of energy, but have not achieved commercialization owing to some biological and technical inefficiency. Modern methods of recombinant strain development for improved efficacy are suffering due to inadequate knowledge of genome and limited molecular tools available for their manipulation.ResultsIn the present study, microalga Scenedesmus quadricauda LWG002611 was selected as the preferred organism for lipid production as it contained high biomass (0.37 g L−1 day−1) and lipid (102 mg L−1 day−1), compared to other oleaginous algae examined in the present study as well as earlier reports. It possessed suitable biodiesel properties as per the range defined by the European biodiesel standard EN14214 and petro-diesel standard EN590:2013. To investigate the potential of S. quadricauda LWG002611 in details, the genome of the organism was assembled and annotated. This was the first genome sequencing and assembly of S. quadricauda, which predicted a genome size of 65.35 Mb with 13,514 genes identified by de novo and 16,739 genes identified by reference guided annotation. Comparative genomics revealed that it belongs to class Chlorophyceae and order Sphaeropleales. Further, small subunit ribosomal RNA gene (18S rRNA) sequencing was carried out to confirm its molecular identification. S. quadricauda LWG002611 exhibited higher number of genes related to major activities compared to other potential algae reported earlier with a total of 283 genes identified in lipid metabolism. Metabolic pathways were reconstructed and multiple gene homologs responsible for carbon fixation and triacylglycerol (TAG) biosynthesis pathway were identified to further improve this potential algal strain for biofuel production by metabolic engineering approaches.ConclusionHere we present the first draft genome sequence, genetic characterization and comparative evaluation of S. quadricauda LWG002611 which exhibit high biomass as well as high lipid productivity. The knowledge of genome sequence, reconstructed metabolic pathways and identification of rate-limiting steps in TAG biosynthesis pathway will strengthen the development of molecular tools towards further improving this potentially one of the major algal strains for biofuel production.

Effect of living cells of microalgae or their extracts on soil enzyme activities

ABSTRACTThe enzymatic activity of the soil and potential plant growth can both be affected by the addition of different substances, such as biostimulants. The final objective of this work was to evaluate the effect of Chlorella vulgaris, Scenedesmus quadricauda or their extracts applied directly into the soil, by monitoring the complex soil-microorganism-plant system. Experiments were conducted in pots using agricultural soil and tomato plants in a growth chamber at 25 ± 2 °C illuminated by artificial light with a 16-h photoperiod. The soil biological activity was analyzed by monitoring fluorescein diacetate hydrolysis, dehydrogenases, acid and alkaline phosphomonoesterase and urease activities. Dry weight and chlorophyll index values of tomato plants were also investigated. Results showed that both the microalgae and their extracts positively affected soil biological activity by increasing values of the biochemical index of potential soil fertility (Mw) both in cultivated and uncultivated soils. The highest Mw value was reached in cultivated soil treated for 11 days with the lower concentration of S. quadricauda extract (Mw 9.47). All treatments significantly increased the growth of tomato plants with respect to untreated soil. These results are very promising with a view to improving soil biological activity as well as increasing plant growth.

Treatment of Reverse Osmosis Concentrate Using Microalgae

This study explored how Scenedesmus quadricauda microalga is involved in the degradation and subsequent assimilation of refractory organic matter during remediation of reverse osmosis concentrate. The algal cells were cultivated in the reverse osmosis concentrate with low to high salinities under the given conditions, which resulted in a remarkable increase in the biodegradability of dissolved organic matter, along with robust removal of nutrients (N and P). In this study, hydrogen peroxide from algal-treated wastewater was measured to investigate the mechanism of organic deformation which was associated with algal growth. The degradation of refractory organic matter with microalgae can be considered as more sustainable and cost-effective when compared to commonly used electrochemical oxidation techniques.

