Metabolic responses of eukaryotic microalgae to environmental stress limit the ability of FT-IR spectroscopy for species identification

Conversion of N-doped biochar from carotenoid-extracted Tetraselmis suecica and its application to produce supercapacitors

Microalgae are one of the promising feedstocks for biorefinery, contributing significantly to net-zero emissions through carbon capture and utilization. However, the disposal of microalgal byproducts from the manufacturing process causes additional environmental pollution, thus, a new application strategy is required. In this study, the Tetraselmis suecica byproduct from the carotenoid extraction process was carbonized and converted into biochar. The converted biochar was proved to be nitrogen-doped biochar (NDB), up to 4.69%, with a specific surface area of 206.59 m2/g and was used as an electrode for a supercapacitor. The NDB electrode (NDB-E) in half-cell showed a maximum specific capacitance of 191 F/g. In a full-cell test, the NDB-E exhibited a high energy density of 7.396 Wh/kg and a high-power density of 18,100 W/kg, and maintained specific capacity of 95.5% after charge and discharge of 10,000 cycles. In conclusion, our study demonstrated that the carotenoid-extracted microalgal byproducts are a useful resource for the supercapacitor production. This approach is the first to convert T. suecica into active materials for supercapacitors.

Effects of water washing and KOH activation for upgrading microalgal torrefied biochar

Torrefaction is an effective pathway for microalgal solid biofuel upgrading, and alkali metal activation is also an efficient method to enhance fuel properties. This study explores the comparison of torrefaction alone and KOH activation combined with torrefaction to determine a better operation for biochar production from the microalga Nannochloropsis Oceanica. The results indicate that the HHV ranges of KOH-activated biochar and unactivated biochar are 25.611-32.792 MJ·kg-1 and 25.024-26.389 MJ·kg-1, respectively. Furthermore, KOH-activated biochar is better than unactivated biochar, with less residue, broader pyrolysis and combustion temperature ranges, higher elemental carbon, and less combined carbon. Moreover, KOH-activated biochar is close to the unactivated one from the viewpoint of expense calculation and life cycle assessment and thus possesses a better comprehensive performance. Overall, KOH activation is an efficient method for upgrading microalgal solid biofuel. The results are conducive to exploring further modification of microalgal solid biofuel production with better properties, thus leading to a greener and more efficient approach for upgrading fuel performance.

Influence of hydrothermal carbonization conditions on the porosity, functionality, and sorption properties of microalgae hydrochars

Green microalgae is a possible feedstock for the production of biofuels, chemicals, food/feed, and medical products. Large-scale microalgae production requires large quantities of water and nutrients, directing the attention to wastewater as a cultivation medium. Wastewater-cultivated microalgae could via wet thermochemical conversion be valorised into products for e.g., water treatment. In this study, hydrothermal carbonization was used to process microalgae polycultures grown in municipal wastewater. The objective was to perform a systematic examination of how carbonization temperature, residence time, and initial pH affected solid yield, composition, and properties. Carbonization temperature, time and initial pH all had statistically significant effects on hydrochar properties, with temperature having the most pronounced effect; the surface area increased from 8.5 to 43.6 m2 g-1 as temperature was increased from 180 to 260 °C. However, hydrochars produced at low temperature and initially neutral pH generally had the highest capacity for methylene blue adsorption. DRIFTS analysis of the hydrochar revealed that the pH conditions changed the functional group composition, implying that adsorption was electrostatic interactions driven. This study concludes that un-activated hydrochars from wastewater grown microalgae produced at relatively low hydrothermal carbonization temperatures adsorb methylene blue, despite having low surface area.

Symbiotic relationship between filamentous algae (Halomicronema sp.) and extracellular polymeric substance-producing algae (Chlamydomonas sp.) through biomimetic simulation of natural algal mats

To lower the cost of biomass harvesting, the growth of natural biofilm is considered to be an optimal alternative to microalgae aggregation. This study investigated algal mats that naturally agglomerate into a lump and float on water surfaces. Halomicronema sp., a filamentous cyanobacterium with high cell aggregation and adhesion to substrates, and Chlamydomonas sp., which grows rapidly and produces high extracellular polymeric substances (EPS) in certain environments, are the main microalgae that make up selected mats through next-generation sequencing analysis. These two species play a major role in the formation of solid mats, and showed a symbiotic relationship as the medium and nutritional source, particularly owing to the large amount of EPS formed by the reaction between EPS and calcium ions through zeta potential and Fourier-transform infrared spectroscopy analysis. This led to the formation of an ecological biomimetic algal mat (BAM) that mimics the natural algal mat system, and this is a way to reduce costs in the biomass production process as there is no separate treatment process for harvesting.

Production and use of Scenedesmus acuminatus biomass in synthetic municipal wastewater for integrated biorefineries

Bioethanol production from algal biomass is a promising alternative for sustainable biofuel production. Algae possess a high photosynthetic capacity and an adaptive ability to thrive under harsh environmental conditions. The potential properties of Scenedesmus acuminatus CCALA 436 were assessed in this research for its bioethanol efficiency, and the effects of growing the algae in wastewater and at different concentrations of mepiquat chloride were studied. Also, pre-treatment efficiencies of different concentrations of calcium oxide were carried out on microalgae biomass. Superoxide dismutase, catalase activity, glutathione, and malondialdehyde contents of microalgae were examined, and the changes in chlorophyll, photoprotective carotenoid contents, and protein concentrations were determined. The results revealed that the maximum sugar and ethanol contents of Scenedesmus acuminatus CCALA 436 were 44.7 ± 1.5% and 20.32 g/L, respectively, for 50% wastewater and mepiquat chloride (2.5 mg/L) after pre-treatment with calcium oxide (0.08%). Additionally, the levels of oxidative enzymes varied depending on the wastewater concentrations. These findings indicate Scenedesmus acuminatus CCALA 436 grown in wastewater and mepiquat chloride can be used for the treatment of wastewater and the production of ethanol and high-value products such as carotenoid.

Alkyl carbamate ionic liquids for permeabilization of microalgae biomass to enhance lipid recovery for biodiesel production

Microalgae are potential biomass source for biodiesel production. However, their strong cell walls make efficient lipid extraction problematic. Disrupting the cell wall is a key point in enhancing lipid yield from microalgae biomass. A new type of ionic liquid (IL) has been suggested in this work as a potentially viable solvent to permeabilize the strong microalgae cell structure for the efficient extraction of lipids. Morphological changes in microalgae cells were studied before and after ionic liquid permeabilization to understand the mechanism of ionic liquid treatment. Among the three selected CO₂-based alkyl carbamate ionic liquids, DIMCARP performed with the best extraction efficiency. The effects of extraction variables (temperature, time, ratio ionic liquid/Methanol, and solvent to biomass) on lipid extraction were examined via single-factor experiments coupled with response surface methodology (RSM) using a Box-Behnken design (BBD). The highest lipid yield (16.40%) was obtained after 45 min of extraction at 45 °C using a 9:1 ionic liquid to methanol and 7 mL of solvent to biomass ratio. Transesterification of lipids to make fatty acid methyl esters found that the most common fatty acids were C16:0, C18:2, and C18:3 (19.50%). The quality of the biodiesel made meets European and US standards.

