Poly(hydroxyalkanoate) Production by Cupriavidus necator from Fatty Waste Can Be Enhanced by phaZ1 Inactivation

Although PHAs are regarded as an effective substitute for conventional plastics for a number of medical and agricultural applications1 and food packaging2, their full-scale manufacturing is hampered by high production costs3. Factors affecting the cost of PHAs include raw materials availability, suitable process design, and downstream processing4,5. Since almost 50 % of the total production costs can be attributed to the carbon source for microbial growth and polymer production, the selection of renewable, cheap carbon feedstock, specially generated from industrial or agricultural by-products, can provide a way to reduce the price6,7,8. To that end, different industrial by-products, such as whey9,10, molasses11, starch, and waste oils and glycerol, have been investigated as start materials for PHA production12,13,14,15. In this perspective, fatty residues from slaughterhouse represent a promising raw material. For Europe, the amount of animal lipids, also causing expensive disposal problems, is estimated a half a million tons per year16. However, PHA production from waste oils or fats requires microorganisms that should be both excellent PHA producers as well as equipped with enzymatic activities allowing hydrolysation of triglycerides. Cupriavidus necator (formerly Ralstonia eutropha) is one of the best known bacteria among PHA-producing microorganisms15,17. The production of different kinds of PHAs by C. necator using several inexpensive feedstock, including glycerol, has been recently reported18,19,20,21,22, indicating that some strains of this bacterial species could be used for the conversion of fatty residues into PHA. As an alternative, the use of costly commercial enzymes or genetic modification of microorganisms exhibiting high PHA product yields would be required23. In the case of C. necator, its lipase activities could most likely be improved by physiological/technological studies in terms of biomass production and PHA content, but the help of commercial enzymes may still be necessary. A possible strategy to help increase the final PHA yield in a bacterial strain already possessing both high polymer production ability and acceptable triglyceride hydrolytic activity, could originate from the relevant findings regarding C. necator PHA metabolism, physiology, Poly(hydroxyalkanoate) Production by Cupriavidus necator from Fatty Waste Can Be Enhanced by phaZ1 Inactivation