Trimeric Form of Intracellular ATP Synthase Subunit [beta] of Aggregatibacter actinomycetemcomitans Binds Human Interleukin-1[beta]

Bacterial biofilms resist host defenses and antibiotics partly because of their decreased metabolism. Some bacteria use proinflammatory cytokines, such as interleukin (IL)-1[beta], as cues to promote biofilm formation and to alter virulence. Although one potential bacterial IL-1[beta] receptor has been identified, current knowledge of the bacterial IL-1[beta] sensing mechanism is limited. In chronic biofilm infection, periodontitis, Aggregatibacter actinomycetemcomitans requires tight adherence (tad)-locus to form biofilms, and tissue destroying active lesions contain more IL-1[beta] than inactive ones. The effect of IL-1[beta] on the metabolic activity of A. actinomycetemcomitans biofilm was tested using alamarBlue[TM]. The binding of IL-1[beta] to A. actinomycetemcomitans cells was investigated using transmission electron microscopy and flow cytometry. To identify the proteins which interacted with IL-1[beta], different protein fractions from A. actinomycetemcomitans were run in native-PAGE and blotted using biotinylated IL-1[beta] and avidin-HRP, and identified using mass spectroscopy. We show that although IL-1[beta] slightly increases the biofilm formation of A. actinomycetemcomitans, it reduces the metabolic activity of the biofilm. A similar reduction was observed with all tad-locus mutants except the secretin mutant, although all tested mutant strains as well as wild type strains bound IL-1[beta]. Our results suggest that IL-1[beta] might be transported into the A. actinomycetemcomitans cells, and the trimeric form of intracellular ATP synthase subunit [beta] interacted with IL-1[beta], possibly explaining the decreased metabolic activity. Because ATP synthase is highly conserved, it might universally enhance biofilm resistance to host defense by binding IL-1[beta] during inflammation.