Characterization of a GH36 α-D-Galactosidase Associated with Assimilation of Gum Arabic in Bifidobacterium longum subsp. longum JCM7052

Cross-feeding of bifidobacteria promotes intestinal homeostasis: a lifelong perspective on the host health

Throughout the life span of a host, bifidobacteria have shown superior colonization and glycan abilities. Complex glycans, such as human milk oligosaccharides and plant glycans, that reach the colon are directly internalized by the transport system of bifidobacteria, cleaved into simple structures by extracellular glycosyl hydrolase, and transported to cells for fermentation. The glycan utilization of bifidobacteria introduces cross-feeding activities between bifidobacterial strains and other microbiota, which are influenced by host nutrition and regulate gut homeostasis. This review discusses bifidobacterial glycan utilization strategies, focusing on the cross-feeding involved in bifidobacteria and its potential health benefits. Furthermore, the impact of cross-feeding on the gut trophic niche of bifidobacteria and host health is also highlighted. This review provides novel insights into the interactions between microbe-microbe and host-microbe.

Fabrication, Characterization, and Microbial Biodegradation of Transparent Nanodehydrated Bioplastic (NDB) Membranes Using Novel Casting, Dehydration, and Peeling Techniques

NDBs were fabricated from gum Arabic (GA) and polyvinyl alcohol (PVA) in different ratios using novel techniques (casting, dehydration, and peeling). The GA/PVA blends were cast with a novel vibration-free horizontal flow (VFHF) technique, producing membranes free of air bubble defects with a homogenous texture, smooth surface, and constant thickness. The casting process was achieved on a self-electrostatic template (SET) made of poly-(methyl methacrylate), which made peeling the final product membranes easy due to its non-stick behavior. After settling the casting of the membranous, while blind, the sheets were dried using nanometric dehydration under a mild vacuum stream using a novel stratified nano-dehydrator (SND) loaded with P2O5. After drying the NDB, the dry, smooth membranes were peeled easily without scratching defects. The physicochemical properties of the NDBs were investigated using FTIR, XRD, TGA, DTA, and AFM to ensure that the novel techniques did not distort the product quality. The NDBs retained their virgin characteristics, namely, their chemical functional groups (FTIR results), crystallinity index (XRD data), thermal stability (TGA and DTA), and ultrastructural features (surface roughness and permeability), as well as their microbial biodegradation ability. Adding PVA enhanced the membrane's properties except for mass loss, whereby increasing the GA allocation in the NDB blend reduces its mass loss at elevated temperatures. The produced bioplastic membranes showed suitable mechanical properties for food packaging applications and in the pharmaceutical industry for the controlled release of drugs. In comparison to control samples, the separated bacteria and fungi destroyed the bioplastic membranes. Pseudomonas spp. and Bacillus spp. were the two main strains of isolated bacteria, and Rhizobus spp. was the main fungus. The nano-dehydration method gave the best solution for the prompt drying of water-based biopolymers free of manufacturing defects, with simple and easily acquired machinery required for the casting and peeling tasks, in addition to its wonderful biodegradation behavior when buried in wet soil.

Assimilation of arabinogalactan side chains with novel 3-O-β-L-arabinopyranosyl-α-L-arabinofuranosidase in Bifidobacterium pseudocatenulatum

Aim: Dietary plant fibers affect gut microbiota composition; however, the underlying microbial degradation pathways are not fully understood. We previously discovered 3-O-α-D-galactosyl-α-L-arabinofuranosidase (GAfase), a glycoside hydrolase family 39 enzyme involved in the assimilation of side chains of arabinogalactan protein (AGP), from Bifidobacterium longum subsp. longum (B. longum) JCM7052. Although GAfase homologs are not highly prevalent in the Bifidobacterium genus, several Bifidobacterium strains possess the homologs. To explore the differences in substrate specificity among the homologs, a homolog of B. longum GAfase in Bifidobacterium pseudocatenulatum MCC10289 (MCC10289_0425) was characterized. Methods: Gum arabic, larch, wheat AGP, and sugar beet arabinan were used to determine the substrate specificity of the MCC10289_0425 protein. An amino acid replacement was introduced into GAfase to identify a critical residue that governs the differentiation of substrate specificity. The growth of several Bifidobacterium strains on β-L-arabinopyranosyl disaccharide and larch AGP was examined. Results: MCC10289_0425 was identified to be an unprecedented 3-O-β-L-arabinopyranosyl-α-L-arabinofuranosidase (AAfase) with low GAfase activity. A single amino acid replacement (Asn119 to Tyr) at the catalytic site converted GAfase into AAfase. AAfase releases sugar source from AGP, thereby allowing B. pseudocatenulatum growth. Conclusion: Bifidobacteria have evolved several homologous enzymes with overlapping but distinct substrate specificities depending on the species. They have acquired different fitness abilities to respond to diverse plant polysaccharide structures.

