Autotrophic Cultures Research Articles

A simple and low-cost technique to initiate single-spore cultures of arbuscular mycorrhizal fungi using a superabsorbent polymer

Most species of arbuscular mycorrhizal fungi (AMF) are propagated with a host plant in a pot culture. However, the soil matrix makes it difficult to monitor the establishment and development of the symbiosis. In vitro culturing using Ri T-DNA transformed roots provides a clear medium and a sterile environment which offsets the constraints of the soil matrix. Nevertheless, the sterile conditions and the Ri T-DNA transformed roots provide very different growing conditions compared to a pot culture. Transparent soil based on superabsorbent polymer (SAP) has the potential of combining the advantages of current in vivo and in vitro culture methods without the constraints associated with either technique (opacity and sterility). Here we describe a SAP-based autotrophic culture as an alternative to current in vivo and in vitro culture methods. This system using two-compartment Petri dishes makes it easy to initiate single-spore cultures and to monitor fungal propagation. The SAP-based autotrophic system allowed the establishment of single-spore cultures of seven species (Diversispora varaderana, Funneliformis geosporus, Gigaspora rosea, Racocetra fulgida, Rhizophagus irregularis, R. intraradices and Sclerocystis sp.) from six genera and three families. Cultures were maintained over several months under non-sterile conditions. The Petri dishes avoid the problem of cross contamination and they can be stacked for space optimization. The grains of SAP colonized with new spores were used as inoculum to initiate new cultures in the SAP-based system. The SAP-based autotrophic culture method is a low-cost and low-tech approach, which makes the study of AMF much more accessible.

Se-enrichment of Chlorella vulgaris grown under different trophic states for food supplementation

Most European countries, including Portugal, have soils with low selenium (Se) concentrations. This mineral has antioxidant and chemoprotective functions essential for the human immune system. Despite Se being mostly supplied in the diet in the inorganic form, organic Se is more rapidly assimilated by the organism, presenting lower toxicity. Microalgae can incorporate inorganic Se and metabolize it into less toxic organic forms. In this context, Chlorella vulgaris biomass was tested as a biological carrier for organic Se. For this purpose, C. vulgaris was cultivated under two trophic regimes (auto- and heterotrophic) supplied with sodium selenate. The optimal Na2SeO4 concentration for autotrophic cultivation was 20 mg.L−1. From the total Se absorbed by the biomass, 81 % was organic. The biochemical composition of Se-enriched biomass compared with the non-supplemented was similar (41 vs 42 % proteins, and 5.3 vs 6.2 % lipids, respectively), except for carbohydrates (0.64 vs 2.6 %, respectively). C18:1 and C18:0 were the major fatty acids present, but different profiles were observed. The same was observed for monosaccharides, being glucose the main monosaccharide. Pigments (Chl a, Chl b, and total carotenoids) were similar for both conditions. All potential toxic metals were below the limits regulated by the European Union. Under the optimal Se concentration for autotrophic C. vulgaris growth, most Se was converted into an organic form and 0.72 g biomass would be enough to satisfy human daily Se requirements. C. vulgaris showed a high potential to be used as a biofortified food to correct or prevent Se deficiency-related diseases.

Production of biopolymer precursors beta-alanine and L-lactic acid from CO2 with metabolically versatile Rhodococcus opacus DSM 43205.

Hydrogen oxidizing autotrophic bacteria are promising hosts for conversion of CO2 into chemicals. In this work, we engineered the metabolically versatile lithoautotrophic bacterium R. opacus strain DSM 43205 for synthesis of polymer precursors. Aspartate decarboxylase (panD) or lactate dehydrogenase (ldh) were expressed for beta-alanine or L-lactic acid production, respectively. The heterotrophic cultivations on glucose produced 25 mg L−1 beta-alanine and 742 mg L−1 L-lactic acid, while autotrophic cultivations with CO2, H2, and O2 resulted in the production of 1.8 mg L−1 beta-alanine and 146 mg L−1 L-lactic acid. Beta-alanine was also produced at 345 μg L−1 from CO2 in electrobioreactors, where H2 and O2 were provided by water electrolysis. This work demonstrates that R. opacus DSM 43205 can be engineered to produce chemicals from CO2 and provides a base for its further metabolic engineering.

