A screening method using 15% CO
2
(v/v) as screening stress and a spotting plate method was developed to isolate microalgae with the potential to convert flue gas CO
2
to biomass. A total of six ...microalgal strains, belonging to the genera
Chlorella
,
Heynigia
,
Desmodesmus
, and
Scenedesmus
, were isolated from ponds near metallurgical/cement/power plants. The growth of these isolated strains was dramatically promoted at 5 to 15% CO
2
when they were cultivated in bubble column photobioreactors aerating with 0.03%, 5%, 10%, and 15% CO
2
. The growth of
Heynigia riparia
SX01 in particular showed substantial improvement with the increase of CO
2
concentrations from 5 to 15%. Furthermore, the maximum biomass, overall biomass productivity, maximum biomass productivity, and maximum CO
2
fixation rate of these microalgal strains greatly increased at 5 to 15% CO
2
as well.
Chlorella sorokiniana
GS03 showed the highest values in maximum biomass productivity (0.36 g L
−1
day
−1
) and maximum CO
2
fixation rate (0.66 g L
−1
day
−1
) at 5% CO
2
.
Heynigia riparia
SX01 exhibited the highest values of maximum biomass (3.28 g L
−1
), overall biomass productivity (0.27 g L
−1
day
−1
), maximum biomass productivity (0.39 g L
−1
day
−1
), and maximum CO
2
fixation rate (0.71 g L
−1
day
−1
) at 15% CO
2
. This study provides not only an efficient screening method obtaining microalgae with wide CO
2
tolerance but also microalgal strains utilizing high levels of CO
2
up to 15% to produce biomass, which contributes to further exploration in converting real flue gas CO
2
into biomass feedstock.
Microalgae of the genus
show great potential for large-scale commercial cultivation, as they accumulate large quantities of B-phycoerythrin (B-PE), long chain polyunsaturated fatty acids (LC-PUFAs) ...and exopolysaccharide (EPS). The present study aimed to adjust culture nitrogen concentrations to produce
biomass rich in B-PE, LC-PUFAs and EPS.
SCS-02 was cultured in ASW culture medium with low nitrogen supply (LN, 3.5 mM), medium nitrogen supply (MN, 5.9 mM) or high nitrogen supply (HN, 17.6 mM). HN significantly enhanced the accumulation of biomass, intracellular protein, B-PE and eicosapentaenoic acid. LN increased the intracellular carbohydrate and arachidonic acid content, and promoted the secretion of EPS. The total lipids content was almost unaffected by nitrogen concentration. Based on these results, a semi-continuous two-step process was proposed, which included the production of biomass rich in B-PE and LC-PUFAs with sufficient nitrogen, and induced EPS excretion with limited nitrogen and strong light.
Microalgal polysaccharides have been reported in many studies due to their uniqueness, biocompatibility, and high value, and
Rhodosorus
sp. SCSIO-45730 was an excellent source of polysaccharides and ...β-glucans. However, the polysaccharides from the red unicellular alga
Rhodosorus
sp. SCSIO-45730 have barely been studied. In this work, hot water extraction of
Rhodosorus
sp. SCSIO-45730 polysaccharides (RSP) was optimized using response surface methodology (RSM) based on Box–Behnken design (BBD). The maximum RSP yield (9.29%) was achieved under the optimum extraction conditions: liquid–solid ratio of 50.00 mL g
−1
; extraction temperature of 84 °C; extraction time of 2 h; and extraction times of 5 times. The results of physicochemical characterization showed that RSP had high sulfate and uronic acid with content of 19.58% and 11.57%, respectively, rough layered structure, and mainly contained glucose, galactose, xylose, and galacturonic acid with mass percentages of 34.08%, 28.70%, 12.46%, and 12.10%. Furthermore, four kinds of antioxidant assays were carried out, and the results indicated that RSP had strong scavenging activities on ABTS and hydroxyl radical and moderate scavenging activities on DPPH and ferrous chelating ability. These results indicated that RSP showed potential as a promising source of antioxidants applied in food, pharmaceutical, and cosmetics industry.
