| Summary: | <i>Anoxybacillus amylolyticus</i> is a moderate thermophilic microorganism producing an exopolysaccharide and an extracellular α-amylase able to hydrolyze starch. The synthesis of several biomolecules is often regulated by a quorum sensing (QS) mechanism, a chemical cell-to-cell communication based on the production and diffusion of small molecules named “autoinducers”, most of which belonging to the <i>N</i>-acyl homoserine lactones’ (AHLs) family. There are few reports about this mechanism in extremophiles, in particular thermophiles. Here, we report the identification of a signal molecule, the <i>N</i>-butanoyl-homoserine lactone (C4-HSL), from the milieu of <i>A. amylolyticus</i>. Moreover, investigations performed by supplementing a known QS inhibitor, <i>trans</i>-cinnamaldehyde, or exogenous C4-HSL in the growth medium of <i>A. amylolyticus</i> suggested the involvement of QS signaling in the modulation of extracellular α-amylase activity. The data showed that the presence of the QS inhibitor <i>trans</i>-cinnamaldehyde in the medium decreased amylolytic activity, which, conversely, was increased by the effect of exogenous C4-HSL. Overall, these results represent the first evidence of the production of AHLs in thermophilic microorganisms, which could be responsible for a communication system regulating thermostable α-amylase activity.
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