M. ROMANINO², S. FOLLONIER¹, S. KARMANN³, M. ZINN<sup>1

1</sup>Institute of Life Technologies, HES-SO Valais Wallis, Sion, Switzerland, ²2 Dipartimento di Scienze e Tecnologie Biologiche, Chimiche e Farmaceutiche (STEBICEF), Università degli Studi di Palermo, Italy, ³Department of Biosystems Science and Engineering, ETH Zurich, Basel, Switzerland

As concerns about the environmental impact of petrol-based plastics and their fate in the environment are growing, there is a need to develop sustainable alternatives. Poly(3-hydroxyalkanoates) (PHA) have emerged as promising bio-based polyester candidates due to their unique features in terms of biodegradability and biocompatibility.
We are investigating how to improve the cost-efficiency and sustainability of PHA production with a bioprocess using syngas, the gas mixture obtained from the pyrolysis of organic wastes and made consisting mainly of CO, CO2, H2 and N2. This bioprocess relies on Rhodospirillum rubrum, a purple nonsulfur photosynthetic bacterium able to both metabolize CO and synthesize PHA intracellularly. It is composed of three phases: 1) heterotrophic, aerobic growth on fructose, 2) adaptation to anaerobic growth with fructose as substrate, and 3) PHA production from syngas and acetate.
A cutting-edge process analytical technology platform was set up to monitor both the bioprocess and cell physiology. It involved measurements of dissolved oxygen and redox potential (in-line), exhaust gas concentrations with a mass spectrometer (on-line), cell concentration and PHA content by flow-cytometry (at-line), as well as optical density, dissolved CO, cell dry weight, PHA content and composition by gas chromatography, and substrate concentrations by high pressure liquid chromatography (off-line).
With this approach it was possible to produce 1.6 g L-1 of PHA (PHA content = 18.5 w%) while consuming 14.3 moles of CO and generating 3.7 moles of H2 as valuable byproduct. The cells exhibited a µmax of 0.12 h-1 during the aerobic phase on fructose and grew linearly up to 8.5 g L-1 CDW during the syngas phase as a result of CO mass transfer limitation. The specific uptake rate of fructose was 0.2 g g-1 h-1 during both the aerobic and the anaerobic phase, and the one of acetate during the syngas phase was 0.03 g g-1 h-1. This study clearly showed the potential of the followed strategy while pinpointing which parameters need to be optimized for further improving process productivity (e.g. CO mass transfer and fructose/acetate concentrations).