A physical genome map of the Burkholderia cepacia type strain

Burkholderia cepacia (basonym Pseudomonas cepacia), the type species of the new genus Burkholderia, is of interest, not only because of its broad catabolic capacity and its ability to antagonize soil-borne plant pathogens, but also because of its causative role in infections in man, which are particularly evident in patients with cystic fibrosis. A physical map of the 8.1 Mb genome of the B. cepacia type-strain ATCC 25416 was constructed by applying two-dimensional pulsed-field gel electrophoresis techniques. Placed onto the macrorestriction map were 38 SpeI, 11 SwaI, 11 PacI, 11 PmeI and six I-CeuI sites, resulting in an average resolution of 105 kbp. Random single-hit linearization by irradiation and restriction mapping uncovered the presence of four circular replicons of 3.65 Mb, 3.17 Mb, 1.07 Mb and 200 kbp in size. The largest replicon harbours four rrn operons while the other two Megabase-size replicons each contain a single rrn operon, suggesting that the genome has three chromosomes and a large plasmid. Within the beta subdivision of proteobacteria, the existence of multiple replicons is not confined to B. cepacia. The phylogenetically related species Burkholderia glumae, Burkholderia pickettii, Burkholderia solanacearum, Alcaligenes eutrophus and the so far unassigned Pseudomonas glathei were also found to harbour more than one Megabase-size replicon.