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Journal of Bacteriology, November 2004, p. 7575-7585, Vol. 186, No. 22
0021-9193/04/$08.00+0     DOI: 10.1128/JB.186.22.7575-7585.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

MucA-Mediated Coordination of Type III Secretion and Alginate Synthesis in Pseudomonas aeruginosa

Weihui Wu,1 Hassan Badrane,1 Shiwani Arora,2 Henry V. Baker,1 and Shouguang Jin1*

Department of Molecular Genetics and Microbiology,1 Department of Medicine, University of Florida College of Medicine, Gainesville, Florida2

Received 18 May 2004/ Accepted 17 August 2004

The type III secretion system (T3SS) of Pseudomonas aeruginosa is an important virulence factor. The T3SS of P. aeruginosa can be induced by a low calcium signal or upon direct contact with the host cells. The exact pathway of signal sensing and T3SS activation is not clear. By screening a transposon insertion mutant library of the PAK strain, mutation in the mucA gene was found to cause repression of T3SS expression under both type III-inducing and -noninducing conditions. Mutation in the mucA gene is known to cause alginate overproduction, resulting in a mucoid phenotype. Alginate production responds to various environmental stresses and plays a protective role for P. aeruginosa. Comparison of global gene expression of mucA mutant and wild-type PAK under T3SS-inducing conditions confirmed the down regulation of T3SS genes and up regulation of genes involved in alginate biosynthesis. Further analysis indicated that the repression of T3SS in the mucA mutant was AlgU and AlgR dependent, as double mutants mucA/algU and mucA/algR showed normal type III expression. An algR::Gm mutant showed a higher level of type III expression, while overexpression of the algR gene inhibited type III gene expression; thus, it seems that the AlgR-regulated product inhibits the expression of the T3SS genes. It is likely that P. aeruginosa has evolved tight regulatory networks to turn off the energy-expensive T3SS when striving for survival under environmental stresses.

* Corresponding author. Mailing address: Department of Molecular Genetics and Microbiology, University of Florida College of Medicine, Gainesville, FL 32610. Phone: (352) 392-8323. Fax: (352) 392-3133. E-mail: sjin{at}mgm.ufl.edu.

Journal of Bacteriology, November 2004, p. 7575-7585, Vol. 186, No. 22
0021-9193/04/$08.00+0     DOI: 10.1128/JB.186.22.7575-7585.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.



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