Sequential Aqueous Ammonia Extraction and LiCl/N,N-Dimethyl Formamide Pretreatment for Enhancing Enzymatic Saccharification of Winter Bamboo Shoot Shell

Cold plasma pretreatment reinforces the lignocellulose-derived aldehyde inhibitors tolerance and bioethanol fermentability for Zymomonas mobilis

BACKGROUND

Lignocellulose-derived aldehyde inhibitors seriously blocked the biorefinery of biofuels and biochemicals. To date, the economic production of lignocellulose-based products heavily relied on high productivities of fermenting strains. However, it was expensive and time-consuming for the achievable rational modification to strengthen stress tolerance robustness of aldehyde inhibitors. Here, it aimed to improve aldehyde inhibitors tolerance and cellulosic bioethanol fermentability for the chassis Zymomonas mobilis ZM4 pretreated using energy-efficient and eco-friendly cold plasma.

RESULTS

It was found that bioethanol fermentability was weaker in CSH (corn stover hydrolysates) than that in synthetic medium for Z. mobilis, and thus was attributed to the inhibition of the lignocellulose-derived aldehyde inhibitors in CSH. Convincingly, it further confirmed that the mixed aldehydes severely decreased bioethanol accumulation through additional aldehydes supplementary assays in synthetic medium. After assayed under different processing time (10-30 s), discharge power (80-160 W), and working pressure (120-180 Pa) using cold atmosphere plasma (CAP), it achieved the increased bioethanol fermentability for Z. mobilis after pretreated at the optimized parameters (20 s, 140 W and 165 Pa). It showed that cold plasma brought about three mutation sites including ZMO0694 (E220V), ZMO0843 (L471L) and ZMO0843 (P505H) via Genome resequencing-based SNPs (single nucleotide polymorphisms). A serial of differentially expressed genes (DEGs) were further identified as the potential contributors for stress tolerance via RNA-Seq sequencing, including ZMO0253 and ZMO_RS09265 (type I secretion outer membrane protein), ZMO1941 (Type IV secretory pathway protease TraF-like protein), ZMOr003 and ZMOr006 (16S ribosomal RNA), ZMO0375 and ZMO0374 (levansucrase) and ZMO1705 (thioredoxins). It enriched cellular process, followed by metabolic process and single-organism process for biological process. For KEGG analysis, the mutant was also referred to starch and sucrose metabolism, galactose metabolism and two-component system. Finally, but interestingly, it simultaneously achieved the enhanced stress tolerance capacity of aldehyde inhibitors and bioethanol fermentability in CSH for the mutant Z. mobilis.

CONCLUSIONS

Of several candidate genetic changes, the mutant Z. mobilis treated with cold plasma was conferred upon the facilitated aldehyde inhibitors tolerance and bioethanol production. This work would provide a strain biocatalyst for the efficient production of lignocellulosic biofuels and biochemicals.

Significantly enhanced enzymatic hydrolysis of waste rice hull through a novel surfactant-based deep eutectic solvent pretreatment

The potential of green solvents, specifically deep eutectic solvents (DESs), has piqued the interest of researchers in the field of lignocellulose pretreatment. To enhance the enzymatic digestion efficiency of waste rice hull (RCH), an effective pretreatment approach was developed using the DES [AA][CATB], which was made with acetic acid (AA) and cetyltrimethylammonium bromide (CTAB). The results showed that [AA][CATB] improved enzymatic saccharification by 3.7 times compared to raw RCH and efficiently eliminated lignin (38.7%) and removed xylan (42.9%). The improvement in enzymatic hydrolysis efficiency was then interpreted by a series of characterizations that showed a great morphological changed RCH with an obvious accessibility increase and a lignin surface area and hydrophobicity reduction. This work demonstrates that functional, and easily recoverable DESs have potential for improving the efficiency of lignocellulose pretreatment in biorefineries, providing a promising approach for developing green solvents and achieving more sustainable and efficient biorefinery processes.

Enhanced Enzymatic Saccharification of Tomato Stalk by Combination Pretreatment with NaOH and ChCl:Urea-Thioure in One-Pot Manner

In this study, the mixture of NaOH and deep eutectic solvent (DES) ChCl:UA-TA was firstly used to pretreat waste tomato stalk (TS). The effects of pretreatment time, pretreatment temperature, NaOH dosage, and DES dose were investigated, and the synergistic effects of dilute NaOH and DES combination pretreatment were tested on the influence of enzymatic saccharification. It was found that the relationship between delignification and saccharification rate had a significant linear correction. When TS was pretreated with NaOH (7 wt%)–ChCl:UA-TA (8 wt%) in a solid-to-liquid ratio of 1:10 (wt:wt) at 75 °C for 60 min, the delignification reached 82.1%. The highest yield of reducing sugars from NaOH–ChCl:UA-TA-treated TS could reach 62.5% in an acetate buffer (50 mM, pH 4.8) system containing cellulase (10.0 FPU/g TS) and xylanase (30.0 CBU/g TS) at 50 °C. In summary, effective enzymatic saccharification of TS was developed by a combination pretreatment with dilute NaOH and ChCl:UA-TA, which has potential application in the future.

