maritimum will undoubtedly provide new insights

into the evolutionary history of QS. The production of AHLs was demonstrated for all isolates of T. maritimum analysed (Table 1), therefore being a conserved trait within this species, which is not the case in some other marine pathogens such as Aeromonas salmonicida (Bruhn et al., 2005). Some contradictory results have been published selleck chemical previously regarding the production of AHLs by the genus Flavobacterium belonging to the Bacteroidetes group. While AHL-like activity was detected in a planktonic isolate of Flavobacterium sp. using E. coli MT102 carrying the biosensor plasmid pJBA132 based on the luxR gene from Vibrio fischeri, the presence of AHLs could not be demonstrated by GC-MS (Wagner-Döbler et al., 2005). Furthermore, no AHL activity was found in different pathogenic strains of Flavobacterium psychrophilum using the sensor strains C. violaceum CV026 and Agrobacterium tumefaciens NT1 (Bruhn et al.,

2005). The differences in the AHL activity described probably depend on the assay conditions and the sensor strain utilized. In our experience, data based on the direct evaluation of culture media of marine bacteria, usually MB, should be interpreted with caution, as the media composition could result in inhibition of growth or bioluminescence production by the sensor strain (unpublished data). On the other hand, due to the ability of different compounds to activate the AHL biosensors (Holden et al., 1999), the results should be viewed with caution unless the presence of AHLs can be confirmed by analytical chemical methods. On the basis of our results and as Natural Product Library the detection of the QS activity is strongly dependent on the biosensor strain used and on the culture conditions, it is possible that Sitaxentan AHL-based QS systems are more widespread than described so far (Wagner-Döbler

et al., 2005). An in vivo degradation assay was carried out using two biosensor strains of C. violaceum. Chromobacterium violaceum CV026 was used to detect degradation of short AHLs (C6-HSL), and C. violaceum VIR07 was used to detect degradation of long AHLs (C10-HSL). Complete degradation of C10-HSL was observed after 24 h, but no changes in C6-HSL activity were observed (Fig. 4a). The activity should be cell bound, as no significant degradation was obtained when the C10-HSL was added to cell-free spent culture medium (Fig. 2a). HPLC analysis of the degradation of C10-HSL revealed that 90% of the AHL was degraded after 24 h of exposition to T. maritimum cultures, and no recovery of the AHL could be achieved by medium acidification, which may discard a lactonase-type degrading enzyme (Fig. 4b). Further analyses are required to confirm an acylase-type activity. The presence of AHL degradation enzymes has been described in Gram-negative bacteria, possibly as a mechanism to outcompete Gram-positive neighbours (Roche et al., 2004).