Tolerant Microalgae Research Articles

Biostimulant potential of two agrochemical tolerant microalgae isolated from subtropical clay soil

Biostimulant potential of two agrochemical tolerant microalgae isolated from subtropical clay soil

Photosynthetic and antioxidant responses of Ankistrodesmus flexuosus and Curvastrum pantanale to environmentally relevant copper concentrations

AbstractSince high concentrations of copper (Cu) are known to negatively affect algae, we investigated the effect of environmentally relevant concentrations of Cu on the metabolism and photosynthesis of microalgae. We investigated the photosynthesis and antioxidant responses of two green microalgae, Ankistrodesmus flexuosus and Curvastrum pantanale, to free Cu (1.7 nM–589.0 nM Cu2+), which included environmentally significant values (1.7 nM–21.4 nM Cu2+). The microalgae had similar growth rates at low Cu2+, but C. pantanale had higher growth rates at 7.4 and 21.4 nM Cu2+, and a higher Chl a/b ratio at 1.7–21.4 nM Cu2+. The Fv/Fo of A. flexuosus was not altered by Cu, whereas its relative maximum electron transport rate (rETRm) began to decrease at 7.4 nM Cu2+. The Fv/Fo and rETRm of C. pantanale increased at 21.4 nM Cu2+. The non‐photochemical quenching (NPQ) that was actively dissipated [Y(NPQ)] in A. flexuosus increased with Cu increase, whereas at 589.0 nM Cu2+, the NPQ of C. pantanale decreased and its passive energy dissipation [Y(NO)] increased. C. pantanale had higher photosynthesis at 1.7–21.4 nM Cu2+. Superoxide dismutase (SOD) activity increased in both microalgae at high Cu concentrations, at 21.4 nM Cu2+ for A. flexuosus, and at 589.0 nM Cu2+ for C. pantanale. Thus, environmentally relevant Cu concentrations can favor the survival of tolerant microalgae species, hence shifting the diversity of aquatic biota.

Real-time response counterattack strategy of tolerant microalgae Chlorella vulgaris MBFJNU-1 in original swine wastewater and free ammonia

This work was the first time to systematically clarify the potential tolerance mechanism of an indigenous Chlorella vulgaris MBFJNU-1 towards the free ammonia (FA) during the original swine wastewater (OSW) treatment by transcriptome analysis using C. vulgaris UETX395 as the control group. The obtained results showed that C. vulgaris MBFJNU-1 was found to be more resistant to the high levels of FA (115 mg/L) and OSW in comparison to C. vulgaris UETX395 (38 mg/L). Moreover, the transcriptomic results stated that some key pathways from arginine biosynthesis, electron generation and transmission, ATP synthesis in chloroplasts, and glutathione synthesis of C. vulgaris MBFJNU-1 were greatly related with the OSW and FA. Additionally, C. vulgaris MBFJNU-1 in OSW and FA performed similar results in the common differentially expressed genes from these mentioned pathways. Overall, these obtained results deliver essential details in microalgal biotechnology to treat swine wastewater and high free ammonia wastewater.

Green synthesis of silver nanoparticles from saline tolerant microalgae and their antiviral properties against HIV-1

The microalgae were exposed to silver nitrate (AgNO3) solution and screened for their suitability for production of the nano-silver (nano-Ag). The HIV-1 gag p24 Elisa Assay was used to study the anti-HIV activity of biogenic silver nanoparticles from microalgae Nostoc sp., Lyngbya sp., and Phormidium sp. The antiviral activity of biogenic silver compounds can be explained by their ability to cross the lipophilic membranes and interact with proteins involved in apoptosis. The antiviral activity of silver ion assembled into the V3loop of HIV -GP120. CD4 cell with CXCR4 chemokine receptor binding with its ligand CXCL12 plays an important role in protecting the entry of HIV virus. The role of the extracellular loop from CXCR4 and its mechanism allowed for the binding of HIV glycoprotein. This active site of protein bind with target protein to form protein–protein-ligand interaction to carry out the signals to lead the various pathways such as CXCL12 or SDF-1 protein-mediated kinase, Ras-c-Raf-1-MEK1/2-ERK1/2 dependent pathway, and CD45 cell-mediated pathway. The sulfur-bearing residues located in the glycoprotein knobs would be attractive sites for nanoparticle interaction. Silver nanoparticles are blocked the protease activity of different HIV-1strains with overlooks their tropism. Modification in gp120 among HIV strains is the major determinant site of differing tropism among HIV strains.

