Scenedesmus Armatus Research Articles

Methylparaben changes the community composition, structure, and assembly processes of free-living bacteria, phytoplankton, and zooplankton

Parabens are common contaminants in river and lake environments. However, few studies have been conducted to determine the effects of parabens on bacteria, phytoplankton, and zooplankton communities in aquatic environments. In this study, the effect of methylparaben (MP) on the diversity and community structure of the aquatic plankton microbiome was investigated by incubating a microcosm with MP at 0.1, 1, 10, and 100 μg/L for 7 days. The results of the Simpson index showed that MP treatment altered the α-diversity of free-living bacteria (FL), phytoplankton, and zooplankton but had no significant effect on the α-diversity of particle-attached bacteria (PA). Further, the relative abundances of the sensitive bacteria Chitinophaga and Vibrionimonas declined after MP addition. Moreover, the relative abundances of Desmodesmus sp. HSJ717 and Scenedesmus armatus, of the phylum Chlorophyta, were significantly lower in the MP treatment group than in the control group. In addition, the relative abundance of Stoeckeria sp. SSMS0806, of the Dinophyta phylum, was higher than that in the control group. MP addition also increased the relative abundance of Arthropoda but decreased the relative abundance of Rotifera and Ciliophora. The β-diversity analysis showed that FL and phytoplankton communities were clustered separately after treatment with different MP concentrations. MP addition changed community assembly mechanisms in the microcosm, including increasing the stochastic processes for FL and the deterministic processes for PA and phytoplankton. Structural equation modeling analysis showed a significant negative relationship between bacteria richness and phytoplankton richness, and a significant positive relationship between phytoplankton (richness and community composition) and zooplankton. Overall, this study emphasizes that MP, at environmental concentrations, can change the diversity and structure of plankton microbial communities, which might have a negative effect on ecological systems.

Simultaneous utilization of CO2 and nitrate wastes from compact recirculating aquaculture system for improving algal biomass (Scenedesmus armatus) production

Tilapia cultivation in an air-tight culture tank of a recirculating aquaculture system (RAS) was conducted for 8 days to produce CO2 for growing Scenedesmus armatus in bubble column photobioreactors. The average CO2 concentrations in the headspace of the culture tank were determined at 925 ± 73.4 and 1619 ± 197.7 ppm for fish stocking densities of 3 and 10 kg/m3, respectively. These CO2 concentrations were higher than CO2 concentrations at the tank inlet (496 ± 13.9 ppm) exposed to the atmosphere. Using the captured CO2 and nitrate from the effluent of a commercial tilapia farm for cultivating S. armatus yielded higher algal biomass concentration (621 ± 41.2 mg/L) than using ambient air (410 ± 30.1 mg/L). Insufficient nitrate in RAS effluent is the limiting factor for CO2 utilization and algal biomass production. In conclusion, this study demonstrates the possibility of repurposing CO2 from RAS to enhance algal cultivation.

Microplastics reduce microalgal biomass by decreasing single-cell weight: The barrier towards implementation at scale

Microplastics (MPs) are a widespread environmental threat, especially to aquatic and urban systems. Water quality is vital for biomass production in microalgal-based industries. Here, industrially relevant microalgae Tetraselmis suecica, Scenedesmus armatus, and Nannochloropsis gaditana were exposed to PS- and PE-MPs (polystyrene and polyethylene, respectively – 10-20 μm) contaminated waters (5 and 10 mg/L). Following industrial empirical and ecotoxicological procedures, the production period was established as four days (exponential growth phase). 27-long day experiments were conducted to determine the chronic effects of MPs contamination in microalgal biomass yields. MPs induced different responses in cell density: T. suecica decreased (up to 11 %); S. armatus showed no changes; and N. gaditana increased (up to 6 %). However, all three microalgae exhibited significant decreases in biomass production (up to 24, 48, and 52 %, respectively). S. armatus exposed to PS-MPs and N. gaditana exposed to PE-MPs were the most impacted regarding biomass production. The decrease in biomass yield was due to the reduction in single-cell weight (up to 14, 47, and 43 %), and/or the production of smaller-sized cells (T. suecica). In response to chronic exposure, microalgae showed signs of cell density adaptation. Despite cell density normalizing, biomass production was still reduced compared to biomass production in clean water. Computational modelling highlighted that MPs exposure had a concentration-dependent negative impact on microalgae biomass. The models allow the evaluation of the systematic risks that MPs impose in microalgal-based industries and stimulate actions towards implementing systems to contain/eliminate MPs contamination in the waters used in microalgae production.

