Screening Method for Microalgae with Bioremediation and Plant Biostimulant Potential ^†

Introduction: During the last decades, the high potential of microalgal products in different industrial and agricultural fields has been demonstrated [1]. Microalgae are a sustainable solution in many applications and challenges, from polluted water treatment to plant biostimulants. We aimed to develop a method to select microalgae strains capable of hydrocarbon biodegradation from those with plant biostimulant characteristics. Such strains could be further used in various applications, especially for bio- and/or rhizoremediation of hydrocarbons polluted water and soil. Materials and Methods: Three species of axenic microalgae, with plant biostimulant potential, Chlorella sorokiniana, Desmodesmus communis, and Raphidocelis subcapitata, were cultured in BG11 media in the presence of two long-chain alkanes, decane, and hexadecane, respectively. The concentrations tested were 1% and 5% v:v. The microalgae cultures were kept under atmospheric conditions of light and temperature, with daily orbital manual agitation. The optical densities, biomass quantities, and chlorophyll concentrations were used to determine the effect of the hydrocarbons on microalgae growth [2]. The residual alkanes were quantified at the end of the tests by the GC-MS method to evaluate the potential for bioremediation. Results: Both hydrocarbons stimulated the microalgae growth, especially C16 alkane, the variants with 5% hexadecane recording the highest amounts of weighed biomass. The cultures with Ch. Sorokiniana had almost four-fold higher biomass than control. The hydrocarbon peaks areas from GC-MS chromatograms decreased in the presence of microalgae, mainly in the cultures with Ch. Sorokiniana microalgae. Conclusions: Microalgae were capable of growing in hydrocarbon-supplemented growth media with high rates of alkane biodegradability. Ch. sorokiniana showed the highest efficiency in bioremediation. Furthermore, a significant increase in microalgae biomass quantities was obtained in the presence of 5% hexadecane. Microalgae cultivation in hydrocarbon presence increases the efficiency of producing microalgae biomass with plant biostimulants potential.