Base-Catalyzed Depolymerization of Solid Lignin-Rich Streams Enables Microbial Conversion

Abstract

Lignin valorization offers significant potential to enhance the economic viability of lignocellulosic biorefineries. However, because of its heterogeneous and recalcitrant nature, conversion of lignin to value-added coproducts remains a considerable technical challenge. In this study, we employ base-catalyzed depolymerization (BCD) using a process-relevant solid lignin stream produced via deacetylation, mechanical refining, and enzymatic hydrolysis to enable biological lignin conversion. BCD was conducted with the solid lignin substrate over a range of temperatures at two NaOH concentrations, and the results demonstrate that the lignin can be partially extracted and saponified at temperatures as low as 60 °C. At 120 °C and 2% NaOH, the high extent of lignin solubility was accompanied by a considerable decrease in the lignin average molecular weight and the release of lignin-derived monomers including hydroxycinnamic acids. BCD liquors were tested for microbial growth using seven aromatic-catabolizing bacteria and two yeasts. Three organisms (Pseudomonas putida KT2440, Rhodotorula mucilaginosa, and Corynebacterium glutamicum) tolerate high BCD liquor concentrations (up to 90% v/v) and rapidly consume the main lignin-derived monomers, resulting in lignin conversion of up to 15%. Furthermore, as a proof of concept, muconic acid production from a representative lignin BCD liquor was demonstrated with an engineered P. putida KT2440 strain. These results highlight the potential for a mild lignin depolymerization process to enhance the microbial conversion of solid lignin-rich biorefinery streams.

RETRACTED ARTICLE: Bacterial conversion of depolymerized Kraft lignin

“…This is in agreement with reports by Salvachúa et al on P. fluorescens Pf-5, which was found able to depolymerize HMW lignin, but was not able to consume the produced monomers [21]. In contrast to a few previous reports on the ability of P. putida KT2440 to breakdown HMW lignin [20, 21], no such behavior was observed for EM42 strain, despite its genetic similarities with KT2440 [37]. This could be due to the different lignin source used in this study, since the lignin obtained from corn stover differs much from the technical lignin (Indulin AT) in terms of the structure, primary building blocks and successive breakdown products [45, 46].…”

High value‐added monomer chemicals and functional bio‐based materials derived from polymeric components of lignocellulose by organosolv fractionation

“…A study has been conducted focusing on consolidated bioprocessing (CBP) toward lignin degradation using different types of bacteria under nitrogen‐limiting and nutrient‐rich conditions . The results showed that Pseudomonas putida , Rhodotorula mucilaginosa , and Corynebacterium glutamicum demonstrated strong tolerance to alkaline pretreatment liquor and could rapidly consume the lignin‐derived monomers …”

“…PDC/ bis (2‐hydroxyethyl) 2‐pyrone‐4,6‐dicarboxylate (BHPDC)/bis (2‐hydroxyethyl) terephthalate (OE x ), P (PDCB) x , and PDC‐incorporated PLA,1,4‐BD/SA/PDC, unsaturated polyesters, polyamide, polyurethane, nylon, and other composites, e.g. fiberglass reinforced plastic (FRP) . These polymers have wide applications in many fields.…”

“…233 The results showed that Pseudomonas putida, Rhodotorula mucilaginosa, and Corynebacterium glutamicum demonstrated strong tolerance to alkaline pretreatment liquor and could rapidly consume the lignin-derived monomers. 234 In particular, in current research to the production of chemicals from lignin, Sphingobium sp., which is able to cleave β-O-4 and 5-5 linkages in lignin dimers, 239 and Pseudomona sp., which is able to convert coniferyl alcohol and p-coumarate into dicarboxylic acids through β-ketoadipate pathway 240 are widely used. A number of chemical compounds can be obtained based on aromatic-catabolic fermentation of lignin ( Fig.…”

Across the Board: Mark Mascal on the Challenges of Lignin Biorefining

“…Although pathways have been designed and tested for the production of adipic acid from sugars, there are always going to be cost implications and reservations about using food to make chemicals, and although counterarguments involving nth‐generation biorefineries abound, the real question is whether something besides sugars could be used in the first place. Recent work by Beckham and co‐workers at the US National Renewable Energy Laboratory describes the use of an engineered strain of the microorganism Pseudomonas putida to “biologically funnel” lignin directly towards cis ‐ cis muconic acid, a natural product that can be easily hydrogenated to adipic acid . As if that were not enough, trans ‐ trans muconic esters, which can be produced by isomerization of the natural cis ‐ cis isomer, undergo Diels–Alder cycloaddition with ethylene to give cyclohexene products, the catalytic dehydrogenation of which gives terephthalate (Scheme ), another multimillion‐ton commodity chemical .…”