The Aquila Digital Community Biocontrol and Plant Growth-Promoting Activity of Rhizobacteria From Chinese Fields With Contaminatd Soils

The aim of this study was to inventory the types of plant growth-promoting rhizobacteria (PGPR) present in the rhizosphere of plants grown in soils contaminated with heavy metals, recalcitrant organ-ics, petroleum sewage or salinity in China. We screened 1223 isolates for antifungal activity and about 24% inhibited Rhizoctonia solani or Sclerotinia sclerotiorum . Twenty-four strains inhibitory to R. solani , Gaeumannomyces graminis var. tritici and/or S. sclerotiorum and representing the dominant morphotypes were assayed for PGPR activity. Seven strains contained phlD , prnD , pltC or phzF genes and produced the antibiotics 2,4-diacetylphloroglucinol, pyrrolnitrin, pyoluteorin and phenazines respectively. Six strains contained acdS , which encodes 1-aminocyclopropane-1-carboxylic acid deaminase. Phylogenetic analysis of 16S rDNA and phlD , phzF and acdS genes demonstrated that some strains identified as Pseudomonas were similar to model PGPR Pseudomonas protegens Pf-5, Pseudomonas chlororaphis subsp. aureofaciens 30–84 and P. brassicacearum Q8r1-96. Pseudomonas protegens- and P. chlororaphis- like strains had the greatest biocontrol activity against Rhizoctonia root rot and take-all of wheat. Pseudomonas protegens and P. brassicacearum- like strains showed the greatest promotion of canola growth. Our results indicate that strains from contaminated soils are similar to well-described PGPR found in agricultural soils worldwide. tests for starch hydrolysis, gelatin liquefaction, catalase production, pectin decomposition, indole production and production of phenazine-1-carboxylic acid, 2,4-DAPG, pyrrolnitrin and pyoluteorin. Cellulase activity was determined on carboxy-methylcellulose (CMC) medium (per 1 l: peptone, 10 g; yeast extract, 10 g; sodium CMC, 10 g; NaCl, 5 g; KH 2 PO 4, 1 g; agar, 15 g; pH 7.0). A 10 μ l aliquot of an overnight bacterial was on filter paper (5 mm diameter, 0.5 mm thick) on the surface of CMC agar. To visualize the zone of hydrolysis, plates were incubated at 28°C for 48 h, flooded with an aqueous solution of 0.1% Congo red for 1 h and washed with 1 M NaCl (Ghose, 1987). Protease activity, demonstrated by casein degradation, was indicated by the appearances of zones of clearing around colonies grown on milk agar (per 1 l: dry skim milk, 100 g; agar, 20 g) after incubation at 28°C for 3 days. Siderophores were detected on CAS (chrome azurols) agar plates (Shin et al ., 2011). Antibiotics (phenazine-1-carboxylic acid, pyrrolnitrin, pyoluteorin and DAPG) were isolated from bacterial cultures grown for 5 days on KMB agar by a modification of procedures described by Kraus and Loper (1992). Briefly, cells and spent agar ( c with a and pestle in an equal of acetone. The acetone was evaporated in a hood aqueous