Production of polyhydroxyalkanoates from lipid-rich slaughterhouse waste using a recombinant lipolytic Cupriavidus necator DSM 545 strain

In the last decades, economic and environmental concerns arose about oil shortage and fossil-based economy. These have stimulated scientific community and industry to switch from fossil plastics, that cause pollution and ecosystem damages, to bio-based alternatives such as polyhydroxyalkanoates (PHAs). PHAs are eco-friendly biopolymers accumulated as granules by a large number of bacteria. They can be classified as “green polymers” for their chemical, physical and mechanical traits similar to the traditional plastics. PHAs are also completely biodegradable and biocompatible. Although PHAs have a large range of applications, the high cost of carbon sources used in the process reduce their wide use. Therefore, to make them more competitive in the market, the search for cheap and sustainable substrates is crucial. The huge amount of lipid-rich by-products (over 500,000 ton/year) produced throughout the European Union by slaughtering industry could be interesting low-cost carbon sources for the PHAs production. For this reason, this work focused on the development of microbial processes able to convert slaughterhouse by-products into PHAs. To improve PHAs production from fatty substrates, two genes from Pseudomonas stutzeri BT3, lipC and lipH, having a proficient lipolytic activity, were successfully co-expressed into Cupriavidus necator DSM 545, a well-known PHAs producer but with a low lipolytic activity. The most efficient recombinant strain, selected on the basis of the highest extracellular lipolytic activities, was named C. necator DSM 545 lip11 and applied as PHAs producer from a cluster of lipid-rich residues namely udder, membrane caul, jowl, and slaughterhouse wastewater. In all the tested substrates, the recombinant strain produced PHAs content always higher than those of the parental. The highest PHAs value was achieved from jowl (nearly 65% of cell dry mass) with a final production up to 3 g/L. Noteworthy PHAs cell contents (about 30% of cell dry mass) were obtained by from membrane caul and wastewater. This is the first study reporting the one-step conversion of lipid-rich substrates into PHAs by an engineered C. necator DSM 545 expressing efficient lipases. As a result, this research paves the way to the efficient processing of cheap slaughterhouse by-products into biopolymers.