Bio oil production from microalgae via hydrothermal liquefaction technology under subcritical water conditions

The upsurge in the concerning issues like global warming, environmental pollution and depletion of fossil fuel resources led to the thrust on third generation biofuels. Algal research has gained a lot of importance in the recent years. Effective utilization of algal biomass in a single step is necessary as it can produce Bio-oil (BO), gases and in addition to a variety of valuable products, along with nutrient recovery. Hydrothermal liquefaction technology does not require the energy intensive drying steps and is an attractive approach for the conversion of algae to liquid fuels. This study investigates direct hydrothermal liquefaction (HTL) of microalgae (Algal biomass) to produce bio-oil using a high-pressure batch reactor under subcritical water conditions. Three different micro algae samples namely, Chlorella vulgaris, Botryococcus braunii and Scenedesmus quadricauda have been examined under hydrothermal liquefaction with different water concentrations (1:6, 1:7, 1:8, 1:9 & 1:10 ratio) at certain temperature range (200–320 °C), pressure (60 bars) and reaction time (30 min). Through liquefaction, the highest BO yield achieved with S. quadricauda was 18 wt% at 1:9 ratio. The chemical components of the obtained bio-oil were analyzed via gas chromatography and the results indicated that the algal BO was composed of furan, phenol, acid, and ester derivatives. Moreover, it was found that by increasing the temperatures, the BO yields increased. This was due to the polymerization reactions that converted the small biomass components into heavier molecules. FTIR spectra showed high percentage of Aliphatic, Phenolic, alcoholic, Carboxylic and Hydroxyl groups for solid residues.

Modelling and optimization of wet microalgae Scenedesmus quadricauda lipid extraction using microwave pre-treatment method and response surface methodology

Abstract The process of extracting lipids from high-moisture Scenedesmus quadricauda microalgae biomass disrupted with microwave was examined. The study showed that microwave pre-treatment is effective in algae cell rupture while microwave power was found to be a significant factor to enhance the degree of cell disruption. Though microwave pre-treatment time had some effect, the degree of cell rupture seemed to decrease after a certain pre-treatment time. The total lipid from Scenedesmus quadricauda sp. were extracted using a mixture methanol and sulphuric acid as an organic solvent. In addition, it was discovered that microwave pre-treatment enhances the disruption of microalgae cells to attain a high level of lipid yields. Optimal lipid yield obtained in this study was 49% at power 600 W, heating time of 8 min and extraction time of 3.5 h.

The combined influence of 24‑epibrassinolide and 3‑indoleacetic acid on growth and accumulation of pigments and fatty acids in the microalgae Scenedesmus quadricauda (CPCC-158)

Interest in the use of wastewaters of different origins for the industrial production of microalgal biomass for biofuels and bioproducts has stimulated studies on the influence of a variety of compounds in wastewaters on algal physiology. Following the previously published work on the impact of four single phytohormones on the physiology of the microalga Scenedesmus quadricauda (CPCC-158), we investigated the combined effect of the 24‑epibrassinolide (EBL) and 3‑indoleacetic acid (IAA) on S. quadricauda biosynthesis and biomass production. Synergistic increases in S. quadricauda biomass production, chlorophyll-a accumulation, total carotenoid accumulation, as well as total and major neutral lipid (triacylglyceride) accumulation were observed for most of the mixed hormone trials. Mixed hormones had stimulatory effects on growth and biosynthesis of S. quadricauda, but the influence of mixed hormones on algae growth (maximum 1.6-times greater) was less than their influence on algal biosynthesis (maximum 1.7-, 2.7-, and 3.3-fold for chlorophyll-a, total carotenoids, and fatty acids, respectively) compared with single hormone treatments. The mechanism of EBL and IAA cross-talk is likely specific to targeted biosynthetic pathways. The type of relationship between two mixed phytohormones was assessed with Ting-Chao Chou Test. Our results highlight the need for further research on the combined influence of phytohormones on algae physiology.

