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Journal of Bacteriology, September 1998, p. 4401-4405, Vol. 180, No. 17
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

A 3',5' Cyclic AMP (cAMP) Phosphodiesterase Modulates cAMP Levels and Optimizes Competence in Haemophilus influenzae Rd

Leah P. Macfadyen, Caixia Ma, and Rosemary J. Redfield*

Department of Zoology, University of British Columbia, Vancouver, British Columbia, Canada

Received 27 February 1998/Accepted 25 June 1998

Changes in intracellular 3',5' cyclic AMP (cAMP) concentration regulate the development of natural competence in Haemophilus influenzae. In Escherichia coli, cAMP levels are modulated by a cAMP phosphodiesterase encoded by the cpdA gene. We have used several approaches to demonstrate that the homologous icc gene of H. influenzae encodes a functional cAMP phosphodiesterase and that this gene limits intracellular cAMP and thereby influences competence and other cAMP-dependent processes. In E. coli, expression of cloned icc reduced both cAMP-dependent sugar fermentation and beta -galactosidase expression, as has been shown for cpdA. In H. influenzae, an icc null mutation increased cAMP-dependent sugar fermentation and competence development in strains where these processes are limited by mutations reducing cAMP synthesis. When endogenous production of cAMP was eliminated by a cya mutation, an icc strain was 10,000-fold more sensitive to exogenous cAMP than an icc+ strain. The icc strain showed moderately elevated competence under noninducing conditions, as expected, but had subnormal competence increases at onset of stationary phase in rich medium, and on transfer to a nutrient-limited medium, suggesting that excessive cAMP may interfere with induction. Consistent with this finding, a cya strain cultured in 1 mM cAMP failed to develop maximal competence on transfer to inducing conditions. Thus, by limiting cAMP levels, the H. influenzae cAMP phosphodiesterase may coordinate its responses to nutritional stress, ensuring optimal competence development.

* Corresponding author. Mailing address: Department of Zoology, University of British Columbia, 6270 University Blvd., Vancouver, British Columbia V6T 1Z4, Canada. Phone: (604) 822 3744. Fax: (604) 822 2416. E-mail: Redfield{at}unixg.ubc.ca.

Journal of Bacteriology, September 1998, p. 4401-4405, Vol. 180, No. 17
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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