Zn ²⁺ Increases Siderophore Production in Azotobacter vinelandii

Abstract

When Azotobacter vinelandii was grown in the presence of low levels of iron, the addition of 20 or 40 ,uM ZnSO4 caused earlier production of the catechol siderophores and a dramatic increase in the amount of azotobactin. The level of cellular iron was not significantly lowered in Zn2+-grown cells, which suggested that Zn2+ was not causing more severe, or earlier, iron limitation. Also, Zn2+ did not appear to affect production of the high-molecular-weight outer membrane iron-repressible proteins that presumably function as ferrisiderophore receptors. Spectrophotometric examination of ion binding to the siderophores revealed that while the siderophores appeared to bind Zn2+, only in the case of azotochelin was iron unable to completely overcome any Zn2+-induced changes in the absorption spectra. This appeared to rule out direct competition of Zn2+ with iron for binding to the siderophores. 55Fe uptake was depressed both in Zn2-grown cells and in Zn2-free cells to which Zn2+ was added during the uptake assay, except with azotobactin, with which the level of 55Fe uptake by Zn2+-grown cells was close to control levels. These results suggested two possible sites where Zn2+ could be acting, one involving the biosynthesis of siderophores and possibly the genetic regulation of the iron assimilation system and the other involving an internal point common to iron assimilation by both highand low-affinity iron uptake.

New insights into the metal specificity of the Pseudomonas aeruginosa pyoverdine–iron uptake pathway

“…The presence of metals other than iron is known to stimulate siderophore production in a number of bacteria and fungi (Huyer and Page, 1988;Hofte et al, 1993;Hu and Boyer, 1996). Our data have shown that the presence of Al 3+ , Cu 2+ , Ga 3+ , Mn 2+ , Ni 2+ and Zn 2+ in the culture medium induced PvdI production ( Fig.…”

“…Heavy metals enter the periplasm of Gram-negative bacteria mostly by diffusion; thus, the binding of heavy metal to siderophore dramatically changes the free metal concentration, affecting this diffusion process. Moreover, previous studies in a number of bacteria and fungi show that metals other than iron stimulate siderophore production (Huyer and Page, 1988;Hofte et al, 1993;Hu and Boyer, 1996). This stimulation of siderophore production may protect the bacteria against metal toxicity: the metal is sequestered in the extracellular medium by the siderophore and is thus no longer able to enter the bacterium by diffusion.…”

“…The presence of metals other than iron is known to stimulate siderophore production in a number of bacteria and fungi (Chakrabarty and Roy, 1964;Huyer and Page, 1988;Hofte et al, 1993). This property was investigated for all the metals tested in our screening (Fig.…”

Azotobacter vinelandii gene clusters for two types of peptidic and catechol siderophores produced in response to molybdenum

“…4c). In combination with previous studies (Huyer and Page 1988;Kraepiel et al 2009), molybdenum as well as iron may regulate the siderophore content to effectively express the nitrogenases activity.…”

“…1) (Schaffner et al 1996). Previously published reports indicate that both the iron concentration and composition in the growth media are crucial for the bacterial production of siderophores (Huyer and Page 1988;Kraepiel et al 2009). In this study, molybdenum, which is required for typical nitrogenases, was also found to affect the production of siderophores.…”