The marine microalga Skeletonema marinoi (Sm) has been used as a model to understand the trophic flexibility of marine diatoms. Sm is the most common diatom on the west coast of Sweden, where it forms dense blooms, and a unique collection of hundreds of local strains are available at Algal bank of the University of Gothenburg (GUMACC). Amongst these strains, Sm142 was found to be most productive in photobioreactors simulating the light and temperature on the west coast of Sweden during winter, according to an R&D collaborative project between UGOT and the Research Institutes of Sweden (RISE). Using a combination of different approaches, we showed that the strain Sm142 can grow in mixotrophy using the glycerol as carbon source in winter condition (low light and low temperature). Our results could explain the dominance of this species during the winter season in Nordic countries. Moreover, we found that the addition of glycerol increased the biomass and its lipid content, suggesting that Sm142 could be employed industrially when cultivated under mixotrophy in outdoor system in Sweden during the winter. The data of the mixotrophic growth of the diatom Phaeodactylum tricornutum (Pt) derived from my PhD were used for generating a GSM (in collaboration with the University of Oxford) and were published in Frontiers in plant science (2021). These data were important for the characterisation of mixotrophic growth in diatoms and strengthen the scientific background of this project. This original article together with the minireview focused on the mixotrophy in diatoms published in Physiologia Plantarum (2021) helped with the experimental plan and to select the best conditions to be tested.
Other experiments are ongoing at CNRS to complete the biophysical analysis of Sm for studying the communication between mitochondria and chloroplasts in mixotrophy during the winter (i.e. ECS analysis).
The mixotrophic growth was also tested in the most productive strain Nannochloropsis granulata (Ng) isolated from the Swedish west coast and available in the GUMACC collection. This strain showed the best growth and lipid production in photobioreactors simulating the light and temperature on the west coast of Sweden during summer. In this condition the glycerol increased the biomass and the biotechnological potential of Ng, (i.e. increasing the production of high-value molecules such as carotenoids and EPA) and antitumoral activity in human cell lines. Other experiments are ongoing at SZN to complete the bioassay and metabolomic analysis in order to identify the classes of molecules responsible for the antitumoral activity of Ng. The experiments ongoing at CNRS and at SZN will complete the dataset for the publication of two scientific original articles.
During my fellowship, I also got an opportunity to be co-supervisor of two Master students, for a total of 9 months. These experiences have provided me with the skills to be a good mentor and supervisor. I also had the opportunity to give lectures and practicals during CSW’s academic courses, i.e. microalgae and plant physiology lectures for the course BIO350 'Plant Physiology in a dynamic environment’. This helped me to acquire teaching and communication skills. I presented my work in both national and international conferences, mostly in remote due to the COVID-19 pandemic. I have presented my results in several meetings within our research group at the University of Gothenburg (every two weeks), and at least twice a year with other collaborators of the project from RISE, SZN and CNRS. Moreover, two peer-reviewed, open access articles were published in two journals with an impact factor > 4. All these experiences allowed me to implement both oral and written communication skills. Two other manuscripts are currently in preparation to be submitted for publication in scientific peer-reviewed journals on: 1) the characterization of the mixotrophic growth of Sm142 and understanding the interplay between the chloroplast and mitochondrion in this strain, and 2) the optimal conditions for the mixotrophic cultivation of Ng and on bio-assay analysis. Project results and publications were promoted on the website of the University (
https://www.gu.se/en/research/mixotrophy-in-marine-microalgae-for-renewable-biomass-production-mmm-rebio(s’ouvre dans une nouvelle fenêtre)) and in the social media (LinkedIn, Twitter).
