Synthesis of high-performance antibacterial agent based on incorporated vancomycin into MOF-modified lignin nanocomposites.

The alarming rise in antibiotic resistance necessitates urgent action, particularly against the backdrop of resistant bacteria evolving to render conventional antibiotics less effective, leading to an increase in morbidity, mortality, and healthcare costs. Vancomycin-loaded Metal-Organic Framework (MOF) nanocomposites have emerged as a promising strategy in enhancing the eradication of pathogenic bacteria. This study introduces lignin as a novel synergistic agent in Vancomycin-loaded MOF (Lig-Van-MOF), which substantially enhances the antibacterial activity against drug-resistant bacteria. Lig-Van-MOF exhibits six-fold lower minimum inhibitory concentration (MICs) than free vancomycin and Van-MOF with a much higher antibacterial potential against sensitive and resistant strains of Staphylococcus aureus and Escherichia coli. Remarkably, it reduces biofilms of these strains by over 85 % in minimal biofilm inhibitory concentration (MBIC). Utilization of lignin to modify surface properties of MOFs improves their adhesion to bacterial membranes and boosts the local concentration of Reactive Oxygen Species (ROS) via unique synergistic mechanism. Additionally, lignin induces substantial cell deformation in treated bacterial cells. It confirms the superior bactericidal properties of Lig-Van-MOF against Staphylococcus species, underlining its significant potential as a bionanomaterial designed to combat antibiotic resistance effectively. This research paves the way for novel antibacterial platforms that optimize cost-efficiency and broaden microbial resistance management applications.

Tuning Structural Characteristics of Corn Stover Through Ammonium and Sodium Sulfite (ASS) Pretreatment for Enhanced Enzymatic Hydrolysis.

The ammonia fiber expansion (AFEX) pretreatment of lignocellulosic biomass offers a significant advantage in terms of obtaining high glucan conversion, with the added benefit of ammonia being fully recyclable. However, despite the high efficiency of AFEX in pretreating lignocellulose, relatively high enzyme loading is still required for effective cellulose conversions. In this study, we have updated the AFEX pretreatment method; ammonia and sodium sulfite (ASS) can be used to produce a more digestible substrate. The results demonstrate that ASS-pretreated corn stover (CS) yields a higher fermentable sugar yield compared with AFEX pretreatment, even at lower enzyme loadings. Specifically, at an enzyme loading of 12 mg protein/g glucan, ASS-CS achieved 88.8% glucose and 80.6% xylose yield. Characterization analysis reveals that lignin underwent sulfonation during ASS pretreatment. This modification results in a more negative zeta potential for ASS-CS, indicating a reduction in nonproductive adsorption between lignin and cellulase through increased electrostatic repulsion.

Effects of storage temperature and time on enzymatic digestibility and fermentability of Densifying lignocellulosic biomass with chemicals pretreated corn stover.

A novel pretreatment, Densifying Lignocellulosic biomass with acidic/alkali Chemicals (DLC), was recently invented and owns unique advantages for biomass logistics and fermentation. The pretreatment was largely completed during biomass storage, which renders the storage conditions critical. In this study, the effects of storage temperature (-80 °C to 60 °C) and storage time (up to half a year) on the enzymatic digestibility and fermentability of DLC corn stover (CS) were investigated. DLC-CS containing calcium hydroxide(ch) showed increased enzymatic digestibility with increased storage temperature and time. High glucan conversions (>90%) and ethanol titers (e.g. 73.1 g/L) were achieved after regular steam autoclave of DLC(ch)-CS, without washing or detoxification. DLC-CS containing sulfuric acid(sa) was sensitive to storage conditions, and autoclaved DLC(sa)-CS reached the highest ethanol titer (66.6 g/L) when DLC(sa)-CS was stored at room temperature for 14 days. Results indicated that different ambient temperatures in different regions and seasons have a far-reaching impact on DLC-CS for bioconversion.

Discovery of exolytic heparinases and their catalytic mechanism and potential application.

