Isolation of new cellulase and xylanase producing strains and application to lignocellulosic biomasses hydrolysis and succinic acid production

Development of an efficient chimeric trifunctional xylanase/glucanase/feruloyl esterase and its application in the bioconversion of corn stover into fermentable sugars

Multifunctional enzymes have the potential to enhance hydrolytic efficiency and reduce enzyme cost. In this study, by optimizing linker peptide identity and the order of fusion partners, an efficient trifunctional xylanase/glucanase/feruloyl esterase, named Xyn(Glu)A/FaeB-L1, was obtained through associating the Bacillus bifunctional xylanase/glucanase Xyn(Glu)A with its cognate feruloyl esterase FaeB using a flexible linker peptide (L1). In comparison to the parental enzymes, Xyn(Glu)A/FaeB-L1 displayed similar pH optima for enzyme activity, shifting no more than a single unit. However, the optimal reaction temperature was 5-10 °C lower than that of the parental enzymes. Intriguingly, its catalytic efficiencies (kcat/Km) with wheat arabinoxylan and barley β-glucan measured 1.48- and 8.90-fold that of Xyn(Glu)A, respectively. Similarly, the Xyn(Glu)A/FaeB-L1 kcat/Km for para-nitrophenyl ferulate measured 3.84-fold that of FaeB, which may be attributed to the physical association of the fusion partners. Moreover, Xyn(Glu)A/FaeB-L1 was superior to a mixture of Xyn(Glu)A + FaeB at degrading feruloylated arabinoxylan. Furthermore, Xyn(Glu)A/FaeB-L1 surpassed a commercial cellulase (Cel) in the hydrolysis of pretreated corn stover, also showing synergistic effects when combined with Cel. These results demonstrate the feasibility of constructing efficient chimeric enzymes and the potential of Xyn(Glu)A/FaeB-L1 for the conversion of agricultural by-products into fermentable sugars, making it an attractive candidate for biorefinery applications.

Genomic analysis and synergistic effect with cellulase by Streptomyces thermocarboxydus 12219

In this study, we fully sequenced and analyzed the genome of strain 12219 and identified it as Streptomyces thermocarboxydus. The genome contained a single linear chromosome, 6,950,031 bp in size, with a GC content of 72.21 %. This study predicted a total of 6295 genes, including 128 glycoside hydrolase genes, 21 carbohydrate esterase genes, and 54 carbohydrate-binding module genes. When corncob was used as inducer, strain 12219 secreted cellulases and hemicellulases, with xylanase activity reaching 31.15 U/mL. During the hydrolysis of sodium hydroxide treated corn stover, a notable synergistic effect between the 12219 enzyme cocktail and commercial cellulase was observed. And the maximum degree of synergism reached 1.60. When the amount of the 12219 enzyme cocktail added to the commercial cellulase was 5 mg/g, the release of glucose, xylose, and cellobiose increased by 121.35 %, 178.58 %, and 29.33 %, respectively. These findings suggested that the 12219 enzyme cocktail held great potential for industrial applications.

Effect of enzyme preparation and extrusion puffing treatment on sorghum straw silage fermentation

In this study, the effects on silage performance and microbial community of sorghum straw treated with the addition of enzymes (cellulase (CE), xylanase (XE)) and extrusion puffing technology, combined with SEM, XRD, and FTIR techniques, were thoroughly investigated. The results showed that the enzyme preparations, especially xylanase, significantly improved the nutritional value and fermentation efficiency of straw and enhanced the silage effect. Extruding significantly changes the surface structure of the straw, increasing the surface area and porosity, and promoting the attachment of microorganisms. This study not only optimized the sorghum straw silage performance but also provided technical support for the efficient use of straw resources, which is of great significance for the sustainable development of animal husbandry and the resource utilization of agricultural waste.

Statistical optimization of cellulase production from Bacillus sp. YE16 isolated from yak dung of the Sikkim Himalayas for its application in bioethanol production using pretreated sugarcane bagasse

Cellulolytic bacteria were isolated from yak dung samples collected from different habitats of Sikkim, India. Isolate YE16 from the Yumthang Valley sample showed highest enzyme activity of 7.68 U/mL and was identified as Bacillus sp., which has a sequence similarity of 96.15% with B. velezensis. One factor at a time (OFAT) analysis revealed that an acidic pH of 5 with 37 °C temperature was optimum for maximum enzyme production after 36 hrs of incubation (13.88 U/mL), which was further increased after statistical optimization (34.70 U/mL). Media optimization based on response surface methodology predicted that Carboxymethyl cellulose (CMC) and MgSO4 at concentrations of 30 g/L and 0.525 g/L, respectively, at pH 5.5 to show CMCase activity of 30.612 U/mL, which was consistent with the observed value of 30.25 U/mL and confirmed the model. The crude enzyme also efficiently hydrolyzed alkaline pretreated sugarcane bagasse, releasing 7.09 g/L of glucose equivalent with an ethanol production of 3.05 g.