Green synthesis of silver nanoparticles from saline tolerant microalgae and their antiviral properties against HIV-1

The microalgae were exposed to silver nitrate (AgNO3) solution and screened for their suitability for production of the nano-silver (nano-Ag). The HIV-1 gag p24 Elisa Assay was used to study the anti-HIV activity of biogenic silver nanoparticles from microalgae Nostoc sp., Lyngbya sp., and Phormidium sp. The antiviral activity of biogenic silver compounds can be explained by their ability to cross the lipophilic membranes and interact with proteins involved in apoptosis. The antiviral activity of silver ion assembled into the V3loop of HIV -GP120. CD4 cell with CXCR4 chemokine receptor binding with its ligand CXCL12 plays an important role in protecting the entry of HIV virus. The role of the extracellular loop from CXCR4 and its mechanism allowed for the binding of HIV glycoprotein. This active site of protein bind with target protein to form protein–protein-ligand interaction to carry out the signals to lead the various pathways such as CXCL12 or SDF-1 protein-mediated kinase, Ras-c-Raf-1-MEK1/2-ERK1/2 dependent pathway, and CD45 cell-mediated pathway. The sulfur-bearing residues located in the glycoprotein knobs would be attractive sites for nanoparticle interaction. Silver nanoparticles are blocked the protease activity of different HIV-1strains with overlooks their tropism. Modification in gp120 among HIV strains is the major determinant site of differing tropism among HIV strains.

Dissecting the molecular mechanisms of producing biofuel and value-added products by cadmium tolerant microalgae as sustainable biorefinery approach

Microalgae can reconcile the deteriorating outcomes of environmental pollution by conserving the carbon footprint and generating green energy. Among different pollutants, cadmium (Cd) is one of the most noxious heavy metals that travels the ecological chain via phytoplanktons and stagnates the nutritional quality of aquatic life. In the present study, Scenedesmus sp. IITRIND2, a reported Cd-tolerant algal strain, has been subjected to detailed molecular investigations through metabolomics, gene expression, and biochemical analysis to dissect the pathways involved in Cd tolerance and the carbon flux channelization resulting in enhanced lipid/extracellular polysaccharide (EPS) production. The metabolic rewiring in the tricarboxylic acid (TCA) intermediates, amino acid metabolism, and starch metabolism presented the robust machinery of the cells to channelize the carbon pools for producing neutral lipids of vehicular quality under Cd stress. Further, microalgal cells instigated a defense network comprising organic osmolytes (betaine, ethylene glycol, sugars), antioxidants (glutathione, ascorbate, etc.,) and amino acids (glycine, glutamate, alanine, valine, threonine) suggesting the interplay of glutathione-ascorbate and probable phytochelatin based detoxification pathways as double edge sword to impart tolerance and detoxification of Cd. Moreover, stress-induced response constituted significant changes in the membrane fluidity and production of biodiesel quality lipids along with soluble EPS having paramount biotechnological applications. The outcomes of this study altogether presented an efficient model of algal-based biorefinery approach integrating the process of heavy metal (Cd) remediation and production of biodiesel and value-added products that are essential for a sustainable and circular economy.

Process engineering strategy for large scale outdoor cultivation of Tetradesmus obliquus CT02 coupled with pH guided CO2 feeding

A novel CO2 tolerant microalga Tetradesmus obliquus CT02, was previously evaluated to be a suitable bio refinery platform for synthesis of bioactive molecules, biodiesel, and biofertilizer. In the present study, a process engineering strategy was developed targeting improved growth performance of the strain at large scale under fluctuating outdoor environmental conditions. The strategy relies on maintaining pH of the culture at its optimal value via cascade control with CO2 feeding. The strategy was developed at laboratory scale bubble column photobioreactor under diurnal variation of simulated sunlight intensity and was further validated through growth performance of the strain under outdoor conditions in a 100L airlift bioreactor. Under laboratory condition, 53.3% and 85.16% improvement in biomass concentration (1.87gL-1) and productivity (114.8mgL-1 day-1) was achieved as compared to the uncontrolled pH, respectively. The strategy demonstrated a significant improvement in biomass concentration and productivity by 225.7% and 121.6% respectively, compared to the pH uncontrolled batch, even under outdoor fluctuating environmental condition.

