Algal Suspension Research Articles

Artificial leaf aids analysis of chlorophyll fluorescence and P700 absorbance in studies involving microalgae

SummaryMeasuring chlorophyll fluorescence and P700 absorbance has been widely used to study photosynthesis in both terrestrial plants and algae. However, in order to apply these measurement techniques to study microalgae, a concentrated suspension of algae, which is usually prepared by centrifugation, is required. In this study, instead of using centrifugation, we concentrated microalgae on a nitrocellulose membrane using filtration to create an ‘artificial leaf’ before analysis. Overall, we were able to generate values of the appropriate photosynthetic parameters that were comparable to those obtained when chlorophyll fluorescence and P700 absorbance were measured following centrifugation. There were no statistically significant differences (P > 0.05) between the artificial leaf method and the traditional cuvette method for determining chlorophyll fluorescence or P700 absorbance at appropriate chlorophyll concentrations. We were also able to reduce background noise by using a filter membrane as a carrier. Therefore, an artificial leaf has the potential to be a valuable tool for phycologists interested in studying microalgal photosynthesis by enabling them to eliminate tedious centrifugation steps. In addition, fluorometers commonly used for studying the leaves of higher plants will also be suitable for studying microalgae.

Toxicity of nano-TiO2 on algae and the site of reactive oxygen species production

Given the extensive use of nanomaterials, they may enter aquatic environments and harm the growth of algae, which are primary producers in an aquatic ecosystem. Thus, the balance of an aquatic ecosystem may be destroyed. In this study, Karenia brevis and Skeletonema costatum were exposed to nano-TiO2 (anatase, average particle size of 5–10nm, specific surface area of 210±10m2g−1) to assess the effects of nano-TiO2 on algae. The findings of transmission electron microscopy-energy dispersive X-ray spectroscopy (TEM-EDX) and scanning electron microscopy (SEM) demonstrate aggregation of nano-TiO2 in the algal suspension. Nano-TiO2 was also found to be inside algal cells. The growth of the two species of algae was inhibited under nano-TiO2 exposure. The 72h EC50 values of nano-TiO2 to K. brevis and S. costatum were 10.69 and 7.37mgL−1, respectively. TEM showed that the cell membrane of K. brevis was destroyed and its organelles were almost undistinguished under nano-TiO2 exposure. The malondialdehyde (MDA) contents of K. brevis and S. costatum significantly increased compared with those of the control (p<0.05). Meanwhile, superoxide dismutase (SOD) and catalase activities (CAT) of K. brevis and S. costatum changed in different ways. The reactive oxygen species (ROS) levels in both species were significantly higher than those of the control (p<0.05). The site of ROS production and accumulation in K. brevis and S. costatum under nano-TiO2 exposure was explored with the addition of inhibitors of different electron transfer chains. This study indicated that nano-TiO2 in algal suspensions inhibited the growth of K. brevis and S. costatum. This effect was attributed to oxidative stress caused by ROS production inside algal cells. The levels of anti-oxidative enzymes changed, which destroyed the balance between oxidation and anti-oxidation. Thus, algae were damaged by ROS accumulation, resulting in lipid oxidation and inhibited algae growth. The inhibitors of the electron transfer chain showed that the site of ROS production and accumulation in K. brevis cells was the chloroplast.

Physicochemical effects on sulfite transformation in a lipid-rich Chlorella sp. strain

