Composition and functional comparison of vetiver root endophytic microbiota originating from different geographic locations that show antagonistic activity towards Fusarium graminearum.

Given the current trend towards reducing the use of chemical controls in agriculture, microbial resources such as plant endophytes are being intensively investigated for traits that are conducive to plant protection. Among the various important target pathogens, Fusarium graminearum is a fungal pathogen of cereal crops that is responsible for severe yield losses and mycotoxin contamination in grains. In the present study, we investigated the bacterial endophytic communities from vetiver (Chrysopogon zizanioides (L.) Roberty) roots originating from 5 different geographic locations across Europe and Africa. This study relies on a global 16S metabarcoding approach and the isolation/functional characterization of bacterial isolates. The results we obtained showed that geographical location is a factor that influences the composition and relative abundance of root endophyte communities in vetiver. Three hundred eighty-one bacterial endophytes were isolated and assessed for their in vitro antagonistic activities towards F. graminearum mycelium growth. In total, 46 % of the isolates showed at least 50 % inhibitory activity against F. graminearum. The taxonomic identification of the bioactive isolates revealed that the composition of these functional culturable endophytic communities was influenced by the geographic origins of the roots. The selected communities consisted of 15 genera. Some endophytes in Bacillus, Janthinobacterium, Kosakonia, Microbacterium, Pseudomonas, and Serratia showed strong growth inhibition activity (≥70 %) against F. graminearum and could be candidates for further development as biocontrol agents.

Insight into the mechanisms of plant growth promoting strain SNB6 on enhancing the phytoextraction in cadmium contaminated soil.

Plant growth-promoting rhizobacteria (PGPR) assisted accumulator has been proposed as a phytoextraction method to clean cadmium (Cd) in contaminated soil, while the mechanisms were few studied regrading PGPR-soil-accumulator as an assemble. In this study, we revealed the possible mechanisms of the plant growth-promotion strain SNB6 on enhancing the Cd phytoextration of vetiver grass by the analysis of the whole genome of SNB6, soil biochemical properties and plant growth response. Results showed that SNB6 encoded numerous genes needed for Cd tolerance, Cd mobilization and plant growth promotion. SNB6 increased HOAc-extractable Cd that showed a positive correlation with Cd uptake in accumulator. In addition, SNB6 improved the biochemical activities (bioavailability of nutritional substances, bacterial count, soil respiration and enzyme activity) in rhizosphere soil. Moreover, the antioxidative enzymes activities of accumulator were significantly enhanced by SNB6. Consequently, SNB6 promoted Cd uptake and biomass of accumulator, thus enhancing the Cd phytoextraction. The maximum Cd extractions in root, stem and leaf reached to 289.47 mg/kg, 88.33 mg/kg and 59.38 mg/kg, respectively. Meanwhile, the total biomass of accumulator was increased by 9.68-45.99% in SNB6 treatment. These findings could be conducive to the understanding the mechanisms of PGPR on enhancing the Cd phytoextraction of accumulator.

Sequential anaerobic-aerobic treatment using plant microbe integrated system for degradation of azo dyes and their aromatic amines by-products.

The presence of unused dyes and dye degradation intermediates in the textile industry wastewaters is the major challenge in its treatment. A wide range of treatments including various physicochemical processes are used for this wastewater. Incomplete dye degradation results in hazardous colorless aromatic amine intermediates that are teratogenic in nature. A synergistic plant-microbe system operated in a sequential anaerobic-aerobic mode was evaluated for the complete degradation of a model azo dye methyl red under laboratory conditions. The degradation of methyl red and its break down products 2-aminobenzoic acid and N,N-dimethyl-p-phenylenediamine were analysed by HPLC, FTIR and GC-MS. The vetiver-microbe system had shown enhanced dye degradation. The dye decolourization percentage achieved for integrated plant-microbe treatment system (T) after anaerobic condition was 53.5 ±â€¯6.2% and aerobic condition was 92 ±â€¯3.4%. The removal efficiency of the intermediates 2-ABA and DMPD was found to be 89.79% in the integrated plant-microbe treatment system. The plant-microbe system was most effective in the removal of toxic aromatic amine as seen by lesser phytotoxicity for seed germination and teratogenicity in case of zebrafish development in the treated water.

