A simple method for the preparation of single cells and regeneration of colonies of Botryococcus braunii NIES836

Botryococcus braunii, a colonial alga, is known for notably slow growth; however, the growth rate and hydrocarbon productivity are expected to be improved using genetic modification techniques. Nevertheless, B. braunii has a hydrocarbon-rich extracellular matrix (ECM), and the ECM is a major barrier to DNA transformation. To analyse and utilize genetically modified B. braunii, it is essential to regenerate genetically homogeneous colonies derived from single cells. In this study, we developed a novel, simple method for harvesting viable single cells of B. braunii by centrifugation of the culture and subsequent filtration alone. The harvest of single cells was made possible by culturing B. braunii colonies in AF6 medium until the depletion of nitrogen and phosphorus sources and then releasing the single cells in colonies into the medium. Twenty-day culture of single cells in a 96-well plate resulted in 96% regeneration of colonies, and the regeneration of colonies was also confirmed on agar medium. This is the first report of colony regeneration from single cells of B. braunii. We believe that our method developed in this study will contribute greatly to the advancement of genetic modification techniques for B. braunii.

Oxidative Stress- and Autophagy-Inducing Effects of PSI-LHCI from Botryococcus braunii in Breast Cancer Cells

Botryococcus braunii (B. braunii) is a green microalga primarily found in freshwater, reservoirs, and ponds. Photosynthetic pigments from algae have shown many bioactive molecules with therapeutic potential. Herein, we report the purification, characterization, and anticancer properties of photosystem I light-harvesting complex I (PSI-LHCI) from the green microalga B. braunii UTEX2441. The pigment-protein complex was purified by sucrose density gradient and characterized by its distinctive peaks using absorption, low-temperature (77 K) fluorescence, and circular dichroism (CD) spectroscopic analyses. Protein complexes were resolved by blue native-PAGE and two-dimensional SDS-PAGE. Triple-negative breast cancer MDA-MB-231 cells were incubated with PSI-LHCI for all of our experiments. Cell viability was assessed, revealing a significant reduction in a time- and concentration-dependent manner. We confirmed the internalization of PSI-LHCI within the cytoplasm and nucleus after 12 h of incubation. Cell death mechanism by oxidative stress was confirmed by the production of reactive oxygen species (ROS) and specifically superoxide. Furthermore, we monitored autophagic flux, apoptotic and necrotic features after treatment with PSI-LHCI. Treated MDA-MB-231 cells showed positive autophagy signals in the cytoplasm and nucleus, and necrotic morphology by the permeabilization of the cell membrane. Our findings demonstrated for the first time the cytotoxic properties of B. braunii PSI-LHCI by the induction of ROS and autophagy in breast cancer cells.

Exopolysaccharides from the Energy Microalga Strain Botryococcus braunii: Purification, Characterization, and Antioxidant Activity

Botryococcus braunii, a prestigious energy microalga, has recently received widespread attention because it can secrete large amounts of exopolysaccharides (EPS) with potential applications in food, cosmetics, and nutraceuticals. Unfortunately, the insufficiency of research on the bioactivity and structure–activity relationship of B. braunii EPS has impeded the downstream applications. In the present study, alcohol precipitation, deproteinization, and DEAE-cellulose column chromatography were used to extract and purify B. braunii SCS-1905 EPS. It was found that B. braunii SCS-1905 EPS were high-molecular-weight heteropolysaccharides containing uronic acid (7.43–8.83%), protein (2.30–4.04%), and sulfate groups (1.52–1.95%). Additionally, the EPS primarily comprised galactose (52.34–54.12%), glucose (34.60–35.53%), arabinose (9.41–10.32%), and minor amounts of fucose (1.80–1.99%), with the presence of a pyranose ring linked by a β-configurational glycosidic bond. Notably, the antioxidant activity of crude exopolysaccharides (CEPS) was stronger, and the half maximal inhibitory concentration (IC₅₀) for ABTS and hydroxyl radicals was significantly lower than that of deproteinized exopolysaccharides (DEPS). Overall, this study indicated a potential application of B. braunii SCS-1905 EPS as a natural antioxidant. In summary, B. braunii EPS could be used as a potential feedstock for the production of antioxidant health foods.

In Silico and Cellular Differences Related to the Cell Division Process between the A and B Races of the Colonial Microalga Botryococcus braunii

Botryococcus braunii produce liquid hydrocarbons able to be processed into combustion engine fuels. Depending on the growing conditions, the cell doubling time can be up to 6 days or more, which is a slow growth rate in comparison with other microalgae. Few studies have analyzed the cell cycle of B. braunii. We did a bioinformatic comparison between the protein sequences for retinoblastoma and cyclin-dependent kinases from the A (Yamanaka) and B (Showa) races, with those sequences from other algae and Arabidopsis thaliana. Differences in the number of cyclin-dependent kinases and potential retinoblastoma phosphorylation sites between the A and B races were found. Some cyclin-dependent kinases from both races seemed to be phylogenetically more similar to A. thaliana than to other microalgae. Microscopic observations were done using several staining procedures. Race A colonies, but not race B, showed some multinucleated cells without chlorophyll. An active mitochondrial net was detected in those multinucleated cells, as well as being defined in polyphosphate bodies. These observations suggest differences in the cell division processes between the A and B races of B. braunii.

