Alkaline xylanolytic–cellulolytic multienzyme complex from the novel anaerobic alkalithermophilic bacterium Cellulosibacter alkalithermophilus and its hydrolysis of insoluble polysaccharides under neutral and alkaline conditions

Hydrolysis of ionic liquid-treated substrate with an Iocasia fonsfrigidae strain SP3-1 endoglucanase

Recently, we reported the discovery of a novel endoglucanase of the glycoside hydrolase family 12 (GH12), designated IfCelS12A, from the haloalkaliphilic anaerobic bacterium Iocasia fonsfrigidae strain SP3-1, which was isolated from a hypersaline pond in the Samut Sakhon province of Thailand (ca. 2017). IfCelS12A exhibits high substrate specificity on carboxymethyl cellulose and amorphous cellulose but low substrate specificity on b-1,3;1,4-glucan. Unlike some endoglucanases of the GH12 family, IfCelS12A does not exhibit hydrolytic activity on crystalline cellulose (i.e., Avicel™). High-Pressure Liquid Chromatography (HPLC) and Thin Layer Chromatography (TLC) analyses of products resulting from IfCelS12-mediated hydrolysis indicate mode of action for this enzyme. Notably, IfCelS12A preferentially hydrolyzes cellotetraoses, cellopentaoses, and cellohexaoses with negligible activity on cellobiose or cellotriose. Kinetic analysis with cellopentaose and barely b-D-glucan as cellulosic substrates were conducted. On cellopentaose, IfCelS12A demonstrates a 16-fold increase in activity (KM = 0.27 mM; kcat = 0.36 s-1; kcat/KM = 1.34 mM-1 s-1) compared to the enzymatic hydrolysis of barley b-D-glucan (KM: 0.04 mM, kcat: 0.51 s-1, kcat/KM = 0.08 mM-1 s-1). Moreover, IfCelS12A enzymatic efficacy is stable in hypersaline sodium chlorids (NaCl) solutions (up to 10% NaCl). Specifically, IfCel12A retains notable activity after 24 h at 2M NaCl (10% saline solution). IfCelS12A used as a cocktail component with other cellulolytic enzymes and in conjunction with mobile sequestration platform technology offers additional options for deconstruction of ionic liquid-pretreated cellulosic feedstock. KEY POINTS: • IfCelS12A from an anaerobic alkaliphile Iocasia fronsfrigidae shows salt tolerance • IfCelS12A in cocktails with other enzymes efficiently degrades cellulosic biomass • IfCelS12A used with mobile enzyme sequestration platforms enhances hydrolysis.

Production of a Series of Long-Chain Isomaltooligosaccharides from Maltose by Bacillus subtilis AP-1 and Associated Prebiotic Properties

Bacillus subtilis strain AP-1, which produces α-glucosidase with transglucosidase activity, was used to produce a series of long-chain isomaltooligosaccharides (IMOs) with degree of polymerization (DP) ranging from 2 to 14 by direct fermentation of maltose. A total IMOs yield of 36.33 g/L without contabacillusmination from glucose and maltose was achieved at 36 h of cultivation using 50 g/L of maltose, with a yield of 72.7%. IMOs were purified by size exclusion chromatography with a Superdex 30 Increase column. The molecular mass and DP of IMOs were analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF/MS). Subsequently, linkages in produced oligosaccharides were verified by enzymatic hydrolysis with α-amylase and oligo-α-1,6-glucosidase. These IMOs showed prebiotic properties, namely tolerance to acidic conditions and digestive enzymes of the gastrointestinal tract, stimulation of probiotic bacteria growth to produce short-chain fatty acids and no stimulating effect on pathogenic bacteria growth. Moreover, these IMOs were not toxic to mammalian cells at up to 5 mg/mL, indicating their biocompatibility. Therefore, this research demonstrated a simple and economical method for producing IMOs with DP2–14 without additional operations; moreover, the excellent prebiotic properties of the IMOs offer great prospects for their application in functional foods.

