Growth Kinetics of Nanofrustulum Shiloi Under Different Mixing Conditions in Flat-plate Photobioreactor

Abstract Diatoms are the major group of microalgae which have been utilized by the potential applications as food industries, aquatic feeds, cosmetics, biofuels, and pharmaceuticals. In this study, current approaches were made in order to determine growth rate, biomass productivity, protein, carbohydrate, lipid and fatty acid composition for Nanofrustulum shiloi cultures using both aeration and mixing conditions in flat-plate photobioreactor (PBR). Physical (the intensity of aeration, mixing, light intensity etc.) and chemical (nutritional materials) factors are affecting the growth and bioproduct contents of a diatom. Biomass and lipid productivities of N. shiloi were measured as 31.29 and 36.9622±0.0598 mg L-1 day-1 in flat-plate PBR having the combination of aeration and stirring system, respectively. A slightly higher amount of saturated fatty acids was detected in PBR having only bubbling system while the increase of mono- and poly- unsaturated fatty acids were found in PBR having the combination of aeration and stirring system. Flat-plate PBR design was also investigated for improving not only biomass but also the lipid productivity of N. shiloi.

Crecimiento y composición bioquímica de Thalassiosira pseudonana (Thalassiosirales: Thalassiosiraceae) bajo cultivo semi-continuo en diferentes medios y niveles de irradiancias / Growth and biochemical composition of Thalassiosira pseudonana (Thalassiosirales: Thalassiosiraceae) cultivated in semicontinuous system at different culture media and irradiances

Thalassiosira pseudonana is a marine Bacillariophyta commonly used as live feed in mariculture. The growth rate and biochemical composition of microalgae are highly influenced by environmental factors such as, irradiance and nutrient availability. The aim of this study was to investigate the influence of three irradiances (60, 120 and 180μE/m².s) and two culture media (Algal and Humus) on growth and biochemical composition of this diatom. The microalga was grown semicontinuously at a daily renewal rate of fresh media of 30%, 37‰ salinity, 25±1ºC and constant aeration (200mL/min). The cell densities (cel/mL) and contents of protein, lipid, carbohydrate, chlorophyll a, total carotenoids, and fatty acids, showed significant differences (p<0.05) between treatments. During steady-state phase, the maximal cell density, and lipid and carbohydrate contents were of 4.62x10(6)cel/mL, 20.3±2.28% and 16.6±2.43%, respectively, and were achieved in Humus medium at 180μE/m².s. Moreover, highest protein contents (45.0±5.05%) and total carotenoids (0.5±0.01%) were obtained in Algal medium at 180μE/m².s. Chlorophyll a (0.93±0.04%) was higher at low irradiances in Algal medium. In both media, the fatty acids unsaturation degree was lower with increasing irradiance, being eicosapentaenoic acid, 20:5 n-3 (EPA) most represented (6.20%) in Algal medium at 60μE/m².s. This strain of T. pseudonana showed multiple physiological responses to changes in culture conditions, and may be cultivated with an alternative medium, which reduced the operating costs and allowed a high nutritional biomass production value for animals under culture.

Thalassiosira pseudonana es utilizada como alimento en acuicultura, pero su valor nutricional está influenciado por las condiciones de crecimiento. Sistemas semicontinuos, en fase de estabilización, con tres irradiancias (60, 120 y 180μE/m².s) y dos medios de cultivo (Algal y Humus) fueron las condiciones en las que se determinó el crecimiento y componentes bioquímicos de T. pseudonana. En Humus a 180μE/m².s se obtuvieron las máximas densidades celulares (entre 3.86 y 4.62x10(6)cel/mL) y mayores concentraciones de lípidos y carbohidratos, con porcentajes de 20.3±2.28 y 16.6±2.43, respectivamente. A 180μE/m².s en Algal se observaron los mayores valores de proteínas (45.0±5.05) y carotenoides totales (0.5±0.01). El contenido de clorofila a fue favorecido por baja intensidad de luz, principalmente en Algal, con máximos de 0.9±0.04%. El grado de insaturación de los ácidos grasos disminuyó por incremento de la irradiancia en ambos medios, estando mayoritariamente representados por el ácido eicosapentaenoico, 20:5 n-3 (AEP), con porcentajes máximos (6.20%) en Algal a 60μE/m².s. Los resultados muestran múltiples respuestas fisiológicas de T. pseudonana frente a cambios en las condiciones de crecimiento, las cuales pueden ser aprovechadas para mejorar su valor nutricional como alimento de organismos cultivados, utilizando medios de cultivo alternativos, que disminuyan los costos en la producción microalgal.

The use of water chemistry and benthic diatom communities for qualification of a polluted tropical river in Costa Rica

The water quality of several sections of a tropical river subjected to severe pollution was studied through physico-chemical water analysis and benthic diatom assemblages. The methodology follows the concept of differential species groups and that of its modification for the groups of nutrient-differentiating species for rivers rich in both oxygen and inorganic nutrients. The trophic indication of the latter authors correspond clearly with the results of chemical observations made in this study. The most abundant species found in this river were Navicula goeppertiana, Gomphonema parvulum, Gomphonema sp. aff. pumilum, Nitzschia palea, Nitzschia amphibia, Nitzschia clausii Nitzschia inconspicua, Navicula seminulum, Navicula sp. aff. cryptocephala, Navicula schroeterii var. escambia, Cymbella sinuata and Surirella sp. aff. roba. These species are known to be tolerant to organic pollution and eutrophication. Therefore we may conclude that diatoms are useful for biological monitoring of disturbed tropical rivers