maritimum NCIMB2154T obtained at 24 and 48 h using the
three E. coli JM109 lux-based biosensor strains carrying pSB536, pSB401 or pSB1075 to detect a wide range of AHLs differing in the length of their acyl chain. TLC analysis revealed the presence of short-chain AHLs using the E. coli JM109 pSB536 biosensor (Fig. 1). A search for AHL-type QS signals in extracts obtained from the culture media of another eight representative isolates of T. maritimum using the same technique revealed the presence of short-chain AHL activity in all of them, although differences were recorded in relation to their peak in activity (Table 1). LC-MS analysis confirmed the presence of N-butyryl-l-homoserine lactone (C4-HSL) in the culture media of T. maritimum NCIMB2154T grown in both FMM (Fig. 2) and MB (data not shown). This AHL was unequivocally identified by comparison Forskolin http://www.selleckchem.com/products/gkt137831.html of its mass spectra with those of pure standards (Fig. 3). As this is the
first description of the production of AHLs by a pathogenic member of the CFB cluster, the analyses were carried out simultaneously in both laboratories using different chromatographic conditions. The results confirmed unequivocally the presence of the C4-HSL. So far, no physiological role other than as QS signals has been assigned to AHLs, except as a chelator, for tetramic acid (a derivative of 3-oxo-C12) or antibiotic activity for both 3-oxo-C12-HSL and tetramic acid (Kaufmann et al., 2005; Schertzer et al., 2009). In addition, a role as biosurfactant has been attributed to long-chain AHLs (Daniels et al., 2006). Therefore, even though the physiological features under the control of these molecules in T. maritimum remain to be investigated, the production of C4-HSL by T. maritimum strains extends the paradigm of AHL-mediated QS beyond the Proteobacteria. Fenbendazole As the physiological processes under the control of AHL-mediated QS have so far been described for a limited number of genera of the Alpha-, Beta- and Gammaproteobacteria, many
of them human or plant pathogens (Williams et al., 2007), the ecological significance of AHL-mediated QS has been questioned as a key switch controlling gene expression within bacterial populations in nature (Manefield & Turner, 2002). The fact that genera outside the Proteobacteria produce the same signal molecules, and that AHL-degrading activity has been found in Gram-positive, Gram-negative and Cyanobacteria (Dong & Zhang, 2005; Romero et al., 2008) and in mammalian cells (Chun et al., 2004), reinforces the ecological significance of AHL-mediated QS processes. The presence of AHL-mediated QS beyond the Proteobacteria is not surprising, as a phylogenetic study based on the LuxI/LuxR genes suggested that QS mechanisms were established very early in the evolution of bacteria, although horizontal transfer may have also played an important role in the distribution of QS genes, at least within this group (Lerat & Moran, 2004).