1. ¹Department of Plant Pathology, University of Wisconsin–Madison, Madison, WI, USA
2. ²Department of Chemistry, University of Wisconsin--Madison, Madison, WI, USA
3. ³Department of Bacteriology, University of Wisconsin–Madison, Madison, WI, USA
4. ⁴Microbiology Doctoral Training Program, University of Wisconsin–Madison, Madison, WI, USA

Correspondence: J Handelsman, Department of Bacteriology, University of Wisconsin-Madison, 6159 Microbial Sciences, 1550 Linden Drive, Madison, WI 53706, USA. E-mail: joh@bact.wisc.edu.

⁵Current address: Department of Microbiology, University of Washington School of Medicine, 1959 NE Pacific St, Room K-360, Seattle, WA 98195-7242, USA.

Received 24 April 2008; Revised 22 June 2008; Accepted 23 June 2008; Published online 24 July 2008.

Abstract

The overall goal of this study was to examine the role of quorum-sensing (QS) signals in a multispecies microbial community. Toward this aim, we studied QS signals produced by an indigenous member and an invading pathogen of the microbial community of the cabbage white butterfly (CWB) larval midgut (Pieris rapae). As an initial step, we characterized the QS system in Pantoea CWB304, which was isolated from the larval midgut. A luxI homolog, designated panI, is necessary for the production of N-acyl-L-homoserine lactones (AHLs) by Pantoea CWB304. To determine whether AHL signals are exchanged in the alkaline environment of the midgut, we constructed AHL-sensing bioluminescent reporter strains in Pantoea CWB304 and a panI mutant of this strain. In the gut of the CWB larvae, the reporter in an AHL-deficient Pantoea CWB304 detected AHLs when coinoculated with the wild type. To study the role of AHL signals produced by a community invader, we examined pathogenesis of Pseudomonas aeruginosa PAO1 in CWB larvae. Mortality induced by P. aeruginosa PAO1 was significantly reduced when signaling was interrupted by either a potent chemical inhibitor of QS or mutations in the lasI and rhlI AHL synthases of P. aeruginosa PAO1. These results show that AHLs are exchanged among bacteria in the alkaline gut of CWB larvae and contribute to disease caused by P. aeruginosa PAO1.