Effects of high-strength landfill leachate effluent on stress-induced microalgae lipid production and post-treatment micropollutant degradation

This research investigates the effects of landfill leachate effluent concentrations from moving bed biofilm reactor (MBBR) on stress-induced Chlorella vulgaris and Scenedesmus armatus lipid production and post-treatment micropollutant degradation. The effluent concentrations were varied between 25%, 50%, 75%, and 100% (v/v). The landfill leachate influent was treated using two-stage moving bed biofilm reactor under 24 h and 18 h hydraulic retention time (HRT). The results indicated that the effluent concentration was positively correlated with the stress-induced microalgae lipid production in the post-treatment of residual micropollutants. C. vulgaris and S. armatus completely remove residual micropollutants in the effluent. The superoxide dismutase and peroxidase activity were positively correlated with the cellular lipid content. The lipid content of C. vulgaris and S. armatus cultivated in the 18 h HRT effluent were 31–51% and 51–64%, while those in the 24 h HRT effluent were 15–16% and 5–19%. The optimal condition of microalgae cultivation for the post-treatment of residual micropollutants was 50–75% (v/v) effluent concentrations under 18 h HRT, achieving the highest lipid production of 113–116 mg/L for C. vulgaris and 74–75 mg/L for S. armatus. Essentially, the MBBR landfill leachate effluent holds promising potential as a substrate for microalgae lipid production.

TAXONOMIC STUDIES OF FRESH WATER ALGAE FROM CHISHTIAN CITY, DISTRICT BHAWALNAGAR

Chishtian city was being explored for the collection of fresh water algae in the present study and for those purpose 12 samples of fresh algae from different areas was being collected. From those samples total 28 species was being collected that belong to 16 genera, 11 families, 7 orders and total 4 phylum including, Cyanophycota, Volvocophycota, Bacillariophycota and Chlorophycota. Those samples were being collected from September 2019 to December 2019. After they were classified and identified taxonomically upto species level by using Shameel classification [25,26]. Those 28 species that are being obtained in the total research work: Kingdom Monera has been acknowledged with phylum one; Cyanophycota that omits two classes, two orders, two families four genera and eight species that were following; Chroococus turgidus, Merismopedia punctate, Oscillatoria rubescens, O. priencp, O. tenuis, O. ornate, Spirulina gigantea and Arthospira platensis. Kingdom Protista has been identified with two phylum; Volvocophycota and Bacillariophycota with three classes, four orders, eight families, 11 genera and 18 species which were following; Hydrodictyon reticulatum, Scenedesmus armatus, S. dimorphus, S. bijuga, Cosmerium botrytis, C. microsphinctum, C. pseudopyramiolatum, Closterium turgidum, Fragilaria ulna, F. crotonensis, Ghomphonemia ghosea, Navicula exigua, Nitzschia acicularis, Gyrosigma acuminatum, G. scalproides, Cymbella ventricosa, Cyclotella operculata, C. meneghiniana. Kingdom protoctista have one phylum; Chlorophycota that have 1 class, one order, one family and two species that are following, Spirogyra pratensis and S. acquinoctialis.

