Engineering of Rhodococcus jostii RHA1 for consolidated bioprocessing of lignin-derived compounds

Lignin, the heterogeneous aromatic polymer of plant biomass, has considerable potential as a sustainable source for fuels and chemicals. One approach to transform lignin to target products is to develop bacterial biocatalysts. Rhodococcus jostii RHA1 (RHA1), a soil bacterium, is an attractive chassis for developing tunable lignin biocatalysts due to its potential to form a variety of valuable fermentation products and its ability to grown on lignin-enriched streams, such as corn stover alkaline pretreated liquor (APL). APL contains a wide variety of lignin-derived compounds of different molecular weights. Our aim is to increase the lignolytic capabilities and substrate range of RHA1 to improve the strain’s growth and ability to catabolize APL. To achieve this, we are developing a strain that secretes lignin-modifying enzymes (ligninases), and are identifying and characterizing catabolic pathways that are upregulated during growth on APL. We have engineered RHA1 to efficiently secrete enzymes using the twin-arginine translocation system and tested various ligninases for their effect during APL fermentation. For our second strategy, we performed an RNA-Seq experiment with RHA1 and mapped lignin-specific pathways. The results will inform the engineering of RHA1 towards an efficient lignin converter in order to accumulate specific chemicals.