(123b) Conversion of Aromatic Compounds to Lipids By Engineered Rhodococcus Strains

Henson, W. R., Washington University in St. Louis
Kim, S. J., Washington University in St. Louis
Moon, T. S., Washington University in St. Louis

Lignocellulosic biomass is a renewable feedstock that can be converted to biofuels or high-value products using a biorefinery. However, pretreatment of lignocellulosic biomass often releases toxic inhibitors for the downstream fermentation. In addition, a major component of lignocellulosic biomass, lignin, remains an untapped carbon resource due to its recalcitrance and toxic monomeric units (phenolics). Our work focuses on developing Rhodococcus opacus as a new chassis for conversion of phenolics to triacylglycerol (TAG), a biodiesel precursor. R. opacus is a promising host for bioconversion of phenolics due to its high tolerance to aromatics and its ability to grow on phenolics as a sole carbon source. In addition, R. opacus can accumulate TAGs up to ~80% of cell dry weight (CDW) under nitrogen-limiting conditions. To enhance its innate phenolic-degrading capacity, we applied adaptive evolution, a growth-based strain selection method, by sequentially sub-culturing cells in aromatic compounds as sole carbon sources. After >200 generations, our top adapted strains demonstrated a >50% increase in final optical density (OD600) and >30% increase in growth rate as well as high lipid accumulation compared to the wild type strain. Whole genome sequencing, RNA-seq, and 13C-fingerprinting analysis identified possible phenolic tolerance and utilization mechanisms such as phenolic degradation pathway upregulation. We will present progress towards development of R. opacus as a microbial cell factory.