Identification of a siderophore-producing bacterium Pseudomonas putida A3 and its growth-promoting effects on cucumber seedlings

Bacterial strain A3 with high ability of producing siderophore was isolated from rhizosphere of greenhouse vegetables. The relative siderophore content was measured by chrome azurol S (CAS) assay and was identified using the Shenkers test. The results show that the relative siderophore content is 93.40% and the type is a kind of carboxylate type siderophore. In addition, the strain A3 also has a high ability of solubilizing phosphate and is able to produce indol-3-acetic (IAA) and 1-aminocyclopropane-1-carboxylate (ACC) deaminase under different substrates. According to the morphological, physiological-biochemical properties, API system and the 16S rRNA sequence analysis, the strain A3 is identified as Pseudomonas putida. The results from solution culture experiments reveals that compared to other treatments, the growth of cucumber seedlings is increased under the treatment of siderophore filtrate of strain A3 with 50 mol/L FeCl3 in iron deficiency Hoagland solution, especially for shoot height, root length, leaf length, fresh mass and total leaf chlorophyll content. These may provide strong evidence that the siderophore produced by P. putida A3 is helpful to the growth promotion of cucumber seedlings under low iron conditions.