Publication: Efectos de la calidad cromática de la luz y la salinidad en la producción y composición de la biomasa en microalgas
Authors
Ruohisto, Essi Maiju Helena
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Escuela Internacional de Doctorado
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Pancaldi, Simonetta ; Vera Andújar, Luisa María ; Sánchez Vázquez, Francisco Javier
Publisher
Universidad de Murcia
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DOI
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info:eu-repo/semantics/doctoralThesis
Description
Abstract
Esta Tesis doctoral examinó los efectos de diferentes condiciones lumínicas sobre el rendimiento del crecimiento y la composición bioquímica de microalgas cultivadas tanto en medios de agua dulce como salina. Se establecieron los siguientes objetivos especificos: 1) Estudiar los efectos de diferentes longitudes de onda de luz LED sobre el crecimiento, la fisiología y el metabolismo de Neochloris oleoabundans; 2) Evaluar el crecimiento y la producción microalgal en un entorno salino; 3) Evaluar el efecto de un termociclo diario sobre Neochloris oleoabundans; 4) Analizar métodos económicos y sostenibles para la producción de biomasa microalgal rica en compuestos de valor añadido, utilizando iluminación LED artificial; 5) Evaluar nuevas cepas microalgales en función de su valor biotechnologica.
Se realizaron cultivos en lotes en matraces y fotobiorreactores (PBRs) bajo condiciones controladas de laboratorio, usando medios de agua dulce y salina (BG11 y medios salinos artificiales). Los tratamientos lumínicos incluyeron luz LED monocromática azul, roja, blanca y luz de espectro mixto. La salinidad varió de agua dulce a marina (33 ppm), y se aplicaron termociclos diarios para imitar condiciones naturales. El crecimiento se evaluó mediante densidad óptica, recuento celular y peso seco. La eficiencia fotosintética se evaluó mediante la fluorescencia de la clorofila, utilizando fluorometría PAM. Se realizaron análisis bioquímicos para cuantificar proteínas (ensayo de Bradford) y pigmentos (metodos de espectrofotometría). Los lípidos y los ésteres metílicos de ácidos grasos fueron evaluados mediante microscopía de fluorescencia microscopía electrónica de transmisión y análisis por cromatografía de gases (GC) para determinar los cambios en la producción de lípidos y en los perfiles de ácidos grasos bajo diferentes condiciones de cultivo.
Los Capítulos I y II mostraron que la luz azul incrementó significativamente la biomasa y el contenido de lípidos y carotenoides en N. oleoabundans en agua dulce. La luz roja favoreció una mayor proporción de ácidos grasos poliinsaturados (PUFAs), mientras que la luz blanca promovió el contenido proteico y de ácidos grasos saturados (SFAs). En condiciones salinas, el crecimiento fue menor, pero la biomasa final y los lípidos aumentaron, probablemente como respuesta al estrés. La luz azul en medios salinos también favoreció la producción de pigmentos y SFAs.
El Capítulo III abordó el efecto del termociclo, mostrando que las fluctuaciones térmicas moderadas ralentizaron inicialmente el crecimiento, pero resultaron en mayores densidades celulares sin afectar el rendimiento final. Esto respalda la viabilidad del cultivo al aire libre sin control estricto de temperatura.
En el Capítulo IV se escaló el cultivo a PBRs de laboratorio (1 L), evaluando distintas combinaciones de luz y salinidad. Aunque la luz azul redujo la eficiencia fotosintética, el crecimiento fue similar entre tratamientos. Las condiciones salobres y luz moderada favorecieron el crecimiento y la acumulación de lípidos, mientras que el agua dulce potenció proteínas y pigmentos. Se evaluó también la viabilidad preliminar del uso de N. oleoabundans en un PBR prototípico.
El Capítulo V exploró cepas novedosas (Nannochloropsis sp., Halamphora sp., Fistulifera sp.) aisladas del Mar Menor (Murcia, España), que mostraron características valiosas: alto contenido de EPA y ALA, y producción significativa de pigmentos. La luz azul mejoró el crecimiento de Nannochloropsis y los fotoperiodos cortos favorecieron a Fistulifera. Estas cepas presentan potencial en sectores nutracéutico y farmacéutico.
