Laboratory culture experiments to study the effect of lignite humic acid fractions on iron solubility and iron uptake rates in phytoplankton

Many microorganisms secrete molecules that interact with resources outside of the cell. This includes, for example, enzymes that degrade polymers like chitin, and chelators that bind trace metals like iron. In contrast to direct uptake via the cell surface, such release strategies entail the risk of losing the secreted molecules to environmental sinks, including ‘cheating’ genotypes. Nevertheless, such secretion strategies are widespread, even in the well-mixed marine environment. Here, we investigate the benefits of a release strategy whose efficiency has frequently been questioned: iron uptake in the ocean by secretion of iron chelators called siderophores. We asked the question whether the release itself is essential for the function of siderophores, which could explain why this risky release strategy is widespread. We developed a reaction–diffusion model to determine the impact of siderophore release on iron uptake from the predominant iron sources in marine environments, colloidal or particulate iron, formed due to poor iron solubility. We found that release of siderophores is essential to accelerate iron uptake, as secreted siderophores transform slowly diffusing large iron particles to small, quickly diffusing iron–siderophore complexes. In addition, we found that cells can synergistically share their siderophores, depending on their distance and the size of the iron sources. Our study helps understand why release of siderophores is so widespread: even though a large fraction of siderophores is lost, the solubilization of iron through secreted siderophores can efficiently increase iron uptake, especially if siderophores are produced cooperatively by several cells. Overall, resource uptake mediated via release of molecules transforming their substrate could be essential to overcome diffusion limitation specifically in the cases of large, aggregated resources. In addition, we find that including the reaction of the released molecule with the substrate can impact the result of cooperative and competitive interactions, making our model also relevant for release-based uptake of other substrates.

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Humic acid and iron uptake by plants

Plant and Soil ◽

10.1007/bf02107217 ◽

1978 ◽

Vol 50 (1-3) ◽

pp. 663-670 ◽

Cited By ~ 21

Author(s):

D. J. Linehan

Keyword(s):

Humic Acid ◽

Iron Uptake

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Dietary ascorbic acid raises iron absorption in anaemic rats through enhancing mucosal iron uptake independent of iron solubility in the digesta

British Journal Of Nutrition ◽

10.1079/bjn19970014 ◽

1997 ◽

Vol 77 (1) ◽

pp. 123-131 ◽

Cited By ~ 17

Author(s):

K. J. H. Wienk ◽

J. J. M. Marx ◽

M. Santos ◽

A. G. Lemmens ◽

E. J. Brink ◽

...

Keyword(s):

Ascorbic Acid ◽

Iron Uptake ◽

Iron Absorption ◽

Iron Solubility ◽

Fe Uptake ◽

Isotope Technique ◽

Proximal Intestine ◽

Liquid And Solid Phases ◽

Double Isotope

We studied Fe absorption from FeSO4 in rats with Fe deficiency-induced anaemia that were given an Fe-sufficient purified diet without or with ascorbic acid (10·4 g/kg diet). Attention was focused on mucosal Fe uptake as measured in vivo by a double-isotope technique. Haemoglobin repletion and liver Fe levels were not affected when the ascorbic acid-supplemented diet was given, but apparent Fe absorption and retention of orally administered 59Fe were significantly enhanced. The distribution of Fe between liquid and solid phases of contents of both the stomach and the proximal intestine was not affected by the feeding of the ascorbic acid, but ascorbic acid significantly enhanced mucosal Fe uptake. It is concluded that ascorbic acid in the diet raises mucosal Fe uptake through a mechanism independent of the intestinal Fe solubility.

