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Journal of Bacteriology, February 2002, p. 718-727, Vol. 184, No. 3
0021-9193/01/$04.00+0     DOI: 10.1128/JB.184.3.718-727.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

High-Salinity-Induced Iron Limitation in Bacillus subtilis

Tamara Hoffmann,1 Alexandra Schütz,1,2 Margot Brosius,1,{dagger} Andrea Völker,1,2 Uwe Völker,1,2 and Erhard Bremer1*

Philipps University Marburg, Department of Biology,1 Max-Planck Institute for Terrestrial Microbiology, D-35032 Marburg, Federal Republic of Germany2

Received 22 June 2001/ Accepted 6 November 2001

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.


* Corresponding author. Mailing address: Philipps University Marburg, Department of Biology, Laboratory for Microbiology, Karl-von-Frisch Str., D-35032 Marburg, Federal Republic of Germany. Phone: (49)-6421-2821529. Fax: (49)-6421-2828979. E-mail: bremer{at}mailer.uni-marburg.de.

{dagger} Present address: German Cancer Reseach Center, Department of Tumor Progression and Immune Defense, D-69120 Heidelberg, Federal Republic of Germany.


Journal of Bacteriology, February 2002, p. 718-727, Vol. 184, No. 3
0021-9193/01/$04.00+0     DOI: 10.1128/JB.184.3.718-727.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.




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