Dark stress for improved lipid quantity and quality in bioprospected acid-tolerant green microalgae.

The cost of microalgae cultivation is one of the largest limitations to achieving sustainable, large-scale microalgae production of commercially desirable lipids. Utilizing CO2 as a 'free' carbon source from waste industrial flue gas emissions can offer wide-ranging cost savings. However, these gas streams typically create acidic environments, in which most microalgae cannot survive due to the concentration of CO2 and the presence of other acidic gasses such as NO2 and SO2. To address this situation, we investigated growth of a mixed acid-tolerant green microalgal culture (91% dominated by a single Coccomyxa sp. taxon) bioprospected at pH 2.8 from an acid mine drainage impacted water body. The culture was grown at pH 2.5 and fed with a simulated flue gas containing 6% CO2 and 94% N2. On reaching the end of the exponential growth phase, the culture was exposed to either continued light-dark cycle conditions or continual dark conditions. After three days in the dark, the biomass consisted of 28% of lipids, which was 42% higher than at the end of the exponential phase and 55% higher than the maximum lipid content achieved under light/dark conditions. The stress caused by being continually in the dark also favoured the production of omega-3 and omega-6 polyunsaturated fatty acids (PUFAs; 19.47% and 21.04%, respectively, after 7 days) compared to 7-days of light-dark treatment (1.94% and 9.53%, respectively) and showed an increase in nitrogen content (C:N ratio of 6.4) compared to light-dark treatment (C:N ratio of 11.9). The results of the research indicate that use of acid tolerant microalgae overcomes issues using flue gasses that will create an acidic environment and that applying dark stress is a low-cost stressor stimulates production of desirable dietary lipids.

Recycling banana pseudostem waste as a substrate for microalgae biofilm and their potential in arsenic removal

Arsenic (As) is the most toxic metalloid and class I carcinogen present in the drinking water affecting around 200 M people worldwide. Among various strategies microalgal biofilm based As removal is considered as most suitable option. However, sustainable technologies for As removal from water is scanty. In the present study, banana pseudostem waste was used as a substrate for growing microalgae biofilm (BSB) and its As removal capacity was compared with nylon mesh grown microalgae biofilm (NMB). Response surface methodology optimize initial As concentration as the most important parameter (p < 0.0001) for As removal as compared to substrate area and initial phosphate concentration in both BSB and NMB treatments. BSB treatment removed 97.6% of added arsenite [As(III)] and converted into less toxic forms like arsenate and dimethylarsenic acid within 5 d. The As removal efficiency of BSB treatment is 20% higher than NMB treatment due to the high As accumulation by the banana pseudostem. In both BSB and NMB treatments, As exposure led to change in microalgae community composition towards more tolerant species that produced more proteins and lipids facilitating binding of As and amelioration of induced stress, respectively. The present study signifies the use of banana pseudostem to grow tolerant microalgae for efficient removal of As from water. The study also paves way for proving the concept “waste into wealth” by utilizing the agri-wastes for the sustainable and more economical water treatment process.

Screening and application of Chlorella strains on biosequestration of the power plant exhaust gas evolutions of biomass growth and accumulation of toxic agents.

To use microalgae for the biosequestration of carbon dioxide (CO2) emitted from the coal-fired power plants, the screening of high CO2 tolerant microalgae and their accumulation of toxic agents have attracted significant research attention. This study evaluated 10 Chlorella strains for high CO2 tolerance using combined growth rates and growth periods subjected to logistic parameters. We selected LAMB 31 with high r (0.89 ± 0.10 day-1), high k (6.51 ± 0.19), and medium Tp (5.17 ± 0.15 day) as a candidate for CO2 biosequestration. Correspondingly, six genes involving carbon fixation and metabolism processes were upregulated in LAMB 31 under high CO2 conditions, verifying its high CO2 tolerant ability. LAMB 31 cultures exposed to exhaust gas of power plant under different flow rates grew well, but the high flow rate (0.6 L/h) showed inhibition effects compared with low flow rates (0.2 and 0.3 L/h) at the end of the culturing period. The toxic agents in the exhaust gas including sulfur, arsenic, and mercury accumulated in LAMB 31 biomass but were deemed safe for use in the production of both human food and animal feed based on the National Food Safety Standard in China. This study showed a complete process involving high CO2 tolerant microalgae screening, high CO2 tolerant verification, and in situ application in a power plant. Data results provide valuable information as the basis for future research studies in microalgae application on CO2 mitigation at emission sources.

