Transformation of lipid bodies related to hydrocarbon accumulation in a green alga, Botryococcus braunii (Race B)

A bioprocess engineering approach for the production of hydrocarbons and fatty acids from green microalga under high cobalt concentration as the feedstock of high-grade biofuels

Botryococcus braunii, a colonial green microalga which is well-known for its capacity to synthesize hydrocarbons, has significant promise as a long-term source of feedstock for the generation of biofuels. However, cultivating and scaling up B. braunii using conventional aqua-suspended cultivation systems remains a challenge. In this study, we optimized medium components and light intensity to enhance lipid and hydrocarbon production in a multi-cultivator airlift photobioreactor. BBM 3N medium with 200 μmol/m2/s light intensity and a 16 h light-8 h dark regimen yielded the highest biomass productivity (110.00 ± 2.88 mg/L/day), as well as the highest lipid and hydrocarbon content. Cultivation in a flat-panel bioreactor resulted in significantly higher biomass productivity (129.11 ± 2.74 mg/L/day), lipid productivity (32.21 ± 1.31 mg/L/day), and hydrocarbon productivity (28.98 ± 2.08 mg/L/day) compared to cultivation in Erlenmeyer flasks and open 20-L raceway pond. It also exhibited 20.15 ± 1.03% of protein content including elevated levels of chlorophyll a, chlorophyll b, and carotenoids. This work is noteworthy since it is the first to describe fatty acid and hydrocarbon profiles of B. braunii during cobalt treatment. The study demonstrated that high cobalt concentrations (up to 5 mg/L of cobalt nitrate) during Botryococcus culture affected hydrocarbon synthesis, resulting in high amounts of n-alkadienes and trienes as well as lipids with elevated monounsaturated fatty acids concentration. Furthermore, pyrolysis experiments on microalgal green biomass and de-oiled biomass revealed the lipid and hydrocarbon compounds generated by the thermal degradation of B. braunii that facilitate extra economical value to this system.

Extraction and Separation of Natural Products from Microalgae and Other Natural Sources Using Liquefied Dimethyl Ether, a Green Solvent: A Review

Microalgae are a sustainable source for the production of biofuels and bioactive compounds. This review discusses significant research on innovative extraction techniques using dimethyl ether (DME) as a green subcritical fluid. DME, which is characterized by its low boiling point and safety as an organic solvent, exhibits remarkable properties that enable high extraction rates of various active compounds, including lipids and bioactive compounds, from high-water-content microalgae without the need for drying. In this review, the superiority of liquefied DME extraction technology for microalgae over conventional methods is discussed in detail. In addition, we elucidate the extraction mechanism of this technology and address its safety for human health and the environment. This review also covers aspects related to extraction equipment, various applications of different extraction processes, and the estimation and trend analysis of the Hansen solubility parameters. In addition, we anticipate a promising trajectory for the expansion of this technology for the extraction of various resources.

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.

Humic lakes with inefficient and efficient transfer of matter in planktonic food webs

Humic compounds and related factors are the main constraints for the development of zooplankton in humic lakes, leading to low transfer efficiency in food webs. The results of this study indicated that some zooplankton species could have an advantage under these conditions. We found that the mass development of omnivorous Asplanchna priodonta in temperate humic lakes could be caused by the domination of high nutritional algae such as Gonyostomum semen and Botryococcus braunii. These algae are too large for most zooplankton to ingest, but A. priodonta can feed on a wide range of particles and benefit from this high-nutritional food. Small cladocerans (Ceriodaphnia, Bosmina) might be favored when picoplankton and small algae-dominate humic lakes. Therefore, some zooplankton species could have an advantage and control the development of phytoplankton, leading to the effective transfer of matter and energy in the planktonic food web in humic lakes.

Elucidation of the Potential Hair Growth-Promoting Effect of Botryococcus terribilis, Its Novel Compound Methylated-Meijicoccene, and C32 Botryococcene on Cultured Hair Follicle Dermal Papilla Cells Using DNA Microarray Gene Expression Analysis

A person’s quality of life can be adversely affected by hair loss. Microalgae are widely recognized for their abundance and rich functional components. Here, we evaluated the hair growth effect of a green alga, Botryococcus terribilis (B. terribilis), in vitro using hair follicle dermal papilla cells (HFDPCs). We isolated two types of cells from B. terribilis—green and orange cells, obtained from two different culture conditions. Microarray and real time-PCR results revealed that both cell types stimulated the expression of several pathways and genes associated with different aspect of the hair follicle cycle. Additionally, we demonstrated B. terribilis’ effect on collagen and keratin synthesis and inflammation reduction. We successfully isolated a novel compound, methylated-meijicoccene (me-meijicoccene), and C32 botryococcene from B. terribilis to validate their promising effects. Our study revealed that treatment with the two compounds had no cytotoxic effect on HFDPCs and significantly enhanced the gene expression levels of hair growth markers at low concentrations. Our study provides the first evidence of the underlying hair growth promoting effect of B. terribilis and its novel compound, me-meijicoccene, and C32 botryococcene.