Substrate type and CO2 addition significantly influence succinic acid production of Basfia succiniciproducens

Metabolic engineering has shown that optimizing metabolic pathways' fluxes for industrial purposes requires a methodical approach. Accordingly, in this study, in silico metabolic modeling was utilized to characterize the lesser-known strain Basfia succiniciproducens under different environmental conditions, followed by the use of industrially relevant substrates for succinic acid synthesis. Based on RT-qPCR carried out in flask experiments, we discovered a relatively large difference in the expression levels of ldhA gene compared to glucose in both xylose and glycerol cultures. In bioreactor-scale fermentations, the impact of different gas phases (CO2, CO2/AIR) on biomass yield, substrate consumption, and metabolite profiles was also investigated. In the case of glycerol, the addition of CO2 increased biomass as well as target product formation, while using CO2/AIR gas phase resulted in higher target product yield (0.184 mM⋅mM-1). In case of xylose, using CO2 alone would result in higher succinic acid production (0.277 mM⋅mM-1). The promising rumen bacteria, B. succiniciproducens, has shown to be suitable for succinic acid production from both xylose and glycerol. As a result, our findings present new opportunities for broadening the range of raw materials used in this significant biochemical process. Our study also sheds light on fermentation parameter optimization for this strain, namely that, CO2/AIR supply has a positive effect on target product formation.

Valorisation of hydrothermal liquefaction wastewater in agriculture: effects on tobacco plants and rhizosphere microbiota

Industrial wastewater obtained from hydrothermal liquefaction (HTL-WW) of food wastes for biofuels production could represent a source of crop nutrients since it is characterized by a high amount of organic and inorganic compounds. In the present work, the potential use of HTL-WW as irrigation water for industrial crops was investigated. The composition of the HTL-WW was rich in nitrogen, phosphorus, and potassium with high level of organic carbon. A pot experiment with Nicotiana tabacum L. plants was conducted using diluted wastewater to reduce the concentration of some chemical elements below the official accepted threshold values. Plants were grown in the greenhouse under controlled conditions for 21 days and irrigated with diluted HTL-WW every 24 hours. Soils and plants were sampled every seven days to evaluate, over time, the effect of wastewater irrigation both on soil microbial populations, through high-throughput sequencing, and plant growth parameters, through the measurement of different biometric indices. Metagenomic results highlighted that, in the HTL-WW treated rhizosphere, the microbial populations shifted via their mechanisms of adaptation to the new environmental conditions, establishing a new balance among bacterial and fungal communities. Identification of microbial taxa occurring in the rhizosphere of tobacco plants during the experiment highlighted that the HTL-WW application improved the growth of Micrococcaceae, Nocardiaceae and Nectriaceae, which included key species for denitrification, organic compounds degradation and plant growth promotion. As a result, irrigation with HTL-WW improved the overall performance of tobacco plants which showed higher leaf greenness and increased number of flowers compared to irrigated control plants. Overall, these results demonstrate the potential feasibility of using of HTL-WW in irrigated agriculture.

Preparation and Characterization of New Bioplastics Based on Polybutylene Succinate (PBS)

Sea and environmental pollution due to microplastics are global problems that in recent years have attracted particular interest in the scientific community. The increase in the world population and the consequent consumerism of non-reusable materials are amplifying these problems. In this manuscript, we present novel bioplastics, which are completely biodegradable, for their potential use in food packaging, to replace fossil-fuel-derived plastic films and slow food degradation due to oxidative processes or microbial contamination. In this study, thin films based on polybutylene succinate (PBS) were prepared to reduce pollution, and different percentages by weight (1, 2 and 3 wt%) of extra virgin olive oil (EVO) and coconut oil (CO) were included to improve the chemico-physical properties of the polymer and possibly improve the functionality of the films in terms of prolonged food preservation. Attenuated total reflectance Fourier transform infrared (ATR/FTIR) spectroscopy was used to evaluate the interactions between the polymer and the oil. Furthermore, the mechanical properties and thermal behavior of the films were evaluated as a function of the oil content. A scanning electron microscopy (SEM) micrograph showed the surface morphology and the thickness of the materials. Finally, apple and kiwi were selected for a food-contact test, and the wrapped sliced fruit was monitored and evaluated for 12 days to macroscopically evaluate the oxidative process and/or eventually occurring contamination. The films were shown to reduce the browning of sliced fruit due to oxidation, and no molds were evidenced up to 10/12 days of observation with the addition of PBS, with 3 wt% of EVO achieving the best outcomes.