Bioconversion of Untreated Corn Hull into L-Malic Acid by Trifunctional Xylanolytic Enzyme from Paenibacillus curdlanolyticus B-6 and Acetobacter tropicalis H-1

L-Malic acid (L-MA) is widely used in food and non-food products. However, few microorganisms have been able to efficiently produce L-MA from xylose derived from lignocellulosic biomass (LB). The objective of this work is to convert LB into L-MA with the concept of a bioeconomy and environmentally friendly process. The unique trifunctional xylanolytic enzyme, PcAxy43A from Paenibacillus curdlanolyticus B-6, effectively hydrolyzed xylan in untreated LB, especially corn hull to xylose, in one step. Furthermore, the newly isolated, Acetobacter tropicalis strain H1 was able to convert high concentrations of xylose derived from corn hull into L-MA as the main product, which can be easily purified. The strain H1 successfully produced a high L-MA titer of 77.09 g/l, with a yield of 0.77 g/g and a productivity of 0.64 g/l/h from the xylose derived from corn hull. The process presented in this research is an efficient, low-cost and environmentally friendly biological process for the green production of L-MA from LB.

A novel amylolytic/xylanolytic/cellulolytic multienzyme complex from Clostridium manihotivorum that hydrolyzes polysaccharides in cassava pulp

Some anaerobic bacteria, particularly Clostridium species, produce extracellular cellulolytic and xylanolytic enzymes as multienzyme complexes (MECs). However, an amylolytic/xylanolytic/cellulolytic multienzyme complex (AXC-MEC) from anaerobic bacteria is rarely found. In this work, the glycoprotein AXC-MEC, composed of subunits of amylolytic, xylanolytic, and cellulolytic enzymes, was isolated from crude extracellular enzyme of the mesophilic anaerobic bacterium Clostridium manihotivorum CT4, grown on cassava pulp, using a milled cassava pulp column and Sephacryl S-500 gel filtration chromatography. The isolated AXC-MEC showed a single band upon native-polyacrylamide gel electrophoresis (native-PAGE). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) showed at least eight protein bands of the multienzyme complex which predominantly exhibited amylolytic enzyme activity, followed by xylanolytic and cellulolytic enzyme activities. The AXC-MEC is highly capable of degrading starch and non-starch polysaccharides present in cassava pulp into glucose and oligosaccharides, without conventional pretreatment. Base on the genomic analysis of C. manihotivorum CT4, we found no evidence of the known structural components of the well-known multienzyme complexes from Clostridium species, cellulosomes such as scaffoldin, cohesin, and dockerin, indicating that AXC-MEC from strain CT4 exhibit a different manner of assembly from the cellulosomes. These results suggest that AXC-MEC from C. manihotivorum CT4 is a new MEC capable of hydrolyzing cassava pulp into value-added products, which will benefit the starch industry. KEY POINTS: • Glycoprotein AXC-MEC was first reported in Clostridium manihotivorum. • Unlike cellulosomes, AXC-MEC consists of amylase, xylanase, and cellulase. • Glucose and oligosaccharides were hydrolysis products from cassava pulp by AXC-MEC.

Efficient biological pretreatment and bioconversion of corn cob by the sequential application of a Bacillus firmus K-1 cellulase-free xylanolytic enzyme and commercial cellulases

We used agricultural residue, corn cob, with biorefinery and bioeconomy concepts. At short-time cultivation in corn cob (12 h), Bacillus firmus K-1 produced cellulase-free xylanolytic enzyme, with xylooligosaccharides (XOSs), X₅ and X₆, as the main products, which can be used in a variety of applications. The xylanolytic enzyme produced from B. firmus K-1 effectively degraded xylan in corn cob, which was examined by chemical composition, scanning electron microscope (SEM), and Fourier transform infrared spectroscopy (FTIR). After cultivation, the xylan contained in the corn cob residue was decreased (as biological pretreatment), causing morphological and structural changes, including creating porosity and increasing the surface area and the exposure of cellulose of pretreated corn cob. These results lead to an improvement of cellulose access by cellulases. Commercially available cellulases, Accellerase® 1500 and Cellic® CTec2, yielded significantly higher glucose concentrations from pretreated corn cob compared to untreated corn cob. After saccharification, the lignin-rich corn cob residue can be used as a raw material for other purposes. Moreover, the B. firmus cells, with a low risk to human health, can be used in some applications. This study presents an efficient method for producing high-value-added products from agricultural residue (corn cob) through biological processes which are environmentally friendly and economically viable. KEY POINTS: • High-value-added products were efficiently produced from corn cob by B. firmus K-1. • After biological pretreatment by B. firmus K-1, cellulase can better reach cellulose. • XOSs and cellulose-derived glucose were the main products from corn cob.