Meira siamensis sp. nov., a novel anamorphic ustilaginomycetous yeast species isolated from the vetiver grass phylloplane.

Two strains, DMKU-LV83 and DMKU-LV85, of a novel yeast species were isolated from the phylloplane of vetiver grass collected in Thailand by plating of leaf washings. Analysis of the sequences of the D1/D2 region of the large subunit (LSU) rRNA gene showed that the two strains represent a single novel species and most closely related to Meira miltonrushii. However, the novel species differed from the type strain of M. miltonrushii (MCA 3882T) by 5.5 % nucleotide substitutions in the D1/D2 region and 8.9 % nucleotide substitutions in the ITS region. The phylogenetic analysis based on the D1/D2 region of the LSU rRNA gene confirmed the placement of the novel species in the Meira clade and its close affinity with M. miltonrushii. Therefore, the species Meira siamensis sp. nov. is proposed. The type strain is DMKU-LV83T (=CBS 12860T=BCC 61180T).

Effectiveness of arbuscular mycorrhizal fungi in phytoremediation of lead- contaminated soil by vetiver grass.

A greenhouse experiment was conducted to evaluate the effectiveness of arbuscular mycorrhizal (AM) fungi in phytoremediation of lead (Pb)-contaminated soil by vetiver grass. Experiment was a factorial arranged in a completely randomized design. Factors included four Pb levels (50, 200, 400, and 800 mg kg(-1)) as Pb (NO3)2, AM fungi at three levels (non mycorrhizal (NM) control, Rhizophagus intraradices, Glomus versiforme). Shoot and root dry weights (SDW and RDW) decreased as Pb levels increased. Mycorrhizal inoculation increased SDW and RDW compared to NM control. With mycorrhizal inoculation and increasing Pb levels, Pb uptake of shoot and root increased compared to those of NM control. Root colonization increased with mycorrhizal inoculation but decreased as Pb levels increased. Phosphorus concentration and uptake in shoot of plants inoculated with AM fungi was significantly higher than NM control at 200 and 800 mg Pb kg(-1). The Fe concentration, Fe and Mn uptake of shoot in plants inoculated with Rhizophagus intraradices in all levels of Pb were significantly higher than NM control. Mycorrhizal inoculation increased Pb extraction, uptake and translocation efficiencies. Lead translocation factor decreased as Pb levels increased; however inoculation with AM fungi increased Pb translocation.

Construction of a plant-microbe phytoremediation system: combination of vetiver grass with a functional endophytic bacterium, Achromobacter xylosoxidans F3B, for aromatic pollutants removal.

The endophytic bacterial strain Achromobacter xylosoxidans F3B, which was able to utilize aromatic compounds as a sole carbon source, was inoculated into vetiver grass in this study. A real-time PCR detection method has been developed for confirming the stability of F3B in plants and DGGE profiles were conducted for examining the diversity of endophytes during the remediation process. These results showed that the endophytic bacteria strain F3B could maintain a stable population in plant roots without largely interfering with the diversity of native endophytes. Furthermore, the strain F3B could protect plants against toluene stress and maintain chlorophyll content of leaves, and a 30% reduction of evapotranspiration through vetiver leaves was observed. Our results demonstrate the potential to improve phytoremediation of aromatic pollutants by inoculating functional endophytic bacterial strains.

Comparison of the bacterial community and characterization of plant growth-promoting rhizobacteria from different genotypes of Chrysopogon zizanioides (L.) Roberty (vetiver) rhizospheres.