Diversity, mechanisms and beneficial features of phosphate-solubilizing Streptomyces in sustainable agriculture: A review

Currently, the use of phosphate (P) biofertilizers among many bioformulations has attracted a large amount of interest for sustainable agriculture. By acting as growth promoters, members of the Streptomyces genus can positively interact with plants. Several studies have shown the great potential of this bacterial group in supplementing P in a soluble, plant-available form by several mechanisms. Furthermore, some P-solubilizing Streptomyces (PSS) species are known as plant growth-promoting rhizobacteria that are able to promote plant growth through other means, such as increasing the availability of soil nutrients and producing a wide range of antibiotics, phytohormones, bioactive compounds, and secondary metabolites other than antimicrobial compounds. Therefore, the use of PSS with multiple plant growth-promoting activities as an alternative strategy appears to limit the negative impacts of chemical fertilizers in agricultural practices on environmental and human health, and the potential effects of these PSS on enhancing plant fitness and crop yields have been explored. However, compared with studies on the use of other gram-positive bacteria, studies on the use of Streptomyces as P solubilizers are still lacking, and their results are unclear. Although PSS have been reported as potential bioinoculants in both greenhouse and field experiments, no PSS-based biofertilizers have been commercialized to date. In this regard, this review provides an overview mainly of the P solubilization activity of Streptomyces species, including their use as P biofertilizers in competitive agronomic practices and the mechanisms through which they release P by solubilization/mineralization, for both increasing P use efficiency in the soil and plant growth. This review further highlights and discusses the beneficial association of PSS with plants in detail with the latest developments and research to expand the knowledge concerning the use of PSS as P biofertilizers for field applications by exploiting their numerous advantages in improving crop production to meet global food demands.

Assessment of vine shoots and surplus grape must for succinic acid bioproduction

Vine shoots and surplus grape must were assessed as feedstocks for succinic acid production with Actinobacillus succinogenes and Basfia succiniproducens. After acidic and enzymatic hydrolysis, vine shoots released 35-40 g/L total sugars. Both bacterial species produced 18-21 g/L succinic acid from this hydrolysate in 120 h. Regarding grape must fermentation, A. succinogenes clearly outperformed B. succiniproducens. Yeast extract (a source of organic nitrogen and vitamins) was the only additional nutrient needed by A. succinogenes to grow on grape must. Under mathematically optimized conditions (145.7 g/L initial sugars and 24.9 g/L yeast extract), A. succinogenes generated 88.9 ± 1.4 g/L succinic acid in 96 h, reaching a succinic acid yield of 0.66 ± 0.01 g/g and a sugar consumption of 96.64 ± 0.30%. Substrate inhibition was not observed in grape musts with 125-150 g/L initial sugars, provided that an adequate amount of yeast extract was available for bacteria. Alternative nitrogen sources to yeast extract (red wine lees, white wine lees, urea, NH₄Cl, and choline chloride) were not suitable for A. succinogenes in grape must. KEY POINTS: • Vine shoots and surplus grape must were assessed for succinic acid bioproduction. • Succinic acid bioproduction was 21 g/L with vine shoots and 89 g/L with grape must. • Fermentation was efficient at high sugar loads if organic N supply was adequate.

