Genome size of Myxococcus xanthus determined by pulsed-field gel electrophoresis

Genomic DNA of the myxobacterium Myxococcus xanthus was digested with the rare cutting restriction endonuclease AseI or SpeI, and the restriction products wre separated by pulsed-field gel electrophoresis. Transposons Tn5-132 and Tn5 lac, which contain AseI restriction sites, were used to determine the number of restriction fragments in each band. The size of the genome was determined by adding the molecular sizes of the restriction products. The genomes of strains DK101, MD2, and DZF1 had identical restriction patterns and were estimated to be 9,454 ± 101 kilobase pairs from the AseI digestions and 9,453 ± 106 kilobase pairs from the SpeI digestions. DK1622, which was derived from DK101 by treatment with UV light, has suffered a 220- to 222-kilobase-pair deletion that removed an AseI and an SpeI restriction site. The deleted DNA may consist exclusively of Mx alpha-associated sequences.