Quorum sensing (QS) is a microbial cell-cell communication system that regulates gene expression in response to population density to coordinate collective behaviors. Yet, the role of QS in resolving the stresses caused by the accumulation of toxic metabolic by-products at high cell density is not well defined. In response to cell density, QS could be involved in reprogramming of the metabolic network to maintain population stability. Using unbiased metabolomics, we discovered that Vibrio cholerae mutants genetically locked in a low cell density (LCD) QS state are unable to alter the pyruvate flux to convert fermentable carbon sources into neutral acetoin and 2,3-butanediol molecules to offset organic acid production. As a consequence, LCD-locked QS mutants rapidly lose viability when grown with fermentable carbon sources. This key metabolic switch relies on the QS-regulated small RNAs Qrr1-4 but is independent of known QS regulators AphA and HapR. Qrr1-4 dictate pyruvate flux by translational repression of the enzyme AlsS, which carries out the first step in acetoin and 2,3-butanediol biosynthesis. Consistent with the idea that QS facilitates the expression of a common trait in the population, AlsS needs to be expressed cooperatively in a group of cells. Heterogeneous populations with high percentages of cells not expressing AlsS are unstable. All of the cells, regardless of their respective QS states, succumb to stresses caused by toxic by-product accumulation. Our results indicate that the ability of the bacteria to cooperatively control metabolic flux through QS is critical in maintaining a sustainable environment and overall population stability.

Eudistomin U is a member of a subclass of naturally occurring indole alkaloids known as β-carbolines. These molecules are reported to have diverse biological activity and high binding affinity to DNA, which make them attractive targets for total synthesis. We describe an efficient, five-step synthesis of eudistomin U by employing two key reactions: a Bischler-Napieralski cyclization and a Suzuki cross coupling. We also describe the cytotoxicity of eudistomin U against various cancer cell lines and human pathogens, in which we observed potent antibacterial activity against Gram-positive bacteria.

Eudistomin U is a member of the β-carboline class of heterocyclic amine-containing molecules that are capable of binding to DNA. The structure of eudistomin U is unique since it contains an indole ring at the 1-position of the pyridine ring. While simple β-carbolines are reported to intercalate DNA, an examination of the mode of binding of eudistomin U has been lacking. We report preliminary spectroscopic (UV-Vis, thermal denaturation, CD) and calorimetric (DSC) data on the binding of eudistomin U to DNA, which suggest that eudistomin U binds weakly according to a mechanism that is more complicated than other members of its class.

Natural products have been the leading source of potential drug leads and comprise approximately a third of the drugs on the market. β‐carbolines are a class of naturally occurring, tricyclic aromatic indole alkaloids that have been used to probe the biochemistry of a broad range of ailments. A subclass of β‐carbolines, known as the eudistomins, is reported to have diverse biological activity, as well as a high binding affinity to DNA. Through a novel five‐step synthesis, our lab successfully synthesized the natural product eudistomin U, a derivative of the eudistomin family. Furthermore, we have characterized eudistomin U's cytotoxic activity, as well as the compound's interaction with DNA via spectroscopic and biophysical techniques. We have determined that eudistomin U weakly binds to DNA in a nonspecific fashion, thus DNA binding is most likely not the cause of toxicity observed in the bacterial and cancer cell lines. We hope that future experiments will elucidate how eudistomin U disrupts biochemical pathways.