Oxidative torrefaction of microalga Nannochloropsis Oceanica activated by potassium carbonate for solid biofuel production

Oxidative torrefaction is a promising way for biomass upgrading and solid biofuel production. Alkali metals are considered to be efficient activators for enhancing biofuel upgrading during the thermal reaction process. Herein, the microalga Nannochloropsis Oceanica is selected as the feedstock for assessing potassium carbonate activated effect on solid biofuel production through oxidative torrefaction. The potential of potassium carbonate on microalgal biofuel properties upgrading is deeply explored. SEM observation and BET analysis show that torrefied microalgae can be transformed from a spherical structure with wrinkles to smaller particles with larger surface areas and higher total pore volumes, implying that potassium carbonate is a promising porogen. Moreover, potassium carbonate can significantly change the DTG curve at the temperatures of 250 °C and 300 °C from one peak to two peaks, inferring that the activated effect of potassium carbonate occurs on the torrefied microalgae. ¹³C NMR analysis reveals that the microalgal components significantly change as the torrefaction severity increases, with the decomposition of carbohydrate and protein components. When the potassium carbonate ratio increases from 0:1 to 1:1, the graphitization degree increase from 3.065 to 1.262, along with the increase in the HHV of solid biofuel from 25.024 MJ kg^-1 to 31.890 MJ kg^-1. In total, this study has comprehensively revealed the activated effect of potassium carbonate on improving the properties of microalgal solid biofuel.

Response to nutrient variation on lipid productivity in green microalgae captured using second derivative FTIR and Raman spectroscopy

Two green microalgae species Monoraphidium contortum (M. contortum) and Chlamydomonas sp. that were identified to accumulate lipids were subjected to four different nutrient treatments (NP1-NP4), ranging in nitrate (0.05-5 mM N) and phosphate (2.8-264 μM P) concentrations, at a fixed N:P ratio of ∼18. The effect of nutrient variation on lipid productivity in the species was investigated using second derivative (SD) FTIR and Raman spectroscopy of algal biomass. SD spectral analysis revealed high production of lipid in the form of hydrocarbons (CH) (3000-2800 cm^-1), triacylglycerides (TAGs)(∼1740 cm^-1), saturated (SFA)(∼1440 cm^-1), and unsaturated fatty acids (UFA)(∼3010 cm^-1) for the nutrient deplete condition (NP1) in both species. Changes in signals attributed to lipids in proportion to other biochemical components were consistent with physiological changes expected from nutrient depletion. Relative signal intensities for lipids showed a significant increase in NP1, in particular, CH, TAGs in relation to protein signals (in SD-FTIR), and SFA, UFA in relation to carotenoid signals (in SD-Raman). PCA performed on the negative spectral values of the SD-FTIR and SD-Raman data for the four NP treatments enabled discrimination not only between the species but also between the NP treatments and the timing of harvest. M. contortum was found to contain a relatively higher proportion of CH, TAGs, SFA, and UFA compared to Chlamydomonas sp. Peak areas from the negative SD spectra, informed by PCA analysis, enabled capturing quantifiable changes in a manner that is consistent with known microalgal physiology. SD-FTIR and SD-Raman spectroscopy have been shown to possess superior potential to capture relevant microalgal physiological changes.

Uptake of a plasticizer (di-n-butyl phthalate) impacts the biochemical and physiological responses of barley

BACKGROUND

DBP is one of the most commonly used plasticizers for imparting desirable properties to polymers. The introduction of phthalates is reported to have occurred in the late 1920s, and there has been a significant rise in their release into the environment in past decades due to a lack of covalent bonding with the parent matrix. Because of their numerous applications in day-to-day life, phthalates have become ubiquitous and also classified as endocrine disruptors. Hence, several studies have been conducted to investigate the phthalate-mediated toxicities in animals; however, plants have not been explored to the same amount.

METHODS

Therefore, in the present study, the accumulation and translocation along with morpho-physiological perturbations in barley plants after 15, 30, 60, and 120 days of exposure to di-n-butyl phthalate (DBP) are investigated using standard protocols.

RESULTS

The maximal accumulation and translocation of DBP in the roots and shoots of barley plants was observed after 60 days of exposure. The exposure of DBP from 15 to 120 days was recorded to decline all the morphological indices (i.e., dry weight, net primary productivity, seed number per spike, and seed weight) of barley plants. The pigments content declined under DBP treatment for all exposure durations except 120 days exposure. Carbohydrate content increased after 15-30 days of exposure afterward it was observed to be decreased under 60 and 120 days of exposure. The protein content was declined in DBP stressed plants for 15-120 days. Proline content was increased in all exposure durations and maximal percent increase was recorded in 120 days of exposure. MDA content showed an increase at earlier exposure durations then followed by a decline in long-term exposure. Hydrogen peroxide content increased at all exposure durations. There were significant alterations observed in the activities of all antioxidative enzymes in comparison to the control. Furthermore, DBP stressed plants after 60 days were analyzed for the macromolecular variations using Fourier transform infrared spectroscopy (FTIR).

CONCLUSION

Thus, the outcomes of the current work provide an appraisal of phthalates' uptake and translocation mediated phytotoxic responses in barley plants. These observations can help in developing genetically modified edible plants that are resistant to phthalates uptake, thereby ensuring food security.

Hydrothermal Carbonization of Residual Algal Biomass for Production of Hydrochar as a Biobased Metal Adsorbent

Conversion of residual algal biomass to value-added products is essential for enhancing the economics of algae cultivation. Algal hydrochar produced via hydrothermal carbonization of lipid-extracted Picochlorum oculatum is a material rich in oxygen functional groups and carbon (up to 67.3%) and hence a promising candidate for remediation of wastewaters. The hydrothermal carbonization conditions were optimized and the adsorption capacity of the hydrochar was tested for metal removal. By the end of the remediation process, cumulative removal of Al3+, Cu2+, Fe2+, Mg2+, Mn2+, and Pb2+ reached 89, 98, 75, 88, 75, and 100%, respectively. The adsorption of all metals was found to follow pseudo second-order kinetics and the Langmuir isotherm. Overall, when hydrothermal carbonization is applied to lipid-extracted algae, it generates a promising biobased adsorbent with value-added potential in metal remediation.

