Conversion of aromatic compounds from fractionated industrial hydrolysis lignin byPseudomonas putidaand environmental microbial strains

Abstract

Background The utilization of Pseudomonas putida strain KT2440 was explored in this study as a promising approach for lignin valorization. To this end, dry hydrolysis lignin was used as a feedstock for the first time. Hydrolysis lignin is a product of the enzymatic hydrolysis and separation of cellulose and hemicellulose from the lignin backbone in diverse lignocellulosic sources. Various fractionation techniques were applied to obtain lignin monomers and multimers in solution for use as a growth medium for P. putida, whose tolerance of inhibitory phenolic compounds distinguishes it from most bacteria. Results Physiological evaluations revealed that Pseudomonas putida strain KT2440 exhibited broad pH tolerance ranges, with robust growth observed at elevated pH levels. Batch fermentations using hydrolysis lignin (HL) solutions showed complete consumption of sugars within 24 hours, demonstrating the viability of fractionated HL as a substrate for P. putida cultivation. HPLC analysis of HL monomer concentrations during simulated fed-batch fermentation revealed rapid catabolism of catechol and increased CCMA concentration, followed by stabilization, indicating that CCMA is synthesized more quickly than degraded when the initial catechol concentration is high. Alkaline fractionation of HL revealed comparable sugar profiles in filtered and unfiltered samples, yet the filtered fractionation yielded more than twice as much catechol. Screening of indigenous bacterial strains isolated from various soil and water samples (CELMS Collection, website http://eemb.ut.ee) identified five new candidate strains for CCMA production, two for PCA production, and three for vanillic acid production. Conclusions The novel use of fractionated hydrolysis lignin as a growth medium shows potential for lignin valorization and chemical production. Filtered alkaline fractionation yields more catechol and is superior for cis,cis-muconic acid production; however, unfiltered fractionations may be more suitable for other compounds and upscaling. Further investigation of screened strains could reveal more efficient enzymes, which could be optimized and transformed into P. putida in future research.