A greater insight on the control of the interactions between microalgae and other microorganisms, particularly bacteria, should be useful for enhancing the efficiency of microalgal biomass production ...and associated valuable compounds. Little attention has been paid to the controlled utilization of microalgae-bacteria consortia. However, the studies of microalgal-bacterial interactions have revealed a significant impact of the mutualistic or parasitic relationships on algal growth. The algal growth, for instance, has been shown to be enhanced by growth promoting factors produced by bacteria, such as indole-3-acetic acid. Vitamin B12 produced by bacteria in algal cultures and bacterial siderophores are also known to be involved in promoting faster microalgal growth. More interestingly, enhancement in the intracellular levels of carbohydrates, lipids and pigments of microalgae coupled with algal growth stimulation has also been reported. In this sense, massive algal production might occur in the presence of bacteria, and microalgae-bacteria interactions can be beneficial to the massive production of microalgae and algal products. This manuscript reviews the recent knowledge on the impact of the microalgae-bacteria interactions on the production of microalgae and accumulation of valuable compounds, with an emphasis on algal species having application in aquaculture.
Carotenoids are the most common pigments in nature and are synthesized by all photosynthetic organisms and fungi. Carotenoids are considered key molecules for life. Light capture, photosynthesis ...photoprotection, excess light dissipation and quenching of singlet oxygen are among key biological functions of carotenoids relevant for life on earth. Biological properties of carotenoids allow for a wide range of commercial applications. Indeed, recent interest in the carotenoids has been mainly for their nutraceutical properties. A large number of scientific studies have confirmed the benefits of carotenoids to health and their use for this purpose is growing rapidly. In addition, carotenoids have traditionally been used in food and animal feed for their color properties. Carotenoids are also known to improve consumer perception of quality; an example is the addition of carotenoids to fish feed to impart color to farmed salmon.
Microalgae have been widely recognized as a valuable source of natural, bioactive molecules that can benefit human health. Some molecules of commercial value synthesized by the microalgal metabolism ...have been proven to display anti-inflammatory activity, including the carotenoids lutein and astaxanthin, the fatty acids EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid), and sulphated polysaccharides. These molecules can accumulate to a certain extent in a diversity of microalgae species. A production process could become commercially feasible if the productivity is high and the overall production process costs are minimized. The productivity of anti-inflammatory molecules depends on each algal species and the cultivation conditions, the latter being mostly related to nutrient starvation and/or extremes of temperature and/or light intensity. Furthermore, novel bioprocess tools have been reported which might improve the biosynthesis yields and productivity of those target molecules and reduce production costs simultaneously. Such novel tools include the use of chemical triggers or enhancers to improve algal growth and/or accumulation of bioactive molecules, the algal growth in foam and the surfactant-mediated extraction of valuable compounds. Taken together, the recent findings suggest that the combined use of novel bioprocess strategies could improve the technical efficiency and commercial feasibility of valuable microalgal bioproducts production, particularly anti-inflammatory compounds, in large scale processes.
In the present study, the recovery of valuable molecules of proven anti-inflammatory and antimicrobial activity of the acidophilic microalga Coccomyxa onubensis (C. onubensis) were evaluated using ...green technologies based on ultrasound-assisted extraction (UAE). Using a factorial design (3 × 2) based on response surface methodology and Pareto charts, two types of ultrasonic equipment (bath and probe) were evaluated to recover valuable compounds, including the major terpenoid of C. onubensis, lutein, and the antimicrobial activity of the microalgal extracts obtained under optimal ultrasound conditions (desirability function) was evaluated versus conventional extraction. Significant differences in lutein recovery were observed between ultrasonic bath and ultrasonic probe and conventional extraction. Furthermore, the antimicrobial activity displayed by C. onubensis UAE-based extracts was greater than that obtained in solvent-based extracts, highlighting the effects of the extracts against pathogens such as Enterococcus hirae and Bacillus subtilis, followed by Staphylococcus aureus and Escherichia coli. In addition, gas chromatography–mass spectrometry was performed to detect valuable anti-inflammatory and antimicrobial biomolecules present in the optimal C. onubensis extracts, which revealed that phytol, sterol-like, terpenoid, and even fatty acid structures could also be responsible for the antibacterial activities of the extracts. Moreover, UAE displayed a positive effect on the recovery of valuable molecules, improving biocidal effects. Our study results facilitate the use of green technology as a good tool in algal bioprocess engineering, improving energy consumption and minimizing environmental impacts and process costs, as well as provide a valuable product for applications in the field of biotechnology.
