A group of researchers from the State University of Campinas (Unicamp) has been growing microalgae in the laboratory under controlled conditions to take advantage of 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-carotenes, and other valuable compounds, including phycocyanin, a natural blue pigment," says Luisa Fernanda Ríos, a researcher at the Laboratory of Optimization, Projects and Advanced Control (LOPCA) of the School of Chemical Engineering of Unicamp. She explains that the colors of 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 exchange of air with the environment – such as photobioreactors, in which it is possible to keep the microalgae growth conditions more controlled. Open systems are tanks (raceway ponds, which are shallow artificial ponds) used in the laboratory, but which exchange air with the atmosphere, therefore open to the environment. Proteins, carbohydrates, lipids, pigments and hydrocarbons were extracted and quantified. It is the first time that B. terribilis hydrocarbons have been extracted and characterized, according to the research group.

"Studies in the cultivation of B. terribilis have great economic and environmental relevance, but are rarely treated in the scientific literature," the text states. "Microalgae are the oldest microorganisms, responsible for producing up to 50% of the oxygen we breathe," Ríos explains. "By joining fungi, they created the organic matter we now know 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 has in its composition these microalgae, which have been deposited on the bottom of the sea and land. "Imagine how many important things there are inside the cell of this organism," says Ríos, who holds a PhD in chemical engineering from Unicamp.

Algae under stress

Microalgae are single-celled and reproduce by mitosis – each cell divides into two identical cells, generating exponential multiplication. "What we do in the lab is we grow them and take advantage of all these biocompounds present within the cells. We need to 'kill' them to take advantage of them, but we don't have to worry as they grow very fast, so it would be impossible to end them."

B. terribilis oils are suitable for the synthesis of biofuels, as they are composed of long-chain hydrocarbons and a higher amount of saturated and monounsaturated fatty acids. The study, supported by FAPESP, helps to fill the information gap on cultivation, stress and composition of this microalgae, supporting decision-making on cultivation parameters and applications in a biorefinery context.

The "stress" in this case is the elimination of some important nutrient for the growth of microalgae, such as phosphorus or nitrogen. "When she feels that she does not have some of these nutrients, she begins to accumulate fat, that is, lipids, to try to survive. Thus, we get it to accumulate more of the metabolite of interest. We say that we stress it because we eliminate basic nutrients for growth," explains Ríos. "But we have slowed down 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 to 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 crop.

The article Effects of cultivation systems and nutrient limitation on the growth and metabolite biosynthesis of Botryococcus terribilis, which is also signed by Bianca Ramos Estevam, Rubens Maciel Filho and Leonardo Vasconcelos Fregolente, can be read here.

Source: Um só Planeta