Thermostable Xylanase Production by Geobacillus sp. Strain DUSELR13, and Its Application in Ethanol Production with Lignocellulosic Biomass

Characterization, whole-genome sequence analysis, and protease production of a new thermophilic Bacillus licheniformis strain isolated from Debagh hot spring, Algeria

A new thermophilic strain, designated as Bacillus sp. LMB3902, was isolated from Hammam Debagh, the hottest spring in Algeria (up to 98 °C). This isolate showed high protease production in skim milk media at 55 °C and exhibited significant specific protease activity by using azocasein as a substrate (157.50 U/mg). Through conventional methods, chemotaxonomic characteristics, 16S rRNA gene sequencing, and comparative genomic analysis with the closely related strain Bacillus licheniformis DSM 13 (ATCC 14580 T), the isolate Bacillus sp. LMB3902 was identified as a potentially new strain of Bacillus licheniformis. In addition, the gene functions of Bacillus sp. LMB3902 strain were predicted using the Gene Ontology, Kyoto Encyclopedia of Genes and Genomes, Clusters of Orthologous Groups, Non-Redundant Protein Sequence Database, Swiss-Prot, and Pfam databases. The results showed that the genome size of Bacillus sp. LMB3902 was 4.279.557 bp, with an average GC content of 46%. The genome contained 4.760 predicted genes, including 8 rRNAs, 78 tRNAs, and 24 sRNAs. A total of 235 protease genes were annotated including 50 proteases with transmembrane helix structures and eight secreted proteases with signal peptides. Additionally, the majority of secondary metabolites found by antiSMASH platform showed low similarity to identified natural products, such as fengicin (53%), lichenysin (57%), and surfactin (34%), suggesting that this strain may encode for novel uncharacterized natural products which can be useful for biotechnological applications. This study is the first report that describes the complete genome sequence, taxono-genomics, and gene annotation as well as protease production of the Bacillus genus in this hydrothermal vent.

Optimization and Characterization of an Ultra-Thermostable, Acidophilic, Cellulase-Free Xylanase from a New Obligate Thermophilic Geobacillus thermoleovorans AKNT10 and its Application in Saccharification of Wheat Bran

Microbial xylanases are enzymes of great importance due to their wide industrial applications, especially in the degradation of lignocellulosic biomass into fermentable sugars. This study aimed to describe the production optimization and partial characterization of an ultra-thermostable, acidophilic, cellulase-free xylanase from an obligate thermophilic eubacterium Geobacillus thermoleovorans strain-AKNT10 (Ac.No. LT158229) isolated from a hot-spring of Puga Valley located at an altitude of 4419 m in Ladakh, India. The optimization of cultural conditions improved enzyme yield by 10.49-fold under submerged fermentation. The addition of 1% (w/v) xylose induced the enzyme synthesis by ~ 165 and 371% when supplemented in the fermentation medium containing wheat bran (WB) 1 and 3%, respectively. The supplementation of sucrose reduced the xylanase production by ~ 25%. Results of partial characterization exhibited that xylanase was optimally active at pH 6.0 and 100 °C. Enzyme retained > 75%, > 83%, and > 84% of activity at 4 °C for 28 days, 100 °C for 60 min, and pHs 3-8 for 60 min, respectively. An outstanding property of AKNT10-xylanase, was the retention of > 71% residual activity at extreme conditions (121 °C and 15 psi pressure) for 15 min. Enzymatic saccharification showed that enzyme was also capable to liberate maximum reducing sugars within 4-8 h under optimized conditions thus it could be a potential candidate for the bioconversion of lignocellulosic biomass as well as other industrial purposes. To the best of our knowledge, this is the first report on such an ultra-thermo-pressure-tolerant xylanase optimally active at pH 6 and 100 °C from the genus Geobacillus.

A novel endo-1,4-β-xylanase from Alicyclobacillus mali FL18: Biochemical characterization and its synergistic action with β-xylosidase in hemicellulose deconstruction

A novel endo-1,4-β-xylanase-encoding gene was identified in Alicyclobacillus mali FL18 and the recombinant protein, named AmXyn, was purified and biochemically characterized. The monomeric enzyme worked optimally at pH 6.6 and 80 °C on beechwood xylan with a specific activity of 440.00 ± 0.02 U/mg and a good catalytic efficiency (kcat/KM = 91.89 s-1mLmg-1). In addition, the enzyme did not display any activity on cellulose, suggesting a possible application in paper biobleaching processes. To develop an enzymatic mixture for xylan degradation, the association between AmXyn and the previously characterized β-xylosidase AmβXyl, deriving from the same microorganism, was assessed. The two enzymes had similar temperature and pH optima and showed the highest degree of synergy when AmXyn and AmβXyl were added sequentially to beechwood xylan, making this mixture cost-competitive and suitable for industrial use. Therefore, this enzymatic cocktail was also employed for the hydrolysis of wheat bran residue. TLC and HPAEC-PAD analyses revealed a high conversion rate to xylose (91.56 %), placing AmXyn and AmβXyl among the most promising biocatalysts for the saccharification of agricultural waste.

