Involvement of siderophores in the reduction of metal-induced inhibition of auxin synthesis in Streptomyces spp.

Abstract

Unlike synthetic metal chelators, microbe-assisted phytoremediation provides plants with natural metal-solubilizing chelators which do not constitute a potential source of environmental pollution. Concurrently with microbial chelators, plant growth promotion can be enhanced through bacterially-produced phytohormones. In this work, the simultaneous production of siderophores and auxins by Streptomyces was studied to gain insight for future application in plant growth and phytoremediation in a metal-contaminated soil. Standard auxin and siderophore detection assays indicated that all of the investigated Streptomyces strains can produce these metabolites simultaneously. However, Al(3+), Cd(2+), Cu(2+), Fe(3+) and Ni(2+), or a combination of Fe(3+) and Cd(2+), and Fe(3+) and Ni(2+) affected auxin production negatively, as revealed by spectrophotometry and gas chromatography-mass spectrometry. This effect was more dramatic in a siderophore-deficient mutant. In contrast, except for Fe, all the metals stimulated siderophore production. Mass spectrometry showed that siderophore and auxin-containing supernatants from a representative Streptomyces species contain three different hydroxamate siderophores, revealing the individual binding responses of these siderophores to Cd(2+) and Ni(2+), and thus, showing their auxin-stimulating effects. We conclude that siderophores promote auxin synthesis in the presence of Al(3+), Cd(2+), Cu(2+) and Ni(2+) by chelating these metals. Chelation makes the metals less able to inhibit the synthesis of auxins, and potentially increases the plant growth-promoting effects of auxins, which in turn enhances the phytoremediation potential of plants.

Biosynthesis and Secretion of Indole-3-Acetic Acid and Its Morphological Effects on Tricholoma vaccinum-Spruce Ectomycorrhiza

“…IAA concentrations were determined after T. vaccinum was cultivated in the dark at room temperature for about 4 weeks. Culture filtrates from three or four individual cultures, supplemented with labeled precursors, were sampled weekly and assessed by colorimetric quantification of IAA using a Salkowski assay (43) and gas chromatography-mass spectrometry (GC-MS) (44).…”

Bacterial biosynthesis of 1-aminocyclopropane-1-caboxylate (ACC) deaminase, a useful trait to elongation and endophytic colonization of the roots of rice under constant flooded conditions

“…Importance of IAA production in promoting root growth directly by stimulating plant cell elongation or indirectly by affecting bacterial ACC deaminase activity by PGPR has been greatly recognized (Kennedy et al 2004;Pedraza et al 2004). Similarly, role of phosphatesolubilizing bacteria in plant growth and development and the production of siderophores by PGPR especially under iron-limited conditions has been well documented (Ahmad et al 2008;Dimkpa et al 2008;Richardson et al 2009). One of the most PGP traits shown in many PGPR is to stimulate plant growth by the activity of ACC deaminase that promotes plant growth by decreasing plant ethylene levels.…”

Mecanismos de controle da murcha-de-esclerócio e promoção de crescimento em tomateiro mediados por rizobactérias

“…Sabe-se que parte deste ferro pode ser disponibilizado para as plantas (Glick, 1999) e que essas moléculas estimulam a produção de auxinas (Dimkpa et al, 2008), um hormônio também produzido pelos isolados RR31223 e RR33282. Além disso, os sideróforos têm um papel indireto na promoção de crescimento, pois reduzem a toxicidade causada às plantas por metais pesados (Burd et al, 2000).…”