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A Comparative Study of Iron Uptake Rates and Mechanisms amongst Marine and Fresh Water Cyanobacteria: Prevalence of Reductive Iron Uptake.

Lis H, Kranzler C, Keren N, Shaked Y - Life (Basel) (2015)

Bottom Line: Uniformity in kin/SA suggests similarity in the mechanism of uptake and indeed, all strains were found to employ a reductive step in the uptake of Fe' and FOB.In contrast, different uptake pathways were found for FeAB along with variations in kin/SA.Cyanobacteria combining both uptake strategies benefit from increased flexibility in accessing different Fe-substrates.

View Article: PubMed Central - PubMed

Affiliation: Interuniversity Institute for Marine Sciences in Eilat, Israel. hagarlis@gmail.com.

ABSTRACT
In this contribution, we address the question of iron bioavailability to cyanobacteria by measuring Fe uptake rates and probing for a reductive uptake pathway in diverse cyanobacterial species. We examined three Fe-substrates: dissolved inorganic iron (Fe') and the Fe-siderophores Ferrioxamine B (FOB) and FeAerobactin (FeAB). In order to compare across substrates and strains, we extracted uptake rate constants (kin = uptake rate/[Fe-substrate]). Fe' was the most bioavailable Fe form to cyanobacteria, with kin values higher than those of other substrates. When accounting for surface area (SA), all strains acquired Fe' at similar rates, as their kin/SA were similar. We also observed homogeneity in the uptake of FOB among strains, but with 10,000 times lower kin/SA values than Fe'. Uniformity in kin/SA suggests similarity in the mechanism of uptake and indeed, all strains were found to employ a reductive step in the uptake of Fe' and FOB. In contrast, different uptake pathways were found for FeAB along with variations in kin/SA. Our data supports the existence of a common reductive Fe uptake pathway amongst cyanobacteria, functioning alone or in addition to siderophore-mediated uptake. Cyanobacteria combining both uptake strategies benefit from increased flexibility in accessing different Fe-substrates.

No MeSH data available.


Related in: MedlinePlus

Dissolved inorganic iron (Fe') uptake rate constants (kin = uptake rate/ [Fe']) of Fe-limited cyanobacteria as a function of cell surface area (μm2) on a log-log plot. Each data point represents averaged rate constants from a single study for a single organism. Due to ionic strength differences in the media, only marine species are included in the linear regression analysis. * Crocospherawatsonii WH8501 data was taken from Jacq et al. [46]; all other data points were taken from studies conducted in our laboratory. Uptake rates for Anabaena and Prochlorococcus were normalized to per cell using conversion factors of 158 and 1.4 fg·Chl-a cell−1 respectively.
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life-05-00841-f002: Dissolved inorganic iron (Fe') uptake rate constants (kin = uptake rate/ [Fe']) of Fe-limited cyanobacteria as a function of cell surface area (μm2) on a log-log plot. Each data point represents averaged rate constants from a single study for a single organism. Due to ionic strength differences in the media, only marine species are included in the linear regression analysis. * Crocospherawatsonii WH8501 data was taken from Jacq et al. [46]; all other data points were taken from studies conducted in our laboratory. Uptake rates for Anabaena and Prochlorococcus were normalized to per cell using conversion factors of 158 and 1.4 fg·Chl-a cell−1 respectively.

Mentions: In order to allow comparison between experiments conducted at different iron concentrations, we normalized the uptake rate to [Fe'] (see Equation (1)). The resultant Fe' uptake rate constants (kin) of Fe-limited cyanobacteria extend over two orders of magnitude. Very large species such as Trichodesmium and Anabaena exhibit rate constants of ~10−8 L·cell−1·h−1, while the much smaller open ocean Prochlorococcus and Synechococcus species exhibit constants of ~10−10 L·cell−1·h−1. To examine whether variation in uptake rate constants reflect a difference in the uptake abilities of the various strains or simply a difference in their sizes, we plotted kin values for Fe' as a function of cell surface area (Figure 2). Data points for fresh and brackish water strains (grey symbols) fall above those for marine strains (black symbols). The difference between the two groups may be put down to the higher chemical activity of Fe' in the lower ionic strength media. We estimate that the presence of major ions such as sulphate and chloride at high concentrations in synthetic sea water media may affect the availability of Fe' at the cell surface, resulting in slightly decreased kin values as opposed to the fresh water media. Normalization to the activity coefficients according to Millero and Pierrot [45] greatly reduces scatter between seawater and fresh water data points and places them all along the same straight line (Figure S5). These differences notwithstanding, Figure 2 shows a linear correlation between the cell surface areas and Fe' uptake rate constants of the marine cyanobacterial strains. Forcing the trend line through the origin changes neither the slope nor the correlation co-efficient significantly (y = 7.210 × 10−11, r2 = 0.99), indicating direct proportionality between cell surface area and the Fe' uptake rate constants of cyanobacteria.


