Expression and characterization of a glucose-tolerant β-1,4-glucosidase with wide substrate specificity from Cytophaga hutchinsonii

Characterization of a Novel One-Domain Halotolerant Laccase from Parageobacillus thermoglucosidasius and Its Application in Dye Decolorization

Laccases are widespread multi-copper oxidases and generally classified into three-domain laccases and two-domain laccases. In this study, a novel laccase PthLac from Parageobacillus thermoglucosidasius harbored only one domain of Cu-oxidase_4 and showed no sequence relatedness or structure similarity to three-domain and two-domain laccases. PthLac was heterologously expressed in Escherichia coli, purified, and characterized. The optimum temperature and pH of PthLac on guaiacol were at 60 ℃ and pH 6, respectively. The effects of various metal ions on PthLac were analyzed. All the tested metal ions did not suppress the activity of PthLac, except for 10 mM Cu2+, which increased the activity of PthLac to 316%, indicating that PthLac was activated by Cu2+. Meanwhile, PthLac kept 121% and 69% activity when incubated at concentrations of 2.5 and 3 M NaCl for 9 h, suggesting the long-term halotolerancy of this enzyme. In addition, PthLac showed resistance to the organic solvents and surfactants, and displayed dye decolorization capacity. This study enriched our knowledge about one-domain laccase and its potential industrial applications.

Research progress of diosgenin extraction from Dioscorea zingiberensis C. H. Wright: Inspiration of novel method with environmental protection and efficient characteristics

Diosgenin was the starting materials to synthesize various hormone drugs and mainly generated from Dioscorea zingiberensis C. H. Wright by acidolysis, enzymolysis, microbiological fermentation, and integrated manner. Only acidic hydrolysis with strong acid such as hydrochloric acid or sulfuric acid was used in practice in diosgenin enterprises due to their feasibility and simplicity, nevertheless finally resulting in a great deal of unmanageable wastewater and severely polluted the surrounding environment. Aiming to provide a comprehensive and up-to date information of researches on diosgenin production from this plant, 151 cases were collected from scientific databases including Web of Science, Pubmed, Science Direct, Wiley, Springer, and China Knowledge Resource Integrated (CNKI). Their advantages and disadvantages with different production methods were analyzed based on these available data in this review paper. Considering the fact that nearly all of diosgenin enterprises were closed for the environmental protection and the life health of the people, this review paper was beneficial for providing useful guidelines to develop novel technologies with environmentally-friendly and cleaner features for diosgenin production or facilitate the transformation of other methods like enzymolysis, microbiological fermentation, or integrated methods from laboratory scale to industry scale.

Efficient production of the anti-aging drug Cycloastragenol: insight from two Glycosidases by enzyme mining

The telomerase activator cycloastragenol (CA) is regarded as a potential anti-aging drug with promising applications in the food and medical industry. However, one remaining challenge is the low efficiency of CA production. Herein, we developed an enzyme-based approach by applying two enzymes (β-xylosidase: Xyl-T; β-glucosidase: Bgcm) for efficient CA production. Both key glycosidases, mined by activity tracking or homology sequence screening, were successfully over-expressed and showed prominent enzymatic activity profiles, including widely pH stability (Xyl-T: pH 3.0-8.0; Bgcm: pH 4.0-10.0), high catalytic efficiency (k_cat/K_m: 0.096 mM^-1s^-1 (Xyl-T) and 3.08 mM^-1s^-1 (Bgcm)), and mesophilic optimum catalytic temperature (50 °C). Besides, the putative catalytic residues (Xyl-T: Asp311/Glu 521; Bgcm: Asp311/Glu 521) and the potential substrate-binding mechanism of Xyl-T and Bgcm were predicted by comprehensive computational analysis, providing valuable insight into the hydrolysis of substrates at the molecular level. Notably, a rationally designed two-step reaction process was introduced to improve the CA yield and increased up to 96.5% in the gram-scale production, providing a potential alternative for the industrial CA bio-production. In essence, the explored enzymes, the developed enzyme-based approach, and the obtained knowledge from catalytic mechanisms empower researchers to further engineer the CA production and might be applied for other chemicals synthesis. KEY POINTS: • A β-xylosidase and a β-glucosidase were mined to hydrolyze ASI into CA. • The two recombinant glycosidases showed prominent catalytic profiles. • Two-step enzymatic catalysis for CA production from ASI was developed. Graphical abstract.

Deep Hypersaline Anoxic Basins as Untapped Reservoir of Polyextremophilic Prokaryotes of Biotechnological Interest

Deep-sea hypersaline anoxic basins (DHABs) are considered to be among the most extreme ecosystems on our planet, allowing only the life of polyextremophilic organisms. DHABs’ prokaryotes exhibit extraordinary metabolic capabilities, representing a hot topic for microbiologists and biotechnologists. These are a source of enzymes and new secondary metabolites with valuable applications in different biotechnological fields. Here, we review the current knowledge on prokaryotic diversity in DHABs, highlighting the biotechnological applications of identified taxa and isolated species. The discovery of new species and molecules from these ecosystems is expanding our understanding of life limits and is expected to have a strong impact on biotechnological applications.