SO2 is very rapidly hydrated to sulfurous acid in water solution at pH value above 6.0, whereby sulfite is yielded from the disassociation of protons. We aimed to improve the sulfite transformation efficiency and provide a basis for the direct utilization of SO2 from flue gas by a microalgal suspension. Chlorella sp. XQ-20044 was cultured in a medium with 20 mmol/L sodium sulfite under different physicochemical conditions. Under light conditions, sulfite concentration in the algal suspension reduced linearly over time, and was completely converted into sulfate within 8 h. The highest sulfite transformation rate (3.25 mmol/(L·h)) was obtained under the following conditions: 35°C, light intensity of 300 μmol/(m2·s), NaHCO3 concentration of 6 g/L, initial cell density (OD540) of 0.8 and pH of 9–10. There was a positive correlation between sulfite transformation rate and the growth of Chlorella, with the conditions favorable to algal growth giving better sulfite transformation. Although oxygen in the air plays a role in the transformation of SO2−3 to SO2−4, the transformation is mainly dependent on the metabolic activity of algal cells. Chlorella sp. XQ-20044 is capable of tolerating high sulfite concentration, and can utilize sulfite as the sole sulfur source for maintaining healthy growth. We found that sulfite ≤20 mmol/L had no obvious effect on the total lipid content and fatty acid profiles of the algae. Thus, the results suggest it is feasible to use flue gas for the mass production of feedstock for biodiesel using Chlorella sp. XQ-20044, without preliminary removal of SO2, assuming there is adequate control of the pH.

Recycle of algal residue suspension from acid-catalyzed hot-water extraction (AHE) as substrate of oleaginous yeast Cryptococcus sp.

Algal residue after lipid extraction is problematic, yet its high nutrient content makes it a potential source for microbial cultivation. This study proved that algal residue suspension from acid-catalyzed hot-water extraction (AHE) can be used for oleaginous yeast cultivation. When AHE was applied into Nannochloropsis salina, lipid extraction efficiency over 90% was obtained versus the control extraction method using organic solvent, and a water layer containing algal residue nutrients was also produced. Cryptococcus sp. was cultivated in the algal residue suspensions from AHE and a control experiment, and growth was not observed in the control due to the toxicity of alcohol, whereas yeast can grow well in AHE (final cell density: 2.25±0.4g/L, lipid content: 23±2.2%). The AHE method can be a good lipid extraction option for the recycling of algal residue, having the advantage of excluding organic solvents and dissolving residue without any extra processes.

Enantioselective toxicity and degradation of the chiral insecticide fipronil in Scenedesmus obliguus suspension system.

Fipronil is an effective insecticide, but it presents highly toxic effects in nontarget aquatic organisms. The present study examined the enantioselective toxicity and degradation of fipronil enantiomers in a freshwater algae Scenedesmus obliguus suspension. There was a substantial difference in the acute toxicity of the enantiomers to S. obliguus, with 72-h median effective concentrations (EC50s) of 0.29 mg L(-1) and 1.50 mg L(-1) for the R-fipronil and S-fipronil, respectively. The influences on the concentration of chlorophyll a, chlorophyll b, and carotenoids were determined, and the effects of fipronil on the concentration of chlorophyll a and chlorophyll b were also enantioselective. The degradation of fipronil in algae suspension was enantioselective, with half-lives for R-fipronil and S-fipronil of 2.9 d and 3.2 d, respectively, and the enantiomer fraction reaching 0.65 at the day 17. The enantiomeric differences should be taken into consideration for fipronil risk assessment.

Influence of Field Environmental Factors on Water Transparency

Water transparency is an important parameter describing water optical property. Based on the summarized research results in recent decades, this paper systematically expounded the mechanism of various influencing factors for water transparency in the field environment, and classified the factors into three categories: direct influencing factors (including suspended solids, CDOM and algae), distinct indirect influencing factors (including nutrient concentrations and aquatic plants), and weak indirect influencing factors (including temperature, pH). In different water bodies the contribution impacts of direct influencing factors vary with the different environmental characteristics. Distinct indirect influencing factors usually have composite effects on water transparency, which make the mechanism more complex. Weak indirect influencing factors are constrained by other environmental factors, featuring more uncertainty. According to the analysis of previous researches, the following three aspects should be concerned in further studies: (1) more mechanism researches should be conducted based on field measured data analysis; (2) coupling mechanism of multi-factor for water transparency should be concerned.