Exopolysaccharides from microalgae: production, characterization, optimization and techno-economic assessment

Microalgae cultivation for exopolysaccharide production has getting more attention as a result of their high hydrocarbon biosynthesis skill. The aim of this study is to examine the exopolysaccharide production potential of different species of microalgae. In this context, exopolysaccharides were produced from Chlorella minutissima, Chlorella sorokiniana and Botryococcus braunii microalgae and the effects of carbon and nitrogen content in the growth medium and illumination time on exopolysaccharide production were analyzed statistically using Box-Behnken experimental design. In addition, techno-economic assessment of exopolysaccharide production were also performed by using the most productive microalgae and optimum conditions determined in this study. As a result of the experiments, it was seen that C. minutissima, C. sorokiniana and B. braunii produced 0.245 ± 0.0025 g/L, 0.163 ± 0.0016 g/L and 0.117 ± 0.0007 g/L exopolysaccharide, respectively. Statistically, it was observed that there was an inverse relationship between the exopolysaccharide production and investigated parameters such as illumination period and carbon and nitrogen amounts of culture mediums. The techno-economic assessment comprising microalgal exopolysaccharide (EPS) bioprocess was carried out, and it showed that the system can be considered economically viable, yet can be improved with biorefinery approach.

Channeling of Carbon Flux Towards Carotenogenesis in Botryococcus braunii: A Media Engineering Perspective

Microalgae, due to their unique properties, gained attention for producing promising feedstocks having high contents of proteins, antioxidants, carotenoids, and terpenoids for applications in nutraceutical and pharmaceutical industries. Optimizing production of the high-value renewables (HVRs) in microalgae requires an in-depth understanding of their functional relationship of the genes involved in these metabolic pathways. In the present study, bioinformatic tools were employed for characterization of the protein-encoding genes of methyl erythritol phosphate (MEP) pathway involved in carotenoid and squalene biosynthesis based upon their conserved motif/domain organization. Our analysis demonstrates nearly 200 putative genes showing a conservation pattern within divergent microalgal lineages. Furthermore, phylogenomic studies confirm the close evolutionary proximity among these microalgal strains in the carotenoid and squalene biosynthetic pathways. Further analysis employing STRING predicts interactions among two rate-limiting genes, i.e., phytoene synthase (PSY) and farnesyl diphosphate farnesyl synthase (FPPS), which are specifically involved in the synthesis of carotenoids and squalene. Experimentally, to understand the carbon flux of these rate-limiting genes involved in carotenogenesis, an industrial potential strain, namely, Botryococcus braunii, was selected in this study for improved biomass productivity (i.e., 100 mg L^-1 D^-1) along with enhanced carotenoid content [0.18% dry cell weight (DCW)] when subjected to carbon supplementation. In conclusion, our approach of media engineering demonstrates that the channeling of carbon flux favors carotenogenesis rather than squalene synthesis. Henceforth, employing omics perspectives will further provide us with new insights for engineering regulatory networks for enhanced production of high-value carbon biorenewables without compromising growth.

Cobalt enrichment enhances the tolerance of Botryococcus braunii to high concentration of CO2

This work mainly studied B. braunii adapted to different CO₂ concentrations with cobalt enrichment, and developed a process for CO₂ capture, hydrocarbon production and cobalt removal. The results showed that B. braunii favored rapid growth at 5.0% (v/v) CO₂, and the highest biomass was 1.89 g.L^-1 with 4.5 mg.L^-1 of cobalt. Hydrocarbon productivity in high concentration CO₂ (5.0% and 10.0%) with cobalt enrichment was higher than that in Chu 13 medium. The change in cobalt removal efficiency mainly corresponded to the growth of B. braunii. The LCE of B. braunii in cobalt-rich with high CO₂ concentration (5.0% and 10.0%) was 15.7%, and 14.9%, respectively, which was higher than that in normal medium. CO₂ fixation rates were also higher in cobalt enrichment coupled with high CO₂ concentration. This study not only provides ideas for the removal of toxic metal cobalt, but also has great potential for CO₂ biofixation.

High-value chemicals from Botryococcus braunii and their current applications - A review

Botryococcus braunii is known for its high yield of extracellular hydrocarbons and polysaccharides. Hydrocarbons, especially botryococcenes and squalene can be used as not only fuels but also alternative feedstock for other fossil-based products. Exopolysaccharides excreted from B. braunii can be used as scaffolds for polyesters production, and have a notable potential for synthesis of nanoparticles. B. braunii is also a rich source of carotenoids, especially the unique secondary carotenoids such as botryoxanthins that have never been found in other microalgae. The morphology, physiology, and outer cell walls of B. braunii are complex. Understanding the colony structure shall provide insights into the mechanism of cell growth and chemicals secretion. It is possible to improve the production economics of the alga with advanced culture systems. Moreover, investigation of metabolic pathways for B. braunii may help us understand their regulation and provide valuable information for strain selection and optimal production of high-value chemicals.

Associated bacteria of Botryococcus braunii (Chlorophyta)

Botryococcus braunii (Chlorophyta) is a green microalga known for producing hydrocarbons and exopolysaccharides (EPS). Improving the biomass productivity of B. braunii and hence, the productivity of the hydrocarbons and of the EPS, will make B. braunii more attractive for industries. Microalgae usually cohabit with bacteria which leads to the formation of species-specific communities with environmental and biological advantages. Bacteria have been found and identified with a few B. braunii strains, but little is known about the bacterial community across the different strains. A better knowledge of the bacterial community of B. braunii will help to optimize the biomass productivity, hydrocarbons, and EPS accumulation. To better understand the bacterial community diversity of B. braunii, we screened 12 strains from culture collections. Using 16S rRNA gene analysis by MiSeq we described the bacterial diversity across 12 B. braunii strains and identified possible shared communities. We found three bacterial families common to all strains: Rhizobiaceae, Bradyrhizobiaceae, and Comamonadaceae. Additionally, the results also suggest that each strain has its own specific bacteria that may be the result of long-term isolated culture.

