High added value metabolites production in photobioreactors (PBR) using microalgae encapsulated in hybrid material (VALOALGUE* project)

///Key words: Gaussia luciferase, Chlamydomonas reinhardtii, microalgae, photobioreactor, encapsulation

Currently, several scientific researches threat about culture of microalgae, due to their ability to produce metabolites like lipids or saccharides. Mass culture of microalgae should allow the production of bio-sourced molecules technologically interesting (bioethanol, biofuel,...).
But microalgae can also produce, in smaller quantity, high added value metabolites, naturally produced or resulting from a genetic transformation.

Chlamydomonas reinhardtii can be considered as a model for this kind of researches. In fact, this microalgae can be modified for the purpose of producing and excreting a selected metabolite like recombinant proteins.
However, given the size of microalgae, free cell cultures are not workable to collect molecules in the culture media. The encapsulation of the microalgae in a porous material should be able, at the same time, to hold in microalgae and to allow diffusion of metabolites. The recovery of the metabolites present in the culture medium should therefore be easier.

In this research, Chlamydomonas reinhardtii has been modified to produce Gaussia luciferase, a recombinant protein that has the particularity to emit light in presence of its substrate (coelenterazine):

Coelenterazine + O2 Coelenteramide + CO2 + Light (485nm)

Nowadays, Gaussia luciferase does not present any particular interest, but was selected for its quantification by bioluminescence property. After proving the effectiveness of the concept, some more interesting recombinant proteins will be study.

One of the challenges of the project is the choice of the porous material because it must meet several criteria:
- The material and the production protocol have to be biocompatible
- It has to hold in microalgae and allow the diffusion of nutrients and the excreted metabolites
- It has to show good mechanical resistance
Alginate and alginate/silica beads are currently being investigated and especially the biocompatibility and the diffusion of the Gaussia luciferase.

The design of the photobioreactor and the influence of various parameters will be a great part of the study. In fact, each parameter will have a influence on the process, and most of them have to be tested (design: fluidized bed, bubble column, airlift,... and the parameters: medium culture, beads diameter, beads/medium ratio, ...)

To this must also be added the development of methods to recover the Gaussia luciferase (purification) on a small scale first but also on the industrial process, and the material recycling after the beads life cycle.

***VALOALGUE is part of the global project 'Algae Factory', funded by ERDD***