A mannanase, ManA, of the polycentric anaerobic fungus Orpinomyces sp. strain PC-2 has carbohydrate binding and docking modules

Effects of β-mannanase supplementation on intestinal health and growth of nursery pigs

Two experiments were conducted using 120 pigs to test the hypothesis that supplementation of β-mannanase could reduce digesta viscosity, enhance nutrient digestion, and improve intestinal health and growth of nursery pigs. In experiment 1, 48 crossbred barrows were randomly allotted to four treatments with increasing levels of β-mannanase at 0, 200, 400, and 600 U/kg in feeds. All pigs were euthanized on day 12 to collect jejunal digesta to measure digesta viscosity and ileal digesta to measure apparent ileal digestibility (AID) of dry matter (DM), gross energy (GE), neutral detergent fiber (NDF), and acid detergent fiber (ADF). In experiment 2, 72 nursery pigs were randomly allotted to three treatments with increasing levels of β-mannanase at 0, 400, and 600 U/kg in feeds. Plasma collected on day 9 was used to measure tumor necrosis factor-α (TNF-α), immunoglobulin G (IgG), malondialdehyde (MDA), and protein carbonyl (PC). All pigs were euthanized on day 10 to collect duodenal and jejunal tissues to evaluate the production of TNF-α, IL-6, and MDA, morphology, crypt cell proliferation, and expression of tight junction proteins in the jejunum. Data were analyzed using the MIXED procedure for polynomial contrasts and the NLMIXED procedure for broken-line analysis of SAS. In experiment 1, β-mannanase supplementation tended to have quadratic effects on digesta viscosity (P = 0.085) and AID of GE (P = 0.093) in the pigs. In experiment 2, jejunal digesta viscosity of the pigs was reduced (P < 0.05) when β-mannanase was supplemented at 360 U/kg of feed. β-Mannanase supplementation linearly reduced (P < 0.05) TNF-α, IgG, MDA, and PC in the duodenum, and TNF-α, IgG, and MDA in the jejunum of the pigs. β-Mannanase supplementation linearly increased (P < 0.05) villus height to crypt depth ratio and crypt cell proliferation in the jejunum. β-Mannanase supplementation tended to linearly improve (P = 0.083) expression of zonula occludens-1 in the jejunum. In conclusion, supplementation of β-mannanase at 360 U/kg reduced the digesta viscosity and up to 600 U/kg positively affected intestinal health and growth of pigs by reducing inflammation and oxidative stress whilst enhancing structure and barrier function in the jejunum.

Enzymatic and biophysical characterization of a novel modular cellulosomal GH5 endoglucanase multifunctional from the anaerobic gut fungus Piromyces finnis

Cellulases from anaerobic fungi are enzymes less-studied biochemically and structurally than cellulases from bacteria and aerobic fungi. Currently, only thirteen GH5 cellulases from anaerobic fungi were biochemically characterized and two crystal structures were reported. In this context, here, we report the functional and biophysical characterization of a novel multi-modular cellulosomal GH5 endoglucanase from the anaerobic gut fungus Piromyces finnis (named here PfGH5). Multiple sequences alignments indicate that PfGH5 is composed of a GH5 catalytic domain and a CBM1 carbohydrate-binding module connected through a CBM10 dockerin module. Our results showed that PfGH5 is an endoglucanase from anaerobic fungus with a large spectrum of activity. PfGH5 exhibited preference for hydrolysis of oat β-glucan, followed by galactomannan, carboxymethyl cellulose, mannan, lichenan and barley β-glucan, therefore displaying multi-functionality. For oat β-glucan, PfGH5 reaches its optimum enzymatic activity at 40 °C and pH 5.5, with Km of 7.1 μM. Ion exchange chromatography analyzes revealed the production of oligosaccharides with a wide degree of polymerization indicated that PfGH5 has endoglucanase activity. The ability to bind and cleave different types of carbohydrates evidence the potential of PfGH5 for use in biotechnology and provide a useful basis for future investigation and application of new anaerobic fungi enzymes.

Molecular advancements on over-expression, stability and catalytic aspects of endo-β-mannanases

The hydrolysis of mannans by endo-β-mannanases continues to gather significance as exemplified by its commercial applications in food, feed, and a rekindled interest in biorefineries. The present review provides a comprehensive account of fundamental research and fascinating insights in the field of endo-β-mannanase engineering in order to improve over-expression and to decipher molecular determinants governing activity-stability during harsh conditions, substrate recognition, polysaccharide specificity, endo/exo mode of action and multi-functional activities in the modular polypeptide. In-depth analysis of the available literature has also been made on rational and directed evolution approaches, which have translated native endo-β-mannanases into superior biocatalysts for satisfying industrial requirements.