Effects of incident light intensity and light path length on cell growth and oil accumulation in Botryococcus braunii (Chlorophyta)

Botryococcus braunii was cultured in different light path length under different incident light intensity to investigate the effect of light on alga growth as well as hydrocarbon and fatty acid accumulation. Results indicated that longer light path length required higher incident light intensity in order to meet the light requirement of algal growth and hydrocarbon accumulation during the course of cultivation. However, hydrocarbon profile was only affected by the incident light intensity and not influenced by the light path length. High incident light intensity enhanced the accumulation of hydrocarbons with longer carbon chains. Besides, the fatty acid content and profiles were significantly influenced by both incident light intensity and light path. Higher fatty acid content and higher percentage of C18 and monounsaturated fatty acid components were achieved at the higher incident light intensity and lower light path length. Taken together, these results are benefit to improve its biomass and oil productivity through the optimization of light and photobioreactor design.

Comparative transcriptome analyses of oleaginous Botryococcus braunii race A reveal significant differences in gene expression upon cobalt enrichment

BACKGROUND

Botryococcus braunii is known for its high hydrocarbon content, thus making it a strong candidate feedstock for biofuel production. Previous study has revealed that a high cobalt concentration can promote hydrocarbon synthesis and it has little effect on growth of B. braunii cells. However, mechanisms beyond the cobalt enrichment remain unknown. This study seeks to explore the physiological and transcriptional response and the metabolic pathways involved in cobalt-induced hydrocarbon synthesis in algae cells.

RESULTS

Growth curves were similar at either normal or high cobalt concentration (4.5 mg/L), suggesting the absence of obvious deleterious effects on growth introduced by cobalt. Photosynthesis indicators (decline in Fv/Fm ratio and chlorophyll content) and reactive oxygen species parameters revealed an increase in physiological stress in the high cobalt concentration. Moreover, cobalt enrichment treatment resulted in higher crude hydrocarbon content (51.3% on day 8) compared with the control (43.4% on day 8) throughout the experiment (with 18.2% improvement finally). Through the de novo assembly and functional annotation of the B. braunii race A SAG 807-1 transcriptome, we retrieved 196,276 non-redundant unigenes with an average length of 1086 bp. Of the assembled unigenes, 89,654 (45.7%), 42,209 (21.5%), and 32,318 (16.5%) were found to be associated with at least one KOG, GO, or KEGG ortholog function. In the early treatment (day 2), the most strongly upregulated genes were those involved in the fatty acid biosynthesis and metabolism and oxidative phosphorylation, whereas the most downregulated genes were those involved in carbohydrate metabolism and photosynthesis. Genes that produce terpenoid liquid hydrocarbons were also well identified and annotated, and 21 (or 29.2%) were differentially expressed along the cobalt treatment.

CONCLUSIONS

Botryococcus braunii SAG 807-1 can tolerate high cobalt concentration and benefit from hydrocarbon accumulation. The time-course expression profiles for fatty acid biosynthesis, metabolism, and TAG assembly were obtained through different approaches but had equally satisfactory results with the redirection of free long-chain fatty acid and VLCFA away from TAG assembly and oxidation. These molecules served as precursors and backbone supply for the fatty acid-derived hydrocarbon accumulation. These findings provide a foundation for exploiting the regulation mechanisms in B. braunii race A for improved photosynthetic production of hydrocarbons.

Effects of limonene, n-decane and n-decanol on growth and membrane fatty acid composition of the microalga Botryococcus braunii

Botryococcus braunii is a promising microalga for the production of biofuels and other chemicals because of its high content of internal lipids and external hydrocarbons. However, due to the very thick cell wall of B. braunii, traditional chemical/physical downstream processing very often is not as effective as expected and requires high amounts of energy. In this cases, the application of two-phase aqueous-organic solvent systems could be an alternative to cultivate microalgae allowing for a simultaneous extraction of the valuable compounds without significant negative effects on cell growth. Two-phase systems have been applied before, however, there are no studies so far on the mechanisms used by microalgae to survive in contact with solvents present as a second-phase. In this study, the effects of the solvents limonene, n-decane and n-decanol on growth of the microalga B. braunii as well as the adaptive cell response in terms of their phospholipid fatty acid contents were analized. A concentration-dependent negative effect of all three solvents on cell growth was observed. Effects were accompanied by changes of the membrane fatty acid composition of the alga as manifested by a decrease of the unsaturation . In addition, an association was found between the solvent hydrophobicity (given as log octanol–water partition coefficient (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\text {P}_{O-W}$$\end{document}PO-W) values) and their toxic effects, whereby n-decanol and n-decane emerged as the most and least toxic solvent respectively. Among the tested solvents, the latter promises to be the most suitable for a two-phase extraction system.

