Cross-talk Between Iron and Nitrogen Regulatory Networks in Anabaena (Nostoc) sp. PCC 7120: Identification of Overlapping Genes in FurA and NtcA Regulons

López-Gomollón, Sara; Hernández, José Ángel; Pellicer, Silvia; Angarica, Vladimir Espinosa; Peleato, M. Luisa; Fillat, Marı́a F.

doi:10.1016/j.jmb.2007.09.010

Cited by 90 publications

(83 citation statements)

References 72 publications

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“…Interestingly, in this study we observed the upregulation of N and Fe transporters in Fe-limited cultures, suggesting that these two nutrients interact and coregulate photosynthesis, transcriptional regulation, and redox control pathways in M. aeruginosa as they do in Anabaena (66).…”

Section: Discussionmentioning

confidence: 48%

Physiological and Proteomic Responses of Continuous Cultures of Microcystis aeruginosa PCC 7806 to Changes in Iron Bioavailability and Growth Rate

Yeung

D’Agostino

Poljak

et al. 2016

Appl Environ Microbiol

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The hepatotoxin microcystin (MCYST) is produced by a variety of freshwater cyanobacterial species, including Microcystis aeruginosa. Interestingly, MCYST-producing M. aeruginosa strains have been shown to outcompete their nontoxic counterparts under iron-limiting conditions. However, the reasons for this are unclear. Here we examined the proteomic response of M. aeruginosa PCC 7806 continuous cultures under different iron and growth regimes. Iron limitation was correlated with a global reduction in levels of proteins associated with energy metabolism and photosynthesis. These proteomic changes were consistent with physiological observations, including reduced chlorophyll a content and reduced cell size. While levels of MCYST biosynthesis proteins did not fluctuate during the study period, both intra-and extracellular toxin quotas were significantly higher under iron-limiting conditions. Our results support the hypothesis that intracellular MCYST plays a role in protecting the cell against oxidative stress. Further, we propose that extracellular MCYST may act as a signaling molecule, stimulating MCYST production under conditions of iron limitation and enhancing the fitness of bloom populations. IMPORTANCEMicrocystin production in water supply reservoirs is a global public health problem. Understanding the ecophysiology of hepatotoxic cyanobacteria, including their responses to the presence of key micronutrient metals such as iron, is central to managing harmful blooms. To our knowledge, this was the first study to examine proteomic and physiological changes occurring in M. aeruginosa continuous cultures under conditions of iron limitation at different growth rates. C yanobacteria ("blue-green algae") proliferate in warm stratified water bodies rich in nitrogen and phosphorus (1, 2). Cyanobacterial blooms can have a negative impact on the appearance, taste, and odor of water, and their subsequent decay can lead to oxygen depletion and fish kills (3). However, of greatest concern to public health is their production of potent toxins. Microcystis aeruginosa (Kützing) Lemmermann is a common bloom-forming cyanobacterial species that produces hepatotoxic microcystins (MCYSTs) (1). These nonribosomally synthesized peptides inhibit eukaryotic protein phosphatases, leading to liver necrosis in acute doses and hepatocellular carcinoma in chronic low doses (4, 5).There is strong evidence that the production of MCYST is a direct function of cell division (6). It is therefore not surprising that parameters affecting cyanobacterial growth rate (e.g., nutrients, trace metals, temperature, pH, and light) have been correlated with fluctuating MCYST levels in batch culture experiments (7-9).Recent molecular studies suggest that iron (Fe) and nitrogen (N) also play a role in regulating the expression of MCYST biosynthesis (mcy) genes. In M. aeruginosa, for example, the mcy promoter region contains binding sites for the ferric uptake regulator (Fur) and the global nitrogen regulator (NtcA) (10, 11). Despite these genetic clu...

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Section: Discussionmentioning

confidence: 48%

Physiological and Proteomic Responses of Continuous Cultures of Microcystis aeruginosa PCC 7806 to Changes in Iron Bioavailability and Growth Rate

Yeung

D’Agostino

Poljak

et al. 2016

Appl Environ Microbiol

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“…The fine tuning of NtcA by 2-OG might have evolved from evolutionary pressure whereby cyanobacteria needed NtcA to regulate the expression of a much wider spectrum of genes than does CAP in E. coli. In fact, NtcA not only activates the expression of genes involved in nitrogen metabolism upon the 2-OG accumulation induced by nitrogen deprivation, but it also controls many genes involved in other functions such as photosynthesis and oxidative stress response (33)(34)(35). In addition to functioning as an activator, in some cases NtcA acts as a repressor (36).…”

Section: Discussionmentioning

confidence: 99%

Structural basis for the allosteric control of the global transcription factor NtcA by the nitrogen starvation signal 2-oxoglutarate