Production of Succinic Acid From Basfia succiniciproducens

Basfia succiniciproducens is a facultative anaerobic capnophilic bacterium, isolated from rumen, that naturally produces high amounts of succinic acid by fixing CO2 and using fumarate as final electron acceptor. This metabolic feature makes it one of the ideal candidates for developing biotechnological industrial routes that could eventually replace the polluting and environment unfriendly petrochemical ones that are still main sources for the production of this value-added compound. In fact, due to the large number of applications of succinic acid that range from the more traditional ones as food additive or pharmaceutical intermediate to the most recent as building block for biopolymers and bioplastic, increasing demand and market size growth are expected in the next years. In line with a “green revolution” needed to preserve our environment, the great challenge is the establishment of commercially viable production processes that exploit renewable materials and in particular preferably non-food lignocellulosic biomasses and waste products. In this review, we describe the currently available literature concerning B. succiniciproducens since the strain was first isolated, focusing on the different renewable materials and fermentation strategies used to improve succinic acid production titers to date. Moreover, an insight into the metabolic engineering approaches and the key physiological characteristics of B. succiniciproducens deduced from the different studies are presented.

Nanomaterial conjugated lignocellulosic waste: cost-effective production of sustainable bioenergy using enzymes

The demand for novel and renewable sources of energy has increased as a result of rapid population growth, limited sources of bioenergy, and environmental pollution, caused by excessive use of fossil fuels. The need to meet future energy demands have motivated researchers to search for alternative and sustainable sources of energy. The bioconversion of lignocellulosic waste (agricultural and food waste) into biofuels shows competitive promises. Lignocellulosic waste is easily accessible and has a large enzyme system that can be immobilised onto nano-matrices. Consequently, resulting in higher biofuel production and process efficiency. However, the excessive production cost of the current procedures, which involve physical, chemical, and enzymatic reactions, is limited. The use of nanomaterials has recently been shown to concentrate lignocellulosic waste, therefore, reviewing the quest for efficient production of sustainable and cost-effective development of bioenergy from lignocellulosic wastes. This review paper explores the advanced strategies of using nanobiotechnology to combine enzyme-conjugated nanosystems for the cost-effective production of sustainable bioenergy solutions. This research will help to develop an inexpensive, eco-friendly technology for biofuels production and also help overcome the environmental burden of lignocellulosic waste worldwide.

Identification and characterization of a novel endo-β-1,4-glucanase from a soil metagenomic library

A cosmid clone cZFYN1413 with CMCase activity was identified from a soil metagenomic library. The sequence analysis of a subclone of cZFYN1413 revealed an endo-β-1,4-glucanase gene ZFYN1413 belonging to glycoside hydrolase family 6 and a transmembrane region in the N-terminal of ZFYN1413. Expression of ZFYN1413 in Escherichia coli BL21 (DE3) resulted in ZFYN1413-87, which was a truncated protein cleaved in transmembrane region of ZFYN1413. ZFYN1413-87 was expressed and its enzyme properties were studied. ZFYN1413-87 possessed strong endo-β-1,4-glucanase activity, and 52% of the activity could be retained after the protein was treated in buffer of pH 3.0 for 2 h. The study provided a special example of endo-β-1,4-glucanase in GH6 family.

Enzyme Production Potential of Penicillium oxalicum M1816 and Its Application in Ferulic Acid Production

The present study focused on isolating an efficient enzyme production microorganism for ferulic acid (FA) production from wheat bran. A wild-type cellulase-, xylanase-, and feruloyl esterase-producing strain was isolated and identified as Penicillium oxalicum M1816. The genome was sequenced and assembled into 30.5 Mb containing 8301 predicted protein-coding genes. In total, 553 genes were associated with carbohydrate metabolism. Genomic CAZymes analysis indicated that P. oxalicum M1816, comprising 39 cellulolytic enzymes and 111 hemicellulases (including 5 feruloyl esterase genes), may play a vital role in wheat bran degradation and FA production. The crude enzyme of strain M1816 could release 1.85 ± 0.08 mg·g-1 FA from de-starched wheat bran (DSWB) at 12 h, which was significantly higher than other commercial enzymes. Meanwhile, when the strain M1816 was cultured in medium supplemented with DSWB, up to 92.89% of the total alkali-extractable FA was released. The process parameters of solid-state fermentation were optimized to enhance enzyme production. The optimized wheat bran Qu of P. oxalicum M1816 was applied to huangjiu fermentation, and the FA content was increased 12.4-fold compared to the control group. These results suggest that P. oxalicum M1816 is a good candidate for the development of fermented foods bio-fortified with FA.

