Non-photoautotrophic cultivation of microalgae: an overview

Abstract

Microalgae are a heterogeneous group of microorganisms that produces biomass from which can be extracted various products such as proteins, carbohydrates, pigments and oils with profile containing saturated fatty acids, polyunsaturated and monounsaturated. These microorganisms have different forms of energetic metabolism, especially the photoautotrophic, heterotrophic, and mixotrophic photoautotrophic. Understanding these metabolic forms allows to apply microalgae strategies of cultivation aiming to increase algal biomass production, and its co-products in large scales. Traditionally, the microalgae cultivation is done by exploiting their photoautotrophic metabolism. However, studies have point out some advantages in the production of biomass of these microorganisms by using other metabolic pathways. Thus, this review aims to present an overview of the forms of non-photoautotrophic microalgae metabolism and considerations on the different systems of biomass production of these microorganisms. In the heterotrophic metabolism, sources of carbon that have stood out the most for microalgae are: glucose, glycerol and acetic acid. Nevertheless, there are several studies that present alternative sources of culture medium, such as agro-industrial and sanitary waste. The mixotrophic can be defined as the metabolism when photosynthesis and oxidation of external organic carbon take place at the same time. In the photoherotrophic metabolism is the light energy source and the organic compound is a carbon source. The non-photoautotrophic cultivation systems are high potential, mainly for increasing production with better productivity and scaling up. However, it should be noted that information about these microalgae cultivation systems on a large scale for a competitive production is scarce.