Docking analysis of models for 4-hydroxy-3-methylbut-2-enyl diphosphate reductase and a ferredoxin from Botryococcus braunii, race B

The green microalga Botryococcus braunii Showa, which produces large amounts of triterpene hydrocarbons, exclusively uses the 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway for isoprenoid biosyntheses, and the terminal enzyme in this pathway, 4-hydroxy-3-methylbut-2-enyl diphosphate reductase (HDR), is regarded as a light-dependent key regulatory enzyme. In order to investigate the possible association of HDR and ferredoxin in this organism, we constructed tertiary structure models of B. braunii HDR (BbHDR) and one of ferredoxin families in the alga, a photosynthetic electron transport F (BbPETF)-like protein, by using counterparts from E. coli and Chlamydomonas reinhardtii as templates, respectively, and performed docking analysis of these two proteins. After docked models are superimposed onto their counterpart proteins in a non-photosynthetic organism, Plasmodium falciparum, the BbPETF-like protein comes in contact with the backside of BbHDR, which was defined in a previous report (Rekittke et al. 2013), and the distance of the two Fe-S centers is 14.7 Å. This distance is in almost the same level as that for P. falicarum, 12.6 Å. To our knowledge, this is the first model suggesting the possible association of HDR with a ferredoxin in O₂-evolving photosynthetic organisms.

Isolation and characterization of 4-hydroxy-3-methylbut-2-enyl diphosphate reductase gene from Botryococcus braunii, race B

The B race of a green microalga Botryococcus braunii Kützing produces triterpene hydrocarbons that is a promising source for biofuel. In this algal race, precursors of triterpene hydrocarbons are provided from the 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway. The terminal enzyme of this pathway, 4-hydroxy-3-methylbut-2-enyl diphosphate reductase (HDR) is regarded as one of the key enzymes that affect yields of products in terpene biosynthesis. In order to better understand the MEP pathway of the alga, cDNA and genomic clones of HDR were obtained from B. braunii Showa strain. B. braunii HDR (BbHDR) is encoded on a single copy gene including a 1509-bp open reading frame that was intervened by 6 introns. The exon-intron structure of BbHDR genes did not show clear relation to phylogeny, while its amino acid sequence reflected phyla and classes well. BbHDR sequence was distinctive from that of the HDR protein from Escherichia coli in the residues involved in hydrogen-bond network that surrounds substrate. Introduction of BbHDR cDNA into an E. coli HDR deficient mutant resulted in recovery of its auxotrophy. BbHDR expression level was upregulated from the onset of liquid culture to the 24th day after inoculation with a 2.5-fold increase and retained its level in the subsequent period.

Effects of hydrostatic pressure and supercritical carbon dioxide on the viability of Botryococcus braunii algae cells

In bio-based industries, Botryococcus braunii is identified as a potential resource for production of hydrocarbons having a wide range of applications in chemical and biopolymer industries. For a sustainable production platform, the algae cultivation should be integrated with downstream processes. Ideally the algae are not harvested, but the product is isolated while cultivation and growth is continued especially if the doubling time is slow. Consequently, hydrocarbons can be extracted while keeping the algae viable. In this study, the effects of pressure on the viability of B. braunii cells were tested hydrostatically and under supercritical CO₂ conditions. Viability was determined by light microscopy, methylene blue uptake and by re-cultivation of the algae after treatments to follow the growth. It was concluded that supercritical CO₂ was lethal to the algae, whereas hydrostatic pressure treatments up to 150 bar have not affected cell viability and recultivation was successful.

Light-harvesting complexes of Botryococcus braunii

The colonial green alga Botryococcus braunii (BB) is a potential source of biofuel due to its natural high hydrocarbon content. Unfortunately, its slow growth limits its biotechnological potential. Understanding its photosynthetic machinery could help to identify possible growth limitations. Here, we present the first study on BB light-harvesting complexes (LHCs). We purified two LHC fractions containing the complexes in monomeric and trimeric form. Both fractions contained at least two proteins with molecular weight (MW) around 25 kDa. The chlorophyll composition is similar to that of the LHCII of plants; in contrast, the main xanthophyll is loroxanthin, which substitutes lutein in most binding sites. Circular dichroism and 77 K absorption spectra lack typical differences between monomeric and trimeric complexes, suggesting that intermonomer interactions do not play a role in BB LHCs. This is in agreement with the low stability of the BB LHCII trimers as compared to the complexes of plants, which could be related to loroxanthin binding in the central (L1 and L2) binding sites. The properties of BB LHCII are similar to those of plant LHCII, indicating a similar pigment organization. Differences are a higher content of red chlorophyll a, similar to plant Lhcb3. These differences and the different Xan composition had no effect on excitation energy transfer or fluorescence lifetimes, which were similar to plant LHCII.

3D reconstruction of endoplasmic reticulum in a hydrocarbon-secreting green alga, Botryococcus braunii (Race B)

Based on 3D sections through cells of Botryococcus braunii, the structure of three domains of endoplasmic reticulum, and their spatial and functional relationships to other organelles are clarified. Oil production by photosynthetic microalgae has attracted attention since these oils can be converted into renewable, carbon-neutral fuels. The green alga B. braunii accumulates large amounts of hydrocarbons, 30-50% of cell dry weight, in extracellular spaces rather than its cytoplasm. To advance the knowledge of hydrocarbon biosynthesis and transport pathways in this alga, we utilized transmission EM combined with rapid freezing and image reconstruction. We constructed detailed 3D maps distinguishing three ER domains: rdER with ribosomes on both sides, rsER with ribosomes on one side, and sER without ribosomes. The rsER and sER domains were especially prominent during the oil body formation and oil secretion stages. The ER contacted the chloroplasts, oil bodies, or plasma membrane via the rsER domains, oriented with the ribosome-free surface facing the organelles. We discuss the following transport pathway for hydrocarbons and their precursors in the cytoplasm: chloroplast → endoplasmic reticulum (ER) → oil bodies → ER → plasma membrane → secretion. This study represents the first 3D study of the three-domain classification (rdER, rsER and sER) of the ER network among eukaryotic cells. Finally, we propose the novel features of the ERs in plant cells that are distinct from the latest proposed model for the ERs in mammalian cells.