Biosynthesis of silver nanoparticles with antimicrobial and anticancer properties using two novel yeasts

AgNPs are nanomaterials with many potential biomedical applications. In this study, the two novel yeast strains HX-YS and LPP-12Y capable of producing biological silver nanoparticles were isolated. Sequencing of ribosomal DNA-ITS fragments, as well as partial D1/D2 regions of 26S rDNA indicated that the strains are related to species from the genus Metschnikowia. The BioAgNPs produced by HX-YS and LPP-12Y at pH 5.0-6.0 and 26 °C ranged in size from 50 to 500 nm. The antibacterial activities of yeast BioAgNPs against five pathogenic bacteria were determined. The highest antibacterial effect was observed on P. aeruginosa, with additional obvious effects on E. coli ATCC8099 and S. aureus ATCC10231. Additionally, the BioAgNPs showed antiproliferative effects on lung cancer cell lines H1975 and A579, with low toxicity in Beas 2B normal lung cells. Therefore, the AgNPs biosynthesized by HX-YS and LPP-12Y may have potential applications in the treatment of bacterial infections and cancer.

Microbioreactor (micro-Matrix) potential in aerobic and anaerobic conditions with different industrially relevant microbial strains

Microscale fermentation systems are important high throughput tools in clone selection, and bioprocess set up and optimization, since they provide several parallel experiments in controlled conditions of pH, temperature, agitation, and gas flow rate. In this work we evaluated the performance of biotechnologically relevant strains with different respiratory requirements in the micro‐Matrix microbioreactor. In particular Escherichia coli K4 requires well aerated fermentation conditions to improve its native production of chondroitin‐like capsular polysaccharide, a biomedically attractive polymer. Results from batch and fed‐batch experiments demonstrated high reproducibility with those obtained on 2 L reactors, although highlighting a pronounced volume loss for longer‐term experiments. Basfia succiniciproducens and Actinobacillus succinogenes need CO₂ addition for the production of succinic acid, a building block with several industrial applications. Different CO₂ supply modes were tested for the two strains in 24 h batch experiments and results well compared with those obtained on lab‐scale bioreactors. Overall, it was demonstrated that the micro‐Matrix is a useful scale‐down tool that is suitable for growing metabolically different strains in simple batch process, however, a series of issues should still be addressed in order to fully exploit its potential.

Complete genome sequencing and comparative genome characterization of the lignocellulosic biomass degrading bacterium Pseudomonas stutzeri MP4687 from cattle rumen

We report the complete genome sequencing of novel Pseudomonas stutzeri strain MP4687 isolated from cattle rumen. Various strains of P. stutzeri have been reported from different environmental samples including oil-contaminated sites, crop roots, air, and human clinical samples, but not from rumen samples, which is being reported here for the first time. The genome of P. stutzeri MP4687 has a single replicon, 4.75 Mb chromosome and a G + C content of 63.45%. The genome encodes for 4,790 protein coding genes including 164 CAZymes and 345 carbohydrate processing genes. The isolate MP4687 harbors LCB hydrolyzing potential through endoglucanase (4.5 U/mL), xylanase (3.1 U/mL), β-glucosidase (3.3 U/mL) and β-xylosidase (1.9 U/mL) activities. The pangenome analysis further revealed that MP4687 has a very high number of unique genes (>2100) compared to other P. stutzeri genomes, which might have an important role in rumen functioning.

Isolation and Selection of Streptomyces Species from Semi-arid Agricultural Soils and Their Potential as Producers of Xylanases and Cellulases

The Mezquital Valley (MV), Mexico, is a semi-arid region whose main economic activity is agriculture, this zone is characterized by the use of wastewater for crop irrigation. This condition has increased the amount nutrients in soils, organic carbon content and native microorganisms. The Streptomyces species are a group of saprophytic bacteria that represent between 20 and 60% of the total microbial population in soils, capable of producing metabolites of commercial importance. In this work, Streptomyces species were isolated from agricultural soils of the MV and was evaluated the production of endoglucanases (CMCase) and xylanases (Xyl) in Solid-State Cultivation (SSC). From soil samples, 73 possible strains of Streptomyces species were isolated for their ability to produce CMCase and Xyl in SSC. The study also included its characterization by morphological characteristics. Of the isolated microorganisms, 38 strains were selected as strong enzyme producers according to the measurement of the halo generated in plate and by growth on barley straw as only carbon source. Two different sizes of barley straw particle were tested, finding that the greatest enzymatic activity was observed in particle size 12. Three strains of Streptomyces species were chosen which presented the best catalytic capacities, a maximum of 100.69 AU Xyl/gram dry matter (gdm), 82 AU Xyl/gdm and 26.02 AU CMCase/gdm for strains 30, 28 and 12, respectively. The strains were identified by ribosomal gen16s sequence and identified as S. flavogriseus, S. virginiae and S. griseoaurantiacus. It is the first report of endogluconase and xylanolytic activity by S. virginiae isolated from a semi-arid soil.

