Biochar-mediated enhanced ethanol fermentation (BMEEF) in Zymomonas mobilis under furfural and acetic acid stress

Abstract

Background: Pretreatment of lignocellulosic biomass generates different types of inhibitors (e.g., furfural and acetic acid), which could remarkably inhibit subsequent ethanol fermentation. Here, biochar as an additive in the fermentation broth was first applied to enhance ethanol production by Z. mobilis wild-type strain ZM4 in the presence of typical inhibitors. Results:This study showed that the biochar-mediated tolerance to furfural and acetic acid for the strain Z. mobilis ZM4 was the highest reported level, resulting in much higher ethanol productivity under stress conditions than that in non-treated conditions. Further analysis showed that adsorptive detoxification was not the controlling factor for enhanced ethanol production under stress conditions, attributed to its low removal of furfural (< 20%) and incapability of acetic acid removal. When biochar was filtered from the biochar-treated inhibitor-containing broth, it still showed enhanced ethanol production. Furthermore, Z. mobilis immobilized on biochar was also observed. Thus, biochar extracts in the fermentation broth and cell immobilization on biochar might be the controlling factors for enhanced ethanol production under stress conditions. Conclusions:These results indicate that biochar-mediated enhanced ethanol fermentation (BMEEF) might be a promising strategy for ethanol production from lignocellulosic biomass.

Acetaldehyde Stimulation of the Growth of Zymomonas mobilis Subjected to Ethanol and Other Environmental Stresses: Effect of Other Metabolic Electron Acceptors and Evidence for a Mechanism

“…The lesser stimulation of growth in Z. mobilis cultures exposed to stresses other than ethanol stress is likely due to the fact that ethanol stress is most likely to have a direct effect on the redox balance by depleting NAD + [10,14], which then reduces the ability to generate sufficient ATP for growth to commence. Most other stresses explored in this study facilitate their stress effect through other physiological means [8,[40][41][42] that have no direct influence on the intracellular redox balance. In case of ethanol stress and the ameliorating effect of acetaldehyde, enzyme alcohol dehydrogenase is pivotal in causing and rectifying the redox imbalance.…”

Development of Biochar-Based Whole-Cell Biocatalysts for the Production of l-Tryptophan and l-Phenylalanine

“…Previous studies have documented that attached bacteria are more active than their free counterparts and exhibit differences in a variety of microbial behaviors, physiological changes, and gene expression because of the interaction between the bacteria and solid phase. 14,41,42 Furthermore, probably attributed to changes in membrane permeability and the architecture of the membrane, the immobilized E. coli cells would have increased resistance to toxic compounds, antibiotics, and other antimicrobial agents in batch fermentation. 43 Therefore, free cells are more vulnerable than immobilized cells to the unfavorable environments during repeated batch fermentation and cell vitality is significantly reduced after each batch, suggesting that free cells are generally not applicable for reuse in the production of the target compound.…”

“…1 The rationally designed whole-cell biosynthesis or transformation can be significantly enhanced and repeatedly used when biochar is used as a cell carrier or fermentation additive to form biocatalysts; however, it is necessary to further enhance the adsorption and immobilization efficiency between cells and biochar. 14,15 L-tryptophan (L-Trp) and L-phenylalanine (L-Phe) are essential aromatic amino acids for mammals that must be ingested from the diet and are the precursors of many important biomolecules. 16,17 L-Trp plays a crucial role in body growth and endocrine regulation, including mood, learning, sleep, and even metabolism or food cravings, 16 whereas L-Phe is a precursor for the formation of catecholamine neurotransmitters and hormones involved in motivational behaviors.…”

Molecular mechanism of engineered Zymomonas mobilis to furfural and acetic acid stress

“…Its 1 mol of ATP is produced by a glucose molecule using the Enter-Doudoroff (ED) pathway [ 13 ]. However, various inhibitors are naturally produced during the hydrolysis process that inhibits cell growth and efficiency of microbial fermentation, such as furfural, vanillin, acetic acid, 5-hydroxymethyl furfural, aldehydes, phenols, and other organic acids [ 14 , 15 ]. These inhibitors are detrimental to Z. mobilis growth and ethanol fermentation [ 16 ].…”