Modulation of Neurogenesis through the Promotion of Energy Production Activity Is behind the Antidepressant-Like Effect of Colonial Green Alga, Botryococcus braunii

Algae have been recognized as important resources providing functional components due to their capacity to exert beneficial effects on health. Therefore, there is increasing interest in investigating the biological activity of algae. In this study, we evaluated the antidepressant-like effect of the administration of 100 mg/kg/day of the ethanol extract of colonial green alga Botryococcus braunii (EEB) for 14 consecutive days in the forced swimming test (FST)-induced depression in imprinting control region (ICR) mice. Imipramine, a commercial antidepressant drug, was used as a positive control. In addition, we investigated the molecular mechanisms underlying the effect of EEB by measuring ATP production and by assessing any change in gene expression at the end of the treatment using real-time polymerase chain reaction (PCR) and microarray assays. We showed that the immobility time in the water-administered control (FST stress) group gradually increased from day 1 to day 14. However, treatment with EEB caused a significant decrease of immobility time in the FST compared with that in the FST stress group. Microarray and real-time PCR results revealed that EEB treatment induced variation in the expression of several genes associated with neurogenesis, energy metabolism, and dopamine synthesis. Interestingly, we revealed that only EEB treatment enhanced the promotion of energy production, while treatment with imipramine was ineffective. Our study provides the first evidence that B. braunii enhances energy production, which may contribute to the modulation of neurogenesis and to the enhancement of dopaminergic function, in turn potentially underlying the antistress- and antidepressant-like effects that we observed.

ROS Detection in Botryococcus braunii Colonies with CellROX Green Reagent

We analyzed the reactive oxygen species (ROS) accumulation in the colony-forming green microalga Botryococcus braunii in response to several stress inducers such as NaCl, NaHCO₃, salicylic acid (SA), methyl jasmonate, and acetic acid. A staining assay using the fluorescent dye CellROX Green was used. CellROX Green is a fluorogenic probe used for measuring oxidative stress in live cells. The dye is weakly fluorescent inside cells in a reduced state but exhibits bright green photostable fluorescence upon oxidation by ROS and subsequent binding to DNA. The large amount of liquid hydrocarbons produced and excreted by B. braunii, creates a highly hydrophobic extracellular environment that makes difficult to study short times defense responses on this microalga. The procedure developed here allowed us to detect ROS in this microalga even within a short period of time (in minutes) after treatment of cells with different stress inducers.

Molecular cloning and functional characterization of NADPH-dependent cytochrome P450 reductase from the green microalga Botryococcus braunii, B race

The green microalga Botryococcus braunii of the B race accumulates various lipophilic compounds containing a 10,11-oxidosqualene epoxide moiety in addition to large amounts of triterpene hydrocarbons. While 2,3-squalene epoxidases have already been isolated and characterized from the alga, the enzyme that catalyzes the 10,11-epoxidation of squalene has remained elusive. In order to obtain a molecular tool to explore a 10,11-squalene epoxidase, cDNA cloning of an NADPH-dependent cytochrome P450 reductase (CPR) that is required by both squalene epoxidases and cytochrome P450 enzymes was carried out. The isolated cDNA contained an open reading frame (1998 bp) that encoded for a protein with 665 amino acid residues with a predicted molecular weight of 71.46 kDa and a theoretical pI of 5.49. Analysis of the deduced amino acid sequence revealed the presence of conserved motifs, including FMN, FAD, and NADPH binding domains, which are typical of other CPRs and necessary for enzyme activity. By truncation of the N-terminal transmembrane anchor and addition of a 6× His-tag, BbCPR was heterologously produced in Escherichia coli and purified by Ni-NTA affinity chromatography. The purified recombinant enzyme showed optimal reducing activity of cytochrome c at around a neutral pH at a temperature range of 30-37°C. For steady state kinetic parameters, the recombinant enzyme had a k_m for cytochrome c and NADPH of 11.7±1.6 and 9.4±1.4 μM, and a k_cat for cytochrome c and NADPH of 2.78±0.09 and 3.66±0.11 μmol/min/mg protein, respectively. This is the first study to perform the functional characterization of a CPR from eukaryotic microalgae.

Toxicity and bioremediation of As(III) and As(V) in the green microalgae Botryococcus braunii: A laboratory study

Worldwide threats of fuel shortages in the near future and climate change because of greenhouse gas emissions are posing severe challenges and therefore it is vital to search for sustainable ways of preventing the consequences. The dual use of microalgae for phycoremediation and biomass production for sustainable biofuel production is a viable choice. Phycoremediation of As(III) and As(V) ions using microalgae was investigated in a two-staged batch reactor. Accumulation and toxicity of inorganic arsenic forms (As(III) and As(V)) to green microalgae Botryococcus braunii depend on environmental factors. Dissolved oxygen and pH cycles did not significantly differ due to the absence or presence of arsenic (either As(III) or As(V)) ions in the culture. Monod model was utilized for representing the growth kinetics of microalgae in pure media containing various concentrations of nitrate ions. Maximum specific growth rate and saturation constant were found to be 0.14788 d^-1 and 0.00105 g/L, respectively. With the increase in concentration of phosphate in growth medium, the growth of microalgae increased. Media with NaCl (1.0 g/L) and NaHCO₃ (1 g/L) resulted in higher maximum biomass concentration. Effect of coexisting ions on phycoremediation of As(III) and As(V) ions using microalgae was studied.

