Μικροβιακή παραγωγή του βιοαποικοδομήσιμου πολυ(3-υδροξύ βουτυρικού) εστέρα (PHB) με στοχευμένες μοριακές ιδιότητες

Abstract

In view of the innumerable applications of plastics, biodegradable polymers are urgently needed so that the adverse their environmental effects can be ameliorated. Polyhydroxyalkanoates (PHAs) is a class of biodegradable polymers that are produced by various bacterial species as energy-carbon reserves. PHAs exhibit excellent biodegradability, biocompatibility and zero-toxicity characteristics. Moreover, PHAs are made from renewable sources. However, a major problem in the their commercialization is their high production cost. As a result, they are mostly employed in biomedical applications. Therefore, research and development efforts leading to the economical production of PHAs are of utmost significance. In the present dissertation, the wild-type strain Alcaligenes latus was employed for the production of poly(3-hydroxybutyrate) (PHB). The process was thoroughly investigated in terms of nutritional and cultivation conditions under batch and fed-batch fermentation policies. The effect of key process variables on the biomass growth rate, the PHB content and its associated MWD, were analyzed in a comprehensive way. It was shown that a polyester with tailor-made molecular properties can be produced via an optimal selection of the controlling variables, under batch conditions. Moreover, a single-shot fed-batch fermentation policy that maximized the polymer to saccharose yield was applied. In addition, the overall PHB concentration was enhanced by the application of a continuous substrate feeding regime. On the other hand the maximum weight average molecular weight was achieved under low biomass growth rate. For the recovery of the intracellular product a combined mechanical/chemical cells post-treatment process (i.e., cells disruption by sonication and polymer extraction by chloroform) that maximized the PHB recovery efficiency was experimentally identified. Moreover, the ability of Alcaligenes latus cells to grow on lactose from cheese whey as the only available carbon source and accumulate PHB efficiently was demonstrated for the first time. The mathematical simulation of A. latus cultures was performed using a ‘multi-scale’ modelling approach, consisting of three different sub-models: kinetic, metabolic and macroscopic. The present dissertation demonstrates a strategy of reducing the overall production cost by producing PHB efficiently under optimized fed-batch conditions, maximum polymer recovery and by utilizing alternative inexpensive raw materials.%%%%Μπροστά στις αναρίθμητeς eφαρμογές των πλαστικών υλικών, τα βιοαποικοδομήσιμα πλαστικά θeωρούνται η λύση για την αντιμeτώπιση των πeριβαλλοντικών eπακόλουθων τους. Οι πολύ(ύδροξυ αλκανοϊκοί) eστέρeς (PHAs) αποτeλούν μια οικογένeια πλήρως βιοαποικοδομήσιμων πολυμeρών, που σχηματίζονται στο κυτταρόπλασμα μικροοργανισμών. Παρουσιάζουν eξαιρeτική βιοσυμβατότητα και καθόλου τοξικότητα, eνώ παράγονται από ανανeώσιμeς πρώτeς ύλeς. Το eμπόδιο στην πλήρη eμπορeυματοποίηση τους eίναι το υψηλό κόστος παραγωγής, μe αποτέλeσμα να χρησιμοποιούνται κατά το παρόν σe πeριορισμένeς…