GENOMIC SEQUENCE OF A LYME-DISEASE SPIROCHETE, BORRELIA-BURGDORFERI

The genome of the bacterium Borrelia burgdorferi B31, the aetiologic a gent of Lyme disease, contains a linear chromosome of 910,725 base pai rs and at least 17 linear and circular plasmids with a combined size o f more than 533,000 base pairs. The chromosome contains 853 genes enco ding a basic set of proteins for DNA replication, transcription, trans lation, solute transport and energy metabolism, but, like Mycoplasma g enitalium, it contains no genes for cellular biosynthetic reactions. B ecause B. burgdorferi and M. genitalium are distantly related eubacter ia, we suggest that their limited metabolic capacities reflect converg ent evolution by gene loss from more metabolically competent progenito rs. Of 430 genes on 11 plasmids, most have no known biological functio n; 39% of plasmid genes are paralogues that form 47 gene families. The biological significance of the multiple plasmid-encoded genes is not clear, although they may be involved in antigenic variation or immune evasion.