Versatile applications of freshwater and marine water microalgae in dairy wastewater treatment, lipid extraction and tetracycline biosorption

In this study, freshwater (Scenedesmus quadricauda, Sq) and marine water (Tetraselmis suecica, Ts) microalgae were used for the treatment of dairy wastewater (DWW). Sq and Ts showed the highest biomass productivity as 0.47 and 0.61 g/L, respectively. Removal efficiencies of total nitrogen (TN), phosphate (PO43−), and total organic carbon (TOC) were observed as 86.21, 89.83 and 64.47% by Sq and 44.92, 42.18 and 40.16% by Ts, respectively. After wastewater treatment, lipids were extracted from microalgal biomasses. Fatty acid methyl esters (FAMEs) analysis revealed that saturated fatty acids (SFAs) are dominant in Sq and polyunsaturated fatty acids (PUFAs) in Ts. After lipid extraction, removal of tetracycline (TC) from water by microalgal biomasses was also investigated. Maximum adsorption capacities of Sq and Ts were found to be 295.34 and 56.25 mg/g, respectively. Results of this study revealed the versatile applications of microalgae for wastewater treatment, lipid production and TC removal from water.

The strong reaction of simple phenolic acids during oxidative stress caused by nickel, cadmium and copper in the microalga Scenedesmus quadricauda

This work has analysed the influence of CdCl2, NiCl2 and CuCl2 on simple phenolic acids, such as the 3PPP (phenylpyruvic, phenylacetic, and 4-hydroxyphenylpyruvic) and 2DR (3,4-dihydroxyphenylacetic and rosmarinic) phenolic acids for the first time and studied their interactions with antioxidant systems and the glutathione-ascorbate cycle in the freshwater green microalga Scenedesmus quadricauda. The compounds investigated are related to both the catabolic and anabolic pathways of l-phenylalanine and l-tyrosine, the main molecules in the biosynthesis of polyphenols. The concentrations of the simple phenolic acids responded significantly to NiCl2, CdCl2 and CuCl2 at 5, 20 and 40 μM concentrations. The 3PPP phenolic acid concentrations after 24 h were always higher in metal-treated cells than in controls, while the 2DR concentrations were significantly lower in the metal-treated cells than the controls. The GSH/GSSG ratio was lower in all experimental groups treated with the selected metals (especially so at 40 μM). Pearson correlation analysis indicated a strong negative correlation between ascorbate and rosmarinic acid content (−0.670; p < 0.05) in NiCl2-treated samples and reduced glutathione and 3,4-dihydroxyphenylacetic content (−0.700; p < 0.05) in CdCl2-treated samples. The GSSG content in samples exposed to CuCl2 was correlated with the concentrations of all of the investigated phenolic acids (4 negative, 1 positive).

Interactive effects of temperature and copper toxicity on photosynthetic efficiency and metabolic plasticity in Scenedesmus quadricauda (Chlorophyceae)

Warming and copper (Cu) toxicity are two key abiotic stressors that strongly affect cell growth, photosynthetic rate, and metabolism in microalgae. In this study, a freshwater chlorophyte, Scenedesmus quadricauda, was exposed to various concentrations of copper sulfate (300, 600, and 1000 μM nominal concentrations of CuSO4·5H2O) at 25 and 35 °C. The changes in cell density, photosynthetic parameters, in vivo absorption spectra, reactive oxygen species (ROS) levels, and metabolic profile were analyzed. The effects of copper toxicity on the physiology and biochemistry of microalgae were highly dependent on water temperature. The interactive effects of both stressors induced significant impact on the photosynthetic parameters such as maximum quantum yield (Fv/Fm), saturation irradiance (Ek), and non-photochemical quenching (NPQ). Temperature induced significant impact on cell density, Ek and NPQ, while the Cu toxicity significantly affected the Fv/Fm and NPQ. Changes in the in vivo absorption spectra and high levels of reactive oxygen species (ROS) were observed across different treatments. Overall, S. quadricauda adapted to the two abiotic stresses via NPQ and metabolic restructuring. Key metabolites including glycine, proline, hexadecanoic acid, propanoic acid, octadecanoic acid, galactose, lactose, and sucrose were involved in the microalgal response. The synergistic effects of temperature and Cu stresses on microalgae might affect community tolerance and species distribution in the long run.