High oleic acid biosynthesis and its absolute quantification by GC/MS in oleaginous Scenedesmus sp. SVMIICT1 cultivated in dual stress phase

High photosynthetic rates and high lipid content make microalgae a promising source for the industrial production of edible oils. Enhancement of oleic acid production in microalgae is an important area in the algae-based edible oils research. This study employed the mixotrophic mode of nutrition with a nutrient-rich growth phase (GP) followed by two different stress phases (SPs), including nitrate depletion (single stress phase; SSP) and nitrate depletion with salinity (dual stress phase; DSP). In DSP, higher oleic acid (C18:1) content was observed and considered the same for autotrophic mode. In addition to DSP, it evaluated the role of nitrate to phosphate ratio in GP towards fatty acid biosynthesis. The relative and absolute quantities of fatty acids were measured in mixotrophic and autotrophic cultivations. Higher oleic acid was obtained at 250 mM NaCl DSP condition in mixotrophic cultivation compared to other conditions. Whereas autotrophic mode microalgae cultivated in dual stress phase (DSP for A-GP-1N1P, DSP for A-GP-1N2P, DSP for A-GP-1N4P, and DSP for A-GP-1N6P) resulted in ~30 % (w/w) of total fatty acids with 55 % of Oleic acid in absolute quantity. Overall, the study depicted a distinct influence of nitrate, nitrate to phosphate ratio, nitrate depletion (single stress), and dual stress on the oleic acid yield. The application of dual stress to microalgae cultivation is a new approach to oleic acid enhancement. • Nitrate depletion and salinity in stress phase influenced oleic acid biosynthesis. • Study achieved 30 % of total fatty acids with 55 % of Oleic acid in absolute quantity. • Nitrates and phosphates in growth phase also influenced fatty acids production. • Nitrates increment in mixotrophic growth phase negligibly affected oleogenesis. • Biosynthesis of fatty acids is interdependent with growth phase and stress phase.

Using chlorella vulgaris for nutrient removal from hydroponic wastewater: experimental investigation and economic assessment.

The study evaluated the use of Chlorella vulgaris for bioremediating hydroponic wastewater and producing biomass under different cultivation modes and to explore the economic implications of microalgal biofuels. Total nitrogen (TN) removal efficiency was 98.5% in mixotrophic conditions and 96% in heterotrophic conditions, and total phosphorus (TP) was completely removed (>99%) in both cultivation conditions. TN removal was higher for that which was cultivated under the mixotrophic mode of cultivation. The maximum biomass production (1.26 g/L) and biomass productivity (0.1108 g/L/day) were also reported for mixotrophic conditions. Lipid content was slightly higher for that which was cultivated under heterotrophic conditions: 33 wt% on an ash-free dry weight (AFDW) basis. The highest lipid production was obtained under mixotrophic growth (0.341 g/L). Higher net profit was obtained for both mixotrophic and heterotrophic cultivations: 30.6 million $/year for a plant capacity of 3.29 × 104 tone/year and 30.12 million $/year for a plant capacity of 3.17 × 104 tone/year respectively. Sensitivity analysis showed that biodiesel and nutritious supplements from soluble protein have the greatest impact on the process economics regarding mixotrophic cultivation, while biodiesel and feeds from insoluble protein have the largest effect on the process economics regarding heterotrophic and autotrophic cultivations.

Heterotrophic vs autotrophic production of microalgae: Bringing some light into the everlasting cost controversy

Heterotrophic or autotrophic? This is the continuous question the industry faces when microalgae production is the endeavor. Surprisingly, nowadays specialists have not reached a consensus on which is the most economical option. The current work analyses costs for heterotrophic and autotrophic cultivation of microalgae at an industrial scale. Heterotrophic cultivation of microalgae results in a production cost of 4.00 €·kg−1 of dry weight as a centrifuged paste. This is within the range of autotrophic costs, but still above the production cost in some photobioreactors. The study also identifies the current limitations on the technology and studies the effect on the cost of overcoming these. Once achieved, the advances in the process could result in a heterotrophic production cost reduced to 1.08 €·kg−1. Autotrophic cultivation seems competitive with heterotrophic production. It is time to leap forward in the autotrophic production scale to achieve the critical reduction in production cost.

