Workflow for shake flask and plate cultivations with fats for polyhydroxyalkanoate bioproduction

Since natural resources for the bioproduction of commodity chemicals are scarce, waste animal fats (WAF) are an interesting alternative biogenic residual feedstock. They appear as by-product from meat production, but several challenges are related to their application: first, the high melting points (up to 60 °C); and second, the insolubility in the polar water phase of cultivations. This leads to film and clump formation in shake flasks and microwell plates, which inhibits microbial consumption. In this study, different flask and well designs were investigated to identify the most suitable experimental set-up and further to create an appropriate workflow to achieve the required reproducibility of growth and product synthesis. The dissolved oxygen concentration was measured in-line throughout experiments. It became obvious that the gas mass transfer differed strongly among the shake flask design variants in cultivations with the polyhydroxyalkanoate (PHA) accumulating organism Ralstonia eutropha. A high reproducibility was achieved for certain flask or well plate design variants together with tailored cultivation conditions. Best results were achieved with bottom baffled glass and bottom baffled single-use shake flasks with flat membranes, namely, >6 g L^-1 of cell dry weight (CDW) with >80 wt% polyhydroxybutyrate (PHB) from 1 wt% WAF. Improved pre-emulsification conditions for round microwell plates resulted in a production of 14 g L^-1 CDW with a PHA content of 70 wt% PHB from 3 wt% WAF. The proposed workflow allows the rapid examination of fat material as feedstock, in the microwell plate and shake flask scale, also beyond PHA production. KEY POINTS: • Evaluation of shake flask designs for cultivating with hydrophobic raw materials • Development of a workflow for microwell plate cultivations with hydrophobic raw materials • Production of polyhydroxyalkanoate in small scale experiments from waste animal fat.