One of the first organisms in which quorum sensing was observed were Myxobacteria, a group of gram-negative bacteria, found mainly in soil and also common to marine and freshwater systems. The cellular membranes of autotrophic bacteria contain mono-unsaturated fatty acids. The specific composition and abundance of membrane fatty acids can be used to identify specific genera of bacterial populations in natural environments (e.g., mining lakes, etc.). δ2-cis-Hexadecenoic acid is an unusual fatty acid unique to some Myxococcus species.