From Insect Communication to Bacterial Communication

Abstract

One of the driving forces in the early stages of the ISCE and the Journal of Chemical Ecology was the aim to unravel the chemistry and biology of insect communication. Since then, a remarkable number of insect pheromones have been identified, probably for about 1,000 species, and the mysteries of their formation and perception elucidated, in some cases in great detail. We now have a pretty good picture how the chemical message is triggered, produced, released, perceived, processed, and transformed into behavior. A driving force for this was the potential application of many of these insect pheromones.During this time period, the analytical techniques became much more sensitive, new ideas popped-up, and the genomic area arrived. Bacteria were not much on the radar of chemical ecologists 40 years ago, but this changed and nowadays we have become much more interested in the role bacteria play in shaping our environment. Bacteria may influence the production and formation of insect pheromones when thriving on a host, but they also can communicate with each other. A typical phenomenon observed is "quorum-sensing", a trait found in many bacteria. A physiological change in a bacterial population is performed when the pheromone concentration is above a certain threshold level. The concentration of this autoinducer is enlarged by a positive feedback loop.One would think that the sensitive modern techniques and the genomic information at hand would allow easy elucidation of many bacterial semiochemicals, but surprisingly this is not the case. If one looks at the known structures of bacterial pheromones, autoinducers, or quorumsensing compounds, not much more than two handfuls of structural types are described. Nevertheless, similar to insect pheromones for which agricultural application is a driving force, potential pharmaceutical and life science applications stimulate research in bacterial communication, e.g., in biofilm inhibition or antibiotics research.The most explored compounds used in bacterial communication systems are N-acylhomoserine lactones (AHLs) used by Gram-negative bacteria (Dickschat 2010). The AHL-dependent information transfer is the best and most investigated bacterial communication system, and its understanding in all its variants complements that of insect pheromone systems, covering aspects from biosynthesis, perception, degradation, and evoked physiological effects. One reason might be the ease of how genetic information is nowadays at hand. Research on bacterial communication often starts on a genetic level, using homology approaches. By this method, one easily finds similar systems in other bacteria, but not entirely new systems with potential different structures. The major question is whether this predominance of AHLs is indeed a true picture of the reality. Or, are there many more signaling systems working with different compounds, maybe with similar importance to the AHLs? Probably the answer is yes. An example is the recent identification of photopyrones produced by the insect pathogenic pr...