Identification of New N‐Acylhomoserine Lactone Signalling Compounds of Dinoroseobacter shibae DFL‐12^T by Overexpression of luxI Genes

Abstract

Bacteria of the Roseobacter clade are widespread in the ocean and occur in many different habitats. In the genome of Dinoroseobacter shibae DFL-12, luxI homologous genes that encode synthases responsible for the formation of N-acylhomoserine lactones (AHLs) have been described. These compounds are known autoinducers that regulate several biological traits-namely, flagella formation and cell differentiation-in D. shibae through quorum sensing. The AHLs produced by D. shibae mainly consisted of N-octadecadienoylhomoserine lactone (C18:2-AHL) and N-octadecenoylhomoserine lactone (C18:1-HSL). In the wild type these AHLs are synthesized only in low abundance. The luxI genes were therefore expressed in Escherichia coli; this resulted in the formation of AHLs mostly different from those found in the D. shibae wild type. A luxI1 -deficient mutant of D. shibae was then reprovided with an overexpressed luxI1 gene. This strain produced large amounts of C18:2-AHL and C18:1-AHL, allowing full characterization of these compounds by mass spectrometric techniques and derivatization. Synthesis of the proposed structures confirmed that the major compound is (2E,11Z)-N-octadeca-2,11-dienoylhomoserine lactone (6, C18:2-HSL), accompanied by (Z)-N-octadec-11-enoylhomoserine lactone (5, C18:1-HSL). AHL 6 has not been reported before from other organisms and contains an unusual 2E double bond.

You are what you talk: quorum sensing induces individual morphologies and cell division modes in Dinoroseobacter shibae

“…The constitutive heterologous expression of each synthase in a non-AHL-producing E. coli resulted in the production of long-chain AHLs (Supplementary Figure S1). GC-MS analysis (Neumann et al, 2013) showed that when expressed in E. coli, the main compound produced by LuxI 1 was the wild-type signal C18en-HSL. In addition, small amounts of C16-HSL, C15-HSL and C14-HSL were found.…”

“…As the deletion of only one synthase leads to a complete loss of AHL production, the contribution of LuxI 2 and LuxI 3 to AHL synthesis in D. shibae appears to be dependent on the presence and level of the signal molecules provided by LuxI 1 . The wild-type signals C18en-HSL and C18dien-HSL were strongly overproduced in the D. shibae DluxI 1 strain carrying pDP1, and thus it was possible to purify these novel signals and determine their absolute configuration (Neumann et al, 2013). Both C18en-HSL and C18dien-HSL were then chemically synthesized and their effect on the phenotype and transcriptome of the DluxI 1 deletion strain was studied.…”

“…In order to study the response of the non-AHL-producing mutant DluxI 1 to AHLs, synthetic signals C8-, C18en-and C18dien-HSL as well as C18-HSL were added to DluxI 1 cultures at final concentrations of 500 nM. The C18-HSL has not been detected in D. shibae, neither in rich medium nor in minimal medium (Neumann et al, 2013). Moreover, all of the AHLs found in D. shibae cultures have one or two double bonds in the acyl side chain.…”

Phaeobacter sp. Strain Y4I Utilizes Two Separate Cell-to-Cell Communication Systems To Regulate Production of the Antimicrobial Indigoidine

“…While roseobacters are known to produce long-chain AHLs with various degrees of oxidation and side-chain saturation (11,30,34,35,46), the full complement of AHLs synthesized by lineage members and the contribution of these chemical signals to roseobacter ecology are not yet known. Here we identified a novel AHL, 3OHC 12:1 -HSL, in Phaeobacter sp.…”

“…Thus, bacteria possessing luxIR homologs produce and release AHLs into the external environment (7). At high cell densities, AHL concentrations can reach a threshold concentration, bind to the corresponding cognate cytoplasmic LuxR proteins, and affect transcription of various genetic loci (8)(9)(10)(11). AHLs have also been shown to activate regulators other than the corresponding cognate LuxR, suggesting that cross talk may play an important role in intra-and interspecies interactions (12)(13)(14)(15)(16)(17).…”