Community-level genetic profiles of actinomycetales in long-term biowaste-amended soils

Actinomycetales is an order of actinobacteria that have an important role in the decomposition of organic matter. Their abundance and distribution can reflect a good level of soil fertility as well as biological activity. In this research study, actinomycetal diversity in soil was investigated under various field treatments with biowastes. Initially, unvegetated agricultural soil plots of 4 m² had been annually amended with increasing rates of municipal solid waste compost (MSWC at 40, 80 and 120 t ha^-1 year^-1) and farmyard manure (FM at 40 and 120 t ha^-1 year^-1) for eight consecutive years. Control consisted of unamended soil and all treatments were distributed in four randomized complete blocks. At the end of the experimental period, total DNA was extracted from fresh topsoil samples (0-20 cm) then nested PCR-DGGE sequencing method was applied to assess the long-term effect of treatments on the diversity of actinomycetes. Analytical outcomes revealed the presence of ten actinomycetal families with Streptomycetaceae, Pseudonocardiaceae and Nocardioidaceae being the most dominant regardless to changes in experimental conditions. Besides, the long-term accumulation of both biowastes in soil affected the diversity of actinomycetal communities in different ways including contribution, stimulation or inhibition. Interestingly, soil treated with MSWC at an equivalent rate of 40 t ha^-1 year^-1 was likely to provide optimal growth conditions for major identified genera because it showed the highest actinomycetal diversity as compared to the rest of the treatments.

The ROK-family regulator Rok7B7 directly controls carbon catabolite repression, antibiotic biosynthesis, and morphological development in Streptomyces avermitilis

Carbon catabolite repression (CCR) is a common phenomenon in bacteria that modulates expression of genes involved in uptake of alternative carbon sources. In the filamentous streptomycetes, which produce half of all known antibiotics, the precise mechanism of CCR is yet unknown. We report here that the ROK-family regulator Rok7B7 pleiotropically controls xylose and glucose uptake, CCR, development, as well as production of the macrolide antibiotics avermectin and oligomycin A in Streptomyces avermitilis. Rok7B7 directly repressed structural genes for avermectin biosynthesis, whereas it activated olmRI, the cluster-situated activator gene for oligomycin A biosynthesis. Rok7B7 also directly repressed the xylose uptake operon xylFGH, whose expression was induced by xylose and repressed by glucose. Both xylose and glucose served as Rok7B7 ligands. rok7B7 deletion led to enhancement and reduction of avermectin and oligomycin A production, respectively, relieved CCR of xylFGH, and increased co-uptake efficiency of xylose and glucose. A consensus Rok7B7-binding site, 5'-TTKAMKHSTTSAV-3', was identified within aveA1p, olmRIp, and xylFp, which allowed prediction of the Rok7B7 regulon and confirmation of 11 additional targets involved in development, secondary metabolism, glucose uptake, and primary metabolic processes. Our findings will facilitate methods for strain improvement, antibiotic overproduction, and co-uptake of xylose and glucose in Streptomyces species.

Isolation of Thermostable Lignocellulosic Bacteria From Chicken Manure Compost and a M42 Family Endocellulase Cloning From Geobacillus thermodenitrificans Y7

The composting ecosystem provides a potential resource for finding new microorganisms with the capability for cellulose degradation. In the present study, Congo red method was used for the isolating of thermostable lignocellulose-degrading bacteria from chicken manure compost. A thermophilic strain named as Geobacillus thermodenitrificans Y7 with acid-resident property was successfully isolated and employed to degrade raw switchgrass at 60°C for 5 days, which resulted in the final degradation rates of cellulose, xylan, and acid-insoluble lignin as 18.64, 12.96, and 17.21%, respectively. In addition, GC-MS analysis about aromatic degradation affirm the degradation of lignin by G. thermodenitrificans Y7. Moreover, an endocellulase gene belong to M42 family was successfully cloned from G. thermodenitrificans Y7 and expressed in Escherichia coli BL21. Recombinant enzyme Cel-9 was purified by Ni-NTA column based the His-tag, and the molecular weight determined as 40.4 kDa by SDA-PAGE. The characterization of the enzyme Cel-9 indicated that the maximum enzyme activity was realized at 50°C and pH 8.6 and, Mn2+ could greatly improve the CMCase enzyme activity of Cel-9 at 10 mM, which was followed by Fe2+ and Co2+. Besides, it also found that the β-1,3-1,4, β-1,3, β-1,4, and β-1,6 glucan linkages all could be hydrolyzed by enzyme Cel-9. Finally, during the application of enzyme Cel-9 to switchgrass, the saccharification rates achieved to 1.81 ± 0.04% and 2.65 ± 0.03% for 50 and 100% crude enzyme, respectively. All these results indicated that both the strain G. thermodenitrificans Y7 and the recombinant endocellulase Cel-9 have the potential to be applied to the biomass industry.