Conclusiones principales: 1) La calidad de la luz impacta la composición bioquímica de N. oleoabundans: la luz azul incrementa lípidos y la roja favorece los PUFAs; 2) Las fluctuaciones térmicas moderadas no afectan la productividad de biomasa, permitiendo el cultivo exterior; La salinidad no limita el crecimiento en PBRs de laboratorio y puede aumentar la acumulación lipídica; Las nuevas cepas poseen potencial para biorrefinerías por sus perfiles únicos de lípidos y pigmentos.
This doctoral thesis assessed the effects of different lighting conditions on the growth performance and biochemical composition of microalgae cultivated in both freshwater and saline media. To reach the main objective, the following aims were established: 1) To study the effects of different LED light wavelengths on growth, physiology and metabolism of Neochloris oleoabundans; 2) To assess microalgal growth and production in saline environment; 3) To assess the effect of a daily thermocycle on Neochloris oleoabundans; 4) To evaluate economical and sustainable methods to produce microalgal biomass containing value-added molecules for biotechnological applications using artificial LED illumination; 5) To assess novel microalgal strains for their biotechnological value. A combination of batch cultivation experiments was conducted in flasks and photobioreactors (PBRs) under laboratory conditions using both freshwater and saline media (BG11 and artificial brackish and seawater media) to simulate different aquatic environments. Light treatments included monochromatic blue, red, and white LED light, as well as mixed-spectrum illumination. Salinity ranged from freshwater to seawater (33 ppm) and diurnal temperature fluctuation (thermocycle) was introduced to mimic natural outdoor conditions. Growth was assessed as optical density (OD), cell count, and dry weight (DW) while biochemical analyses included protein quantification (Bradford assay), and pigment analysis (spectrophotometric methods). The assessment on the photosynthetic efficiency was based on chlorophyll fluorescence using PAM fluorometry. Lipids and fatty acid methyl esters were assessed via fluorescence microscopy, transmission electron microscopy and GC analysis to determine changes in lipid production and fatty acid profiles under different growth conditions. Chapters I and II demonstrated that blue light significantly enhanced biomass production, and lipid and carotenoid content in N. oleoabundans under freshwater conditions. In contrast, red light supported a higher proportion of polyunsaturated fatty acids (PUFAs), including omega-3 and omega-6, while white light promoted the highest protein content and level of saturated fatty acids (SFAs). Under saline conditions, overall growth was impaired, while final biomass and lipid accumulation increased-likely as a stress-induced reaction. Use of saline media under blue light also promoted production of pigments and saturated fatty acids. Chapter III assessed the effect of thermocycle, revealing that moderate diurnal temperature changes initially slowed microalgal growth, but eventually resulted in higher cell densities. Overall biomass yield remained equivalent, suggesting that N. oleoabundans tolerates moderate thermal variation, supporting its viability for outdoor cultivation without strict temperature control. Chapter IV scaled up cultivation to lab-scale PBRs (1 L) testing different light conditions together with salinity. While blue light reduced photosynthetic efficiency, overall growth remained comparable across the light treatments. Brackish conditions and moderate light irradiance supported optimal growth performance, which also favoured lipid accumulation, while freshwater supported higher protein and pigment yield. This chapter also included a preliminary feasibility evaluation of N. oleoabundans in a prototypal PBR. Chapter V explored the biotechnological potential of novel strains, Nannochloropsis sp., Halamphora sp., Fistulifera sp., isolated from the Mar Menor (Murcia, Spain). These strains exhibited valuable traits, including high content of EPA and ALA and notable pigment production. Blue light enhanced the growth of Nannochloropsis, while shorter photoperiods favoured Fistulifera. These results suggest potential applications in the nutraceutical and pharmaceutical sectors. This Thesis reached the following conclusions: 1) Light quality has a significant impact on the biochemical composition of N. oleoabundans; blue light enhances lipid accumulation, while red light promotes PUFA production; 2) Moderate temperature fluctuations do not impede biomass productivity, in support of outdoor cultivation; 3) Salinity does not restrict growth in lab-scale PBRs; instead, it can enhance better biomass yield with high lipid content; 4) Novel strains hold potential for microalgal biorefineries due to their unique fatty acid and pigment profiles.