Biogenic gradients in algal density affect the emergent properties of spatially self-organized mussel beds

Theoretical models highlight that spatially self-organized patterns can have important emergent effects on the functioning of ecosystems, for instance by increasing productivity and affecting the vulnerability to catastrophic shifts. However, most theoretical studies presume idealized homogeneous conditions, which are rarely met in real ecosystems. Using self-organized mussel beds as a case study, we reveal that spatial heterogeneity, resulting from the large-scale effects of mussel beds on their environment, significantly alters the emergent properties predicted by idealized self-organization models that assume homogeneous conditions. The proposed model explicitly considers that the suspended algae, the prime food for the mussels, are supplied by water flow from the seaward boundary of the bed, which causes in combination with consumption a gradual depletion of algae over the simulated domain. Predictions of the model are consistent with properties of natural mussel patterns observed in the field, featuring a decline in mussel biomass and a change in patterning. Model analyses reveal a fundamental change in ecosystem functioning when this self-induced algal depletion gradient is included in the model. First, no enhancement of secondary productivity of the mussels comparing with non-patterns states is predicted, irrespective of parameter setting; the equilibrium amount of mussels is entirely set by the input of algae. Second, alternate stable states, potentially present in the original (no algal gradient) model, are absent when gradual depletion of algae in the overflowing water layer is allowed. Our findings stress the importance of including sufficiently realistic environmental conditions when assessing the emergent properties of self-organized ecosystems.

Removal of Microcystis aeruginosa by potassium ferrate (VI): Impacts on cells integrity, intracellular organic matter release and disinfection by-products formation

Abstract Bench scale tests were conducted to study the effect of potassium ferrate (VI) on cell integrity, intracellular organic matter release and disinfection by-products formation of Microcystis aeruginosa . The simulated algal suspension was prepared a concentration of 1.0 × 10 6 cells/mL and the cytoplasmic membrane integrity was measured with flow cytometry. Results showed that a quick inactivation was achieved after ferrate (VI) oxidation, although no obvious cell lysis was observed. Intracellular organic matter (IOM) release increased with ferrate (VI) dosage and contributed to the formation of trihalomethanes (THM) and haloacetic acids (HAA) as chlorination by-products. However, enhanced coagulation of ferrate (VI) significantly removed M. aeruginosa cells and decreased the algal organic matters (AOMs). Furthermore, the concentrations of THM and HAA were reduced by 71.1% and 67.1%, respectively. Consequently, this study demonstrated potassium ferrate (VI) could act as a dual-functional chemical reagent (i.e., oxidant and coagulant) and may be potentially used in addressing the algal-rich drinking water.

Ultraviolet radiation dose calculation for algal suspensions using UVA and UVB extinction coefficients

Although the biological importance of ultraviolet light (UVR) attenuation has been recognised in marine and freshwater environments, it is not generally considered in in vitro ecotoxicological studies using algal cell suspensions. In this study, UVA and UVB extinction were determined for cultures of algae with varying cell densities, and the data were used to calculate the corresponding extinction coefficients for both UVA and UVB wavelength ranges. Integrating the Beer–Lambert equation to account for changes in the radiation intensity reaching each depth, from the surface until the bottom of the experimental vessel, we obtained the average UVA and UVB intensity to which the cultured algal cells were exposed. We found that UVR intensity measured at the surface of Chlamydomonas reinhardtii cultures lead to a overestimation of the UVR dose received by the algae by 2–40 times. The approach used in this study allowed for a more accurate estimation of UVA and UVB doses.

Govindjee, an institution, at his 80th (really 81st) birthday in Třeboň in October, 2013: a pictorial essay