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.

Detection of the oil-producing microalga Botryococcus braunii in natural freshwater environments by targeting the hydrocarbon biosynthesis gene SSL-3

The green microalga Botryococcus braunii produces hydrocarbon oils at 25-75% of its dry weight and is a promising source of biofuel feedstock. Few studies have examined this species' ecology in natural habitats, and few wild genetic resources have been collected due to difficulties caused by its low abundance in nature. This study aimed to develop a real-time PCR assay for specific detection and quantification of this alga in natural environments and to quantify spatiotemporal variations of wild B. braunii populations in a tropical pond. We designed PCR primers toward the hydrocarbon biosynthesis gene SSL-3 and examined amplification specificity and PCR efficiency with 70 wild strains newly isolated from various environments. The results demonstrated that this PCR assay specifically amplified B. braunii DNA, especially that of B-race strains, and can be widely used to detect wild B. braunii strains in temperate and tropical habitats. Field-testing in a tropical pond suggested a diurnal change in the abundance of B. braunii in surface water and found B. braunii not only in surface water, but also at 1-1.5 m deep and in bottom sediments. This method can contribute to efficient genetic resource exploitations and may also help elucidate the unknown ecology of B. braunii.

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.

Light Acclimation of the Colonial Green Alga Botryococcus braunii Strain Showa

In contrast to single cellular species, detailed information is lacking on the processes of photosynthetic acclimation for colonial algae, although these algae are important for biofuel production, ecosystem biodiversity, and wastewater treatment. To investigate differences between single cellular and colonial species, we studied the regulation of photosynthesis and photoprotection during photoacclimation for the colonial green alga Botryococcus braunii and made a comparison with the properties of the single cellular species Chlamydomonas reinhardtii We show that B. braunii shares some high-light (HL) photoacclimation strategies with C. reinhardtii and other frequently studied green algae: decreased chlorophyll content, increased free carotenoid content, and increased nonphotochemical quenching (NPQ). Additionally, B. braunii has unique HL photoacclimation strategies, related to its colonial form: strong internal shading by an increase of the colony size and the accumulation of extracellular echinenone (a ketocarotenoid). HL colonies are larger and more spatially heterogenous than low-light colonies. Compared with surface cells, cells deeper inside the colony have increased pigmentation and larger photosystem II antenna size. The core of the largest of the HL colonies does not contain living cells. In contrast with C. reinhardtii, but similar to other biofilm-forming algae, NPQ capacity is substantial in low light. In HL, NPQ amplitude increases, but kinetics are unchanged. We discuss possible causes of the different acclimation responses of C. reinhardtii and B. braunii Knowledge of the specific photoacclimation processes for this colonial green alga further extends the view of the diversity of photoacclimation strategies in photosynthetic organisms.

Non-invasive magnetic resonance imaging of oils in Botryococcus braunii green algae: Chemical shift selective and diffusion-weighted imaging

Botryococcus braunii is an oleaginous green algae with the distinctive property of accumulating high quantities of hydrocarbons per dry weight in its colonies. Large variation in colony structure exists, yet its implications and influence of oil distribution and diffusion dynamics are not known and could not be answered due to lack of suitable in vivo methods. This publication seeks to further the understanding on oil dynamics, by investigating naturally relevant large (700–1500μm) and extra-large (1500–2500μm) sized colonies of Botryococcus braunii (race B, strain Showa) in vivo, using a comprehensive approach of chemical shift selective imaging, chemical shift imaging and spin echo diffusion measurements at high magnetic field (17.6T). Hydrocarbon distribution in large colonies was found to be localised in two concentric oil layers with different thickness and concentration. Extra-large colonies were highly unstructured and oil was spread throughout colonies, but with large local variations. Interestingly, fluid channels were observed in extra-large colonies. Diffusion-weighted MRI revealed a strong correlation between colony heterogeneity, oil distribution, and diffusion dynamics in different parts of Botryococcus colonies. Differences between large and extra-large colonies were characterised by using T₂ weighted MRI along with relaxation measurements. Our result, therefore, provides first non-invasive MRI means to obtain spatial information on oil distribution and diffusion dynamics in Botryococcus braunii colonies.

