Green Microalgae Species Research Articles

Evaluation of toxicity of zinc oxide nanorods on green microalgae of freshwater and marine ecosystems

Zinc oxide (ZnO) nanomaterials (NMs) are widely used in the manufacture of several commercial products like foods, packaging, cosmetics, medicines and healthcare formulations and anti-fouling paints. These NMs can pollute water bodies when they become bioavailable. In this context, this study investigated the toxicity of ZnO nanorods (NRs) on green microalgae from freshwater and marine ecosystems, to better understand the behavior of this NM on each environment. Two green microalgae species, Desmodesmus subspicatus (freshwater) and Tetraselmus sp. (marine), were evaluated by chronic toxicity tests and oxidative stress induction by the enzymatic activity of catalase (CAT). The exposition assays were performed using three different concentrations of ZnO NRs (0.1, 1.0, and 10 mg/L, and a negative control). ZnO NRs significantly affected the growth rate of both tested chlorophytes. The chronic toxicity test showed LOEC (Lowest Observed Effect Concentration) levels of 10 mg/L (72 h) for D. subspicatus and 1.0 mg/L (24 h) for Tetraselmis sp. It was observed NOEC (No Observed Effect Concentration) levels of 1.0 mg/L to D. subspicatus was (at 72 h) and of <0.1 mg/L for Tetraselmis sp . (at 24 h). In the enzymatic activity tests of D. subspicatus exposed to ZnO NRs, the CAT activity caused significant changes at the concentration at 10 mg/Lof ZnO NRs when compared to the control test, but for Tetraselmis sp. no change was observed in CAT activity. These results indicate that D. subspicatus was more sensitive to the effects of ZnO NRs at the concentration of 10 mg/L after 72 h, while oxidative stress of this alga was also observed at the same concentration. The results of this study show the importance of further investigating the toxicological effects of ZnO NRs on green microalgae from distinct aquatic environments and of evaluating the toxicological response of these microalgae in culture media. • Ecotoxicity of zinc oxide nanorods (ZnO NR) was evaluated on freshwater and marine green microalgae. • Freshwater microalgae showed more sensitivity than marine microalgae to ZnO NR. • ZnO NR induced oxidative stress in freshwater microalgae, evidenced by a change in CAT activity. • The response to ZnO NR toxicity is affected by the nature of the organism and its ecosystem.

Efficiency of Daphnia magna in removal of green microalgae cultivated in Nordic recirculating aquaculture system wastewater

The increase of global aquaculture production has boosted the development of recirculating aquaculture systems not only because they reduce water use but also provide opportunities for waste management and the use of released nutrients. The dissolved nutrients can be efficiently removed from recirculating aquaculture system wastewater by microalgae, and microalgae can be harvested from the wastewater with low costs by zooplankton such as Daphnia. The purpose of this study was to evaluate the feasibility of using microalgae and Daphnia for bioremediation of recirculating aquaculture system wastewater in Nordic conditions. We evaluated the growth and filtration efficiency of the waterflea Daphnia magna on four green microalgae species cultured at 17 ± 0.3 °C in recirculating aquaculture system wastewater as compared to microalgae medium. There was no difference in the growth of Daphnia fed with Monoraphidium griffithii and Selenastrum sp. cultured in either media, while with Chlamydomonas reinhardtii and Haematococcus pluvialis growth of Daphnia was slower when cultured in wastewater than in algae medium. Higher filtration efficiency was achieved with the Daphnia density of 100 individuals L−1, than with higher tested densities (200 and 300 ind. L−1). After 48 h, Daphnia had removed 80% of M. griffithii, 70% of H. pluvialis, but only 20% of Selenastrum sp. from the wastewater. Phosphate was re-released to water after 72 h feeding on Selenastrum sp., but not when feeding on M. griffithii. Taken together, of the four tested green microalgae, M. griffithii was found to be the most suitable microalga species for the microalgae-Daphnia bioremediation system. The results support the potential of using microalgae and Daphnia for bioremediation and for producing biomass in Nordic recirculating aquaculture system wastewater.