Abridgement of Microbial Esterases and Their Eminent Industrial Endeavors

Esterases are hydrolases that contribute to the hydrolysis of ester bonds into both water-soluble acyl esters and emulsified glycerol-esters containing short-chain acyl groups. They have garnered significant attention from biotechnologists and organic chemists due to their immense commercial value. Esterases, with their diverse and significant properties, have become highly sought after for various industrial applications. Synthesized ubiquitously by a wide range of living organisms, including animals, plants, and microorganisms, these enzymes have found microbial esterases to be the preferred choice in industrial settings. The cost-effective production of microbial esterases ensures higher yields, unaffected by seasonal variations. Their applications span diverse sectors, such as food manufacturing, leather tanneries, paper and pulp production, textiles, detergents, cosmetics, pharmaceuticals, biodiesel synthesis, bioremediation, and waste treatment. As the global trend shifts toward eco-friendly and sustainable practices, industrial processes are evolving with reduced waste generation, lower energy consumption, and the utilization of biocatalysts derived from renewable and unconventional raw materials. This review explores the background, structural characteristics, thermostability, and multifaceted roles of bacterial esterases in crucial industries, aiming to optimize and analyze their properties for continued successful utilization in diverse industrial processes. Additionally, recent advancements in esterase research are overviewed, showcasing novel techniques, innovations, and promising areas for further exploration.

Enhanced production of a recombinant xylanase (XT6): optimization of production and purification, and scaled-up batch fermentation in a stirred tank bioreactor

The endoxylanase XT6 produced by Geobacillus stearothermophilus is a desirable candidate for industrial applications. In this study, the gene encoding XT6 was cloned using the pET-28a expression vector and expressed in Escherichia coli BL21 (DE3) cells. Recombinant XT6 production was improved by optimizing cell lysis (sonication, chemical, and enzymatic lysis) and expression conditions. Sonication in a 0.05 M sodium phosphate (pH 6.0) buffer resulted in the highest xylanase activity (16.48 U/ml). Screening and optimization of induction conditions using the Plackett-Burman Design and Box-Behnken Design (BBD) approaches revealed that cell density pre-induction (OD600 nm), post-induction incubation time, and IPTG concentration significantly (p < 0.05) influenced the expression levels of XT6 (16.48 U/ml to 40.06 U/ml) representing a 3.60-fold increase. BBD resulted in a further 8.74-fold increase in activity to 144.02 U/ml. Batch fermentation in a 5-l stirred tank bioreactor at 1 vvm aeration boosted recombinant xylanase production levels to 165 U/ml suggesting that heterologous expression of the XT6 enzyme is suitable for scaled-up production. The pure enzyme with a molecular weight of 43 kDa and a 15.69-fold increase in purity was obtained using affinity chromatography and a cobalt column. Future studies will include application of the purified recombinant xylanase to animal feed.

Lignocellulolytic extremozymes and their biotechnological applications

Lignocellulolytic enzymes are used in different industrial and environmental processes. The rigorous operating circumstances of these industries, however, might prevent these enzymes from performing as intended. On the other side, extremozymes are enzymes produced by extremophiles that can function in extremely acidic or basic; hot or cold; under high or low salinity conditions. These severe conditions might denature the normal enzymes that are produced by mesophilic microorganisms. The increased stability of these enzymes has been contributed to a number of conformational modifications in their structures. These modifications may result from a few amino acid substitutions, an improved hydrophobic core, the existence of extra ion pairs and salt bridges, an increase in compactness, or an increase in positively charged amino acids. These enzymes are the best option for industrial and bioremediation activities that must be carried out under difficult conditions due to their improved stability. The review, therefore, discusses lignocellulolytic extremozymes, their structure and mechanisms along with industrial and biotechnological applications.

Genome sequencing analysis of a novel thermophilic strain Geobacillus sp. CX412

The thermophilic spore-forming strain Geobacillus sp. CX412 was isolated from hot spring soil in Tengchong City, Yunnan Province, China. We sequenced the complete genome of Geobacillus sp. CX412 using PacBio SMRT Sequencing. Genome-scale phylogenetic analysis and average nucleotide identity (ANI) results indicated that Geobacillus sp. CX412 is a novel species in the genus Geobacillus. The metabolic potential of Geobacillus sp. CX412 based on COG, KEGG, and CAZymes analysis demonstrated that Geobacillus sp. CX412 was a highly adaptable strain with an unusually high number of 73 annotated transposons in the genome, which is relatively rare in Geobacillus. Compared with the near-derived strains, it was found that Geobacillus sp. CX412 has the unique β-lactam resistance and more active metabolism (more than 50.5–100.1%). Additionally, its genome encodes glycoside hydrolases and other genes related to lignocellulose breakdown, suggesting that Geobacillus sp. CX412 has a considerable biomass degradation potential. Thus, Geobacillus sp. CX412 is a new thermophilic bacterial species that add to the increasing repertoire of known lignocellulose degraders.

