Ke Xing

Biodiversity, bioactive natural products and biotechnological potential of plant-associated endophytic actinobacteria

Endophytic actinobacteria, which exist in the inner tissues of living plants, have attracted increasing attention among taxonomists, ecologists, agronomists, chemists and evolutionary biologists. Numerous studies have indicated that these prolific actinobacteria appear to have a capacity to produce an impressive array of secondary metabolites exhibiting a wide variety of biological activity, such as antibiotics, antitumor and anti-infection agents, plant growth promoters and enzymes, and may contribute to their host plants by promoting growth and enhancing their ability of withstanding the environmental stresses. These microorganisms may represent an underexplored reservoir of novel species of potential interest in the discovery of novel lead compounds and for exploitation in pharmaceutical, agriculture and industry. This review focuses on new findings in the isolation methods, bio- and chemical diversity of endophytic actinobacteria and reveals the potential biotechnological application. The facing problems and strategies for biodiversity research and bioactive natural products producing are also discussed.

Chitosan antimicrobial and eliciting properties for pest control in agriculture: a review

In agriculture, current control of pathogens relies mainly on chemical fertilizers and pesticides. However, alternative solutions are needed due to concerns for public health, environmental protection, and development of resistant pests. Chitosan is a nontoxic, biodegradable biopolymer showing antimicrobial and plant-immunity eliciting properties. Here, we review chitosan antimicrobial activities, modes of action, and the elicitation of plant defense responses. The major points are the following: (1) Chitosan exhibits various inhibitory efficiency against bacteria, fungi, and viruses; (2) the five main modes of action of chitosan are electrostatic interactions, plasma membrane damage mechanism, chitosan-DNA/RNA interactions, metal chelation capacity of chitosan, and deposition onto the microbial surface; (3) the elicitation of plant defense responses by chitosan may be related to various pathogenesis-related proteins, defense-related enzymes, and secondary metabolites accumulation, as well as the complex signal transduction network. The facing problems and strategies for antimicrobial mechanism research and agricultural application of chitosan are also discussed.

Synthesis and in vitro antifungal efficacy of oleoyl-chitosan nanoparticles against plant pathogenic fungi

An antifungal dispersion system was prepared by oleoyl-chitosan (O-chitosan) nanoparticles, and the antifungal activity against several plant pathogenic fungi was investigated. Under scanning electron microscopy, the nanoparticles formulation appeared to be uniform with almost spherical shape. The particle size of nanoparticles was around 296.962 nm. Transmission electron microscopy observation showed that nanoparticles could be well distributed in potato dextrose agar medium. Mycelium growth experiment demonstrated that Nigrospora sphaerica, Botryosphaeria dothidea, Nigrospora oryzae and Alternaria tenuissima were chitosan-sensitive, while Gibberella zeae and Fusarium culmorum were chitosan-resistant. The antifungal index was increased as the concentration of nanoparticles increased for chitosan-sensitive fungi. Fatty acid analyses revealed that plasma membranes of chitosan-sensitive fungi were shown to have lower levels of unsaturated fatty acid than chitosan-resistant fungi. Phylogenetic analysis based on ITS gene sequences indicated that two chitosan-resistant fungi had a near phylogenetic relationship. Results showed that O-chitosan nanoparticles could be a useful alternative for controlling pathogenic fungi in agriculture.

Nocardia endophytica sp. nov., an endophytic actinomycete isolated from the oil-seed plant Jatropha curcas L.

A novel actinomycete, designated strain KLBMP 1256(T), was isolated from a surface-sterilized stem of the oil-seed plant Jatropha curcas L. collected from Sichuan Province, south-west China, and was characterized to determine its taxonomic position. Phylogenetic analyses based on 16S rRNA gene sequences indicated that the isolate was closely related to members of the genus Nocardia in the family Nocardiaceae, being most closely related to Nocardia callitridis CAP 290(T) (98.4 % similarity) and Nocardia nova JCM 6044(T) (97.5 %). Levels of 16S rRNA gene sequence similarity between strain KLBMP 1256(T) and the type strains of other recognized species of the genus Nocardia were less than 97 %. Chemotaxonomic data supported the affiliation of the new isolate to the genus Nocardia. However, the novel strain could be distinguished from its closest phylogenetic neighbour, N. callitridis CAP 290(T), by a range of phenotypic properties. The combination of low DNA-DNA relatedness values and phenotypic differences from N. callitridis CAP 290(T) indicated that strain KLBMP 1256(T) represents a novel species of the genus Nocardia, for which the name Nocardia endophytica sp. nov. is proposed. The type strain is KLBMP 1256(T) ( = KCTC 19777(T)  = CCTCC AA 2010004(T)).

