| Summary: | Aggregatibacter actinomycetemcomitans is associated with aggressive forms of periodontitis. The mechanisms that control the expression of virulence factors are essentially unknown. Histone-like nucleoid structuring protein, H-NS, is a DNA binding protein that has been shown to influence hundreds of genes in Gram-negative bacteria. H-NS usually acts as a transcriptional silencer and has a negative influence on gene expression. H-NS has not been studied in A. actinomycetemcomitans before, and its effects on gene expression in this species were lacking. This study aimed to investigate if lack of H-NS expression might result in apparent phenotypical differences regarding gene expression with emphasis on virulence. For this we have used the A. actinomycetemcomitans rough-colony serotype a strain, D7S, its smooth-colony derivative D7SS, and hns mutants of D7S and D7SS. Our results show that smooth colony strain D7SS releases a larger amount of vesicles as compared to the rough D7S. The D7S hns mutant appeared to exhibit pili that were shorter than those of the parental strain, and this was not due to altered expression of RcpA in the hns mutant. As judged by Silver-staining, and Western blot analysis, H-NS may influence the level of several proteins. Taken together, our study supports that H-NS is involved in the regulation of virulence factor expression in A. actinomycetemcomitans.
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