Abstract
Members of the diffusible signal factor (DSF) family are a novel class of quorum sensing (QS) signals in diverse Gram-negative bacteria. Although previous studies have identified RpfF as a key enzyme for the biosynthesis of DSF family signals, many questions in their biosynthesis remain to be addressed. In this study with the phytopathogen Xanthomonas campestris pv. campestris (Xcc), we show that Xcc produces four DSF-family signals (DSF, BDSF, CDSF and IDSF) during cell culture, and that IDSF is a new functional signal characterized as cis-10-methyl-2-dodecenoic acid. Using a range of defined media, we further demonstrate that Xcc mainly produces BDSF in the presence of carbohydrates; leucine and valine are the primary precursor for DSF biosynthesis; isoleucine is the primary precursor for IDSF biosynthesis. Furthermore, our biochemical analyses show that the key DSF synthase RpfF has both thioesterase and dehydratase activities, and uses 3-hydroxydedecanoyl-ACP as a substrate to produce BDSF. Finally, our results show that the classic fatty acid synthesis elongation cycle is required for the biosynthesis of DSF-family signals. Taken all together, these findings establish a general biosynthetic pathway for the DSF-family quorum sensing signals.
Highlights
diffusible signal factor (DSF) represents a novel structural class of quorum sensing (QS) signals with the cis-2-unsaturated fatty acid moiety in diverse Gram-negative bacteria pathogens[1,2,3]
Liquid chromatography-mass spectrometry (LC-MS) analysis confirmed that the three compounds in peaks A, B and C were the previously identified DSF-family signals DSF, BDSF and CDSF (Fig. 1b and Supplementary Fig. S1d–f)
The spectrometry data of fraction D suggested a new member of DSF-family signals (IDSF), the characterization of which will be discussed
Summary
DSF (diffusible signal factor) represents a novel structural class of quorum sensing (QS) signals with the cis-2-unsaturated fatty acid moiety in diverse Gram-negative bacteria pathogens[1,2,3]. Enzymogenes, was determined to be 13-methyltetradecanoic acid[11] These findings show that production of multiple DSF-like signals is a common attribute in various bacterial species; the term “DSF family signals” was proposed to describe all the DSF-like signals[6]. RpfB in Xcc and Xyllela fastidiosa was found to be a fatty acyl-CoA ligase required for the degradation of long chain fatty acids[18,19]. These findings suggest that Xcc and Xyllela fastidiosa might have developed a fine-tuned system to control DSF-family signals biosynthesis and degradation. Among the DSF-family signals produced, DSF and CDSF are branched-chain fatty acids. The metabolic origins of DSF-family signals require further investigation
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