Intra- and Interspecies Regulation of Gene Expression byActinobacillus actinomycetemcomitansLuxS

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.

COLONIZATION BY <i>PORPHYROMONAS</i> <i>GINGIVALIS</i> AND <i>PREVOTELLA INTERMEDIA</i> FROM TEETH TO OSSEOINTEGRATED IMPLANT REGIONS

“…Kolenbrander demonstrated that dental plaque is a unique ecosystem and these multiple bacterial species form a community 14) . Recent studies have demonstrated that periodontopathic bacteria produced extracellular signals 5,8,9) . Moreover, although the immunological response related to phagocytosis is able to eliminate bacteria on the surface of biofilm, phagocytic cells cannot phagocytose or kill the bacterial cells within the biofilm 14) .…”

Transcriptional and antagonistic responses of Pseudomonas fluorescens Pf0-1 to phylogenetically different bacterial competitors

“…Among the genes that are upregulated during interspecific bacterial interactions are often the genes involved in the production of antibiotics, suggesting that antibiosis may be a common defensive or offensive strategy in microbial interactions (Fong et al, 2001;Harrison et al, 2008;Garbeva and de Boer, 2009). In addition, genes that confer resistance against toxins were also found to be upregulated during competitive interactions, suggesting protection against self-intoxication or against toxins produced by other members of the microbial community (Dantas et al, 2008;Martinez 2008Martinez , 2009.…”

Modulation of Iron-Uptake Systems by a Mutation of luxS Encoding an Autoinducer-2 Synthase in Vibrio vulnificus

“…19) Various and intricate links between LuxS or AI-2-QSS and IUS expression have been reported in some bacteria. [20][21][22][23][24][25][26] However, the presence of such links remains undetermined in V. vulnificus. AI-2 production through the enzymatic action of LuxS is the prerequisite step for AI-2 signaling.…”