Biochemical characterization and antifungal activity of an endo-1,3-beta-glucanase of Paenibacillus sp. isolated from garden soil

Biological control of wood decay against fungal infection

Wood (timber) is an important raw material for various purposes, and having biological composition it is susceptible to deterioration by various agents. The history of wood protection by impregnation with synthetic chemicals is almost two hundred years old. However, the ever-increasing public concern and the new environmental regulations on the use of chemicals have created the need for the development and the use of alternative methods for wood protection. Biological wood protection by antagonistic microbes alone or in combination with (bio)chemicals, is one of the most promising ways for the environmentally sound wood protection. The most effective biocontrol antagonists belong to genera Trichoderma, Gliocladium, Bacillus, Pseudomonas and Streptomyces. They compete for an ecological niche by consuming available nutrients as well as by secreting a spectrum of biochemicals effective against various fungal pathogens. The biochemicals include cell wall-degrading enzymes, siderophores, chelating iron and a wide variety of volatile and non-volatile antibiotics. In this review, the nature and the function of the antagonistic microbes in wood protection are discussed.

Bacillus graminis sp. nov., an endophyte isolated from a coastal dune plant

A Gram-stain-positive endophytic bacterium, designated strain YC6957T, was isolated from surface-sterilized roots of a halophyte (Elymus mollis Trin.) inhabiting coastal tidal flats of Namhae Island, located on the southern coast of Korea, and was subjected to a polyphasic taxonomic study. Cells were facultatively anaerobic, endospore-forming rods to coccoid rods, motile by a single flagellum. Strain YC6957T was catalase-positive, oxidase-negative and able to grow in the presence of 0–8 % (w/v) NaCl, with optimum growth at 4–5 % (w/v) NaCl. Growth occurred at 15–45 °C (optimal growth at 30–35 °C) and pH 6.0–8.5 (optimal growth at pH 7.0–8.0). The predominant isoprenoid quinone was menaquinone 7 (MK-7). The major cellular fatty acids were C16 : 0 (11.3 %), iso-C15 : 0 (19.2 %) and anteiso-C15 : 0 (36.4 %). The cell-wall peptidoglycan contained meso-diaminopimelic acid. The major polar lipids were diphosphatidylglycerol, phosphatidylglycerol and phosphatidylethanolamine. The DNA G+C content was 41.6 mol%. Phylogenetic analysis based on the 16S rRNA gene sequence revealed that the isolate belonged to the genus Bacillus. Strain YC6957T exhibited high 16S rRNA gene sequence similarity to its closest neighbours, Bacillus ruris LMG 22866T (96.14 %), Bacillus lentus NCIMB 8773T (95.97 %) and Bacillus galactosidilyticus LMG 17892T (95.91 %), and less than 95.84 % similarity to all other type strains in the genus Bacillus. On the basis of the phylogenetic, physiological and biochemical data, it is suggested that strain YC6957T represents a novel species of the genus Bacillus, for which the name Bacillus graminis sp. nov. is proposed. The type strain is YC6957T ( = KACC 13779T  = DSM 22162T).

Curdlan complexes as a potential food-grade delivery system: genistein case study

Complexes of curdlan and genistein were prepared using four different methods. The total amount of genistein in curdlan–genistein complexes prepared at 40°C (system I) was significantly higher (2.3 mg/100 mg dry matter) than that in other systems studied: curdlan–genistein complexes prepared at 60°C (system II; 1.8 mg/100 mg dry matter); curdlan–genistein gel complexes (system III; 1.0 mg/100 mg dry matter); and curdlan–genistein dimethyl sulfoxide complexes (system IV; 1.8 mg/100 mg dry matter). x-ray diffraction results indicate that complexation of curdlan with genistein changes the crystalline nature of the pure components. Particle size analysis, atomic force microscopy and scanning electron microscopy imaging of curdlan–genistein complexes showed strong difference in particle size, surface and distribution in comparison with pure curdlan, confirming our assumption of a molecular interaction between curdlan and genistein and the formation of a new structure, which was revealed at the nanoscale level. All the curdlan–genistein complexes showed prolonged genistein release of up to 72 h, enhanced upon enzymatic digestion of curdlan by lyticase, thus opening the possibility of release regulation by the incorporation of lyticase in the delivery system. It is therefore suggested that the complexes could be used as a delivery system for the protection and slow release of genistein in the digestive tract.