Effect of phytochemical vanillic acid on the growth and lipid accumulation of freshwater microalga Euglena gracilis

A feasible approach against the low yield of microalgae biomass involves the use of a stimulator for microalgal growth. In this research, vanillic acid present in the hydrolysate of agricultural waste, was applied to the cultivation of unicellular microalga Euglena gracilis. At the optimal dosage of 800 mg L^-1 vanillic acid, biomass yield at treatment increased 2.08-fold. Correspondingly, the content of chlorophyll a and carotenoids was 3.48 and 2.69 fold than of the control ground, respectively. Increased in cell aspect ratio demonstrated that the alga was more active after vanillic acid treatment. Furthermore, relative lipid and carbohydrate content were analyzed using Fourier transform infrared spectroscopy, the result showed that vanillic acid increased the lipid content in algal cells without sacrificing biomass, which would be a promising way for future biofuel production.

Metabolite Quantification by Fourier Transform Infrared Spectroscopy in Diatoms: Proof of Concept on Phaeodactylum tricornutum

Diatoms are feedstock for the production of sustainable biocommodities, including biofuel. The biochemical characterization of newly isolated or genetically modified strains is seminal to identify the strains that display interesting features for both research and industrial applications. Biochemical quantification of organic macromolecules cellular quotas are time-consuming methodologies which often require large amount of biological sample. Vibrational spectroscopy is an essential tool applied in several fields of research. A Fourier transform infrared (FTIR) microscopy-based imaging protocol was developed for the simultaneous cellular quota quantification of lipids, carbohydrates, and proteins of the diatom Phaeodactylum tricornutum. The low amount of sample required for the quantification allows the high throughput quantification on small volume cultures. A proof of concept was performed (1) on nitrogen-starved experimental cultures and (2) on three different P. tricornutum wild-type strains. The results are supported by the observation in situ of lipid droplets by confocal and brightfield microscopy. The results show that major differences exist in the regulation of lipid metabolism between ecotypes of P. tricornutum.

Copper Adsorption to Microplastics and Natural Particles in Seawater: A Comparison of Kinetics, Isotherms, and Bioavailability

The growing use of plastics has led to microplastics (MPs) being ubiquitously distributed in marine environments. Although previous studies have emphasized MPs as important metal-transport vectors, few have considered the differences between these anthropogenic particles and their coexisting natural counterparts in sequestering metals in seawater. Here, we compared Cu adsorption to pristine and naturally aged MPs (polystyrene and polyethylene) with that to algae particles and sediments and assessed the bioavailability of the adsorbed Cu by a gut juice extraction assay. Adsorption kinetics and isotherms consistently showed that natural particles bound far more Cu to their surfaces than MPs. The rougher surfaces, greater specific surface areas, and lower ζ-potentials of natural particles contributed to their stronger Cu adsorption capacity than pristine or aged MPs. Natural particles also contained more diverse functional groups for binding Cu, with oxygen-containing groups playing a dominant role. Adsorbed Cu on natural particles was less extractable by sipunculan gut juice than that on MPs, indicating their higher Cu affinity. Overall, our study suggests that natural particles outcompete MPs in carrying metals in the water column and transferring them to marine organisms in today's environmental context. This work provides new insights for assessing the risks of MPs in marine environments.

Synchrotron Radiation-Fourier Transformed Infrared microspectroscopy (μSR-FTIR) reveals multiple metabolism alterations in microalgae induced by cadmium and mercury

Toxic metals such as cadmium (Cd) and mercury (Hg) represent a threat to photosynthetic organisms of polluted aquatic ecosystems, and knowledge about mechanisms of toxicity is essential for appropriate assessment of environmental risks. We used Synchrotron Radiation-Fourier Transformed Infrared microspectroscopy (μSR-FTIR) to characterise major changes of biomolecules caused by Cd and Hg in the model green microalga Chlamydomonas reinhardtii. μSR-FTIR showed several metabolic alterations in different biochemical groups such as carbohydrates, proteins, and lipids in a time-dose dependent manner, with the strongest changes occurring at concentrations above 10 μM Cd and 15 μM Hg after short-term (24 h) treatments. This occurred in a context where metals triggered intracellular oxidative stress and chloroplast damage, along with autophagy induction by overexpressing AUTOPHAGY-RELATED PROTEIN 8 (ATG8). Thin layer chromatography analysis confirmed that toxic metals promoted remarkable changes in lipid profile, with higher degree of esterified fatty acid unsaturation as detected by gas chromatography coupled with mass spectrometry. Under Cd stress, there was specifically higher unsaturation of free fatty acids, while Hg led to stronger unsaturation in monogalactosyldiacylglycerol. μSR-FTIR spectroscopy proved as a valuable tool to identify biochemical alterations in microalgae, information that could be exploited to optimise approaches for metal decontamination.

Oxidative torrefaction performance of microalga Nannochloropsis Oceanica towards an upgraded microalgal solid biofuel

Microalgae are a promising feedstock for carbon-neutral biofuel production due to their superior cellular composition. Alternatively, oxidative torrefaction has been recognized as a potential thermochemical technique for microalgal solid biofuel upgrading. Herein, by using microalga N. oceanica as a feedstock, several characterizations are adopted for evaluating the potential of oxidative torrefaction towards microalgal solid biofuel production. The oxidatively torrefied microalgae can be upgraded as lignite. After in-depth analysis, significant change in the surface microstructure of oxidatively torrefied microalgae is largely changed (via wrinkle and fragmentation) The hydrophobicity, thermal decomposition, thermal stability, and aromatization of oxidatively torrefied microalgae can be largely enhanced as the oxidative torrefaction severity increase. With the increasing torrefaction temperature, the hydrophobicity of oxidative torrefied microalgae gradually improved. The decomposition of C-2/3/5, and -OCH₃, the CO bonds of CH₃CO-, and the aromatization occurs via oxidative torrefaction according to the NMR analysis. For XPS analysis, torrefaction operation significantly decreases the carbide carbon and enhances the graphitization. As a result, the thermal stability of oxidatively torrefied microalgae is improved. Conclusively, the information obtained in this study can provide insights into the evaluation of oxidative torrefaction performance and fuel properties of microalgal solid biofuel, which may help accelerate the advancement of oxidative torrefaction industrialization.

