Isolation and Identification of Plant Growth-Promoting Bacteria Highly Effective in Suppressing Root Rot in Fava Beans.

In this study, 18 plant growth-promoting bacterial (PGPB) strains were isolated from the rhizosphere of both Red silk-cotton tree (Bombax malabaricum) and Chinese banyan (Ficus retusa). Culture morphology was observed and genotypic characterization was accomplished by sequencing partial 16S rRNA gene. Plant growth promotion traits and antagonistic activities of the strains against phytopathogenic fungi were evaluated. Among all strains, Bacillus thuringiensis (MN419208) exert the highest indole acetic acid (38 µg/ml), produced exopolysaccharides (587.2 µg/ml), and fixed nitrogen which in turn increased both fresh and dry weights of bean plants by 41.5% and 18.8%, respectively. In another greenhouse experiment studying the antifungal activities of seven strains and their co-culture against Rhizoctonia solani (LN735538), B. sonorensis MN419205, B. wiedmannii MN419207, B. subtilis MN419218, and the mixture of (MN419207) and (MN419208) reduced total damping off from 81.7% in control to 30%, 35%, 35%, and 38.3%, respectively, and reduced disease severity index from 33.3% to 20.5%, 22.5%, 14.2%, and 19.3% as well. Our data indicate that these strains are effective in promoting plant growth and in inhibiting R. solani infection nonetheless field experiments are needed to examine their effectiveness as a viable alternative to chemical fertilizers and conventional pesticides.

Using nanoparticles from water treatment residuals to reduce the mobility and phytoavailability of Cd and Pb in biosolid-amended soils.

Heavy metal pollution in soils amended with biosolids has been a serious problem worldwide for clean food production. Laboratory and greenhouse experiments were performed to assess the impact of water treatment residual nanoparticles (nWTRs), at different application rates (0.1, 0.2 and 0.3%), on immobilization and phytoavailability of Cd and Pb to canola (Brassica napus L.) plants in soils amended with biosolids spiked with three different rates of Cd or Pb. Application of nWTRs significantly increased the residual fractions of Cd and Pb in metal-spiked biosolid-amended soil and thereby increased the immobilization of Cd and Pb in the amended soil. The greatest immobilization of Cd and Pb was exhibited at an application rate of 0.3% nWTRs. In addition, the application of nanoparticles to the biosolid-amended soil significantly increased canola grain yield and significantly decreased Cd and Pb phytoavailability due to immobilization of Cd and Pb in the contaminated soil. The results demonstrate, for the first time, the capability of nanoscale WTRs in stabilizing heavy metals in contaminated soils and restoring degraded agricultural land.

Isolation and Characterization of a Novel Imidacloprid-Degrading Mycobacterium sp. Strain MK6 from an Egyptian Soil.

Thus far, only a small number and types of bacteria with limited ability in degrading imidacloprid have been reported. Also, genes regulating imidacloprid (IMDA) degradation have yet to be discovered. To study this in more detail, an enrichment technique was used to isolate consortia and pure cultures of IMDA-degrading bacteria. Through this approach, we successfully isolated a novel bacterium capable of completely degrading IMDA as a sole nitrogen source. The bacterium was subsequently identified as Mycobacterium sp. strain MK6 by sequence analysis of its 16S rRNA gene (Genbank accession number KR052814 ). BLASTn searches indicated that 16S rRNA gene from Mycobacterium sp. strain MK6 was 99% identical to several Mycobacterium spp. Mycobacterium sp. strain MK6 transformed 99.7% added IMDA (150 µg mL(-1)) in <2 weeks (t1/2 = 1.6 days) to 6-chloronicotinic acid (6-CNA) as its major metabolite. Although the isolated strain and mixed bacterial consortia were able to degrade IMDA, they failed to grow further on 6-CNA, indicating a lack of IMDA mineralization to carbon dioxide. Small amounts of the desnitro-olefin and desnitro-degradates of IMDA were observed during the incubation but did not accumulate in culture medium.

Sorption-desorption of imidacloprid onto a lacustrine Egyptian soil and its clay and humic acid fractions.

Sorption-desorption of the insecticide imidacloprid 1-[(6-chloro-3-pyridinyl)-methyl]-N-nitro-2-imidazolidinimine onto a lacustrine sandy clay loam Egyptian soil and its clay and humic acid (HA) fractions was investigated in 24-h batch equilibrium experiments. Imidacloprid (IMDA) sorption-desorption isotherms onto the three sorbents were found to belong to a non-linear L-type and were best described by the Freundlich model. The value of the IMDA adsorption distribution coefficient, Kd(ads), varied according to its initial concentration and was ranged 40-84 for HA, 14-58 for clay and 1.85-4.15 for bulk soil. Freundlich sorption coefficient, Kf(ads), values were 63.0, 39.7 and 4.0 for HA, clay and bulk soil, respectively. The normalized soil Koc value for imidacloprid sorption was ∼800 indicating its slight mobility in soils. Nonlinear sorption isotherms were indicated by 1/n(ads) values <1 for all sorbents. Values of the hysteresis index (H) were <1, indicating the irreversibility of imidacloprid sorption process with all tested sorbents. Gibbs free energy (ΔG) values indicated a spontaneous and physicosorption process for IMDA and a more favorable sorption to HA than clay and soil. In conclusion, although the humic acid fraction showed the highest capacity and affinity for imidacloprid sorption, the clay fraction contributed to approximately 95% of soil-sorbed insecticide. Clay and humic acid fractions were found to be the major two factors controlling IMDA sorption in soils. The slight mobility of IMDA in soils and the hysteresis phenomenon associated with the irreversibility of its sorption onto, mainly, clay and organic matter of soils make its leachability unlikely to occur.