Volatile compounds as bacterial communication signals: State of art, limitations and future perspectives.

Bacteria emit a wide diversity of volatile compounds as byproducts of their metabolism. Despite their increasing recognition as essential mediators of microbial interactions, their role as true communication signals and the molecular mechanisms of their perception remain incompletely understood. This review explores the biological functions of bacterial volatile compounds in a microbiological communication framework, emphasizing the distinctions between stricto sensu signaling molecules and cues. Although there are several volatile compounds that act as signals between species, there is a significant knowledge gap in terms of the underlying molecular mechanisms. To address this issue, bacterial gene regulatory systems and quorum sensing pathways are considered. We suggest that transmembrane receptors are the best targets for volatile signals. Moreover, volatile-mediated signaling may play distinct biological roles depending on the molecules involved. Survival-related information, such as stress or nutrients, may be conveyed by compounds acting as interspecies signals, which may require highly sensitive sensors. Volatiles that function as autoinducers seem to provide information on spatial confinement and population context, and may require sensors with lower sensitivity. This work supports the view that volatile-mediated signaling represents a distinct mode of bacterial communication completing classical communication pathways and proposes suitable methodology to decipher it.