Toxicity evaluation and preparation of CoWO4 nanoparticles towards microalga Dunaliella salina

The increasing use of nanoparticles and their many applications increases the likelihood of their presence in the environment. This possibility of presence necessitates the study of the effect of these substances on aquatic species. In this research, CoWO4 nanoparticles were synthesized by the ultrasonic method. Various conditions in the synthesis process were investigated to obtain the appropriate size of the nanoparticles. After selecting the optimum particles, these nanoparticles were used to investigate their effect on the growth of Dunaliella salina. For this purpose, the algal cells were subjected to three different concentrations of nanoparticles (15, 30, and 60 mg/L). The study results on algae growth parameters showed that these parameters depend on the value of nanoparticles. At 15 and 30 mg/L concentrations of the nanoparticles, numbers of cells, specific growth, biomass, and pigments showed a significant boost compared to the mentioned parameters of the control treatment. Measurement of malondialdehyde (MDA) showed that this parameter was directly related to the increase in the concentration of nanoparticles. At 60 mg/L of the nanoparticles, the MDA level was higher than the control and other treatments. This increase reflects the destructive effect of the nanoparticles on algal cells. Finally, the results showed that algae could be useful for studying the environmental effects of nanoparticles and their safety.

Hydrothermal carbonization of microalgae biomass produced in agro-industrial effluent: Products, characterization and applications

Hydrothermal carbonization is a thermochemical treatment whose objective is to convert carbohydrate components of a given biomass into carbon-rich material in an aqueous medium. Biomass of wastewater grown microalgae is among the various potential biomasses for this route. However, operational parameters of hydrothermal carbonization for different types of biomass are still being investigated. In general, larger temperature ranges (180-260 °C) are applied to woody biomasses, which have fibrous and/or ligneous structures and, therefore, are more thermally stable than algae biomass. This study presents the hydrothermal carbonization of microalgae biomass cultivated in an agro-industrial effluent. For this purpose, a Parr reactor was operated at different temperatures (130, 150 and 170 °C) and retention times (10, 30 and 50 min). Results showed improvements in the properties of the hydrochar, mainly energy yield and carbon concentration, after the thermochemical treatment. Energy recovery was improved, as well as hydrophobicity of the carbonized material. It was observed that in the retention time of 10 min, the increase in temperature provided an increase of 7.53% in the yield of solids. On the other hand, in the retention times of 30 and 50 min, when the temperature was increased, the solid yield decreased 6.70% and 0.92%, respectively. Thus, the highest yield of solids (77.72%) and energy (78.21%) was obtained at the temperature of 170 °C and retention time of 10 min. There was a high ash content in the raw biomass (32.99%) and an increase of approximately 3% in the carbonized material, regardless of the applied treatment. With the exception of potassium and sodium, the other macro and micronutrients were concentrated in the hydrochar after thermochemical treatment, indicating the potential of the material for agriculture application, in addition to energy use. Results showed that the retention time was the most significant operational parameter of the process.

Enhancement of biomass yield and lipid accumulation of freshwater microalga Euglena gracilis by phenolic compounds from basic structures of lignin

Introducing biomass-derived additives into microalgae cultivation to increase its yield has been regarded as a more cost-effective and environment-friendly method compared with gene-editing and nutrients supplementation. In this research, feasibility of three major phenolic compounds from lignin's basic structures (guaiacyl-, hydroxyphenyl- and syringyl- types) for freshwater microalga Euglena gracilis cultivation was evaluated. The results indicated that trans-4-hydroxy-3-methoxycinnamic acid (HMA), 4-hydroxybenzaldehyde (HBA), and syringaldehyde (SRA) could all promote microalgae growth in a phytohormone-like role, and the highest promotion effect was achieved under HMA treatment. HMA at 0.5 g·L^-1 enhanced the cell biomass yield by 2.30 times, while HBA and SRA at the concentration of 0.1 g·L^-1 increased the yield by 1.30 and 1.21 times, respectively. In addition, increased carotenoids and lipid biosynthesis were also observed under the treatments of phenolic compounds, which would contribute to the microalgae biofuel production, since the growth and lipid accumulation of E. gracilis were simultaneously enhanced.

Synchrotron FTIR spectromicroscopy as a tool for studying populations and individual living cells of green algae

Fourier transform infrared (FTIR) spectromicroscopy was used to study individual living cells of three closely-related species of the green algal genus Chlamydomonas. Three types of spectral variation were observed between individual cells within a single culture, as well as between different cultures: variation around a mean, individual outliers, and the presence of subpopulations. By understanding and controlling this variation, we were able to spectroscopically differentiate between the three closely-related species. Spectral differences were confirmed using principal component analysis, leading to an understanding of the biochemical differences between species. This work highlights the additional information obtained by studying individual cells, and has implications for more traditional bulk measurements.

Hemiselmis andersenii and Chlorella stigmatophora As New Sources of High-value Compounds: A Lipidomic Approach

To unlock the potential of Chlorella stigmatophora (Trebouxiophyceae, Chlorophyta) and Hemiselmis andersenii (Cryptophyceae, Cryptophyta) as natural reactors for biotechnological exploitation, their lipophilic extracts were characterized using Fourier Transform Infrared spectroscopy with Attenuated Total Reflectance (FTIR-ATR) and Gas Chromatography-Mass Spectrometry (GC-MS) before and after alkaline hydrolysis. The GC-MS analysis enabled the identification of 62 metabolites-namely fatty acids (27), aliphatic alcohols (17), monoglycerides (7), sterols (4), and other compounds (7). After alkaline hydrolysis, monounsaturated fatty acids increased by as much as 87%, suggesting that the esterified compounds were mainly neutral lipids. Hemiselmis andersenii yielded the highest Σω3/Σω6 ratio (7.26), indicating that it is a good source of ω3 fatty acids, in comparison to C. stigmatophora (Σω3/Σω6 = 1.24). Both microalgae presented significant amounts of aliphatic alcohols (6.81-10.95 mg · g dw^-1 ), which are recognized by their cholesterol-lowering properties. The multivariate analysis allowed visualization of the chemical divergence among H. andersenii lipophilic extracts before and after alkaline hydrolysis, as well as species-specific differences. Chlorella stigmatophora showed to be a valuable source of essential fatty acids for nutraceuticals, whereas H. andersenii, due to its high chemical diversity, seems to be suitable for different fields of application.

