Obtaining Bioproducts from the Studies of Signals and Interactions between Microalgae and Bacteria.

The applications of microalgae biomass have been widely studied worldwide. The classical processes used in outdoor cultivations of microalgae, in closed or open photobioreactors, occur in the presence of bacteria. Understanding how communication between cells occurs through quorum sensing and evaluating co-cultures allows the production of microalgae and cyanobacteria to be positively impacted by bacteria, in order to guarantee safety and profitability in the production process. In addition, the definition of the effects that occur during an interaction, promotes insights to improve the production of biomolecules, and to develop innovative products. This review presents the interactions between microalgae and bacteria, including compounds exchanges and communication, and addresses the development of new pharmaceutical, cosmetic and food bioproducts from microalgae based on these evaluations, such as prebiotics, vegan skincare products, antimicrobial compounds, and culture media with animal free protein for producing vaccines and other biopharmaceutical products. The use of microalgae as raw biomass or in biotechnological platforms is in line with the fulfillment of the 2030 Agenda related to the Sustainable Development Goals (SDGs).

Semicontinuous system for the production of recombinant mCherry protein in Chlamydomonas reinhardtii.

Biotechnology advances have allowed bacteria, yeasts, plants, mammalian and insect cells to function as heterologous protein expression systems. Recently, microalgae have gained attention as an innovative platform for recombinant protein production, due to low culture media cost, compared to traditional systems, as well as the fact that microalgae such as Chlamydomonas reinhardtii are considered safe (GRAS) by the Food and Drug Administration (FDA). Previous studies showed that recombinant protein production in traditional platforms by semicontinuous process increased biomass and bio product productivity, when compared to batch process. As there is a lack of studies on semicontinuous process for recombinant protein production in microalgae, the production of recombinant mCherry fluorescent protein was evaluated by semicontinuous cultivation of Chlamydomonas reinhardtii in bubble column photobioreactor. This semicontinuous cultivation process was evaluated in the following conditions: 20%, 40%, and 60% culture portion withdrawal. The highest culture withdrawal percentage (60%) provided the best results, as an up to 161% increase in mCherry productivity (454.5 RFU h-1 - Relative Fluorescence Unit h-1 ), in comparison to batch cultivation (174.0 RFU h-1 ) of the same strain. All cultivations were carried out for 13 days, at pH 7, temperature 25°C and, by semicontinuous process, two culture withdrawals were taken during the cultivations. Throughout the production cycles, it was possible to obtain biomass concentration up to 1.36 g L-1 .

Application of Physicochemical Treatment Allows Reutilization of Arthrospira platensis Exhausted Medium : An Investigation of Reusing Medium in Arthrospira platensis Cultivation.

Since cultivations of Arthrospira platensis have a high water demand, it is necessary to develop treatment methods for reusing the exhausted medium that may prevent environmental problems and obtaining useful biomass. The exhausted Schlösser medium obtained from A. platensis batch cultivation in bench-scale mini-tanks was treated by varying concentrations of different coagulants, ferric chloride (6, 10, and 14 mg L-1) or ferric sulfate (15, 25, and 35 mg L-1) and powdered activated carbon (PAC, 30 and 50 mg L-1). Such treated effluent was restored with NaNO3 and reused in new cultivations of A. platensis performed in Erlenmeyer flasks. Reusing media through the cultivation of A. platensis showed satisfactory results, particularly in the medium treated with ferric chloride and PAC. The maximum cell concentration obtained in the flasks was 1093 mg L-1, which corresponded to the medium treated with ferric chloride (6 mg L-1) and PAC (30 mg L-1). This cellular growth was higher than in the medium treated with ferric sulfate and PAC, in which values of maximum cell concentration did not exceed 796 mg L-1. The cultures in the media after treatment did not modify the biomass composition. Thus, combined coagulation/adsorption processes, commonly used in water treatment processes, can be efficient and viable for treating exhausted medium of A. platensis, allowing the production of such biomass with the reduction of production cost and saving water.

Photosynthetic efficiency and rate of CO2 assimilation by Arthrospira (Spirulina) platensis continuously cultivated in a tubular photobioreactor.

