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Journal of Bacteriology, December 1999, p. 7373-7380, Vol. 181, No. 23
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Transcription Regulation of the Colicin K cka Gene Reveals Induction of Colicin Synthesis by Differential Responses to Environmental Signals

Irena Kuhar and Darja Zgur-Bertok*

Department of Biology, Biotechnical Faculty, University of Ljubljana, Vecna pot 111, 1000 Ljubljana, Slovenia

Received 26 May 1999/Accepted 23 September 1999

Colicin-producing strains occur frequently in natural populations of Escherichia coli, and colicinogenicity seems to provide a competitive advantage in the natural habitat. A cka-lacZ fusion was used to study the regulation of expression of the colicin K structural gene. Expression is growth phase dependent, with high activity in the late stationary phase. Nutrient depletion induces the expression of cka due to an increase in ppGpp. Temperature is a strong signal for cka expression, since only basal-level activity was detected at 22°C. Mitomycin C induction demonstrates that cka expression is regulated to a lesser extent by the SOS response independently of ppGpp. Increased osmolarity induces a partial increase, while the global regulator integration host factor inhibits expression in the late stationary phase. Induction of cka was demonstrated to be independent of the cyclic AMP-Crp complex, carbon source, RpoS, Lrp, H-NS, pH, and short-chain fatty acids. In contrast to colicin E1, cka expression is independent of catabolite repression and is partially affected by anaerobiosis only upon SOS induction. These results indicate that while different colicins are expressed in response to some common signals such as nutrient depletion, the expression of individual colicins could be further influenced by specific environmental cues.

* Corresponding author. Mailing address: Department of Biology, Biotechnical Faculty, University of Ljubljana, Vecna pot 111, 1000 Ljubljana, Slovenia. Phone: 386 61 123 33 88. Fax: 386 61 273 390. E-mail: Darja.Zgur{at}uni-Lj.Si.

Journal of Bacteriology, December 1999, p. 7373-7380, Vol. 181, No. 23
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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