The efficacy of low-frequency ultrasound pulses in cell disaggregation of
Chroococcidiopsis
sp. aggregates has been studied as a possible strategy to improve the productivity and operation of the ...cultures. The modulation of the ultrasound pulses allowed to almost disaggregate most of the cyanobacterial aggregates completely while retaining cellular viability in terms of photosynthetic efficiency. In this study we used a strain isolated from the endolithic habitat of the Atacama Desert, the driest desert in the world due to the extremely scarce rainfall, low level of relative humidity and extremely high incident solar radiation. To survive these conditions and reduce the cell exposure to the incident UV radiation,
Chroococcidiopsis
sp. grows in the form of aggregates, diminishing the associated photo-oxidative damage. However, this adaptation strategy can reduce the availability of both light and nutrients to the growing cells. This study showed that the low-frequency ultrasound pulses were efficient in disaggregating
Chroococcidiopsis
sp. aggregates, improving light and nutrient availability to the cells. Our results revealed also that the modulated use of ultrasound pulses resulted in a decreased cell sedimentation velocity which becomes advantageous at large scale. The length of the ultrasound pulses can be optimized to achieve complete disaggregation of the aggregates without affecting cell viability. The preservation of cell viability is considered an advantage for eventual large-scale production as disaggregating of the aggregates can result in more homogeneous cultures with less energy needed to perform mechanical agitation. Additionally, our results indicated an improved growth of cyanobacterium in disaggregated cultures.
An economically feasible microalgal lipid industry heavily relies on the selection of suitable strains. Because microalgae lipid content increases under a range of adverse conditions (e.g. nutrient ...deprivation, high light intensity), photosynthetic activity is usually strongly reduced. As a consequence, lipid productivity rapidly declines overtime, after reaching a maximum within the first days of cultivation. The microalgae
Chlorella vulgaris
,
Chlorococcum littorale
,
Nannochloropsis oculata
,
Nannochloropsis
sp.,
Neochloris oleoabundans
,
Stichococcus bacillaris
and
Tetraselmis suecica
were compared on fatty acid content and productivity, and also on photosynthetic activity under nitrogen (N) starvation. Cultures in N-replete conditions were used as reference. Photosystem II (PSII) maximum efficiency was followed during the experiment, as proxy for the change in photosynthetic activity of the cells. Strains with a high capacity for both lipid accumulation as well as high photosynthetic activity under N starvation exhibited a high lipid productivity over time. Among the tested strains,
Nannochloropsis
sp. showed highest fatty acid content (45 %
w
/
w
) and productivity (238 mg L
−1
day
−1
) as well as PSII maximum efficiency, demonstrating to be the most suitable strain, of those tested, for lipid production. This study highlights that for microalgae, maintaining a high photosynthetic efficiency during stress is the key to maintain high fatty acid productivities overtime and should be considered when selecting strains for microalgal lipid production.
Microalgae: Fast-Growth Sustainable Green Factories Forján, Eduardo; Navarro, Francisco; Cuaresma, María ...