Bioprospecting of indigenous marine microalgae with ammonium tolerance from aquaculture ponds for microalgae cultivation with ammonium-rich wastewaters

We isolated fifty-two strains from the marine aquaculture ponds in Malaysia that were evaluated for their lipid production and ammonium tolerance and four isolates were selected as new ammonium tolerant microalgae with high-lipid production: TRG10-p102 Oocystis heteromucosa (Chlorophyceae); TRG10-p103 and TRG10-p105 Thalassiosira weissflogii (Bacillariophyceae); and TRG10-p201 Amphora coffeiformis (Bacillariophyceae). Eicosapentenoic acid (EPA) in three diatom strain was between 2.6 and 18.6 % of total fatty acids, which were higher than in O. heteromucosa. Only A. coffeiformi possessed arachidonic acid. Oocystis heteromucosa naturally grew at high ammonium concentrations (1.4–10 mM), whereas the growth of the other strains, T. weissflogii and A. coffeiformi, were visibly inhibited at high ammonium concentrations (>1.4 mM-NH4). However, two strains of T. weissflogii were able to grow at up to 10 mM-NH4 by gradually acclimating to higher ammonium concentrations. The ammonium tolerant strains, especially T. weissflogii which have high EPA contents, were identified as a valuable candidate for biomass production utilizing NH4-N media, such as ammonium-rich wastewater.

Bioprospecting and characterization of temperature tolerant microalgae from Bonaire

Control of temperature is a major challenge for industrial microalgae production in photobioreactors outdoors. Strains with tolerance for high temperatures can reduce the cost of production as active temperature control is not required. In this study, marine photoautotrophic microorganisms were isolated to reduce the need for control of high temperature.Twenty-two samples were taken from different saline waters on the Caribbean island Bonaire. During strain enrichment, a temperature of 40 °C was used as selective pressure and strains with the highest growth rate were selected. We isolated and identified 59 strains, after which 5 were selected for characterization on growth rate and biomass composition. Picochlorum sp. and Leptolyngbya sp. showed optimal growth at 40 °C and 35 °C with a growth rate of 0.12 h−1 during daytime, respectively. The strains contain 62.1% and 68.2% of protein and have varying fatty acid compositions suitable for application as edible oil and biofuel.

Green synthesis of silver nanoparticles using microalgae acclimated to high CO2

Silver nanoparticle (AgNP) synthesis using microalgae is a promising low-cost sustainable alternative. High CO2 tolerant microalgae have not yet been explored for this application. This study pretends to determine the potential of an environmental green algae Desmodesmus abundans acclimated to low and high CO2 (LCA and HCA strains, respectively) as a platform for AgNPs synthesis and evaluate the effect of pH (5, 7.5, 11) and biological component (cells, supernatant and both components) in comparison to a collection strain Spirulina platensis. Exponential grown cultures were centrifuged, the pellet resuspended in 10 mM AgNO3 prepared in water or supernatant at different pH and incubated for 40 h (24 °C, continuous light). After, the filtrated solution was characterized using UV–visible absorption spectra, Zetasizer and scanning electron microscopy coupled to energy-dispersive X-ray spectroscopy. Results showed drastic differences between strains. No nanoparticles were observed with strain LCA, except at pH 11 using the pellet, which generated large particles (127.8 ± 14.8 nm diameter, −26.7 ± 2.4 mV zeta potential). In contrast, the HCA strain in these conditions showed the smallest AgNPs with the lowest zeta potential (14.9 ± 6.4 nm, −32.7 ± 5.3 mV). When the supernatant was conserved, HCA exhibited AgNPs in all pH solutions, with smallest sizes at pH 11 (27.7 ± 14.0 nm, −20.0 ± 1.8 mV). In addition, the HCA supernatant alone showed reducing potential for AgNP synthesis (51.8 ± 20.7 nm, −17.4 ± 1.3 mV). S. platensis also generated AgNPs in all conditions, but nanoscale particles were observed only at pH 11 (18.3 ± 7.5 nm, −33.9 ± 2.4 mV). In conclusion, high CO2 atmospheres seem to potentiate AgNPs synthesis by microalgae with interesting properties accordingly to biological component employed, representing a potential byproduct in CO2 mitigation systems.

