Phylogenetic diversity of bacterial endophytes of Panax notoginseng with antagonistic characteristics towards pathogens of root-rot disease complex.

Endophytes play an important role in protection of host plants from infection by phytopathogens. Endophytic bacteria were isolated from five different parts (root, stem, petiole, leaf and seed) of Panax notoginseng and evaluated for antagonistic activity against Fusarium oxysporum, Ralstonia sp. and Meloidogyne hapla, three major pathogens associated with root-rot disease complex of P. notoginseng. From 1000 endophytic bacterial strains evaluated in vitro, 104 strains exhibited antagonistic properties against at least one of these three pathogens. Phylogenetic analyses of their 16S rRNA gene sequences showed that these 104 antagonistic bacteria belong to four clusters: Firmicutes, Proteobacteria, Actinobacteria and Bacteroidetes/Chlorobi. Members of the Firmicutes, in particular the Bacillus spp., were predominant in all analyzed tissues. The root was the main reservoir for antagonistic bacteria. Of the 104 antagonists, 51 strains showed antagonistic activities to one pathogen only, while 43 and 10 displayed the activities towards two and all three pathogens, respectively. The most dominant species in all tissues were Bacillus amyloliquefaciens subsp. plantarum and Bacillus methylotrophicus, which were represented by eight strains with broad antagonistic spectrum to the all three test pathogens of root-rot disease complex of P. notoginseng.

[Phylogenic diversity of soil chemotatic bacteria in a phosphorous-rich area around Dianchi Lake of Yunnan Province, Southwest China].

Phosphate-solubilizing bacteria (PSB) were isolated from 100 soil samples collected from a phosphorous-rich area around the Dianchi Lake of Yunnan Province, Southwest China. The chemotatic PSB strains were screened by cheA gene detection, and their chemotaxis was verified by the method of soft agar plate. The tricalcium phosphate (TCP)-solubilizing activities of PSB were determined with molybdenum blue spectrophotometry. Based on 16S rRNA sequences, the phylogenic relationships of the PSB were analyzed. A total of 145 PSB strains with a diameter of phosphate-solubilizing halo zone ranged from 0.5 cm to 2 cm were isolated, among which, 37 strains were chemotactic. The 37 chemotactic strains showed chemotaxis towards four test attractants, and exhibited TCP-solubilizing activity. Phylogenic analysis revealed that the 37 chemotatic strains were belonged to 17 species of 10 genera, in which, Pseudomonas was dominant (9 strains of 5 species), followed by Enterobacter (8 strains of 3 species). Only one species (Bacillus aryabhattai) was isolated from Bacillus, but 9 strains were identified.

Diversity and chemotaxis of soil bacteria with antifungal activity against Fusarium wilt of banana.

The chemotactic response of bacteria to root exudates plays an important role in the colonization of bacteria in the rhizosphere. In this study, 420 strains of antifungal bacteria against Fusarium oxysporum f. sp. cubense (Foc) were screened for chemotaxis based on a cheA molecular diagnostic method. A total of 124 strains with antifungal efficiencies of 27.26-67.14 % generated a characteristic band of cheA. The chemotaxis of 97 bacterial strains producing a cheA band was confirmed using the drop assay and swarm plate assay using catechol, p-hydroxybenzoic acid, salicylic acid, and asparagine as the attractants. A phylogenetic analysis based on restriction fragment length polymorphisms (RFLPs) and 16S rDNA sequences indicated that the 124 chemotactic antagonists of Foc were affiliated with 18 species of Paenibacillaceae, Bacillaceae, Streptomycineae, Enterobacteriaceae, and Pseudomonadaceae. The chemical composition of banana root exudates were analyzed by GC-MS, and 62 compounds, including alkanes, alkenes, naphthalenes, benzenes, and alcohols, were evaluated. Five representative antagonists of Foc showed 1.76- to 7.75-fold higher chemotactic responses than the control to seven compounds in banana root exudates, as determination by capillary assays.