Proteomic Dissection of the Cellulolytic Machineries Used by Soil-Dwelling Bacteroidetes

Bacteria of the phylum Bacteroidetes are regarded as highly efficient carbohydrate metabolizers, but most species are limited to (semi)soluble glycans. The soil Bacteroidetes species Cytophaga hutchinsonii and Sporocytophaga myxococcoides have long been known as efficient cellulose metabolizers, but neither species conforms to known cellulolytic mechanisms. Both species require contact with their substrate but do not encode cellulosomal systems of cell surface-attached enzyme complexes or the polysaccharide utilization loci found in many other Bacteroidetes species. Here, we have fractionated the cellular compartments of each species from cultures growing on crystalline cellulose and pectin, respectively, and analyzed them using label-free quantitative proteomics as well as enzymatic activity assays. The combined results enabled us to highlight enzymes likely to be important for cellulose conversion and to infer their cellular localization. The combined proteomes represent a wide array of putative cellulolytic enzymes and indicate specific and yet highly redundant mechanisms for cellulose degradation. Of the putative endoglucanases, especially enzymes of hitherto-unstudied glycoside hydrolase family, 8 were abundant, indicating an overlooked important role during cellulose metabolism. Furthermore, both species generated a large number of abundant hypothetical proteins during cellulose conversion, providing a treasure trove of targets for future enzymology studies. IMPORTANCE Cellulose is the most abundant renewable polymer on earth, but its recalcitrance limits highly efficient conversion methods for energy-related and material applications. Though microbial cellulose conversion has been studied for decades, recent advances showcased that large knowledge gaps still exist. Bacteria of the phylum Bacteroidetes are regarded as highly efficient carbohydrate metabolizers, but most species are limited to (semi)soluble glycans. A few species, including the soil bacteria C. hutchinsonii and S. myxococcoides, are regarded as cellulose specialists, but their cellulolytic mechanisms are not understood, as they do not conform to the current models for enzymatic cellulose turnover. By unraveling the proteome setups of these two bacteria during growth on both crystalline cellulose and pectin, we have taken a significant step forward in understanding their idiosyncratic mode of cellulose conversion. This report provides a plethora of new enzyme targets for improved biomass conversion.

Effects of the histone-like protein HU on cellulose degradation and biofilm formation of Cytophaga hutchinsonii

Cytophaga hutchinsonii, belonging to Bacteroidetes, is speculated to use a novel cell-contact mode to digest cellulose. In this study, we identified a histone-like protein HU, CHU_2750, in C. hutchinsonii, whose transcription could be induced by crystalline but not amorphous cellulose. We constructed a CHU_2750-deleted mutant and expressed CHU_2750 in Escherichia coli to study the gene's functions. Our results showed that although the deletion of CHU_2750 was not lethal to C. hutchinsonii, the mutant displayed an abnormal filamentous morphology, loose nucleoid, and obvious defects in the degradation of crystalline cellulose and cell motility. Further study indicated that the mutant displayed significantly decreased cell surface and intracellular endoglucanase activities but with β-glucosidase activities similar to the wild-type strain. Analyses by real-time quantitative PCR revealed that the transcription levels of many genes involved in cellulose degradation and/or cell motility were significantly downregulated in the mutant. In addition, we found that CHU_2750 was important for biofilm formation of C. hutchinsonii. The main extracellular components of the biofilm were analyzed, and the results showed that the mutant yielded significantly less exopolysaccharide but more extracellular DNA and protein than the wild-type strain. Collectively, our findings demonstrated that CHU_2750 is important for cellulose degradation, cell motility, and biofilm formation of C. hutchinsonii by modulating transcription of certain related genes, and it is the first identified transcriptional regulator in these processes of C. hutchinsonii. Our study shed more light on the mechanisms of cellulose degradation, cell motility, and biofilm formation by C. hutchinsonii.

A highly glucose-tolerant GH1 β-glucosidase with greater conversion rate of soybean isoflavones in monogastric animals

In the feed industry, β-glucosidase has been widely used in the conversion of inactive and bounded soybean isoflavones into active aglycones. However, the conversion is frequently inhibited by the high concentration of intestinal glucose in monogastric animals. In this study, a GH1 β-glucosidase (AsBG1) with high specific activity, thermostability and glucose tolerance (IC50 = 800 mM) was identified. It showed great glucose tolerance against substrates with hydrophobic aryl ligands (such as pNPG and soy isoflavones). Using soybean meal as the substrate, AsBG1 exhibited higher hydrolysis efficiency than the GH3 counterpart Bgl3A with or without the presence of glucose in the reaction system. Furthermore, it is the first time to find that the endogenous β-glucosidase of soybean meal, mostly belonging to GH3, plays a role in the hydrolysis of soybean isoflavones and is highly sensitive to glucose. These findings lead to a conclusion that the GH1 rather than GH3 β-glucosidase has prosperous application advantages in the conversion of soybean isoflavones in the feed industry.

The unusual cellulose utilization system of the aerobic soil bacterium Cytophaga hutchinsonii

Cellulolytic microorganisms play important roles in global carbon cycling and have evolved diverse strategies to digest cellulose. Some are 'generous,' releasing soluble sugars from cellulose extracellularly to feed both themselves and their neighbors. The gliding soil bacterium Cytophaga hutchinsonii exhibits a more 'selfish' strategy. It digests crystalline cellulose using cell-associated cellulases and releases little soluble sugar outside of the cell. The mechanism of C. hutchinsonii cellulose utilization is still poorly understood. In this review, we discuss novel aspects of the C. hutchinsonii cellulolytic system. Recently developed genetic manipulation tools allowed the identification of proteins involved in C. hutchinsonii cellulose utilization. These include periplasmic and cell-surface endoglucanases and novel cellulose-binding proteins. The recently discovered type IX secretion system is needed for cellulose utilization and appears to deliver some of the cellulolytic enzymes and other proteins to the cell surface. The requirement for periplasmic endoglucanases for cellulose utilization is unusual and suggests that cello-oligomers must be imported across the outer membrane before being further digested. Cellobiohydrolases or other predicted processive cellulases that play important roles in many other cellulolytic bacteria appear to be absent in C. hutchinsonii. Cells of C. hutchinsonii attach to and glide along cellulose fibers, which may allow them to find sites most amenable to attack. A model of C. hutchinsonii cellulose utilization summarizing recent progress is proposed.