Microalgae from aeroterrestrial environments: scenedesmus vacuolatus as a potential resource for mass cultivation

Microalgae are promising microorganisms deserving attention within the vast array of new biotechnologies. They are employed in many commercial applications: human and animal nutrition, pharmaceutical and cosmetical components, wastewater treatments. One of the critical factor for the industrial uses of microalgae is the production of biomass. So two types of cultivation system have been developed to increase the biomass production: liquid cultivations and immobilized cultivations. Moreover the biomass production depends on the type of organisms. Scenedesmus vacuolatus is known to have high biomass productivity among green algae, and has been frequently tested for biotechnological applications. Understanding the real potentiality of cultivation of this alga still needs new experimental evidences. In my dissertation, I focus the attention to the possible use of Scenedesmus vacuolatus as a model organism for massive cultivation and, consequently, to develop an industrial production, either in liquid- or immobilized-culture systems. To assess potential applications of Scenedesmus vacuolatus in the fields of biomass production, it is necessary to characterize its growth and photosynthetic activity. Different sets of experiments have been carried out in both type of cultivations liquid and immobilized. Firstly, I analyze several Scenedesmus vacuolatus strains and I prove the best candidate for my experiments is 053. Secondly, in liquid culture, thanks to the support of kinetic model I highlight the bottleneck of the photosynthesis process in photobioreactor in different operating conditions is photoinhibition. Moreover, in liquid culture, Scenedesmus vacuolatus shows a very good growth performances in enclosed photobioreactors achieving high biomass in presence of 2% CO2. Thirdly, in the study of immobilized cultivation, thanks to the combination of photograph imaging analysis and pulse amplitude modulation fluorimetry, I study the first steps of the adhesion process of this microalga in submerged condition and analyze its physiological state. Also in this case, Scenedesmus vacuolatus shows positive outcomes: it has a good ability of attachment and the adhesion process is scarcely influenced by the kind of carrier used. Eventually, by studying growth of Scenedesmus vacuolatus on a on a porous substrate bioreactor (the Twin Layer system), the performances of Scenedesmus vacuolatus in liquid systems are shown lower than that ones in attached cultivation and also in this case the addition of CO2 is necessary to increase the productivity. Comparison with data obtained from other organisms in other experiments on porous substrate bioreactor shows that immobilized cultivation of Scenedesmus vacuolatus based on Twin-layer system allows to achieve very good values of biomass productivity and light yield and confirms that also in immobilized cultivation Scenedesmus vacuolatus is a good candidate for industrial uses.