Lecture 13.doc

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University of Alberta
Microbiology (Biological Sciences)
Nicolas Vozza

Lecture 13 1 CELL TO CELL SIGNALLING III Additional AHL Functions (Kaufmann et al, Jan 2005 PNAS) During a study to determine the lifespan of Pa. LasI AHL in water, it was discovered that 3oxoC12 underwent an unexpected reaction to a compound belonging to a class of compounds called tetramic acids. (compound 4) These compounds have potent antibacterial activity. Structure resembles known antibacterials and antifungals. A variety of AHLs were subjected to the same conditions and all formed tetramic acids irrespective of chain length. Significant antibacterial activity was found for compound 4 towards all tested Gram + bacteria, and none was found towards any Gram – bacteria. The activity is biologically relevant because AHL concentrations are high and other antibacterials have similar activities. Lecture 13 2 Bacillus’ lactonase (Aii) activity protected from compound 1 (AHL), but not compound 4. Maybe this activity is useful not only to disrupt QS, but also to reduce toxicity. Lactobacillus reutercyclin is bactericidal as it acts as a proton-ionophore (carries ions), dissipating the transmembrane change in pH and leading to cell lysis (probably due to its high hydrophobicity). Structural resemblance between compound 4 and antibacterials is shaded. Interestingly, 3oxoC12 also demonstrated cytotoxicity. Dual role: Not due to tetramic acid formed since the experiment did not run long enough for spontaneous conversion. B. cereus strains producing a penicillinase were resistant to C12 AHL and not to compound 4. Lecture 13 3 Because B. cereus produce lactonases, perhaps signaling interference or “quorum quenching” is not the real goal of these enzymes Instead they may permit survival of cytotoxicity. This would eliminate toxic effects of 1 and prevent formation of 4. And maybe 3 oxoC12 AHL evolved as signaling molecules because of their fortuitous cytotoxic abilities, and their ability to convert to tetramic acids, which are resistant to lactonase degradation. But wait… Compound 4 also has the structure of a simple siderophore, complexing 1 Fe for every 3 tetramic acids Lecture 13 4 The affinity constant for compound 4 is quite high, much higher than one of Pa.’s normal siderophores, and similar to other iron chelators. Whether iron complexation i
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