A Comparative Study of Iron Uptake Rates and Mechanisms amongst Marine and Fresh Water Cyanobacteria: Prevalence of Reductive Iron Uptake.

Lis H, Kranzler C, Keren N, Shaked Y - Life (Basel) (2015)

Dissolved inorganic iron (Fe') uptake rate constants (kin = uptake rate/ [Fe']) of Fe-limited cyanobacteria as a function of cell surface area (μm2) on a log-log plot. Each data point represents averaged rate constants from a single study for a single organism. Due to ionic strength differences in the media, only marine species are included in the linear regression analysis. * Crocospherawatsonii WH8501 data was taken from Jacq et al. [46]; all other data points were taken from studies conducted in our laboratory. Uptake rates for Anabaena and Prochlorococcus were normalized to per cell using conversion factors of 158 and 1.4 fg·Chl-a cell−1 respectively.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4390881&req=5

life-05-00841-f002: Dissolved inorganic iron (Fe') uptake rate constants (kin = uptake rate/ [Fe']) of Fe-limited cyanobacteria as a function of cell surface area (μm2) on a log-log plot. Each data point represents averaged rate constants from a single study for a single organism. Due to ionic strength differences in the media, only marine species are included in the linear regression analysis. * Crocospherawatsonii WH8501 data was taken from Jacq et al. [46]; all other data points were taken from studies conducted in our laboratory. Uptake rates for Anabaena and Prochlorococcus were normalized to per cell using conversion factors of 158 and 1.4 fg·Chl-a cell−1 respectively.
Mentions: In order to allow comparison between experiments conducted at different iron concentrations, we normalized the uptake rate to [Fe'] (see Equation (1)). The resultant Fe' uptake rate constants (kin) of Fe-limited cyanobacteria extend over two orders of magnitude. Very large species such as Trichodesmium and Anabaena exhibit rate constants of ~10−8 L·cell−1·h−1, while the much smaller open ocean Prochlorococcus and Synechococcus species exhibit constants of ~10−10 L·cell−1·h−1. To examine whether variation in uptake rate constants reflect a difference in the uptake abilities of the various strains or simply a difference in their sizes, we plotted kin values for Fe' as a function of cell surface area (Figure 2). Data points for fresh and brackish water strains (grey symbols) fall above those for marine strains (black symbols). The difference between the two groups may be put down to the higher chemical activity of Fe' in the lower ionic strength media. We estimate that the presence of major ions such as sulphate and chloride at high concentrations in synthetic sea water media may affect the availability of Fe' at the cell surface, resulting in slightly decreased kin values as opposed to the fresh water media. Normalization to the activity coefficients according to Millero and Pierrot [45] greatly reduces scatter between seawater and fresh water data points and places them all along the same straight line (Figure S5). These differences notwithstanding, Figure 2 shows a linear correlation between the cell surface areas and Fe' uptake rate constants of the marine cyanobacterial strains. Forcing the trend line through the origin changes neither the slope nor the correlation co-efficient significantly (y = 7.210 × 10−11, r2 = 0.99), indicating direct proportionality between cell surface area and the Fe' uptake rate constants of cyanobacteria.

Bottom Line: Uniformity in kin/SA suggests similarity in the mechanism of uptake and indeed, all strains were found to employ a reductive step in the uptake of Fe' and FOB.In contrast, different uptake pathways were found for FeAB along with variations in kin/SA.Cyanobacteria combining both uptake strategies benefit from increased flexibility in accessing different Fe-substrates.

View Article: PubMed Central - PubMed

Affiliation: Interuniversity Institute for Marine Sciences in Eilat, Israel. hagarlis@gmail.com.

ABSTRACT
In this contribution, we address the question of iron bioavailability to cyanobacteria by measuring Fe uptake rates and probing for a reductive uptake pathway in diverse cyanobacterial species. We examined three Fe-substrates: dissolved inorganic iron (Fe') and the Fe-siderophores Ferrioxamine B (FOB) and FeAerobactin (FeAB). In order to compare across substrates and strains, we extracted uptake rate constants (kin = uptake rate/[Fe-substrate]). Fe' was the most bioavailable Fe form to cyanobacteria, with kin values higher than those of other substrates. When accounting for surface area (SA), all strains acquired Fe' at similar rates, as their kin/SA were similar. We also observed homogeneity in the uptake of FOB among strains, but with 10,000 times lower kin/SA values than Fe'. Uniformity in kin/SA suggests similarity in the mechanism of uptake and indeed, all strains were found to employ a reductive step in the uptake of Fe' and FOB. In contrast, different uptake pathways were found for FeAB along with variations in kin/SA. Our data supports the existence of a common reductive Fe uptake pathway amongst cyanobacteria, functioning alone or in addition to siderophore-mediated uptake. Cyanobacteria combining both uptake strategies benefit from increased flexibility in accessing different Fe-substrates.

No MeSH data available.


Related in: MedlinePlus