Split internal-loop photobioreactor for Scenedesmus sp. microalgae: Culturing and hydrodynamics

In this study, the evaluation of the performance of the split internal loop photobioreactor for culturing a species of green microalgae, Scenedesmus sp. under different operating superficial gas velocity and during a different time of growth ( i.e. , starting for the first day until end day of the culturing process) was addressed. The evaluation of the performance of the split internal loop photobioreactor was included assessing the density, pH, temperature, viscosity, surface tension, the optical density, cell population, dry biomass, and chlorophyll of the culture medium of the microalgae culturing. Additionally, the hydrodynamics of a Split Internal-Loop Photobioreactor with microalgae culturing was comprehensively quantified. Radioactive particle tracking (RPT) and gamma-ray computed tomography (CT) techniques were applied for the first time to quantify and address the influence of microalgae culture on the hydrodynamic parameters. The hydrodynamics parameters such as local liquid velocity field, shear stresses, turbulent kinetic energy, and local gas holdup profiles were measured at different superficial gas velocities as well as under different times of algae growth. The obtained results indicate that the flow distribution may significantly affect the performance of the photobioreactor, which may have substantial effects on the cultivation process. The obtained experimental data can serve as benchmark data for the evaluation and validation of computational fluid dynamics (CFD) codes and their closures. This, in turn, allows us to develop efficient reactors and consequently improving the productivity and selectivity of these photobioreactors.

Nitrate and phosphate removal from treated wastewater by Chlorella vulgaris under various light regimes within membrane flat plate photobioreactor

AbstractThe membrane photobioreactor (MPBR) is a well‐operated system concerning microalgae cultivation and nutrients assimilation from wastewater effluent. In the present paper, a sample of pulp and paper wastewater was primarily treated by activated sludge system (ACS), and the concentration of nitrate and phosphate decreased as about 26 and 10%, respectively. Then, it was transferred into six flat plate MPBR systems with 5 L capacity and 0.45 μm membrane pore size for the secondary treatment process (nitrate and phosphate assimilation) by Chlorella vulgaris (green microalgae) species during six cultivation periods. In this section, the effects of different light intensities (100 and 300 μmol m−2 s−1) and light–dark cycles (24–0, 16–8, and 12–12) on nitrate and phosphate uptake through the treated pulp and paper wastewater effluent after 24 hr were investigated. The maximum photosynthetic productivity and nitrate‐phosphate removals after 24 hr (nitrate: 57% and phosphate: 43%) were recorded for the culture under 300 μmol m−2 s−1 and 24–0 light–dark regime within the MPBR system.

Microalgae biomass as an additional ingredient of gluten-free bread: Dough rheology, texture quality and nutritional properties

Microalgae have been widely used as a source of functional ingredients such as pigments, antioxidants, vitamins, and omega-3 polyunsaturated fatty acids. They also represent a promising alternative source of protein. The objective of this study was to evaluate the impact of the addition of two green microalgae species (Nannochloropsis gaditana L2 and Chlamydomonas sp. EL5) on the techno-functional and nutritional properties of gluten-free bread. Microalgae biomass was added in the amounts of 1.0 and 3.0 g/100 g of flour. The behavior of the dough during the mixing as well as the physicochemical properties of the prepared breads were investigated. Gluten-free bread with N. gaditana L2 and Chlamydomonas sp. EL5 presented significantly higher protein and higher levels of lipids and ash, compared with the control bread. The incorporation of 3% microalgae biomass revealed a 100% increase in iron and calcium contents. The fatty acid profile of supplemented bread changed in a species-specific manner with a particular increase in linolenic acid (18:3 ω3) and a decrease in ω3/ω6 ratio. Besides, due to its original biochemical composition, mainly the highly protein content, microalgae incorporation was found to bring an overall structuring effect on the gluten-free bread texture. However, the dough mixing properties were not affected significantly by microalgae addition. A significant change in color was recorded in doughs, breads, crusts and crumbs. This was caused by the presence of pigment in microalgae biomass, which turned into more intense green-yellow tonalities. A sensory analysis revealed that the supplemented breads scored highest for nearly all the sensory parameters with the 3% N. gaditana L2 bread as the preferred one in terms of global appreciation. This innovative approach gives new insights of the possibility of improving gluten-free products, structurally and nutritionally, using only microalgae as a natural and a sustainable food ingredient.

