Nickel limitation and zinc toxicity in a urea‐grown diatom

Egleston, Eric S.; Morel, François M. M.

doi:10.4319/lo.2008.53.6.2462

Cited by 30 publications

(19 citation statements)

References 48 publications

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“…No significant difference in expression of the urease enzyme was detected between the Fe-replete and Fe-limited cultures. Although previous reports have observed the urease enzyme to be present under Fe and N limitation [19], [47], urease requires nickel (Ni) as a cofactor when processing urea [60], [61]. The Ni-ABC transporter (NikA) was identified to be the most down-regulated protein in Fe-limited cells (−2.87 fold; Table S2).…”

Section: Discussionmentioning

confidence: 96%

“…The Ni-ABC transporter (NikA) was identified to be the most down-regulated protein in Fe-limited cells (−2.87 fold; Table S2). Egleston and Morel [60] demonstrated that the presence of Ni is essential for urease when diatoms are using urea as their primary N source. The down-regulation of the Ni-transporting enzymes suggests that urease was not actively utilized and urea was not a primary N source during Fe limitation.…”

Section: Discussionmentioning

confidence: 99%

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Diatom Proteomics Reveals Unique Acclimation Strategies to Mitigate Fe Limitation

et al. 2013

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Phytoplankton growth rates are limited by the supply of iron (Fe) in approximately one third of the open ocean, with major implications for carbon dioxide sequestration and carbon (C) biogeochemistry. To date, understanding how alteration of Fe supply changes phytoplankton physiology has focused on traditional metrics such as growth rate, elemental composition, and biophysical measurements such as photosynthetic competence (Fv/Fm). Researchers have subsequently employed transcriptomics to probe relationships between changes in Fe supply and phytoplankton physiology. Recently, studies have investigated longer-term (i.e. following acclimation) responses of phytoplankton to various Fe conditions. In the present study, the coastal diatom, Thalassiosira pseudonana, was acclimated (10 generations) to either low or high Fe conditions, i.e. Fe-limiting and Fe-replete. Quantitative proteomics and a newly developed proteomic profiling technique that identifies low abundance proteins were employed to examine the full complement of expressed proteins and consequently the metabolic pathways utilized by the diatom under the two Fe conditions. A total of 1850 proteins were confidently identified, nearly tripling previous identifications made from differential expression in diatoms. Given sufficient time to acclimate to Fe limitation, T. pseudonana up-regulates proteins involved in pathways associated with intracellular protein recycling, thereby decreasing dependence on extracellular nitrogen (N), C and Fe. The relative increase in the abundance of photorespiration and pentose phosphate pathway proteins reveal novel metabolic shifts, which create substrates that could support other well-established physiological responses, such as heavily silicified frustules observed for Fe-limited diatoms. Here, we discovered that proteins and hence pathways observed to be down-regulated in short-term Fe starvation studies are constitutively expressed when T. pseudonana is acclimated (i.e., nitrate and nitrite transporters, Photosystem II and Photosystem I complexes). Acclimation of the diatom to the desired Fe conditions and the comprehensive proteomic approach provides a more robust interpretation of this dynamic proteome than previous studies.

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Section: Discussionmentioning

confidence: 96%

Section: Discussionmentioning

confidence: 99%

Diatom Proteomics Reveals Unique Acclimation Strategies to Mitigate Fe Limitation

et al. 2013

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“…In surface waters, Ni speciation is dominated by complexation with organic ligands (Xue et al 2001). Ni limitation has been observed in the marine diatom Thalassiosira weissflogii when provided with urea as nitrogen source, as the diatom requires Ni for use as a cofactor with the urease enzyme (Egleston and Morel 2008;Price and Morel 1991). It has been suggested that in marine systems, partial complexation of Ni to organic ligands and the slow reaction kinetics of Ni exchange reactions may result in Ni limitation (Price and Morel 1991).…”

