Contributions of six lineage-specific internalin-like genes to invasion efficiency of Listeria monocytogenes.
Listeria monocytogenes strains are divided into at least three lineages, which seem to differ in virulence. Internalins are surface-attached or secreted proteins that encode leucine-rich repeats, and L. monocytogenes encodes species-specific as well as lineage-specific internalin and internalin-like genes. Internalins A and B have previously been shown to be critical for L. monocytogenes host cell invasion. Transcription of selected internalins is regulated by the virulence gene regulator PrfA and/or the stress-responsive alternative sigma factor sigma(B). We hypothesized that lineage-specific internalin-like genes may contribute to differential virulence and niche adaptation of the L. monocytogenes lineages. Initial quantitative real time, reverse transcriptase PCR (RT-PCR) showed that the six selected lineage-specific internalin-like genes were transcribed in cells grown at 16 degrees and 37 degrees C. Lineage-specific internalin-like gene, lineage II (lsiIIX) showed significantly higher transcript levels in log-phase cells grown at 37 degrees C as compared to 16 degrees C. The gene lsiIA was preceded by a putative sigma(B)-dependent promoter and showed sigma(B)-dependent transcription. None of the null mutants in lineage-specific internalin-like genes differed from their respective parent strain in ability to invade either human intestinal epithelial or hepatocyte-like cell lines. All three mutants in lineage I-specific internalin-like genes exhibited the same growth condition-dependent invasion phenotype as their parent strain ( approximately 1.5 log higher invasion efficiency when grown at 30 degrees C without aeration versus 37 degrees C with aeration). Despite structural similarities to internalins with known roles in host cell attachment and invasion, none of the six lineage-specific internalin-like genes characterized here appear to contribute to invasion. Combined with the observation that some nonpathogenic Listeria species also carry internalin genes, our findings suggest a broad role of Listeria internalins, not limited to attachment and invasion of human cells. Due to the wide host range of L. monocytogenes and the fact that transcription of internalin-like genes can differ considerably depending on growth condition, elucidating the function of different internalins and internalin-like genes will remain a challenge.
Milillo
Sara R
SR
Department of Food Science, Cornell University, Ithaca, New York, USA. srm43@cornell.edu
Wiedmann
Martin
M
D001422:Bacterial Adhesion / Q000502:physiology; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism*; D018938:Caco-2 Cells / Q000382:microbiology; D015964:Gene Expression Regulation, Bacterial; D056945:Hep G2 Cells / Q000382:microbiology; D006801:Humans; D008089:Listeria monocytogenes / Q000235:genetics / Q000378:metabolism* / Q000472:pathogenicity; D008390:Markov Chains; D012329:RNA, Bacterial / Q000032:analysis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012808:Sigma Factor / Q000378:metabolism*; D013045:Species Specificity; D013696:Temperature; D014158:Transcription, Genetic
D001426:Bacterial Proteins; D012329:RNA, Bacterial; C079011:SigB protein, Bacteria; D012808:Sigma Factor; C069761:internalin protein, Bacteria