Production and biochemical characterization of partially purified cellulase-free, thermo-acidophilic endoxylanase from Lysinibacillus fusiformis strain TB7 using kolanut husk as feedstock

Xylanases have become very important enzymes in many industrial processes for the valorization of xylan-rich lignocellulosic wastes. Here, some physicochemical and kinetic properties of a purified endoxylanase produced on kolanut husk-based medium by Lysinibacillus fusiformis are presented. The crude enzyme solution was first subjected to precipitation with solid ammonium sulphate and further purified on DEAE-Sephadex A-50 anion-exchange and Sephadex G-100 gel filtration columns chromatography prior to biochemical characterization. The purified endoxylanase was 21 kDa as determined by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and was thermostable, exhibiting optimum activity at 60 °C and pH 5.0. The K _m and V _max were respectively estimated to be 29.5 mg/ml and 125 μmol/min/ml using Birchwood xylan as substrate. Activity of the enzyme was enhanced by Na⁺, Ca²⁺, Mn²⁺, Mg²⁺ and K⁺ at concentration of 5 mM but inhibited by Hg²⁺, Cu²⁺, Pb²⁺, Fe³⁺, EDTA, SDS and Urea. The purified endoxylanase showed high hydrolytic activity on Birchwood xylan and kolanut husk but extremely poor or no activity on carboxymethyl cellulose, starch or pectin. This L. fusiformis strain TB7 endoxylanase has desirable properties useful for biotechnological applications in laundry, fuels, feeds, paper and pulp industries.

Fusarium graminearum as a producer of xylanases with low cellulases when grown on wheat bran

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Endophytic fungi of cacao had important xylanase activity when grown on wheat bran.

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F. graminearum strain Ec220 produced xylanases with low cellulolytic activity.

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Xylanase production was optimized using response surface methodology.

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Proteomic analysis revealed similarities with previously reported xylanases.

The xylanolytic potential of endophytic fungi isolated from leaves of Theobroma cacao was explored for the first time. Four fungal strains showed significant amounts of xylanase activity and low cellulase levels when grown on wheat bran as the sole carbon source. Strain Ec220 of Fusarium graminearum had the highest xylanase production (1.79 U/ml), whereas its cellulase activity was minimal (0.24 U/ml). Optimal conditions for xylanase production were: 154 h of incubation time, pH 5.79 and 29.8 °C. Furthermore, two protein spots detected by two-dimensional gel electrophoresis showed molecular weights (26.05 and 27.70 kDa) and isoelectric points (6.18 and 9.20) corresponding to previously reported F. graminearum xylanases, Xyl A and Xyl B, respectively. Therefore, endophytic fungi of T. cacao can be an important source of xylanolytic activities when cultured on wheat bran, and xylanases with low cellulases found in strain Ec220 require further characterization as they show promise for possible industrial applications.

Genomic Analysis Provides New Insights Into Biotechnological and Industrial Potential of Parageobacillus thermantarcticus M1

Parageobacillus thermantarcticus strain M1 is a Gram-positive, motile, facultative anaerobic, spore forming, and thermophilic bacterium, isolated from geothermal soil of the crater of Mount Melbourne (74°22′ S, 164°40′ E) during the Italian Antarctic Expedition occurred in Austral summer 1986–1987. Strain M1 demonstrated great biotechnological and industrial potential owing to its ability to produce exopolysaccharides (EPSs), ethanol and thermostable extracellular enzymes, such as an xylanase and a β-xylosidase, and intracellular ones, such as xylose/glucose isomerase and protease. Furthermore, recent studies revealed its high potential in green chemistry due to its use in residual biomass transformation/valorization and as an appropriate model for microbial astrobiology studies. In the present study, using a systems-based approach, genomic analysis of P. thermantarcticus M1 was carried out to enlighten its functional characteristics. The elucidation of whole-genome organization of this thermophilic cell factory increased our understanding of biological mechanisms and pathways, by providing valuable information on the essential genes related to the biosynthesis of nucleotide sugar precursors, monosaccharide unit assembly, as well as the production of EPSs and ethanol. In addition, gene prediction and genome annotation studies identified genes encoding xylanolytic enzymes that are required for the conversion of lignocellulosic materials to high-value added molecules. Our findings pointed out the significant potential of strain M1 in various biotechnological and industrial applications considering its capacity to produce EPSs, ethanol and thermostable enzymes via the utilization of lignocellulosic waste materials.