Effect of pH on biomass production and carbohydrate accumulation of Chlorella vulgaris JSC-6 under autotrophic, mixotrophic, and photoheterotrophic cultivation

Microalgal biomass, known as the third generation feedstock for biofuels production, is currently being explored mainly for lipids and functional components. However, the potential of microalgal carbohydrates has not been evaluated. In this investigation, Chlorella vulgaris JSC-6 was used for carbohydrates production from CO2 and fatty acids under different cultivation strategies to meet the requirements of a CO2-neutral and clean fermentation system for biofuel production. Autotrophic cultivation resulted in better carbon assimilation and carbohydrate accumulation; about 1.4 g CO2 could be converted to 1 g biomass, of which 50% are carbohydrates. Assimilation of fatty acids in photoheterotrophic and mixotrophic modes was influenced by pH, and pH 7–7.5 supported butyrate and acetate assimilation. The maximum carbohydrate content (49.86%) was attained in mixotrophic mode, and the ratio of the simple sugars glucose-xylose-arabinose was 1:0.11:0.02. The higher glucose content makes the microalgal biomass a suitable feedstock for sugar-based fermentations.

The Effect of Autotrophic Cultivation of Platymonas subcordiformis in Waters from the Natural Aquatic Reservoir on Hydrogen Yield

Biological processes run by microalgae are prospective but still little known methods of hydrogen production. A prerequisite for their increased advancement is the development of economically viable and efficient technologies. The study presented in this manuscript focused on determining the efficiency of biohydrogen production by P. subcordiformis using a culture medium prepared based on natural waters. The rate of P. subcordiformis biomass growth reached 317.6 ± 42.3 mgODM/dm3·d and ensured a biomass concentration of 3493 ± 465 mgODM/dm3. The percentage concentration of hydrogen in the biogas reached 63.2 ± 1.4%, and its production rate ranged from 0.53 ± 0.05 cm3/h to 0.70 ± 0.01 cm3/h.

Applicability of water from the Bay of Gdańsk as a growth medium for mixotrophic culture of Platymonas subcordiformis.

P. subcordiformis is a potentially promising species with commercial, environmental and technological viability for industrial applications. The great potential of these microalgae lies in their fast biomass growth, pollution resistance, and compatibility with different culture media. This study aimed to determine the efficiency of P. subcordiformis biomass production in a medium prepared with water from the Bay of Gdańsk. The tested medium supported high biomass growth rates which reached 317.58 ± 42.31 mgV⁢S/dm3⋅d in the best-performing variant, with a final concentration of 3493.3 ± 465.4 mgV⁢S/dm3⋅d. In the autotrophic culture, nitrogen and phosphorus removal exceeded 98%. Amending the mixotrophic culture with glucose did not affect P. subcordiformis concentrations. However, it did significantly limit the demand for nutrients in the biomass and reduced chlorophyll a production in the cells.

Photosynthesis, competition, and wastewater treatment characteristics of the microalga Monoraphidium sp. Dek19 at cool temperatures

