A group of researchers from the State University of Campinas (Unicamp) has been cultivating microalgae in the laboratory under controlled conditions to use their metabolites, especially lipids, with the main objective of producing biofuel. The work was described in an article published in the journal Biomass Conversion and Biorefinery.
“It is also possible to extract protein and carbohydrates and use them as food, in addition to obtaining products that can be used in the cosmetic area, such as beta-carotene, and other valuable compounds, including phycocyanin, a natural blue pigment”, says Luisa Fernanda Ríos , researcher at the Optimization, Projects and Advanced Control Laboratory (LOPCA) at the Faculty of Chemical Engineering at Unicamp. She explains that the colors of the seas and rivers result from the presence of microalgae, which can be blue, green or brown.
The work, signed by four LOPCA scientists, analyzes and compares, for the first time, the growth and productivity of the species Botryococcus terribilis in closed and open systems. Closed systems are those in which there is no air exchange with the environment – such as photobioreactors, in which it is possible to maintain more controlled microalgae growth conditions. Open systems are tanks (raceway ponds, which are shallow artificial lagoons) used in laboratories, but which exchange air with the atmosphere, therefore open to the environment. Proteins, carbohydrates, lipids, pigments and hydrocarbons were extracted and quantified. This is the first time that hydrocarbons from B. terribilis have been extracted and characterized, according to the research group.
“Studies on B. terribilis cultivation have great economic and environmental relevance, but are rarely addressed in the scientific literature”, states the text. “Microalgae are the oldest microorganisms, responsible for producing up to 50% of the oxygen we breathe,” explains Ríos. “Combining with fungi, they created the organic matter we know today as plants.”
Microalgae grow through the phenomenon of photosynthesis identical to that of plants, that is, they receive carbon dioxide (CO2) from the atmosphere and energy from the sun and transform them into oxygen. Thus, they accumulate different types of metabolites, such as proteins, carbohydrates and lipids – and, to a lesser extent, carotenoids, chlorophyll and vitamins.
Oil also contains these microalgae in its composition, which were deposited at the bottom of the sea and land. “Imagine how many important things are inside the cell of this organism”, highlights Ríos, who has a PhD in chemical engineering from Unicamp.
Algae under stress
Microalgae are unicellular and reproduce through mitosis – each cell divides into two identical cells, generating exponential multiplication. “What we do in the laboratory is cultivate them and use all these biocompounds present inside the cells. We need to 'kill' them to take advantage of them, but we don't need to worry, as they grow very quickly, so it would be impossible to get rid of them.”
B. terribilis oils are suitable for the synthesis of biofuels, as they are composed of long-chain hydrocarbons and a greater amount of saturated and monounsaturated fatty acids. The study, supported by FAPESP, helps fill the gap in information about the cultivation, stress and composition of this microalgae, supporting decision-making about cultivation parameters and applications in a biorefinery context.
The “stress” in this case is the elimination of some important nutrient for microalgae growth, such as phosphorus or nitrogen. “When it feels like it doesn’t have any of these nutrients, it starts to accumulate fat, that is, lipids, to try to survive. This way, we can accumulate more of the metabolite of interest. We say we stress it, because we eliminate basic nutrients for growth”, explains Ríos. “But we reduce the growth rate of the microalgae and, therefore, the percentage of other metabolites, such as protein and carbohydrates, so it is very important to know which compound is of interest to us and make a balance that suits the study.”
The stress condition increased the production of lipids and hydrocarbons by up to 49% and 29%, respectively, but the percentage of proteins decreased from 32% to 26%. The percentage of carbohydrates (15%) and pigments (0,41%-0,86%) remained similar in the stressed and non-stressed crops.
O article Effects of cultivation systems and nutrient limitation on the growth and metabolite biosynthesis of Botryococcus terribilis, is also signed by Bianca Ramos Estevam, Rubens Maciel Filho and Leonardo Vasconcelos Fregolente.
