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Applied and Environmental Microbiology, January 2009, p. 45-53, Vol. 75, No. 1
0099-2240/09/$08.00+0     doi:10.1128/AEM.01723-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Two Dissimilar N-Acyl-Homoserine Lactone Acylases of Pseudomonas syringae Influence Colony and Biofilm Morphology{triangledown}

Ryan W. Shepherd and Steven E. Lindow*

Department of Plant and Microbial Biology, University of California, Berkeley, California 94720-3102

Received 25 July 2008/ Accepted 30 October 2008

Plant aerial surfaces comprise a complex habitat for microorganisms, and many plant-associated bacteria, such as the pathogen Pseudomonas syringae, exhibit density-dependent survival on leaves by utilizing quorum sensing (QS). QS is often mediated by diffusible signals called N-acyl-homoserine lactones (AHLs), and P. syringae utilizes N-3-oxo-hexanoyl-DL-homoserine lactone (3OC6HSL) to control traits influencing epiphytic fitness and virulence. The P. syringae pathovar syringae B728a genome sequence revealed two putative AHL acylases, termed HacA (Psyr_1971) and HacB (Psyr_4858), which are N-terminal nucleophile hydrolases that inactivate AHLs by cleaving their amide bonds. HacA is a secreted AHL acylase that degrades only long-chain (C ≥ 8) AHLs, while HacB is not secreted and degrades all tested AHLs. Targeted disruptions of hacA, hacB, and hacA and hacB together do not alter endogenous 3OC6HSL levels under the tested conditions. Surprisingly, targeted disruptions of hacA alone and hacA and hacB together confer complementable phenotypes that are very similar to autoaggregative phenotypes seen in other species. While AHL acylases might enable P. syringae B728a to degrade signals of competing species and block expression of their QS-dependent traits, these enzymes also play fundamental roles in biofilm formation.

* Corresponding author. Mailing address: Department of Plant and Microbial Biology, University of California—Berkeley, Berkeley, CA 94720-3102. Phone: (510) 642-4174. Fax: (510) 642-4995. E-mail: icelab{at}berkeley.edu

{triangledown} Published ahead of print on 7 November 2008.

Applied and Environmental Microbiology, January 2009, p. 45-53, Vol. 75, No. 1
0099-2240/09/$08.00+0     doi:10.1128/AEM.01723-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.



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