Abstract
N-acylhomoserine lactones (AHLs), bacterial signaling compounds involved in quorum-sensing, are a structurally diverse group of compounds. We describe here the identification, synthesis, occurrence and biological activity of a new AHL, N-((2E,5Z)-2,5-dodecadienoyl)homoserine lactone (11) and its isomer N-((3E,5Z)-3,5-dodecadienoyl)homoserine lactone (13), occurring in several Roseobacter group bacteria (Rhodobacteraceae). The analysis of 26 strains revealed the presence of 11 and 13 in six of them originating from the surface of the macroalgae Fucus spiralis or sediments from the North Sea. In addition, 18 other AHLs were detected in 12 strains. Compound identification was performed by GC/MS. Mass spectral analysis revealed a diunsaturated C12 homoserine lactone as structural element of the new AHL. Synthesis of three likely candidate compounds, 11, 13 and N-((2E,4E)-2,4-dodecadienoyl)homoserine lactone (5), revealed the former to be the natural AHLs. Bioactivity test with quorum-sensing reporter strains showed high activity of all three compounds. Therefore, the configuration and stereochemistry of the double bonds in the acyl chain seemed to be unimportant for the activity, although the chains have largely different shapes, solely the chain length determining activity. In combination with previous results with other Roseobacter group bacteria, we could show that there is wide variance between AHL composition within the strains. Furthermore, no association of certain AHLs with different habitats like macroalgal surfaces or sediment could be detected.
Highlights
N-acylhomoserine lactones (AHLs) are well known signalling compounds used by Gram-negative bacteria for quorum-sensing (QS)-driven cell-to-cell communication
We currently look into the inventory of AHLs occurring in Roseobacter group bacteria
In an extension of this study we investigated 16 strains obtained from one location of samples of the algae Fucus spiralis, collected from a single location (Neuharlingersiel, German Wadden Sea), nine strains from Norwegian trench sediments [19] and one sea water strain from the German/Danish coast to test for the occurrence of specific AHL signatures
Summary
N-acylhomoserine lactones (AHLs) are well known signalling compounds used by Gram-negative bacteria for quorum-sensing (QS)-driven cell-to-cell communication. QS is a cell density-dependant mechanism to regulate physiological traits like antibiotic production, cell differentiation or biofilm formation [1,2,3,4,5,6,7]. AHLs constitute a γ-lactone ring and an acyl side chain that is usually even-numbered and unbranched, ranging in chain length from C4 –C18 [3]. Mar. Drugs 2019, 17, 20; doi:10.3390/md17010020 www.mdpi.com/journal/marinedrugs. Functional groups like hydroxy- or carbonyl-group can be present at C-3 of the acyl chain
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