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Abstract Background Public databases now contain multitude of complete bacterial genomes, including several genomes of the same species. The available data offers new opportunities to address questions about bacterial genome evolution, a task that requires reliable fine comparison data of closely related genomes. Recent analyses have shown, using pairwise whole genome alignments, that it is possible to segment bacterial genomes into a common conserved backbone and strain-specific sequences called loops. Results Here, we generalize this approach and propose a strategy that allows systematic and non-biased genome segmentation based on multiple genome alignments. Segmentation analyses, as applied to 13 different bacterial species, confirmed the feasibility of our approach to discern the 'mosaic' organization of bacterial genomes. Segmentation results are available through a Web interface permitting functional analysis, extraction and visualization of the backbone/loops structure of documented genomes. To illustrate the potential of this approach, we performed a precise analysis of the mosaic organization of three E. coli strains and functional characterization of the loops. Conclusion The segmentation results including the backbone/loops structure of 13 bacterial species genomes are new and available for use by the scientific community at the URL: http://genome.jouy.inra.fr/mosaic.

• R(US) is a major dominant gene controlling quantitative resistance, inherited from Populus trichocarpa, whereas R(1) is a gene governing qualitative resistance, inherited from P. deltoides. • Here, we report a reiterative process of concomitant fine-scale genetic and physical mapping guided by the P. trichocarpa genome sequence. The high-resolution linkage maps were developed using a P. deltoides × P. trichocarpa progeny of 1415 individuals. R(US) and R(1) were mapped in a peritelomeric region of chromosome 19. Markers closely linked to R(US) were used to screen a bacterial artificial chromosome (BAC) library constructed from the P. trichocarpa parent, heterozygous at the locus R(US) . • Two local physical maps were developed, one encompassing the R(US) allele and the other spanning r(US) . The alignment of the two haplophysical maps showed structural differences between haplotypes. The genetic and physical maps were anchored to the genome sequence, revealing genome sequence misassembly. Finally, the R(US) locus was localized within a 0.8-cM interval, whereas R(1) was localized upstream of R(US) within a 1.1-cM interval. • The alignment of the genetic and physical maps with the local reorder of the chromosome 19 sequence indicated that R(US) and R(1) belonged to a genomic region rich in nucleotide-binding site leucine-rich repeat (NBS-LRR) and serine threonine kinase (STK) genes., (© 2011 INRA. New Phytologist © 2011 New Phytologist Trust.)