The effects of ionizing radiation on the structure and antioxidative and metal-binding capacity of the cell wall of microalga Chlorella sorokiniana

The impact of ionizing radiation on microorganisms such as microalgae is a topic of increasing importance for understanding the dynamics of aquatic ecosystems in response to environmental radiation, and for the development of efficient approaches for bioremediation of mining and nuclear power plants wastewaters. Currently, nothing is known about the effects of ionizing radiation on the microalgal cell wall, which represents the first line of defence against chemical and physical environmental stresses. Using various microscopy, spectroscopy and biochemical techniques we show that the unicellular alga Chlorella sorokiniana elicits a fast response to ionizing radiation. Within one day after irradiation with doses of 1-5 Gy, the fibrilar layer of the cell wall became thicker, the fraction of uronic acids was higher, and the capacity to remove the main reactive product of water radiolysis increased. In addition, the isolated cell wall fraction showed significant binding capacity for Cu²⁺, Mn²⁺, and Cr³⁺. The irradiation further increased the binding capacity for Cu²⁺, which appears to be mainly bound to glucosamine moieties within a chitosan-like polymer in the outer rigid layer of the wall. These results imply that the cell wall represents a dynamic structure that is involved in the protective response of microalgae to ionizing radiation. It appears that microalgae may exhibit a significant control of metal mobility in aquatic ecosystems via biosorption by the cell wall matrix.

Interactions between polystyrene nanoparticles and Chlamydomonas reinhardtii monitored by infrared spectroscopy combined with molecular biology

For several decades, use of nanoparticles (NP) on a global scale has been generating new potential sources of organism disruption. Recent studies have shown that NP can cause modifications on the biochemical macromolecular composition of microalgae and raised questions on the toxicity of plastic particles, which are widespread in the aquatic environment. Polystyrene (PS) particles are among the most widely used plastics in the world. In our experimentation, a combined approach of infrared spectroscopy and molecular biology (real-time PCR) has been applied in order to better apprehend the consequences of interactions between Chlamydomonas reinhardtii, freshwater microalgae and PS NP. Two references have been used, nitrogen deprivation -a well-documented stressor-, and gold nanoparticles (Au-NP). As regards biochemical composition, our experiments show a differing microalga response, according to the NP to which they have been exposed. Results with infrared spectroscopy and gene expression methods are consistent and illustrate variation among several carbohydrates (galactose…). Furthermore, PS-NP seem to react in the same direction as nitrogen limitation, thereby supporting the hypothesis that PS-NP can induce response mechanisms to environmental changes in microalgae. This study highlighted the interest of combining infrared spectroscopy and gene expression as means of monitoring microalgae response to nanoplastics.

Mechanisms of detoxification of high copper concentrations by the microalga Chlorella sorokiniana

Microalgae have evolved mechanisms to respond to changes in copper ion availability, which are very important for normal cellular function, to tolerate metal pollution of aquatic ecosystems, and for modulation of copper bioavailability and toxicity to other organisms. Knowledge and application of these mechanisms will benefit the use of microalgae in wastewater processing and biomass production, and the use of copper compounds in the suppression of harmful algal blooms. Here, using electron microscopy, synchrotron radiation-based Fourier transform infrared spectroscopy, electron paramagnetic resonance spectroscopy, and X-ray absorption fine structure spectroscopy, we show that the microalga Chlorella sorokiniana responds promptly to Cu2+ at high non-toxic concentration, by mucilage release, alterations in the architecture of the outer cell wall layer and lipid structures, and polyphosphate accumulation within mucilage matrix. The main route of copper detoxification is by Cu2+ coordination to polyphosphates in penta-coordinated geometry. The sequestrated Cu2+ was accessible and could be released by extracellular chelating agents. Finally, the reduction in Cu2+ to Cu1+ appears also to take place. These findings reveal the biochemical basis of the capacity of microalgae to adapt to high external copper concentrations and to serve as both, sinks and pools of environmental copper.

A new integrated HPTLC - ATR/FTIR approach in marine algae bioprofiling

The aim of this study was to evaluate marine algae extracts in terms of their anti-inflammatory activity using a combination of chromatographic separation and chemical detection with subsequent infrared vibrational spectroscopy identification. Extraction parameters, chemical fingerprint, and the activity levels were considered for the method optimization. High-performance thin-layer chromatography (HPTLC) combined with microchemical derivatization, was used to separate and detect bioactive compounds with antioxidant activity and anti-inflammatory activities, and to detect different classes of terpenoids. Infrared attenuated total reflectance (ATR) spectral analysis of the bands with bioactive compounds, identified sulfated polysaccharides to be responsible for the anti-inflammatory activity in extracts of brown algae Carpoglossum confluens and Phyllospora comosa. Steroids as unique antioxidants with significant free radical scavenging activities were observed in extracts of brown algae Cystophora platylobium, Cystophora retorta, Carpoglossum confluens and Phyllospora comosa. HPTLC combined with biochemical assays and FTIR-ATR spectrometry was demonstrated to be a straightforward strategy for bioprofiling marine algae extracts.

Hydrochar production from high-ash low-lipid microalgal biomass via hydrothermal carbonization: Effects of operational parameters and products characterization

This study aims to produce hydrochar from high-ash low-lipid Chlorella vulgaris biomass via hydrothermal carbonization (HTC) process. The effects of hydrothermal temperature and retention time with respect to the physicochemical properties of hydrochar were studied in the range of 180-250 °C and 0.5-4 h, respectively. It was found that the hydrothermal temperature had resulted in a significant reduction of hydrochar yield as compared to the retention time. The raw microalgal biomass was successfully converted into an energy densified hydrochar via an optimized HTC reaction, with higher heating value (HHV) of 24.51 kJ/g, which was approximately two-times higher than that of raw biomass. In addition, the overall carbon recovery rate and energy yield were in the range of 53.2-86.4% and 46.9-76.6%, respectively. The high quality of the produced hydrochar was further supported by the plot of van Krevelen diagram and combustion behaviour analysis. Besides, the aqueous phase collected from HTC process could be further used as nutrients source to cultivate C. vulgaris, in which up to 70% of the biomass yield could be attained as compared to the control cultivation condition. The reusability of the aqueous phase collected from HTC process as an alternative nutrients source to cultivate microalgal indicated the feasibility and positive integration of HTC process in microalgal biofuel processing chain.

Effect of two lignocellulose related sugar alcohols on the growth and metabolites biosynthesis of Euglena gracilis

It is an effective solution to overcome the bottlenecks of commercial production of microalgal biomass by providing cost-effective and environment-friendly organic carbon sources for microalgal mixotrophic growth. In this study, effects of lignocellulose-related mannitol and xylitol on the growth, photosynthetic pigment content, cell morphology, and metabolites biosynthesis of freshwater microalga Euglena gracilis were investigated. The results revealed that both mannitol and xylitol effectively promoted the growth of E. gracilis, and at the optimal dosage of 4 g·L^-1, the biomass yield was increased by 4.64-fold and 3.18-fold, respectively. Increase of cell aspect ratio was only observed in mannitol treatment groups, indicating that E. gracilis had different physiological responses to mannitol and xylitol. Fourier transform infrared spectroscopy combined with multivariate analysis was applied to analyze the cellular components. The lipid content of E. gracilis was significantly promoted by these two sugar alcohols, which would increase its potential in biofuel production.

