Campylobacter jejuni proteins Cj0952c and Cj0951c affect chemotactic behaviour towards formic acid and are important for invasion of host cells A. Malik Tareen,3 Javid Iqbal Dasti,3 Andreas E. Zautner, Uwe Groß and Raimond Lugert Correspondence Raimond Lugert rlugert@gwdg.de Received 3 March 2010 Revised 23 June 2010 Accepted 20 July 2010 University Medical Center Go ¨ ttingen, Institute for Medical Microbiology, Kreuzbergring 57, 37075 Go ¨ ttingen, Germany Campylobacter jejuni, an important food-borne bacterial pathogen in industrialized countries and in the developing world, is one of the major causes of bacterial diarrhoea. To identify genes which are important for the invasion of host cells by the pathogen, we screened altogether 660 clones of a transposon-generated mutant library based on the clinical C. jejuni isolate B2. Thereby, we identified a clone with a transposon insertion in gene cj0952c. As in the well-characterized C. jejuni strain NCTC 11168, the corresponding protein together with the gene product of the adjacent gene cj0951c consists of two transmembrane domains, a HAMP domain and a putative MCP domain, which together are thought to act as a chemoreceptor, designated Tlp7. In this report we show that genes cj0952c and cj0951c (i) are important for the host cell invasion of the pathogen, (ii) are not translated as one protein in C. jejuni isolate B2, contradicting the idea of a postulated read-through mechanism, (iii) affect the motility of C. jejuni, (iv) alter the chemotactic behaviour of the pathogen towards formic acid, and (v) are not related to the utilization of formic acid by formate dehydrogenase. INTRODUCTION Campylobacter jejuni is a Gram-negative, spiral-shaped bacterium which is a major cause of bacterial diarrhoea in both developing and industrialized countries (Altekruse et al., 1999; Friedman et al., 2000). The infection is also characterized by fever and abdominal cramps, and in rare cases Guillain–Barre ´ syndrome can emerge as a post- infection complication (Allos, 2001). Despite its importance as a human pathogen, little is known about the mechanisms by which C. jejuni causes disease, although several publications have described potential virulence factors (Dasti et al., 2010). Putative adhesion factors have been identified, e.g. the fibronectin- binding proteins CadF and FlpA (Konkel et al., 1997, 2010), the autotransporter CapA, and a surface-exposed lipoprotein, JIpA (Jin et al., 2001). In addition, the sialylated lipooligosaccharide outer core of C. jejuni has been demonstrated to be an important factor for the invasion of epithelial cells (Guerry et al., 2000; Louwen et al., 2008). Moreover, C. jejuni synthesizes a set of pro- teins which are secreted by the flagellar export apparatus during co-culture of the pathogen with epithelial cells, and these are referred to as Campylobacter invasion antigens (Cia proteins) (Konkel et al., 1999). Although the function of these proteins is still unknown, mutation of ciaB results in a significant reduction of competency to invade host cells (Konkel et al., 2004). Motility of C. jejuni has been shown to be an intestinal colonization factor (Morooka et al., 1985), and O-linked glycosylation of flagellin is crucial for the attachment of the bacterium to intestinal epithelial cells (Yao et al., 1994). In addition, the motility of the pathogen is linked to chemotaxis, which was initially described by Hugdahl et al. (1988). In the genome sequence of C. jejuni NCTC 11168, orthologues of the chemotaxis genes cheA, cheW, cheV, cheY, cheR and cheB have been identified, in which cheA encodes a histidine protein kinase activated by chemoreceptors. CheW interacts with the histidine kinase CheA, mediating the signal from the receptor, while CheY represents a chemotaxis regulator that interacts with the flagellar motor in a phosphorylated form. Furthermore, the proteins CheR and CheB serve as methyltransferase and methylesterase, respectively, for reversible chemoreceptor methylation (Hazelbauer et al., 2008). Finally, the presence of two aerotaxis genes and 10 putative chemoreceptor genes, designated Tlps for transducer-like proteins, has been revealed. These chemoreceptors can be further Abbreviation: MCP, methyl-accepting chemotaxis protein. 3These authors contributed equally to this work. Microbiology (2010), 156, 3123–3135 DOI 10.1099/mic.0.039438-0 039438 G 2010 SGM Printed in Great Britain 3123