Neighbour-joining tree of LuxI family members in Serratia. The phylogenetic tree was generated using MEGA 4. LuxI family members in Serratia are clustered into two groups according to the AHL patterns. SplI and SpsI from G3 were in group A and group B, respectively. The significance of each branch is bootstrap value calculated for 1000 subsets. Scale bar indicates the mean number of substitutions per site.