Freshwater pond microalgae for biofuel: Strain isolation, identification, cultivation and fatty acid content

Abstract. Perdana BA, Dharma A, Zakaria IJ, Syafrizayanti. 2021. Freshwater pond microalgae for biofuel: Strain isolation, identification, cultivation, and fatty acid content. Biodiversitas 22: 505-511. Microalgae have capability to produce fatty acid for biofuel, drugs, and nutraceutical foods development. This study was carried out to obtain a new strain candidate for fatty acid production. The methods were used in this study include isolation of microalgae species from freshwater ponds of Andalas University, Padang, Indonesia. Molecular identification of microalgae was carried out with specific 18S rRNA primer, F-P73, and R-P47. Microalgae growth was measured by cell density and optical density method using various wavelengths (400, 500, and 680 nm). Total lipid was extracted using Bligh & Dyer method. Fatty acid analyses were conducted using gas chromatography-mass spectroscopy. Microalgae were isolated i.e Chlorella emersonii MAUA001, Mychonastes rotundus MAUA002, Scenedesmus dimorphus MAUA003, and Scenedesmus armatus MAUA004. The result exhibited M. rotundus was the highest lipid content, it was about 28.8% biomass weight. Fatty acid profiles of microalgae were dominated by monounsaturated (MUFA) and saturated fatty acid (SFA). The highest content of fatty acid species found in C. emersonii with octadecenoic acid (C18:1) was 47.74% total lipid. This work showed that C. emersonii has potential as biodiesel due to high saturated fatty acid.

Effect of salinity on mixed microalgae grown in anaerobic liquid digestate

AbstractIn this study, mixed microalgal culture dominated by Chlorella vulgaris and Scenedesmus armatus was grown in Anaerobic Liquid Digestate (ALD) at different NaCl concentrations ranging between 0 and 100 mM. Highest lipid and carbohydrate amounts were observed as 38.4 and 36.2%, respectively, when the salinity was 50 mM NaCl. However, the protein content was drastically decreased to 12.8% with increased NaCl concentration. Furthermore, the algal biomass was subsequently decreased along with the total chlorophyll amount with increased NaCl concentration. Algal species showed diverse response to salinity stress and demonstrated a cost‐effective approach towards the cultivation of mixed microalgae within digestate and provided insight that ALD and/or other wastewaters can be diluted with seawater instead of tap water in the future studies. This study could be further converted into biofuels because of an increase in lipid content along with the digestate treatment, which will help to valorize ALD and bring into economy.

Toxic effects of single animal hormones and their mixtures on the growth of Chlorella vulgaris and Scenedesmus armatus

In their environments, aquatic organisms are simultaneously exposed to mixtures of several endocrine disrupting compounds, including hormones. However, most of the toxicity studies so far focused on effects of single contaminants. The available information on the potential toxicity of combined hormones on microalgae is extremely limited. For these reasons the aim of this study was to evaluate the individual and mixture effect of estrone (E1), ß-estradiol (E2), estriol (E3), 17-α-ethinylestradiol (EE2), progesterone (PRO), 5-pregnen-3β-ol-20-one (PRE), levonorgestrel (LG) and testosterone (TST) on Chlorella vulgaris and Scenedesmus armatus. Green algae cells were exposed to different concentrations (0.1–100 mg L−1) of hormones for 14 days. Biomass in the form of dry weight and chlorophyll a was examined. The decreasing order of toxicity (based on EC50, 14d) to Chlorella vulgaris and Scenedesmus armatus was: EE2>PRO > E2>PRE > TST > E3>LG > E1 and EE2>PRO > TST > E2>PRE > LG > E1>E3, respectively. Chlorella vulgaris was more sensitive to the effects of hormones than Scenedesmus armatus. Although mixed hormones were more toxic to green algae than single hormones, in the ecosystem mixtures can pose higher ecological risk than single pollutants. Therefore, data on the toxicology of both single and mixed hormones is very valuable for assessment of the possibility of adverse ecological effects caused by these pollutants. Furthermore, these results suggest that environmental exposure to hormone mixtures may cause toxicity levels different to the sum of those of the single hormones and provides a basic understanding of their toxic effect on algae.

