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Journal of Bacteriology, June 2008, p. 4181-4188, Vol. 190, No. 12
0021-9193/08/$08.00+0     doi:10.1128/JB.01873-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Negative Regulation of Quorum-Sensing Systems in Pseudomonas aeruginosa by ATP-Dependent Lon Protease{triangledown}

Akiko Takaya,1* Fumiaki Tabuchi,1 Hiroko Tsuchiya,1 Emiko Isogai,2 and Tomoko Yamamoto1

Department of Microbiology and Molecular Genetics, Graduate School of Pharmaceutical Sciences, Chiba University, Chiba, 263-8522, Japan,1 Department of Preventive Dentistry, Health Sciences University of Hokkaido, Ishikari-Tobetsu, Hokkaido, 061-0293, Japan2

Received 29 November 2007/ Accepted 1 April 2008

Lon protease, a member of the ATP-dependent protease family, regulates numerous cellular systems by degrading specific substrates. Here, we demonstrate that Lon is involved in the regulation of quorum-sensing (QS) signaling systems in Pseudomonas aeruginosa, an opportunistic human pathogen. The organism has two acyl-homoserine lactone (HSL)-mediated QS systems, LasR/LasI and RhlR/RhlI. Many reports have demonstrated that these two systems are regulated and interconnected by global regulators. We found that lon-disrupted cells overproduce pyocyanin, the biosynthesis of which depends on the RhlR/RhlI system, and show increased levels of a transcriptional regulator, RhlR. The QS systems are organized hierarchically: the RhlR/RhlI system is subordinate to LasR/LasI. To elucidate the mechanism by which Lon negatively regulates RhlR/RhlI, we examined the effect of lon disruption on the LasR/LasI system. We found that Lon represses the expression of LasR/LasI by degrading LasI, an HSL synthase, leading to negative regulation of the RhlR/RhlI system. RhlR/RhlI was also shown to be regulated by Lon independently of LasR/LasI via regulation of RhlI, an HSL synthase. In view of these findings, it is suggested that Lon protease is a powerful negative regulator of both HSL-mediated QS systems in P. aeruginosa.

* Corresponding author. Mailing address: Department of Microbiology and Molecular Genetics, Graduate School of Pharmaceutical Sciences, Chiba University, Chiba, 263-8522, Japan. Phone and fax: (81) 43-290-2929. E-mail: akiko{at}p.chiba-u.ac.jp

{triangledown} Published ahead of print on 11 April 2008.

Journal of Bacteriology, June 2008, p. 4181-4188, Vol. 190, No. 12
0021-9193/08/$08.00+0     doi:10.1128/JB.01873-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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