Cryo-XPS analysis reveals surface composition of microalgae

Green microalgae are widely used for wastewater treatment, food/feed and pigment production, as well as for aquaculture. However, very little is known about their surface composition, which can determine algae behavior in nature and influence their processing. In this work, we use cryo-XPS to characterize the surface chemical composition of three different microalgae species. We investigate the applicability of a data treatment method, developed for bacteria, deconvoluting C 1s with respect to protein, lipid and polysaccharide. We discuss how substances unique to algae contribute to the C 1s spectra and how this affects the transferability of the method to microalgae. Two species of green microalgae isolated from Northern Sweden, Chlorella vulgaris 13-1 and Coelastrella sp. 3-4, were compared to reference culture collection strain, Scenedesmus obliquus RISE (UTEX 417). Cryo-XPS data indicate that surfaces of Coelastrella sp. 3-4 and C. vulgaris 13-1 cells are dominated by protein and carbohydrates. However, the carbohydrate content was higher for C. vulgaris. The reference strain shows the highest content of proteins and has an increased amount of lipids compared to the other two. Estimation of the cell surface hydrophobicity suggests that the hydrophobicity increases in the order: C. vulgaris < Coelastrella sp. < S. obliquus.

HPLC-PDA-MS/MS as a strategy to characterize and quantify natural pigments from microalgae

Interest in pigment composition of microalgae species is growing as new natural pigments sources are being sought. However, we still have a limited number of species of microalgae exploited to obtain these compounds. Considering these facts, the detailed composition of carotenoids and chlorophylls of two species of green microalgae (Chlorella sorokiniana and Scenedesmus bijuga) were determined for the first time by high-performance liquid chromatography coupled to diode array and mass spectrometry detectors (HPLC-PDA-MS/MS). A total of 17 different carotenoids were separated in all the extracts. Most of the carotenoids present in the two microalgae species are xanthophylls. C. sorokiniana presented 11 carotenoids (1408.46 μg g−1), and S. bijuga showed 16 carotenoids (1195.75 μg g−1). The main carotenoids detected in the two microalgae were all-trans-lutein and all-trans-β-carotene. All-trans-lutein was substantially higher in C. sorokiniana (59.01%), whereas all-trans-β-carotene was detected in higher quantitative values in S. bijuga (13.88%). Seven chlorophyll compounds were identified in both strains with different proportions in each species. Concentrations of chlorophyll representing 7.6% and 10.2% of the composition of the compounds present in the biomass of C. sorokiniana and S. bijuga, respectively. Relevant chlorophyll compounds are reported for the first time in these strains. The data obtained provide significant insights for microalgae pigment composition databases.

Effects of metal quantity and quality to the removal of zinc and copper by two common green microalgae (Chlorophyceae) species

SUMMARYAppearance of metals as pollutants in the environment is an increasing global problem. Microalgae as subjects of biological remediation methods may provide a cost‐effective and environmentally friendly alternative to the removal of metals during wastewater treatment. Despite the high number of data in the topic, there is still little information on how the type and the concentration of the metal affect the process of removal. In this study, correlations among the algal species, quality and quantity of metals and characteristics of metal removal mechanism were investigated at lower metal concentrations (0.2–5.0 mg L−1) during zinc and copper removal of the green algae Desmodesmus communis and Monoraphidium pusillum. Analyses of the results proved that there is a statistically significant interaction (P &lt; 0.05) between algal species and quality and concentration of the metals, that is, they have a significant effect on the mode and extent of removal. Both metals were mainly extracellularly bound, but at concentrations of 0.2–1.4 mg L−1, intracellular proportion could exceed the extracellular adsorption. Although there were differences between the two algae, generally copper appeared in a higher intracellular proportion than zinc in the whole studied concentration range. Overall, the quality and initial concentration of the metal is decisive for the way of removal, the knowledge of which is useful for planning post treatment retention times or post treatment processes of the used biomass during wastewater treatment.

