FASTA and Blast searches confirm that these genes are absent from some of the tested strains as already observed in the analysis complete genomes (53) (54) (55) . In a large number of cases, we are able to find a well-conserved homologous gene in another species (Table 5) . It is interesting to note that some of the suggested donors using our 12 000 signature database are in agreement with the species found by alignment methods. When no homologous gene is found, the proposed donors give credit to the known mechanisms of gene transfer (bacteriophages or plasmids) ( Table 5) .