Metabolic acclimation mechanism in microalgae developed for CO2 capture from industrial flue gas

Microalgae are the potential choice in diverting carbon emission from industrial plants. Owing to the high CO2 concentrations, industrial flue gas can constrain the growth of most microalgae. A continuous transfer procedure was developed to select a tolerant microalgae species to feed on CO2-rich industrial flue gas. The ability to capture CO2 by the developed microalgae species is verified in a closed gas bag system and the bubble column reactors. A total of 432 metabolic molecules were collected from the microalgae culture subject to the ambient (0.04% CO2) and the CO2-elevated (15%) treatments, 37 of which showed significantly different concentrations. These 37 metabolites were found to enhance the cellular physiology mechanisms of the microalgae to thrive in the high concentrations of CO2. The productivity of microalgae was shown to be improved for industrial applications.

Investigation of Chlorella vulgaris UTEX 265 Cultivation under Light and Low Temperature Stressed Conditions for Lutein Production in Flasks and the Coiled Tree Photo-Bioreactor (CTPBR).

Lutein has an increasing share in the pharmaceutical and nutraceutical market due to its benefits to eye health. Microalgae may be a potential source for lutein production while the expense limits the commercialization. In this study, a coiled tubular tree photobioreactor (CTPBR) design was investigated for cultivating the cold tolerant microalgae Chlorella vulgaris UTEX 265 under various conditions for lutein production. The influence and interaction of light irradiance strength, lighting cycle, and temperature on microalgae and lutein production efficiency at low temperature range were also studied in flasks via response surface method (RSM). The results demonstrated that 14h day-light, 120μmol photons m-2s-1, and 10°C was the optimal condition for algae growth and lutein production at low temperature experimental ranges. C. vulgaris UTEX 265 showed good potential to produce lutein in cold weather, and the optimum lutein production was contrary to the specific lutein content but corresponds to the trend of optimum growth. Additionally, fast growth (μ=1.50day-1) and good lutein recovery (11.98mgg-1day-1) in CTPBR were also achieved at the low irradiance stress condition and the low temperature photo-inhibition conditions.

A comparative study of the growth of Tetraselmis sp. in large scale fixed depth and decreasing depth raceway ponds

In this study, an alternative approach was proposed where excess seawater would be added only during inoculation (DD) rather than daily addition (FD). Growth and metabolite contents of Tetraselmis sp. weren’t affected for daily increase of 2% NaCl salinity. Tetraselmis sp. was then cultured in DD and FD pond. In DD pond, initial culture depth was 23.5cm and its depth reduced as no water was added; for FD pond, everyday sterilized seawater was added to maintain 20cm depth. DD pond had higher biomass productivity compared to FD pond, until DD pond was deeper than FD pond; metabolite content and FAME profile of Tetraselmis sp. were also similar in both cultures. Therefore, considering the simplicity in operation, halo tolerant microalgae can be grown in DD pond method.

Cultivation of Nannochloropsis salina in municipal wastewater or digester centrate

Meaningful use of biofuels for transportation depends on utilization of water from non-traditional, non-potable resources. Here it is hypothesized that (i) reclaimed wastewater or nutrient-rich side streams derived from municipal wastewater treatment are suitable for that purpose and (ii) use of those waters for algal growth can promote water quality through nutrient management. Experiments showed that metals levels in municipal wastewaters are unlikely to inhibit algal growth and lipid production, at least by metals tolerant microalgae like Nannochloropsis salina. Cells grew without inhibition in treated municipal wastewater or centrate derived from wastewater treatment at additions up to 75 percent v/v in their normal growth medium minus nitrogen and phosphorus. Although wastewater provides a suitable nutrient source for algal growth, not enough municipal wastewater is available to support a meaningful biofuels industry without efficient water recycling and nutrient recovery/reuse from spent algae.