This doctoral thesis assessed the effects of different lighting conditions on the growth performance and biochemical composition of microalgae cultivated in both freshwater and saline media. To reach the main objective, the following aims were established: 1) To study the effects of different LED light wavelengths on growth, physiology and metabolism of Neochloris oleoabundans; 2) To assess microalgal growth and production in saline environment; 3) To assess the effect of a daily thermocycle on Neochloris oleoabundans; 4) To evaluate economical and sustainable methods to produce microalgal biomass containing value-added molecules for biotechnological applications using artificial LED illumination; 5) To assess novel microalgal strains for their biotechnological value. A combination of batch cultivation experiments was conducted in flasks and photobioreactors (PBRs) under laboratory conditions using both freshwater and saline media (BG11 and artificial brackish and seawater media) to simulate different aquatic environments. Light treatments included monochromatic blue, red, and white LED light, as well as mixed-spectrum illumination. Salinity ranged from freshwater to seawater (33 ppm) and diurnal temperature fluctuation (thermocycle) was introduced to mimic natural outdoor conditions. Growth was assessed as optical density (OD), cell count, and dry weight (DW) while biochemical analyses included protein quantification (Bradford assay), and pigment analysis (spectrophotometric methods). The assessment on the photosynthetic efficiency was based on chlorophyll fluorescence using PAM fluorometry. Lipids and fatty acid methyl esters were assessed via fluorescence microscopy, transmission electron microscopy and GC analysis to determine changes in lipid production and fatty acid profiles under different growth conditions. Chapters I and II demonstrated that blue light significantly enhanced biomass production, and lipid and carotenoid content in N. oleoabundans under freshwater conditions. In contrast, red light supported a higher proportion of polyunsaturated fatty acids (PUFAs), including omega-3 and omega-6, while white light promoted the highest protein content and level of saturated fatty acids (SFAs). Under saline conditions, overall growth was impaired, while final biomass and lipid accumulation increased-likely as a stress-induced reaction. Use of saline media under blue light also promoted production of pigments and saturated fatty acids. Chapter III assessed the effect of thermocycle, revealing that moderate diurnal temperature changes initially slowed microalgal growth, but eventually resulted in higher cell densities. Overall biomass yield remained equivalent, suggesting that N. oleoabundans tolerates moderate thermal variation, supporting its viability for outdoor cultivation without strict temperature control. Chapter IV scaled up cultivation to lab-scale PBRs (1 L) testing different light conditions together with salinity. While blue light reduced photosynthetic efficiency, overall growth remained comparable across the light treatments. Brackish conditions and moderate light irradiance supported optimal growth performance, which also favoured lipid accumulation, while freshwater supported higher protein and pigment yield. This chapter also included a preliminary feasibility evaluation of N. oleoabundans in a prototypal PBR. Chapter V explored the biotechnological potential of novel strains, Nannochloropsis sp., Halamphora sp., Fistulifera sp., isolated from the Mar Menor (Murcia, Spain). These strains exhibited valuable traits, including high content of EPA and ALA and notable pigment production. Blue light enhanced the growth of Nannochloropsis, while shorter photoperiods favoured Fistulifera. These results suggest potential applications in the nutraceutical and pharmaceutical sectors. This Thesis reached the following conclusions: 1) Light quality has a significant impact on the biochemical composition of N. oleoabundans; blue light enhances lipid accumulation, while red light promotes PUFA production; 2) Moderate temperature fluctuations do not impede biomass productivity, in support of outdoor cultivation; 3) Salinity does not restrict growth in lab-scale PBRs; instead, it can enhance better biomass yield with high lipid content; 4) Novel strains hold potential for microalgal biorefineries due to their unique fatty acid and pigment profiles.
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