[Coupling of Hydrocarbon Accumulation and Cobalt Removal During Treatment of Cobalt Enriched Industrial Wastewater with Botryococcus braunii Biofilm Attached Cultivation]

Industrial wastewater pollution is an increasing problem. The wastewater infiltrated cobalt is a key to purify wastewater because it is seriously hazardous and hard to treat. Traditional management method of heavy metals in industrial wastewater is difficult to apply. To seek for "green ecological" feasible approaches of industrial wastewater treatment, this paper studied the effect of industrial wastewater containing cobalt on the growth and hydrocarbon accumulation of Botryococcus braunii SAG 807-1 with biofilm attached cultivation. The research results obtained were as follows:B.braunii with biofilm attached cultivation could treat industrial wastewater, and 4.5 mg·L^-1 cobalt could accelerate the accumulation of hydrocarbon while having little influence on the growth of B.braunii, the ability of B.braunii with biofilm attached cultivation to remove Co²⁺ from industrial wastewater was 1473.9 μmol·g^-1, which was much higher than the report of P. littoralis culture. Through the study in this paper, the theoretical basis for the coupling of production of green high energy fuel hydrocarbon and industrial wastewater treatment was established.

Enhancement of pigment extraction from B. braunii pretreated using CO2 rapid depressurization

Extraction of compounds from microalgae requires cell disruption as a pretreatment to increase extraction yield. Botryococcus braunii is a microalga with a significant content of carotenoids and other antioxidant compounds, such as chlorophylls. Cell disruption of B. braunii using CO₂ rapid depressurization was studied as a pretreatment for the extraction of carotenoid and chlorophyll pigments. We studied the effect of temperature (21–49 °C) and pressure (6–13 MPa) during static compression on pigment recovery with supercritical CO₂ at 40 °C, 30 MPa and solvent flow of 4.7 L NPT/min. Within the experimental region, the extraction yield of carotenoids and chlorophylls increased by 2.4- and 2.2-fold respectively. Static compression conditions of high pressure and low temperature increased the extraction of carotenoids and especially chlorophylls. We selected 21 °C and 13 MPa as the cell disruption condition, which produced 1.91 g/kg d.s. of carotenoids and 14.03 mg/kg d.s. of chlorophylls. Pretreated microalga gave a 10-fold higher chlorophyll extraction yield compared to the untreated sample. While for carotenoids and tocopherols were 1.25 and 1.14-fold higher, respectively. Additionally, antioxidant activity of pretreated microalga (33.22 mmol TE/kg oil) was significantly higher than the value for the untreated samples (29.11 mmol TE/kg oil) (p ≤ 0.05). Confocal microscopy images showed morphological differences between micro-colonies with and without disruption treatment, suggesting that partial cell disruption by rapid depressurization improved the extraction of microalga compounds.

The use of artificial neural network for modelling of phycoremediation of toxic elements As(III) and As(V) from wastewater using Botryococcus braunii

In the present study, a thorough investigation has been done on the removal efficiency of both As(III) and As (V) from synthetic wastewater by phycoremediation of Botryococcus braunii algal biomass. Artificial neural networks (ANNs) are practised for predicting % phycoremediation efficiency of both As(III) and As(V) ions. The influence of several parameters for example initial pH, inoculum size, contact time and initial arsenic concentration (either As(III) or As(V)) was examined systematically. The maximum phycoremediation of As(III) and As(V) was found to be 85.22% and 88.15% at pH9.0, equilibrium time of 144h by using algal inoculum size of 10% (v/v) and initial arsenic concentration of 50mg/L. The data acquired from laboratory scale experimental set up was utilized for training a three-layer feed-forward back propagation (BP) with Levenberg-Marquardt (LM) training algorithm having 4:5:1 architecture. A comparison between the experimental data and model outputs provided a high correlation coefficient (R(2)all_ANN equal to 0.9998) and exhibited that the model was capable for predicting the phycoremediation of both As(III) and As(V) from wastewater. The network topology was optimized by changing number of neurons in hidden layers. ANNs are efficient to model and simulate highly non-liner multivariable relationships. Absolute error and Standard deviation (SD) with respect to experimental output were calculated for ANN model outputs. The comparison of phycoremediation efficiencies of both As(III) and As(V) between experimental results and ANN model outputs exhibited that ANN model can determine the behaviour of As(III) and As(V) elimination process under various circumstances.

Nitrogen deprivation-induced de novo transcriptomic profiling of the oleaginous green alga Botryococcus braunii 779

To assess the effect of nitrogen deprivation (ND), a moderately growing A-race Botryococcus braunii subisolate 779 was subjected to nitrogen deprivation for 3 days. De novo transcriptome was assembled and annotated by using Trinity software and Basic Local Alignment Search Tools (BLAST), respectively. Comparative analysis indicates that transcriptomes of A-races differ from those of B-races. Furthermore, majority of the homologous ESTs in A-race but not B-race transcriptomes were unknown sequences. Upon ND, level of photosynthetic transcripts, but not photosynthetic efficiency was downregulated. Unlike hydrocarbon contents, ESTs involved in hydrocarbon biosynthesis were not upregulated. Taken together, our results imply that A- and B-races belong to different B. braunii subspecies. Upon ND, excess photosynthetic transcripts are recycled for nitrogen; and hydrocarbon accumulation is not via de novo biosynthesis. Here we describe in details the data contents and analytic methodologies associated with the data uploaded to Gene Expression Omnibus (accession number GSE71296).

