Limits...
Siderophore-Mediated Iron Dissolution from Nontronites Is Controlled by Mineral Cristallochemistry.

Parrello D, Zegeye A, Mustin C, Billard P - Front Microbiol (2016)

Bottom Line: Both nontronites released Fe in a particle concentration-dependent manner when incubated with the wild-type P. aeruginosa strain, however iron released from NAu-2 was substantially greater than from NAu-1.The structural Fe present on the edges of NAu-2 rather than NAu-1 particles appears to be more bio-accessible, indicating that the distribution of Fe, in the tetrahedron and/or in the octahedron sites, governs the solubilisation process.Furthermore, we also revealed that P. aeruginosa could acquire iron when in direct contact with mineral particles in a siderophore-independent manner.

View Article: PubMed Central - PubMed

Affiliation: Laboratoire Interdisciplinaire des Environnements Continentaux, UMR 7360 Centre National de la Recherche Scientifique - Université de LorraineVandœuvre-lès-Nancy, France; Civil and Environmental Engineering, University of MissouriColumbia, MO, USA.

ABSTRACT
Bacteria living in oxic environments experience iron deficiency due to limited solubility and slow dissolution kinetics of iron-bearing minerals. To cope with iron deprivation, aerobic bacteria have evolved various strategies, including release of siderophores or other organic acids that scavenge external Fe(III) and deliver it to the cells. This research investigated the role of siderophores produced by Pseudomonas aeruginosa in the acquisition of Fe(III) from two iron-bearing colloidal nontronites (NAu-1 and NAu-2), comparing differences in bioavailability related with site occupancy and distribution of Fe(III) in the two lattices. To avoid both the direct contact of the mineral colloids with the bacterial cells and the uncontrolled particle aggregation, nontronite suspensions were homogenously dispersed in a porous silica gel before the dissolution experiments. A multiparametric approach coupling UV-vis spectroscopy and spectral decomposition algorithm was implemented to monitor simultaneously the solubilisation of Fe and the production of pyoverdine in microplate-based batch experiments. Both nontronites released Fe in a particle concentration-dependent manner when incubated with the wild-type P. aeruginosa strain, however iron released from NAu-2 was substantially greater than from NAu-1. The profile of organic acids produced in both cases was similar and may not account for the difference in the iron dissolution efficiency. In contrast, a pyoverdine-deficient mutant was unable to mobilize Fe(III) from either nontronite, whereas iron dissolution occurred in abiotic experiments conducted with purified pyoverdine. Overall, our data provide evidence that P. aeruginosa indirectly mobilize Fe from nontronites primarily through the production of pyoverdine. The structural Fe present on the edges of NAu-2 rather than NAu-1 particles appears to be more bio-accessible, indicating that the distribution of Fe, in the tetrahedron and/or in the octahedron sites, governs the solubilisation process. Furthermore, we also revealed that P. aeruginosa could acquire iron when in direct contact with mineral particles in a siderophore-independent manner.

No MeSH data available.


Related in: MedlinePlus

Time profiles of acetate (A), methanoate (B), and oxalate (C) production by PAO1 WT (filled symbols) and PAO1 ΔpvdA (empty symbols) in a medium containing NAu-1 (squares) and NAu-2 (circles). Values are means of triplicate measurements.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4814481&req=5

Figure 3: Time profiles of acetate (A), methanoate (B), and oxalate (C) production by PAO1 WT (filled symbols) and PAO1 ΔpvdA (empty symbols) in a medium containing NAu-1 (squares) and NAu-2 (circles). Values are means of triplicate measurements.

Mentions: As shown previously, bacteria can close the concentration gap between mineral solubility and Fe requirement by solubilizing partially iron containing minerals. This process can be achieved by lowering the external pH and/or by the excretion of low molecular weight organic acids able chelate iron (Balland et al., 2010). The analysis of the culture media during the incubation time revealed the presence of oxalate, methanoate, and acetate (Figure 3). Acetate was the main organic molecule released, up to 340 mg L−1, while less than 10 mg L−1 of oxalate was present in the media. The results point out that PAO1 WT and PAO1 ΔpvdA produced the same low molecular weight organic molecules regardless the crystallographic structure of nontronite (NAu-1 vs. NAu-2). Despite some variations in organic acids profiles (e.g., higher level of acetate released by PAO1 ΔpvdA compared to the wild-type strain; Figure 3A), the solubilisation of iron cannot be attributed solely to the production of these organic compounds as no Fe was detected in the assays run with PAO1 ΔpvdA. However, we cannot rule out the possibility that they play a role in the dissolution process in the presence of siderophores. Indeed, it has been proposed that oxalate act in conjunction with siderophores and such synergic effect facilitates the dissolution of Fe from sparingly soluble minerals (Kraemer, 2004; Dehner et al., 2010).