A novel AA10 from Paenibacillus curdlanolyticus and its synergistic action on crystalline and complex polysaccharides

Lytic polysaccharide monooxygenases (LPMOs) play an important role in the degradation of complex polysaccharides in lignocellulosic biomass. In the present study, we characterized a modular LPMO (PcAA10A), consisting of a family 10 auxiliary activity of LPMO (AA10) catalytic domain, and non-catalytic domains including a family 5 carbohydrate-binding module, two fibronectin type-3 domains, and a family 3 carbohydrate-binding module from Paenibacillus curdlanolyticus B-6, which was expressed in a recombinant Escherichia coli. Comparison of activities between full-length PcAA10A and the catalytic domain polypeptide (PcAA10A_CD) indicates that the non-catalytic domains are important for the deconstruction of crystalline cellulose and complex polysaccharides contained in untreated lignocellulosic biomass. Interestingly, PcAA10A_CD acted not only on cellulose and chitin, but also on xylan, mannan, and xylan and cellulose contained in lignocellulosic biomass, which has not been reported for the AA10 family. Mutation of the key residues, Trp51 located at subsite - 2 and Phe171 located at subsite +2, in the substrate-binding site of PcAA10A_CD revealed that these residues are substantially involved in broad substrate specificity toward cellulose, xylan, and mannan, albeit with a low effect toward chitin. Furthermore, PcAA10A had a boosting effect on untreated corn hull degradation by P. curdlanolyticus B-6 endo-xylanase Xyn10D and Clostridium thermocellum endo-glucanase Cel9A. These results suggest that PcAA10A is a unique LPMO capable of cleaving and enhancing lignocellulosic biomass degradation, making it a good candidate for biotechnological applications. KEY POINTS: • PcAA10A is a novel modular LPMO family 10 from Paenibacillus curdlanolyticus. • PcAA10A showed broad substrate specificity on β-1,4 glycosidic linkage substrates. • Non-catalytic domains are important for degrading complex polysaccharides. • PcAA10A is a unique LPMO capable of enhancing lignocellulosic biomass degradation.

Biological Pretreatment by Solid-State Fermentation of Oat Straw to Enhance Physical Quality of Pellets

Pelleting can increase the efficiency of handling and transportation of biomass. Pretreatment obtains lignin fragments by disrupting the lignocellulosic structure of biomass and ensures the high-quality compressed pellets. In this study, solid-state fermentation (SSF) is used as a biological method to improve the quality of pellets of oat straw. SSF of oat straw using Trametes versicolor 52J (TV52J) and Phanerochaete chrysosporium (PC) was conducted. Response surface methodology (RSM) was employed by using a four-factor, three-level Box–Behnken design with fermentation time (days), moisture content (%), particle size (mm), and fermentation temperature (°C) as independent parameters. Pellet density, dimensional stability, and tensile strength were the response variables. The optimization options of fermentation time (33.96 and 35 days), moisture content (70%), particle size (150 and 50 mm), and fermentation temperature (22°C) of oat straw pretreated with these two fungal strains were obtained. The microscopic structural changes of oat straw caused by biological pretreatment were investigated by scanning electron microscopy (SEM). Observation results of SEM showed that the connection between single fibers became relatively loose, and this was beneficial to improve the physical quality of the pellets.

Development of novel economical methodologies for zymographic analysis of purified xylano-pectinolytic enzymes using agrowaste-based substrates

In this study, zymographic analysis for xylanase and pectinase enzymes has been carried out using agrowaste residues, wheat bran and citrus peel as well as their extracts. Isozymic forms of xylanase as well as pectinase enzyme displayed comparable zymographic bands onto agar petriplates containing either commercial substrates (xylan and pectin), agrowaste-based substrates (wheat bran and citrus peel), or polysaccharides extracted from these agrowastes (crude xylan and pectin extracted from wheat bran and citrus peel, respectively), indicating the fact that agro residues and their extracts can be utilized as a substitute of cost-intensive commercial substrates, xylan and pectin for zymographic analysis. This is the first report revealing the zymographic analysis of xylano-pectinolytic enzymes using agro-based solid residues particles or polysaccharides extracted from agro-based residues.

