MICROBIAL PROCESSING OF ORGANIC WASTE STREAMS INTO PHAs AND OTHER HIGH VALUE BIO-PRODUCTS

In the last years, economic and environmental concerns arose for oil shortage and climate change; for these reasons the scientific community focused on possible oil substitutes. In this perspectives, the production of new energy, materials and chemicals of non-fossil origin, could be based on biological resources such as biomasses. The efforts of the microbiology group of DAFNAE are mainly devoted to the exploitation of waste and residual biomasses for the production of high value bio-products such as polyhydroxyalkanoates (PHAs), bioethanol and biohydrogen. PHAs are today considered among the most promising substitutes for petrol-based plastics nevertheless their substitution over the conventional plastics is limited by their expensive manufacturing because of the costly raw materials used as carbon sources and the complex downstream phase of PHAs recovery from bacterial cells. Possible solutions could be i) the utilization of cheap wastes of agro-food origin as carbon sources and ii) the simplification of downstream purification processes. To these aims, Cupriavidus necator DSM545, a well-known PHAs accumulator, has been genetically modified in order to acquire the ability of metabolizing lactose from whey (dairy industry) or lipids (from slaughterhouse) and the capacity to produce nuclease to facilitate downstream processes. In the first case, the modified strains resulted able to grow using whey or lipids as carbon sources, accumulating up to 30 and 60% of PHAs, respectively. In the second case, the recombinant C. necator DSM 545 resulted in an effective decrease of viscosity of bacterial cells lysates, thus avoiding the use of costly commercial nucleases for an efficient downstream. Bioethanol is a fuel obtained from renewable resources and it could be a promising alternative to petrol fuels. First generation bioethanol is mainly produced from corn and sugarcane, thus conflicting with food and feed production . On the contrary, bioethanol from residual and lignocellulosic biomass has environmental impact lower than fossil fuels and would not threaten food supplies. Unfortunately, Saccharomyces cerevisiae, the yeast used for industrial bioethanol production, is not equipped with suitable hydrolytic activities and thus cannot directly utilize starchy and lignocellulosic wastes as feedstock without the use of commercial enzymes. Recent studies were focused to develop a “Consolidated bioprocessing” (CBP), approach where a single yeast is able to hydrolyse starch and lignocellulose and ferment the resulting sugars into ethanol. . With this purpose, novel and robust S. cerevisiae strains were recently engineered at DAFNAE to secrete efficient cellulases and amylases for the efficient saccharification and fermentation of starchy and cellulosic by-products up to 65 g/L ethanol.