Inexpensive and universal growth media for biomass production of microalgae

<p>New challenges for industrial microbiology and biotechnology of algae are to increase the efficiency of microalgae growth rates and decrease the cultivation costs. Algae could be cultivated in fresh water as well as in salty sea water or wastewater. Microalgae biomass can be used as a sorbent to remove microcontaminants (e.g. heavy metals, biogens) from wastewater. The obtained results showed that there is a possibility of application of a cheap and universal growing medium (Bf) despite common fertilizers: Bristol or BG-11 to cultivate Chlorella vulgaris and Scenedesmus armatus. The mixotrophic condition can be useful for cultivation of Chlorella vulgaris and Scenedesmus armatus. The highest concentrations of algal biomass for both species were determined after the application of the Bf medium, lower after the BG-11 medium and the lowest after the Br medium in autotrophic as well as mixotrophic conditions. The number of C. vulgaris cells in mixotrophic conditions was higher than S. armatus. The utilization of cheap growing media will lowering the production costs of algal biomass on a large scale.</p>

Biodiesel production from Scenedesmus armatus using egg shell waste as nanocatalyst

Direct transesterification of microalgal biomass has potential to reduce the cost and simplify the microalgal biodiesel production. In this study, CaO nanocatalyst was synthesized from chicken-egg shell waste for direct transesterification. The effect of the transesterification reaction parameters which include; reaction time, catalyst concentration and stirring rate were optimized by using response surface methodology with CCD (central composite design) matrix. The maximum 90.44 % FAME (fatty methyl ester) yield was obtained under optimized conditions of 1.61 wt/wt catalyst ratio with 4h reaction time and stirring rate 85 rpm at 75 °C reaction temperature. The CaO nanocatalyst showed a good catalytic stability upto five cycles.

Production of biodiesel from freshwater microalgae and evaluation of fuel properties based on fatty acid methyl ester profile

ABSTRACTEleven freshwater microalgal strains of Chlorella sorokiniana BTA4015; Chlorella sp. BTA4032, C. variabilis BTA4036; Chlorella sp. BTA4071; C. variabilis BTA4109; C. variabilis BTA4121; Chlorella sp. BTA4146; Chlamydomonas asymmetrica BTA4028; C. asymmetrica BTA4154; Scenedesmus armatus BTA4076 and Scenedesmus regularis BTA4112 were isolated from northeast India and identified through internal transcribed spacer 2 region sequence alignment. Algal strains cultured in 20 L carboys in outdoor condition in tap water enriched with NPK showed doubling time ranged between 1.5–6.8 d, lipid content (4.5–9.1% dry wt), biomass productivity (6–26 mg L−1 d−1) and lipid productivity (0.31–1.99 mg L−1 d−1). The biodiesel properties of iodine value, saponification value, cetane number, high heating value, oxidation stability, allylic and bis-allylic position equivalent, kinematic viscosity, cold filter plugging point, cloud point, pour point and C18:3 were calculated from fatty acid profile. Equally weighted parameters for biodiesel component using Preference Ranking Organization Method for Enrichment Evaluation and Graphical Analysis for Interactive Assistance analysis ranked Chlorella variabilis BTA4109 & BTA4036, C. sorokiniana BTA4015 the most suitable strains meeting the EN14214 biodiesel standard. The biomass productivity for the three strains recorded 20.83, 26.04 and 6.83 mg L−1 d−1 whereas the lipid productivity recorded 0.95, 1.89 and 0.32 mg L−1 d−1 respectively.

Effect of daytime CO2 supplement on productivity and biochemical composition of Scenedesmus armatus under outdoor cultivation

ABSTRACTThe cultivation of Scenedesmus armatus was carried out under outdoor Thailand climate conditions. The highest actual growth rate occurred at around 9:00 a.m. to 3:00 p.m., with a wide pH range of 6.4 to 11. The supply of CO2 had slight influence on growth characteristics but did exert some observable effects on nutritional accumulations. Adding CO2 from 2 to 15% by volume in the aeration (0.2 vvm) caused an increase in lipid and protein from 19.8 to 25.6 and 37.8 to 48.2% w/w, respectively, whereas carbohydrate decreased from 42.5 to 26.2% w/w. Scenedesmus armatus cultivated with 2% CO2-enriched air provided the highest the average of the average biomass productivity of 91.25 mg L−1 d−1, which corresponded to a CO2 fixation of 165 mg CO2 L−1 d−1 with the average lipid, protein, and carbohydrate productivities of 22.24, 38.34, and 30.67 mg L−1 d−1.

