Production of diatom lipid extracts: optimization of culture in a biomimetic photobioreactor and extraction with high selectivity and low environmental impact

Currently, the market for lipids, including carotenoids, is growing rapidly, particularly in the biofuel, healthcare, cosmetics, and dietary supplement sectors. Lipids can exhibit antioxidant and antibacterial properties, contribute to the prevention of chronic cardiovascular diseases and certain types of cancer, and support the immune system, among other things. Some benthic diatoms can be considered oilseeds and constitute a very interesting source of lipids with biological activity, notably antibacterial activity (Cointet et al. 2021). However, while the valorization of this family of compounds is promising, the valorization of each of its constituents offers greater added value.

This project proposes to intensify the culture of an oleaginous diatom (Staurosira sp. NCC182) and the fractionation of its lipid content. This diatom produces bioactive lipids (Cointet et al. 2021), mainly triglycerides. The three main fatty acids are: palmitoleic acid 9-16:1 (50%), palmitic acid 16:0 (29%), and EPA 5,8,11,14,17-20:5 (6%). Several fractions, containing either triglycerides, pigments, or glycolipids, exhibit bacterial activity against two Gram-positive bacteria, Bacillus subtilis and Staphylococcus aureus.

It therefore seems wise to extend the preliminary work undertaken by the supervisory team of this thesis on the culture of this diatom, with the aim of optimizing and intensifying its culture but also its refining via the extraction and fractionation of its lipids.

One of the project's objectives is to optimize the culture of this benthic diatom in biomimetic immobilized culture or intermittent fluidized bed bioreactors, whereas until now this culture has been carried out in air-lift bioreactors, which are poorly suited to the benthic growth mode of the diatom. An experimental design will be implemented in which different values ​​of process control parameters will be set (hydraulic and solid (biomass) residence time, biological loading, biomass support, etc.). Subsequently, their individual effects and their interactions with the biological response will be analyzed. The cultures will be characterized by monitoring biomass growth parameters and its fine lipid composition, as well as by bioactivity tests.

The objective is also to extract and fractionate lipid molecules from biomass (triglycerides, sterols, hydrocarbons, glycolipids, phospholipids, carotenoids). Another unique aspect of this project is the implementation of a highly selective refining process with a low environmental impact. The siliceous frustule will be mechanically broken down using a ball mill, followed by centrifugation. Conventional operating parameters will be adopted for these operations in order to focus on the original step of the refining process: the "extraction-purification" coupling. Lipid extraction will be carried out using "green" solvents that are less toxic than conventional organic solvents. Fractionation will be performed using new, resistant, and selective filtration membranes in organic media; membrane filtration is more often used in aqueous solutions. Solvent-membrane coupling allows for a wider range of operating parameters compared to filtration alone, and therefore increases the degree of selectivity, since steric exclusion (molecular size) is complemented by solubility mechanisms in solvents.

However, this complicates the understanding of the mechanisms involved in fractionation selectivity. Solubility tests will be performed with different solvents, followed by a parametric study of the solvent-membrane system. The use of environmentally friendly solvents will be prioritized. The subsequent multivariate statistical analysis will optimize the fractionation of molecules in terms of selectivity, permeability, and standardization of the final lipid extracts produced, taking into account the variability of the input material (biomass). A bottom-up approach (progressively increasing the complexity of the filter matrix) could be implemented by reconstituting model filter juices from standard molecules in order to elucidate the mechanisms and interactions involved in molecule separation.

In order to candidate : https://amethis.doctorat.org/amethis-client/prd/consulter

      Filter by thesis supervisor / MASSE Anthony

Location of the thesis: GEPEA laboratory / ISOMer - UR 21 60

Supervisors: Anthony MASSE (GEPEA),

                      Gaëtane WIELGOSZ (ISOMer - UR 21 60),

                       Aurélie MOSSION (ISOMer - UR 21 60).

Skills:

• The candidate must have skills in (Bio)Process Engineering, Biotechnology and Biochemistry.
• Experience in microalgae cultivation would be appreciated.
• He/she must have a strong interest in experimental research.
• The candidate will have to demonstrate rigour, autonomy and dynamism.