Bio-harvesting and pyrolysis of the microalgae Botryococcus braunii

The microalgae Botryococcus braunii is widely recognized as a potentially important biofuel-feedstock whose commercial exploitation is limited by difficulties with its cultivation and harvesting. In this study, two B. braunii strains, Kossou-4 and Overjuyo-3 were successfully cultured at a 500 l-scale for 60-days. Harvesting by bio-flocculation with Aspergillus fumigatus at an optimum ratio of 1:40 of fungus to microalgal culture resulted in up to 98% recovery of biomass in the two strains. Ultimate analysis (C, N, H, S, ash, high heating value) and pyrolysis (analytical and preparative pyrolysis and GC-MS assays) showed that co-harvesting with fungi did not cause any impairment of the feedstock value of the microalgal biomass. This work represents the first report on the successful culturing and harvesting of these strains at a 500 l-scale using bio-flocculation. The use of A. fumigatus represents an efficient and economical method for the harvest of B. braunii for biofuel production.

Catalytic gasification of oil-extracted residue biomass of Botryococcus braunii

Catalytic gasification of the oil-extracted residue biomass of Botryococcus braunii was demonstrated in a laboratory-scale continuous feeding dual bed reactor. Steam gasification at 1023 K over Ni-Fe/Mg/Al catalyst can completely reform tar derived from pyrolysis of the residue biomass into C1 gases and hydrogen, and has achieved 91%-C conversion to gaseous product (CO+CO2+CH4). Composition of product gas has higher contents of CO and H2 with their ratio (H2/CO) of around 2.4 which is slightly H2-rich syngas. Maximum hydrogen yield of 74.7 mmol g-biomass(-1) obtained in this work is much higher than that from gasification of other algal biomass reported in literature. The residue biomass of B. braunii can be a superior renewable source of syngas or hydrogen.

Transcriptomic analysis of a moderately growing subisolate Botryococcus braunii 779 (Chlorophyta) in response to nitrogen deprivation

BACKGROUND

The colonial microalga Botryococcus braunii has been brought to people's attention for its conspicuous ability to accumulate a variety of lipids including hydrocarbons. B. braunii strains are classified into 3 races based on the types of hydrocarbons. A and B races are known to accumulate high level of lipids. However, their extreme slow growth rate has impeded its application for renewable biofuel production.

RESULTS

In this study, we report the transcriptomic response of a moderately growing subisolate from the culture of Botryococcus sp. CCALA-779 upon nitrogen deprivation (ND). We show that the subisolate has an average growth rate of 0.52 g l(-1) day(-1) under photoautotrophic growth conditions and lipid content is enhanced to 75 % of CDW upon ND. Both rDNA sequence and hydrocarbon composition analyses indicate that the subisolate belongs to A race B. braunii. Hence, it is designated as B. braunii 779. We show that B. braunii 779 transcriptome shares homology to majority of the A race but not B race B. braunii ESTs, suggesting that transcriptomes of A race differ from that of B race. We found that many homologous ESTs between A races 779 and Bot-88 are unknown sequences, implying that A race contains many unknown genes. Pathway-based transcriptomic analysis indicates that energy metabolisms are among the top expressed functions in log-phase cells, indicating that the slow growth rate is a result that energy flow is directed to lipid biosynthesis but not population growth. Upon ND, reconfiguration of metabolisms for reducing power is apparent, suggesting that B. braunii 779 is rapidly adapting under ND condition by transcriptomic reprogramming.

CONCLUSIONS

Taken together, our result shows that the subisolate B. braunii 779, similar to the Gottingen strain, is useful for biofuel production. Difference between transcriptomes of A and B races implies that different races of B. braunii strains belong to different sub-species. Furthermore, there are many novel genes that are unique to A race, suggesting that sequences of many enzymes involved in hydrocarbon biosynthesis are not currently known. We propose that B. braunii transcriptomes provide a rich source for discovery of novel genes involved in hydrocarbon biosynthesis.

Complete mitochondrial genome of a hydrocarbon-producing green alga Botryococcus braunii strain Showa

Complete mitochondrial genome of Botryococcus braunii strain Showa was assembled and annotated. It contains 31 protein-coding genes, 23 tRNA genes and 3 rRNA (23S, 16S, 5S rRNA) genes. The 31 protein-coding genes include 5 atp genes, 3 cox genes, 9 nad genes, 12 ribosomal protein genes, cob and tatC genes. The presence of extra non-coding regions makes it currently the largest mitochondrial genome in Trebouxiophyceae. Phylogenetic analysis showed Botryococcus braunii strain Showa clustered into Trebouxiophyceae clade and had close genetic relationship with algae Coccomyxa sp. C-169.

Extraction of lipids from microalgae using CO2-expanded methanol and liquid CO2

The use of CO2-expanded methanol (cxMeOH) and liquid carbon dioxide (lCO2) is proposed to extract lipids from Botryococcus braunii. When compressed CO2 dissolves in methanol, the solvent expands in volume, decreases in polarity and so increases in its selectivity for biodiesel desirable lipids. Solid phase extraction of the algal extract showed that the cxMeOH extracted 21 mg of biodiesel desirable lipids per mL of organic solvent compared to 3mg/mL using either neat methanol or chloroform/methanol mixture. The non-polar lCO2 showed a high affinity for non-polar lipids. Using lCO2, it is possible to extract up to 10% neutral lipids relative to the mass of dry algae. Unlike extractions using conventional solvents, these new methods require little to no volatile, flammable, or chlorinated organic solvents.