Production, characteristics, and biotechnological applications of microbial xylanases

Microbial xylanases have gathered great attention due to their biotechnological potential at industrial scale for many processes. A variety of lignocellulosic materials, such as sugarcane bagasse, rice straw, rice bran, wheat straw, wheat bran, corn cob, and ragi bran, are used for xylanase production which also solved the great issue of solid waste management. Both solid-state and submerged fermentation have been used for xylanase production controlled by various physical and nutritional parameters. Majority of xylanases have optimum pH in the range of 4.0-9.0 with optimum temperature at 30-60 °C. For biochemical, molecular studies and also for successful application in industries, purification and characterization of xylanase have been carried out using various appropriate techniques. Cloning and genetic engineering are used for commercial-level production of xylanase, to meet specific economic viability and industrial needs. Microbial xylanases are used in various biotechnological applications like biofuel production, pulp and paper industry, baking and brewing industry, food and feed industry, and deinking of waste paper. This review describes production, characteristics, and biotechnological applications of microbial xylanases.

Production of glycoprotein bioflocculant from untreated rice straw by a CAZyme-rich bacterium, Pseudomonas sp. HP2

It has been reported that certain biomass-degrading bacteria can produce bioflocculant through directly utilizing untreated biomass as carbon source. However, little is known about the synthesis mechanism of bioflocculant in these bacteria. In this study, a biomass-degrading bacterium Pseudomonas sp. HP2 showing excellent production ability of bioflocculant was isolated from the forest soil. The HP2 strain secreted alkali-thermo-tolerant CMCase and xylanase, with the maximum activities of 0.06 and 1.07 U ml^-1, respectively, when the untreated rice straw was used as carbon source. The maximum flocculating efficiency with the value of 92.5% was produced from untreated rice straw by HP2 strain. Component analysis showed that this bioflocculant was abundant in the amino acids and monosaccharides with the total contents of 384.9 and 478.3 mg g^-1 dry bioflocculant, respectively. The most amino acid and monosaccharide in this bioflocculant were proline and rhamnose, which accounted for 26.5% and 33.3% of total amino acids and total monosaccharides, respectively. To explore the synthesis mechanism of bioflocculant in HP2, the genome of HP2 strain was measured by Illumina HiSeq PE150 platform. The results showed that the genome of HP2 strain possessed abundant CAZy family related genes, which may play an important role in biomass degradation and bioflocculant synthesis.

Efficient production of succinic acid in engineered Escherichia coli strains controlled by anaerobically-induced nirB promoter using sweet potato waste hydrolysate

Succinic acid has attracted interest worldwide as a precursor of many industrially crucial chemicals. Biosynthesis of succinic acid from biomass is developing as an environmentally friendly strategy now. Conversion of sweet potato waste (SPW) to succinic acid could implement high-value utilization of biomass, cut cost of the fermentation process and reduce the pollution of environment. Engineered Escherichia coli (E. coli) strain HD134 under the control of anaerobically-induced nirB promoter from Salmonella enterica (P_SnirB) could produce about 16.30 g/L succinic acid with a yield of 0.83 g/g after 48 h on glucose. With SPW hydrolysate as the substrate, 18.65 g/L succinic acid with a yield of 0.94 g/g after 48 h fermentation achieved. Compared to SD134 under Trc control induced with Isopropyl β-D-Thiogalactoside (IPTG), this concentration and yield represented an 8.56% and 6.82% increase, respectively. The use of anaerobically-induced P_SnirB not only could attain higher production of succinic acid than IPTG-induced Trc promoter, but omit cost of expensive exogenous inducers. The efficient production of succinic acid from SPW was firstly studied by anaerobically-induced P_SnirB control, which achieved relative lower cost compared to glucose as substrate and IPTG as the inducer. This novel fermentation process conduces to the cosmically industrial succinic acid bioproduction.