Zhao

Jiang

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

101

112

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2-oxogluatarate (2-OG), a metabolite of the highly conserved Krebs cycle, not only plays a critical role in metabolism, but also constitutes a signaling molecule in a variety of organisms ranging from bacteria to plants and animals. In cyanobacteria, the accumulation of 2-OG constitutes the signal of nitrogen starvation and NtcA, a global transcription factor, has been proposed as a putative receptor for 2-OG. Here we present three crystal structures of NtcA from the cyanobacterium Anabaena : the apoform, and two ligand-bound forms in complex with either 2-OG or its analogue 2,2-difluoropentanedioic acid. All structures assemble as homodimers, with each subunit composed of an N-terminal effector-binding domain and a C-terminal DNA-binding domain connected by a long helix (C-helix). The 2-OG binds to the effector-binding domain at a pocket similar to that used by cAMP in catabolite activator protein, but with a different pattern. Comparative structural analysis reveals a putative signal transmission route upon 2-OG binding. A tighter coiled-coil conformation of the two C-helices induced by 2-OG is crucial to maintain the proper distance between the two F-helices for DNA recognition. Whereas catabolite activator protein adopts a transition from off-to-on state upon cAMP binding, our structural analysis explains well why NtcA can bind to DNA even in its apoform, and how 2-OG just enhances the DNA-binding activity of NtcA. These findings provided the structural insights into the function of a global transcription factor regulated by 2-OG, a metabolite standing at a crossroad between carbon and nitrogen metabolisms.

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“…For each sample, 10 g of total RNA was separated on a 1.5% agarose denaturing formaldehyde gel in MOPS buffer (47) and then transferred by capillary action to a Magnacharge nylon membrane (GE Osmonics) with 10ϫ SSPE (1ϫ SSPE is 0.18 M NaCl, 10 mM NaH 2 PO 4 , and 1 mM EDTA [pH 7.7]) (18). DNA probes were amplified by PCR with appropriate primers (Table 2), labeled with [␣- 32 P]dCTP by random-primer labeling, and purified on Micro Bio-Spin P-30 columns (Bio-Rad). Blots were blocked, hybridized with radioactively labeled DNA probes, and washed using standard protocols (47) and then were exposed to a phosphorimager plate and scanned with a BAS-5000 phosphorimager (Fujifilm).…”

Section: Methodsmentioning

confidence: 99%

“…A sigB2 sigD double mutant can form proheterocysts but is unable to grow diazotrophically, possibly due to extensive fragmentation of filaments upon nitrogen deprivation (27). The failure to find any single sigma factor that is essential for heterocyst development suggests that the cyanobacterial group 2 sigma factors have partially overlapping functions, which has hampered genetic analysis (3,27,32,39,58).…”

mentioning

confidence: 99%

The sigE Gene Is Required for Normal Expression of Heterocyst-Specific Genes in Anabaena sp. Strain PCC 7120

et al. 2011

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The filamentous cyanobacterium Anabaena (Nostoc) sp. strain PCC 7120 produces specialized cells for nitrogen fixation called heterocysts. Previous work showed that the group 2 sigma factor sigE (alr4249; previously called sigF) is upregulated in differentiating heterocysts 16 h after nitrogen step-down. We now show that the sigE gene is required for normal heterocyst development and normal expression levels of several heterocyst-specific genes. Mobility shift assays showed that the transcription factor NtcA binds to sites in the upstream region of sigE and that this binding is enhanced by 2-oxoglutarate (2-OG). Deletions of the region containing the NtcA binding sites in P sigE -gfp reporter plasmids showed that the sites contribute to normal developmental regulation but are not essential for upregulation in heterocysts. Northern RNA blot analysis of nifH mRNA revealed delayed and reduced transcript levels during heterocyst differentiation in a sigE mutant background. Quantitative reverse transcription-PCR (qRT-PCR) analyses of the sigE mutant showed lower levels of transcripts for nifH, fdxH, and hglE2 but normal levels for hupL. We developed a P nifHD -gfp reporter construct that showed strong heterocyst-specific expression. Time-lapse microscopy of the P nifHD -gfp reporter in a sigE mutant background showed delayed development and undetectable green fluorescent protein (GFP) fluorescence. Overexpression of sigE caused accelerated heterocyst development, an increased heterocyst frequency, and premature expression of GFP fluorescence from the P nifHD -gfp reporter.

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Cross-talk Between Iron and Nitrogen Regulatory Networks in Anabaena (Nostoc) sp. PCC 7120: Identification of Overlapping Genes in FurA and NtcA Regulons

Cited by 90 publications

References 72 publications

Physiological and Proteomic Responses of Continuous Cultures of Microcystis aeruginosa PCC 7806 to Changes in Iron Bioavailability and Growth Rate

Physiological and Proteomic Responses of Continuous Cultures of Microcystis aeruginosa PCC 7806 to Changes in Iron Bioavailability and Growth Rate

Structural basis for the allosteric control of the global transcription factor NtcA by the nitrogen starvation signal 2-oxoglutarate

The sigE Gene Is Required for Normal Expression of Heterocyst-Specific Genes in Anabaena sp. Strain PCC 7120

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