Section: Nickel In Escherichia Colimentioning

confidence: 98%

Metallophores and Trace Metal Biogeochemistry

et al. 2014

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Trace metal limitation not only affects the biological function of organisms, but also the health of ecosystems and the global cycling of elements. The enzymatic machinery of microbes helps to drive critical biogeochemical cycles at the macroscale, and in many cases, the function of metalloenzyme-mediated processes may be limited by the scarcity of essential trace metals. In response to these nutrient limitations, some organisms employ a strategy of exuding metallophores, biogenic ligands that facilitate the uptake of metal ions. For example, bacterial, fungal, and graminaceous plant species are known to use Fe(III)-binding siderophores for nutrient acquisition, providing the best known and most thoroughly studied example of metallophores. However, recent breakthroughs have suggested or established the role of metallophores in the uptake of several other metallic nutrients. Furthermore, these metallophores may influence environmental trace metal fate and transport beyond nutrient acquisition. These discoveries have resulted in a deeper understanding of trace metal geochemistry and its relationship to the cycling of carbon and nitrogen in natural systems. In this review, we provide an overview of the current state of knowledge on the biogeochemistry of metallophores in trace metal acquisition, and explore established and potential metallophore systems.Electronic supplementary material The online version of this article (

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“…However, in field studies with diverse plankton assemblages, it has been difficult to distinguish which phytoplankton taxonomic group contributes the largest percentage of community urease activity (Solomon 2006). Urease activity in larger phytoplankton may be inhibited from a lack of Ni 2+ (needed for the metallocenter of urease; Oliveira & Antia 1986, Egleston & Morel 2008 or by metabolites produced in the cell (urease activity measured in in vitro assays decreases with increasing biomass in the assay; Solomon et al 2007). It has also been observed that most urea uptake in the field may be by eukaryotic phytoplankton, while much of the urease activity may be due to smaller phytoplankton and bacteria (Solomon 2006).…”

Section: Regulation Of Urea Catabolismmentioning

confidence: 99%

Role of urea in microbial metabolism in aquatic systems: a biochemical and molecular review

Solomon

Collier²,

Berg³

et al. 2010

Aquat. Microb. Ecol.

234

238

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Urea synthesized commercially and formed naturally as a by-product of cellular metabolism is an important source of nitrogen (N) for primary producers in aquatic ecosystems. Although urea is usually present at ambient concentrations below 1 µM-N, it can contribute 50% or more of the total N used by planktonic communities. Urea may be produced intracellularly via purine catabolism and/or the urea cycle. In many bacteria and eukaryotes, urea in the cell can be broken down by urease into NH 4 + and CO 2 . In addition, some bacteria and eukaryotes use urea amidolyase (UALase) to decompose urea. The regulation of urea uptake appears to differ from the regulation of urease activity, and newly available genomic sequence data reveal that urea transporters in eukaryotic phytoplankton are distinct from those present in Cyanobacteria and heterotrophic bacteria with different energy sources and possibly different enzyme kinetics. The diverse metabolic pathways of urea transport, production, and decomposition may contribute to differences in the role that urea plays in the physiology and ecology of different species, and in the role that each species plays in the biogeochemistry of urea. This review summarizes what is known about urea sources and availability, use of urea as an organic N growth source, rates of urea uptake, enzymes involved in urea metabolism (i.e. urea transporters, urease, UALase), and the biochemical and molecular regulation of urea transport and metabolic enzymes, with an emphasis on the potential for genomic sequence data to continue to provide important new insights.

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Nickel limitation and zinc toxicity in a urea‐grown diatom

Cited by 30 publications

References 48 publications

Diatom Proteomics Reveals Unique Acclimation Strategies to Mitigate Fe Limitation

Diatom Proteomics Reveals Unique Acclimation Strategies to Mitigate Fe Limitation

Metallophores and Trace Metal Biogeochemistry

Role of urea in microbial metabolism in aquatic systems: a biochemical and molecular review

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