Phycoremediation of Wastewater: Heavy Metal and Nutrient Removal Processes

Abstract Phycoremediation is the use of algae for the removal or biotrans-formation of pollutants from wastewater. The study is a novel at-tempt to integrate nutrient (N and P) removal and some heavy met-als (iron, manganese and zinc) bioaccumulation from municipal wastewater using two microalgae species: Chlorella vulgaris and Scenedesmus armatus. The Chlorella vulgaris showed higher re-moval of total nitrogen (TN) both in influent and effluent waste water than Scenedesmus armatus. Nevertheless, more than 51% of total phosphorus (TP) in effluent and 36% in influent wastewaters were removed by Scenedesmus armatus. More efficient microalga in heavy metal removal in influent wastewater was Scenedesmus armatus. The results showed that Chlorella vulgaris was appropriate for TN removal and bioaccumulation of heavy metals from effluent wastewater. Nevertheless, Scenedesmus armatus was highly pref-erable for heavy metals removal from influent wastewater.

珠三角河网水域栅藻（Scenedesmus）时空分布特征研究

珠三角河网水域是珠江之水流入南海的必经之地，对2012年该水域浮游植物群落中的栅藻种类丰富度和生物量的时空特征及其环境影响因子进行系统阐析。调查期间共发现栅藻24种（包括变种、变型），其中具刺和无刺种类分别为11种和13种。出现率高且生物量贡献率大的物种仅3种，包括被甲栅藻原变种（<em>Scenedesmus armatus </em>var.<em> armatus</em>）、被甲栅藻博格变种双尾变型（<em>S</em>. <em>armatus</em> var. <em>boglariensis f. bicaudatus</em>）和二形栅藻（<em>S. dimorphus</em>），分析认为这3个物种在栅藻种群中的生态优势很可能与其形态特征存在一定的关联。栅藻种类丰富度的季节分布呈现丰水期高于枯水期的特征，空间分布呈现河网中部站位低于外侧站位的特征。此外，种类丰富度的空间分布格局存在季节差异，丰水季节呈现河网中部站位明显低于外侧站位的特征，而枯水季节西江沿线站位种类丰富度明显偏低。分析认为，水温和径流是影响栅藻种类丰富度季节变动的关键因素；同时，径流也是影响总种类丰富度空间分布格局的关键因素，而水温和营养盐是影响不同季节种类丰富度的空间格局的重要因素。栅藻种群生物量的季节分布呈现丰水期高于枯水期的特征，空间分布表现为珠江桥站位的生物量明显高于其它站位。分析认为，径流和水温是决定种群生物量季节变动的关键因素，而营养盐、水体稳定性和盐度是决定生物量空间分布格局的关键因素。栅藻生物量与种类丰富度的关系基本符合单峰模型，且偏重于单峰模型的上升区，丰富了全球多样性模式的分级特征和区域特征。;The Pearl River Delta (PRD) in Guangdong province is one of the most economically prosperous areas in China. A large number of domestic and industrial wastes are produced together with the economic development and 10% of waste output in growth rate has been estimated in the past few years. The complicated river web of the delta, which is characterized as criss-cross and multiple river channels, is the essential entrance for the Pearl River water entering into the South China Sea. Many studies have been focusing on physical and chemical factors of this region, but few referred to aquatic organisms, especially in recent years. To understand the temporal and spatial distribution pattern of <em>Scenedesmus</em>, a common green algal group of riverine phytoplankton community, seasonal investigation has been carried out in the river web area in 2012. The thirteen representative sampling sites settled covered almost the whole area and shaped in umbrella-type. The coherence between the biomass of each taxa and environmental factors was also analyzed using PCA method to evaluate the key factors for explaining the interaction mechanisms. Also, the regional characteristics of phytoplankton biodiversity pattern were evaluated from the genus level based on the results.<br>During the investigation, the total 24 taxonomic species (including variant and derivative) were identified, including 11 taxa with spines and 13 taxa none. Although several species showed high occurrence rate, their contribution to total phytoplankton biomass was low, and less than 1% in terms of averages. However, relative abundance between different taxa was closely related to their occurrence rate. Three species (<em>S. armatus</em> var. <em>armatus</em>, <em>S. armatus</em> var. <em>boglariensis f. bicaudatus</em>, <em>S. dimorphus</em>) showed relatively high values in both occurrence and biomass, which was assumed related to their special morphological features. Seasonal variation pattern of both species richness and biomass indicated high in wet seasons and low in dry seasons, water temperature and discharge have been found to be responsible for this through the PCA analysis. Water temperature mainly influenced the growth and physiological conditions of <em>Scenedesmus</em>, while discharge mainly determined the exterior supplement of the algae. The spatial distribution pattern of total species richness showed high in outside stations and low in central stations, but this pattern had apparent seasonal differences. The patterns of May and August were in accordance with that of the total, and the patterns of March and December just showed high values in sampling sites close to Guangzhou. Through the PCA analysis, discharge, water temperature and nutrients have been found to be the key factors to influence this spatial pattern. The spatial distribution pattern of biomass showed extremely higher in ZJQ than those in other stations. Nutrients, water stability and salinity have been found to be the key factors for the spatial pattern through the PCA analysis. In addition, the relationship between <em>Scenedesmus</em> biomass and species richness was analyzed, and it was in consistent with the global phytoplankton biodiversity pattern, and had an incline to ascending part of the model, which also promotes the grading and regional understanding of the global diversity pattern.