Genomic and proteomic biases inform metabolic engineering strategies for anaerobic fungi

Anaerobic fungi (Neocallimastigomycota) are emerging non-model hosts for biotechnology due to their wealth of biomass-degrading enzymes, yet tools to engineer these fungi have not yet been established. Here, we show that the anaerobic gut fungi have the most GC depleted genomes among 443 sequenced organisms in the fungal kingdom, which has ramifications for heterologous expression of genes as well as for emerging CRISPR-based genome engineering approaches. Comparative genomic analyses suggest that anaerobic fungi may contain cellular machinery to aid in sexual reproduction, yet a complete mating pathway was not identified. Predicted proteomes of the anaerobic fungi also contain an unusually large fraction of proteins with homopolymeric amino acid runs consisting of five or more identical consecutive amino acids. In particular, threonine runs are especially enriched in anaerobic fungal carbohydrate active enzymes (CAZymes) and this, together with a high abundance of predicted N-glycosylation motifs, suggests that gut fungal CAZymes are heavily glycosylated, which may impact heterologous production of these biotechnologically useful enzymes. Finally, we present a codon optimization strategy to aid in the development of genetic engineering tools tailored to these early-branching anaerobic fungi.

Secretory expression of β-mannanase in Saccharomyces cerevisiae and its high efficiency for hydrolysis of mannans to mannooligosaccharides

Degradation of mannans is a key process in the production of foods and prebiotics. β-Mannanase is the key enzyme that hydrolyzes 1,4-β-D-mannosidic linkages in mannans. Heterogeneous expression of β-mannanase in Pichia pastoris systems is widely used; however, Saccharomyces cerevisiae expression systems are more reliable and safer. We optimized β-mannanase gene from Aspergillus sulphureus and expressed it in five S. cerevisiae strains. Haploid and diploid strains, and strains with constitutive promoter TEF1 or inducible promoter GAL1, were tested for enzyme expression in synthetic auxotrophic or complex medium. Highest efficiency expression was observed for haploid strain BY4741 integrated with β-mannanase gene under constitutive promoter TEF1, cultured in complex medium. In fed-batch culture in a fermentor, enzyme activity reached ~ 24 U/mL after 36 h, and production efficiency reached 16 U/mL/day. Optimal enzyme pH was 2.0-7.0, and optimal temperature was 60 °C. In studies of β-mannanase kinetic parameters for two substrates, locust bean gum galactomannan (LBG) gave K_m = 24.13 mg/mL and V_max = 715 U/mg, while konjac glucomannan (KGM) gave K_m = 33 mg/mL and V_max = 625 U/mg. One-hour hydrolysis efficiency values were 57% for 1% LBG, 74% for 1% KGM, 39% for 10% LBG, and 53% for 10% KGM. HPLC analysis revealed that the major hydrolysis products were the oligosaccharides mannose, mannobiose, mannotriose, mannotetraose, mannopentaose, and mannohexaose. Our findings show that this β-mannanase has high efficiency for hydrolysis of mannans to mannooligosaccharides, a type of prebiotic, suggesting strong potential application in food industries.

Mannoside recognition and degradation by bacteria

Mannosides constitute a vast group of glycans widely distributed in nature. Produced by almost all organisms, these carbohydrates are involved in numerous cellular processes, such as cell structuration, protein maturation and signalling, mediation of protein-protein interactions and cell recognition. The ubiquitous presence of mannosides in the environment means they are a reliable source of carbon and energy for bacteria, which have developed complex strategies to harvest them. This review focuses on the various mannosides that can be found in nature and details their structure. It underlines their involvement in cellular interactions and finally describes the latest discoveries regarding the catalytic machinery and metabolic pathways that bacteria have developed to metabolize them.

Gene cloning, expression, and biochemical characterization of an alkali-tolerant β-mannanase from Humicola insolens Y1

