title: Intra- and interspecies regulation of gene expression by Actinobacillus actinomycetemcomitans LuxS.
abstract: The cell density-dependent control of gene expression is employed by many bacteria for regulating a variety of physiological functions, including the generation of bioluminescence, sporulation, formation of biofilms, and the expression of virulence factors. Although periodontal organisms do not appear to secrete acyl-homoserine lactone signals, several species, e.g., Porphyromonas gingivalis, Prevotella intermedia, and Fusobacterium nucleatum, have recently been shown to secrete a signal related to the autoinducer II (AI-2) of the signal system 2 pathway in Vibrio harveyi. Here, we report that the periodontal pathogen Actinobacillus actinomycetemcomitans expresses a homolog of V. harveyi luxS and secretes an AI-2-like signal. Cell-free conditioned medium from A. actinomycetemcomitans or from a recombinant Escherichia coli strain (E. coli AIS) expressing A. actinomycetemcomitans luxS induced luminescence in V. harveyi BB170 >200-fold over controls. AI-2 levels peaked in mid-exponential-phase cultures of A. actinomycetemcomitans and were significantly reduced in late-log- and stationary-phase cultures. Incubation of early-log-phase A. actinomycetemcomitans cells with conditioned medium from A. actinomycetemcomitans or from E. coli AIS resulted in a threefold induction of leukotoxic activity and a concomitant increase in leukotoxin polypeptide. In contrast, no increase in leukotoxin expression occurred when cells were exposed to sterile medium or to conditioned broth from E. coli AIS(-), a recombinant strain in which luxS was insertionally inactivated. A. actinomycetemcomitans AI-2 also induced expression of afuA, encoding a periplasmic iron transport protein, approximately eightfold, suggesting that LuxS-dependent signaling may play a role in the regulation of iron acquisition by A. actinomycetemcomitans. Finally, A. actinomycetemcomitans AI-2 added in trans complemented a luxS knockout mutation in P. gingivalis by modulating the expression of the luxS-regulated genes uvrB and hasF in this organism. Together, these results suggest that LuxS-dependent signaling may modulate aspects of virulence and the uptake of iron by A. actinomycetemcomitans and induce responses in other periodontal organisms in mixed-species oral biofilm.
authors.affiliation: Department of Biochemistry, School of Dental Medicine, University of Pennsylvania, Philadelphia 19104-6002, USA.
authors.forename: K P
authors.initials: KP
authors.lastname: Fong
authors.forename: W O
authors.initials: WO
authors.lastname: Chung
authors.forename: R J
authors.initials: RJ
authors.lastname: Lamont
authors.forename: D R
authors.initials: DR
authors.lastname: Demuth
mesh_terms: D016976:Aggregatibacter actinomycetemcomitans / Q000235:genetics*; D001426:Bacterial Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D013437:Carbon-Sulfur Lyases; D002352:Carrier Proteins / Q000096:biosynthesis; D002450:Cell Communication / Q000502:physiology*; D017077:Culture Media, Conditioned; D005098:Exotoxins / Q000096:biosynthesis; D015964:Gene Expression Regulation, Bacterial; D006714:Homoserine / Q000031:analogs & derivatives* / Q000096:biosynthesis*; D007501:Iron / Q000378:metabolism; D007783:Lactones; D009055:Mouth / Q000382:microbiology; D016966:Porphyromonas gingivalis / Q000235:genetics; D011994:Recombinant Proteins / Q000378:metabolism; D013045:Species Specificity; D014733:Vibrio / Q000235:genetics
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; D017077:Culture Media, Conditioned; D005098:Exotoxins; D007783:Lactones; C091088:N-octanoylhomoserine lactone; D011994:Recombinant Proteins; C018579:leukotoxin; D006714:Homoserine; D007501:Iron; D013437:Carbon-Sulfur Lyases; C117753:LuxS protein, Bacteria