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Fur-type transcriptional repressors and metal homeostasis in the cyanobacterium Synechococcus sp. PCC 7002.

Ludwig M, Chua TT, Chew CY, Bryant DA - Front Microbiol (2015)

Bottom Line: Metal homeostasis in microorganisms comprises two elements: metal acquisition from the environment and detoxification or excretion of excess metal ions.PCC 7002.One Fur-type regulator controls genes for iron acquisition (Fur); one controls genes for zinc acquisition (Zur); and the third controls two genes involved in oxidative stress (Per).

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park PA, USA.

ABSTRACT
Metal homeostasis is a crucial cellular function for nearly all organisms. Some heavy metals (e.g., Fe, Zn, Co, Mo) are essential because they serve as cofactors for enzymes or metalloproteins, and chlorophototrophs such as cyanobacteria have an especially high demand for iron. At excessive levels, however, metals become toxic to cyanobacteria. Therefore, a tight control mechanism is essential for metal homeostasis. Metal homeostasis in microorganisms comprises two elements: metal acquisition from the environment and detoxification or excretion of excess metal ions. Different families of metal-sensing regulators exist in cyanobacteria and each addresses a more or less specific set of target genes. In this study the regulons of three Fur-type and two ArsR-SmtB-type regulators were investigated in a comparative approach in the cyanobacterium Synechococcus sp. PCC 7002. One Fur-type regulator controls genes for iron acquisition (Fur); one controls genes for zinc acquisition (Zur); and the third controls two genes involved in oxidative stress (Per). Compared to other well-investigated cyanobacterial strains, however, the set of target genes for each regulator is relatively small. Target genes for the two ArsR-SmtB transcriptional repressors (SmtB (SYNPCC7002_A2564) and SYNPCC7002_A0590) are involved in zinc homeostasis in addition to Zur. Their target genes, however, are less specific for zinc and point to roles in a broader heavy metal detoxification response.

No MeSH data available.


Related in: MedlinePlus

Relative transcript abundances for Synechococcus 7002 wild type cultures grown at altered zinc levels compared to standard growth conditions and of the SYNPCC7002_A2564 (smtB) and SYNPCC7002_A0590 deletion mutants compared to the Synechococcus 7002 wild type. The scatter plots show (A) the RTAs of a wild type Synechococcus 7002 culture grown in presence of high zinc (102 μM) compared to a culture grown under standard conditions; (B) the RTAs of a culture of wild type Synechococcus 7002 culture grown under zinc limitation compared to a culture grown under standard conditions; (C) RTAs of the SYNPCC7002_A2564 (smtB) deletion mutant compared to the wild type, both grown under standard conditions; (D) RTAs of the SYNPCC7002_A0590 deletion mutant compared to a wild type culture, both grown under standard conditions. The values for the wild type under standard conditions were calculated as the mean of three independent biological replicates. The gray lines show twofold changes in either direction. Selected genes are identified by gene locus or abbreviated locus tag number. For details, see text.
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Figure 4: Relative transcript abundances for Synechococcus 7002 wild type cultures grown at altered zinc levels compared to standard growth conditions and of the SYNPCC7002_A2564 (smtB) and SYNPCC7002_A0590 deletion mutants compared to the Synechococcus 7002 wild type. The scatter plots show (A) the RTAs of a wild type Synechococcus 7002 culture grown in presence of high zinc (102 μM) compared to a culture grown under standard conditions; (B) the RTAs of a culture of wild type Synechococcus 7002 culture grown under zinc limitation compared to a culture grown under standard conditions; (C) RTAs of the SYNPCC7002_A2564 (smtB) deletion mutant compared to the wild type, both grown under standard conditions; (D) RTAs of the SYNPCC7002_A0590 deletion mutant compared to a wild type culture, both grown under standard conditions. The values for the wild type under standard conditions were calculated as the mean of three independent biological replicates. The gray lines show twofold changes in either direction. Selected genes are identified by gene locus or abbreviated locus tag number. For details, see text.

Mentions: Synechococcus 7002 cultures grown at high Zn2+ concentration (100 μM) and a culture grown in the presence of 50 μM TPEN were subjected to transcriptome profiling. Very few genes showed a variation of the transcript level in the culture grown at a high zinc level compared to a culture grown in A+ medium under standard conditions (Figure 4A): smtA (encoding a metallothionein, see above), czcA (annotated as cation efflux system protein CzcA) and, interestingly, sigH (sigma factor H; SYNPCC7002_A2111) and the adjacent ORF SYNPCC7002_A2110 (hypothetical protein; not well conserved according to BLAST searches) had higher transcript levels. The sigH gene and ORF SYNPCC7002_A2110 have been reported to be co-transcribed, but the function of the latter remained obscure (Inoue-Sakamoto et al., 2007). SYNPCC7002_G0137 (annotated as MotA/TolQ/ExbB proton channel family protein, a biopolymer transport protein) and SYNPCC7002_G0138 (annotated as TonB-dependent siderophore receptor) showed lower transcript levels.


