CqsA – CqsS quorum‐sensing signal‐receptor specificity in P hotobacterium angustum

Summary Quorum sensing ( QS ) is a process of bacterial cell–cell communication that relies on the production, detection and population‐wide response to extracellular signal molecules called autoinducers. The QS system commonly found in vibrios and photobacteria consists of the CqsA synthase/ CqsS receptor pair. V ibrio cholerae   CqsA / S synthesizes and detects ( S )‐3‐hydroxytridecan‐4‐one ( C 10‐ CAI ‐1), whereas V ibrio harveyi produces and detects a distinct but similar molecule, ( Z )‐3‐aminoundec‐2‐en‐4‐one ( E a‐ C 8‐ CAI ‐1). To understand the signalling properties of the larger family of CqsA–CqsS pairs, here, we characterize the P hotobacterium angustum   CqsA / S system. Many photobacterial cqsA genes harbour a conserved frameshift mutation that abolishes CAI ‐1 production. By contrast, their cqsS genes are intact. Correcting the P . angustum   cqsA reading frame restores production of a mixture of CAI ‐1 moieties, including C 8‐ CAI ‐1, C 10‐ CAI ‐1, E a‐ C 8‐ CAI ‐1 and E a‐ C 10‐ CAI ‐1. This signal production profile matches the P . angustum   CqsS receptor ligand‐detection capability. The receptor exhibits a preference for molecules with 10‐carbon tails, and the CqsS S er 168 residue governs this preference. P . angustum can overcome the cqsA frameshift to produce CAI ‐1 under particular limiting growth conditions presumably through a ribosome slippage mechanism. Thus, we propose that P . angustum uses CAI ‐1 signalling for adaptation to stressful environments.