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

Abstract

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.

Dual transcriptional profiling of a bacterial/fungal confrontation: Collimonas fungivorans versus Aspergillus niger

“…This would be consistent with the elevated expression of Cf_2775, which codes for a putative permease for the alternative nitrogen source allantoin. Also upregulated were genes Cf_2912-2916 (in cluster H) and Cf_2987-2991 (in cluster C), both of which code for an UrtABCDE-type transporter of urea (Valladares et al, 2002).…”

A Novel Mechanism, Linked to Cell Density, Largely Controls Cell Division in Synechocystis

“…transfers lead to the generation of reducing power, which supply metabolic processes such as the CalvinBenson cycle and nitrogen uptake and reduction (Valladares et al, 2002;. The efficiency of CO 2 fixation and assimilation is, at least partially, under the control of a carbon concentration mechanism, which increases the CO 2 concentration around the Rubisco catalytic site (Price et al, 1998), allowing it to operate close to its V max (Badger et al, 2006).…”

“…The efficiency of CO 2 fixation and assimilation is, at least partially, under the control of a carbon concentration mechanism, which increases the CO 2 concentration around the Rubisco catalytic site (Price et al, 1998), allowing it to operate close to its V max (Badger et al, 2006). Synechocystis can take up and metabolize different nitrogen sources (nitrate, nitrite, ammonium, urea, and some amino acids; Quintero et al, 2000;Valladares et al, 2002;Muro-Pastor et al, 2005). Intriguingly, the control of the expression and activity of transporters and enzymes related to nitrogen metabolism is regulated by a complex network involving 2-oxoglutarate, NtcA (nitrogen control factor of cyanobacteria), PII (nitrogen regulatory protein PII), and PipX (PII-interacting protein X; Alfonso et al, 2001;Herrero et al, 2001;Llácer et al, 2010;Zhao et al, 2010;Espinosa et al, 2014;Lüddecke and Forchhammer, 2015).…”

Urea and nickel utilization in marine cyanobacteria as evaluated by incubation, proteomic, and uptake techniques

“…In the gyre N+N increased slightly in the urea treatments (presumably cellular leakage via grazing and/or viral lysis), and completely displaced N+N consumption while allowing greater phosphate drawdown as compared with the nitrate additions ( Table 4). In the upwelling site the N+N decreased in all treatments (no leakage), however the N+N drawdown was less in urea treatments than both nitrate amended bottles and the control (Table 5) The prospect of local plankton rapidly adjusting their physiology to make use of an alternative organic nitrogen species, and shift up response to urea in particular is supported both by cyanobacteria culture experiments and genomic evidence (Valladares et al 2002). Moreover, urea need not be an abundant nitrogen species for it to play a significant role; for example it may be rapidly cycling with low leakage and high uptake by and from biota.…”

“…Genomic evidence shows that the cytoplasmic soluble nickel-containing urease is common in cyanobacteria and with low environmental urea concentrations it is suggested by Collier et al (1999) that a high-affinity urea transport system should exist. However, urease is also noted as a constitutive enzyme and internal cycling of urea can be independent from assimilation of external urea for phytoplankton nutrition (Valladares et al 2002;Dupont et al 2008;Nunn et al 2009;Allen et al 2011), even for a diatom strain of Cyclotella when grown on nitrate in the absence of urea (Oliveira and Antia 1986). Genomic and transcriptomic tools have brought new insight into the importance of urea.…”