Monoraphidium sp. Dek19 (M. Dek19) is a versatile cold-adapted microalga suitable for treatment of municipal wastewater and production of biofuels from cellular lipids. This study investigated the growth and photosynthetic properties of M. Dek19 which allow it to phycoremediate effluent under cool conditions. Autotrophic cultures grown in tertiary effluent reached greater cell densities at 10 °C than at 22 °C. At both temperatures, this alga could completely deplete polluting PO43− and NO32− ions during growth to stationary phase. M. Dek19 also grew prolifically in primary effluent from an earlier water treatment stage. NH4+ was removed as an alternate N-source, and algal photosynthesis had potential for energy-saving oxygenation of downstream aerobic treatments, including the activated sludge step. In mixed algal culture at a cool temperature (10 °C), M. Dek19 outcompeted Chlorella sp. However, at 22 °C this advantage was diminished, and the population of M. Dek19 cells declined. Photosynthetic O2 evolution by log-phase M. Dek 19 cells at 22 °C showed light saturation at 100 μmol photons m−2 s−1. At 10 °C, photosynthetic rates were 50% lower, light saturation decreased to 60 μmol photons m−2 s−1, yet the cells grew to higher cell densities under cooler conditions. At stationary phase, maximal photosynthesis declined by 50%, indicating self-shading effects. Concurrently, cellular Chlorophyll (Chl) content increased 2-fold, and Chl a/b ratios increased from 1.7 to 3.72. This indicated an acclimation to lower light penetration as the culture matured. The potential for biofuel production was evident from the elevated neutral lipid content of M. Dek19 as nutrients were depleted from the wastewater. We conclude that M. Dek19 is well-adapted to low temperatures and light levels found in winter at many water treatment facilities in colder climates. Thus, M. Dek19 offers a means to phycoremediate municipal wastewater in geographical areas where outdoor growth of algae has previously been discounted as impractical.

The Effect of Trophic Modes on Biomass and Lipid Production of Five Microalgal Strains

Five microalgae strains, namely Isochrysis galbana, Microchloropsis gaditana, Scenedesmus obliquus, Nannochloropsis oculata and Tetraselmis suecica, were selected as potential candidates for polyunsaturated fatty acids’ production, evaluating biomass productivity and their capacity to accumulate high lipid contents under different trophic modes. Microalgae strains were cultivated in the presence of 1% glucose using mixotrophic and heterotrophic conditions, while autotrophic cultures served as control experiments. The results demonstrate that S. obliquus performed the highest biomass productivity that reached 0.13 and 0.14 g L−1 d−1 under mixotrophic and heterotrophic conditions, respectively. I. galbana and S. obliquus utilized elevated contents of glucose in mixotrophy, removing 55.9% and 95.6% of the initial concentration of the carbohydrate, respectively, while glucose consumption by the aforementioned strains also remained high under heterotrophic cultivation. The production of lipids was maximal for I. galbana in mixotrophy and S. obliquus in heterotrophy, performing lipid productivities of 24.85 and 22.77 mg L−1 d−1, respectively. The most abundant saturated acid detected for all microalgae strains evaluated was palmitic acid (C16:0), while oleic and linolenic acids (C18:1n9c/C18:3n3) comprised the most abundant unsaturated fatty acids. I. galbana performed the highest linoleic acid (C18:2n6c) content under heterotrophic nutrition, which reached 87.9 mg g−1 of ash-free dry weight. Among the microalgae strains compared, the biomass and lipid production monitored for I. galbana and S. obliquus confirm that both strains could serve as efficient bioproducers for application in algal biorefineries.

Growth Performance, Biochemical Composition and Nutrient Recovery Ability of Twelve Microalgae Consortia Isolated from Various Local Organic Wastes Grown on Nano-Filtered Pig Slurry

This paper demonstrated the growth ability of twelve algae-microbial consortia (AC) isolated from organic wastes when a pig slurry-derived wastewater (NFP) was used as growth substrate in autotrophic cultivation. Nutrient recovery, biochemical composition, fatty acid and amino acid profiles of algae consortia were evaluated and compared. Three algae-microbial consortia, i.e., a Chlorella-dominated consortium (AC_1), a Tetradesmus and Synechocystis co-dominated consortium (AC_10), and a Chlorella and Tetradesmus co-dominated consortium (AC_12) were found to have the best growth rates (µ of 0.55 ± 0.04, 0.52 ± 0.06, and 0.58 ± 0.03 d−1, respectively), which made them good candidates for further applications. The ACs showed high carbohydrates and lipid contents but low contents of both proteins and essential amino acids, probably because of the low N concentration of NFP. AC_1 and AC_12 showed optimal ω6:ω3 ratios of 3.1 and 3.6, which make them interesting from a nutritional point of view.

Improved growth of bait microalgae Isochrysis and aquacultural wastewater treatment with mixotrophic culture.

