Abstract

The biosynthesis of polyhydroxyalkanoates (PHAs) and their production cost depend on the type of carbon source, the performance of the production strain, the bioprocess itself, and finally the downstream processing. In the past 10 years additional aspects increased in importance, such as abundance of the substrate, sustainability of the carbon source (favoring waste sources), and finally reproducibility of monomeric unit composition and purity of the product. Moreover, the choice of a carbon source depends also on the kind of PHA to be produced which is indirectly determined by the final application. In order to design the optimal bioprocess for medium-chain-length (mcl-) PHA production process parameters (e.g. specific substrate uptake rates and related PHA productivity, required oxygen transfer rates) and the properties of the carbon source (e.g. functional groups, range of substrate toxicity and solubility) also play a decisive role and thus influence the selection of the bioreactor. In case of short-chain-length (scl-) PHAs, e.g. poly(3-hydroxybutyrate), mainly aspects of availability, sustainability, and costs of the carbon source are relevant since larger production volumes are anticipated. Here, fed-batch and in a few cases continuous cultures are the bioprocesses of choice. Considering the above mentioned issues, we focus our PHA related research on i) bioprocess design, ii) process analytical technology (PAT), and iii) production of bulk and tailored PHAs for industrial and medical applications. In i) particular novel production strains in combination with selected growth conditions (e.g., multiple-nutrient-limited growth, microaerobic growth) are assessed for high PHA yields and ability to control PHA properties using automated fed-batch, auxostats, and continuous cultures. In ii) new PATs to quantify biomass and PHA content (e.g. radio-frequency impedance measurements, flow cytometry and NIR) are developed to help monitoring bioprocesses. Finally, in iii) local wastes from fruit and wine production are investigated for cheap mcl-PHA production and the synthesis from pure fatty acids of tailor-made PHAs for medical applications is designed. In case of scl-PHA production, we established a syngas fermentation platform that will be addressed in the talk in particular.