An evaluation of thermal characteristics of bacterium Actinobacillus succinogenes for energy use and circular bioeconomy

The thermal characteristics of Actinobacillus succinogenes (AS) from pyrolysis, torrefaction, and combustion are analyzed to evaluate the potential of this biomass as a renewable fuel. AS pyrolysis can be classified into four stages, and its main decomposition zone is at 200-500 °C. The solid yield of AS after 60 min torrefaction is over 60 wt%, and the torrefaction severity index map indicates that a high torrefaction temperature with a short duration has a more profound influence on its decomposition. The Py-GC/MS analysis of AS suggests that the volatile products from 500 °C pyrolysis are similar to microalgae-derived pyrolysis bio-oils. The combustibility index (S) of AS is 4.07 × 10^-7 which is much higher than that of lignite coal (0.39 × 10^-7) and bituminous coal (0.18 × 10^-7), and close to those of biochar and bio-oil. The obtained results are conducive to the development of microorganisms as fuel to achieve a circular bioeconomy.

CaCl2 pretreatment improves gamma toxicity tolerance in microalga Chlorella vulgaris

The Chlorella vulgaris has been generally recognized as a promising microalgal model to study stress-related responses due to its ability to withstand against ionizing and non-ionizing radiation. The objective of the present study was to investigate the effect of CaCl₂ pre-treatment at different concentrations on the responses of microalga C. vulgaris under gamma radiation toxicity. Changes in growth, physiological parameters and biochemical compositions of the algae pretreated with 0.17 (normal), 5, and 10 mM CaCl₂ were analyzed under 300 Gy gamma irradiation and compared to those of gamma-free control. The results showed that parameters including specific growth rate, cell size, chlorophyll and protein contents, ascorbate peroxidase (APX), and superoxide dismutase (SOD) activity, Ferric Reducing Antioxidant Power (FRAP), and the ratios of nucleic acid to protein negatively affected by gamma irradiation. All these parameters, except for the ratios of nucleic acid to protein significantly increased in the algae when pretreated with a CaCl₂ content higher than normal concentration. The analysis also showed that parameters including catalase activity, proline, and carotenoid content, the level of lipid peroxidation, and electrolyte leakage (EL) significantly increased under gamma irradiation but not affected significantly under different CaCl₂ pre-treatments. Additionally, specific growth rate, chlorophyll a and protein content, APX and SOD activity, FRAP, lipid peroxidation, electrolyte leakage, and the ratios of nucleic acid to protein were the only parameters that significantly affected by the interaction of gamma toxicity and CaCl₂ pretreatment. Overall, the results suggested that regardless of the CaCl₂ effect, the algal cells responded to gamma radiation more efficiently by increasing proline, carotenoids content, and CAT activity. More important, it was concluded that calcium had an essential role in modifying the detrimental effect of gamma toxicity on the algae mainly by increasing the activity of ascorbate peroxidase and superoxide dismutase and maintaining the reducing antioxidant power (FRAP) of the cells at a high level.

Identification to species level of live single microalgal cells from plankton samples with matrix-free laser/desorption ionization mass spectrometry

INTRODUCTION

Marine planktonic communities are complex microbial consortia often dominated by microscopic algae. The taxonomic identification of individual phytoplankton cells usually relies on their morphology and demands expert knowledge. Recently, a live single-cell mass spectrometry (LSC-MS) pipeline was developed to generate metabolic profiles of microalgae.

OBJECTIVE

Taxonomic identification of diverse microalgal single cells from collection strains and plankton samples based on the metabolic fingerprints analyzed with matrix-free laser desorption/ionization high-resolution mass spectrometry.

METHODS

Matrix-free atmospheric pressure laser-desorption ionization mass spectrometry was performed to acquire single-cell mass spectra from collection strains and prior identified environmental isolates. The computational identification of microalgal species was performed by spectral pattern matching (SPM). Three similarity scores and a bootstrap-derived confidence score were evaluated in terms of their classification performance. The effects of high and low-mass resolutions on the classification success were evaluated.

RESULTS

Several hundred single-cell mass spectra from nine genera and nine species of marine microalgae were obtained. SPM enabled the identification of single cells at the genus and species level with high accuracies. The receiver operating characteristic (ROC) curves indicated a good performance of the similarity measures but were outperformed by the bootstrap-derived confidence scores.

CONCLUSION

This is the first study to solve taxonomic identification of microalgae based on the metabolic fingerprints of the individual cell using an SPM approach.

Exploring Pavlova pinguis chemical diversity: a potentially novel source of high value compounds

To uncover the potential of Pavlova pinguis J.C. Green as a natural source of value added compounds, its lipophilic extracts were studied before and after alkaline hydrolysis using gas chromatography-mass spectrometry (GC-MS). The GC-MS analysis of the lipophilic extracts showed a wide chemical diversity including 72 compounds distributed by fatty acids (29), sterols (14), fatty alcohols (13) and other lipophilic compounds (16). Fatty acids represented the main class of identified compounds presenting myristic, palmitic, palmitoleic and eicosapentaenoic acids as its main components. Through the ∑ω6/∑ω3 ratio (0.25) and sterol composition it was possible to observe that P. pinguis is a valuable source of ω3 fatty acids and stigmasterol (up to 43% of total sterols). After alkaline hydrolysis, fatty acids and fatty alcohols content increased by 32 and 14% respectively, in contrast to, monoglycerides which decreased by 84%. The long chain alcohols content enables the exploitation of this microalga as a source of these bioactive compounds. Smaller amounts of sugars and other compounds were also detected. The present study is a valuable reference to the metabolite characterization of P. pinguis and shows the potential of this microalga for nutraceutical and pharmaceutical industries.

Finding of phytase: Understanding growth promotion mechanism of phytic acid to freshwater microalga Euglena gracilis

To better understand the promotion effect of phytic acid and its uptake mechanism in freshwater microalga Euglena gracilis, cell growth, photosynthetic pigment content and cell morphology of E. gracilis were evaluated under four conditions: phosphorus deficient group (CMP-), single phosphate treatment group (CMP+), single phytic acid treatment group (CMPA-), and phosphate-phytic acid mixed treatment group (CMPA+). The results showed that phytic acid could serve as the sole phosphorus source for the growth of E. gracilis, and phytase which catalyzes the hydrolysis of phytic acid was discovered for the first time in E. gracilis. Fourier transform infrared spectroscopy combined with multivariate analysis showed the good recognition of metabolites from different culture conditions especially focusing on relative carbohydrate or lipid contents. Phytic acid derived from agro-wastes is a cheap growth promoter for E. gracilis, and this E. gracilis with high nutritional value is applicable to animal feed while minimizing environmental impact.