Biotechnological approaches to develop bacterial chitinases as a bioshield against fungal diseases of plants

Fungal diseases of plants continue to contribute to heavy crop losses in spite of the best control efforts of plant pathologists. Breeding for disease-resistant varieties and the application of synthetic chemical fungicides are the most widely accepted approaches in plant disease management. An alternative approach to avoid the undesired effects of chemical control could be biological control using antifungal bacteria that exhibit a direct action against fungal pathogens. Several biocontrol agents, with specific fungal targets, have been registered and released in the commercial market with different fungal pathogens as targets. However, these have not yet achieved their full commercial potential due to the inherent limitations in the use of living organisms, such as relatively short shelf life of the products and inconsistent performance in the field. Different mechanisms of action have been identified in microbial biocontrol of fungal plant diseases including competition for space or nutrients, production of antifungal metabolites, and secretion of hydrolytic enzymes such as chitinases and glucanases. This review focuses on the bacterial chitinases that hydrolyze the chitinous fungal cell wall, which is the most important targeted structural component of fungal pathogens. The application of the hydrolytic enzyme preparations, devoid of live bacteria, could be more efficacious in fungal control strategies. This approach, however, is still in its infancy, due to prohibitive production costs. Here, we critically examine available sources of bacterial chitinases and the approaches to improve enzymatic properties using biotechnological tools. We project that the combination of microbial and recombinant DNA technologies will yield more effective environment-friendly products of bacterial chitinases to control fungal diseases of crops.

Carbohydrate-binding properties of a separately folding protein module from β-1,3-glucanase Lic16A of Clostridium thermocellum

The multi-modular non-cellulosomal endo-1,3(4)-β-glucanase Lic16A from Clostridium thermocellum contains a so-called X module (denoted as CBMX) near the N terminus of the catalytic module (191–426 aa). Melting of X-module-containing recombinant proteins revealed an independent folding of the module. CBMX was isolated and studied as a separate fragment. It was shown to bind to various insoluble polysaccharides, including xylan, pustulan, chitin, chitosan, yeast cell wall glucan, Avicel and bacterial crystalline cellulose. CBMX thus contains a hitherto unknown carbohydrate-binding module (CBM54). It did not bind soluble polysaccharides on which Lic16A is highly active. Ca2+ ions had effects on the binding, e.g. stimulated complex formation with chitosan, which was observed only in the presence of Ca2+. The highest affinity to CBMX was shown for xylan (binding constant K=3.1×104 M−1), yeast cell wall glucan (K=1.4×105 M−1) and chitin (K=3.3.105 M−1 in the presence of Ca2+). Lic16A deletion derivatives lacking CBMX had lower affinity to lichenan and laminarin and a slight decrease in optimum temperature and thermostability. However, the specific activity was not significantly affected.

Inter-kingdom encounters: recent advances in molecular bacterium-fungus interactions

Interactions between bacteria and fungi are well known, but it is often underestimated how intimate and decisive such associations can be with respect to behaviour and survival of each participating organism. In this article we review recent advances in molecular bacterium-fungus interactions, combining the data of different model systems. Emphasis is given to the positive or negative consequences these interactions have on the microbe accommodating plants and animals. Intricate mechanisms of antagonism and tolerance have emerged, being as important for the biological control of plants against fungal diseases as for the human body against fungal infections. Bacterial growth promoters of fungal mycelium have been characterized, and these may as well assist plant-fungus mutualism as disease development in animals. Some of the toxins that have been previously associated with fungi are actually produced by endobacteria, and the mechanisms that lie behind the maintenance of such exquisite endosymbioses are fascinating. Bacteria do cause diseases in fungi, and a synergistic action between bacterial toxins and extracellular enzymes is the hallmark of such diseases. The molecular study of bacterium-fungus associations has expanded our view on microbial communication, and this promising field shows now great potentials in medicinal, agricultural and biotechnological applications.