Biodeinking of waste papers using combinatorial fungal enzymes and subsequent production of butanol from effluent

The present study aimed to enzymatic deinking of waste papers and to valorize the effluent for biobutanol production. Application of fungal enzymatic cocktail (cellulase, amylase, xylanase, pectinase, lipase, and ligninase) on office used paper, newspaper, and ballpen written paper leading to improvement in brightness (84.91, 72.51, 76.69 % ISO), InKd (82.89, 68.95, 76.49%), κ-number (12.9, 13.6, and 13.1), opacity (27.91, 30.07, and 2.85%), tensile strength (49.24, 45.31, and 46.98 Nm/g), respectively and indices were consistent with chemical treated pulps. The quality of effluent generated during enzymatic deinking in respect to BOD and COD level was eco-friendlier than the chemical process. The enzyme-treated effluent was employed as supporting substrate for butanol (18.4 g/l) production by Clostridium acetobutylicum ATCC824. Material balance and life cycle assessment of the whole processes were evaluated to validate its industrial and environmental relevance.

Current status and applications of genus Geobacillus in the production of industrially important products-a review

The genus Geobacillus is one of the most important genera which mainly comprises gram-positive thermophilic bacterial strains including obligate aerobes, denitrifiers and facultative anaerobes having capability of endospore formation as well. The genus Geobacillus is widely distributed in nature and mostly abundant in extreme locations such as cool soils, hot springs, hydrothermal vents, marine trenches, hay composts and dairy plants. Due to plasticity towards environmental adaptation, the Geobacillus sp. shows remarkable genome diversification and acquired many beneficial properties, which facilitates their exploitation for many biotechnological applications. Many thermophiles are of biotechnological importance and having considerable interest in commercial applications for the production of industrially important products. Recently, due to catabolic versatility especially in the degradation of hemicellulose and starch containing agricultural waste and rapid growth rates, these microorganisms show potential for the production of biofuels, thermostable enzymes and bioremediation. This review mainly summarizes the status of Geobacillus sp. including its notable properties, biotechnological studies and its potential application in the production of industrially important products.

Saccharification of lignocellulosic biomass using an enzymatic cocktail of fungal origin and successive production of butanol by Clostridium acetobutylicum

A multistep approach was undertaken for biobutanol production targeting valorization of agricultural waste. Optimum production of lignocellulolytic enzymes [CMCase (3822.93U/mg), FPase (3640.93U/mg), β-glucosidase (3873.92U/mg), xylanase (3460.24U/mg), pectinase (3359.57U/mg), α-amylase (4136.54U/mg), and laccase (3863.16U/mg)] was accomplished through solid-substrate fermentation of pretreated mixed substrates (wheat bran, sugarcane bagasse and orange peel) by Aspergillus niger SKN1 and Trametes hirsuta SKH1. Partially purified enzyme cocktail was employed for saccharification of the said substrate mixture into fermentable sugar (69.23 g/L, product yield of 24% w/w). The recovered sugar with vegetable extract supplements was found as robust fermentable medium that supported 16.51 g/L biobutanol production by Clostridium acetobutylicum ATCC824. The sequential bioprocessing of low-priced substrates and exploitation of vegetable extract as growth factor for microbial butanol production will open a new vista in biofuel research.

Advances in pretreatment of lignocellulosic biomass for bioenergy production: Challenges and perspectives

As a clean and renewable energy, bioenergy is one of the most promising alternatives to fossil fuels. Lignocellulose possesses great potential for bioenergy production, but the recalcitrant and heterogeneous structure limits its application. Pretreatment technology offers an effective solution to fractionate the main components of the lignocellulose and uncover the available cellulose. The obtained feedstock can be applied to bioconversion into energy, e.g., bioethanol, biogas, biohydrogen, etc. Here, the current state of lignocellulose pretreatment technologies was comprehensively reviewed, the advances in bioenergy production from pretreated lignocellulose was described, with particular attention to key challenges involved. Several new strategies for overcoming pretreatment barriers to realize highly efficient lignocellulose bioconversion were highlighted. The insights given in this review will facilitate further development on lignocellulosic bioenergy production, towards addressing the global energy crisis and climate change related to the use of fossil fuels.

Bioprospecting of xylanase producing fungal strains: Multilocus phylogenetic analysis and enzyme activity profiling

The study aims to explore potential xylanase-producing indigenous fungi isolated from soil and vegetable wastes containing plant degraded matter, reporting multilocus phylogenetic analysis and xylanase enzyme activity from selective strains. Four potential xylanolytic fungi were identified through distinct primary and secondary screening of 294 isolates obtained from the samples. Morphological characterization and multigene analysis (ITS rDNA, 18S rDNA, LSU rDNA, β-tubulin, and actin gene) confirmed them as Aspergillus sp. AUMS56, Aspergillus tubingensis AUMS60 and AUMS64, and Aspergillus fumigatus AUKEMS24; achieving crude xylanase activities (through submerged fermentation using corn cobs) of 18.9, 32.29, 30.68, and 15.82 U ml^-1 , respectively. AUMS60 and AUMS64 (forming lineage with A. tubingensis and Aspergillus niger in the same phylogroup with 100% Bayesian posterior probability support) secreted single xylanase (Xyn60; 36 kDa) and multiple xylanases (Xyn64A and Xyn64B; 33.4 and 19.8 kDa) respectively, having pH optima of 6.0 and exhibiting maximal activity at 60°C. These enzymes were highly stable at 40°C (120 h) and retained more than 70% activity at 50°C and at pH 5-6 (upon 72 h incubation). Our analysis suggested these enzymes to be endoxylanases demonstrating substrate hydrolysis within 15 min of reaction and maximum efficiency of xylanases from AUMS60 and AUMS64 achieving 51.1% (13 h) and 52.2% (24 h) saccharification, respectively. They also showed enhanced catalytic activity with various cations. Based on our investigation on xylan hydrolysis, we believe that these xylanases may find significant industrial applications as they have a real potential of working as a bio-catalytic cocktail (patent file number: IN E1/38213/2020-DEL) for the enhanced saccharification of lignocelluloses.