This research of mixotrophic microalgae Isochrysis 3011 with glycerol was combined with the treatment of aqua-cultural wastewater, different initial concentrations, and optimized light intensities. The algae growth rate, removal efficiencies of total nitrogen (TN) and total phosphorus (TP) were determined. Results showed that the suitable initial concentration was 0.4g L-1, and the optimum light intensity was 60µmolm-2s-1. The growth of the mixotrophic group was better than that of the autotrophic culture. The biomass yield of the mixotrophic group with glycerol was 0.17g L-1 d-1, and the removal rates of TN and TP were 73.39% and 95.61%, respectively. The content of total lipid and total protein in mixotrophic group were higher than the values of the autotrophic group. This indicates that aquaculture wastewater treatment with mixotrophic bait microalgae can obtain superior micro-algal biomass, which is also a potential technology for wastewater utilization and ecological protection.

Micro-Bioreactors in Space: Case Study of a Yeast (Saccharomyces cerevisiae) Bioreactor With a Non-Invasive Monitoring Method

Bioreactors in space have applications from basic science to microbial factories. Monitoring bioreactors in microgravity has challenges with respect to fluidics, aeration, sensor size, sample volume and disturbance of medium and cultures. We present a case study of the development of small bioreactors and a non-invasive method to monitor dissolved oxygen, pH, and biomass of yeast cultures. Two different bioreactor configurations were tested for system volumes of 60 ml and 10.5 ml. For both configurations, the PreSens SFR vario, an optical sensor array, collected data autonomously. Oxygen and pH in the cultures were monitored using chemically doped spots, 7 mm in diameter, that were fixed to the bottom of sampling chambers. Spots emitted a fluorescent signal for DO and pH when reacted with oxygen molecules and hydrogen ions, respectively. Biomass was sensed using light reflectance at centered at 605 nm. The, optical array had three light detectors, one for each variable, that returned signals that were pre- and post-calibrated. For heterotrophic cultures requiring oxygen and respiring carbon dioxide, a hollow fiber filter, in-line with the optical array, oxygenated cells and remove carbon dioxide. This provided oxygen levels that were sufficient to maintain aerobic respiration for steady state conditions. Time series of yeast metabolism in the two bioreactors are compared and discussed. The bioreactor configurations can be easily be modified for autotrophic cultures such that carbon dioxide is enhanced and oxygen removed, which would be required for photosynthetic algal cultures.

Screening of Gas Substrate and Medium Effects on 2,3-Butanediol Production with C. ljungdahlii and C. autoethanogenum Aided by Improved Autotrophic Cultivation Technique

Gas fermentation by acetogens of the genus Clostridium is an attractive technology since it affords the production of biochemicals and biofuels from industrial waste gases while contributing to mitigate the carbon cycle alterations. The acetogenic model organisms C. ljungdahlii and C. autoethanogenum have already been used in large scale industrial fermentations. Among the natural products, ethanol production has already attained industrial scale. However, some acetogens are also natural producers of 2,3-butanediol (2,3-BDO), a platform chemical of relevant industrial interest. Here, we have developed a lab-scale screening campaign with the aim of enhancing 2,3-BDO production. Our study generated comparable data on growth and 2,3-BDO production of several batch gas fermentations using C. ljungdahlii and C. autoethanogenum grown on different gas substrates of primary applicative interest (CO2 · H2, CO · CO2, syngas) and on different media featuring different compositions as regards trace metals, mineral elements and vitamins. CO · CO2 fermentation was found to be preferable for the production of 2,3-BDO, and a fair comparison of the strains cultivated in comparable conditions revealed that C. ljungdahlii produced 3.43-fold higher titer of 2,3-BDO compared to C. autoethanogenum. Screening of different medium compositions revealed that mineral elements, Zinc and Iron exert a major positive influence on 2,3-BDO titer and productivity. Moreover, the CO2 influence on CO fermentation was explored by characterizing C. ljungdahlii response with respect to different gas ratios in the CO · CO2 gas mixtures. The screening strategies undertaken in this study led to the production of 2.03 ± 0.05 g/L of 2,3-BDO, which is unprecedented in serum bottle experiments.

