The two-component sensor kinase KdpD is required for Salmonella typhimurium colonization of Caenorhabditis elegans and survival in macrophages Rosanna A. Alegado, 1† Chui-Yoke Chin, 3 Denise M. Monack 1 and Man-Wah Tan 1,2,4 * 1 Departments of Microbiology and Immunology, and 2 Genetics, Stanford University School of Medicine, Stanford, CA 94305, USA. 3 School of Biosciences and Biotechnology, Faculty of Science and Technology, Universiti Kebangsaan Malaysia, 43600 UKM Bangi Selangor D.E., Malaysia. 4 Department of Microbial Pathogenesis, Genentech, Inc., South San Francisco, CA 94080, USA. Summary The ability of enteric pathogens to perceive and adapt to distinct environments within the meta- zoan intestinal tract is critical for pathogenesis; however, the preponderance of interactions between microbe- and host-derived factors remain to be fully understood. Salmonella enterica serovar Typhimurium is a medically important enteric bac- terium that colonizes, proliferates and persists in the intestinal lumen of the nematode Caenorhabdi- tis elegans. Several Salmonella virulence factors important in murine and tissue culture models also contribute to worm mortality and intestinal persistence. For example, PhoP and the virulence plasmid pSLT are virulence factors required for resistance to the C. elegans antimicrobial peptide SPP-1. To uncover additional determinants required for Salmonella typhimurium pathogenesis in vivo, we devised a genetic screen to identify bacterial mutants defective in establishing a persistent infection in the intestine of C. elegans. Here we report on identification of 14 loci required for persistence in the C. elegans intestine and characterization of KdpD, a sensor kinase of a two-component system in S. typhimurium patho- genesis. We show that kdpD mutants are profoundly attenuated in intestinal persistence in the nematode and in macrophage survival. These findings may be attributed to the essential role KdpD plays in promoting resistance to osmotic, oxidative and antimicrobial stresses. Introduction Salmonella typhimurium is a causative agent of food poi- soning and persistently colonizes the gastrointestinal tract of livestock and poultry (Isaacson and Kinsel, 1992; Lede- boer and Jones, 2005). Perception and integration of mul- tiple external signals are integral to the ability of this pathogen to co-ordinate an appropriate response that enables survival in distinct niches within the host. Because asymptomatic carriers have the potential to serve as vectors for zoonotic outbreaks, an appreciation for the molecular basis of adaptation and survival of this pathogen within the host is critical for stemming endemic disease. Although a modest number of environmental stimuli have been identified that induce Salmonella survival and virulence genes, the majority of signals that enterobacte- ria respond to in vivo remain poorly understood. Survival in the stomach and small intestine is reliant on a number of factors that respond to extrinsic cues specific to microenvironments within the host in order to choreo- graph proper induction or repression of S. typhimurium genes, including the two-component systems, signalling modules comprised of a sensor histidine kinase that phos- phorylates a cognate response regulator (Finlay and Falkow, 1997). Two-component systems are typically positioned at the apex of complex signalling cascades (Valdivia and Falkow, 1996; Kwon and Ricke, 1998; Lee et al., 2000; Kim and Falkow, 2004; Rychlik and Barrow, 2005). For example, the two-component systems PhoP/ PhoQ and BarA/SirA regulate genes on the Salmonella pathogenicity island (SPI)-1 (Johnston et al., 1996; Ahmer et al., 1999; Altier et al., 2000), a virulence locus required for invasion of intestinal cells that is induced under con- ditions of low oxygen and high osmolarity (Galan, 1996). In addition, the two-component systems PhoP/PhoQ, EnvZ/OmpR and SsrA/SsrB regulate SPI-2 (Deiwick Received 3 January, 2011; revised 1 July, 2011; accepted 5 July, 2011. *For correspondence. E-mail tan.man-wah@gene.com; Tel. (+1) 650 467 6746; Fax (+1) 650 225 6103. † Present address: Department of Molecular and Cell Biology, UC Berkeley, Berkeley, CA 94720, USA. Cellular Microbiology (2011) 13(10), 1618–1637 doi:10.1111/j.1462-5822.2011.01645.x First published online 24 August 2011 © 2011 Blackwell Publishing Ltd cellular microbiology