In this article, we firstly report a highly alkali-tolerant fungal β-mannanase from Humicola insolens Y1. The full-length cDNA of the β-mannanase, designated as man5A, has an open reading frame of 1,233 bp that encodes a 411-amino acid polypeptide (Man5A) with a calculated molecular mass of 42.3 kDa. The deduced sequence of Man5A comprises a putative 20-residue signal peptide and a catalytic domain belonging to glycoside hydrolase family 5, and displays 61–85% identities with hypothetical proteins and 32–39% with experimentally verified fungal β-mannanases. Purified recombinant Man5A produced by Pichia pastoris has a specific activity of 1,122 U mg−1 and exhibits optimal activity at pH 5.5 and 70°C. Distinct from other reported fungal β-mannanases, Man5A is highly alkali tolerant, exhibiting 45 and 36% of the maximal activity at pH 8.0 and 9.0, respectively, and more than 10% activity even at pH 10.0. Moreover, Man5A has excellent pH stability at pH 5.0–12.0 and is highly thermostable at 50°C. The higher frequency of alkaline amino acids (Arg and Lys), greater pKa values of the catalytic residues, and more positively charged residues on the surface of Man5A might be the causes. Man5A has strong resistance to various neutral and alkaline proteases, retaining more than 97% of the activity after proteolytic treatment for 1 h. The superior characteristics of Man5A make it more advantageous for the application in the kraft pulp industry.

An overview of mannan structure and mannan-degrading enzyme systems

Hemicellulose is a complex group of heterogeneous polymers and represents one of the major sources of renewable organic matter. Mannan is one of the major constituent groups of hemicellulose in the wall of higher plants. It comprises linear or branched polymers derived from sugars such as D-mannose, D-galactose, and D-glucose. The principal component of softwood hemicellulose is glucomannan. Structural studies revealed that the galactosyl side chain hydrogen interacts to the mannan backbone intramolecularly and provides structural stability. Differences in the distribution of D-galactosyl units along the mannan structure are found in galactomannans from different sources. Acetyl groups were identified and distributed irregularly in glucomannan. Some of the mannosyl units of galactoglucomannan are partially substituted by O-acetyl groups. Some unusual structures are found in the mannan family from seaweed, showing a complex system of sulfated structure. Endohydrolases and exohydrolases are involved in the breakdown of the mannan backbone to oligosaccharides or fermentable sugars. The main-chain mannan-degrading enzymes include beta-mannanase, beta-glucosidase, and beta-mannosidase. Additional enzymes such as acetyl mannan esterase and alpha-galactosidase are required to remove side-chain substituents that are attached at various points on mannan, creating more sites for subsequent enzymatic hydrolysis. Mannan-degrading enzymes have found applications in the pharmaceutical, food, feed, and pulp and paper industries. This review reports the structure of mannans and some biochemical properties and applications of mannan-degrading enzymes.

The cellulase/hemicellulase system of the anaerobic fungus Orpinomyces PC-2 and aspects of its applied use

Anaerobic fungi, first described in 1975 by Orpin, live in close contact with bacteria and other microorganisms in the rumen and caecum of herbivorous animals, where they digest ingested plant food. Seventeen distinct anaerobic fungi belonging to five different genera have been described. They have been found in at least 50 different herbivorous animals. Anaerobic fungi do not possess mitochondria, but instead have hydrogenosomes, which form hydrogen and carbon dioxide from pyruvate and malate during fermentation of carbohydrates. In addition, they are very oxygen- and temperature-sensitive, and their DNA has an unusually high AT content of from 72 to 87 mol%. My initial reason for studying anaerobic fungi was because they solubilize lignocellulose and produce all enzymes needed to efficiently hydrolyze cellulose and hemicelluloses. Although some of these enzymes are found free in the medium, most of them are associated with cellulosomal and polycellulosomal complexes, in which the enzymes are attached through fungal dockerins to scaffolding proteins; this is similar to what has been found for cellulosomes from anaerobic bacteria. Although cellulosomes from anaerobic fungi share many properties with cellulosomes of anaerobic cellulolytic bacteria and have comparable structures, their structures differ in their amino acid sequences. I discuss some features of the cellulosome of the anaerobic fungus Orpinomyces sp. PC-2 and some possible uses of its enzymes in industrial settings.

Consolidated bioprocessing for bioethanol production using Saccharomyces cerevisiae

Consolidated bioprocessing (CBP) of lignocellulose to bioethanol refers to the combining of the four biological events required for this conversion process (production of saccharolytic enzymes, hydrolysis of the polysaccharides present in pretreated biomass, fermentation of hexose sugars, and fermentation of pentose sugars) in one reactor. CBP is gaining increasing recognition as a potential breakthrough for low-cost biomass processing. Although no natural microorganism exhibits all the features desired for CBP, a number of microorganisms, both bacteria and fungi, possess some of the desirable properties. This review focuses on progress made toward the development of baker's yeast (Saccharomyces cerevisiae) for CBP. The current status of saccharolytic enzyme (cellulases and hemicellulases) expression in S. cerevisiae to complement its natural fermentative ability is highlighted. Attention is also devoted to the challenges ahead to integrate all required enzymatic activities in an industrial S. cerevisiae strain(s) and the need for molecular and selection strategies pursuant to developing a yeast capable of CBP.