Extremophilic Prokaryotic Endoxylanases: Diversity, Applicability, and Molecular Insights

Extremophilic endoxylanases grabbed attention in recent years due to their applicability under harsh conditions of several industrial processes. Thermophilic, alkaliphilic, and acidophilic endoxylanases found their employability in bio-bleaching of paper pulp, bioconversion of lignocellulosic biomass into xylooligosaccharides, bioethanol production, and improving the nutritious value of bread and other bakery products. Xylanases obtained from extremophilic bacteria and archaea are considered better than fungal sources for several reasons. For example, enzymatic activity under broad pH and temperature range, low molecular weight, cellulase-free activity, and longer stability under extreme conditions of prokaryotic derived xylanases make them a good choice. In addition, a short life span, easy cultivation/harvesting methods, higher yield, and rapid DNA manipulations of bacterial and archaeal cells further reduces the overall cost of the product. This review focuses on the diversity of prokaryotic endoxylanases, their characteristics, and their functional attributes. Besides, the molecular mechanisms of their extreme behavior have also been presented here.

Role of extremophiles and their extremozymes in biorefinery process of lignocellulose degradation

Technological advances in the field of life sciences have led to discovery of organisms that live in harsh environmental conditions referred to as extremophiles. These organisms have adapted themselves to thrive in extreme habitat giving these organisms an advantage over conventional mesophilic organisms in various industrial applications. Extremozymes produced by these extremophiles have high tolerance to inhospitable environmental conditions making them an ideal enzyme system for various industrial processes. A notable application of these extremophiles and extremozymes is their use in the degradation of recalcitrant lignocellulosic biomass and application in biorefineries. For maximum utilization of the trapped carbon source from this obstinate biomass, pretreatment is a necessary step that requires various physiochemical and enzymatic treatments. From search for novel extremophiles and extremozymes to development of various genetic and protein engineering techniques, investigation on extremozymes with enhanced stability and efficiency is been done. Since extremozymes are easily calibrated to work under such conditions, they have become an emerging topic in the research field of biofuel production. The review discusses the various extremozymes that play an important role in lignocellulose degradation along with recent studies on their molecular and genetic evolution for industrial application and production of biofuels and various value-added products.

Hemicellulases from Penicillium and Talaromyces for lignocellulosic biomass valorization: A review

The term hemicellulose groups different polysaccharides with heterogeneous structures, mannans, xyloglucans, mixed-linkage β-glucans and xylans, which differ in their backbone and branches, and in the type and distribution of glycosidic linkages. The enzymatic degradation of these complex polymers requires the concerted action of multiple hemicellulases and auxiliary enzymes. Most commercial enzymes are produced by Trichoderma and Aspergillus species, but recent studies have disclosed Penicillium and Talaromyces as promising sources of hemicellulases. In this review, we summarize the current knowledge on the hemicellulolytic system of these genera, and the role of hemicellulases in the disruption and synthesis of glycosidic bonds. In both cases, the enzymes from Penicillium and Talaromyces represent an interesting alternative for valorization of lignocellulosic biomass in the current framework of circular economy.

Conversion of Wheat Bran to Xylanases and Dye Adsorbent by Streptomyces thermocarboxydus

Agro-byproducts can be utilized as effective and low-cost nutrient sources for microbial fermentation to produce a variety of usable products. In this study, wheat bran powder (WBP) was found to be the most effective carbon source for xylanase production by Streptomyces thermocarboxydus TKU045. The optimal media for xylanase production was 2% (w/v) WBP, 1.50% (w/v) KNO₃, 0.05% (w/v) MgSO₄, and 0.10% (w/v) K₂HPO₄, and the optimal culture conditions were 50 mL (in a 250 mL-volume Erlenmeyer flask), initial pH 9.0, 37 °C, 125 rpm, and 48 h. Accordingly, the highest xylanase activity was 6.393 ± 0.130 U/mL, 6.9-fold higher than that from un-optimized conditions. S. thermocarboxydus TKU045 secreted at least four xylanases with the molecular weights of >180, 36, 29, and 27 kDa when cultured on the WBP-containing medium. The enzyme cocktail produced by S. thermocarboxydus TKU045 was optimally active over a broad range of temperature and pH (40–70 °C and pH 5–8, respectively) and could hydrolyze birchwood xylan to produce xylobiose as the major product. The obtained xylose oligosaccharide (XOS) were investigated for 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity and the growth effect of lactic acid bacteria. Finally, the solid waste from the WBP fermentation using S. thermocarboxydus TKU045 revealed the high adsorption of Congo red, Red 7, and Methyl blue. Thus, S. thermocarboxydus TKU045 could be a potential strain to utilize wheat bran to produce xylanases for XOS preparation and dye adsorbent.