Biodiesel synthesis by direct transesterification of microalga Botryococcus braunii with continuous methanol reflux

Direct transesterification of Botryococcus braunii with continuous acyl acceptor reflux was evaluated. This method combines in one step lipid extraction and esterification/transesterification. Fatty acid methyl esters (FAME) synthesis by direct conversion of microalgal biomass was carried out using sulfuric acid as catalyst and methanol as acyl acceptor. In this system, once lipids are extracted, they are contacted with the catalyst and methanol reaching 82%wt of FAME yield. To optimize the reaction conditions, a factorial design using surface response methodology was applied. The effects of catalyst concentration and co-solvent concentration were studied. Hexane was used as co-solvent for increasing lipid extraction performance. The incorporation of hexane in the reaction provoked an increase in FAME yield from 82% (pure methanol) to 95% when a 47%v/v of hexane was incorporated in the reaction. However, the selectivity towards non-saponifiable lipids such as sterols was increased, negatively affecting biodiesel quality.

Effect of cobalt enrichment on growth and hydrocarbon accumulation of Botryococcus braunii with immobilized biofilm attached cultivation

The effects of cobalt enrichment on the growth and hydrocarbon accumulation were studied with biofilm attached cultivation. Under biofilm attached cultivation conditions, the microalga Botryococcus braunii survived high concentration of cobalt (50× normal level). The crude hydrocarbon content as well as the long C chain component (C31) increased under Co enrichment treatment indicating the activity of key enzyme that catalyze hydrocarbon synthesis might be enhanced by Co enrichment. The reduced carbohydrate and protein contents accompanied by increased hydrocarbon content for Co enrichment treatment indicating the Co was also an effective factor that controls the carbon flow of B. braunii. Under Co enrichment treatment, totally 1473.9 μmol of Co element was consumed to produce one gram of algal biomass, indicating this attached cultivation method is high efficient in heavy metal elements removal.

Botryococcus braunii cells: ultrasound-intensified outdoor cultivation integrated with in situ magnetic separation

An integrated system combining ultrasound-intensified outdoor cultivation of Botryococcus braunii with in situ magnetic harvesting of the algal cells was developed. The algal cells were cultivated in 200 L plastic bag reactors, and seven five-minute ultrasonic treatments at a four-day interval using a fixed frequency of 40 kHz and a total power of 300 W improved algal cell biomass and hydrocarbon productivity. The algal cells were harvested using functional magnetic particles and a magnetic separator, and a recovery efficiency of 90% was obtained under continuous operation at a flow rate of 100mL/min using the in situ magnetic separation system. The overall production cost using the integrated system was US$ 25.14 per kilogram of B. braunii dry biomass. The system developed in this study provides a base for the industrial production of B. braunii.

Effects of nitrogen source and nitrogen supply model on the growth and hydrocarbon accumulation of immobilized biofilm cultivation of B. braunii

The immobilized biofilm cultivation was a promising method to greatly improve the biomass productivity of microalga Botryococcus braunii, which was considered as an feedstock of renewable biofuel. In this research, the effects of different nitrogen sources and supply methods on growth and hydrocarbon production of B. braunii under immobilized biofilm cultivation (attached cultivation) were studied. Of the total 5 different nitrogen sources, NaNO₃ was selected as the best one with which the high biomass productivity and hydrocarbon productivity of 6.45 gm(-2)d(-1) and 2.79 gm(-2)d(-1) were obtained respectively. The optimized nitrogen concentration was 0.99 mM for non-circulating medium supply model, while for the circulating model, the optimized nitrogen concentration as well as medium volume was 1.49 mM and 1.2L, respectively. Furthermore, nitrogen inputs based on growth of 1 kg dry algae biomass was only 28.92 g with circulating model. Attached cultivation was high efficient in light, nutrient and water utilization.

Culture of the green microalga Botryococcus braunii Showa with LED irradiation eliminating violet light enhances hydrocarbon production and recovery

The green microalga Botryococcus braunii (B. braunii), race B, was cultured under light-emitting diode (LED) irradiation with and without violet light. This study examined the effect of violet light on hydrocarbon recovery and production in B. braunii. C34 botryococcene hydrocarbons were efficiently extracted by thermal pretreatments at lower temperatures when the alga was cultured without violet light. The hydrocarbon content was also higher (approximately 3%) in samples cultured without violet light. To elucidate the mechanism of effective hydrocarbon recovery and production, we examined structural components of the extracellular matrix (ECM). The amounts of extracellular carotenoids and water-soluble polymers extracted by thermal pretreatment from the ECM were decreased when the alga was cultured without violet light. These results indicate that LED irradiation without violet light is more effective for hydrocarbon recovery and production in B. braunii. Furthermore, structural ECM components are closely involved in hydrocarbon recovery and production in B. braunii.

Desiccation tolerance of Botryococcus braunii (Trebouxiophyceae, Chlorophyta) and extreme temperature tolerance of dehydrated cells

Botryococcus braunii Kützing, a green colonial microalga, occurs worldwide in both freshwater and brackish water environments. Despite considerable attention to B. braunii as a potential source of renewable fuel, many ecophysiological properties of this alga remain unknown. Here, we examined the desiccation and temperature tolerances of B. braunii using two newly isolated strains BOD-NG17 and BOD-GJ2. Both strains survived through 6- and 8-month desiccation treatments but not through a 12-month treatment. Interestingly, the desiccation-treated cells of B. braunii gained tolerance to extreme temperature shifts, i.e., high temperature (40 °C) and freezing (-20 °C). Both strains survived for at least 4 and 10 days at 40 and -20 °C, respectively, while the untreated cells barely survived at these temperatures. These traits would enable long-distance dispersal of B. braunii cells and may account for the worldwide distribution of this algal species. Extracellular substances such as polysaccharides and hydrocarbons seem to confer the desiccation tolerance.