Gram-negative bacterial quorum sensing is mainly regulated by an extracellularly produced N-acylhomoserine lactone (AHL). AHL consists of a lactone ring and an acyl chain, which generally varies from C₄ to C₁₈ in length and affords species-specific variety. In this study, we developed an ultra-high performance liquid chromatography tandem mass spectrometry system and detected two kinds of long chain AHLs with chain length C₂₀ from the reverse-phase thin layer chromatography-fractionated cultured supernatant of the marine photosynthetic bacterium Rhodovulum sulfidophilum. By fragmentation search analysis to detect compounds with a homoserine lactone ring moiety for data dependent acquisition, a minor AHL, presumed to be 3-OH-C₁₈-homoserine lactone (HSL), was also found. Among the detected C₂₀-HSLs, 3-OH-C₂₀-HSL was structurally identified and 3-OH-C_20:1-HSL was strongly suggested. To our knowledge, this is the first report to show a novel AHL with the longest C₂₀ acyl side chain found to date. Abbreviations: AGC: automatic gain control; AHL: N-acylhomoserine lactone; CD: cyclodextrin; CID: collision induced dissociation; DDA: data dependent acquisition; EPI: enhanced product ion; FISh: fragment ion search; HCD: high energy collisional dissociation; HSL: homoserine lactone; IT: injection time; LC: liquid chromatography; MS: mass spectrometry; PRM: parallel reaction monitoring; RP: reverse phase; SRM: selected reaction monitoring; TLC: thin layer chromatography; UHPLC: ultra high performance liquid chromatography Novel longest acyl chained HSL produced by R. sulfidophilum.

Gram-negative bacterial quorum sensing is mainly regulated by an extracellularly produced N-acylhomoserine lactone (AHL). AHL consists of a lactone ring and an acyl chain, which generally varies from C₄ to C₁₈ in length and affords species-specific variety. In this study, we developed an ultra-high performance liquid chromatography tandem mass spectrometry system and detected two kinds of long chain AHLs with chain length C₂₀ from the reverse-phase thin layer chromatography-fractionated cultured supernatant of the marine photosynthetic bacterium Rhodovulum sulfidophilum. By fragmentation search analysis to detect compounds with a homoserine lactone ring moiety for data dependent acquisition, a minor AHL, presumed to be 3-OH-C₁₈-homoserine lactone (HSL), was also found. Among the detected C₂₀-HSLs, 3-OH-C₂₀-HSL was structurally identified and 3-OH-C_20:1-HSL was strongly suggested. To our knowledge, this is the first report to show a novel AHL with the longest C₂₀ acyl side chain found to date. Abbreviations: AGC: automatic gain control; AHL: N-acylhomoserine lactone; CD: cyclodextrin; CID: collision induced dissociation; DDA: data dependent acquisition; EPI: enhanced product ion; FISh: fragment ion search; HCD: high energy collisional dissociation; HSL: homoserine lactone; IT: injection time; LC: liquid chromatography; MS: mass spectrometry; PRM: parallel reaction monitoring; RP: reverse phase; SRM: selected reaction monitoring; TLC: thin layer chromatography; UHPLC: ultra high performance liquid chromatography Novel longest acyl chained HSL produced by R. sulfidophilum.