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High-salinity-induced iron limitation in Bacillus subtilis.

ABSTRACT: Proteome analysis of Bacillus subtilis cells grown at low and high salinity revealed the induction of 16 protein spots and the repression of 2 protein spots, respectively. Most of these protein spots were identified by mass spectrometry. Four of the 16 high-salinity-induced proteins corresponded to DhbA, DhbB, DhbC, and DhbE, enzymes that are involved in the synthesis of 2,3-dihydroxybenzoate (DHB) and its modification and esterification to the iron siderophore bacillibactin. These proteins are encoded by the dhbACEBF operon, which is negatively controlled by the central iron regulatory protein Fur and is derepressed upon iron limitation. We found that iron limitation and high salinity derepressed dhb expression to a similar extent and that both led to the accumulation of comparable amounts of DHB in the culture supernatant. DHB production increased linearly with the degree of salinity of the growth medium but could still be reduced by an excess of iron. Such an excess of iron also partially reversed the growth defect exhibited by salt-stressed B. subtilis cultures. Taken together, these findings strongly suggest that B. subtilis cells grown at high salinity experience iron limitation. In support of this notion, we found that the expression of several genes and operons encoding putative iron uptake systems was increased upon salt stress. The unexpected finding that high-salinity stress has an iron limitation component might be of special ecophysiological importance for the growth of B. subtilis in natural settings, in which bioavailable iron is usually scarce.

SUBMITTER: Hoffmann T

PROVIDER: S-EPMC139516 | biostudies-literature | 2002 Feb

REPOSITORIES: biostudies-literature

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High-salinity-induced iron limitation in Bacillus subtilis.

Hoffmann Tamara T Schütz Alexandra A Brosius Margot M Völker Andrea A Völker Uwe U Bremer Erhard E

Journal of bacteriology 20020201 3

Proteome analysis of Bacillus subtilis cells grown at low and high salinity revealed the induction of 16 protein spots and the repression of 2 protein spots, respectively. Most of these protein spots were identified by mass spectrometry. Four of the 16 high-salinity-induced proteins corresponded to DhbA, DhbB, DhbC, and DhbE, enzymes that are involved in the synthesis of 2,3-dihydroxybenzoate (DHB) and its modification and esterification to the iron siderophore bacillibactin. These proteins are ...[more]

PMID: 11790741

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Project description:Potassium is the most abundant metal ion in every living cell. This ion is essential due to its requirement for the activity of the ribosome and many enzymes but also because of its role in buffering the negative charge of nucleic acids. As the external concentrations of potassium are usually low, efficient uptake and intracellular enrichment of the ion is necessary. The Gram-positive bacterium Bacillus subtilis possesses three transporters for potassium, KtrAB, KtrCD, and the recently discovered KimA. In the absence of the high-affinity transporters KtrAB and KimA, the bacteria were unable to grow at low potassium concentrations. However, we observed the appearance of suppressor mutants that were able to overcome the potassium limitation. All these suppressor mutations affected amino acid metabolism, particularly arginine biosynthesis. In the mutants, the intracellular levels of ornithine, citrulline, and arginine were strongly increased, suggesting that these amino acids can partially substitute for potassium. This was confirmed by the observation that the supplementation with positively charged amino acids allows growth of B. subtilis even at the extreme potassium limitation that the bacteria experience if no potassium is added to the medium. In addition, a second class of suppressor mutations allowed growth at extreme potassium limitation. These mutations result in increased expression of KtrAB, the potassium transporter with the highest affinity and therefore allow the acquisition and accumulation of the smallest amounts of potassium ions from the environment.IMPORTANCE Potassium is essential for every living cell as it is required for the activity for many enzymes and for maintaining the intracellular pH by buffering the negative charge of the nucleic acids. We have studied the adaptation of the soil bacterium Bacillus subtilis to life at low potassium concentrations. If the major high-affinity transporters are missing, the bacteria are unable to grow unless they acquire mutations that result in the accumulation of positively charged amino acids such as ornithine, citrulline, and arginine. Supplementation of the medium with these amino acids rescued growth even in the absence of externally added potassium. Moreover, these growth conditions, which the bacteria experience as an extreme potassium limitation, can be overcome by the acquisition of mutations that result in increased expression of the high-affinity potassium transporter KtrAB. Our results indicate that positively charged amino acids can partially take over the function of potassium.

Dataset Information

High-salinity-induced iron limitation in Bacillus subtilis.

Publications

High-salinity-induced iron limitation in Bacillus subtilis.

Similar Datasets

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