Govindjee (one name only), who himself is an institution, has been recognized and honored by many in the past for he is a true ambassador of "Photosynthesis Research" to the World. He has been called "Mr. Photosynthesis", and compared to the Great Wall of China. To us in Třeboň, he has been a great research collaborator in our understanding of chlorophyll a fluorescence in algae and in cyanobacteria, and more than that a friend of the Czech "Photosynthesis" group, from the time of Ivan Šetlík (1928-2009) and of Zdeněk Šesták (1932-2008). Govindjee's 80th (really 81st) birthday was celebrated by the Institute of Microbiology, Laboratory of Photosynthesis, by toasting him with an appropriate drink of a suspension of green algae grown at the institute itself. After my presentation, on October 23, 2013, of Govindjee's contributions to photosynthesis, and his intimate association with the photosynthetikers (in Jack Myers's words) of the Czech Republic, Govindjee gave us his story of how he began research in photosynthesis in the late 1950s. This was followed by a talk on October 25 by him on "Photosynthesis: Stories of the Past." Everyone enjoyed his animated talk-it was full of life and enjoyment. Here, I present a brief pictorial essay on Govindjee at his 80th (really 81st) birthday in Třeboň during October 23-25, 2013.

Use of a Combined Technology of Ultrasonication, Three-Phase Partitioning, and Aqueous Enzymatic Oil Extraction for the Extraction of Oil fromSpirogyrasp.

Algal oil fromSpirogyrasp. was extracted using a combined technology of ultrasonication, three-phase partitioning, and aqueous enzymatic oil extraction. Ultrasonication was done to rupture the cell wall and papain was used for an easier release of the trapped oil. The salt concentration for three-phase partitioning, preincubation period with (or without) the protease, and its operational temperature were optimized for a maximum possible yield of the oil and the effect of ultrasonication, and three-phase partitioning with (or without) the protease were studied. It was found that under optimized conditions at 50% ammonium sulphate concentration usingtert-butanol (in 1 : 1, v/v ratio) a presonicated and papain treated algal suspension could produce 24% (w/w, dry weight) oil within few hours which was ten times higher as compared to the oil obtained by Soxhlet extraction using hexane and two times higher than the oil obtained without using the protease.

New Bio-Flocculatious Effect and Its Examination

Algaetechnology is a significant scope of the international research and developmental work because it’s a green technology that reduces the utterance of impurities and works as a renewing energy source. The CO2 from stack gases of the various flows of manufacturing and the nitrogen from certain technical wastewater are necessary for the plants even as algae. The transaction of CO2 with this object and the utilization stand a good chance by hungarian clime with the teamwork from the technical environment. The technology is a new solution in Hungary which eases utterance of the impurities. As a result of our research we expanded alga polities which utilize the CO2 from refinery’s stack gas and they grow intensively in the continental clime, too. The critical points of the technology are the concentration of the algae suspension and the extraction because of the high investment and operating costs and high operational time. The algae technology in this direction depends on this step. Our aim is to separate the algae mass faster and more economical from the starter solution. The optimization of the separating operations and technologies takes notice of the environmental and economic aspects.

The use of microalgae and their culture medium for biogas production in an integrated cycle

Vinasse is a residue produced in large quantities as a sub-product of ethanol production. Anaerobic digestion of vinasse can yield large amounts of biogas, but often difficulties arise in maintaining stable operation, due to the acidity of the material (which has a pH between 3.5 and 5) and a strong tendency to further acidification. Anaerobically digested vinasse can be used as part of a culture medium for microalgae cultivation, for the production of biodiesel and other compounds, whilst the excess CO2 produced in the ethanol fermentation can be used to stimulate algal growth. During algae cultivation, the pH of the culture medium has a strong tendency to increase; therefore, recycling of the spent culture medium or the concentrated algae suspension to the anaerobic digester treating vinasse was considered an option for pH stabilization there. Batch tests, however, showed that alkalinity of the spent culture broth, in spite of its high pH, is too low (only 350 mgCaCO3L(-1)) to help stabilise the pH of vinasse digestion. Alkalinity of the algae suspension is higher and digestion of a mixture of vinasse and a suspension of algae results in efficient biogas production, but still the alkalinity is insufficient to stabilise the pH in a range suitable for methanogenic microorganisms; hence, the addition of additional alkalinity, for instance as sodium bicarbonate or urea, remains necessary.