Nitrogen and phosphorus removal from anaerobically digested wastewater by microalgae cultured in a novel membrane photobioreactor

BackgroundWith the further development of anaerobic digestion, an increasing output of anaerobically digested wastewater (ADW), which typically contained high concentrations of ammonium, phosphate, and suspended solids, was inevitable. Microalgae cultivation offered a potential waste-to-value strategy to reduce the high nutrient content in ADW and obtain high value-added microalgae. However, ADW generally contained a mass of pollutants (suspended solids, competitors, etc.), which could inhibit microalgae growth and even result in microalgae death by limiting light utilization. Thus, it is highly imperative to solve the problem by a novel modified photobioreactor for further practical applications.ResultsFour microalgae species, Scenedesmus dimorphus, Scenedesmus quadricauda, Chlorella sorokiniana, and Chlorella vulgaris ESP-6, were cultivated in the membrane photobioreactor (MPBR) fed with ADW to investigate the efficiency of ammonia and phosphorus removal. The results showed that C. sorokiniana had the best performance for the removal of ammonia and phosphorus from ADW. The highest amount of C. sorokiniana biomass was 1.15 g/L, and the removal efficiency of phosphate (66.2%) peaked at an ammonia concentration of 128.5 mg/L after 9 days’ incubation. Moreover, the MPBR with 0.1 μm membrane pore size had the best ammonia and phosphate removal efficiencies (43.9 and 64.9%) at an ammonia concentration of 128.5 mg/L during 9 days’ incubation. Finally, the continuous multi-batch cultivation of C. sorokiniana was performed for 45 days in MPBR, and higher removal ammonia amount (18.1 mg/day) and proteins content (45.6%) were obtained than those (14.5 mg/day and 37.4%) in an normal photobioreactor.ConclusionIn this study, a novel MPBR not only eliminated the inhibitory effects of suspended solid and microorganisms, but also maintained a high microalgae concentration to obtain a high amount of ammonia and phosphate removal. The research provided a theoretical foundation for the practical application of MPBRs in various wastewater treatment schemes without pretreatment by algae, which could be used as biofuels or protein feed.

Root exudated algicide of Eichhornia crassipes enhances allelopathic effects of cyanobacteria Microcystis aeruginosa on green algae

Eichhornia crassipes is an invasive, floating macrophyte and may have biocontrol functions on harmful cyanobacteria blooms. Eichhornia produces N-phenyl-2-naphthylamine (PNA), a compound which can inhibit algae. However, the impact of PNA on allelopathic effects of the cyanobacterium Microcystis aeruginosa on other phytoplankton species is not clear. In this study, we tested whether PNA can influence the allelopathic effect of M. aeruginosa on the green alga Scenedesmus quadricauda. S. quadricauda was more sensitive to PNA than M. aeruginosa, with 72 h-EC50 values of 0.42 and 3.66 mg L−1, respectively. In addition, PNA significantly enhanced allelopathy by M. aeruginosa on S. quadricauda. Consequently, PNA had a greater impact on the green algae when Microcystis was present. In complex ecosystems with multiple species that release allelopathic substances, unintended interspecific interactions may occur, where allelopathy plays an important role under artificial or even natural contexts. It is hard to predict the competition outcomes among allelopathic organisms in these complex ecosystems, therefore a precautionary approach is required for biological control of algae.