Ultraviolet Fluorescence LiDAR (UFL) as a Measurement Tool for Water Quality Parameters in Turbid Lake Conditions

Despite longstanding contributions to oceanography, similar use of fluorescence light detection and ranging (LiDAR) in lake settings is not routine. The potential for ship-mounted, multispectral Ultraviolet Fluorescence LiDAR (UFL) to provide rapid, high-resolution data in variably turbid and productive lake conditions are investigated here through a series of laboratory tank and field measurements carried out on Lake Balaton, Hungary. UFL data, calibrated empirically to a set of coinciding conventionally-analyzed samples, provide simultaneous estimates of three important parameters-chlorophyll a(chla), total suspended matter (TSM) and colored dissolved organic matter (CDOM). Successful UFL retrievals from both laboratory and field measurements were achieved for chla (0.01–378 mg∙m−3; R = 0.83–0.92), TSM (0.1–130 g∙m−3; R = 0.90–0.96) and CDOM (0.003–0.125 aCDOM(440); R = 0.80–0.97). Fluorescence emission at 685 nm is shown through tank measurements to display robust but distinct relationships with chla concentration for the two cultured algae species investigated (cyanobacteria, Cylindrospermopsis raciborskii, and chlorophyta, Scenedesmus armatus). The ratio between fluorescence emissions measured at 650 nm, related to the phycocyanin fluorescence maximum, to that at 685 nm is demonstrated to effectively distinguish these two species. Validation through both laboratory measurements and field measurements confirmed that site specific calibration is necessary. This study presents the first known assessment and application of ship-mounted fluorescence LiDAR in freshwater lake conditions and demonstrates the use of UFL in measuring important water quality parameters despite the more complicated hydro-optic conditions of inland waters.