Critical reviews in environmental science and technology,
08/2015, Letnik:
45, Številka:
16
Journal Article
Recenzirano
Microalgae are definitely on the way to become a sustainable, fast-growing natural green source for highly demanded market products. Research is currently looking at promising outstanding ...applications of microalgae among which are the production of biofuels from the fatty acids present in biomass, functional foods enriched with microalgae healthy bioactive molecules, and greenhouse gas mitigation (CO
2
consuming) based on high cell density microalgae cultures technology. Besides, other traditional microalgae applications are currently increasing in competitiveness in a growing market demand for green biomass, in which microalgae are widely recognized as a healthy, sustainable, and biological renewable resource. Among these traditional applications, microalgae are being used to improve the nutritional quality in animal feed, particularly in aquaculture, therapeutic agent source, and antioxidant activity. In addition, microalgae also show to be functional in waste effluents treatment to remove N and P, thus preventing eutrophication, heavy metals, and others contaminants. This review intends to offer a comprehensive overview of basic aspects of microalgae physiology, massive production of biomass, and current fields of applications at industrial scale.
The productivity of a vertical outdoor photobioreactor was quantitatively assessed and compared to a horizontal reactor. Daily light cycles in southern Spain were simulated and applied to grow the ...microalgae Chlorella sorokiniana in a flat panel photobioreactor.
The maximal irradiance around noon differs from 400μmolphotonsm−2s−1 in the vertical position to 1800μmolphotonsm−2s−1 in the horizontal position. The highest volumetric productivity was achieved in the simulated horizontal position, 4gkg culture−1d−1. The highest photosynthetic efficiency was found for the vertical simulation, 1.3g of biomass produced per mol of PAR photons supplied, which compares favorably to the horizontal position (0.85gmol−1) and to the theoretical maximal yield (1.8gmol−1). These results prove that productivity per unit of ground area could be greatly enhanced by placing the photobioreactors vertically.
Agricultural fertilisers (NPKs) have been recognised as an alternative to make microalgae cultivation cheaper as well as simpler in terms of the preparation of the medium.
Botryococcus braunii
, a ...green microalga, has the almost unique capacity to accumulate and excrete large amounts of long-chain hydrocarbons and/or interesting groups of polysaccharides which can be further converted into bio-products. However, limitations in growth are currently hindering its industrial production. In this work, the use of different agricultural fertilisers (NPKs) was evaluated for the cultivation of two
B. braunii
races (A and B) in terms of productivity and final media labour and cost. Results corroborated that fertilisers-based media are easier to prepare and their prices are considerably lower compared to common culture media. At the same time, good growth performance and photosynthetic efficiency can be maintained and carbohydrate and hydrocarbon productivities can be further enhanced. However, special attention should be given to each particular strain since different behaviour in growth and metabolite production can be observed depending on the media composition. The significantly higher productivities obtained, together with the important reduction in media price when using commercial fertilisers and the advantages related to the easiness to prepare the culture media based on NPK fertilizers, represent an important achievement for the development of an industry based on these renewable products.
Current interest in the production of commercial biopolymers which are derived from renewable resources arises from the necessity to move from a fossil-based to a more sustainable economy. Microalgae ...are considered potential biopolymer producers although their use at an industrial scale is not feasible yet. In this sense, medium optimisation and operational conditions can be considered the first steps leading to growth and product productivity enhancement which are a prerequisite to boost the microalgae industry. This manuscript describes medium optimisation for two promising strains of the green alga
Botryococcus braunii
,
B. braunii
CCALA-778 (race A) and
B. braunii
AC761 (race B), which are natural producers of (exo)polysaccharides and hydrocarbons of high interest in the biopolymers industry. Medium optimisation was based on a three-step research process: (i) a literature survey to identify macro- and micronutrients that could be limiting
Botryococcus
growth, (ii) a 3-level factorial design experiment in microwell plates to evaluate modified media accordingly and (iii) validation of previous results in batch cultivation in Roux flasks. The results obtained show the significant impact of culture media optimisation in the growth dynamics and valuable compound accumulation of
B. braunii.
Attention should be given to each particular
Botryococcus
race and media should be defined accordingly. But overall, the new optimised media resulted in higher productivities which may contribute to reach sustainability of
Botryococcus
cultivation.
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