Characterization of a quorum-sensing communication based on gamma-butyrolactones in Rhodococcus erythropolis
Quorum sensing (QS) enables bacteria to coordinate collective behaviors, including the production of secondary metabolites with potential biotechnological applications, through the synthesis and detection of small signaling molecules. In Streptomyces, QS is well-described and mainly mediated by 2,3-disubstituted γ-butyrolactones (GBLs), which play key roles in the regulation of secondary metabolism and spore production. Despite their importance, GBL-based QS systems remain poorly characterized in other actinomycetal genera. Here, we investigated the distribution, structure, and function of GBL biosynthetic and regulatory systems within the genus Rhodococcus, focusing on the biocontrol strain Rhodococcus erythropolis R138. Comparative genomic analyses revealed that the scbA and scbR homologs, which are involved in GBL biosynthesis and detection, respectively, are widely conserved among Rhodococcus species and are organized within a conserved GBL gene cluster. Structural modeling using AlphaFold showed a high degree of conservation between ScbA and ScbR from Streptomyces coelicolor and their homologs in R. erythropolis R138. By combining liquid chromatography–mass spectrometry analyses with a GBL-specific reporter assay, we demonstrated that R. erythropolis R138 produces biologically active GBL(−like) molecules. Production of the investigated GBL molecules required the scbA gene, which restored spore production and promoted colony development in the scbA-deleted S. coelicolor strain during interaction with R. erythropolis R138. Transcriptional analyses further showed that both ScbR and a LuxR-like regulator may contribute to the fine-tuned regulation of scbA expression, revealing a complex regulatory network controlling GBL biosynthesis. This study provides novel and unexpected insights into the involvement of a LuxR homolog in regulating a QS system in Gram-positive bacteria. Together, these results demonstrate that functional GBL-based QS systems are conserved and active in R. erythropolis and likely widespread in the genus. This study expands current knowledge of QS in Actinomycetota and highlights the potential role of GBL signaling in regulating biotechnologically and ecologically relevant traits in Rhodococcus.