A new reactor design for harvesting algae through electrocoagulation-flotation in a continuous mode

The low energy requirements to grow microalgae combined with the very fast reproduction gives microalgae unique abilities to utilize them for industrial and environmental applications. However, harvesting these algae still remains energy consuming and, as a consequence, expensive. In this work a new electrocoagulation-flotation set-up with a tubular coaxial reactor, developed by Noah Water Solutions, is investigated for the autonomous harvesting of the green microalgae species Chlorella vulgaris. No pH adjustment or other pretreatments were applied in order to make the method applicable in the field. With this type of electrocoagulation-flotation reactor the algae were on average a factor 100 more concentrated, i.e. starting from the influent microalgae suspension of 0.2 g·L−1 up to 18.5 g·L−1 with iron electrodes and 35.2 g·L−1 with aluminum electrodes. Moreover, with this reactor type only low currents (0.8 A for Fe and 0.3 A for Al) had to be applied, resulting in low energy consumptions (2.0 kWh·kg−1 for Fe and 1.1 kWh·kg−1 for Al). Remaining metal concentration in the harvested algae was low, i.e. 0.6% for the Fe electrodes and 0.3% for the Al electrodes. Combining these results with the autonomous and continuous removal of the concentrated algae makes this tubular electrocoagulation-flotation reactor excellent for harvesting microalgae on industrial scale.

Biotechnological Assessment of Culture Conditions on the Stress-Induced Carotenoid Production of Dunaliella salina and Growth Kinetics of Chlorophyceae Microalgae Strains

Microalgae are potential sources of a wide range of bioproducts. It is essential to choose the proper microalgae strain and culture condition to achieve an efficient production. The production yield of carotenoids by Dunaliella salina under the stress-induced culture conditions of nitrogen deprivation and excessive light intensity was evaluated. Also, a survey at laboratorial scale of the growth kinetics under different culture conditions of photoperiod, aeration, and agitation was performed for the seven species of green microalgae Ankistrodesmus fusiformis, Chlamydocapsa bacillus, Desmodesmus brasiliensis, Kirchneriella lunaris, Pseudokirchneriella subcapitata, and Scenedesmus obliquus. As a result, aeration of atmospheric air is enough to improve the growth kinetics of the seven species studied. Production of carotenoids was enhanced under stress by excessive light intensity. Although D. salina does not grow effectively under nitrogen deprivation, this stress condition may be used to quickly stimulate carotenoid production once the culture reaches a high cellular population.

Salt Tolerance and Desalination Abilities of Nine Common Green Microalgae Isolates

In recent years, decline of freshwater resources has been recognized as one of the main environmental problems on global level. In addition to the increasing extent of primary salinization due to climate change, secondary salinization caused by human interventions is also a significantly increasing problem, therefore, the development of various chemical-free, biological desalination and removal procedures will become increasingly important. In the present study, the salinity tolerance, salinity, and nutrient reducing ability of nine common freshwater microalgae species from the genera Chlorella, Chlorococcum, Desmodesmus, Scenedesmus, and Monoraphidium were investigated. Our results proved that the studied green microalgae species are halotolerant ones, which are able to proliferate in environments with high salt concentrations. Furthermore, most of the species were able to reduce conductivity and remove significant amounts of chloride (up to 39%) and nutrients (more than 90% nitrate). The results proved that nitrate removal of the studied species was not influenced by salt concentration, only indirectly via growth inhibition. However, the results also highlighted that N:P ratio of the medium has primarily importance in satisfactory phosphorous removal. It can be concluded that assemblages of the studied microalgae species could be able to adapt to changing conditions even of salt-rich wastewaters and improve water quality during bioremediation processes.

Toxicity of methylparaben to green microalgae species and derivation of a predicted no effect concentration (PNEC) in freshwater ecosystems.

