Mixotrophy in marine microalgae for renewable biomass production

Project Information

MMM-REBIO

Grant agreement ID: 844909

DOI

10.3030/844909

Project closed

EC signature date 10 April 2019

Start date 4 November 2019

End date 3 November 2021

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 191 852,16

EU contribution

€ 191 852,16

Coordinated by

GOETEBORGS UNIVERSITET
Sweden

Periodic Reporting for period 1 - MMM-REBIO (Mixotrophy in marine microalgae for renewable biomass production)

Reporting period: 2019-11-04 to 2021-11-03

Summary of the context and overall objectives of the project

Microalgae are unicellular photosynthetic microorganisms that have originated from endosymbiotic events in which a heterotrophic ancestor fused with various photoautotrophic (photosynthetic) organisms. Thanks to this evolutionary history, they possess both photosynthetic and respiratory organelles (chloroplasts and mitochondria, respectively) and hence exhibit trophic flexibility. Although most microalgae are photoautotrophs, some of them are also able to use organic carbon via respiration either in the dark (heterotrophs) or in a light-dependent manner (mixotrophs). Mixotrophy is the trophic mode in which both CO2 and organic carbon are assimilated simultaneously thanks to the activation of both respiration and photosynthesis. It can be employed as a method to increase the productivity of microalgae cultivated in low light conditions. To minimize the additional cost of organic carbon supplementation, industrial wastewater and biodiesel waste (i.e. glycerol) are often used for algae cultivation and biomass production.
Although mixotrophy is a common method to increase productivity in algal industrial cultivation (or in R&D studies), only a handful research projects have focused on understanding the underlying molecular processes in microalgae. The overall goal of the MMMREBIO project was to use the mixotrophic growth as a strategy to maximize the outdoor productivity of selected microalgal species on the Swedish west coast during the whole year combining both applied and basic research.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

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) and in the social media (LinkedIn, Twitter).

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The scientific findings from MMMREBIO have advanced the knowledge on the mixotrophic metabolism of the diatom Sm. Diatoms are the most abundant and large group of microalgae that dominate both fresh and marine waters. The study of mixotrophy in diatoms is very important, a topic so far only poorly explored, for the scientific community, especially for both ecological and physiological experts. As far as we know, our work is the first evidence on the ability of Sm of adopting the mixotrophic metabolism during the winter. This finding could explain the ecological success of this diatom in Swedish west coast. However, to fully understand the mechanism of mixotrophy in Sm and to determine the conservation in all diatoms are too ambitious topics to be solved in such a short time. Further analyses are ongoing at CNRS to acquire new knowledge on the communication between chloroplast and mitochondrion in Sm.
We also showed that the mixotrophic cultivation can be used as a strategy to increase the biotechnological potential of local strains in an outdoor system on the Swedish west coast.
Particularly interesting were the results of Ng that, when grown in mixotrophy, increased both biomass and the production of high-value molecules for employment in several fields such as pharmaceutical, food, feed, or biofuel. These findings are very important for R&D microalgal research and rise keen interest in microalgae cultivation companies in Sweden.

WPs and tasks description