Different effect of nitrogen sources in autotrophic and mixotrophic culture of Scenedesmus sp for biomass and carotenoids production using acidic coal mine drainage effluents

In the present study, the conditions for autotrophic and mixotrophic culture of Scenedesmus sp were established. Effluents from acidic coal mine drains were used to study biomass and carotenoid production, both under autotrophic and mixotrophic conditions in relation to the effect of different sources of nitrogen: sodium nitrate, urea and ammonium phosphate. Pollutant removal was determined, such as COD, TOC, heavy metals, ions and total suspended solids. Batch cultures lasted nine days and biomass production, carotenoids and pollutant removal were compared in each condition. The highest biomass concentration reached was 1.2 g/L in the mixotrophic culture with urea, followed by the culture with sodium nitrate of 0.9 g/L in a C/N ratio of 6:1. The highest carotenoid specific concentration was reached in the mixotrophic culture with sodium nitrate, 19.43 mg carotenoids /g biomass. The culture with ammonium phosphate was found to be inhibitory for the growth of the microalgae with the lowest results of all the parameters except for the autotrophic culture where the concentration of carotenoids was very similar to those reached with sodium nitrate and urea. Finally, the mixotrophic culture with urea presented the highest removal percentages, being 86.97% for total iron, 58.29% for chlorides and 92.5% for COD.

Laminaria japonica hydrolysate promotes fucoxanthin accumulation in Phaeodactylum tricornutum

Fucoxanthin (Fx) has gained a growing attention due to the remarkable biological activities. The limited biomass of was the restrictive factor for Fx production in Phaeodactylum tricornutum. In this study, Laminaria japonica hydrolysate (LPH) with a low addition proportion of 1.5 ml/L, was proved to promote fucoxanthin accumulation and cell growth simultaneously. Fx topped at 27.9 mg/L after 10-d cultivation in the LPH group, with a biomass of 1.59 g/L and a Fx content of 17.55 mg/g. Three key plant hormones in LPH were screened responsible for promoting fucoxanthin accumulation. Transcriptomic analysis and qRT-PCR results showed that genes related to Fx formation were generally up- regulated. The study demonstrated that LPH addition was a feasible and efficient strategy to enhance production of fucoxanthin, facilitating the scale-up production of Fx in autotrophic culture.

Autotrophic and mixotrophic biomass production of the acidophilic Galdieria sulphuraria ACUF 64

Abstract Galdieria sulphuraria is an acidophilic microalga isolated in proximity of sulfuric ponds where pH is below 3 and most organisms cannot grow. We cultivated G. sulphuraria ACUF 64 free of contamination for over 2 months in a medium containing organic carbon at pH 1.7 with continuous, high intensity, lighting. We compared biomass productivity of chemostat and repeated batch cultivations. The optimal biomass density in autotrophic and mixotrophic cultures was identified. In autotrophy biomass productivity was 28.3 g x ·m −2 ·day −1 , 1.8 to 7.7-fold higher than previously reported. Autotrophy was compared to ‘oxygen balanced’ mixotrophy where intracellular recirculation of O 2 and CO 2 take place. Aeration was not needed and 92% of the substrate carbon was converted into biomass. In mixotrophy biomass productivity was 1.8 times higher than autotrophic culture and linear growth was maintained at high biomass concentration (9.7 g x ·L −1 ). Light tolerance and high productivity in dense culture make our strain promising for mixotrophic outdoor cultivation. • Highest Galdieria sulphuraria autotrophic productivity (29 g·m −2 ·day −1 ) • Highest Galdieria sulphuraria mixotrophic productivity (51 g·m −2 ·day −1 ) • Oxygen balanced mixotrophy does not need aeration and 92% of substrate converted into biomass. • Galdieria sulphuraria can be cultivated at high light intensity. • In mixotrophy linear growth maintained at high biomass concentration (340 g x ·m −2 ).

Combined Production of Astaxanthin and β-Carotene in a New Strain of the Microalga Bracteacoccus aggregatus BM5/15 (IPPAS C-2045) Cultivated in Photobioreactor.

