Molecular cloning and characterization of a thermostable and halotolerant endo-β-1,4-glucanase from Microbulbifer sp. ALW1

A novel salt-adapted bifunctional glucanase/mannanase from Klebsiella pneumoniae and its application in oligosaccharide production

Klebsiella pneumoniae exhibits extensive glycohydrolase activity in the gut microbiota. However, there are few studies on glucomannanase of Klebsiella pneumoniae. This study cloned and characterized a bifunctional mannanase/glucanase (GH8-3995) of K.pneumoniae MY2023. GH8-3995 exhibited excellent pH and salt tolerance, maintaining over 95 % activity in 5 M NaCl and over 80 % activity at pH 10. The results of oligosaccharides hydrolysis showed that GH8-3995 requires substrates to contain at least four glucose residues. The three-dimensional (3D) protein structure showed that GH8-3995 had a large catalytic cleavage on its surface, which was beneficial for binding enzymes and substrates. Molecular docking simulations and point mutation experiments demonstrated that D43 and E53 were the key binding sites of GH8-3995. Meanwhile, Alphafold3 predicted that E53 was also a key site for GH8-3995 to bind with Na+. In the application of oligosaccharide preparation, GH8-3995 predominantly produced oligosaccharides with DP > 4 from barley β-glucan and konjac glucomannan. This study investigated the enzymatic properties of GH8-3995 and analyzed the composition of its enzymatic hydrolysis products. The enzyme digestion characteristics and tolerance of GH8-3995 provided more possibilities for its application in producing cellooligosaccharides and mannanoligosaccharides.

Genomic Functional Analysis and Cellulase Characterization for the Enzyme-Producing Strain Bacillus subtilis Y4X3 Isolated from Saline-Alkaline Soil in Xinjiang, China

Biotechnological research and application of microbial enzyme production have consistently been focal points for scientific inquiry and industrial advancement. In this study, Bacillus subtilis Y4X3 was isolated from saline-alkaline soil in Xinjiang, China. Extracellular enzyme production analysis revealed that B. subtilis Y4X3 can secrete various enzymes, including cellulase, xylanase, protease, and amylase. Sequencing and assembly of the complete genome of this strain revealed a genome size of 4,215,636 bp with 43.51% C + G content, including 4438 coding genes. Genome annotation was performed with databases to predict gene functions in B. subtilis Y4X3, and a variety of genes related to carbohydrate metabolism were identified. A cellulase-encoding gene was subsequently cloned from the genome and heterologously expressed in Escherichia coli. The optimum pH and temperature for the purified cellulase Cel5A were 5.0 and 60 °C, respectively. Stability analysis revealed that Cel5A remained stable at pH 5.0-9.0 and 20-60 °C; after 1 h at pH 9.0, the relative enzyme activity still exceeded 60%. Additionally, Cel5A was positively affected by various metal ions and exhibited good tolerance to multiple chemical reagents. The results indicate that B. subtilis Y4X3 has the potential to produce a variety of industrial enzymes and could serve as a promising candidate for more efficient and cost-effective industrial applications; the characterized thermostable and alkali-resistant cellulase Cel5A also has potential applications in biotechnology and industry.

Cellulolytic enzymes in Microbulbifer sp. Strain GL-2, a marine fish intestinal bacterium, with emphasis on endo-1,4-β-glucanases Cel5A and Cel8

Cellulose is an abundant biomass on the planet. Various cellulases from environmental microbes have been explored for industrial use of cellulose. Marine fish intestine is of interest as one source of new enzymes. Here, we report the discovery of genes encoding two β-glucosidases (Bgl3A and Bgl3B) and four endo-1,4-β-glucanases (Cel5A, Cel8, Cel5B, and Cel9) as part of the genome sequence of a cellulolytic marine bacterium, Microbulbifer sp. Strain GL-2. Five of these six enzymes (excepting Cel5B) are presumed to localize to the periplasm or outer membrane. Transcriptional analysis demonstrated that all six genes were highly expressed in stationary phase. The transcription was induced by cello-oligosaccharides rather than by glucose, suggesting that the cellulases are produced primarily for nutrient acquisition following initial growth, facilitating the secondary growth phase. We cloned the genes encoding two of the endo-1,4-β-glucanases, Cel5A and Cel8, and purified the corresponding recombinant enzymes following expression in Escherichia coli. The activity of Cel5A was observed across a wide range of temperatures (10-40 ˚C) and pHs (6-8). This pattern differed from those of Cel8 and the commercial cellulase Enthiron, both of which exhibit decreased activities below 30 ˚C and at alkaline pHs. These characteristics suggest that Cel5A might find use in industrial applications. Overall, our results reinforce the hypothesis that marine bacteria remain a possible source of novel cellulolytic activities.

Microbial β-glucanases: production, properties, and engineering

Lignocellulosic biomass, which mainly consists of cellulose and hemicellulose, is the most abundant renewable biopolymer on earth. β-Glucanases are glycoside hydrolases (GHs) that hydrolyze β-glucan, one of the dominant components of the plant cell wall, into cello-oligosaccharides and glucose. Among them, endo-β-1,4-glucanase (EC 3.2.1.4), exo-glucanase/cellobiohydrolase (EC 3.2.1.91), and β-glucosidase (EC 3.2.1.21) play critical roles in the digestion of glucan-like substrates. β-Glucanases have attracted considerable interest within the scientific community due to their applications in the feed, food, and textile industries. In the past decade, there has been considerable progress in the discovery, production, and characterization of novel β-glucanases. Advances in the development of next-generation sequencing techniques, including metagenomics and metatranscriptomics, have unveiled novel β-glucanases isolated from the gastrointestinal microbiota. The study of β-glucanases is beneficial for research and development of commercial products. In this study, we review the classification, properties, and engineering of β-glucanases.

Characterisation of marine bacterium Microbulbifer sp. ALW1 with Laminaria japonica degradation capability

Marine bacterium Microbulbifer sp. ALW1 was revealed to be able to effectively degrade Laminaria japonica thallus fragments into fine particles. Polysaccharide substrate specificity analysis indicated that ALW1 could produce extracellular alginate lyase, laminarinase, fucoidanase and cellulase. Based on alignment of the 16 S rRNA sequence with other reference relatives, ALW1 showed the closest relationship with Microbulbifer aggregans CCB-MM1T. The cell morphology and some basic physiological and biochemical parameters of ALW1 cells were characterised. ALW1 is a Gram-negative, rod- or oval-shaped, non-spore-forming and non-motile bacterium. The DNA–DNA relatedness values of ALW1 with type strains of M. gwangyangensis (JCM 17,800), M. aggregans (JCM 31,875), M. maritimus (JCM 12,187), M. okinawensis (JCM 16,147) and M. rhizosphaerae (DSM 28,920) were 28.9%, 43.3%, 41.2%, 35.4% and 45.6%, respectively. The major cell wall sugars of ALW1 were determined to be ribose and galactose, which differed from other closely related species. These characteristics indicated that ALW1 could be assigned to a separate species of the genus Microbulbifer. The complete genome of ALW1 contained one circular chromosome with 4,682,287 bp and a GC content of 56.86%. The putative encoded proteins were categorised based on their functional annotations. Phenotypic, physiological, biochemical and genomic characterisation will provide insights into the many potential industrial applications of Microbulbifer sp. ALW1.

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