Biostimulant activity of humic-like substances from agro-industrial waste on Chlorella vulgaris and Scenedesmus quadricauda

ABSTRACTThe use of microalgae in a number of sectors, including biodiesel, feed and food production, is proving to be of great interest. An evaluation was made of the possible biostimulant effects on Chlorella vulgaris and Scenedesmus quadricauda of humic-like substances (HLs) extracted from agro-industrial wastes. These included digestate from the waste of an agro-livestock farm (D-HL), oil extraction residues from rape (B-HL, Brassica napus L.) and tomato residues (T-HL). The microalgal growth medium (BG11) was supplemented with HLs to evaluate their effect on biomass yield as well as carbohydrate, chlorophylls a and b, lipid and fatty acid contents. Our results showed that the HLs used in the test are effective biostimulants of C. vulgaris and S. quadricauda. The biostimulant effect seems to depend on the type of extract used for cultivating the microalgae, the concentration and the species treated. Among the extracts applied to the growth medium, D-HL and T-HL seem to have a significant effect on microalgal biomass and lipid production. Although B-HL showed no significant effect on the biomass and lipid content of C. vulgaris and S. quadricauda, its presence in the growth medium increased the saturated:unsaturated fatty acid ratio (SFA/UFA) and stimulated the sugar metabolism of the microalgae by increasing their carbohydrate and chlorophyll content.

Comparison of growth characteristics and nitrogen removal capacity of five species of green algae

Five common used green algae species, Chlorella vulgaris, Chlorococcum sp. GD, Parachlorella kessleri TY, Scenedesmus obliquus, and Scenedesmus quadricauda, were evaluated for their growth and nitrogen removal properties when being cultivated in synthetic wastewater with ammonium and nitrate as nitrogen sources. The five microalgae could adapt wastewater with different kinds of nitrogen sources, but the growth potential and nitrogen removal ability were species-dependent. Parachlorella kessleri TY cultivated in wastewater with ammonium and nitrate had higher biomass concentration of 2750 and 2765 mg L−1, respectively, compared to C. vulgaris, S. obliquus, and S. quadricauda. Chlorococcum sp. GD in wastewater with nitrate had the highest biomass concentration of 3095 mg L−1. Although all microalgae showed a good removal efficiency of nitrogen (ammonium: 85.30–97.03%; nitrate: 100%) after 7 days of cultivation, Chlorococcum sp. GD and P. kessleri TY removed 85–90.24% of ammonium and 100% of nitrate within 2–3 days, which was faster than the other three microalgae. It was also found that the growth and pollutant removal of microalgae in wastewater with nitrate was superior to those of microalgae in wastewater with ammonium. This was caused by the inhibitory effect of the low pH when microalgae were cultivated in wastewater with ammonium as the nitrogen source. Based on the results above, the growth and nitrogen removal was closely related to the microalgal species and the pH of the wastewater.

The Effects of Interspecific Interactions Between Bloom Forming Cyanobacteria and Scenedesmus quadricauda (Chlorophyta) on Their Photophysiology

Eutrophication and enhanced external nutrient loading of lakes and seas are most clearly reflected by increased cyanobacterial blooms, which are often toxic. Freshwater cyanobacteria produce a number of bioactive secondary metabolites, some of which have allelopathic properties, significantly influencing the biological processes of other algae, thereby affecting species composition and succession of the phytoplankton. The goal of this work was to investigate the influence of bloom-forming cyanobacterial exudates on the photophysiology of the green alga Scenedesmus quadricauda by chlorophyll fluorescence analysis. We were able to prove the effect of algal cell-free fltrates on the performance of S. quadricauda and demonstrate for the first time that the freshwater picocyanobacterium Cyanobium gracile has strong negative impact on the coexisting green alga. Neither the cyanotoxin (MYC, CYN and ATX) producing, nor the non-toxic strains showed any systematic effect on the production of S. quadricauda. Various strains of the cyanobacterium Cylindrospermopsis raciborskii inhibited the performance of the green alga independently of their origin. Our results urge further studies for a better understanding of the factors affecting the release of allelopathic compounds and the mechanisms of their effects on target organisms.