Molecular approaches [PCR-denaturing gradient gel electrophoresis (DGGE)] were used to determine whether three different vetiver (Chrysopogon zizanioides) genotypes, commercially used in Brazil and considered economically important over the world, select specific bacterial populations to coexist in their rhizospheres. DGGE profiles revealed that the predominant rhizospheric bacterial community hardly varies regarding the vetiver genotype. Moreover, using traditional cultivation methods, bacterial strains were isolated from the different rhizospheres. Colonies presenting different morphologies (83) were selected for determining their potential for plant growth promotion. More than half of the strains tested (57.8%) were amplified by PCR using nifH-based primers, specific for the enzyme nitrogenase reductase. The production of siderophores was observed in 88% of the strains, while the production of antimicrobial substances was detected in only 14.5% of the isolates when Micrococcus sp. was used as the indicator strain. Production of indole-3-acetic acid and the solubilization of phosphate were observed in 55.4% and 59% of the isolates, respectively. In total, 44 strains (53%) presented at least three characteristics of plant growth promotion and were submitted to amplified ribosomal DNA restriction analysis. Twenty-four genetic groups were formed at 100% similarity and one representative of each group was selected for their identification by partial 16S rRNA gene sequencing. They were affiliated with the genera Acinetobacter, Comamonas, Chryseobacterium, Klebsiella, Enterobacter, Pantoea, Dyella, Burkholderia, or Pseudomonas. These strains can be considered of great importance as possible biofertilizers in vetiver.

[Diversity of associated nitrogen-fixing bacteria isolated from the pioneer plants-Vetiver zizanioides].

OBJECTIVE: Vetiver zizanioides is a perennial grass of the Poaceae family, known of its silage, soil and water conservation role. The aim of the study was to collect and identify the resources of the nitrogen-fixing bacteria associated with Vetiver zizanioides. METHODS: Associated nitrogen-fixing bacteria isolated from Vetiver zizanioides were studied by SDS-PAGE whole-cell protein patterns, insert sequence (IS)-PCR finger printing, utilization of sole carbon sources and 16S rRNA gene sequence analysis. RESULTS: Based on the results of finger printing analysis, protein patterns and biological test, isolates were grouped into 6 clusters, except 4 single strains. Phylogenetic analysis of 16S rDNA sequences indicated that isolates belonged to Herbaspirillum frisingense, Enterobacter ludwigii, Pseudacidovorax intermedius, Mitsuaria chitosanitabida, Pseudomonas putida, Pseudomonas fluorescens, Burkholderia vietnamiensis and Enterobacter cloacae. CONCLUSION: The nitrogen fixers associated with Vetiver zizanioides showed great diversity and may have a potential application for the grass forage and agriculture.

The microbial community of Vetiver root and its involvement into essential oil biogenesis.

Vetiver is the only grass cultivated worldwide for the root essential oil, which is a mixture of sesquiterpene alcohols and hydrocarbons, used extensively in perfumery and cosmetics. Light and transmission electron microscopy demonstrated the presence of bacteria in the cortical parenchymatous essential oil-producing cells and in the lysigen lacunae in close association with the essential oil. This finding and the evidence that axenic Vetiver produces in vitro only trace amounts of oil with a strikingly different composition compared with the oils from in vivo Vetiver plants stimulated the hypothesis of an involvement of these bacteria in the oil metabolism. We used culture-based and culture-independent approaches to analyse the microbial community of the Vetiver root. Results demonstrate a broad phylogenetic spectrum of bacteria, including alpha-, beta- and gamma-Proteobacteria, high-G+C-content Gram-positive bacteria, and microbes belonging to the Fibrobacteres/Acidobacteria group. We isolated root-associated bacteria and showed that most of them are able to grow by using oil sesquiterpenes as a carbon source and to metabolize them releasing into the medium a large number of compounds typically found in commercial Vetiver oils. Several bacteria were also able to induce gene expression of a Vetiver sesquiterpene synthase. These results support the intriguing hypothesis that bacteria may have a role in essential oil biosynthesis opening the possibility to use them to manoeuvre the Vetiver oil molecular structure.