Combined pretreatment of sugarcane bagasse using alkali and ionic liquid to increase hemicellulose content and xylanase production

BACKGROUND

Lignin in sugarcane bagasse (SB) hinders its utilization by microorganism, therefore, pretreatment methods are employed to make fermentable components accessible to the microbes. Multivariate analysis of different chemical pretreatment methods can aid to select the most appropriate strategy to valorize a particular biomass.

RESULTS

Amongst methods tested, the pretreatment by using sodium hydroxide in combination with methyltrioctylammonium chloride, an ionic liquid, (NaOH+IL) was the most significant for xylanase production by Bacillus aestuarii UE25. Investigation of optimal levels of five significant variables by adopting Box-Behnken design (BBD) predicted 20 IU mL^- 1 of xylanase and experimentally, a titer of 17.77 IU mL^- 1 was obtained which indicated the validity of the model. The production kinetics showed that volumetric productivity of xylanase was much higher after 24 h (833.33 IU L^- 1 h^- 1) than after 48 h (567.08 IU L^- 1 h^- 1). The extracted xylan from SB induced more xylanase in the fermentation medium than pretreated SB or commercially purified xylan. Nuclear Magnetic Resonance, Fourier transform infrared spectroscopy and scanning electron microscopy of SB indicated removal of lignin and changes in the structure of SB after NaOH+IL pretreatment and fermentation.

CONCLUSION

Combined pretreatment of SB with alkali and methyltrioctylammonium chloride appeared better than other chemical methods for bacterial xylanase production and for the extraction of xylan form SB.

The Complete Genome Sequence of a Bacterial Strain with High Alkalic Xylanase Activity Isolated from the Sludge Near a Papermill

Many organisms secrete xylanase, an import group of proteins hydrolyzing xylan, and thus are able to use xylan as their carbon source. In this study, we sequenced the whole genome of a bacterial strain, YD01, which was isolated from the sludge near the sewage discharge outlet of a papermill and showed high alkalic xylanase activity. Its genome consists of a chromosome and two plasmids. Six rRNA genes, 46 tRNA genes, 3136 CDSs as well as 955 repetitive sequences were predicted. 3046 CDSs were functionally annotated. Phylogenetic analysis on 16S rRNA shows that YD01 is a new species in Microbacterium genus and is taxonomically close to M. jejuense THG-C31^T and M. kyungheense THG-C26^T. A comparative study on phylogenetic trees of 16S rRNA and xylanase genes suggests that xylanase genes in YD01 may originate from horizontal gene transfer instead of ancestral gene duplication.

Revisiting the scope and applications of food enzymes from extremophiles

Microorganisms from extreme environments tend to undergo various adaptations due to environmental conditions such as extreme pH, temperature, salinity, heavy metals, and solvents. Thus, they produce enzymes with unique properties and high specificity, making them useful industrially, particularly in the food industries. Despite these enzymes' remarkable properties, only a few instances can be reported for actual exploitation in the food industry. This review's objectives are to highlight the properties of these enzymes and their prospects in the food industry. First, an introduction to extremophilic organisms is presented, followed by the categories and application of food enzymes from extremophiles. Then, the unique structural features of extremozymes are shown. This review also covers the prospective applications of extremozymes in the food industry in a broader sense, including degradation of toxins, deconstruction of polymers into monomers, and catalysis of multistep processes. Finally, the challenges in bioprocessing of extremozymes and applications in food are presented. PRACTICAL APPLICATIONS: Enzymes are important players in food processing and preservation. Extremozymes, by their nature, are ideal for a broad range of food processing applications, particularly those that require process conditions of extreme pH, temperature, and salinity. As the global food industry grows, so too will grow the need to research and develop food products that are diverse, safe, healthy, and nutritious. There is also the need to produce food in a sustainable way that generates less waste or maximizes waste valorization. We anticipate that extremozymes can meet some of the research and development needs of the food industry.