Enhanced enzymatic saccharification of sorghum straw by effective delignification via combined pretreatment with alkali extraction and deep eutectic solvent soaking

Hydrogen bond donor (HBD) in ChCl-based deep eutectic solvent (DESs) had significant influence on the Sorghum straw (SS) pretreatment. Lactic acid (LAC) was chosen as the appropriate HBD for preparing ChCl-based DES to pretreat Sorghum straw (SS). Furthermore, sequential pretreatment with dilute sodium hydroxide (0.75 wt%) for 1 h at 121 °C and ChCl:LAC soaking at 140 °C for 40 min was applied to pretreat SS for removing lignin (78.4%) and xylan (67.6%). Hydrolysis for 72 h, the reducing sugar yield reached 94.9%. Moreover, relationships of delignification and xylan removal with saccharification were explored after pretreatment. Finally, the fermentability of SS-hydrolysates was verified by bioethanol fermentation by S. cerevissiae with the yield of 0.45 g ethanol/g glucose. No significant inhibition was observed on ethanol fermentation. Obviously, establishment of high-efficient combination pretreatment with alkali extraction and ChCl:LAC soaking was successfully demonstrated for enhancing enzymatic saccharification of SS.

The Pretreatment of Lignocelluloses With Green Solvent as Biorefinery Preprocess: A Minor Review

Converting agriculture and forestry lignocellulosic residues into high value-added liquid fuels (ethanol, butanol, etc.), chemicals (levulinic acid, furfural, etc.), and materials (aerogel, bioresin, etc.) via a bio-refinery process is an important way to utilize biomass energy resources. However, because of the dense and complex supermolecular structure of lignocelluloses, it is difficult for enzymes and chemical reagents to efficiently depolymerize lignocelluloses. Strikingly, the compact structure of lignocelluloses could be effectively decomposed with a proper pretreatment technology, followed by efficient separation of cellulose, hemicellulose and lignin, which improves the conversion and utilization efficiency of lignocelluloses. Based on a review of traditional pretreatment methods, this study focuses on the discussion of pretreatment process with recyclable and non-toxic/low-toxic green solvents, such as polar aprotic solvents, ionic liquids, and deep eutectic solvents, and provides an outlook of the industrial application prospects of solvent pretreatment.

Aqueous Ammonia Pre-treatment of Wheat Straw: Process Optimization and Broad Spectrum Dye Adsorption on Nitrogen-Containing Lignin

Biorefineries need cost-efficient pretreatment processes that overcome the recalcitrance of plant biomass, while providing feasible valorization routes for lignin. Here we assessed aqueous ammonia for the separation of lignin from hydrothermally pretreated wheat straw prior to enzymatic saccharification. A combined severity parameter was used to determine the effects of ammonia concentration, treatment time and temperature on compositional and physicochemical changes [utilizing elemental analysis, cationic dye adsorption, FTIR spectroscopy, size-exclusion chromatography (SEC), and 31P nuclear magnetic resonance (NMR) spectroscopy] as well as enzymatic hydrolysability of straw. Pretreatment at the highest severity (20% NH3, 160°C) led to the maximum hydrolysability of 71% in a 24 h reaction time at an enzyme dosage of 15 FPU/g of pretreated straw. In contrast, hydrolysabilities remained low regardless of the severity when a low cellulase dosage was used, indicating competitive adsorption of cellulases on nitrogen-containing lignin. In turn, our results showed efficient adsorption of cationic, anionic and uncharged organic dyes on nitrogen-containing lignin, which opens new opportunities in practical water remediation applications.

Enhanced bioreduction synthesis of ethyl (R)-4-chloro-3-hydroybutanoate by alkalic salt pretreatment

In this study, biomass-hydrolysate was used for enhancing the bioreduction of ethyl 4-chloro-3-oxobutanoate (COBE). Firstly, dilute alkalic salt pretreatment was attempted to pretreat bamboo shoot shell (BSS). It was found that enzymatic in situ hydrolysis of 20-50 g/L BSS pretreated with dilute alkalic salts (0.4% Na₂CO₃, 0.032% Na₂S) at 7.5% sulfidity by autoclaving at 110 °C for 40 min gave sugar yields at 59.9%-73.5%. Moreover, linear relationships were corrected on solid recovery-total delignification-sugar yield. In BSS-hydrolysates, xylose and glucose could promote the reductase activity of recombinant E. coli CCZU-A13. Compared with glucose, hydrolysate could increase the reductase activity by 1.35-folds. Furthermore, the cyclohexane-hydrolysate (10:90, v/v) biphasic media containing ethylene diamine tetraacetic acid (EDTA, 40 mM) and l-glutamine (150 mM) was built for the effective biosynthesis of ethyl (R)-4-chloro-3-hydroxybutanoate [(R)-CHBE] (94.6% yield) from 500 mM COBE. In conclusion, this strategy has high potential for the effective biosynthesis of (R)-CHBE (>99% e.e.).

Analysis of the Long Time Behavior of Enzymatic Cellulose Hydrolysis Kinetics

Enzymatic hydrolysis of biomass to produce sugars that can be converted to fuels and other valuable chemicals, is viewed as the prime technology for utilization of this renewable resource. To accelerate technology development, models are needed that are able to accurately predict the hydrolysis rate so that reactors can be tailored to the multitude of processing conditions and substrates that can be used. Of particular interest is the ability to predict the long time conversion in the hydrolysis reaction which dictates the maximum possible sugar concentration. It is our aim in this article to develop a simple model which is able to predict the long-term conversion of cellulose to soluble sugars. Drawing on the analogy from the theory of reactions in continuous mixtures, it is shown that analysis of the long time kinetics of hydrolysis by examining the behavior of the “lump” of the reacting material results in a simple expression which is capable of predicting the kinetics. Many features of actual enzyme systems can be included in the development of the hydrolysis model, such as the large size of the enzyme molecules, adsorption onto substrate, inhibition by different factors (solvent, glucose etc.), but, when the analysis is carried out to calculate the total sugar concentration, it is shown that the equations reduce to a simple expression. Analysis of this model is given with comparison to other models and experimental data available in the literature. In addition to predicting the long-term kinetics, it is shown that the model does a surprising job of predicting the initial hydrolysis rates as well.