Similar to other photosynthetic microorganisms, the cyanobacterium Arthrospira platensis can be used to produce pigments, single cell proteins, fatty acids (which can be used for bioenergy), food and feed supplements, and biofixation of CO(2) . Cultivation in a specifically designed tubular photobioreactor is suitable for photosynthetic biomass production, because the cultivation area can be reduced by distributing the microbial cells vertically, thus avoiding loss of ammonia and CO(2) . The aim of this study was to investigate the influence of light intensity and dilution rate on the photosynthetic efficiency and CO(2) assimilation efficiency of A. platensis cultured in a tubular photobioreactor in a continuous process. Urea was used as a nitrogen source and CO(2) as carbon source and for pH control. Steady-state conditions were achieved in most of the runs, indicating that continuous cultivation of this cyanobacterium in a tubular photobioreactor could be an interesting alternative for the large-scale fixation of CO(2) to mitigate the greenhouse effect while producing high protein content biomass.

Cultivo contínuo de Arthrospira (Spirulina) platensis em fotobiorreator tubular utilizando uréia como fonte de nitrogênio e CO2 puro ou proveniente de fermentação alcoólica / Continuous cultivation of Arthrospira (Spirulina) platensis in tubular photobioreactor using urea as nitrogen source and CO2 from cylinder or produced by alcoholic fermentation

A aplicabilidade do processo de produção de microrganismos fotossintetizantes depende da obtenção de altas concentrações de biomassa e para isso seria interessante o emprego de fotobiorreatores tubulares. Eles permitem redução da área de cultivo e menor perda de CO2 e nitrogênio amoniacal por volatilização. Em uma primeira etapa deste trabalho, Arthrospira platensis foi cultivada por processo contínuo, avaliando-se diferentes valores de vazão específica de alimentação (D = 0,2 a 1,0 dia-1) e diferentes intensidades luminosas (I = 60 e 120 µmol fótons.m-2.s-1). Verificou-se que 120 µmol fótons.m-2.s-1 associada a D igual a 0,2 dia-1 resultou em maior valor de concentração celular em regime permanente (XP = 2446 ± 74 mg.L-1.d-1), mas o mesmo I associado a maior valor de D (0,6 dia-1) levou ao melhor valor de produtividade em células (PX = 938,73 mg.L-1.d-1). Foi possível a obtenção do regime permanente em quase todos os ensaios, o que indica que o cultivo contínuo de A. platensis em fotobiorreator tubular, usando uréia como fonte de nitrogênio, pode levar a resultados satisfatórios. Considerando a preocupação em relação à substituição de combustíveis fósseis por biocombustíveis, é iminente o crescente aumento da produção de etanol ainda nos próximos anos, e esse trabalho propõe o uso do CO2 liberado pela fermentação alcoólica na produção de microrganismos fotossintetizantes como A. platensis. Para isso, em uma segunda etapa, A. platensis foi cultivada por processo contínuo, com I igual a 120 µmol fótons.m-2.s-1, empregando uréia e CO2 proveniente de fermentação alcoólica para manutenção de pH e reposição da fonte de carbono. O uso desse CO2, sem tratamento prévio, associado a D igual a 0,6 dia-1 e concentração de uréia de 3,2 mM no meio de alimentação, permitiu a obtenção de PX igual a 839 ± 25 mg.L-1.d-1, o que está próximo de 938 ± 30mg.L-1.d-1, obtido com CO2 puro de cilindro. Estes resultados mostram que o uso de CO2 de fermentação alcoólica, associado a...

