[Isolation and identification of cultivable myxobacteria in the rhizosphere soils of medicinal plants].

OBJECTIVE: We isolated myxobacteria and explored their diversity from the rhizosphere soils of some medicinal plants. METHODS: We used the helper bacteria baiting technique to isolate myxobacteria from the rhizosphere soils collected in South China Botanical Garden and Nanling National Forest Park. The myxobacteria were identified by morphological characteristics and 16S rDNA gene sequences analysis. RESULTS: A total of 50 strains were isolated from 22 soil samples, which were identified into 7 genera, Myxococcus (18), Corallococcus (11), Cystobacter (7), Archangium (8), Stigmatella (1), Chondromyces (4) and Pyxidicoccus (1). The dominant genera were Myxococcus and Corallococcus. CONCLUSION: Environmental factors were associated with the diversity of myxobactria. Myxobacteria better adapt in high organic matter content and neutral pH environments. The strains of Myxococcus and Corallococcus had a good adaptability for different pH. Meanwhile, the dependence of the strains of Myxococcus and Cystobacter on organic carbon content was not too obvious, and they can also be found in the poor soils. Our findings provided an important scientific base for the development and utilization of myxobacteria resources.

Diversity and distribution of anaeromyxobacter strains in a uranium-contaminated subsurface environment with a nonuniform groundwater flow.

Versaphilic Anaeromyxobacter dehalogenans strains implicated in hexavalent uranium reduction and immobilization are present in the fractured saprolite subsurface environment at the U.S. Department of Energy Integrated Field-Scale Subsurface Research Challenge (IFC) site near Oak Ridge, TN. To provide insight into the in situ distribution of Anaeromyxobacter strains in this system with a nonuniform groundwater flow, 16S rRNA gene-targeted primers and linear hybridization (TaqMan) probes were designed for Oak Ridge IFC Anaeromyxobacter isolates FRC-D1 and FRC-W, along with an Anaeromyxobacter genus-targeted probe and primer set. Multiplex quantitative real-time PCR (mqPCR) was applied to samples collected from Oak Ridge IFC site areas 1 and 3, which are not connected by the primary groundwater flow paths; however, transport between them through cross-plane fractures is hypothesized. Strain FRC-W accounted for more than 10% of the total quantifiable Anaeromyxobacter community in area 1 soils, while strain FRC-D1 was not detected. In FeOOH-amended enrichment cultures derived from area 1 site materials, strain FRC-D1 accounted for 30 to 90% of the total Anaeromyxobacter community, demonstrating that this strain was present in situ in area 1. The area 3 total Anaeromyxobacter abundance exceeded that of area 1 by 3 to 5 orders of magnitude, but neither strain FRC-W- nor FRC-D1-like sequences were quantifiable in any of the 33 area 3 groundwater or sediment samples tested. The Anaeromyxobacter community in area 3 increased from <10(5) cells/g sediment outside the ethanol biostimulation treatment zone to 10(8) cells/g sediment near the injection well, and 16S rRNA gene clone library analysis revealed that representatives of a novel phylogenetic cluster dominated the area 3 Anaeromyxobacter community inside the treatment loop. The combined applications of genus- and strain-level mqPCR approaches along with clone libraries provided novel information on patterns of microbial variability within a bacterial group relevant to uranium bioremediation.

Hexavalent uranium supports growth of Anaeromyxobacter dehalogenans and Geobacter spp. with lower than predicted biomass yields.

The stimulation of bacteria capable of reducing soluble U(VI) to sparingly soluble U(IV) is a promising approach for containing U(VI) plumes. Anaeromyxobacter dehalogenans is capable of mediating this activity; however, its ability to couple U(VI) reduction to growth has not been established. Monitoring the increase in 16S rRNA gene copy numbers using quantitative real-time PCR (qPCR) in cultures provided with U(VI) as an electron acceptor demonstrated growth, and 7.7-8.6 x 10(6) cells were produced per mumole of U(VI) reduced. This biomass yield was lower than predicted based on the theoretical free energy changes associated with U(VI)-to-U(IV) reduction. Lower than predicted growth yields with U(VI) as electron acceptor were also determined in cultures of Geobacter lovleyi and Geobacter sulfurreducens suggesting that U(VI) reduction is inefficient or imposes an additional cost to growing cells. These findings have implications for U(VI) bioremediation because Anaeromyxobacter spp. and Geobacter spp. contribute to radionuclide immobilization in contaminated subsurface environments.