Urea degradation by picophytoplankton in the euphotic zone of Lake Biwa

Mitamura, Osamu; Kawashima, M.; Maeda, Hiroto

doi:10.1007/s102010070025

Cited by 16 publications

(7 citation statements)

References 29 publications

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“…, 1996; Gaudin et al. , 1987; Mitamura et al. , 2000a,b), this particularly high substrate affinity is very likely to allow saturation of AtDUR3‐mediated substrate transport into root cells in most soils.…”

Section: Discussionmentioning

confidence: 99%

AtDUR3 represents the major transporter for high‐affinity urea transport across the plasma membrane of nitrogen‐deficient Arabidopsis roots

Kojima¹,

Bohner²,

et al. 2007

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SummaryDespite the fact that urea is a ubiquitous nitrogen source in soils and the most widespread form of nitrogen fertilizer used in agricultural plant production, membrane transporters that might contribute to the uptake of urea in plant roots have so far been characterized only in heterologous systems. Two T-DNA insertion lines, atdur3-1 and atdur3-3, that showed impaired growth on urea as a sole nitrogen source were used to investigate a role of the H + /urea co-transporter AtDUR3 in nitrogen nutrition in Arabidopsis. In transgenic lines expressing AtDUR3-promoter:GFP constructs, promoter activity was upregulated under nitrogen deficiency and localized to the rhizodermis, including root hairs, as well as to the cortex in more basal root zones. Protein gel blot analysis of two-phase partitioned root membrane fractions and whole-mount immunolocalization in root hairs revealed the plasma membrane to be enriched in AtDUR3 protein. Expression of the AtDUR3 gene in nitrogen-deficient roots was repressed by ammonium and nitrate but induced after supply of urea. Higher accumulation of urea in roots of wild-type plants relative to atdur3-1 and atdur3-3 confirmed that urea was the substrate transported by AtDUR3. Influx of 15 N-labeled urea in atdur3-1 and atdur3-3 showed a linear concentration dependency up to 200 lM external urea, whereas influx in wild-type roots followed saturation kinetics with an apparent K m of 4 lM. The results indicate that AtDUR3 is the major transporter for high-affinity urea uptake in Arabidopsis roots and suggest that the high substrate affinity of AtDUR3 reflects an adaptation to the low urea levels usually found in unfertilized soils.

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Section: Discussionmentioning

confidence: 99%

AtDUR3 represents the major transporter for high‐affinity urea transport across the plasma membrane of nitrogen‐deficient Arabidopsis roots

Kojima¹,

Bohner²,

et al. 2007

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“…The presence of transporters with a high affinity for urea suggests that some cyanobacteria can take up the urea that may be found at very low concentrations in their natural environments. Recent determinations in some natural water bodies have indicated the presence of urea at 0.1–3 μM concentrations (Cho et al , 1996; Mitamura et al , 2000a,b), and it has been suggested that cyano‐bacterial phytoplankton use urea as a nitrogen source in a lake in which this substrate is found at 0.1–0.6 μM (Mitamura et al , 2000a).…”

Section: Discussionmentioning

confidence: 99%

An ABC‐type, high‐affinity urea permease identified in cyanobacteria

Valladares¹,

Montesinos²,

Herrero³

et al. 2002

Molecular Microbiology

132

118

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Summary Urea is an important nitrogen source for many microorganisms, but urea active transporters have not been characterized at a molecular level in any bacterium. Cells of Synechocystis sp. PCC 6803 and Anabaena sp. PCC 7120 exhibited the capacity to take up [14C]‐urea from low‐concentration (<1 μM) urea solutions. The Ks of Anabaena cells for urea was about 0.11 μM, and the observed uptake activity involved the transport and metabolism of urea. In contrast to urease, which was constitutively ex‐pressed, expression of the high‐affinity urea uptake activity was subjected to nitrogen control. In an Anabaena ureG (urease–) mutant, a concentrative, active transport of urea could be demonstrated. We found that a mutant of open reading frame (ORF) sll0374 from the Synechocystis genomic sequence lacked urea transport activity. This ORF encoded a conserved component of an ABC‐type transporter, but it is not clustered together with any other possible transporter‐encoding gene. An Anabaena homologue of sll0374, urtE, was isolated and found to be part of a cluster of genes, urtABCDE, putatively encoding all the elements of an ABC‐type permease. Although the longest transcript that we could detect only covered urtABC, the impairment of urea transport by inactivation of urtA, urtB or urtE suggested that the whole gene cluster is expressed producing the urea permease. Expression was induced under nitrogen‐limiting conditions, and a complex promoter regulated by the cyanobacterial global nitrogen control transcription factor NtcA was found upstream from urtA. Our work adds urea to the known substrates of the versatile class of ABC‐type transporters and suggests the involvement of a transporter of this superfamily in urea scavenging by some bacteria in natural environments.

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“…Urease is needed to use urea as a nitrogen source [ 70 ] and probably also for arginine catabolism [ 71 ]. Urea appears to be a major nitrogen resource in the sea, and it has been suggested that both marine and freshwater cyanobacteria use it as a nitrogen source [ 72 , 73 ]; in some cases, the urease operon has been shown to be controlled by the nitrogen global regulator, NtcA [ 70 , 73 , 74 ]. The second Ni-containing enzymes are hydrogen-metabolizing/producing enzymes, named hydrogenases.…”

Section: Nickel and Cobalt Two Essential Metals For Cyanobacteriamentioning

confidence: 99%

Metals in Cyanobacteria: Analysis of the Copper, Nickel, Cobalt and Arsenic Homeostasis Mechanisms

Huertas

López‐Maury

Giner‐Lamia

et al. 2014

Life

127

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Traces of metal are required for fundamental biochemical processes, such as photosynthesis and respiration. Cyanobacteria metal homeostasis acquires an important role because the photosynthetic machinery imposes a high demand for metals, making them a limiting factor for cyanobacteria, especially in the open oceans. On the other hand, in the last two centuries, the metal concentrations in marine environments and lake sediments have increased as a result of several industrial activities. In all cases, cells have to tightly regulate uptake to maintain their intracellular concentrations below toxic levels. Mechanisms to obtain metal under limiting conditions and to protect cells from an excess of metals are present in cyanobacteria. Understanding metal homeostasis in cyanobacteria and the proteins involved will help to evaluate the use of these microorganisms in metal bioremediation. Furthermore, it will also help to understand how metal availability impacts primary production in the oceans. In this review, we will focus on copper, nickel, cobalt and arsenic (a toxic metalloid) metabolism, which has been mainly analyzed in model cyanobacterium Synechocystis sp. PCC 6803.

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Urea degradation by picophytoplankton in the euphotic zone of Lake Biwa

Cited by 16 publications

References 29 publications

AtDUR3 represents the major transporter for high‐affinity urea transport across the plasma membrane of nitrogen‐deficient Arabidopsis roots

AtDUR3 represents the major transporter for high‐affinity urea transport across the plasma membrane of nitrogen‐deficient Arabidopsis roots

An ABC‐type, high‐affinity urea permease identified in cyanobacteria

Metals in Cyanobacteria: Analysis of the Copper, Nickel, Cobalt and Arsenic Homeostasis Mechanisms

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