Anaerobic regulation of Actinobacillus actinomycetemcomitans leukotoxin transcription is ArcA/FnrA-independent and requires a novel promoter element

David Kolodrubetz, Linda Phillips, Chris Jacobs, Alex Burgum, Ellen Kraig

Research output: Contribution to journalArticle

19 Scopus citations


The periodontal pathogen, Actinobacillus actinomycetemcomitans, produces a 116-kDa leukotoxin that appears to help the bacterium evade the innate host immune response. The expression of leukotoxin is induced when cells are grown anaerobically, a condition found in the subgingival crevice. This regulation most likely occurs at the transcriptional stage since the levels of leukotoxin RNA are induced by hypoxic growth. In order to map the leukotoxin promoter element(s) responsible for oxygen regulation, deletion and linker-scanning mutations were cloned into a transcriptional reporter gene plasmid and then tested in A. actinomycetemcomitans grown aerobically or anaerobically. A 35-bp DNA element, at position -36 to -70, was found to be responsible for the repression of leukotoxin synthesis in aerobically grown A. actinomycetemcomitans. The sequence of this oxygen response element (ORE) does not match the consensus binding sites for known DNA binding proteins, not even Fnr or ArcA which play major roles in oxygen regulation in other bacteria. However, since sequence analysis alone cannot disprove a role for the Fnr or ArcAB pathways in leukotoxin regulation, the genes for the Fnr and ArcA homologues in A. actinomycetemcomitans were identified, mutated by targeted insertional mutagenesis and assessed for loss of oxygen regulation. Deletion of either fnr or arcA altered the expression of numerous A. actinomycetemcomitans proteins, but leukotoxin expression was still repressed by oxygen. These results, coupled with the promoter mutation analyses, lead to the conclusion that A. actinomycetemcomitans employs a novel pathway in the aerobic/anaerobic regulation of leukotoxin synthesis.

Original languageEnglish (US)
Pages (from-to)645-653
Number of pages9
JournalResearch in Microbiology
Issue number9
Publication statusPublished - Nov 2003



  • Actinobacillus actinomycetemcomitans
  • Bacterial gene expression regulation
  • Bacterial toxin

ASJC Scopus subject areas

  • Microbiology
  • Molecular Biology

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