Siderophore-Mediated Iron Dissolution from Nontronites Is Controlled by Mineral Cristallochemistry.

Parrello D, Zegeye A, Mustin C, Billard P - Front Microbiol (2016)

Time profiles of acetate (A), methanoate (B), and oxalate (C) production by PAO1 WT (filled symbols) and PAO1 ΔpvdA (empty symbols) in a medium containing NAu-1 (squares) and NAu-2 (circles). Values are means of triplicate measurements.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4814481&req=5

Figure 3: Time profiles of acetate (A), methanoate (B), and oxalate (C) production by PAO1 WT (filled symbols) and PAO1 ΔpvdA (empty symbols) in a medium containing NAu-1 (squares) and NAu-2 (circles). Values are means of triplicate measurements.
Mentions: As shown previously, bacteria can close the concentration gap between mineral solubility and Fe requirement by solubilizing partially iron containing minerals. This process can be achieved by lowering the external pH and/or by the excretion of low molecular weight organic acids able chelate iron (Balland et al., 2010). The analysis of the culture media during the incubation time revealed the presence of oxalate, methanoate, and acetate (Figure 3). Acetate was the main organic molecule released, up to 340 mg L−1, while less than 10 mg L−1 of oxalate was present in the media. The results point out that PAO1 WT and PAO1 ΔpvdA produced the same low molecular weight organic molecules regardless the crystallographic structure of nontronite (NAu-1 vs. NAu-2). Despite some variations in organic acids profiles (e.g., higher level of acetate released by PAO1 ΔpvdA compared to the wild-type strain; Figure 3A), the solubilisation of iron cannot be attributed solely to the production of these organic compounds as no Fe was detected in the assays run with PAO1 ΔpvdA. However, we cannot rule out the possibility that they play a role in the dissolution process in the presence of siderophores. Indeed, it has been proposed that oxalate act in conjunction with siderophores and such synergic effect facilitates the dissolution of Fe from sparingly soluble minerals (Kraemer, 2004; Dehner et al., 2010).

Bottom Line: Both nontronites released Fe in a particle concentration-dependent manner when incubated with the wild-type P. aeruginosa strain, however iron released from NAu-2 was substantially greater than from NAu-1.The structural Fe present on the edges of NAu-2 rather than NAu-1 particles appears to be more bio-accessible, indicating that the distribution of Fe, in the tetrahedron and/or in the octahedron sites, governs the solubilisation process.Furthermore, we also revealed that P. aeruginosa could acquire iron when in direct contact with mineral particles in a siderophore-independent manner.

View Article: PubMed Central - PubMed

Affiliation: Laboratoire Interdisciplinaire des Environnements Continentaux, UMR 7360 Centre National de la Recherche Scientifique - Université de LorraineVandœuvre-lès-Nancy, France; Civil and Environmental Engineering, University of MissouriColumbia, MO, USA.

ABSTRACT
Bacteria living in oxic environments experience iron deficiency due to limited solubility and slow dissolution kinetics of iron-bearing minerals. To cope with iron deprivation, aerobic bacteria have evolved various strategies, including release of siderophores or other organic acids that scavenge external Fe(III) and deliver it to the cells. This research investigated the role of siderophores produced by Pseudomonas aeruginosa in the acquisition of Fe(III) from two iron-bearing colloidal nontronites (NAu-1 and NAu-2), comparing differences in bioavailability related with site occupancy and distribution of Fe(III) in the two lattices. To avoid both the direct contact of the mineral colloids with the bacterial cells and the uncontrolled particle aggregation, nontronite suspensions were homogenously dispersed in a porous silica gel before the dissolution experiments. A multiparametric approach coupling UV-vis spectroscopy and spectral decomposition algorithm was implemented to monitor simultaneously the solubilisation of Fe and the production of pyoverdine in microplate-based batch experiments. Both nontronites released Fe in a particle concentration-dependent manner when incubated with the wild-type P. aeruginosa strain, however iron released from NAu-2 was substantially greater than from NAu-1. The profile of organic acids produced in both cases was similar and may not account for the difference in the iron dissolution efficiency. In contrast, a pyoverdine-deficient mutant was unable to mobilize Fe(III) from either nontronite, whereas iron dissolution occurred in abiotic experiments conducted with purified pyoverdine. Overall, our data provide evidence that P. aeruginosa indirectly mobilize Fe from nontronites primarily through the production of pyoverdine. The structural Fe present on the edges of NAu-2 rather than NAu-1 particles appears to be more bio-accessible, indicating that the distribution of Fe, in the tetrahedron and/or in the octahedron sites, governs the solubilisation process. Furthermore, we also revealed that P. aeruginosa could acquire iron when in direct contact with mineral particles in a siderophore-independent manner.

No MeSH data available.


Related in: MedlinePlus