Soft X-Ray Imaging of Cellular Carbon and Nitrogen Distributions in Heterocystous Cyanobacteria

Soft x-ray microscopy (SXM) is a minimally invasive technique for single-cell high-resolution imaging as well as the visualization of intracellular distributions of light elements such as carbon, nitrogen, and oxygen. We used SXM to observe photosynthesis and nitrogen fixation in the filamentous cyanobacterium Anabaena sp. PCC 7120, which can form heterocysts during nitrogen starvation. Statistical and spectroscopic analyses from SXM images around the K-absorption edge of nitrogen revealed a significant difference in the carbon-to-nitrogen (C/N) ratio between vegetative cells and heterocysts. Application of this analysis to soft x-ray images of Anabaena sp. PCC 7120 revealed inhomogenous C/N ratios in the cells. Furthermore, soft x-ray tomography of Anabaena sp. PCC 7120 revealed differing cellular C/N ratios, indicating different carbon and nitrogen distributions between vegetative cells and heterocysts in three dimensions.

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.

Extraction of hydrocarbons from freshwater green microalgae (Botryococcus sp.) biomass after phycoremediation of domestic wastewater

This study was undertaken to analyze the efficiency of Botryococcus sp. in the phycoremediation of domestic wastewater and to determine the variety of hydrocarbons derived from microalgal oil after phycoremediation. The study showed a significant (p < 0.05) reduction of pollutant loads of up to 93.9% chemical oxygen demand, 69.1% biochemical oxygen demand, 59.9% total nitrogen, 54.5% total organic carbon, and 36.8% phosphate. The average dry weight biomass produce was 0.1 g/L of wastewater. In addition, the dry weight biomass of Botryococcus sp. was found to contain 72.5% of crude oil. The composition analysis using Gas Chromatogram - Mass Spectrometry (GC-MS) found that phthalic acid, 2-ethylhexyltridecyl ester (C₂₉H₄₈O₄), contributed the highest percentage (71.6%) of the total hydrocarbon compounds to the extracted algae oil. The result of the study suggests that Botryococcus sp. can be used for effective phycoremediation, as well as to provide a sustainable hydrocarbon source as a value-added chemical for the bio-based plastic industry.

Extracellular Metabolites from Industrial Microalgae and Their Biotechnological Potential

Industrial microalgae, as a big family of promising producers of renewable biomass feedstock, have been commercially exploited for functional food, living feed and feed additives, high-value chemicals in nutraceuticals, cosmeceuticals, and chemical reagents. Recently, microalgae have also been considered as a group that might play an important role in biofuel development and environmental protection. Almost all current products of industrial microalgae are derived from their biomass; however, large amounts of spent cell-free media are available from mass cultivation that is mostly unexploited. In this contribution we discuss that these media, which may contain a remarkable diversity of bioactive substances are worthy to be recovered for further use. Obviously, the extracellular metabolites from industrial microalgae have long been neglected in the development of production methods for valuable metabolites. With the advances in the last ten years, more and more structures and properties from extracellular metabolites have been identified, and the potential utilization over wide fields is attracting attention. Some of these extracellular metabolites can be potentially used as drugs, antioxidants, growth regulators or metal chelators. The purpose of this review is to provide an overview of the known extracellular metabolites from industrial microalgae which might be of commercial interest. The attention mainly focuses on the reports of extracellular bioactive metabolites and their potential application in biotechnology.

Metabolic engineering of higher plants and algae for isoprenoid production

Isoprenoids are a class of compounds derived from the five carbon precursors, dimethylallyl diphosphate, and isopentenyl diphosphate. These molecules present incredible natural chemical diversity, which can be valuable for humans in many aspects such as cosmetics, agriculture, and medicine. However, many terpenoids are only produced in small quantities by their natural hosts and can be difficult to generate synthetically. Therefore, much interest and effort has been directed toward capturing the genetic blueprint for their biochemistry and engineering it into alternative hosts such as plants and algae. These autotrophic organisms are attractive when compared to traditional microbial platforms because of their ability to utilize atmospheric CO2 as a carbon substrate instead of supplied carbon sources like glucose. This chapter will summarize important techniques and strategies for engineering the accumulation of isoprenoid metabolites into higher plants and algae by choosing the correct host, avoiding endogenous regulatory mechanisms, and optimizing potential flux into the target compound. Future endeavors will build on these efforts by fine-tuning product accumulation levels via the vast amount of available "-omic" data and devising metabolic engineering schemes that integrate this into a whole-organism approach. With the development of high-throughput transformation protocols and synthetic biology molecular tools, we have only begun to harness the power and utility of plant and algae metabolic engineering.