Viability of Chlamydomoans reinhardtii encapsulated in alginate/silica beads

The microalga Chlamydomonas reinhardtii is used in a wide range of fields: e.g. production of recombinant proteins, hydrogen photoproduction or biosorption of heavy metals either in free cells cultures or in encapsulated forms (e.g. immobilized cells in alginate beads).
As a first step this study presents viability results (O2 production rates) of encapsulated Chlamydomonas reinhardtii in alginate/silica beads of various compositions.
The material is made of pure alginate solution or alginate/silica mixture containing microalgae dropped in a coacervation bath containing BaCl2 or CaCl2 and a polycation (poly(diallyldimethylammonium chloride)). The choice of the different experimental conditions has been given by Taguchi approach (type of salt (CaCl2/BaCl2), salt and polycation concentrations in the coacervation bath, duration of the coacervation step and alginate/silica ratio).
The beads are kept in TAP-HCl medium with light cycles 12:12 at ambient temperature. The O2 production is measured during one month using an OxyLab (Hansatech) equipped with a DW2 chamber.
Oxygen production and cells retention in the beads were better using BaCl2 as cross-linking agent than CaCl2 (leading to important bleaching and cell leakage within the first week). During the first two weeks, the O2 production yield ranged from 0.1 to 0.42 µmol O2.min-1.gbeads-1 (with use of BaCl2 as cross-linker) while it did not exceed 0.1 µmol O2.min-1.gbeads-1 for beads cross-linked with CaCl2. The next two weeks, the results were quite similar in both cases (BaCl2 or CaCl2 as cross-linker) with a maximum oxygen production of 0.1 µmol O2.min-1.gbeads-1.
Further studies have to be conducted: characterization of the mechanical strength of the beads, O2 production under different light cycles and/or illumination, optimisation of the composition of the culture medium, behaviour of the beads in a photobioreactor in order to find the best material composition for Chlamydomonas reinhardtii encapsulation.