HOMOLOGIES BETWEEN HETEROGENEOUS EXTRACHROMOSOMAL DNA POPULATIONS OF HALOBACTERIUM-HALOBIUM AND 4 NEW HALOBACTERIAL ISOLATES

Heterogeneous collections of covalently-closed circular DNA (cccDNA) comprise up to 10% of the total DNA of H. halobium and 4 other halophilic strains (SB3, GRA, GRB and GN101) recently isolated from different sources. All of thee bacteria have purple membrane, bacterioruberin and gas vacuoles as characteristic phenotypic markers. Most of the major cccDNA species of these isolates are not homologous to pHH1, the main 150 kb [kilobase] cccDNA of H. halobium NRC817. Only GN101 and SB3 have a cccDNA which is partly homologous to pHH1. In GN101 the homology is to the halobacterial insertion sequence ISH23 found in pHH1. In SB3 the homology is to ISH26, a new insertion sequence isolated from H. halobium NRC817 which has a size of 1400 base pairs. Extensive homologies exist between the minor cccDNA species in all 5 strains indicating that this cccDNA species is highly conserved and possibly originates from (or is part of) the chromosome. A 1.6 kb high copy number cccDNA species is present in 3 independently isolated GN101, GRB and SB3. This 1.6 kb cccDNA is not homologous to any other extrachromosomal or chromosomal DNA.