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Microbial iron uptake in the naturally fertilized waters in the vicinity of the Kerguelen Islands: phytoplankton–bacteria interactions

Biogeosciences ◽

10.5194/bg-12-1893-2015 ◽

2015 ◽

Vol 12 (6) ◽

pp. 1893-1906 ◽

Cited By ~ 15

Author(s):

M. Fourquez ◽

I. Obernosterer ◽

D. M. Davies ◽

T. W. Trull ◽

S. Blain

Keyword(s):

Microbial Community ◽

Iron Uptake ◽

Heterotrophic Bacteria ◽

Size Fraction ◽

Kerguelen Islands ◽

Carbon Cycles ◽

Carbon Biomass ◽

Uptake Rates ◽

Fe Uptake ◽

Tightly Coupled

Abstract. Iron (Fe) uptake by the microbial community and the contribution of three different size fractions was determined during spring phytoplankton blooms in the naturally Fe-fertilized area off the Kerguelen Islands (KEOPS2). Total Fe uptake in surface waters was on average 34 ± 6 pmol Fe L-1 d-1, and microplankton (> 25 μm size fraction; 40–69%) and pico-nanoplankton (0.8–25 μm size fraction; 29–59%) were the main contributors. The contribution of heterotrophic bacteria (0.2–0.8 μm size fraction) to total Fe uptake was low at all stations (1–2%). Iron uptake rates normalized to carbon biomass were highest for pico-nanoplankton above the Kerguelen Plateau and for microplankton in the downstream plume. We also investigated the potential competition between heterotrophic bacteria and phytoplankton for the access to Fe. Bacterial Fe uptake rates normalized to carbon biomass were highest in incubations with bacteria alone, and dropped in incubations containing other components of the microbial community. Interestingly, the decrease in bacterial Fe uptake rate (up to 26-fold) was most pronounced in incubations containing pico-nanoplankton and bacteria, while the bacterial Fe uptake was only reduced by 2- to 8-fold in incubations containing the whole community (bacteria + pico-nanoplankton + microplankton). In Fe-fertilized waters, the bacterial Fe uptake rates normalized to carbon biomass were positively correlated with primary production. Taken together, these results suggest that heterotrophic bacteria are outcompeted by small-sized phytoplankton cells for the access to Fe during the spring bloom development, most likely due to the limitation by organic matter. We conclude that the Fe and carbon cycles are tightly coupled and driven by a complex interplay of competition and synergy between different members of the microbial community.

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Spectroscopic and conformational properties of size-fractions separated from a lignite humic acid

Chemosphere ◽

10.1016/j.chemosphere.2007.04.043 ◽

2007 ◽

Vol 69 (7) ◽

pp. 1032-1039 ◽

Cited By ~ 43

Author(s):

Pellegrino Conte ◽

Riccardo Spaccini ◽

Daniela Šmejkalová ◽

Antonio Nebbioso ◽

Alessandro Piccolo

Keyword(s):

Humic Acid ◽

Size Fractions ◽

Conformational Properties ◽

Lignite Humic Acid

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Phosphate Uptake by Microorganisms in Lake Water: Deviations from Simple Michaelis–Menten Kinetics

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f86-041 ◽

1986 ◽

Vol 43 (2) ◽

pp. 319-328 ◽

Cited By ~ 10

Author(s):

Stephen J. Tarapchak ◽

Lynn R. Herche

Keyword(s):

Lake Michigan ◽

Simulation Analysis ◽

Phosphate Uptake ◽

Laboratory Culture ◽

Microbial Populations ◽

Culture Studies ◽

Equation Analysis ◽

Uptake Rates ◽

Order Of Magnitude ◽

Substrate Concentrations

Orthophosphate (31Pi) uptake rates by natural Lake Michigan microbial assemblages were measured to test a hypothesis that the instantaneous velocity of 31Pi uptake at low added substrate concentrations is higher than predicted by the simple Michaelis–Menten equation. Analysis of data from most experiments verified this prediction: 31Pi turnover times (Tcalc) obtained by back-extrapolating from "low" substrate regions in Woolf plots ranged from 25% to nearly 3000% of those calculated from "high" substrate regions. Simulation analysis demonstrated that deviations in Tcalc could be at least an order of magnitude higher than previously predicted. Large (>1000%) discrepancies from the simple Michaelis–Menten equation could be caused by "skewed" or "clumped" distributions, where the range in both species half-saturation constants (Kt) and relative abundances is very wide and species with the lowest Kt values are most abundant. A comparison of Kt values for mixed microbial assemblages in Lake Michigan (0.16–19.4 μg P∙L−1) with those from laboratory culture studies (11–364 μg P∙L−1) demonstrates that natural microbial populations have adapted to P-limited environments by synthesizing uptake systems that have Kt values at least an order of magnitude below those detected in culture studies.

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