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GROWTH OF MICROALGA HAEMATOCOCCUS PLUVIALIS IN MIXOTROPHIC CONDITIONS WITH ALTERNATIVE SOURCES OF CARBON AND CULTURE MEDIUM
BRUNO SCARDOELI TRUZZI, LúCIA HELENA SIPAúBA TAVARES
3 BIOTECNOLOGIA E INOVAçõES
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algal biomass, sugar cane molasses, growth conditions.
Microalgae may develop under different culture conditions, such as autotrophic, heterotrophic and mixotrophic conditions. Growth in mixotrophic conditions has been studied in depth due to its flexibility and high biomass. However, only certain species of microalgae may develop in such conditions due to the fact that culture is performed in the light or in the dark, with organic compounds as energy sources and sources of organic or inorganic carbon. The microalga Haematococcus pluvialis is highly relevant from the biotechnological point of view and its culture is usually undertaken in autotrophic conditions. However, several studies suggest its adaptation capacity in mixotrophic conditions. Current analysis cultivates H. pluvialis in mixotrophic condition, or rather, with sugar cane molasses as alternative source of carbon. Two culture media were employed: the inorganic nutrient NPK 10-10-10 and the organic nutrient macrophyte medium. Molasses were tested in natura and hydrolyzed. Experiments were done in triplicate at a 2-L scale during 28 days, evaluating cell growth, nutrients available in culture and biochemical composition. With regard to growth, H. pluvialis showed great culture potential in mixotrophic condition, producing high cell density. Hydrolysis converts sucrose into sugars, such as glucose and fructose, facilitating their availability. Hydrolyzed molasses provide better cell productivity. Maximum cell density was reported with hydrolyzed molasses in the two culture media, with 4.06 x 105 cell.mL-1 for NPK medium and 2.40 x 105 cell.mL-1 for macrophyte medium. In in natura molasses, cell density reached 2.44 and 1.77 x 105 cell.mL-1, respectively. Initial availability of phosphorus and total nitrogen was higher in culture with in natura molasses. Hydrolysis of molasses slightly decreased nutrient levels but kept them at the required levels for the best development of H. pluvialis. Results show greater availability of phosphorus and total nitrogen in culture with hydrolyzed molasses, and indicated an accumulation of extracellular compounds which are usually produced in prolonged cultures. Low rates of accumulated lipids were reported at the end of the experiment in the two culture media (0.5- 2.5% dry weight) due to high concentrations of nitrogen and phosphorus available in the culture. However, protein rates were high and greater in cultures with hydrolyzed molasses, 47.5% and 28.5% for NPK and macrophyte media, respectively. H. pluvialis features favorable characteristics for the culture of mixotrophic conditions and molasses hydrolysis enhanced better algal development.