The marine red microalga
can simultaneously synthesize long-chain polyunsaturated fatty acids, including eicosapentaenoic acid (C20:5, EPA) and arachidonic acid (C20:4, ARA). However, the ...distribution and synthesis pathways of EPA and ARA in
are not clearly understood. In this study,
CCALA 415 was cultured in nitrogen-replete and nitrogen-limited conditions. Fatty acid content determination, transcriptomic, and lipidomic analyses were used to investigate the synthesis of ARA and EPA. The results show that membrane lipids were the main components of lipids, while storage lipids were present in a small proportion in CCALA 415. Nitrogen limitation enhanced the synthesis of storage lipids and ω6 fatty acids while inhibiting the synthesis of membrane lipids and ω3 fatty acids. A total of 217 glycerolipid molecular species were identified, and the most abundant species included monogalactosyldiglyceride (C16:0/C20:5) (MGDG) and phosphatidylcholine (C16:0/C20:4) (PC). ARA was mainly distributed in PC, and EPA was mainly distributed in MGDG. Among all the fatty acid desaturases (FADs), the expressions of Δ5FAD, Δ6FAD, Δ9FAD, and Δ12FAD were up-regulated, whereas those of Δ15FAD and Δ17FAD were down-regulated. Based on these results, only a small proportion of EPA was synthesized through the ω3 pathway, while the majority of EPA was synthesized through the ω6 pathway. ARA synthesized in the ER was likely shuttled into the chloroplast by DAG and was converted into EPA by Δ17FAD.
Oleaginous microalgae can accumulate large amounts of storage lipids that have many potential applications such as in the production of biodiesel and health products. All of the energy for the ...synthesis of lipids in microalgae is derived from photosynthesis. To date, however, the quantitative relationship between photosynthesis and lipid accumulation rate in microalgae is still unclear. In this study,
Nannochloropsis
sp. was selected to explore this relationship by investigating changes in lipid accumulation, photosynthetic efficiency, and the electron transport chain under nutrients limitation and replenishment. The results of the study demonstrated that lipids were the main form of storage of carbon and energy for this microalga. The alternative electron transport chain played an important role in photo-protection and lipid accumulation. The photosynthetic efficiency of this microalga showed a strong correlation with lipid accumulation rate (
R
2
= 0.959), with higher photosynthetic efficiency translating to higher lipid accumulation rates during the lipid accumulation stage of the growth cycle. The results of the present study indicated that nutrient depletion might not be the best signal to understand when microalgae begin to accumulate oil, as it appears that photosynthetic efficiency also has a large role in the rate of oil accumulation. Additionally, the study shows that excessive light might not be needed in later stages of growth for lipid accumulation, which in turn would alleviate the damage to microalgae caused by strong light making large-scale cultivation more cost-effective.
A novel method using ethanol was proposed for extracting lipids from wet microalga Picochlorum sp. at room temperature and pressure. In this study, Central Composite design (CCD) was applied to ...investigate the optimum conditions of lipid extraction. The results revealed that the solvent to biomass ratio had the largest effect on lipid extraction efficiency, followed by extraction time and temperature. A high lipid extraction yield (33.04% of the dry weight) was obtained under the following extraction conditions: 5 mL solvents per gram of wet biomass for 37 min with gentle stirring at room temperature. The extraction yield was comparable to that obtained by the widely used Bligh-Dyer method. Furthermore, no significant differences in the distribution of lipid classes and fatty acid composition were observed according to different extraction methods. In conclusion, these results indicated that the proposed procedure using ethanol could extract lipids from wet biomass efficiently and had giant potential for lipid extraction at large scale.
