Lipid production from non-sugar compounds in pretreated lignocellulose hydrolysates by Rhodococcus jostii RHA1

The non-sugar compounds such as lignin derived phenolic compounds, furans, and organic acids generated from biomass pretreatment are often inhibitors to microbial growth and function, leading to lower ethanol yield in cellulosic ethanol biorefinery. In this study, phenols (vanillin, vanillate), furans (furfural, 5-hydroxymethylfurfural), and organic acids (acetate), which mimic the complex components of the non-sugar compounds in pretreated biomass hydrolysate, were either mixed with benzoate or used individually as carbon sources to investigate their effects on the growth and lipid accumulation of Rhodococcus jostii RHA1. Higher consumption rates of benzoate than that of vanillate, as well as different lipid yields from them, suggested that the strain preferred to employ the catechol branch of the β-ketoadipate pathway to catabolize benzoate and plausibly distinctly routed carbon to lipid biosynthesis when fed on different aromatics. Compared to benzoate, acetate was less favorable by R. jostii RHA1 for lipid synthesis, again emphasizing that carbon contribution to either lipid synthesis or cell biomass was selective, using different compounds as carbon sources. Among the five selected non-sugar compounds, the presence of 5-hydroxymethylfurfural (5-HMF) promoted the highest lipid yield at 0.46 g lipid g−1 CDW by using benzoate as the main carbon source. Furthermore, the oxidation pathway of furfural and 5-HMF was predicted for the first time in R. jostii RHA1 based on the characterization of the products by NMR.