Fur-type transcriptional repressors and metal homeostasis in the cyanobacterium Synechococcus sp. PCC 7002.

Ludwig M, Chua TT, Chew CY, Bryant DA - Front Microbiol (2015)

Relative transcript abundances for Synechococcus 7002 wild type cultures grown at altered zinc levels compared to standard growth conditions and of the SYNPCC7002_A2564 (smtB) and SYNPCC7002_A0590 deletion mutants compared to the Synechococcus 7002 wild type. The scatter plots show (A) the RTAs of a wild type Synechococcus 7002 culture grown in presence of high zinc (102 μM) compared to a culture grown under standard conditions; (B) the RTAs of a culture of wild type Synechococcus 7002 culture grown under zinc limitation compared to a culture grown under standard conditions; (C) RTAs of the SYNPCC7002_A2564 (smtB) deletion mutant compared to the wild type, both grown under standard conditions; (D) RTAs of the SYNPCC7002_A0590 deletion mutant compared to a wild type culture, both grown under standard conditions. The values for the wild type under standard conditions were calculated as the mean of three independent biological replicates. The gray lines show twofold changes in either direction. Selected genes are identified by gene locus or abbreviated locus tag number. For details, see text.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4628125&req=5

Figure 4: Relative transcript abundances for Synechococcus 7002 wild type cultures grown at altered zinc levels compared to standard growth conditions and of the SYNPCC7002_A2564 (smtB) and SYNPCC7002_A0590 deletion mutants compared to the Synechococcus 7002 wild type. The scatter plots show (A) the RTAs of a wild type Synechococcus 7002 culture grown in presence of high zinc (102 μM) compared to a culture grown under standard conditions; (B) the RTAs of a culture of wild type Synechococcus 7002 culture grown under zinc limitation compared to a culture grown under standard conditions; (C) RTAs of the SYNPCC7002_A2564 (smtB) deletion mutant compared to the wild type, both grown under standard conditions; (D) RTAs of the SYNPCC7002_A0590 deletion mutant compared to a wild type culture, both grown under standard conditions. The values for the wild type under standard conditions were calculated as the mean of three independent biological replicates. The gray lines show twofold changes in either direction. Selected genes are identified by gene locus or abbreviated locus tag number. For details, see text.
Mentions: Synechococcus 7002 cultures grown at high Zn2+ concentration (100 μM) and a culture grown in the presence of 50 μM TPEN were subjected to transcriptome profiling. Very few genes showed a variation of the transcript level in the culture grown at a high zinc level compared to a culture grown in A+ medium under standard conditions (Figure 4A): smtA (encoding a metallothionein, see above), czcA (annotated as cation efflux system protein CzcA) and, interestingly, sigH (sigma factor H; SYNPCC7002_A2111) and the adjacent ORF SYNPCC7002_A2110 (hypothetical protein; not well conserved according to BLAST searches) had higher transcript levels. The sigH gene and ORF SYNPCC7002_A2110 have been reported to be co-transcribed, but the function of the latter remained obscure (Inoue-Sakamoto et al., 2007). SYNPCC7002_G0137 (annotated as MotA/TolQ/ExbB proton channel family protein, a biopolymer transport protein) and SYNPCC7002_G0138 (annotated as TonB-dependent siderophore receptor) showed lower transcript levels.

Bottom Line: Metal homeostasis in microorganisms comprises two elements: metal acquisition from the environment and detoxification or excretion of excess metal ions.PCC 7002.One Fur-type regulator controls genes for iron acquisition (Fur); one controls genes for zinc acquisition (Zur); and the third controls two genes involved in oxidative stress (Per).

View Article: PubMed Central - PubMed

Affiliation: Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park PA, USA.

ABSTRACT
Metal homeostasis is a crucial cellular function for nearly all organisms. Some heavy metals (e.g., Fe, Zn, Co, Mo) are essential because they serve as cofactors for enzymes or metalloproteins, and chlorophototrophs such as cyanobacteria have an especially high demand for iron. At excessive levels, however, metals become toxic to cyanobacteria. Therefore, a tight control mechanism is essential for metal homeostasis. Metal homeostasis in microorganisms comprises two elements: metal acquisition from the environment and detoxification or excretion of excess metal ions. Different families of metal-sensing regulators exist in cyanobacteria and each addresses a more or less specific set of target genes. In this study the regulons of three Fur-type and two ArsR-SmtB-type regulators were investigated in a comparative approach in the cyanobacterium Synechococcus sp. PCC 7002. One Fur-type regulator controls genes for iron acquisition (Fur); one controls genes for zinc acquisition (Zur); and the third controls two genes involved in oxidative stress (Per). Compared to other well-investigated cyanobacterial strains, however, the set of target genes for each regulator is relatively small. Target genes for the two ArsR-SmtB transcriptional repressors (SmtB (SYNPCC7002_A2564) and SYNPCC7002_A0590) are involved in zinc homeostasis in addition to Zur. Their target genes, however, are less specific for zinc and point to roles in a broader heavy metal detoxification response.

No MeSH data available.


Related in: MedlinePlus