Listening to a New Language: DSF-Based Quorum Sensing in Gram-Negative Bacteria

Several types of QS signals have been identified in Gram-negative bacteria since the 1980s. Autoinducer 2 (AI-2) is another type of widely detected QS signal, which was identified originally in Vibrio harVeyi and subsequently in other Gram-negative bacteria species. Apart from the above-mentioned QS signals, the diffusible signal factor (DSF), which was originally identified in Xanthomonas campestris pv campestris (Xcc), represents another interesting type of QS signal found in Gram-negative bacterial pathogens. Crude DSF extracts were initially prepared by extraction of culture supernatants of Xcc using 0.3 volumes of sodium bicarbonate-equilibrated ethyl acetate. DSF-family signals share a fatty acid carbon chain with variations in chain length, double-bond configuration, and side-chain. X. campestris pv campestris (Xcc) is the causal agent of black rot of cruciferous plants, which is possibly the most important disease of crucifers worldwide.