Heparinases (Hepases) are critical tools for the studies of highly heterogeneous heparin (HP)/heparan sulfate (HS). However, exolytic heparinases urgently needed for the sequencing of HP/HS chains remain undiscovered. Herein, a type of exolytic heparinases (exoHepases) is identified from the genomes of different bacteria. These exoHepases share almost no homology with known Hepases and prefer to digest HP rather than HS chains by sequentially releasing unsaturated disaccharides from their reducing ends. The structural study of an exoHepase (BIexoHep) shows that an N-terminal conserved DUF4962 superfamily domain is essential to the enzyme activities of these exoHepases, which is involved in the formation of a unique L-shaped catalytic cavity controlling the sequential digestion of substrates through electrostatic interactions. Further, several HP octasaccharides have been preliminarily sequenced by using BIexoHep. Overall, this study fills the research gap of exoHepases and provides urgently needed tools for the structural and functional studies of HP/HS chains.

Facile synthesis of manganese oxide modified lignin nanocomposites from lignocellulosic biorefinery wastes for dye removal.

In this study, a facile method to prepare MnO2 nanodots modified lignin nanocomposite (MnO2@LNP) was developed for efficient dye removal. The MnO2@LNP displayed hierarchical spherical nanostructures, where the MnO2 nanodots were evenly dispersed within the lignin nanosphere. Compared with lignin nanoparticles, the as-prepared MnO2@LNP exhibits higher surface area and can be separated after adsorption. It showed excellent adsorption capacity (806 mg/g) towards a typical cationic dye, methylene blue (MB), at a fast removal rate, where more than 80% of adsorption capacity was reached within 5 min at room temperature. The high adsorption capacity was contributed by the high surface area and negative charge on the adsorbent. The adsorption process is pH-responsive and exothermic, and the spent adsorbent can be reused for at least five cycles. This study displayed an efficient method to prepare MnO2@LNP for the high-value utilization of lignin-derived from lignocellulosic biorefinery.

Understanding the structural characteristics of water-soluble phenolic compounds from four pretreatments of corn stover and their inhibitory effects on enzymatic hydrolysis and fermentation.

BACKGROUND: For bioethanol production from lignocellulosic biomass, phenolics derived from pretreatment have been generally considered as highly inhibitory towards enzymatic hydrolysis and fermentation. As phenolics are produced from lignin degradation during pretreatment, it is likely that the pretreatment will exert a strong impact on the structure of phenolics, resulting in varied levels of inhibition of the bioconversion process. Despite the extensive studies on pretreatment, it remains unclear how pretreatment process affects the properties of generated phenolics and how the inhibitory effect of phenolics from different pretreatment varies on enzymatic hydrolysis and fermentation. RESULTS: In this study, the structural properties of phenolic compounds derived from four typical pretreatment [dilute acid (DA), liquid hot water pretreatment (LHW), ammonia fiber expansion (AFEX) and alkaline pretreatment (AL)] were characterized, and their effect on both enzymatic hydrolysis and fermentation were evaluated. The inhibitory effect of phenolics on enzymatic hydrolysis followed the order: AFEX > LHW > DA > AL, while the inhibitory effect of phenolics on Zymomonas mobilis 8b strain fermentation followed the order: AL > LHW > DA > AFEX. Interestingly, this study revealed that phenolics derived from AFEX showed more severe inhibitory effect on enzymatic hydrolysis than those from the other pretreatments at the same phenolics concentrations (note: AFEX produced much less amount of phenolics compared to AL and DA), while they exhibited the lowest inhibitory effect on fermentation. The composition of phenolics from different pretreatments was analyzed and model phenolics were applied to explore the reason for this difference. The results suggested that the amide group in phenolics might account for this difference. CONCLUSIONS: Pretreatment process greatly affects the properties of generated phenolics and the inhibitory effects of phenolics on enzymatic hydrolysis and fermentation. This study provides new insight for further pretreatment modification and hydrolysate detoxification to minimize phenolics-caused inhibition and enhance the efficiency of enzymatic hydrolysis and fermentation.

Boosting Ethanol Productivity of Zymomonas mobilis 8b in Enzymatic Hydrolysate of Dilute Acid and Ammonia Pretreated Corn Stover Through Medium Optimization, High Cell Density Fermentation and Cell Recycling.

The presence of toxic degradation products in lignocellulosic hydrolysate typically reduced fermentation rates and xylose consumption rate, resulting in a decreased ethanol productivity. In the present study, Zymomonas mobilis 8b was investigated for high cell density fermentation with cell recycling to improve the ethanol productivity in lignocellulosic hydrolysate. The fermentation performances of Z. mobilis 8b at various conditions were first studied in yeast extract-tryptone medium. It was found that nutrient level was essential for glucose and xylose co-fermentation by Z. mobilis 8b and high cell density fermentation with cell recycling worked well in yeast extract-tryptone medium for 6 rounds fermentation. Z. mobilis 8b was then studied in enzymatic hydrolysates derived from dilute acid (DA) pretreated corn stover (CS) and ammonia pretreated CS for high cell density fermentation with cell recycling. Ethanol productivity obtained was around three times higher compared to traditional fermentation. Ethanol titer and metabolic yield were also enhanced with high cell density fermentation. Z. mobilis 8b cells showed high recyclability in ammonia pretreated CS hydrolysate.