Lipid production is an important indicator for assessing microalgal species for biodiesel production. In this work, the effects of medium composition on lipid production by Scenedesmus sp. were ...investigated using the response surface methodology. The results of a Plackett-Burman design experiment revealed that NaHCO₃, NaH₂PO4·2H₂O and NaNO₃ were three factors significantly influencing lipid production, which were further optimized by a Box-Behnken design. The optimal medium was found to contain 3.07 g L⁻¹ NaHCO₃, 15.49 mg L⁻¹ NaH₂PO4·2H₂O and 803.21 mg L⁻¹ NaNO₃. Using the optimal conditions previously determined, the lipid production (304.02 mg·L⁻¹) increased 54.64% more than that using the initial medium, which agreed well with the predicted value 309.50 mg L⁻¹. Additionally, lipid analysis found that palmitic acid (C16:0) and oleic acid (C18:1) dominantly constituted the algal fatty acids (about 60% of the total fatty acids) and a much higher content of neutral lipid accounted for 82.32% of total lipids, which strongly proved that Scenedesmus sp. is a very promising feedstock for biodiesel production.
•A common newly isolated strain of Nannochloropsis gaditana was investigated.•The influence of cultivation period on growth and lipid properties were examined.•Most of the examined items linear ...changed with the cultivation period extension.•Lipid productivity revealed a growth cessation in 16days.•All of the biofuel properties satisfied the specifications of biodiesel standard.
This work reported for the first time the detailed impacts of cultivation period on growth dynamics and biochemical composition of a microalga strain Nannochloropsis gaditana 1049. The results shown either the biomass accumulation, lipid content, neutral lipid content, monounsaturated fatty acids composition or the favorable fatty acid profile of C16–C18 increased along with the cultivation period extension, but the lipid productivity displayed a decrease since cultured for 16days, with the highest value reached 289.51±16.34mgL−1d−1. Biodiesel properties of this microalga also changed with the cultivation period extension, with average unsaturated degree decreased from 1.24±0.03 to 0.59±0.02, cloud point increased from 3.39±0.40°C to 12.14±0.32°C, cetane number increased from 54.59±0.20 to 58.96±0.16 and iodine number reduced sharply from 105.15±2.24gI2/100g to 56.44±1.76gI2/100g, which all satisfied the specifications of biodiesel standard.
Microalgae oil is an optimal feedstock for nutraceutical, pharmaceutical and biodiesel production, but its high levels of chlorophyll limit its large-scale application. To date, few effective ...approaches have been developed to remove chlorophyll from microalgae oil. The main purpose of this study was to present a preprocessing method of algae oil feedstock (Scenedesmus) to remove chlorophyll by saponification. The results showed that 96% of chlorophyll in biomass was removed. High quality orange transparent oil could be extracted from the chlorophyll reduced biomass. Specifically, the proportion of neutral lipids and saturation levels of fatty acids increased, and the pigments composition became carotenoids-based. The critical parameters of chlorophyll reduced biodiesel conformed to the standards of the USA, China and EU. Sodium copper chlorophyllin could be prepared from the bleaching effluent. The results presented herein offer a useful pathway to improve the quality of microalgae oil and reduce the cost of microalgae biodiesel.
Phaeodactylum tricornutum
is a potential livestock for the combined production of eicosapentaenoic acid (EPA) and fucoxanthin. In this study, six marine diatom strains identified as
P. tricornutum
...were cultured and their total lipid, fatty acid composition and major photosynthetic pigments determined. It was found that the cell dry weight concentration and mean growth rate ranged between 0.24–0.36 g/L and 0.31–0.33/d, respectively. Among the strains, SCSIO771 presented the highest total lipid content, followed by SCSIO828, and the prominent fatty acids in all strains were C16:0, C16:1, C18:1, and C20:5 (EPA). Polyunsaturated fatty acids, including C16:2, C18:2, and EPA, comprised a significant proportion of the total fatty acids. EPA was markedly high in all strains, with the highest in SCSIO828 at 25.65% of total fatty acids. Fucoxanthin was the most abundant pigment in all strains, with the highest in SCSIO828 as well, at 5.50 mg/g. The collective results suggested that strain SCSIO828 could be considered a good candidate for the concurrent production of EPA and fucoxanthin.
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