Resolving Mixed Algal Species in Hyperspectral Images

We investigated a lab-based hyperspectral imaging system's response from pure (single) and mixed (two) algal cultures containing known algae types and volumetric combinations to characterize the system's performance. The spectral response to volumetric changes in single and combinations of algal mixtures with known ratios were tested. Constrained linear spectral unmixing was applied to extract the algal content of the mixtures based on abundances that produced the lowest root mean square error. Percent prediction error was computed as the difference between actual percent volumetric content and abundances at minimum RMS error. Best prediction errors were computed as 0.4%, 0.4% and 6.3% for the mixed spectra from three independent experiments. The worst prediction errors were found as 5.6%, 5.4% and 13.4% for the same order of experiments. Additionally, Beer-Lambert's law was utilized to relate transmittance to different volumes of pure algal suspensions demonstrating linear logarithmic trends for optical property measurements.

Comparison of cell rupturing by ozonation and ultrasonication for algal lipid extraction from Chlorella vulgaris

Cell disruption is essential for lipid collection from cultivated microalgae. This study examines the performance of ultrasonication (US), conventional bubbling ozonation (CBO), and pressure-assisted ozonation (PAO) as a cell rupturing technique to obtain algal lipid from a freshwater unicellular microalgae Chlorella vulgaris, which was grown in BG11 medium at a temperature of 25°C and illuminated by artificial lighting with light/dark cycle of 12 h/12 h. Changes in total organic carbon, total nitrogen, total phosphorous, and chlorophyll contents in the algae suspension after ozonation and US treatments were measured to evaluate the effectiveness of cell rupture by these techniques. Lipid yields of 21 and 27 g/100 g biomass were obtained using US and PAO, respectively. Lipid yields of about 5 g/100 g biomass were obtained using CBO. In all rupturing treatments, C16 and C18 compounds were found to be predominant accounting for 90% of the fatty acids. Using US for rupturing, fatty acids of C16:0, C18:1, and C18:2 were predominant, accounting for 76±4.2% of all the fatty acids. Using CBO and PAO involving ozone, fatty acids of C16:0 and C18:0 were predominant, accounting for 63–94% of the products. The results suggest that saturated fatty acid methyl ester (FAME) products are predominant with oxidative ozonation rupturing while unsaturated FAME products of lower-melting points predominant with physical ultrasonic rupturing means. PAO was an effective cell rupture method for biodiesel production with high lipid yield and more saturated hydrocarbon products.

The Energy Balance of Separation Opportunities in Microalgae Technologies

Algae technology is at the focus of international research and development, since it is a green technology that reduces emissions of harmful chemicals and can be considered as a renewable energy source. Carbon dioxide from stack gases and the nitrogen content of wastewater can be considered as food sources for plants and algae. The utilisation of carbon dioxide by algae technologies depends on the technical environment and logistics of teamwork. This technology is a new opportunity in Hungary for decreasing emissions. We grew algae populations to utilise the carbon dioxide from a refinery’s stack gas in the continental climate of Hungary. Critical parameters of the technology are the concentration of the algae suspension and extract, because of high investment and operating costs as well as the long operation time, which determines the feasibility of the algae technology. Our specific aim was to separate the algae mass faster and more efficiently from the starting solution. The optimisation of separation operations and technologies took into consideration environmental and economic aspects.

EFFECT OF ANABAENA VAGINICOLA INOCULUM ON GROWTH OF POT PLANTS

Although much attention has been paid to study of nitrogen fixation by blue-green algae in paddy fields, algae are also beneficial for plant by producing plant - growth promoters like auxins, cytokinins, abscisic acid and ethylene. Monoalgal cultures was carried out by growing the isolates in nitrate free BG-11 medium in two liter container at 24° and a 12/12 h light-dark cycle at artificial illumination (2,000-2,500 Lux) with constant stirring and aeration. After three weeks culture was harvested and used as an inoculum. Five healthy seedlings were grown in 1 liter pots (14 cm diam.) including 60% peat, 25% sand and 15% normal soil. No fertilizer was applied, but 400 milliliters algal suspension (OD=0.3) was sprayed on treated and BG-11 medium for untreated pots. The pots were arranged in a completely randomized design in an experimental greenhouse. Growth of plants was evaluated by measuring plant height, root length, number leaf and flowers after 50 days planting. From the results described in this paper, it is clearly showed that the algal culture contained some substances that can promote growth of the plants. Result of this finding also has led to the recognition that addition of algal inoculums positively affected plant height and plant root length.