Enhanced butanol-hydrogen coproduction by Clostridium beijerinckii with biochar as cell's carrier

In this study, the effects of biochar on the fermentation performance of butanol-hydrogen coproduction by Clostridium beijerinckii F-6 were investigated. Results showed that the biochar with rich porous and graphitized structure can significantly promote the coproduction of butanol and hydrogen. The productivity of butanol and hydrogen reached 0.148 g/L/h and 0.299 mmol/L/h with biochar addition which were 20.23% and 48.76% higher than that in control without biochar addition, respectively. Moreover, the whole energy conversion efficiency calculated based on the heat value showed increment from 43.69% to 51.75% with biochar addition. Combined analysis of organic acids accumulation and oxidation-reduction potential fluctuation proved that biochar can regulate reducing power during fermentation and accelerate the conversion of acid phase to solvent phase. Scanning electron microscope images showed that biochar acted as carriers for cells absorption. Confirmation experiment further proved that biochar enhanced the butanol tolerant ability of Clostridium beijerinckii F-6.

Genomic analysis of Burkholderia sp. ISTR5 for biofunneling of lignin-derived compounds

BACKGROUND

Lignin is the second most abundant natural polymer on earth. Industries using lignocellulosic biomass as feedstock generate a considerable amount of lignin as a byproduct with minimal usage. For a sustainable biorefinery, the lignin must be utilized in improved ways. Lignin is recalcitrant to degradation due to the complex and heterogeneous structure. The depolymerization of lignin and its conversion into specific product stream are the major challenges associated with lignin valorization. The blend of oligomeric, dimeric and monomeric lignin-derived compounds (LDCs) generated during depolymerization can be utilized by microbes for production of bioproducts.

RESULTS

In the present study, a novel bacterium Burkholderia sp. strain ISTR5 (R5), a proteobacteria belonging to class betaproteobacteria, order Burkholderiales and family Burkholderiaceae, was isolated and characterized for the degradation of LDCs. R5 strain was cultured on 12 LDCs in mineral salt medium (MSM) supplemented with individual compounds such as syringic acid, p-coumaric acid, ferulic acid, vanillin, vanillic acid, guaiacol, 4-hydroxybenzoic acid, gallic acid, benzoic acid, syringaldehyde, veratryl alcohol and catechol. R5 was able to grow and utilize all the selected LDCs. The degradation of selected LDCs was monitored by bacterial growth, total organic carbon (TOC) removal and UV-Vis absorption spectra in scan mode. TOC reduction shown in the sample contains syringic acid 80.7%, ferulic acid 84.1%, p-coumaric acid 85.9% and benzoic acid 83.2%. In UV-Vis absorption spectral scan, most of the lignin-associated peaks were found at or near 280 nm wavelength in the obtained absorption spectra. Enzyme assay for the ligninolytic enzymes was also performed, and it was observed that lignin peroxidase and laccase were predominantly expressed. Furthermore, the GC-MS analysis of LDCs was performed to identify the degradation intermediates from these compounds. The genomic analysis showed the robustness of this strain and identified various candidate genes responsible for the degradation of aromatic or lignin derivatives, detoxification mechanism, oxidative stress response and fatty acid synthesis. The presence of peroxidases (13%), laccases (4%), monooxygenases (23%), dioxygenase (44%), NADPH: quinone oxidoreductases (16%) and many other related enzymes supported the degradation of LDCs.

CONCLUSION

Numerous pathway intermediates were observed during experiment. Vanillin was found during growth on syringic acid, ferulic acid and p-coumaric acid. Some other intermediates like catechol, acetovanillone, syringaldehyde and 3,4-dihydroxybenzaldehyde from the recognized bacterial metabolic pathways existed during growth on the LDCs. The ortho- and meta cleavage pathway enzymes, such as the catechol-1,2-dioxygenase, protocatechuate 3,4-dioxygenase, catechol-2,3-dioxygenase and toluene-2,3-dioxygenase, were observed in the genome. In addition to the common aromatic degradation pathways, presence of the epoxyqueuosine reductase, 1,2-epoxyphenylacetyl-CoA isomerase in the genome advocates that this strain may follow the epoxy Coenzyme A thioester pathway for degradation.

A detailed overview of xylanases: an emerging biomolecule for current and future prospective

Xylan is the second most abundant naturally occurring renewable polysaccharide available on earth. It is a complex heteropolysaccharide consisting of different monosaccharides such as l-arabinose, d-galactose, d-mannoses and organic acids such as acetic acid, ferulic acid, glucuronic acid interwoven together with help of glycosidic and ester bonds. The breakdown of xylan is restricted due to its heterogeneous nature and it can be overcome by xylanases which are capable of cleaving the heterogeneous β-1,4-glycoside linkage. Xylanases are abundantly present in nature (e.g., molluscs, insects and microorganisms) and several microorganisms such as bacteria, fungi, yeast, and algae are used extensively for its production. Microbial xylanases show varying substrate specificities and biochemical properties which makes it suitable for various applications in industrial and biotechnological sectors. The suitability of xylanases for its application in food and feed, paper and pulp, textile, pharmaceuticals, and lignocellulosic biorefinery has led to an increase in demand of xylanases globally. The present review gives an insight of using microbial xylanases as an “Emerging Green Tool” along with its current status and future prospective.

