Thiarubrine A, a dithiacyclohexadiene polyine from the roots of Chaenactis douglasii, and a related dithiacyclohexadiene from Rudbeckia hirta exhibit strong light-independent antibacterial and antifungal activity. This activity is enhanced by exposure to visible light. Visible light also converts the compounds to the corresponding thiophenes. These are antibiotic only when irradiated with UV-A. Dithiacyclohexadienes are the first polyines to exhibit such complex mechanisms of toxicity towards microorganisms.

Escherichia coli and Saccharomyces cereuisiae by phenylheptatriyne from Bidenspilosa. Can. J. Microbiol. 26: 698-705.The photosensitizing action of 7-phenylhepta-2,4,6triyne (PHT), a polyacetylenic compound isolated from Bidens pilosa L. (Asteraceae), has been studied using Escherichia coli and Saccharomycrs cereuisiae as the test organisms. The survival curves for E. colitreated with PHTand ultraviolet (UV) radiation wereobtained and have been interpreted quantitatively on the basis ofa target theory model. The number of "targets" in the cell that must be destroyed before cell death occurs was estimated at six, whereas the dose, Do, that reduced the surviving fraction of the population to I/e of its value was estimated to be 280 J/m2. Survival was enhanced in aerobic conditions as compared with anaerobic conditions, which is strong evidence that PHT does not behave as a photodynamic sensitizer in vivo. This view was confirmed by work with azide (a quencher of singlet oxygen), D 2 0 (which increases the lifetime of singlet oxygen), and superoxide dismutase (which scavenges superoxide radicals). None of these treatments modified the survival curves significantly, indicating that activated species of 0, are probably not involved in photosensitizations with PHT in vivo.Cell respiration was found to be rapidly inhibited by mild treatments of PHT and UV radiation, suggesting that nuclear metabolism is not the primary target of photosensitization as is the case with another group of photosensitizers, the furanocoumarins. The available evidence indicates that PHT is a representative of a new class of phototoxic compounds. A mechanism of action involving production of free radicals is proposed. ARNASON, THOR, CHI-KIT WAT. KELSEY DOWNUM, ETSUO YAMAMOTO, ELIZABETH GRAHAM et G. H. NEIL TOWERS. 1980. Photosensitization of Eschrrichia coli and Saccharotnyces crreuisiae by phenylheptatriyne from Bidenspilosa. Can. J. Microbiol. 26: 698-705. Nous avons etudie, en utilisant Escherichia coli et Saccharornyces cereuisiae comme organismes tests, l'effet photosensibilisateur du 7-phknylhepta-2,4,6triyne (PHT), un compose polyacktylenique isole de Bidens pilosa L. (Asteraceae). Nous avons obtenu des courbes de survie pour des cellules d'E.coli traitees au PHTet aux rayons ultraviolets(UV); ces courbesont ete interpretees quantitativement partir d'un modele reposant sur la theorie des cibles. Le nombre de "cibles" qui doivent itre detrouites avant que la mort cellulaire ne survienne a etC estime a six; quant a la dose Do qui reduit a I/e le fraction des survivants, elle a ete estimee a 280 J/m2. La survie etait meilleure sous des conditions aerobies qu'anairobies: ceci renforce I'evidence que le PHT ne se comporte pas comme un sensibilisateur photodynamique in vivo. Ce point a ete confirme en verifiant les effets de I'azoture (extincteur de I'oxygene singulet), du D,O (qui prolonge la durke de vie de I'oxygene singulet) et de la superoxyde dismutase (qui capte les radicaux superoxyde). Aucun de ces traitements n'a modifii de f a~o n s...

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