Bacterial transformation of monomeric aromatic compounds of black liquor

LAURA E. NAVAS; GARA DEXTER; MIJUNG CHO; SOO-KYEONG JANG; SHAWN D. MANSFIELD; SCOTT RENNECKAR; WILLIAM W. MOHN,; LINDSAY ELTIS

Virtual por COVID-19

Congreso; 43rd Symposium on Biomaterials, Fuels and Chemicals; 2021

Society for Industrial Microbiology and Biotechnology

Lignin is the most abundant aromatic biopolymer in the biosphere and its sustainable valorization is essential to the success of next generation biorefineries. Many pulp and paper mills, exemplifying present day biorefineries, utilize a kraft pulping process that generates an under-utilized, lignin-rich stream called black liquor. In this study, we solvent-extracted the aromatic compounds from softwood black liquor that had been subjected to the Lignoforce process and subsequently screened bacteria for their ability to grow on the extracts. Among the four solvents employed, acetone extracted the greatest amount of monoaromatic compounds from the black liquor. GC-MS analysis of these extracts revealed that guaiacol and vanillin were present in the black liquor at concentrations of 1.9 and 1.4 mM, respectively. Acetovanillone, 4-ethanol guaiacol, vanillate, and 4-propanol guaiacol were also present in significant quantities. A number of bacterial strains grew on minimal media supplement with the black liquor extracts to 1 mM aromatic compounds, including Pseudomonas putida KT2442, Sphingobium sp. SYK-6, and three strains of Rhodoccocus rhodochrous: EP4, GD01, and GD02. The two latter strains were isolated for their ability to grow on acetovanillone. Interestingly, the extracts inhibited the growth of other rhodococcal strains, including R. jostii RHA1 and R. opacus PD630. Of the five strains that grew on the extracts, only GD01 and GD02 depleted the six major monoaromatic compounds in the acetone extract. This result was replicated using a mixture of these six compounds in the same proportion as in the extract and largely reflected the known catabolic capabilities of each strain. Thus, KT2442 completely consumed vanillin and vanillate after 72 h, and some of the 4-ethanol guaiacol. By contrast, SYK-6 did not degrade the guaiacol or 4-ethanol guaiacol, and EP4 consumed all the compounds except acetovanillone. We are currently elucidating the acetovanillone catabolic pathways of GD01, GD02, and SYK-6. Overall, our results clearly establish that bacteria are able to catabolize the major monoaromatic components of black liquor and provide a basis for designing biocatalysts to valorize these under-utilized components.