Efficient Enzyme-Assisted Extraction and Conversion of Polydatin to Resveratrol From Polygonum cuspidatum Using Thermostable Cellulase and Immobilized β-Glucosidase

Resveratrol, a bioactive compound in high quantities in Polygonum cuspidatum, has well-known health benefits. However, it mainly exists in its glycosidic form, polydatin, in plants. To increase the production of resveratrol for various uses in medicine, foods, and cosmetics, an efficient deglycosylation technique is needed for converting polydatin into resveratrol. We screened a new cellulolytic strain of Bacillus from herb compost, and we optimized parameters within the fermentation process using response surface methodology with a Box-Behnken design. The yield of cellulase reached 2701.08 U/L, corresponding to values that were 5.4 times as high as those under unoptimized conditions. The Bacillus cellulase possessed good thermostablity and was stable under both acidic and neutral conditions. The cellulase was then used in the pretreatment of P. cuspidatum root. After incubation at 50°C for 4 h with shaking at 150 rpm, the contents of piceid and resveratrol were determined to be 7.60 ± 0.15 and 9.72 ± 0.29 mg/g, respectively. To obtain complete deglycosylation, immobilized β-glucosidase (bgl2238) was added to the cellulase-treated extracts of P. cuspidatum root to convert residual polydatin into resveratrol. After the first cycle, the contents of piceid and resveratrol were determined to be 0 and 13.69 ± 0.30 mg/g, respectively. Moreover, enzyme activity showed little loss during up to 4 consecutive cycles. These results demonstrated that the immobilized β-glucosidase possessed high deglycosylation activity and outstanding operational stability. The mixture of Bacillus cellulase and immobilized bgl2238 appears promising as a means to increase the supply of resveratrol in the medicine market worldwide.

A novel thermostable GH10 xylanase with activities on a wide variety of cellulosic substrates from a xylanolytic Bacillus strain exhibiting significant synergy with commercial Celluclast 1.5 L in pretreated corn stover hydrolysis

BACKGROUND

Cellulose and hemicellulose are the two largest components in lignocellulosic biomass. Enzymes with activities towards cellulose and xylan have attracted great interest in the bioconversion of lignocellulosic biomass, since they have potential in improving the hydrolytic performance and reducing the enzyme costs. Exploring glycoside hydrolases (GHs) with good thermostability and activities on xylan and cellulose would be beneficial to the industrial production of biofuels and bio-based chemicals.

RESULTS

A novel GH10 enzyme (XynA) identified from a xylanolytic strain Bacillus sp. KW1 was cloned and expressed. Its optimal pH and temperature were determined to be pH 6.0 and 65 °C. Stability analyses revealed that XynA was stable over a broad pH range (pH 6.0-11.0) after being incubated at 25 °C for 24 h. Moreover, XynA retained over 95% activity after heat treatment at 60 °C for 60 h, and its half-lives at 65 °C and 70 °C were about 12 h and 1.5 h, respectively. More importantly, in terms of substrate specificity, XynA exhibits hydrolytic activities towards xylans, microcrystalline cellulose (filter paper and Avicel), carboxymethyl cellulose (CMC), cellobiose, p-nitrophenyl-β-d-cellobioside (pNPC), and p-nitrophenyl-β-d-glucopyranoside (pNPG). Furthermore, the addition of XynA into commercial cellulase in the hydrolysis of pretreated corn stover resulted in remarkable increases (the relative increases may up to 90%) in the release of reducing sugars. Finally, it is worth mentioning that XynA only shows high amino acid sequence identity (88%) with rXynAHJ14, a GH10 xylanase with no activity on CMC. The similarities with other characterized GH10 enzymes, including xylanases and bifunctional xylanase/cellulase enzymes, are no more than 30%.

CONCLUSIONS

XynA is a novel thermostable GH10 xylanase with a wide substrate spectrum. It displays good stability in a broad range of pH and high temperatures, and exhibits activities towards xylans and a wide variety of cellulosic substrates, which are not found in other GH10 enzymes. The enzyme also has high capacity in saccharification of pretreated corn stover. These characteristics make XynA a good candidate not only for assisting cellulase in lignocellulosic biomass hydrolysis, but also for the research on structure-function relationship of bifunctional xylanase/cellulase.