AEM Accepts, published online ahead of print on 30 October 2009

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Appl. Environ. Microbiol. doi:10.1128/AEM.01715-09
Copyright (c) 2009, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Examination of Xenorhabdus nematophila lipases in pathogenic and mutualistic host interactions reveals a role for xlpA in nematode progeny production

Gregory R. Richards and Heidi Goodrich-Blair^*

Department of Bacteriology, University of Wisconsin-Madison

^* To whom correspondence should be addressed. Email: hgblair{at}bact.wisc.edu.

Xenorhabdus nematophila is a -proteobacterium and broad host-range insect pathogen. It is also a symbiont of Steinernema carpocapsae, the nematode vector that transports the bacterium between insect hosts. X. nematophila produces several secreted enzymes, including hemolysins, lipases, and proteases, which are thought to contribute to virulence or nutrient acquisition for the bacterium and its nematode host in vivo. X. nematophila has two lipase activities with distinct in vitro specificities for Tween and lecithin. The gene encoding the Tween lipase, xlpA, has been identified and is not required for X. nematophila virulence in one insect host, the tobacco hornworm Manduca sexta. However, the gene encoding the lecithin-specific lipase activity is not currently known. Here, we identify X. nematophila estA, a gene encoding a putative lecithinase and show that an estA mutant lacks in vitro lipase activity against lecithin but has wild-type virulence in M. sexta. X. nematophila secondary form phenotypic variants have higher in vitro lecithinase activity and estA transcript levels than primary form variants and estA tanscription is negatively regulated by NilR, a repressor of nematode colonization factors. We establish a role for xlpA, but not estA, in supporting production of nematode progeny during growth in Galleria mellonella insects. Future research is aimed at characterizing the biological roles of estA and xlpA in other insect hosts.