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- Reducing nutrient requirement using nitrogen-fixing bacteria for microalgae cultivationPublication . Melkonyan, Lusine; Ferreira, Alice; Bastos, Carolina R. V.; Figueiredo, Daniel; Lopes da Silva, Teresa; Avetisova, Gayane; Karapetyan, Zh.; Toplaghaltsyan, A.; Gouveia, LuisaABSTRACT: In environments, microalgae have been observed to coexist with bacteria. Different nitrogen-fixing bacteria (NFB) were isolated from Armenian soils and their growth was evaluated in co-cultivation with the microalga Tetradesmus obliquus and cyanobacteria Synechocystis sp. PCC 6803. The most effective mutualistic consortium was T. obliquus-NFB5 (Sphingobacterium sp. L13G8). This resulted an increase in both populations, chlorophyll fluorescence, biomass protein, carbohydrate content, an effect on lipid metabolism, without the need for external nitrogen. The findings demonstrated the significance of employing NFB for microalga growth, as they facilitate the essential nitrogen provision in N-free Bristol medium. Moreover, in mutualistic consortia, microalgae facilitate the exudation of dissolved organic carbon and O2 to bacteria, which, in turn, become available for bacteria, thereby reducing the necessity for energy-consuming aeration processes in co-cultivation. In return, the bacteria provide the microalgae with CO2, B vitamins and demineralize N2, P, S, thereby further supporting the growth of microalgae.
- Monitoring C. vulgaris Cultivations Grown on Winery Wastewater Using Flow CytometryPublication . Lopes da Silva, Teresa; Silva, Thiago; França, Bruna Thomazinho; Ribeiro, Belina; Reis, AlbertoABSTRACT: Winery wastewater (WWW), if released untreated, poses a serious environmental threat due to its high organic load. In this study, Chlorella vulgaris was cultivated in diluted WWW to assess its suitability as a culture medium. Two outdoor cultivation systems-a 270 L raceway and a 40 L bubble column-were operated over 33 days using synthetic medium (control) and WWW. A flow cytometry (FC) protocol was implemented to monitor key physiological parameters in near-real time, including cell concentration, membrane integrity, chlorophyll content, cell size, and internal complexity. At the end of cultivation, the bubble column yielded the highest cell concentrations: 2.85 x 106 cells/mL (control) and 2.30 x 106 cells/mL (WWW), though with lower proportions of intact cells (25% and 31%, respectively). Raceway cultures showed lower cell concentrations: 1.64 x 106 (control) and 1.54 x 106 cells/mL (WWW), but higher membrane integrity (76% and 36% for control and WWW cultures, respectively). On average, cells grown in the bubble column had a 22% larger radius than those in the raceway, favouring sedimentation. Heterotrophic cells were more abundant in WWW cultures, due to the presence of organic carbon, indicating its potential for use as animal feed. This study demonstrates that FC is a powerful, real-time tool for monitoring microalgae physiology and optimising cultivation in complex effluents like WWW.