Siderophores mediate reduced and increased uptake of cadmium byStreptomyces tendaeF4 and sunflower (Helianthus annuus), respectively

Abstract

Aims: As a toxic metal, cadmium (Cd) affects microbial and plant metabolic processes, thereby potentially reducing the efficiency of microbe or plant‐mediated remediation of Cd‐polluted soil. The role of siderophores produced by Streptomyces tendae F4 in the uptake of Cd by bacteria and plant was investigated to gain insight into the influence of siderophores on Cd availability to micro‐organisms and plants. Methods and Results: The bacterium was cultured under siderophore‐inducing conditions in the presence of Cd. The kinetics of siderophore production and identification of the siderophores and their metal‐bound forms were performed using electrospray ionization mass spectrometry. Inductively coupled plasma spectroscopy was used to measure iron (Fe) and Cd contents in the bacterium and in sunflower plant grown in Cd‐amended soil. Siderophores significantly reduced the Cd uptake by the bacterium, while supplying it with iron. Bacterial culture filtrates containing three hydroxamate siderophores secreted by S. tendae F4 significantly promoted plant growth and enhanced uptake of Cd and Fe by the plant, relative to the control. Furthermore, application of siderophores caused slightly more Cd, but similar Fe uptake, compared with EDTA. Bioinoculation with Streptomyces caused a dramatic increase in plant Fe content, but resulted only in slight increase in plant Cd content. Conclusion: It is concluded that siderophores can help reduce toxic metal uptake in bacteria, while simultaneously facilitating the uptake of such metals by plants. Also, EDTA is not superior to hydroxamate siderophores in terms of metal solubilization for plant uptake. Significance and Impact of the Study: The study showed that microbial processes could indirectly influence the availability and amount of toxic metals taken up from the rhizosphere of plants. Furthermore, although EDTA is used for chelator‐enhanced phytoremediation, microbial siderophores would be ideal for this purpose.

Survival Strategies of the Plant-Associated Bacterium Enterobacter sp. Strain EG16 under Cadmium Stress

“…4a and b). This result suggests that EG16 cells exposed to Cd have an increased requirement for Fe, which may help to counteract Cd toxicity (23).…”

“…Microbes have developed several metal resistance mechanisms in response to heavy metal stress, including intracellular and/or extracellular sequestration, efflux systems to export excess metal ions from bacterial cells, and the transformation of metals into a less toxic form by enzymatic detoxification (23)(24)(25)(26). It has been widely accepted that in the model bacterium Cupriavidus metallidurans, these mechanisms appear to be cooperative, not metal specific, and are controlled by a complex regulatory network involving several clusters of genes and functions (1,27).…”

<i>Bacillus subtilis Strains</i> with Antifungal Activity against the Phytopathogenic Fungi

“…It was suggested that the synthesis of siderophores is associated with growth-promoting and antagonistic activity against phytopathogens [3]. In the soil, ability to produce siderophores plays a central role in the capacity of different bacteria to promote plant development due to increasing the iron absorption by plants and defense of plants from toxic metals such as nickel and cadmium [39] [40]. The antagonism against pathogenic bacteria and fungi is based on the iron binding by sidero-phore-producing bacteria that limits iron availability for other microorganisms and primarily for phytopathogenic micromycetes [41].…”

Effects of EDDS and plant-growth-promoting bacteria on plant uptake of trace metals and PCBs from e-waste–contaminated soil

“…This result is consistent with a previous report that EDDS was most effective in terms of solubilizing soil Cu for root uptake and translocation into aboveground biomass [17,19]. The high root concentration of metals (Cu or Zn) in the DGS6 + EDDS treatment group could be the result of: (1) the high biomass and the presence of dissolved metals in the soil solution, which would increase the root volume and allow roots to adsorb more metals; and (2) siderophores produced by the inoculant DGS6, which would solubilize metals and facilitate metal uptake by plant roots [29,36]. In the present study, the plant tissues were washed with only DIW before freeze drying instead of being soaked in solution (such as CaCl 2 ) to dissolve metals bound to the cell walls, which would contribute to the root uptake of metals.…”