The spent culture supernatant ofPseudomonas syringaecontains azelaic acid

Pseudomonas syringae pv. actinidiae (PSA) is an emerging kiwifruit bacterial pathogen which since 2008 has caused considerable losses. No quorum sensing (QS) signaling molecule has yet been reported from PSA and the aim of this study was to identify possible intercellular signals produced by PSA. A metabolome analysis resulted in the identification of 83 putative compounds, one of them was the nine carbon saturated dicarboxylic acid azelaic acid which for several reasons was decided to further study. Firstly azelaic acid, which is a straight chained nine-carbon (C9) saturated dicarboxylic acid, has been reported in plants as mobile signal that primes systemic defenses. Secondly its structure, which is associated with fatty acid biosynthesis, is similar to other known bacterial QS signals like the Diffusible Signal Facor (DSF). Analytical and structural studies by NMR spectroscopy confirmed that in the PSA spent supernatant azelaic acid was present. Quantification studies further revealed that 20 µg/L of azelaic acid was present and was also found in spent supernatants of several other P. syringae pathovars. An RNAseq transcriptome study however did not reveal whether azelaic acid behaved as a QS molecule. This is the first report of the possible natural biosynthesis of azelaic acid by bacteria.