Statistical Methods for Rapid Quantification of Proteins, Lipids, and Carbohydrates in Nordic Microalgal Species Using ATR-FTIR Spectroscopy

Attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy is a simple, cheap, and fast method to collect chemical compositional information from microalgae. However, (semi)quantitative evaluation of the collected data can be daunting. In this work, ATR-FTIR spectroscopy was used to monitor changes of protein, lipid, and carbohydrate content in seven green microalgae grown under nitrogen starvation. Three statistical methods-univariate linear regression analysis (ULRA), orthogonal partial least squares (OPLS), and multivariate curve resolution-alternating least squares (MCR-ALS)-were compared in their ability to model and predict the concentration of these compounds in the biomass. OPLS was found superior, since it i) included all three compounds simultaneously; ii) explained variations in the data very well; iii) had excellent prediction accuracy for proteins and lipids, and acceptable for carbohydrates; and iv) was able to discriminate samples based on cultivation stage and type of storage compounds accumulated in the cells. ULRA models worked well for the determination of proteins and lipids, but carbohydrates could only be estimated if already determined protein contents were used for scaling. Results obtained by MCR-ALS were similar to ULRA, however, this method is considerably easier to perform and interpret than the more abstract statistical/chemometric methods. FTIR-spectroscopy-based models allow high-throughput, cost-effective, and rapid estimation of biomass composition of green microalgae.

Phytotoxic metabolites produced by Verticillium dahliae Kleb. in olive wilting: a chemical and spectroscopic approach for their molecular characterisation

Most of the symptoms associated with Verticillium wilt disease in olive cultivation are due to complexes excreted by Verticillium dahliae. In this study chemical and physico-chemical techniques were combined to investigate how the molecular structure of phytotoxins isolated from two pathotypes of Verticillium dahliae, defoliating, D, and non-defoliating, ND, grown on two different media, Verticillium-dahliae-Medium (VdM) and Simulated Xylem-fluid-Medium (SXM), can affect their aggressiveness. Data obtained highlight important structural differences, both in term of elemental composition and in functional groups distribution. Such peculiarities strongly affect their solubility, resulted higher for the phytotoxins from D pathotype. This property likely induces serious modifications of the conformational state of the proteinaceous component, making tyrosine residues accessible to the phosphate ion. A phosphorylation mechanism would thus be promoted, that is going to interfere with the function of the involved proteins in intracellular signalling networks, likely by altering its role in modulating the plant's response.

Optimal cultivation towards enhanced biomass and floridean starch production by Porphyridium marinum

Optimal conditions for maximal biomass and starch production by the marine red microalgae Porphyridium marinum were investigated. Box-Behnken Design was used to model the effect of light intensity, NaNO₃ concentration and salinity on the growth of microalgae but also on their starch and protein contents. These three factors increased biomass production by 13.6% in optimized conditions. A maximum starch production (140.21 μg·mL^-1), 30.6% higher than that of the control, was attained at a light intensity of 100 μmol photons·m^-2·s^-1, a NaNO₃ concentration of 1 g·L^-1 and a NaCl concentration of 20 g·L^-1. FT-IR spectroscopy was used to estimate the biochemical composition (carbohydrate accumulation) of P. marinum and revealed significant changes (P < 0.05) depending on culture conditions. FT-IR analysis highlighted also that the culture conditions leading to highest starch production by P. marinum corresponded to lowest sulfated polysaccharide and protein contents.

Metabolic adaptation of a Chlamydomonas acidophila strain isolated from acid mine drainage ponds with low eukaryotic diversity

The diversity and biological characteristics of eukaryotic communities within acid mine drainage (AMD) sites is less well studied than for prokaryotic communities. Furthermore, for many eukaryotic extremophiles the potential mechanisms of adaptation are unclear. This study describes an evaluation of eight highly acidic (pH 1.6-3.1) and one moderately acidic (pH 5.6) metal-rich acid mine drainage ponds at a disused copper mine. The severity of AMD pollution on eukaryote biodiversity was examined, and while the most species-rich site was less acidic, biodiversity did not only correlate with pH but also with the concentration of dissolved and particulate metals. Acid-tolerant microalgae were present in all ponds, including the species Chlamydomonas acidophila, abundance of which was high in one very metal-rich and highly acidic (pH 1.6) pond, which had a particularly high PO₄-P concentration. The C. acidophila strain named PM01 had a broad-range pH tolerance and tolerance to high concentrations of Cd, Cu and Zn, with bioaccumulation of these metals within the cell. Comparison of metal tolerance between the isolated strain and other C. acidophila strains previously isolated from different acidic environments found that the new strain exhibited much higher Cu tolerance, suggesting adaptation by C. acidophila PM01 to excess Cu. An analysis of the metabolic profile of the strains in response to increasing concentrations of Cu suggests that this tolerance by PM01 is in part due to metabolic adaptation and changes in protein content and secondary structure.

Characterization and application of microalgae hydrochar as a low-cost adsorbent for Cu(II) ion removal from aqueous solutions

Hydrochar prepared from the hydrothermal liquefaction of microalgae is characterized and investigated for copper removal from aqueous solution. Two hydrochars were prepared at 210 °C (HD210) and 250 °C (HD250). The effect of the initial solution pH, the initial Cu(II) concentration, the contact time, and the temperature will be investigated. According to the elemental analysis, the volatile matter in the hydrochars was lower and ash content was higher than those of microalgae. Also, pore characteristic analysis revealed that the surface area of the HD250 was higher than that of the HD210 suggesting a higher potential for the adsorption process. FTIR analysis and Boehm titration showed that both hydrochars contained oxygen-containing functional groups (OFG) on the surface which were effective for the copper removal. The adsorption experiments indicated that the amount of copper adsorbed reached a maximum value at the pH of 5 which was considered as the optimum solution pH. In addition, HD250 had a higher amount of copper adsorption than that of HD210 at all values of the solution pH. The adsorption data at the optimum solution pH was well fitted by the Langmuir's isotherm model and the adsorption process could be well described by the pseudo-2nd order kinetic model. Moreover, thermodynamic analysis revealed that copper adsorption onto the hydrochar was a physical endothermic process.