Identification and Signature Sequences of Bacterial Δ4,5Hexuronate-2-O-Sulfatases.

Glycosaminoglycan (GAG) sulfatases, which catalyze the hydrolysis of sulfate esters from GAGs, belong to a large and conserved sulfatase family. Bacterial GAG sulfatases are essential in the process of sulfur cycling and are useful for the structural analysis of GAGs. Only a few GAG-specific sulfatases have been studied in detail and reported to date. Herein, the GAG-degrading Photobacterium sp. FC615 was isolated from marine sediment, and a novel Δ4,5hexuronate-2-O-sulfatase (PB2SF) was identified from this bacterium. PB2SF specifically removed 2-O-sulfate from the unsaturated hexuronate residue located at the non-reducing end of GAG oligosaccharides produced by GAG lyases. A structural model of PB2SF was constructed through a homology-modeling method. Six conserved amino acids around the active site were chosen for further analysis using site-directed mutagenesis. N113A, K141A, K141H, H143A, H143K, H205A, and H205K mutants exhibited only feeble activity, while the H310A, H310K, and D52A mutants were totally inactive, indicating that these conserved residues, particularly Asp52 and His310, were essential in the catalytic mechanism. Furthermore, bioinformatic analysis revealed that GAG sulfatases with specific degradative properties clustered together in the neighbor-joining phylogenetic tree. Based on this finding, 60 Δ4,5hexuronate-2-O-sulfatases were predicted in the NCBI protein database, and one with relatively low identity to PB2SF was characterized to confirm our prediction. Moreover, the signature sequences of bacterial Δ4,5hexuronate-2-O-sulfatases were identified. With the reported signature motifs, the sulfatase sequence of the Δ4,5hexuronate-2-O-sulfatase family could be simply identified before cloning. Taken together, the results of this study should aid in the identification and further application of novel GAG sulfatases.

Correction to: Developing fast enzyme recycling strategy through elucidating enzyme adsorption kinetics on alkali and acid pretreated corn stover.

[This corrects the article DOI: 10.1186/s13068-018-1315-5.].

Developing fast enzyme recycling strategy through elucidating enzyme adsorption kinetics on alkali and acid pretreated corn stover.

BACKGROUND: Although various pre-treatment methods have been developed to disrupt the structure of lignocellulosic biomass, high dosage of cellulases is still required to hydrolyze lignocellulose to fermentable sugars. Enzyme recycling via recycling unhydrolyzed solids after enzymatic hydrolysis is a promising strategy to reduce enzyme loading for production of cellulosic ethanol. RESULTS: To develop effective enzyme recycling method via recycling unhydrolyzed solids, this work investigated both enzymatic hydrolysis kinetics and enzyme adsorption kinetics on dilute acid and dilute alkali pre-treated corn stover (CS). It was found that most of the hydrolysable biomass was hydrolyzed in the first 24 h and about 40% and 55% of the enzymes were adsorbed on unhydrolyzed solids for dilute alkali-CS and dilute acid-CS, respectively, at 24 h of enzymatic hydrolysis. Lignin played a significant role in such adsorption and lignin materials derived from dilute acid-CS and dilute alkali-CS possessed different enzyme adsorption properties. Enzyme recycling was performed by recycling unhydrolyzed solids after 24 h enzymatic hydrolysis for five successive rounds, and successfully reduced 40% and 50% of the enzyme loadings for hydrolysis of dilute alkali-CS and for hydrolysis of dilute acid-CS, respectively. CONCLUSIONS: This study presents that the enzymes adsorbed on the unhydrolyzed solids after short-time hydrolysis could be recycled effectively for efficient enzymatic hydrolysis. Lignin derived from dilute acid-CS has higher enzyme adsorption capacity than the lignin derived from dilute alkali-CS, which led to more enzymes recycled. By applying the enzyme recycling strategy developed in this study, the enzyme dosage needed for effective cellulose hydrolysis can be significantly reduced.