Novel bioprocess for the cultivation of microalgae in hydroponic growing system of tomato plants

Hydroponic growing systems and the application of natural biostimulant substances are becoming very attractive option for crop cultivation due to their economic relevance since they allow reduction in the use of fertilizer and increase the yield. In order to perform a hydroponic co-cultivation system of microalgae (Chlorella vulgaris or Scenedesmus quadricauda) and tomato plants, grown in Hoagland nutrient solution, their mutual effect and the influence of a natural biostimulant obtained by alkaline extraction from a digestate of agro-livestock residues (DHL) were evaluated. The results showed that the co-cultivation system positively affected the growth of both tomato plants and microalgae. The best option, aimed to a mutual benefit for both cultures, resulted to be the co-cultivation system of tomato plants and S. quadricauda in the presence of DHL, positively affecting the growth of tomato plants along with a great increase in microalgal biomass.

The growth and lipid accumulation of Scenedesmus quadricauda during batch mixotrophic/heterotrophic cultivation using xylose as a carbon source

To overcome the bottlenecks of high cost and low production yields that restrict the commercial production of microalgae biodiesel, the use of xylose was evaluate by Scenedesmus quadricauda FACHB-1297, which was shown to be capable of mixotrophic and heterotrophic growth and lipid production on xylose, rich in the waste streams from pulp and paper industry, with increases in lipid productivities of 35.8-fold (mixotrophic) and 9.2-fold (heterotrophic) in comparison to photoautotrophic lipid yields. Five doses of xylose were tested to determine the effects and mechanisms of the carbon source on microalgae in mixotrophic mode. At the optimal xylose dosage of 4 g/L, the highest lipid content (38.61%) and productivity (139.55 mg/L/d) were achieved besides maximum biomass productivity (361.4 mg/L/d), nutrient removal efficiency of 68.4% (nitrogen), 97.2% (phosphorus) and 35.2% (xylose). Those indicated that S. quadricauda FACHB-1297 was suitable for further development of using xylose from certain waste streams for biofuel production.

INFLUENCE OF NANOCOMPOSITE Ag/AgCl ON THE CULTURE OF MICROALGAE SCENEDESMUS QUADRICAUDA AND PHAEODACTYLUM TRICORNUTUM

The toxicity of the Ag/AgCl nanocomposite was evaluated at different concentrations in chronic experiments for 41 days using standard freshwater and marine plant test organisms of Scenedesmus quadricauda (0.05, 0.1, 0.5 and 1.0 mg/l) and Phaeodactylum tricornutum (0.25, 0.5, 1.0, and 2.0 mg/L). Comparative sensitivity of test organisms in acute experiments (72 hours) in terms of LC50 was carried out. It was established that the green alga of S. quadricauda is more sensitive to the Ag/AgCl nanocomposite (LC50 = 0.02 mg/l) than the marine diatomea P. tricornutum (LC50 = 0.3 mg/l). The greatest algicidal effect on the growth of S. quadricauda culture was provided by the nanocomposite in concentrations of 1 and 0.5 mg/l, at which the culture did not grow during the experiment. And at concentrations of 0.1 and 0.05 mg/l the algostatic effect was observed for 10 and 1 days, respectively, after which the culture resumed growth. In the culture of P. tricornutum at concentrations of 1.0 and 2.0 mg/l there was a prolonged inhibition of growth, but after 25 days at 1.0 mg/l the number of cells began to increase. In the presence of 0.5 mg/l the culture resumed growth after 4 days of lag phase and overtook the number of control. At the concentration of 0.25 mg/l the growth of P. tricornutum was either at or above the control level. The difference in the response of the two species of algae can be explained both by the individual feature of the species and by the more complex composition of the marine nutrient medium, which reduces the toxicity of the nanocomposite. According to analytical electron microscopy silver from Ag/AgCl nanocomposites within a day falls inside the cells of S. quadricauda and P. tricornutum algae, passing unimpeded both through the cell wall and the cell membrane.