Phytoplankton yield changes after enrichment in microcosm experiments: Applications for predicting progressive eutrophication in a mesotrophic lake, South Africa

Established microcosms containing surface water from the mesotrophic Lake Mokolo were subjected to enrichment of different concentrations with phosphorus. The microcosms were sampled through a 20 day succession period to determine the net effects of increased concentrations of phosphorus in the water column on the phytoplankton community structure during the winter and summer seasons. A significant increase in chlorophyll a (chl-a) was observed when treatments of 30, 40 and 60 µg L-1 P were compared to the controls. On day zero in both the winter and summer microcosm experiments, all four phosphorus treatments had similar species diversity of phytoplankton of the specific seasoned tested (winter: Margalef index = 223; summer: Margalef index = 347). However, 13 days after the addition of 40 and 60 µg L-1 P, the phytoplankton community exhibited a strikingly different species richness (winter: Margalef index = 123; summer: Margalef index = 114). In the winter microcosm experiments, the green alga Scenedesmus armatus dominated the phytoplankton composition at enrichment levels of 40 and 60 µg L-1 P up to day 20. The biovolume of the dinophyceae Ceratium hirundinella declined rapidly after the addition of 40 µg L-1 P in the different summer microcosms. In the summer microcosms, Spondylosium secedens and Microcystis aeruginosa dominated the 40 and 60 µg L-1 P microcosm enrichment experiments. Key words: Scenedesmus armatus, southern Hemisphere lake, enrichment, cyanobacteria, threshold phosphorus concentrations, chlorophyll a (chl-a) concentration

Cadmium effect on the growth, photosynthesis, ultrastructure and phytochelatin content of green microalga Scenedesmus armatus: A study at low and elevated CO 2 concentration

Short-term experiments were carried out to examine the toxicity of cadmium chloride (CdCl 2) at a concentration of 93 μM (EC 50/24) to green microalga Scenedesmus armatus, cultured at low (0.1%) and elevated (2%) concentration of CO 2. Cadmium did not affect the viability of cells cultured for 24 h in both CO 2 variants but markedly inhibited the growth of algae. This inhibition was more pronounced in cultures aerated with 0.1% (about 50% of control) than with 2% CO 2 (about 75% of control) and did not change during 72 h of culture. Cadmium inhibited the rate of oxygen evolution ( P oxy.) (70% of control) of cells cultured at 0.1% CO 2 and had no effect on P oxy. of cells cultured at 2% CO 2. The values of the chlorophyll fluorescence parameters, i.e. F M (maximum fluorescence yield), F V (variable fluorescence), F V/ F M (maximum quantum yield of PSII), Φ PSII (effective quantum yield of PSII) and qP (photochemical quenching) were reduced by cadmium treatment in algae grown at 0.1% CO 2 concentration, whereas F 0 (initial fluorescence yield) remained unaffected. In high-CO 2 grown cells only F V was significantly reduced. Cd-treated cells synthesized several thiol-containing peptides identified by HPLC as a dimer (PC 2), a trimer (PC 3) and a tetramer (PC 4) of phytochelatins (PC S). High-CO 2 grown cells produced significantly more PCs than low-CO 2 grown cells and their individual appearance depended on the time of exposure and CO 2 level. The ultrastructural analysis of low-CO 2 grown cells showed in chloroplasts an increased number of small starch grains visible around the pyrenoid. In the enhanced vacuome compartment, various types of vacuoles were clearly seen in Cd-treated cells. Vacuoles containing non-membranous, electron-opaque deposits of an undefined structure and myelin-like figures were especially observed. The results suggest that algae living in conditions of elevated CO 2 are better protected against cadmium than those at ordinary CO 2 level, and productive processes are less affected than the growth ones.

