, 2004). The marine bacteria Tenacibaculum maritimum (formerly Flexibacter maritimus) (Suzuki et al., 2001) is a filamentous member of the CFB group causing the fish ‘gliding bacterial disease’ or tenacibaculosis/flexibacteriosis

(Avendaño-Herrera et al., 2004). Tenacibaculum maritimum belongs to the CFB cluster, which is also see more known as Bacteroidetes (Ludwig & Klenk, 2001), and constitutes one of the dominant heterotrophic bacterial groups in aquatic habitats. The fact that T. maritimum shifts abruptly from a biofilm to a planktonic mode of growth, a characteristic that could be related to a QS-controlled process (Rice et al., 2005; Wagner-Döbler et al., 2005), led us to investigate the possible production and degradation of AHLs by this fish pathogen. The T. maritimum strains NCIMB2154T, NCIMB2153 and NCIMB2158 were obtained from The National Collections of Industrial, Food and Marine Bacteria Ltd (Aberdeen, UK). In addition, six strains isolated in our laboratory from fish farm disease outbreaks from Spain and Portugal were used. These strains belong to the main serotypes and clonal lineages described within this pathogen (Table 1) (Avendaño-Herrera et al., 2004, 2006), and were confirmed as T. maritimum by PCR-based analysis (Toyama et al., 1996).

The strains were routinely cultured at 20 °C on F. maritimus MAPK Inhibitor Library in vivo medium (FMM) agar or broth (Pazos et al., 1996) and on marine broth (MB, Difco) for some of the experiments. Liquid cultures were inoculated with a 10% volume of a 24-h liquid culture and maintained in a shaker at 100 r.p.m. Cultures were double-checked for purity on Marine Agar (Difco) and FMM before and after each experiment. Three lux-based

Escherichia coli JM109 AHL biosensor strains that respond to AHLs with different side chain lengths were used for the detection of AHL production (Swift Thalidomide et al., 1997; Winson et al., 1998). The biosensor strains were grown at 37 °C in Luria–Bertani (LB) broth or agar supplemented with the adequate antibiotics. Additionally, the AHL biosensor strains Chromobacterium violaceum CV026 (McClean et al., 1997) and C. violaceum VIR07 (Morohoshi et al., 2008) were used for the AHL-degradation assays in solid plates as explained below (McClean et al., 1997). These strains were routinely cultured on LB medium supplemented with kanamycin (50 μg mL−1) at 30 °C. Samples (100 mL) from cultures of nine different strains of T. maritimum grown in liquid FMM were obtained 24 and 48 h after inoculation, acidified to pH 2 with HCl 1 M in a shaker at 200 r.p.m. for 12 h at 20 °C, to ensure the absence of any AHL lactonolysis products, and extracted with dichloromethane as described previously (Yates et al., 2002). Dried extracts were reconstituted in 1 mL ethyl acetate and stored at −20 °C until further analysis.