Bioadsorption and bioaccumulation of chromium trivalent in Cr(III)-tolerant microalgae: A mechanisms for chromium resistance

Anthropogenic activity constantly releases heavy metals into the environment. The heavy metal chromium has a wide industrial use and exists in two stable oxidation states: trivalent and hexavalent. While hexavalent chromium uptake in plant cells has been reported that an active process by carrying essential anions, the cation Cr(III) appears to be taken up inactively. Dictyosphaerium chlorelloides (Dc1M), an unicellular green alga is a well-studied cell biological model organism. The present study was carried out to investigate the toxic effect of chromium exposures on wild-type Cr(III)-sensitive (Dc1Mwt) and Cr(III)-tolerant (Dc1MCr(III)R30) strains of these green algae, and to determine the potential mechanism of chromium resistance. Using cell growth as endpoint to determine Cr(III)-sensitivity, the IC50(72) values obtained show significant differences of sensitivity between wild type and Cr(III)-tolerant cells. Scanning electron microscopy (SEM) showed significant morphological differences between both strains, such as decrease in cell size or reducing the coefficient of form; and transmission electron microscopy (TEM) revealed ultrastructural changes such as increased vacuolization and cell wall thickening in the Cr(III)-tolerant strain with respect to the wild-type strain. Energy dispersive X-ray analysis (SEM/XEDS) revealed that Cr(III)-tolerant D. chlorelloides cells are able to accumulate considerable amounts of chromium distributed in cell wall (bioadsorption) as well as in cytoplasm, vacuoles, and chloroplast (bio-accumulation). Morphological changes of Cr(III)-tolerant D. chlorelloides cells and the presence of these electron-dense bodies in their cell structures can be understood as a Cr(III) detoxification mechanism.

Enhanced CO2 sequestration by a novel microalga: Scenedesmus obliquus SA1 isolated from bio-diversity hotspot region of Assam, India

The present study aimed to isolate a high CO2 and temperature tolerant microalga capable of sequestering CO2 from flue gas. Microalga strain SA1 was isolated from a freshwater body of Assam and identified as Scenedesmus obliquus (KC733762). At 13.8±1.5% CO2 and 25 °C, maximum biomass (4.975±0.003 g L(-1)) and maximum CO2 fixation rate (252.883±0.361 mg L(-1) d(-1)) were obtained which were higher than most of the relevant studies. At elevated temperature (40 °C) and 13.8±1.5% CO2 maximum biomass (0.883±0.001 g L(-1)) was obtained. The carbohydrate, protein, lipid, and chlorophyll content of the CO2 treated SA1 were 30.87±0.64%, 9.48±1.65%, 33.04±0.46% and 6.03±0.19% respectively, which were higher than previous reports. Thus, SA1 could prove to be a potential candidate for CO2 sequestration from flue gas as well as for the production of value added substances.

Bioprospecting the thermal waters of the Roman baths: isolation of oleaginous species and analysis of the FAME profile for biodiesel production

The extensive diversity of microalgae provides an opportunity to undertake bioprospecting for species possessing features suited to commercial scale cultivation. The outdoor cultivation of microalgae is subject to extreme temperature fluctuations; temperature tolerant microalgae would help mitigate this problem. The waters of the Roman Baths, which have a temperature range between 39°C and 46°C, were sampled for microalgae. A total of 3 green algae, 1 diatom and 4 cyanobacterial species were successfully isolated into ‘unialgal’ culture. Four isolates were filamentous, which could prove advantageous for low energy dewatering of cultures using filtration.Lipid content, profiles and growth rates of the isolates were examined at temperatures of 20, 30, 40°C, with and without nitrogen starvation and compared against the oil producing green algal species, Chlorella emersonii. Some isolates synthesized high levels of lipids, however, all were most productive at temperatures lower than those of the Roman Baths. The eukaryotic algae accumulated a range of saturated and polyunsaturated FAMEs and all isolates generally showed higher lipid accumulation under nitrogen deficient conditions (Klebsormidium sp. increasing from 1.9% to 16.0% and Hantzschia sp. from 31.9 to 40.5%). The cyanobacteria typically accumulated a narrower range of FAMEs that were mostly saturated, but were capable of accumulating a larger quantity of lipid as a proportion of dry weight (M. laminosus, 37.8% fully saturated FAMEs). The maximum productivity of all the isolates was not determined in the current work and will require further effort to optimise key variables such as light intensity and media composition.