Abstract
Faced with current environmental and societal challenges, it is important to develop clean and sustainable technologies. Advances in microbiology and the rise of biotechnology now make it possible to propose effective solutions to some of these challenges, related among others to the decrease of fossil resources or pollution produced by industrial activity. Microorganisms have many qualities. They are able to respond to certain stimuli, to produce complex molecules, some are also able to transform the sun's light energy with always high energy efficiency and remarkable selectivity. Nevertheless, their intensive exploitation and the need for long-term viability in artificial environments lead to increasingly drastic conditions for the use of these microorganisms. It is therefore essential to design strategies to protect them and facilitate their handling.By drawing inspiration from the biomineralisation processes that are common in Nature, it is possible to modify the environment around these microorganisms by surrounding them with a protective abiotic material, such as diatoms and chicken eggs, where shells at different scales protect biological material.
The objective of this work is to design a method to encapsulate cyanobacteria Synechococcus sp. PCC 7002 within a silica-based nanoshell within the purpose to contain and protect them improving the use of these photosynthetic prokaryotes. The synthesis of hybrid organic-inorganic material is a key point of this work. This can be obtained by using the layer-by-layer method and various additives that will direct the sol-gel synthesis of the silica material.
First, six materials are obtained following the deposition of six different polycations (poly(allylamine) hydrochloride, poly(diallyldimethylammonium chloride), poly(ethyleneimine), poly-l-arginine hydrochloride, poly-l-lysine hydrochloride, diethylaminoethyl dextran hydrochloride) around the cells. This preliminary layer serves as a support for the subsequent deposition of silica obtained after the addition of silicic acid. By comparing these materials, it has been shown that the organic component of the hybrid nanoshell has a real influence on its properties. By modifying the nature and size of polyelectrolytes, it is therefore possible to induce certain properties to the abiotic matrix.
In this context, the addition of aromatic groups, by adding poly(styrene sulfonate), which absorbs ultraviolet radiation, has protected the cells from its harmful effects. Despite the modification of the direct environment of the cell wall, cyanobacteria have retained their properties useful for bioremediation. The biosorption capacities of some heavy metals ions (Cd2+, Cu2+ et Pb2+) by cyanobacteria are thus very similar before and after the encapsulation process. Their recycling has also been shown to be possible without loss of functionality after five cycles.
Then, the use of organically modified silanes was considered in order to control the interfaces of the material by inserting organic groups. This allows the interface between the cells and the silica material to be controlled using amino organosilanes. The use of these silica materials has also allowed the addition of sulfhydryl groups on the surface, thus creating anchor points for possible grafting. These groups have thus made it possible to insert magnetic particles on the surface of the nanoshell and thus confer a certain mobility on cyanobacteria. The successful grafting of cyanobacteria onto previously treated glass slides opens the way for new types of multifunctional and innovative hybrid systems.
| Date of Award | 18 Jan 2019 |
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| Original language | English |
| Awarding Institution |
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| Sponsors | Fund for Research Training in Industry and Agriculture (FRIA) |
| Supervisor | Stephane Vincent (President), BAO LIAN SU (Supervisor), Marc Boutry (Jury), Fabrice Franck (Jury), Pierre Van Cutsem (Jury) & Alain KRIEF (Jury) |