Hydroponic farming produces large amounts of wastewater overloaded with nutrients, mineral pollutants, and organic matter. Thus, disposal of agricultural effluents is an emerging challenge of important environmental and economic impact. Exploring means to effectively recycle and reutilize wastewaters, microalgae offer an innovative solution for viable bioremediation, while simultaneously producing high value bioproducts with various biotechnological applications1 . In the present study, effluent water from hydroponic cultures was used for isolating naturally present microalgal species that may possibly be of biochemical interest and play a crucial role in wastewater treatment.
Material and Methods
The isolati on process of indigenous microalgae strains from hydroponic effluents was roughly divided in five successive steps: size separation, general enrichment and 3 separation stages including serial dilution, agar plating, agar streaking and micropipette isolation. Four different strains were isolated and characterized with morphological, biokinetic and molecular taxonomy methods. The microalgal strains were subsequently cultured under steady conditions in both commonly used media and hydroponic water effluents in order to estimate a) the potentiality of hydroponic wastewater as an alternative medium for microalgae b) microalgae exploitation for wastewater bioremediation c) the valorization of the biomass derived and its potent in vitro bioactivities . Nutrient removal from the microalgae cultures was measured as well as total biochemical characterization (primary and secondary metabolites) was determined to microalgae biomass . Custom made extracts were also produced in order to evaluate in vitro potential bioactivity on human cell line Caco-2.
Our results revealed that all microalgae species included in the study were able to efficiently grow in hydroponic water effluents utilizing the available nutrients (Fig.1)
Using the TufA and RBCL genes from the isolated microalgae strains and the corresponding sequences from reference strains deposited in NCBI a concatenated phylogenetic tree was created using the Maximum Likelihood method (Bootstrap 1000, Kimura 2-parameter) (Fig. 2). Based on the results, it’s safe to state that PR2 exhibits strong resemblance to C. reinhardtii and PR4 strongly resembles S. reticulata and S. rubescens.
Biochemical characterization of microalgae biomass ( Table 1 ) highlighted the high-efficiency biomass of the isolated strains using hydroponic effluents. In order to obtain more data on the accumulation of a wide range of compounds spanning both primary and secondary metabolism , GC-MS based metabolomic platform was also used .
Custom produced extracts from the above microalgae presented no cytotoxicity on Caco2 cells whereas PR4 (0.1-2.5μg/ml) exhibited even greater viability of Caco-2 vs to control ( Fig 3 ). T he ability of these extracts to protect Caco2 cells against H2O2 induced oxidative stress was also demonstrated (Fig. 4). To this end, t ranscriptome analysis of Caco2 cells pre-treated with PR2 (0,5μg/ml) and PR4 (0,1μ g/ml) followed by H2O2 induced stress revealed significant alternation at several human genes expression.
1 Yuling Song, Lijun Wang, Xi Qiang, Wenhui Gu, Zengling Ma, Guangce Wang, The promising way to treat wastewater by microalgae: Approaches, mechanisms, applications and challenges, Journal of Water Process Engineering, Volume 49, 2022, 103012, ISSN 2214-7144.
Acknowledgments: The project is funded by the General Secretariat for Research and Technology of the Ministry of Development and Investments under the PRIMA Programme. PRIMA is an Art.185 initiative supported and co-funded under Horizon 2020, the European Union’s Programme for Research and Innovation.