ABSTRACT This study aimed to explore the effects of two siderophore-producing bacterial strains on iron absorption and plant growth of peanut in calcareous soil. Two siderophore-producing bacterial strains, namely, YZ29 and DZ13, isolated from the rhizosphere soil of peanut, were identified as Paenibacillus illinoisensis and Bacillus sp., respectively. In potted experiments, YZ29 and DZ13 enhanced root activity, chlorophyll and active iron content in leaves, total nitrogen, phosphorus and potassium accumulation of plants and increased the quality of peanut kernels and plant biomass over control. In the field trial, the inoculated treatments performed better than the controls, and the pod yields of the three treatments inoculated with YZ29, DZ13, and YZ29 + DZ13 (1:1) increased by 37.05%, 13.80% and 13.57%, respectively, compared with the control. Based on terminal restriction fragment length polymorphism analysis, YZ29 and DZ13 improved the bacterial community richness and species diversity of soil surrounding the peanut roots. Therefore, YZ29 and DZ13 can be used as candidate bacterial strains to relieve chlorosis of peanut and promote peanut growth. The present study is the first to explore the effect of siderophores produced by P. illinoisensis on iron absorption.

A diversidade genética de bactérias de rizosfera de tabaco produtoras de sideróforos foi estudada por meio da técnica de análise de restrição do DNA ribossomal amplificado (ARDRA), homologia de seqüência de 16s rRNA e métodos de análise filogenética. Observou-se que 85% do total de 354 isolados produziram sideróforos em meio liquido com restrição de ferro. Entre os 299 isolados produtores de sideróforos identificou-se 28 padrões ARDRA, que representaram 14 gêneros bacterianos diferentes, pertencentes a seis divisões bacterianas: ?-, ?-, ?-Proteobacteria, Sphingobacteria, Bacilli e Actinobacteria. ?-Proteobacteria, consistindo de Pseudomonas, Enterobacter, Serratia, Pantoea, Erwinia e Stenotrophomonas, pertenceram a 18 grupos ARDRA. Os resultados também mostraram uma diversidade maior de bactérias produtoras de sideróforos do que a relatada em outros estudos. Por exemplo, Sphingobacterium (isolados G-2-21-1 e G-2-27-2), Pseudomonas poae (isolado G-2-1-1), Enterobacter endosymbiont (isolados G-2-10-2 e N-5-10), Delftia acidovorans (isolado G-1-15) e Achromobacter xylosoxidans (isolados N-46-1HH e N-5-20), capazes de produzir sideróforos em condições de baixa disponibilidade de ferro, foram relatados pela primeira vez. Isolados Gram negativos foram encontrados com maior freqüência, correspondendo a mais de 95% da freqüência total. Entre as bactérias Gram positivas, foram encontrados apenas os gêneros Bacillus e Rhodococcus, com 1,7% da freqüência total. Além disso, neste ambiente houve predominância de Pseudomonas e Enterobacter, com 44,5% e 24,7% da freqüência total, respectivamente. Verificou-se também que 75% dos isolados com alta porcentagem de unidades de sideróforos (% entre 40 e 60) pertenceram a Pseudomonas. Pseudomonas sp. G-229-21, selecionado neste estudo, apresenta potencial de aplicação em solos com baixo teor de ferro para prevenção de doenças fúngicas em plantas.

The genetic diversity of siderophore-producing bacteria of tobacco rhizosphere was studied by amplified ribosomal DNA restriction analysis (ARDRA), 16S rRNA sequence homology and phylogenetics analysis methods. Studies demonstrated that 85% of the total 354 isolates produced siderophores in iron limited liquid medium. A total of 28 ARDRA patterns were identified among the 299 siderophore-producing bacterial isolates. The 28 ARDRA patterns represented bacteria of 14 different genera belonging to six bacterial divisions, namely ?-, ?-, ?-Proteobacteria, Sphingobacteria, Bacilli,and Actinobacteria. Especially, ?-Proteobacteria consisting of Pseudomonas, Enterobacter, Serratia, Pantoea, Erwinia and Stenotrophomonasgenus encountered 18 different ARDRA groups. Results also showed a greater siderophore-producing bacterial diversity than previous researches. For example, Sphingobacterium (isolates G-2-21-1 and G-2-27-2), Pseudomonas poae (isolate G-2-1-1), Enterobacter endosymbiont (isolates G-2-10-2 and N-5-10), Delftia acidovorans (isolate G-1-15), and Achromobacter xylosoxidans (isolates N-46-11HH and N-5-20) were reported to be able to producesiderophores under low-iron conditions for the first time. Gram-negative isolates were more frequently encountered, with more than 95% total frequency. For Gram-positive bacteria, the Bacillus and Rhodococcus were the only two genera, with 1.7% total frequency. Furthermore, the Pseudomonas and Enterobacter were dominant in this environment, with 44.5% and 24.7% total frequency, respectively. It was also found that 75 percent of the isolates that had the high percentages of siderophore units (% between 40 and 60) belonged to Pseudomonas. Pseudomonas sp. G-229-21 screened out in this study may have potential to apply to low-iron soil to prevent plant soil-borne fungal pathogen diseases.