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Journal of Bacteriology, December 2008, p. 7947-7956, Vol. 190, No. 24
0021-9193/08/$08.00+0     doi:10.1128/JB.00968-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Influence of the Pseudomonas Quinolone Signal on Denitrification in Pseudomonas aeruginosa{triangledown}

Masanori Toyofuku,{dagger} Nobuhiko Nomura,*{dagger} Eriko Kuno, Yosuke Tashiro, Toshiaki Nakajima, and Hiroo Uchiyama

Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan

Received 15 July 2008/ Accepted 8 October 2008

Denitrification is a well-studied respiratory system that is also important in the biogeochemical nitrogen cycle. Environmental signals such as oxygen and N-oxides have been demonstrated to regulate denitrification, though how denitrification is regulated in a bacterial community remains obscure. Pseudomonas aeruginosa is a ubiquitous bacterium that controls numerous genes through cell-to-cell signals. The bacterium possesses at least two N-acyl-L-homoserine lactone (AHL) signals. In our previous study, these quorum-sensing signals controlled denitrification in P. aeruginosa. In addition to the AHL signals, a third cell-to-cell communication signal, 2-heptyl-3-hydroxy-4-quinolone, referred to as the Pseudomonas quinolone signal (PQS), has been characterized. In this study, we examined the effect of PQS on denitrification to obtain more insight into the respiratory regulation in a bacterial community. Denitrification in P. aeruginosa was repressed by PQS, which was partially mediated by PqsR and PqsE. Measuring the denitrifying enzyme activities indicated that nitrite reductase activity was increased by PQS, whereas PQS inhibited nitric oxide reductase and the nitrate-respiratory chain activities. This is the first report to demonstrate that PQS influences enzyme activities, suggesting this effect is not specific to P. aeruginosa. Furthermore, when iron was supplied to the PQS-added medium, denitrifying activity was almost restored, indicating that the iron chelating property of PQS affected denitrification. Thus, our data indicate that PQS regulates denitrification primarily through iron chelation. The PQS effect on denitrification was relevant in a condition where oxygen was limited and denitrification was induced, suggesting its role in controlling denitrification where oxygen is present.

* Corresponding author. Mailing address: Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan. Phone and fax: 81-29-853-6627. E-mail: nomunobu{at}sakura.cc.tsukuba.ac.jp

{triangledown} Published ahead of print on 17 October 2008.

{dagger} Both authors contributed equally to this study.

Journal of Bacteriology, December 2008, p. 7947-7956, Vol. 190, No. 24
0021-9193/08/$08.00+0     doi:10.1128/JB.00968-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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