IN SITU ALLELOPATHIC POTENTIAL OF MYRIOPHYLLUM VERTICILLATUM (HALORAGACEAE) AGAINST SELECTED PHYTOPLANKTON SPECIES1

The potential allelopathic impact of Myriophyllum verticillatum L. under in situ conditions was determined in a series of field and laboratory experiments. Coexistence experiments were performed in a lake dominated by M. verticillatum (Van Goor) Meffert where we exposed three unialgal phytoplankton cultures in dialysis tubes to macrophyte exudates regularly during the vegetated period. Plant content and exudation of polyphenolic compounds were determined, and the inhibitory activity of polyphenol‐containing extracts was tested in bioassays with cyanobacteria. To account for possible resource interference, we monitored growth and photosynthesis of phosphorus‐limited and unlimited cyanobacterium Limnothrix redekei in dialysis tubes exposed to M. verticillatum in aquaria.A high allelopathic potential of M. verticillatum was concluded from high tissue concentrations of total phenolic compounds of 6%–12% of dry matter, the demonstrated release of bioactive polyphenols into the surrounding medium, and the inhibition of cyanobacteria by extracts. We could not unambiguously demonstrate the exudation of polyphenols by M. verticillatum in situ due to interference with allochthonous humic compounds. In laboratory experiments, L. redekei exhibited significantly reduced maximum relative electron transport rates when co‐cultivated in dialysis tubes with M. verticillatum. The field dialysis tube experiment confirmed this result, accompanied by a decline of chl a and PSII activity for L. redekei and the diatom Stephanodiscus minutulus (Kütz.) Greve et Möller, but not for the green alga Scenedesmus armatus Chodat in August. At other times, either no effects or stimulatory effects were observed with all species. Nutrient limitation of the target species may have masked allelopathic effects, and M. verticillatum may have enhanced phytoplankton growth due to phosphorus leakage.

Toxic effects of anthraquinone and phenanthrenequinone upon Scenedesmus strains (green algae) at low and elevated concentration of CO 2

Short-term (24 h) experiments were performed to examine the effect of anthraquinone (ANTQ) and phenanthrenequinone (PHEQ) on two Scenedesmus armatus strains (B1-76 and 276-4d) grown in a batch culture system aerated with CO 2 at a low (0.1%) or elevated (2%) concentration. ANTQ at concentrations within the range of 0.156–1.250 mg dm −3 inhibited the growth of B1-76 population in a concentration-dependent manner, and calculated EC 50 for low-CO 2 cells was 0.56 mg dm −3. The toxic effect of ANTQ on this strain was more pronounced in high-CO 2 cells, where not only growth but also photosynthesis, respiration and SOD activity were significantly inhibited. In contrast, except for SOD activity, no ANTQ effects on strain 276-4d were found. PHEQ at concentrations within the range of 0.063–0.125 mg dm −3 inhibited the growth of B1-76 population in a concentration-dependent manner. The value of EC 50 for low-CO 2 B1-76 cells was 0.10 mg dm −3. PHEQ inhibited the growth of both strains regardless of CO 2 concentration. In B1-76 cells affected by PHEQ, inhibition of photosynthesis was independent of the CO 2 level, whereas the SOD activity was much higher in cultures aerated with 2% than with 0.1% CO 2. Higher toxicity of PHEQ to strain 276-4d grown at 2% CO 2 was accompanied by strong inhibition of photosynthesis, while in low-CO 2 cells this process was slightly stimulated. The SOD activity in both low- and high-CO 2 cells of strain 276-4d treated with PHEQ was 2–3 times higher compared with the controls. The pattern of SOD isoforms (PAGE analysis) obtained from cells exposed to ANTQ or PHEQ did not change compared with the controls, but the location of the SOD isoforms bands on gel was affected by the concentration of CO 2. The results suggest that the strain-specific toxicity of ANTQ and PHEQ may result from oxidative stress. In addition, carbon dioxide appears to play an important role in the toxicity of quinones to algae.

Points of commitment to reproductive events as a tool for analysis of the cell cycle in synchronous cultures of algae

Methods for determining the points of commitment for cell division are described for species of green algae dividing by multiple fission, both forming coenobia (Scenedesmus quadricauda) and releasing single daughter cells (Chlamydomonas eugametos, Scenedesmus armatus). The timing of commitment points was followed in detail in synchronous cultures of S. quadricauda grown under various light intensities, illumination regimes, and temperatures. The pre-commitment periods were rate limiting, while the post-commitment periods remained more or less constant under various light intensity. Temperature, on the other hand, affected both periods in a similar manner and they were prolonged with decreasing temperature.