Biopharmaceutical applications of α-galactosidases

α-Galactosidases are exoglycosidases that are active on galactose-containing side chains in oligosaccharides, polysaccharides, glycolipids, and glycoproteins. α-Galactosidases are gaining increased interest in human medicine, especially in the enzyme replacement therapy for Fabry's disease. α-Galactosidases with regioselectivity toward α-1,3-linked galactose find application in xenotransplantation and blood group transformation. The use of α-galactosidases as a therapeutic agent in alleviating the postprandial symptoms of irritable bowel syndrome is much acclaimed. The excellent therapeutic applications of α-galactosidases have led to an upwelling of worldwide research interventions to identify novel α-galactosidases with improved catalytic efficiency. In addition to these therapeutic applications, α-galactosidases also have interesting applications in the industrial sectors like food, feed, probiotics, sugar, and paper pulp. The current review focuses on the diverse therapeutic applications of α-galactosidases and their prospects.

Mechanism of cooperative degradation of gum arabic arabinogalactan protein by Bifidobacterium longum surface enzymes

Gum arabic is an arabinogalactan protein (AGP) that is effective as a prebiotic for the growth of bifidobacteria in the human intestine. We recently identified a key enzyme in the glycoside hydrolase (GH) family 39, 3-O-α-d-galactosyl-α-l-arabinofuranosidase (GAfase), for the assimilation of gum arabic AGP in Bifidobacterium longum subsp. longum. The enzyme released α-d-Galp-(1→3)-l-Ara and β-l-Arap-(1→3)-l-Ara from gum arabic AGP and facilitated the action of other enzymes for degrading the AGP backbone and modified sugar. In this study, we identified an α-l-arabinofuranosidase (BlArafE; encoded by BLLJ_1850), a multidomain enzyme with both GH43_22 and GH43_34 catalytic domains, as a critical enzyme for the degradation of modified α-l-arabinofuranosides in gum arabic AGP. Site-directed mutagenesis approaches revealed that the α1,3/α1,4-Araf double-substituted gum arabic AGP side chain was initially degraded by the GH43_22 domain and subsequently cleaved by the GH43_34 domain to release α1,3-Araf and α1,4-Araf residues, respectively. Furthermore, we revealed that a tetrasaccharide, α-l-Rhap-(1→4)-β-d-GlcpA-(1→6)-β-d-Galp-(1→6)-d-Gal, was a limited degradative oligosaccharide in the gum arabic AGP fermentation of B. longum subsp. longum JCM7052. The oligosaccharide was produced from gum arabic AGP by the cooperative action of the three cell surface-anchoring enzymes, GAfase, exo-β1,3-galactanase (Bl1,3Gal), and BlArafE, on B. longum subsp. longum JCM7052. Furthermore, the tetrasaccharide was utilized by the commensal bacteria.

IMPORTANCE Terminal galactose residues of the side chain of gum arabic arabinogalactan protein (AGP) are mainly substituted by α1,3/α1,4-linked Araf and β1,6-linked α-l-Rhap-(1→4)-β-d-GlcpA residues. This study found a multidomain BlArafE with GH43_22 and GH43_34 catalytic domains showing cooperative action for degrading α1,3/α1,4-linked Araf of the side chain of gum arabic AGP. In particular, the GH43_34 domain of BlArafE was a novel α-l-arabinofuranosidase for cleaving the α1,4-Araf linkage of terminal galactose. α-l-Rhap-(1→4)-β-d-GlcpA-(1→6)-β-d-Galp-(1→6)-d-Gal tetrasaccharide was released from gum arabic AGP by the cooperative action of GAfase, GH43_24 exo-β-1,3-galactanase (Bl1,3Gal), and BlArafE and remained after B. longum subsp. longum JCM7052 culture. Furthermore, in vitro assimilation test of the remaining oligosaccharide using Bacteroides species revealed that cross-feeding may occur from bifidobacteria to other taxonomic groups in the gut.

Identification and Characterization of a Thermostable GH36 α-Galactosidase from Anoxybacillusvitaminiphilus WMF1 and Its Application in Synthesizing Isofloridoside by Reverse Hydrolysis

An α-galactosidase-producing strain named Anoxybacillus vitaminiphilus WMF1, which catalyzed the reverse hydrolysis of d-galactose and glycerol to produce isofloridoside, was isolated from soil. The α-galactosidase (galV) gene was cloned and expressed in Escherichia coli. The galV was classified into the GH36 family with a molecular mass of 80 kDa. The optimum pH and temperature of galV was pH 7.5 and 60 °C, respectively, and it was highly stable at alkaline pH (6.0-9.0) and temperature below 65 °C. The specificity for p-nitrophenyl α-d-galactopyranoside was 70 U/mg, much higher than that for raffinose and stachyose. Among the metals and reagents tested, galV showed tolerance in the presence of various organic solvents. The kinetic parameters of the enzyme towards p-nitrophenyl α-d-galactopyranoside were obtained as Km (0.12 mM), Vmax (1.10 × 10-3 mM s-1), and Kcat/Km (763.92 mM-1 s-1). During the reaction of reverse hydrolysis, the enzyme exhibited high specificity towards the glycosyl donor galactose and acceptors glycerol, ethanol and ethylene glycol. Finally, the isofloridoside was synthesized using galactose as the donor and glycerol as the acceptor with a 26.6% conversion rate of galactose. This study indicated that galV might provide a potential enzyme source in producing isofloridoside because of its high thermal stability and activity.