Use of bacteria for improving the lignocellulose biorefinery process: importance of pre-erosion

Abstract

BackgroundBiological pretreatment is an important alternative strategy for biorefining lignocellulose and has attracted increasing attention in recent years. However, current designs for this pretreatment mainly focus on using various white rot fungi, overlooking the bacteria. To the best of our knowledge, for the first time, we evaluated the potential contribution of bacteria to lignocellulose pretreatment, with and without a physicochemical process, based on the bacterial strain Pandoraea sp. B-6 (hereafter B-6) that was isolated from erosive bamboo slips. Moreover, the mechanism of the improvement of reducing sugar yield by bacteria was elucidated via analyses of the physicochemical changes of corn stover (CS) before and after pretreatment.ResultsThe digestibility of CS pretreated with B-6 was equivalent to that of untreated CS. The recalcitrant CS surface provided fewer mediators for contact with the extracellular enzymes of B-6. A pre-erosion strategy using a tetrahydrofuran–water co-solvent system was shown to destroy the recalcitrant CS surface. The optimal condition for pre-erosion showed a 6.5-fold increase in enzymatic digestibility compared with untreated CS. The pre-erosion of CS can expose more phenolic compounds that were chelated to oxidized Mn3+ and also provided mediators for combination with laccase, which was attributable to B-6 pretreatment. B-6 pretreatment following pre-erosion exhibited a sugar yield that was 91.2 mg/g greater than that of pre-erosion alone and 7.5-fold higher than that of untreated CS. This pre-erosion application was able to destroy the recalcitrant CS surface, thus leading to a rough and porous architecture that better facilitated the diffusion and transport of lignin derivatives. This enhanced the ability of laccase and manganese peroxidase secreted by B-6 to improve the efficiency of this biological pretreatment.ConclusionBacteria were not found useful alone as a biological pretreatment, but they significantly improved enzymatic digestion after lignocellulose breakdown via other physicochemical methods. Nonetheless, phenyl or phenoxy radicals were used by laccase and manganese peroxidase in B-6 for lignin attack or lignin depolymerization. These particular mediators released from the recalcitrance network of lignocellulose openings are important for the efficacy of this bacterial pretreatment. Our findings thus offer a novel perspective on the effective design of biological pretreatment methods for lignocellulose.Electronic supplementary materialThe online version of this article (10.1186/s13068-018-1146-4) contains supplementary material, which is available to authorized users.

Utilization of all components in biomass through high reducing sugar production and lignin nanoparticles preparation

“…In addition, the yield of the reducing sugar increased from 10.19 g/l (TH21) to 26.28 g/l (120 ℃ for 4 h, TH24) with the prolongation of reaction time under 120 ℃. This is 3.74 and 11.40-fold higher than that of the untreated sample (84.70 mg/g, that is 2.12 g/l [17]). This phenomenon is attributed to the breakdown of the biomass recalcitrance structure.…”

“…The CS used in this study was found to consist of 34.9% of cellulose, 38.5% of hemicellulose, 13.9% of lignin, and 12.7% of other non-organic and organic components [17]. The mass loss of CS under the reaction condition of TH21 was 36.14%.…”

“…In our previous studies, a new strategy involved a synergy of lignocelluloses pretreatment by THF-H 2 O and bacterial strain to enhance enzymatic hydrolysis was developed [17,18]. The pretreatment of CS with THF-H 2 O alone had a high lignin removal efficiency and retained a large amount of cellulose for sugar production.…”

Recent advances in lignin valorization with bacterial cultures: microorganisms, metabolic pathways, and bio-products

“…With further researches, inherent enzymes and metabolic pathways involved in lignin degradation by these bacteria have been characterized, including enzymes/pathways catalyzing oxidative and hydroxylation reactions, depolymerizing phenolic and non-phenolic lignin polymers, demethylation reactions and opening the aromatic rings of lignin-based compounds [33, 40–45]. Now, some of these bacteria have been used in treatment of sewages from pulp and paper industry, degradation heterogeneous compounds, and pretreatment of lignocellulosic biomass [46–49]. In particular, among these isolates, some strains (e.g., Pseudomonas putida KT2440, Sphingobium sp.…”

Derived high reducing sugar and lignin colloid particles from corn stover

“…In our previous studies, a new strategy involved a synergy of lignocelluloses pretreatment by THF-H 2 O and bacterial strain to enhance enzymatic hydrolysis was developed [24,25]. The result showed THF-H 2 O had a high lignin removal efficiency and retained a large amount of cellulose for sugar production.…”