CYCLO(-PHE-PRO)

A new butyrolactone, 7″-hydroxybutyrolactone III (1) and three new cycloheptanetriones, terretrione A-C (2-4), together with five known compounds, butyrolactone I, cyclo(Leu-Pro), cyclo(Val-Pro), cyclo(Ile-Pro), cyclo(Phe-Pro), were isolated from mangrove-associated marine fungus Aspergillus terreus. The structures of these compounds were elucidated on the basis of physical data analysis (NMR, high resolution-electrospray ionization (HR-ESI)-MS), especially by 2D-NMR techniques. These compounds showed weak cytotoxicity in vitro against HCT-8, Bel-7402, BGC-823, A2780 cell lines.

We report the detection by gas chromatography/mass spectrometry and liquid chromatography/mass spectrometry analyses of the secreted 2,5-diketopiperazines (DKPs) cyclo(-Ala-Pro), cyclo(-Gly-Pro), cyclo(-Val-Pro), cyclo(-Ile-Pro), cyclo(-Leu-Pro), cyclo(-Pro-Pro), cyclo(-HyP-Pro), cyclo(-Met-Pro), and cyclo(-Phe-Pro) produced by Bacillus pumilus. The study focuses on a marine isolate and a laboratory test strain of B. pumilus with capabilities to lyse pregrown living cell lawns of different bacterial species, among them Arthrobacter citreus. Chromatographic methods were used to analyze induced bioactive compounds. At least 13 different DKPs are produced by B. pumilus. Both strains respond with an increased production of the DKPs cyclo(-Gly-Pro), cyclo(-Ala-Pro), and cyclo(-Val-Pro) to the presence of pasteurized A. citreus cells after 4 h in a nutrient-poor liquid medium. In agar diffusion assays, these DKPs did not cause lysis zones in living cell lawns, but they did inhibit further growth of several pregrown test bacteria in microplates even at concentrations as low as 1 μg ml(-1).

Vibrio cholerae is an aquatic organism that causes the severe acute diarrheal disease cholera. The ability of V. cholerae to cause disease is dependent upon the production of two critical virulence determinants, cholera toxin (CT) and the toxin-coregulated pilus (TCP). The expression of the genes that encode for CT and TCP production is under the control of a hierarchical regulatory system called the ToxR regulon, which functions to activate virulence gene expression in response to in vivo stimuli. Cyclic dipeptides have been found to be produced by numerous bacteria, yet their biological function remains unknown. V. cholerae has been shown to produce cyclo(Phe-Pro). Previous studies in our laboratory demonstrated that cyclo(Phe-Pro) inhibited V. cholerae virulence factor production. For this study, we report on the mechanism by which cyclo(Phe-Pro) inhibited virulence factor production. We have demonstrated that exogenous cyclo(Phe-Pro) activated the expression of leuO, a LysR-family regulator that had not been previously associated with V.