A Pseudomonas sp. isolated from calcareous soil can tolerate stress by phenolic compounds exuded by red clover (Trifolium pratense L.) roots and secrete siderophores

摘要

Red clover (Trifolium pratense L. cv. kenland) has been reported to be an iron (Fe)-efficient plant and releases phenolic compounds in large quantities under iron deficiency. Since most phenolic compounds are toxic to many microorganisms they would have great impact on microbial communities in the rhizosphere of red clover. In the present study, one predominant bacterium was isolated from calcareous soils with root exudates collected from a hydroponic culture of red clover grown under iron-deficientconditions. This strain could not degrade or utilize phenol as a carbon source, but it tolerated phenol when present at up to 600 mg l~(-1). The 16S rDNA sequencing analysis identified the strain as belonging to the genus Pseudomonas. This strain can grow almost equally well in a Fe-free liquid culture medium as in a medium with FeCl_3 (10 mu M). Both CAS (Chrome azurol S) assay and iron-hydroxides solubilization tests showed that this strain secreted siderophore and solubilised iron from insoluble Fe(OH)_3. The potential utilization of this strain to overcome iron deficiency in alkaline soils will be discussed.