Improved glycerol utilization by a triacylglycerol-producing Rhodococcus opacus strain for renewable fuels

• Published in: Biotechnology for biofuels 2015-02, Vol.8 (1), p.31-31, Article 31
• Main Authors: Kurosawa, Kazuhiko, Radek, Andreas, Plassmeier, Jens K, Sinskey, Anthony J
• Format: Article
• Language: English
• Subjects: Analysis; bacteria; biofuels; Biomass energy; bioprocessing; biotechnology; cost effectiveness; Dextrose; evolutionary adaptation; feedstocks; Fermentation; fuel production; Glucose; Glycerin; Glycerol; Innovations; Instrument industry; Rhodococcus opacus; triacylglycerols; Triglycerides; value added; xylose
• ISSN: 1754-6834; 1754-6834
• DOI: 10.1186/s13068-015-0209-z

BACKGROUND: Glycerol generated during renewable fuel production processes is potentially an attractive substrate for the production of value-added materials by fermentation. An engineered strain MITXM-61 of the oleaginous bacterium Rhodococcus opacus produces large amounts of intracellular triacylglycerols (TAGs) for lipid-based biofuels on high concentrations of glucose and xylose. However, on glycerol medium, MITXM-61 does not produce TAGs and grows poorly. The aim of the present work was to construct a TAG-producing R. opacus strain capable of high-cell-density cultivation at high glycerol concentrations. RESULTS: An adaptive evolution strategy was applied to improve the conversion of glycerol to TAGs in R. opacus MITXM-61. An evolved strain, MITGM-173, grown on a defined medium with 16 g L⁻¹glycerol, produced 2.3 g L⁻¹of TAGs, corresponding to 40.4% of the cell dry weight (CDW) and 0.144 g g⁻¹of TAG yield per glycerol consumed. MITGM-173 was able to grow on high concentrations (greater than 150 g L⁻¹) of glycerol. Cultivated in a medium containing an initial concentration of 20 g L⁻¹glycerol, 40 g L⁻¹glucose, and 40 g L⁻¹xylose, MITGM-173 was capable of simultaneously consuming the mixed substrates and yielding 13.6 g L⁻¹of TAGs, representing 51.2% of the CDM. In addition, when 20 g L⁻¹glycerol was pulse-loaded into the culture with 40 g L⁻¹glucose and 40 g L⁻¹xylose at the stationary growth phase, MITGM-173 produced 14.3 g L⁻¹of TAGs corresponding to 51.1% of the CDW although residual glycerol in the culture was observed. The addition of 20 g L⁻¹glycerol in the glucose/xylose mix resulted in a TAG yield per glycerol consumed of 0.170 g g⁻¹on the initial addition and 0.279 g g⁻¹on the pulse addition of glycerol. CONCLUSION: We have generated a TAG-producing R. opacus MITGM-173 strain that shows significantly improved glycerol utilization in comparison to the parental strain. The present study demonstrates that the evolved R. opacus strain shows significant promise for developing a cost-effective bioprocess to generate advanced renewable fuels from mixed sugar feedstocks supplemented with glycerol.