Improvement of the poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) production by dual feeding with levulinic acid and sodium propionate in Cupriavidus necator.

In the context of increasing volatility of oil prices, replacement of petroleum based plastics by bioplastics is a topic of increasing interest. Poly(hydroxyalkanoate)s (PHAs) are among the most promising families in this field. Controlling composition of the polymer on the monomeric level remains a pivotal issue. This control is even more difficult to achieve when the polymer is not synthesized by chemists, but produced by nature, in this case, bacteria. In this study mechanism and role of two 3-hydroxyvalerate (3-HV) inducing substrates on the production of PHBV with high, 80%, 3-HV content were evaluated. It was found that levulinic acid contributes to biomass and bio-polymer content enhancement, whereas sodium propionate mainly contributes to 3-HV enhancement. Optimized proportions of feeding substrates at 1 g/L and 2.5 g/L, respectively for levulinic acid and sodium propionate allowed a 100% productivity enhancement, at 3.9 mg/L/hour, for the production of PHBV with 80% 3-HV.

From organic pollutants to bioplastics: insights into the bioremediation of aromatic compounds by Cupriavidus necator.

Organic pollution by aromatic compounds is of increasing concern to our environment. Therefore, the transformation of aromatic pollutants into valuable aliphatic and biodegradable bioplastics was studied. Since benzoic acid was found to be the key compound for such bioremediation processes, its transformation, and metabolic pathways of digestion, by Cupriavidus necator were specifically analysed. It was found that the degradation of aromatic compounds follows the 2,3-dioxygenase pathway in this strain and that the batch transformations of benzoic acid with either fresh or adapted cells were limited to an initial concentration of 2.5 g/L of pollutant. The repeated fed-batch with partial withdrawal process, however, showed a 17.5-fold improvement, thus allowing the transformation of a total of 43.7 g/L in 12 weeks.

Novel approach for productivity enhancement of polyhydroxyalkanoates (PHA) production by Cupriavidus necator DSM 545.

In the global context of increased concerns for our environment, the use of bioplastics as a replacement for existing petroleum-based polymers is an important challenge. Indeed, bioplastics hardly meet economical and technical constraints. One, of the most promising among currently studied bioplastics, is the polyhydroxyalkanoate (PHA). To circumvent the economical issue for this particular biopolymer one solution can be the enhancement of the overall productivity by the improvement of the nutritional medium of the microorganism producing the biopolymer. Thus, several nutrition media, supplemented or not with sodium glutamate, were tested for the growth and the PHA production by Cupriavidus necator DSM 545 strain. The most efficient for the biomass and the PHA production improvement were found to be the Luria broth (LB) and the Bonnarme's media, both supplemented with 10 g/L sodium glutamate. Hence the overall productivity was 33 times enhanced comparing to traditional cultivation methods. These results open a new route for the PHA production by C. necator which appears to be more suitable on a rich, or enriched, medium with no limiting factors.

Enhancing the 3-hydroxyvalerate component in bioplastic PHBV production by Cupriavidus necator.

In the current context of global warming, the substitution of conventional plastics with bioplastics is a challenge. To take up this challenge, we must meet different technical and economic constraints. In the case of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), the technical properties can be modulated by varying the 3-hydroxyvalerate content. 3-Hydroxyvalerate (3-HV) enhancement is an issue; therefore, simultaneous evaluation of several 3-hydroxyvalerate-enhancing substrates through fractional factorial design of experiments is described. Eight substrates citric, valeric, propionic, and levulinic acids; propanol; pentanol; and sodium propionate were studied for 3-HV enhancement, and sodium glutamate was studied for biomass and polyhydroxyalkanoate (PHA) enhancement. The most efficient 3-hydroxyvalerate-enhancing factors were levulinic acid, sodium propionate, and pentanol; however, pentanol, at a concentration of 1 g/L, had an extremely negative influence on biomass production and the PHA content of cells. The effect of the inoculum nutrient composition on the final 3-HVcontent was also evaluated. These results showed that the most efficient combination for the production of high 3-HVcontent in PHBV was primary inoculum growth on mineral medium followed by fermentation for 48 h with levulinic acid and sodium propionate (at 1 g/L) as the only carbon sources. This allowed us to produce PHBV with a 3-HVcontent of 80 mol % and overall volumetric and specific productivities of 2 mg/L/h and 3.9 mg/g(CDW) /h, respectively, with the addition of only 2 g/L of inducing substances.