Le-Ni Sun

Isolation and characterization of plant growth-promoting rhizobacteria from wheat roots by wheat germ agglutinin labeled with fluorescein isothiocyanate

AbstactThirty-two isolates were obtained from wheat rhizosphere by wheat germ agglutinin (WGA) labeled with fluorescein isothiocyanate (FITC). Most isolates were able to produce indole acetic acid (65.6%) and siderophores (59.3%), as well as exhibited phosphate solubilization (96.8%). Fourteen isolates displayed three plant growth-promoting traits. Among these strains, two phosphate-dissolving ones, WS29 and WS31, were evaluated for their beneficial effects on the early growth of wheat (Triticum aestivum Wan33). Strain WS29 and WS31 significantly promoted the development of lateral roots by 34.9% and 27.6%, as well as increased the root dry weight by 25.0% and 25.6%, respectively, compared to those of the control. Based on 16S rRNA gene sequence comparisons and phylogenetic positions, both isolates were determined to belong to the genus Bacillus. The proportion of isolates showing the properties of plant growth-promoting rhizobacteria (PGPR) was higher than in previous reports. The efficiency of the isolation of PGPR strains was also greatly increased by WGA labeled with FITC. The present study indicated that WGA could be used as an effective tool for isolating PGPR strains with high affinity to host plants from wheat roots. The proposed approach could facilitate research on biofertilizers or biocontrol agents.

Caulobacter flavus sp. nov., a stalked bacterium isolated from rhizosphere soil.

A Gram-stain-negative, aerobic, yellow-pigmented and rod-shaped bacterium with a single polar flagellum or a stalk, designated strain RHGG3T, was isolated from rhizosphere soil of cultivated watermelon (Citrullus lanatus) collected from Hefei, China. Optimal growth of strain RHGG3T was observed at pH 7.0 and 28-30 °C. Cells were catalase-positive and oxidase-negative. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain RHGG3T belonged to the genus Caulobacter and showed the highest 16S rRNA gene sequence similarities to Caulobacter segnis ATCC 21756T (98.6 %), Caulobacter vibrioides CB51T (98.3 %) and Caulobacter henricii ATCC 15253T (97.2 %). The G+C content of the genomic DNA was 70 mol%. Strain RHGG3T contained Q-10 as the sole ubiquinone and the major fatty acids (>8 %) were 11-methyl C18 : 1ω7c, C18 : 1ω7c, C16 : 0, C15 : 0 and summed feature 3 (C16 : 1ω7c and/or iso-C15 : 0 2-OH). The polar lipids were various unknown glycolipids, phosphatidylglycerol and phosphoglycolipids. DNA-DNA relatedness of strain RHGG3T to type strains of the most closely related species (Caulobacter segnis ATCC 21756T, Caulobacter vibrioides DSM 4738 and Caulobacter henricii ATCC 15253T) was 32.4-40.9 %. Based on polyphasic taxonomy analysis (phylogenetic, unique phenotypic traits, chemotaxonomic and DNA-DNA hybridizations), strain RHGG3T represents a novel species of the genus Caulobacter, for which the name Caulobacter flavus sp. nov. is proposed. The type strain is RHGG3T ( = CGMCC 1.15093T = KCTC 42581T = JCM 30763T).

Complete genome sequence of a novel chlorpyrifos degrading bacterium, Cupriavidus nantongensis X1

Cupriavidus nantongensis X1 is a chlorpyrifos degrading bacterium, which was isolated from sludge collected at the drain outlet of a chlorpyrifos manufacture plant. It is the first time to report the complete genome sequence of C. nantongensis species, which has been reported as a novel species of Cupriavidus genus. It could provide further pathway information in chlorpyrifos degradation.

C aulobacter rhizosphaerae sp. nov., a stalked bacterium isolated from rhizosphere soil

The Gram-reaction-negative, aerobic, white- to pale-yellow-coloured and rod-shaped bacterium with a single polar flagellum or a stalk, designated strain 7F14T, was isolated from rhizosphere soil of cultivated watermelon (Citrullus lanatus) collected from Hefei, China. Growth of strain 7F14T was observed at pH 6.0-9.0, 10-30 °C and in the presence of 0-1 % (w/v) NaCl. Cells were catalase-negative and oxidase-positive. Phylogenetic analyses based on 16S rRNA gene sequences indicated that strain 7F14T formed a phyletic lineage within the genus Caulobacter of the family Caulobacteraceae and showed the highest 16S rRNA gene sequence similarities to Caulobacter henricii ATCC 15253T (98.66 %), Caulobacter segnis ATCC 21756T (98.27 %), Caulobacter vibrioides CB51T (97.92 %) and Caulobacter flavus RHGG3T (97.44 %). The G+C content of the genomic DNA was 68.6 mol%. Strain 7F14T contained Q-10 as the sole ubiquinone and 11-methyl C18 : 1ω7c, C18 : 1ω7c, C16 : 0 and summed feature 3 (C16 : 1ω7c and/or iso-C15 : 0 2-OH) as the major fatty acids. The polar lipids profile consisted of phosphatidylglycerol, an unknown phosphoglycolipid, five unknown glycolipids, an unknown phospholipid and three unknown lipids. DNA-DNA relatedness values to the most closely related type strains Caulobacter henricii DSM 4730T and Caulobacter segnis DSM 7131T were 26.0 and 19.7 %, respectively. Based on unique phenotypic traits, and phylogenetic, chemotaxonomic and DNA-DNA hybridization results, strain 7F14T should be classified as a representative of a novel species of the genus Caulobacter, for which the name Caulobacter rhizosphaerae sp. nov. is proposed. The type strain is 7F14T (=CGMCC 1.15915T=KCTC 52515T).

