Maculosin is a diketopiperazine formed by the fusion of tyrosine and proline, reported as a secondary metabolite of fungi and bacteria. In Pseudomonas aeruginosa, maculosin is capable of activating N-acylhomoserine lactones (AHLs). Maculosin is also capable of activating or antagonizing other LuxR-based quorum-sensing systems. While the mode of action of maculosin is not known, its activity suggests the existence of cross talk among bacterial signalling systems. Maculosin was identified as a host-specific toxin produced by Alternaria alternata on spotted knapweed.
Graz, C. J. M., et al. J. Pharm. Pharmacol. 52, 75, (2000)