Modestobacter roseus sp. nov., an endophytic actinomycete isolated from the coastal halophyte Salicornia europaea Linn., and emended description of the genus Modestobacter.

A novel actinomycete, designated strain KLBMP 1279(T), was isolated from surface-sterilized roots of a coastal halophyte, Salicornia europaea Linn., collected from Jiangsu Province, in the east of China. The taxonomic status of this organism was established using a polyphasic approach. 16S rRNA gene sequence analysis indicated that strain KLBMP 1279(T) was closely related to Modestobacter marinus 42H12-1(T) (99.5% 16S rRNA gene sequence similarity), Modestobacter versicolor CP153-2(T) (98.4%) and Modestobacter multiseptatus AA-826(T) (97.5%). Chemotaxonomic characteristics were consistent with its assignment to the genus Modestobacter in that the isolate had meso-diaminopimelic acid as the diagnostic diamino acid in the cell wall, MK-9(H4) as major menaquinone and a polar lipid profile containing diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol, phosphatidylinositol mannosides, two unknown aminophospholipids and an unknown phospholipid. The predominant fatty acids were iso-C16:0, iso-C15:0 and C17:1ω8c. The DNA G+C content was 71.7 mol%. However, DNA-DNA hybridization assays as well as physiological and biochemical analyses differentiated strain KLBMP 1279(T) from its closest phylogenetic relatives. On the basis of phenotypic, chemotaxonomic and phylogenetic evidence, the isolate KLBMP 1279(T) represents a novel species of the genus Modestobacter, for which the name Modestobacter roseus sp. nov. is proposed; the type strain is KLBMP 1279(T) (=KCTC 19887(T)=NBRC 108673(T)=DSM 45764(T)). An emended description of the genus Modestobacter is also proposed.

Glycomyces phytohabitans sp. nov., a novel endophytic actinomycete isolated from the coastal halophyte in Jiangsu, East China

A novel endophytic actinomycete, designated strain KLBMP 1483T, was isolated from the stem of the coastal plant Dendranthema indicum (Linn.) Des Moul collected from Nantong, in East China. Phylogenetic analysis showed that strain KLBMP 1483T was affiliated with the genus Glycomyces within the family Glycomycetaceae and shared the highest 16S rRNA gene sequence similarities with the type strains of Glycomyces arizonensis NRRL B-16153T (96.7%) and Glycomyces tenuis IFO 15904T (96.2%), and lower similarities (94.1–95.1%) to the other members of the genus Glycomyces, which distinguished KLBMP 1483T from representatives of the genus Glycomyces. The whole-cell hydrolysates contained meso-diaminopimelic acid, glucose, xylose and galactose. The polar lipids were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylinositol, phosphatidylinositol mannosides, two unknown aminophospholipids, two phosphoglycolipids, two unknown phospholipids and one unknown lipid. MK-10(H4) was the predominant menaquinone. The major fatty acids were iso-C15:0, anteiso-C15:0, iso-C16:0, iso-C16:1 G and anteiso-C17:0. On the basis of the phenotypic and genotypic characteristics presented in this study, strain KLBMP 1483T represents a novel species, for which the name Glycomyces phytohabitans sp. nov. is proposed. The type strain is KLBMP 1483T (NBRC 109116T=DSM 45766T).

Effect of O-chitosan nanoparticles on the development and membrane permeability of Verticillium dahliae

Verticillium dahliae, which causes wilting in over 300 woody and herbaceous plant species, is a representative of fungal plant diseases for which effective controls are still needed. In this study, the antifungal action of oleoyl-chitosan nanoparticles was investigated against V. dahliae. Media containing oleoyl-chitosan nanoparticles dramatically decreased the mycelium growth. The highest antifungal indexes were observed on media amended with 2mg/mL nanoparticles. Optical microscopy showed that spore germination and hyphae morphology were affected. Scanning electron microscopy and transmission electron microscopy demonstrated degenerative alterations including crumpled hyphae and spores, thickened cell walls, disappeared membranous organelles, massive vacuolation of the cytoplasm, and cell wall-plasmalemma separation. Fluorescence microscopy showed that nanoparticles were internalized by fungal cells. The sharp increase in the release of intracellular components and decrease of total cellular protein concentration demonstrated damaged cell membranes. Overall, the results indicate that oleoyl-chitosan nanoparticles have the potential to control phytopathogens in agriculture.

