Optimization of Rhodococcus erythropolis JCM3201^T Nutrient Media to Improve Biomass, Lipid, and Carotenoid Yield Using Response Surface Methodology

The oleaginous bacterium Rhodococcus erythropolis JCM3201^T offers various unique enzyme capabilities, and it is a potential producer of industrially relevant compounds, such as triacylglycerol and carotenoids. To develop this strain into an efficient production platform, the characterization of the strain’s nutritional requirement is necessary. In this work, we investigate its substrate adaptability. Therefore, the strain was cultivated using nine nitrogen and eight carbon sources at a carbon (16 g L⁻¹) and nitrogen (0.16 g L⁻¹) weight ratio of 100:1. The highest biomass accumulation (3.1 ± 0.14 g L⁻¹) was achieved using glucose and ammonium acetate. The highest lipid yield (156.7 ± 23.0 mg g⁻¹_DCW) was achieved using glucose and yeast extract after 192 h. In order to enhance the dependent variables: biomass, lipid and carotenoid accumulation after 192 h, for the first time, a central composite design was employed to determine optimal nitrogen and carbon concentrations. Nine different concentrations were tested. The center point was tested in five biological replicates, while all other concentrations were tested in duplicates. While the highest biomass (8.00 ± 0.27 g L⁻¹) was reached at C:N of 18.87 (11 g L⁻¹ carbon, 0.583 g L⁻¹ nitrogen), the highest lipid yield (100.5 ± 4.3 mg g⁻¹_DCW) was determined using a medium with 11 g L⁻¹ of carbon and only 0.017 g L⁻¹ of nitrogen. The highest carotenoid yield (0.021 ± 0.001 Abs_454nm mg⁻¹_DCW) was achieved at a C:N of 12 (6 g L⁻¹ carbon, 0.5 g L⁻¹ nitrogen). The presented results provide new insights into the physiology of R. erythropolis under variable nutritional states, enabling the selection of an optimized media composition for the production of valuable oleochemicals or pigments, such as rare odd-chain fatty acids and monocyclic carotenoids.