Methylparaben (MeP) is one of the most used preservatives in the industry; however, the toxic effects on aquatic ecosystems are still poorly understood. Therefore, this study was conducted (1) to identify and compare the toxic effects of MeP on physiological parameters of different green microalgae species, using suitable mathematical models; and (2) to estimate a PNEC value for MeP in freshwater ecosystems, adopting either the deterministic or the probabilistic approaches. Toxicity tests were carried out with three green microalgae (Pseudopediastrum boryanum, Desmodesmus communis, Raphidocelis subcapitata), in which different endpoints such as growth rate, chlorophyll-a, and cell viability were measured and compared through the effective concentration which caused a response in x% of test organisms (ECx). ECx were obtained by adjusting different non-linear regression models for each microalgae dataset. Chlorophyll-a endpoint resulted in the lowest EC50 values, respectively 125, 81.2, 18.3 mg L-1 for D. communis, P. boryanum and R. subcapitata, showing R. subicapitata as the most sensitive, and D. communis as the most tolerant species to MeP (P < 0.05). PNEC was estimated from the present study and previous reports resulting in 5.7 and 65 μg L-1, respectively for the deterministic (PNECd) and the probabilistic (PNECp) approach. The development of chronic assays using test organisms from different ecological groups is encouraged to provide robust PNECp. In this meantime, we recommend the use of the estimated PNECd to support MeP risk assessments and policy formulation.

Flocculation-flotation harvesting mechanism of Dunaliella salina: From nanoscale interpretation to industrial optimization

Dunaliella salina is a green microalgae species industrially exploited for its capacity to produce important amounts of carotenoid pigments. However in low nitrogen conditions in which they produce these pigments, their concentration is low, which results in harvesting difficulties and high costs. In this work, we propose a new solution to efficiently harvest D. salina at the pre-industrial scale, using flocculation/flotation harvesting induced by NaOH addition in the medium. We first show, using numerical simulations and nanoscale atomic force spectroscopy experiments, that sweeping mechanism in formed magnesium hydroxide precipitate is only responsible for D. salina flocculation in hypersaline culture medium upon NaOH addition. Based on this understanding of the flocculation mechanism, we then evaluate the influence of several parameters related to NaOH mixing and magnesium hydroxide precipitation and show that NaOH concentration, mixing, and salinity of the medium can be optimized to achieve high flocculation/flotation harvesting efficiencies in laboratory-scale experiments. We finally successfully scale-up the data obtained at lab-scale to a continuous pre-industrial flotation pilot, and achieve up to 80% of cell recovery. This interdisciplinary study thus provides original results, from the nano to the pre-industrial scale, which allow the successful development of an efficient large-scale D. salina harvesting process. We thus anticipate our results to be the starting point for further optimization and industrial use of this flocculation/flotation harvesting technique.

A selective microalgae strain for biodiesel production in relation to higher lipid profile

Biodiesel have become the important asset by the country especially to build up their economy. Currently, microalgae have been choosing as the source for production of biodiesel based on their advantages. Microalgae are a photosynthetic organism that use light as an energy source and able to produce their own food. These microalgae also produce a lipid that can be used to produce a biodiesel. Using microalgae that contain high lipid profile are very important to make sure the biodiesel can be produce in large quantity in short time and more cost saving. Although many microalgae species have been identified and isolated for lipid production, there is currently no consensus as to which species provide the highest productivity. Different species are expected to function best at different aquatic, geographical and climatic conditions. So, this experiment is conducted to identify which strain of microalgae contains high lipid profile that can be used to convert into the biodiesel. There are three main objectives that involve in this experiment which is to isolate and identify different strain of microalgae from Kuantan Coast, East Coast Peninsular Malaysia, to convert the lipid from microalgae into biodiesel through transesterification, and to estimate higher lipid profile of microalgae species for biodiesel production. Two species of green microalgae were isolated, which is Nannochloropsis sp and Coelastrum sp. Based on lipid extraction and lipid analysis, it shows that the Nannochloropsis sp. have more concentrated of lipid and higher lipid profile compared to Coelastrum sp. Hence, Nannochloropsis sp. are most suitable species that can be used as a biodiesel feedstock due to higher lipid profile of MUFA.

