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Target of rapamycin (TOR) is a master regulator that controls growth and metabolism by integrating external and internal signals. Although there was a great progress in the study of TOR in plants and in the model alga Chlamydomonas, scarce data are available in other green algae. Thus, in this work we studied TOR signaling in Ostreococcus tauri, the smallest free-living eukaryote described to date. This picoalga is particularly important because it has a key site at the base of the green lineage and is part of the marine phytoplankton, contributing to global photosynthesis. We investigated OtTOR complex in silico and experimentally, by using first- and second-generation TOR inhibitors, such as rapamycin and PP242. We analyzed the effect of TOR down-regulation on cell growth and on the accumulation of carbon reserves. The results showed that O. tauri responds to TOR inhibitors more similarly to plants than to Chlamydomonas, being PP242 a valuable tool to study this pathway. Besides, Ottor expression analysis revealed that the kinase is dynamically regulated under nutritional stress. Our data indicate that TOR signaling is conserved in O. tauri and we propose this alga as a good and simple model for studying TOR kinase and its regulation.

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RESUMO

The biotechnological potential of microalgae has been the target of a range of research aimed at using its potential to produce macromolecules with high added value. Particular focus has been given to biofuels' production, such as biohydrogen, biodiesel, and bioethanol from lipids and carbohydrates extracted from microalgal biomass. Bioprospecting and accurate identification of microalgae from the environment are important in the search for strains with better performance. Methodologies that combine morphology and molecular techniques allow more precise knowledge of species. Thereby, this work aimed to identify the new strain LGMM0013 collected at Iraí Reservoir, located in Paraná state, Brazil, and to evaluate the production of biomass, carbohydrates, and lipids from this new microalgal strain. Based on morphology and phylogenetic tree from internal transcribed spacer (ITS), strain LGMM0013 was identified as Desmodesmus abundans. D. abundans accumulated 1500 mg L-1 of dried biomass after 22 days of cultivation in autotrophic conditions, 50% higher than Tetradesmus obliquus (LGMM0001) (Scenedesmaceae-Chlorophyceae), usually grown in photobioreactors located at NPDEAS at the Federal University of Paraná (UFPR) to produce biomass. Analysis of the D. abundans biomass from showed an accumulation of 673.39 mg L-1 of carbohydrates, 130% higher than T. obliquus (LGMM0001). Lipid production was 259.7 mg L-1, equivalent to that of T. obliquus. Nitrogen deprivation increased the production of biomass and carbohydrates in D. abundans LGMM0013, indicating this new strain greater biomass production capacity.

O potencial biotecnológico das microalgas tem sido alvo de uma série de pesquisas que visam utilizar seu potencial para produzir macromoléculas de alto valor agregado. Uma especial atenção tem sido dada à produção de biocombustíveis, como biohidrogênio, biodiesel e bioetanol, a partir de lipídios e carboidratos de microalgas. A bioprospecção e a identificação precisa de microalgas são importantes na busca de linhagens com melhor desempenho em termos de produção de biomassa e lipídios. Metodologias que combinam morfologia e técnicas moleculares permitem uma identificação mais precisa das espécies. Assim, este trabalho teve como objetivo identificar a nova cepa LGMM0013 coletada na Represa do Iraí, localizado no estado do Paraná, Brasil e avaliar a produção de biomassa, carboidratos e lipídios. Com base na morfologia e na árvore filogenética obtida com sequências ITS ("Internal Transcribed Spacer"), a cepa LGMM0013 foi identificada como Desmodesmus abundans. D. abundans acumulou 1500 mg L-1 de biomassa seca após 22 dias de crescimento em condições autotróficas, 50% superior a Tetradesmus obliquus (LGMM0001) (Scenedesmaceae-Chlorophyceae), uma cepa cultivada frequentemente em fotobiorreatores para produção de biomassa no NPDEAS, na Universidade Federal do Paraná (UFPR) para a produção de biomassa. Na análise da biomassa de D. abundans LGMM0013 constatou-se acúmulo de 673,39 mg L-1 de carboidratos, 130% maior que T. obliquus (LGMM0001). A produção de lipídios foi de 259,7 mg L-1, equivalente à de T. obliquus. A privação de nitrogênio aumentou a produção de biomassa e carboidratos em D. abundans LGMM0013, indicando uma maior capacidade de produção de biomassa desta cepa.

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Abstract Microalgae are potential sources of a wide range of bioproducts. It is essential to choose the proper microalgae strain and culture condition to achieve an efficient production. The production yield of carotenoids by Dunaliella salina under the stress-induced culture conditions of nitrogen deprivation and excessive light intensity was evaluated. Also, a survey at laboratorial scale of the growth kinetics under different culture conditions of photoperiod, aeration, and agitation was performed for the seven species of green microalgae Ankistrodesmus fusiformis, Chlamydocapsa bacillus, Desmodesmus brasiliensis, Kirchneriella lunaris, Pseudokirchneriella subcapitata, and Scenedesmus obliquus. As a result, aeration of atmospheric air is enough to improve the growth kinetics of the seven species studied. Production of carotenoids was enhanced under stress by excessive light intensity. Although D. salina does not grow effectively under nitrogen deprivation, this stress condition may be used to quickly stimulate carotenoid production once the culture reaches a high cellular population.

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