Lysinibacillus mangiferahumi sp. nov., a new bacterium producing nematicidal volatiles.

A Gram-positive bacterium, designated M-GX18(T), was isolated from the rhizosphere soil of mango (Guangxi Province, China). The isolate produced nematicidal volatile compounds with activities against the root-knot nematode Meloidogyne incognita. The organism was motile, catalase- and oxidase-positive, spore-forming and rod shaped. The predominant menaquinone was MK-7 and the major cellular fatty acid profiles were iso-C(15:0), anteiso-C(15:0) and iso-C(16:0). The DNA G+C content was 38.9%. A phylogenetic analysis based on 16S rRNA gene sequences showed that this organism represented a new species of the genus Lysinibacillus. Strain M-GX18(T) exhibited high 16S rRNA gene sequence similarity with its closest neighbors Lysinibacillus sphaericus (98.5%), Lysinibacillus fusiformis (98.1%) and Lysinibacillus xylanilyticus (98.6%). The physiological, biochemical and chemotaxonomic data, including DNA-DNA hybridization relatedness data, indicate that strain M-GX18(T) can be distinguished from all the related species of the genus Lysinibacillus. Therefore, on the basis of the polyphasic taxonomic data presented, a new species of the genus Lysinibacillus, Lysinibacillus mangiferahumi, with the type strain M-GX18(T) (=DSM 24076(T) = CCTCC AB 2010389(T)) is proposed.

Sphingobacterium nematocida sp. nov., a nematicidal endophytic bacterium isolated from tobacco.

A novel Gram-negative strain, designated M-SX103(T), was isolated from a fresh leaf of Nicotiana tabacum Linn. collected at Yuxi City, Yunnan province, China, and subjected to a polyphasic taxonomic study. Growth occurred at 10-40 °C, at pH 6.0-9.0 and with 0-3% (w/v) NaCl. The predominant isoprenoid quinone was MK-7. The major cellular fatty acids of strain M-SX103(T) were iso-C(15:0), iso-C(17:0) 3-OH and summed feature 3 (C(16:1)ω7c and/or C(16:1)ω6c). The G+C content of the genomic DNA was 40.6 mol%. Phylogenetic analysis based on 16S rRNA gene sequences showed that the isolate belongs to the genus Sphingobacterium, sharing 95.4-89.7% sequence similarity with type strains of members of the genus Sphingobacterium; it was most closely related to Sphingobacterium composti T5-12(T). On the basis of the taxonomic evidence, a novel species, Sphingobacterium nematocida sp. nov., is proposed. The type strain is M-SX103(T) ( = JCM 17339(T) = CCTCC AB 2010390(T)).

[Changes and analysis of soil quality under different land use types in oasis rim].

The aggravation process of oasisization leads to changes of land use type in oasis rim. In order to discuss the effects of different land use types on soil properties and soil quality, the four land use types located Cele oasis rim in south margin of Tarim Basin, which are the cotton field, orchard, and Caligonum mongolicum Turcz land use type reclaimed by people and nature state land use type covered by Alhagi sparsifolia SHAP, were selected as study object. The relative soil quality index (RI) and the soil quality synthesis index (SQI) were used to analyse the changes of soil quality between four land use types within 0-20 cm, 2040 cm, 40-60 cm soil depth, respectively. Meantime, the fractal theory was used to analyse the particle-size distribution (PSD) property of top soil under different land use types. The results indicated that there was a significant difference in the soil organic matter and total nitrogen in same soil depth between four land use types; the order ranked according to RI was same to the order ranked according to SQI in each soil depth between four land use types. The cotton field and orchard have an obviously positive effect on soil quality of the top soil, however, the soil quality of Alhagi sparsifolia SHAP land use type was gradually increasing along with the increasing soil depth. The soil properties and soil quality of Caligonum mongolicum Turcz land use type were at the lowest level according to the comparison results among all land use types, and the calculation results of PSD fractal dimension also indicated the Caligonum mongolicum Turcz land use type had the worst ability on maintaining soil fine fractions.