Sugar-stimulated CO2 sequestration by the green microalga Chlorella vulgaris

To convert waste CO2 from flue gases of power plants into value-added products, bio-mitigation technologies show promise. In this study, we cultivated a fast-growing species of green microalgae, Chlorella vulgaris, in different sizes of photobioreactors (PBRs) and developed a strategy using small doses of sugars for enhancing CO2 sequestration under light-emitting diode illumination. Glucose supplementation at low levels resulted in an increase of photoautotrophic growth-driven biomass generation as well as CO2 capture by 10% and its enhancement corresponded to an increase of supplied photon flux. The utilization of urea instead of nitrate as the sole nitrogen source increased photoautotrophic growth by 14%, but change of nitrogen source didn't compromise glucose-induced enhancement of photoautotrophic growth. The optimized biomass productivity achieved was 30.4% higher than the initial productivity of purely photoautotrophic culture. The major pigments in the obtained algal biomass were found comparable to its photoautotrophic counterpart and a high neutral lipids productivity of 516.6 mg/(L·day) was achieved after optimization. A techno-economic model was also developed, indicating that LED-based PBRs represent a feasible strategy for converting CO2 into value-added algal biomass.

Survey of the occurrence of desiccation-induced quenching of basal fluorescence in 28 species of green microalgae.

Desiccation-induced chlorophyll fluorescence quenching seems to be an indispensable part of desiccation resistance in the surveyed 28 green microalgal species. Lichens are desiccation tolerant meta-organisms. In the desiccated state photosynthesis is inhibited rendering the photobionts potentially sensitive to photoinhibition. As a photoprotective mechanism, strong non-radiative dissipation of absorbed light leading to quenching of chlorophyll fluorescence has been proposed. Desiccation-induced quenching affects not only variable fluorescence, but also the so-called basal fluorescence, F0. This phenomenon is well-known for intact lichens and some free living aero-terrestrial algae, but it was often absent in isolated lichen algae. Therefore, a thorough screening for the appearance of desiccation-induced quenching was undertaken with 13 different aero-terrestrial microalgal species and lichen photobionts. They were compared with 15 aquatic green microalgal species, among them also three marine species. We asked the following questions: Do isolated lichen algae show desiccation-induced quenching? Are aero-terrestrial algae different in this respect to aquatic algae and is the potential for desiccation-induced quenching coupled to desiccation tolerance? How variable is desiccation-induced quenching among species? Most of the aero-terrestrial algae, including all lichen photobionts, showed desiccation-induced quenching, although highly variable in extent, whereas most of the aquatic algae did not. All algae displaying quenching were also desiccation tolerant, whereas all algae unable to perform desiccation-induced quenching were desiccation intolerant. Desiccation-induced fluorescence quenching seems to be an indispensable part of desiccation resistance in the investigated species.

Comparative uptake study of arsenic, boron, copper, manganese and zinc from water by different green microalgae

This work represents a comparative uptake study of the toxic elements arsenic, boron, copper, manganese and zinc in monometallic and multimetallic solutions by four green microalgae species (Chlamydomonas reinhardtii, Chlorella vulgaris, Scenedesmus almeriensis and an indigenous Chlorophyceae spp.), evaluating the effect of pH and contact time. Maximum removal efficiencies for each toxic element were 99.4% for Mn (C. vulgaris, pH 7.0, 3 h), 91.9% for Zn (Chlorophyceae spp., pH 5.5, 3 h), 88% for Cu (Chlorophyceae spp., pH 7.0, 10 min), 40.7% for As (S. almeriensis, pH 9.5, 3 h) and 38.6% for B (S. almeriensis, pH 5.5, 10 min).B removal efficiencies decreased remarkably in multimetallic solutions (down to 0.2% in C. reinhardtii), except for Chlorophyceae spp., the only species isolated from a polluted environment. FTIR spectra shown the highest interactions for As (1150–1300 cm−1) and Cu (3300, 1741, 1535, 1350–1400 cm−1). Results confirm microalgae biomass as a potential biosorbent for toxic elements.