Biotic Interactions between Two Species of Microalgae in Mixed Culture

Biotic interactions in a mixed culture of two microalgae species—Scenedesmus quadricauda (Turp.) Breb. and Monoraphidium arcuatum (Korsch.) Hind.—used in bioassay in monocultures as test objects were studied. The toxic effect of cell-free filtrates from different “age” monoculture (2, 7, 10, 15, 21, and 28 days) of S. quadricauda on the growth of the “young” test culture of M. arcuatum and, conversely, the toxic effect of cell-free filtrates from the different “age” (2, 7, 10, 15, 21, and 28 days) monoculture of M. arcuatum on the growth of the “young” test culture of S. quadricauda was evaluated. Simultaneously, the toxicity of their own filtrates of different “ages” was monitored by a test culture of each species. The interactions of the species in the mixed culture can be regarded as negative, as an antagonistic one, when both populations inhibit the growth of each other through metabolites and food resource competition, while the effect of S. quadricauda on M. arcuatum is much stronger. The main factor constraining the growth of monoculture S. quadricauda is the rapid depletion of the food resource from the medium and not the inhibition of growth by its own metabolites. The depletion of the food resources from the medium in monoculture of M. arcuatum occurs much later than in monoculture of S. quadricauda. Metabolites of S. quadricauda cause a strong inhibitory effect on the growth of M. arcuatum, and the metabolites of M. arcuatum cause a weak inhibitory effect on the growth of S. quadricauda. The filtrates of the “old” culture of S. quadricauda (21–28 days) cause the greatest inhibitory effect on cell division of M. arcuatum. The filtrates of the “old” culture of S. quadricauda (21–28 days) cause the greatest inhibitory effect on cell division of M. arcuatum. Comparative analysis of the cell number dynamics of two species, S. quadricauda and M. arcuatum, in mono- and two-species algal cultures, as well as experiments with filtrates of these monocultures, showed that the interaction of species can be explained by the food resource competition and allelopathic interaction (exometabolite effect).

Evaluation of copper toxicity using site specific algae and water chemistry: Field validation of laboratory bioassays

Studies of metal toxicity to microalgae have predominantly been conducted using single non-target algae species and without due regard for the chemistry of the treated waters, leading to ineffective or excessive algaecide treatments. In this study, indigenous multi-algal species (Scenedesmus quadricauda, and Scenedesmus subspicatus and Oscillatoria agardhii) were used in laboratory toxicity bioassays under simulated field water chemistry (pH = 7.2, hardness = 196 mg L−1 as CaCO3, and alkalinity = 222 mg L−1 as CaCO3) to determine the optimum copper sulfate treatment dose to control algae growth in an irrigation canal. Toxicity bioassays were conducted using copper sulfate in chelated (with EDTA) and non-chelated (without EDTA) forms to assess the influence of the use of synthetic chelators in toxicity studies. Also, copper toxicity to the indigenous algae species was measured in the non-modified EPA test medium (pH = 7.5, hardness = 92 mg L−1 as CaCO3, alkalinity = 10 mg L−1 as CaCO3 and EDTA= 300 µg L−1) to assess the impact of the water chemistry on algae inhibitory algal dosages. Under simulated water chemistry conditions, lower toxicity was measured in the test flasks with the chelated form of copper (96 h- EC50= 386.67 µg L−1 as Cu) as compared to those with the non-chelated metal (96 h-EC50= 217.17 µg L−1 as Cu). In addition, higher copper toxicity was measured in the test flasks prepared with the non-modified EPA medium using chelated copper (96 h-EC50 = 65.93 µg L−1 as Cu) as compared to their analogous microcosms with modified water chemistry (96 h-EC50= 386.67 µg L−1 as Cu), the increased water hardness and alkalinity in the latter case contributing to the decrease of the metal bioavailability. Results from laboratory experiments showed good correlation with copper dosages used in a small scale field testing to control algae growth, increasing confidence in laboratory bioassays.