Effect of Type and Concentration of Ballasting Particles on Sinking Rate of Marine Snow Produced by the Appendicularian Oikopleura dioica

Ballast material (organic, opal, calcite, lithogenic) is suggested to affect sinking speed of aggregates in the ocean. Here, we tested this hypothesis by incubating appendicularians in suspensions of different algae or Saharan dust, and observing the sinking speed of the marine snow formed by their discarded houses. We show that calcite increases the sinking speeds of aggregates by ~100% and lithogenic material by ~150% while opal only has a minor effect. Furthermore the effect of ballast particle concentration was causing a 33 m d-1 increase in sinking speed for a 5×105 µm3 ml-1 increase in particle concentration, near independent on ballast type. We finally compare our observations to the literature and stress the need to generate aggregates similar to those in nature in order to get realistic estimates of the impact of ballast particles on sinking speeds.

Daphnia predation on the amphibian chytrid fungus and its impacts on disease risk in tadpoles

Direct predation upon parasites has the potential to reduce infection in host populations. For example, the fungal parasite of amphibians, Batrachochytrium dendrobatidis (Bd), is commonly transmitted through a free-swimming zoospore stage that may be vulnerable to predation. Potential predators of Bd include freshwater zooplankton that graze on organisms in the water column. We tested the ability of two species of freshwater crustacean (Daphnia magna and D. dentifera) to consume Bd and to reduce Bd density in water and infection in tadpoles. In a series of laboratory experiments, we allowed Daphnia to graze in water containing Bd while manipulating Daphnia densities, Daphnia species identity, grazing periods and concentrations of suspended algae (Ankistrodesmus falcatus). We then exposed tadpoles to the grazed water. We found that high densities of D. magna reduced the amount of Bd detected in water, leading to a reduction in the proportion of tadpoles that became infected. Daphnia dentifera, a smaller species of Daphnia, also reduced Bd in water samples, but did not have an effect on tadpole infection. We also found that algae affected Bd in complex ways. When Daphnia were absent, less Bd was detected in water and tadpole samples when concentrations of algae were higher, indicating a direct negative effect of algae on Bd. When Daphnia were present, however, the amount of Bd detected in water samples showed the opposite trend, with less Bd when densities of algae were lower. Our results indicate that Daphnia can reduce Bd levels in water and infection in tadpoles, but these effects vary with species, algal concentration, and Daphnia density. Therefore, the ability of predators to consume parasites and reduce infection is likely to vary depending on ecological context.

Pulsed electric field assisted extraction of intracellular valuables from microalgae

This paper discusses the application of pulse electric field (PEF) treatment for the cell disintegration of the fresh water microalgae Auxenochlorella protothecoides. The algae were cultivated under controlled conditions in a closed photo-bioreactor. After algae harvest the algae suspensions were concentrated and PEF treated with square pulses with a duration of 1μs. We investigated the influence of specific treatment energy (52–211kJ/kg suspension), electric field strength (23–43kV/cm) and biomass concentration (36–167g dry weight per kg suspension) on cell disintegration. For all pulse parameters applied, the PEF induced cell disintegration resulted in the release of soluble intracellular matter into the suspension. The disintegration efficiency increased with increasing specific treatment energy, whereas the field strength hardly had any influence. For suspensions with a biomass content of 100g dry weight per kg suspension the electrical energy input necessary for considerable cell rupture was in the range of 1MJ/kg dried algae. This is equivalent to 4.8% of the upper heating value of the algae. Although the treated algae contained lipids, PEF treatment only led to the spontaneous release of soluble components. The selectiveness of the process might offer the opportunity to use PEF treatment in a biorefinery concept, where soluble algae ingredients are extracted before solvent extraction of lipids is performed.