Identification of microorganisms by Fourier-transform infrared spectroscopy

The need for novel techniques of rapid identification of pathogenic microorganisms arises from the massive spread of drug-resistant nosocomial strains and the emergence of centers for biohazard control. Fourier-transform infrared spectroscopy is a promising alternative to mass spectrometry as it is cost-effective, fast and suitable for field use. The aim of this work was to propose an algorithm for the identification of microorganisms in pure cultures based on the analysis of their Fourier transform infrared spectra. The algorithm is based on the automated principal component analysis of infrared spectra. Unlike its analogues described in the literature, the algorithm is capable of identifying bacteria regardless of the culture medium or growth phase. The training sample included the most prevalent causative agents of infections and sepsis in humans: Staphylococcus aureus (n = 67), Enterococcus faecalis (n = 10), Enterococcus faecium (n = 10), Klebsiella pneumoniae (n = 10), Escherichia coli (n = 10), Serratia marcescens (n = 10), Enterobacter cloacae (n = 10), Acinetobacter baumannii (n = 10), Pseudomonas aeruginosa (n = 10), and Candida albicans (n = 10). The model we built successfully passed a series of blind tests involving clinical isolates of 10 methicillin-resistant (MRSA) and 10 methicillin-sensitive (MSSA) Staphylococcus aureus strains as well as pair mixes of these cultures with clinical isolates of Pseudomonas aeruginosa, Escherichia coli, and Klebsiella pneumoniae.

Mixotrophic and heterotrophic production of lipids and carbohydrates by a locally isolated microalga using wastewater as a growth medium

The biomass production and changes in biochemical composition of a locally isolated microalga (Chlorella sp.) were investigated in autotrophic, mixotrophic and heterotrophic conditions, using glucose or glycerol as carbon sources and municipal wastewater as the growth medium. Both standard methods and Multivariate Curve Resolution-Alternating Least Squares (MCR-ALS) analysis of data acquired by Fourier-transform IR (FTIR) spectrometry showed that autotrophic and mixotrophic conditions promoted carbohydrate accumulation, while heterotrophic conditions with glycerol resulted in the highest lipid content and lowest carbohydrate content. Heterotrophic conditions with glycerol as a carbon source also resulted in high oleic acid (18:1) contents and low linolenic acid (18:3) contents, and thus increasing biodiesel quality. The results also show the utility of MCR-ALS for analyzing changes in microalgal biochemical composition.

Two Glycerol-3-Phosphate Dehydrogenases from Chlamydomonas Have Distinct Roles in Lipid Metabolism

The metabolism of glycerol-3-phosphate (G3P) is important for environmental stress responses by eukaryotic microalgae. G3P is an essential precursor for glycerolipid synthesis and the accumulation of triacylglycerol (TAG) in response to nutrient starvation. G3P dehydrogenase (GPDH) mediates G3P synthesis, but the roles of specific GPDH isoforms are currently poorly understood. Of the five GPDH enzymes in the model alga Chlamydomonas reinhardtii, GPD2 and GPD3 were shown to be induced by nutrient starvation and/or salt stress. Heterologous expression of GPD2, a putative chloroplastic GPDH, and GPD3, a putative cytosolic GPDH, in a yeast gpd1Δ mutant demonstrated the functionality of both enzymes. C. reinhardtii knockdown mutants for GPD2 and GPD3 showed no difference in growth but displayed significant reduction in TAG concentration compared with the wild type in response to phosphorus or nitrogen starvation. Overexpression of GPD2 and GPD3 in C. reinhardtii gave distinct phenotypes. GPD2 overexpression lines showed only subtle metabolic phenotypes and no significant alteration in growth. In contrast, GPD3 overexpression lines displayed significantly inhibited growth and chlorophyll concentration, reduced glycerol concentration, and changes to lipid composition compared with the wild type, including increased abundance of phosphatidic acids but reduced abundance of diglycerides, triglycerides, and phosphatidylglycerol lipids. This may indicate a block in the downstream glycerolipid metabolism pathway in GPD3 overexpression lines. Thus, lipid engineering by GPDH modification may depend on the activities of other downstream enzyme steps. These results also suggest that GPD2 and GPD3 GPDH isoforms are important for nutrient starvation-induced TAG accumulation but have distinct metabolic functions.

Widespread green algae Chlorella and Stichococcus exhibit polar-temperate and tropical-temperate biogeography

Chlorella and Stichococcus are morphologically simple airborne microalgae, omnipresent in terrestrial and aquatic habitats. The minute cell size and resistance against environmental stress facilitate their long-distance dispersal. However, the actual distribution of Chlorella- and Stichococcus-like species has so far been inferred only from ambiguous morphology-based evidence. Here we contribute a phylogenetic analysis of an expanded SSU and ITS2 rDNA sequence dataset representing Chlorella- and Stichococcus-like species from terrestrial habitats of polar, temperate and tropical regions. We aim to uncover biogeographical patterns at low taxonomic levels. We found that psychrotolerant strains of Chlorella and Stichococcus are closely related with strains originating from the temperate zone. Species closely related to Chlorella vulgaris and Muriella terrestris, and recovered from extreme terrestrial environments of polar regions and hot deserts, are particularly widespread. Stichococcus strains from the temperate zone, with their closest relatives in the tropics, differ from strains with the closest relatives being from the polar regions. Our data suggest that terrestrial Chlorella and Stichococcus might be capable of intercontinental dispersal; however, their actual distributions exhibit biogeographical patterns.

High-throughput metabolic screening of microalgae genetic variation in response to nutrient limitation

Microalgae produce metabolites that could be useful for applications in food, biofuel or fine chemical production. The identification and development of suitable strains require analytical methods that are accurate and allow rapid screening of strains or cultivation conditions. We demonstrate the use of Fourier transform infrared (FT-IR) spectroscopy to screen mutant strains of Chlamydomonas reinhardtii. These mutants have knockdowns for one or more nutrient starvation response genes, namely PSR1, SNRK2.1 and SNRK2.2. Limitation of nutrients including nitrogen and phosphorus can induce metabolic changes in microalgae, including the accumulation of glycerolipids and starch. By performing multivariate statistical analysis of FT-IR spectra, metabolic variation between different nutrient limitation and non-stressed conditions could be differentiated. A number of mutant strains with similar genetic backgrounds could be distinguished from wild type when grown under specific nutrient limited and replete conditions, demonstrating the sensitivity of FT-IR spectroscopy to detect specific genetic traits. Changes in lipid and carbohydrate between strains and specific nutrient stress treatments were validated by other analytical methods, including liquid chromatography-mass spectrometry for lipidomics. These results demonstrate that the PSR1 gene is an important determinant of lipid and starch accumulation in response to phosphorus starvation but not nitrogen starvation. However, the SNRK2.1 and SNRK2.2 genes are not as important for determining the metabolic response to either nutrient stress. We conclude that FT-IR spectroscopy and chemometric approaches provide a robust method for microalgae screening.