Appropriately designed tubular photobioreactors seem to be suitable for photosynthetic biomass production. It can reduce the cultivation area and provide lower loss of CO2 and ammoniacal nitrogen by volatilization. In a first step of this study, Arthrospira platensis was cultivated by continuous process, testing different values of dilution rate (D = 0.2 to 1.0 d-1) and light intensities (I = 60 and 120 µmol photons.m-2.s-1). The results of these runs showed that the maximum steady-state cell concentration (XS = 2446 ± 74 mg.L-1.d-1) was achieved at 120 µmol photons.m-2.s-1 and D of 0.2 d-1, but the same light intensity associated to higher dilution rate (0.6 d-1) provided the highest cell productivity (PX = 938 ± 30 mg.L-1.d-1), a value appreciably higher than that reported in other studies. Besides, steady-state conditions were achieved in most of the runs indicating that A. platensis continuous cultivation in the tubular photobioreactor, using urea as nitrogen source, can be performed effectively, thus appearing an interesting alternative for the large scale fixation of carbon dioxide to mitigate the green house effect. Taking into account the concern about the substitution of fossil fuel with biofuels, its evident that the ethanol production is going to increase even more in the next years, and this study propose the use of the CO2 released by the alcoholic fermentation for the production of photosynthetic microorganism such as A. platensis. For this purpose, in a second step, cultivations of A. platensis were carried out with 120 µmol photons.m-2.s-1 by continuous process, using urea and CO2 from Alcoholic fermentation for pH maintenance and carbon source replacement. The use of this CO2, without any treatment, associated with a D of 0.6 d-1 and feed urea concentration of 3.2 mM provide us a PX of 839 ± 25 mg.L-1.d-1, which is slightly lower than 938 ±30 mg.L-1.d-1, obtained with pure CO2 from cylinder. Our results showed that the use of CO2 from...

Influence of ammonium chloride feeding time and light intensity on the cultivation of Spirulina (Arthrospira) platensis.

This study dealt with the influence of both the feeding time and light intensity on the fed-batch culture of the cyanobacterium Spirulina (Arthrospira) platensis using ammonium chloride as a nitrogen source. For this purpose, a 2(2) plus star central composite experimental design combined with response surface methodology was employed, and the maximum cell concentration (X(m)), the cell productivity (P(X)), and the yield of biomass on nitrogen (Y(X/N)) were selected as the response variables. The optimum values of X(m) (1,833 mg L(-1)) and Y(X/N) (5.9 g g(-1)) estimated by the model at light intensity of 13 klux and feeding time of 17.2 days were very close to those obtained experimentally under these conditions (X(m) = 1,771 +/- 41 mg L(-1); Y(X/N) = 5.7 +/- 0.17 g g(-1)). The cell productivity was a decreasing function of the ammonium chloride feeding time and a quadratic function of the light intensity. The protein and lipid contents of dry biomass collected at the end of cultivations were shown to decrease with increasing light intensity.

Influence of pH, temperature, and urea molar flowrate on Arthrospira platensis fed-batch cultivation: a kinetic and thermodynamic approach.

Arthrospira platensis was cultivated photoautotrophically at 6.0 klux light intensity in 5.0-L open tanks, using a mineral medium containing urea as nitrogen source. Fed-batch experiments were performed at constant flowrate. A central composite factorial design combined to response surface methodology (RSM) was utilized to determine the relationship between the selected response variables (cell concentration after 10 days, X(m), cell productivity, P(X), and nitrogen-to-cell conversion factor, Y(X/N)) and codified values of the independent variables (pH, temperature, T, and urea flowrate, K). By applying the quadratic regression analysis, the equations describing the behaviors of these responses as simultaneous functions of the selected independent variables were determined, and the conditions for X(m) and P(X) optimization were estimated (pH 9.5, T = 29 degrees C, and K = 0.551 mM/day). The experimental data obtained under these conditions (X(m) = 749 mg/L; P(X) = 69.9 mg/L.day) were very close to the estimated ones (X(m) = 721 mg/L; P(X) = 67.1 mg/L.day). Additional cultivations were carried out under the above best conditions of pH control and urea flowrate at variable temperature. Consistently with the results of RSM, the best growth temperature was 29 degrees C. The maximum specific growth rates at different temperatures were used to estimate the thermodynamic parameters of growth (DeltaH* = 59.3 kJ/mol; DeltaS* = -0.147 kJ/mol.K; DeltaG* = 103 kJ/mol) and its thermal inactivation (DeltaH(D) (o) = 72.0 kJ/mol; DeltaS(D) (o) = 0.144 kJ/mol.K; DeltaG(D) (o) = 29.1 kJ/mol).