High-yield cultivation of Marinococcus M52 for production and recovery of hydroxyectoine.

Ectoine and hydroxyectoine, produced by Halomonas ssp. and Marinococcus ssp., have been extensively characterized and proposed for biotechnological applications. Large-scale production of ectoine was achieved by implementing the so-called "milking process" by Bitop (Witten, Germany) and commercializing compatible solutes as stabilizers for biological systems. However, there is a continuing interest in optimization of the production process for hydroxyectoine alone, as the latter was shown to have greater stabilization capacity. Recently, Marinococcus strain M52 was selected for its ability to convert most ectoine into hydroxyectoine during a prolonged stationary phase. This study reports on the correlation between growth conditions and hydroxyectoine production in Marinococcus M52 cultivation. We demonstrated that a dissolved oxygen content higher than 10% during cultivation leads to more rapid accumulation of hydroxyectoine than of ectoine (with hydroxyectoine up to 1.6 g l-1). In addition, we employed a microfiltration bioprocess to improve biomass and yield of products (reaching 3.6 g l-1 of hydroxyectoine). Finally, we developed a novel extraction method based on osmotic down-shock coupled with thermal permeabilization to recover the desired products from the biomass.

High cell density cultivation of probiotics and lactic acid production.

The commercial interest in functional foods that contain live microorganisms, also named probiotics, is paralleled by the increasing scientific attention to their functionality in the digestive tract. This is especially true of yogurts that contain strains of lactic-acid bacteria of intestinal origin, among these, Lactobacillus delbrueckii ssp. bulgaricus is extensively used in the dairy industry and it has been demonstrated to be a probiotic strain. In this work we describe high cell density cultivations of this microorganism also focusing on the stereospecific production of lactic acid. Key parameters such as medium composition (bactocasitone concentration) and diverse aeration conditions were explored. The results showed that the final concentration of biomass in anaerobic fermentation was lower than the one obtained in microaerophilic conditions, while it gave a very high productivity of lactic acid which was present as a racemic mixture in the permeate. Fermentation experiments carried out with air sparging, even at very low flow-rate, led to the production of the sole L(+) lactic acid giving sevenfold increase in biomass yield in respect to the batch cultivation. Finally, a mathematical model was developed to describe the microfiltration bioprocess applied in this research considering an inhibition kinetic and enucleating a suitable mathematical description for the decrease of the transmembrane flux.