Chemical Pretreatment-Independent Saccharifications of Xylan and Cellulose of Rice Straw by Bacterial Weak Lignin-Binding Xylanolytic and Cellulolytic Enzymes

Complete utilization of carbohydrate fractions is one of the prerequisites for obtaining economically favorable lignocellulosic biomass conversion. This study shows that xylan in untreated rice straw was saccharified to xylose in one step without chemical pretreatment, yielding 58.2% of the theoretically maximum value by Paenibacillus curdlanolyticus B-6 PcAxy43A, a weak lignin-binding trifunctional xylanolytic enzyme, endoxylanase/β-xylosidase/arabinoxylan arabinofuranohydrolase. Moreover, xylose yield from untreated rice straw was enhanced to 78.9% by adding endoxylanases PcXyn10C and PcXyn11A from the same bacterium, resulting in improvement of cellulose accessibility to cellulolytic enzyme. After autoclaving the xylanolytic enzyme-treated rice straw, it was subjected to subsequent saccharification by a combination of the Clostridium thermocellum endoglucanase CtCel9R and Thermoanaerobacter brockii β-glucosidase TbCglT, yielding 88.5% of the maximum glucose yield, which was higher than the glucose yield obtained from ammonia-treated rice straw saccharification (59.6%). Moreover, this work presents a new environment-friendly xylanolytic enzyme pretreatment for beneficial hydrolysis of xylan in various agricultural residues, such as rice straw and corn hull. It not only could improve cellulose saccharification but also produced xylose, leading to an improvement of the overall fermentable sugar yields without chemical pretreatment.IMPORTANCE Ongoing research is focused on improving "green" pretreatment technologies in order to reduce energy demands and environmental impact and to develop an economically feasible biorefinery. The present study showed that PcAxy43A, a weak lignin-binding trifunctional xylanolytic enzyme, endoxylanase/β-xylosidase/arabinoxylan arabinofuranohydrolase from P. curdlanolyticus B-6, was capable of conversion of xylan in lignocellulosic biomass such as untreated rice straw to xylose in one step without chemical pretreatment. It demonstrates efficient synergism with endoxylanases PcXyn10C and PcXyn11A to depolymerize xylan in untreated rice straw and enhanced the xylose production and improved cellulose hydrolysis. Therefore, it can be considered an enzymatic pretreatment. Furthermore, the studies here show that glucose yield released from steam- and xylanolytic enzyme-treated rice straw by the combination of CtCel9R and TbCglT was higher than the glucose yield obtained from ammonia-treated rice straw saccharification. This work presents a novel environment-friendly xylanolytic enzyme pretreatment not only as a green pretreatment but also as an economically feasible biorefinery method.

A novel GH6 cellobiohydrolase from Paenibacillus curdlanolyticus B-6 and its synergistic action on cellulose degradation

We recently discovered a novel glycoside hydrolase family 6 (GH6) cellobiohydrolase from Paenibacillus curdlanolyticus B-6 (PcCel6A), which is rarely found in bacteria. This enzyme is a true exo-type cellobiohydrolase which exhibits high substrate specificity on amorphous cellulose and low substrate specificity on crystalline cellulose, while this showed no activity on substitution substrates, carboxymethyl cellulose and xylan, distinct from all other known GH6 cellobiohydrolases. Product profiles, HPLC analysis of the hydrolysis products and a schematic drawing of the substrate-binding subsites catalysing cellooligosaccharides can explain the new mode of action of this enzyme which prefers to hydrolyse cellopentaose. PcCel6A was not inhibited by glucose or cellobiose at concentrations up to 300 and 100 mM, respectively. A good synergistic effect for glucose production was found when PcCel6A acted together with processive endoglucanase Cel9R from Clostridium thermocellum and β-glucosidase CglT from Thermoanaerobacter brockii. These properties of PcCel6A make it a suitable candidate for industrial application in the cellulose degradation process.