Wide-range antifungal antagonism of Paenibacillus ehimensis IB-X-b and its dependence on chitinase and beta-1,3-glucanase production

Previously, we isolated a strain of Bacillus that had antifungal activity and produced lytic enzymes with fungicidal potential. In the present study, we identified the bacterium as Paenibacillus ehimensis and further explored its antifungal properties. In liquid co-cultivation assays, P. ehimensis IB-X-b decreased biomass production of several pathogenic fungi by 45%-75%. The inhibition was accompanied by degradation of fungal cell walls and alterations in hyphal morphology. Residual medium from cultures of P. ehimensis IB-X-b inhibited fungal growth, indicating the inhibitors were secreted into the medium. Of the 2 major lytic enzymes, chitinases were only induced by chitin-containing substrates, whereas beta-1,3-glucanase showed steady levels in all carbon sources. Both purified chitinase and beta-1,3-glucanase degraded cell walls of macerated fungal mycelia, whereas only the latter also degraded cell walls of intact mycelia. The results indicate synergism between the antifungal action mechanisms of these enzymes in which beta-1,3-glucanase is the initiator of the cell wall hydrolysis, whereas the degradation process is reinforced by chitinases. Paenibacillus ehimensis IB-X-b has pronounced antifungal activity with a wide range of fungi and has potential as a biological control agent against plant pathogenic fungi.

Cloning and functional characterization of a complex endo-beta-1,3-glucanase from Paenibacillus sp

A beta-1,3-glucanase gene, encoding a protein of 1,793 amino acids, was cloned from a strain of Paenibacillus sp. in this study. This large protein, designated as LamA, consists of many putative functional units, which include, from N to C terminus, a leader peptide, three repeats of the S-layer homologous module, a catalytic module of glycoside hydrolase family 16, four repeats of the carbohydrate-binding module of family CBM_4_9, and an analogue of coagulation factor Fa5/8C. Several truncated proteins, composed of the catalytic module with various organizations of the appended modules, were successfully expressed and characterized in this study. Data indicated that the catalytic module specifically hydrolyze beta-1,3- and beta-1,3-1,4-glucans. Also, laminaritriose was the major product upon endolytic hydrolysis of laminarin. The CBM repeats and Fa5/8C analogue substantially enhanced the hydrolyzing activity of the catalytic module, particularly toward insoluble complex substrates, suggesting their modulating functions in the enzymatic activity of LamA. Carbohydrate-binding assay confirmed the binding capabilities of the CBM repeats and Fa5/8C analogue to beta-1,3-, beta-1,3-1,4-, and even beta-1,4-glucans. These appended modules also enhanced the inhibition effect of the catalytic module on the growth of Candida albicans and Rhizoctonia solani.

Mutagenesis of beta-1,3-Glucanase Genes in Lysobacter enzymogenes Strain C3 Results in Reduced Biological Control Activity Toward Bipolaris Leaf Spot of Tall Fescue and Pythium Damping-Off of Sugar Beet

ABSTRACT Lysobacter enzymogenes produces extracellular lytic enzymes capable of degrading the cell walls of fungi and oomycetes. Many of these enzymes, including beta-1,3-glucanases, are thought to contribute to the biological control activity expressed by several strains of the species. L. enzymogenes strain C3 produces multiple extracellular beta-1,3-glucanases encoded by the gluA, gluB, and gluC genes. Analysis of the genes indicates they are homologous to previously characterized genes in the related strain N4-7, each sharing >95% amino acid sequence identity to their respective counterparts. The gluA and gluC gene products encode enzymes belonging to family 16 glycosyl hydrolases, whereas gluB encodes an enzyme belonging to family 64. Mutational analysis indicated that the three genes accounted for the total beta-1,3-glucanase activity detected in culture. Strain G123, mutated in all three glucanase genes, was reduced in its ability to grow in a minimal medium containing laminarin as a sole carbon source. Although strain G123 was not affected in antimicrobial activity toward Bipolaris sorokiniana or Pythium ultimum var. ultimum using in vitro assays, it was significantly reduced in biological control activity against Bipolaris leaf spot of tall fescue and Pythium damping-off of sugar beet. These results provide direct supportive evidence for the role of beta-1,3-glucanases in biocontrol activity of L. enzymogenes strain C3.