Bioflocculation Activity in Harvesting System: A Biotechnology Approach for Microalgae Biomass

A study on Ankistrodesmus sp.—a freshwater green microalgae species—as a bioflocculant based on its physicochemical properties and flocculation rate has been carried out. The molecular identification via 16S rDNA showed 99% resemblance of this green microalga to the Ankistrodesmus fumigatus strain. The optimum batch culture condition for the bioflocculant production was initiated by 10% inoculum (v/v). The low-concentrated bioflocculant of 10% (v/v) is considered as thermostable with a high flocculation rate to harvest the biomass of Chlorella sp. at a pH range of 5 to 9. The source of molasses, the mixture of yeast extract were used as the optimum sources of carbon and Ammonium sulfate were used as the optimum sources of nitrogen in the growth medium. Ankistrodesmus sp. bioflocculant has a high flocculation efficiency over a wide range of pH (5–9) with a low dose requirement of 10% v/v at 25°C. Hence, it is immensely competitive to promote the economic viability of the production process. Accordingly, Ankistrodesmus sp. bioflocculant has a high potential to be applied on an industrial scale in tropical regions as it does not require additional production cost.

Use of fatty acids in the chemotaxonomy of the family Selenastraceae (Sphaeropleales, Chlorophyceae)

The family Selenastraceae includes many species of freshwater green microalgae with morphological characteristics that are so subtly different that it is difficult to discriminate species within it. Therefore, the use of the diacritical characteristics of traditional morphological taxonomy may be ineffective at differentiating among many species of the family. Chemotaxonomy based on fatty acid methyl ester (FAME) can help resolve uncertainties not completely addressed by other approaches, such as molecular studies of some species within the Selenastraceae. Here, we first tested three techniques for the analysis of microalgal FAME to choose the one that would provide the best profiles for chemotaxonomy: 1) direct transesterification (DT) of the biomass followed by gas chromatography coupled to mass spectrometry analysis (GC-MS); 2) extraction using chloroform and methanol, followed by transesterification (T) and then analysis by gas chromatography/flame ionization detector (GC-FID); and 3) extraction with chloroform and methanol and then separation into lipid classes using thin-layer chromatography (TLC) using the Iatroscan-Chromarod system. The tests were conducted on 12 strains (11 species) of Selenastraceae and one outgroup strain. The fatty acid profiles produced by the DT-GC-MS technique yielded the best results for the chemotaxonomy of the Selenastraceae species using 12 FAME. The proportion of the variance in the fatty acid profiles obtained with DT-GC-MS analysis explained by species was 85%, whereas the differences explained by strains was 92%. Therefore, DT-GC-MS was used to analyze other microalgae strains, totaling 15 species of 8 genera of green coccoid microalgae, including the recently described Curvastrum. The results with all strains showed that fatty acid profiles obtained by DT-GC-MS were significantly different (p < 0.001) among strains and among species. The variance in fatty acids profiles explained by separation into strains was 97%, whereas the separation into species explained 93% of the variance. Statistical analyses showed that, for our dataset, the C18 fatty acids 18:3ω3 and 18:4ω6 were indicative of the Selenastraceae. Therefore, fatty acid profiles are a useful auxiliary chemotaxonomic tool for species identification in Selenastraceae.

Ecophysiological strategies for growth under varying light and organic carbon supply in two species of green microalgae differing in their motility

Mixing events in stratified lakes result in microalgae being exposed to varying conditions in light and organic carbon concentrations. Stratified lakes consist of an upper illuminated strata and a lower, darker strata where organic carbon accumulates. Therefore, in this contribution we explore the importance of dissolved organic carbon for growth under various light intensities by measuring some ecophysiological adaptations in two green microalgae. We compared the non-motile Chlorella vulgaris with the flagellated Chlamydomonas acidophila under auto-, mixo-, and heterotrophic growth conditions. In both algae the maximum photosynthetic and growth rates were highest under mixotrophy, and both algae appeared inhibited in their phosphorus acquisition under heterotrophy. Heterotrophic conditions provoked the largest differences as C. vulgaris produced chlorophyll a in darkness and grew as well as in autotrophic conditions, whereas Chl. acidophila bleached and could not grow heterotrophically. Although the fatty acid composition of both phytoplankton species differed, both species reacted in a similar way to changes in their growth conditions, mainly by a decrease of C18:3n-3 and an increase of C18:1n-9 from auto- to heterotrophic conditions. The two contrasting responses within the group of green microalgae suggest that dissolved organic carbon has a high deterministic potential to explain the survival and behaviour of green algae in the deeper strata of lakes.