Parageobacillus thermantarcticus, an Antarctic Cell Factory: From Crop Residue Valorization by Green Chemistry to Astrobiology Studies

Knowledge of Antarctic habitat biodiversity, both marine and terrestrial, has increased considerably in recent years, causing considerable development in the studies of life science related to Antarctica. In the Austral summer 1986–1987, a new thermophilic bacterium, Parageobacillus thermantarcticus strain M1 was isolated from geothermal soil of the crater of Mount Melbourne (74°22′ S, 164°40′ E) during the Italian Antarctic Expedition. In addition to the biotechnological potential due to the production of exopolysaccharides and thermostable enzymes, successful studies have demonstrated its use in the green chemistry for the transformation and valorization of residual biomass and its employment as a suitable microbial model for astrobiology studies. The recent acquisition of its genome sequence opens up new opportunities for the use of this versatile bacterium in still unexplored biotechnology sectors.

Enhanced hydrolysis of lignocellulosic biomass with doping of a highly thermostable recombinant laccase

A highly thermostable laccase from Geobacillus sp. strain WSUCF1 was cloned into Escherichia coli (E. coli) using pRham N-His SUMO expression system. The thermostable laccase with a molecular weight ~30 kDa had a t_1/2 (pH 6.0) of 120 h at 50 °C. The homology modelling for laccase structure showed the presence of Cu active centers with His and Cys residues involved in the active site and ligand binding activity of the enzyme, respectively. The K_m, V_max, K_cat and K_cat/K_m values of the purified enzyme with ABTS were found to be 0.146 mM, 1.52 U/mg, 1037 s^-1 and 7102.7 s^-1 mM^-1, respectively. The doping of recombinant WSUCF1 laccase to commercial enzyme cocktails Accellerase® 1500 and Cellic CTec2 improved the hydrolysis of untreated, alkali and acid treated corn stover by 1.31-2.28 times and bagasse by 1.32-2.02 times. Further, in-house enzyme cocktails with laccase hydrolyzed untreated, alkali and acid treated bagasse and gave 1.44, 1.1, and 0.92 folds higher sugar, respectively, when compared with Accellerase 1500. The results suggested that thermostable laccase can aid in the improved hydrolysis of lignocellulosic biomass.

Improvements of thermophilic enzymes: From genetic modifications to applications

Thermozymes (from thermophiles or hyperthermophiles) offer obvious advantages due to their excellent thermostability, broad pH adaptation, and hydrolysis ability, resulting in diverse industrial applications including food, paper, and textile processing, biofuel production. However, natural thermozymes with low yield and poor adaptability severely hinder their large-scale applications. Extensive studies demonstrated that using genetic modifications such as directed evolution, semi-rational design, and rational design, expression regulations and chemical modifications effectively improved enzyme's yield, thermostability and catalytic efficiency. However, mechanism-based techniques for thermozymes improvements and applications need more attention. In this review, stabilizing mechanisms of thermozymes are summarized for thermozymes improvements, and these improved thermozymes eventually have large-scale industrial applications.

Thermophiles and the applications of their enzymes as new biocatalysts

Ecological and efficient alternatives to industrial processes have sparked interest for using microorganisms and enzymes as biocatalysts. One of the difficulties is finding candidates capable of resisting the harsh conditions in which industrial processes usually take place. Extremophiles, microorganisms naturally found in "extreme" ecological niches, produce robust enzymes for bioprocesses and product development. Thermophiles like Geobacillus, Alyciclobacillus, Anoxybacillus, Pyrococcus and Thermoccocus are some of the extremophiles containing enzymes showing special promise for biocatalysis. Glutamate dehydrogenase used in food processes, laccases and xylanases in pulp and paper processes, nitrilases and transaminases for pharmaceutical drug synthesis and lipases present in detergents, are examples of the increasing use of enzymes for biocatalytic synthesis from thermophilic microorganisms. Some of these enzymes from thermophiles have been expressed as recombinant enzymes and are already in the market. Here we will review recent discoveries of thermophilic enzymes and their current and potential applications in industry.

Thermostable xylanases from thermophilic fungi and bacteria: Current perspective

Thermostable xylanases from thermophilic fungi and bacteria have a wide commercial acceptability in feed, food, paper and pulp and bioconversion of lignocellulosics with an estimated annual market of USD 500 Million. The genome wide analysis of thermophilic fungi clearly shows the presence of elaborate genetic information coding for multiple xylanases primarily coding for GH10, GH11 in addition to GH7 and GH30 xylanases. The transcriptomics and proteome profiling has given insight into the differential expression of these xylanases in some of the thermophilic fungi. Bioprospecting has resulted in identification of novel thermophilic xylanases that have been endorsed by the industrial houses for heterologous over- expression and formulations. The future use of xylanases is expected to increase exponentially for their role in biorefineries. The discovery of new and improvement of existing xylanases using molecular tools such as directed evolution is expected to be the mainstay to meet increasing demand of thermostable xylanases.