Simple SummaryMicroalgae are the richest source of natural carotenoids, valuable pigments, which are key components of functional food, cosmetics, drugs and animal feeding. To date, only two genera of green microalgae are widely used for mass production of carotenoids on an industrial scale, Haematococcus and Dunaliella. They produce astaxanthin and β-carotene, respectively, which are among the most useful carotenoids. In doing so one alga produces only one type of a pigment. In this paper we characterize a new strain of the green microalga Bracteacoccus aggregatus BM5/15 (IPPAS C-2045). It can simultaneously produce both carotenoids (up to 13.1 and 47.9% β-carotene and astaxanthin of cell dry mass, respectively). Growth parameters of the strain cultivated in glass bubble-column photobioreactors for commercial cultivation of microalgae were obtained. We also provide data of microscopic observations, pigment and fatty acid profile of the microalga, which are important biotechnological characteristics. Collectively, new data makes B. aggregatus BM5/15 suitable for industrial production of β-carotene, a pro-vitamin A, and astaxanthin, the most powerful antioxidant.Carotenoids astaxanthin and β-carotene are widely used natural antioxidants. They are key components of functional food, cosmetics, drugs and animal feeding. They hold leader positions on the world carotenoid market. In current work, we characterize the new strain of the green microalga Bracteacoccus aggregatus BM5/15 and propose the method of its culturing in a bubble-column photobioreactor for simultaneous production of astaxanthin and β-carotene. Culture was monitored by light microscopy and pigment kinetics. Fatty acid profile was evaluated by tandem gas-chromatography–mass spectrometry. Pigments were obtained by the classical two-stage scheme of autotrophic cultivation. At the first, vegetative, stage biomass accumulation occurred. Maximum specific growth rate and culture productivity at this stage were 100–200 mg∙L−1∙day−1, and 0.33 day−1, respectively. At the second, inductive, stage carotenoid synthesis was promoted. Maximal carotenoid fraction in the biomass was 2.2–2.4%. Based on chromatography data, astaxanthin and β-carotene constituted 48 and 13% of total carotenoid mass, respectively. Possible pathways of astaxanthin synthesis are proposed based on carotenoid composition. Collectively, a new strain B. aggregatus BM5/15 is a potential biotechnological source of two natural antioxidants, astaxanthin and β-carotene. The results give the rise for further works on optimization of B. aggregatus cultivation on an industrial scale.

Reducing self-shading effects in Botryococcus braunii cultures: effect of Mg2+ deficiency on optical and biochemical properties, photosynthesis and lipidomic profile

Microalgae biomass exploitation as a carbon–neutral energy source is currently limited by several factors, productivity being one of the most relevant. Due to the high absorption properties of light-harvesting antenna, photosynthetic cells tend to capture an excessive amount of energy that cannot be entirely channeled through the electron transfer chain that ends up dissipated as heat and fluorescence, reducing the overall light use efficiency. Aiming to minimize this hurdle, in this work we studied the effect of decreasing concentrations of Magnesium (Mg2+) on the chlorophyll a content, photosynthetic performance, biomass and lipid production of autotrophic cultures of Botryococcus braunii LB 572. We also performed, for the first time, a comparative lipidomic analysis to identify the influence of limited Mg2+ supply on the lipid profile of this algae. The results indicated that a level of 0.0037 g L−1 MgSO4 caused a significant decline on chlorophyll a content with a concomitant 2.3-fold reduction in the biomass absorption coefficient. In addition, the Mg2+ limitation caused a decrease in the total carbohydrate content and triggered lipid accumulation, achieving levels of up to 53% DCW, whereas the biomass productivity remained similar for all tested conditions. The lipidome analysis revealed that the lowest Mg2+ concentrations also caused a differential lipid profile distribution, with an enrichment of neutral lipids and an increase of structural lipids. In that sense, we showed that Mg2+ limitation represents an alternative optimization approach that not only enhances accumulation of neutral lipids in B. braunii cells but also may potentially lead to a better areal biomass productivity due to the reduction in the cellular light absorption properties of the cells.