Internship MsC / Stage Master 2

Context

Dark fermentation (DF) is a process where organic waste is converted by bacteria into hydrogen gas and organic compounds such as volatile fatty acids, and results in a liquid nutrient-rich effluent (DFE). These effluents can be a cheap source for the growth of mixotrophic microalgae such as Chlorella sorokiniana and Euglena gracilis. The lipids accumulated by the algae can be transesterified into fatty acid esters (FAEs) and used as biofuel or platform molecules. However, during algal cultures on DFEs, the fermentative bacteria compete with the microalgae for substrate which can negatively affect the growth yield and valorization potential of the biomass. An innovative approach to this problem, subject of a 5-year project (PEPR B-BEST) called “WAEster”, is the use of the phagotrophic microalga Ochromonas danica, which can in fact consume these bacteria. Since O. danica does not efficiently fix the CO2 released by the bacteria, consortia with Chlorella type algae can maximize carbon capture from the effluents and optimize growth yields. The growth conditions strongly influence the growth and lipid accumulation of the algae, with light intensity being crucial for Chlorella spp. and oxygen (aeration) for O. danica. Shear stress caused by aeration and/or agitation is a factor to be considered since O. danica is relatively fragile due to the lack of a cell wall. With FAEs as the final product of the WAEster process, the level at which lipids can be accumulated and functionalized will finally determine the valorization potential of the produced biomass.

Objective and approach

Cultures of O. danica and Chlorella species on different DFEs were so far done in standard culture conditions without forced aeration. The aim of this study is to optimize growth on DFEs of O. danica and C. vulgaris in consortia, focusing in particular on the influence of light and the effect of aeration, used to control oxygen levels. DFEs will be produced and used untreated, including bacteria, for microalgae cultivation. Different light intensities, aeration setups (bubble size) and oxygen concentrations will be tested. Cultures will be analyzed for algal growth (dry weight, algae cell counting) and biomass composition (lipids, sugars), as well as metabolites in the culture medium (HPLC, GC). Carbon can be analyzed via TIC/TOC or elemental analyzer. Potentially, omics type analyses may be employed to better understand observed physiology. The essential performance parameters are biomass productivity and carbon-based growth yield, with ultimate finalities being lipid content and transesterification into FAEs, the final product of the WAEster process.

Internship location

The internship will take place at the Laboratory of Environmental Biotechnology (LBE – INRAE), located in Narbonne in the south of France (Occitanie).
The research carried out at the LBE aims to develop the concept of environmental biorefinery which consists of treating by-products of human activities (waste, agricultural residues, effluents) and valorizing them into resources of industrial interest (bioenergies, biomolecules, organic fertilizers) while minimizing their environmental and health impact.
The working environment encourages exchanges and collaboration between researchers, doctoral students and interns. In addition, the region offers a particularly pleasant living environment in the summer, with several accessible activities (sailing, climbing, hiking, etc.).
In collaboration with Prof. Maeva Subileau (IRB-IATE, Institut Agro Montpellier), certain aspects of lipid analyses may be addressed during visits of the IRB lab.

Candidate profile

This internship is aimed at BAC+5 level students with good knowledge of general microbiology and processes, interested in applied research but also in understanding metabolic pathways (omics analyses). Practical experience in the culture of microorganisms (particularly algae) is appreciated.

This work will be continued in a PhD position starting in October 2025, and while applying for this internship, candidates may express the wish to pursue this position. An agreement must be reached by June 2025.

Application: Please send a motivation letter and CV

Duration: 6 months starting in mars 2025

Domaine: Microbiology, microalgae bioprocesses

Remuneration : Gratification at € 4.35/hr

Supervision :    

• Dr. Robert van Lis (robert.van-lis_at_inrae.fr)
• Pr. Maeva Subileau (maeva.subileau-at-supagro.fr)