Massilia buxea sp. nov., isolated from a rock surface

A Gram-stain-negative, rod-shaped and motile bacterial strain, designated A9T, was isolated from the surface of rock collected from the shore of Nvshan lake in Mingguang, Anhui province, China. Phylogenetic analysis based on 16S rDNA sequence data showed that strain A9T was affiliated with the genus Massilia and showed the highest sequence similarities to Massilia plicata KCTC 12344T (98.8 %) and Massilia lurida CGMCC 1.10822T (97.9 %). The major fatty acids (>5 %) were summed feature 3 (C16 : 1ω7c and/or C15 : 0 iso 2-OH), C16 : 0 and C18 : 1ω7c. Strain A9T contained Q-8 as the predominant ubiquinone and diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol and an unidentified aminophospholipid as the predominant polar lipids. The DNA G+C content was 69.9 mol%. Mean DNA-DNA relatedness values between strain A9T and its closest phylogenetic relatives, M. plicata KCTC 12344T and M. lurida CGMCC 1.10822T, were 38.8 % and 23.23 %, respectively. On the basis of the results obtained in this study, strain A9T is considered to represent a novel species of the genus Massilia, for which the name Massilia buxea sp. nov. is proposed. The type strain is A9T (=DSM 103547T=CGMCC 1.15931T=KCTC 52429T).

The Role of Wheat Germ Agglutinin in the Attachment of Pseudomonas sp. WS32 to Wheat Root

Wheat germ agglutinin (WGA), which is secreted on the surface of wheat root, has been defined as a protein that reversibly and non-enzymatically binds to specific carbohydrates. However, little attention has been paid to the function of WGA in the attachment of bacteria to their host plants. The aim of this study was to investigate the role of WGA in the attachment of Pseudomonas sp. WS32 to wheat roots. Wheat roots were initially treated with double-distilled water, WGA-H (WGA solution that was heated at 100°C for 15 min) and WGA, independently. Subsequently, the roots were co-incubated with cell solutions (109 cells/ml). A dilution plate method using a solid nutrient medium was employed to determine the adsorption of WS32 to wheat roots. WGA was labeled with fluorescein isothiocyanate and detected using the fluorescent in situ hybridization (FISH) technique. The number of adsorptive WS32 cells on wheat roots was significantly increased when the wheat roots were pretreated with WGA, compared with the control treatment (p = 0.01). However, WGA-H failed to increase the amount of bacterial cells that attached to the wheat roots because of the loss of its physiological activity. The FISH assay also revealed that more cells adhered to WGA-treated wheat roots than to control or WGA-H-treated roots. The results indicated that WGA can mediate Pseudomonas strain WS32’s adherence to wheat seedling roots. The findings of this study provide a better understanding of the processes involved in plant-microbe interactions.

Mucilaginibacter rubeus sp. nov., isolated from rhizosphere soil

A Gram-stain-negative, aerobic, non-motile, rod-shaped and non-spore-forming bacterium, designated EF23T, was isolated from rhizosphere soil of watermelon. Growth of strain EF23T was observed at 10-37 °C, at pH 5.0-9.0 and in the presence of 0-0.5 % (w/v) NaCl. Strain EF23T contained menaquinone 7 (MK-7) as the major isoprenoid quinone, and summed feature 3 (C16:1ω7c and/or iso-C15 : 0 2-OH), iso-C15 : 0, C16 : 0 and iso-C17 : 0 3-OH as the major fatty acids. Phosphatidylethanolamine was identified as the major polar lipid. The genomic DNA G+C content of strain EF23T was 43.7 mol%. Phylogenetic analyses based on 16S rRNA gene sequences showed that strain EF23T was most closely related to Mucilaginibacter gossypii Gh-67T (98.9 % similarity) and Mucilaginibacter gossypiicola Gh-48T (97.6 %). DNA-DNA relatedness values between strain EF23T and M. gossypii KCTC 22380T and M. gossypiicola KCTC 22379T were 31.6 and 53.7 %. On the basis of the evidence presented in this polyphasic taxonomic study, strain EF23T is considered to represent a novel species of the genus Mucilaginibacter, for which the name Mucilaginibacter rubeus sp. nov. is proposed. The type strain is EF23T (=CGMCC 1.15913T=KCTC 52516T).