HIGH-RESOLUTION ALIGNMENT OF A 1-MEGABASE-LONG GENOME REGION OF 3 STRAINS OF RHODOBACTER-CAPSULATUS

A detailed restriction map of the genome of Rhodobacter capsulatus SB1003 was constructed recently by using an ordered set of overlapping cosmids. Pulsed-field gel electrophoresis-generated restriction patterns of the chromosomes of 14 other R. capsulatus strains were compared, Two of them, St. Louis and 2.3.1, were chosen for high-resolution alignment of their genomes with that of SB1003. A 1-Mb segment of the R. capsulatus SB1003 cosmid set was used as a source of ordered probes to group cosmids from the other strains, Selected cosmids were linked into one 800-kb contig and two smaller contigs of 100 kb each, EcoRV and BamHI restriction maps of the newly ordered cosmids were constructed by using lambda terminase, Long-range gene order in the new strains was mainly conserved for the regions studied. However, one large genome rearrangement inverted a 470-kb DNA fragment of the St. Louis strain between the rrnA and rrnB operons, A 50-kb deletion covering three SB1003 probes was found in strain 2.3.1 near rrnB. Conservation of about 50% of the positions of restriction sites in all these strains and nearly 80% for the pair 2.3.1-St. Louis made it possible to produce high-resolution alignment of the contiguous 800-kb genome segment. Ten deletions of 2 to 27 kb, one 30-kb inversion, and three translocations were found in this region. Strong clustering of the positions of polymorphic restriction sites was observed. For a 50-kb size interval, two patterns of the distribution of restriction sites were found, one with about 90% and the other with 5 to 30% conservation of sites. This mosaic structure may be explained by independent acquisition of these divergent regions from other Rhodobacter strains.