Nocardiajiangsuensis sp. nov., an actinomycete isolated from coastal soil

A novel actinomycete strain, designated strain KLBMP S0027T, was isolated from a coastal soil collected from the coastal region of Lianyungang, Jiangsu Province, in east China, and was studied in detail for its taxonomic position. Comparative 16S rRNA gene sequence analysis showed that this strain belonged to the genus Nocardia and was most closely related to Nocardia harenae WS-26T (98.5 %), Nocardiaasiatica NBRC 100129T (98.5 %), Nocardiaabscessus NBRC 100374T (98.2 %), Nocardia brasiliensis NBRC 14402T (98.2 %) and Nocardiacyriacigeorgica NBRC 100375T (98 %), respectively. The strain showed a combination of chemotaxonomic and morphological properties typical of the genus Nocardia. The cell wall contained meso-diaminopimelic acid (type IV), and whole-cell sugars were arabinose, galactose, glucose and ribose. Strain KLBMP S0027T contained MK-8(H4ω-cycl) as the predominant menaquinone; C16 : 0, C18 : 1ω9c, C18 : 0 10-methyl (TBSA) and summed feature 3 (C16 : 1ω7c/C16 : 1ω6c) were the major cellular fatty acids. The polar lipids detected were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol, one unknown glycolipid and two unknown lipids. Mycolic acids were detected. The G+C content of the DNA was 70.5 %. However, a combination of DNA-DNA hybridization and phenotypic data demonstrated that strain KLBMP S0027T could be clearly distinguished from the type strain of the most closely related species, N. harenae WS-26T. On the basis of the data presented from a polyphasic study, it was evident that this strain should be assigned to a novel species of the genus Nocardia, for which the name Nocardia jiangsuensis sp. nov. is proposed. The type strain is KLBMP S0027T (=CGMCC 4.7330T=KCTC 39691T).

Complete genome sequence of Kibdelosporangium phytohabitans KLBMP 1111T, a plant growth promoting endophytic actinomycete isolated from oil-seed plant Jatropha curcas L.

Kibdelosporangium phytohabitans KLBMP 1111(T) is a plant growth promoting endophytic actinomycete isolated from the oil-seed plant Jatropha curcas L. collected from dry-hot valley, in Sichuan, China. The complete genome sequence of this actinomycete consists of one chromosome (11,759,770bp) with no plasmid. From the genome, we identified gene clusters responsible for polyketide and nonribosomal peptide synthesis of natural products, and genes related to the plant growth promoting, such as zeatin, 1-aminocyclopropane-1-carboxylate deaminase (ACCD) and siderophore. The complete genome information may be useful to understand the beneficial interactions between K. phytohabitans KLBMP 1111(T) and host plants.

Complete genome sequence of endophyte Bacillus flexus KLBMP 4941 reveals its plant growth promotion mechanism and genetic basis for salt tolerance

Bacillus flexus KLBMP 4941 is a halotolerant endophyte isolated from the halophyte Limonium sinense. This strain can improve host seedling growth under salt stress conditions. We here report the complete genome information of endophyte KLBMP 4941. It has a circular chromosome and two plasmids for a total genome 4,104,242 bp in size with a G+C content of 38.09%. Genes related to plant growth promotion (PGP), such as those associated with nitrogen fixation, siderophore, spermidine, and acetoin synthesis were found in the KLBMP 4941 genome. Some genes responsible for high salinity tolerance, like genes associated with the Na+/H+ antiporter, glycine betaine transporter, and betaine-aldehyde dehydrogenase were also found in the KLBMP 4941 genome. The genome analysis will provide better understanding of the mechanisms underlying the promotion of plant growth in strain KLBMP 4941 under salt stress conditions and its ability to adapt to coastal salt marsh habitats, and provide a basis for its further biotechnological applications in agriculture.