Genomic rearrangements during evolution of the obligate intracellular parasite Rickettsia prowazekii as inferred from an analysis of 52015 bp nucleotide sequence

Abstract

Summary: In this study a description is given of the sequence and analysis of 52 kb from the 1.1 Mb genome ofRickettsia prowazekii, a member of the α-Proteobacteria. An investigation was made of nucleotide frequencies and amino acid composition patterns of 41 coding sequences, distributed in 10 genomic contigs, of which 32 were found to have putative homologues in the public databases. Overall, the coding content of the individual contigs ranged from 59 to 97%, with a mean of 81%. The genes putatively identified included genes involved in the biosynthesis of nucleotides, macromolecules and cell wall structures as well as citric acid cycle component genes. In addition, a putative identification was made of a member of the regulatory response family of two-component signal transduction systems as well as a gene encoding haemolysin. For one gene, the homologue ofmetK, an internal stop codon was discovered within a region that is otherwise highly conserved. Comparisons with the genomic structures ofEscherichia coli, Haemophilus influenzaeandBacillus subtilishave revealed several atypical gene organization patterns in theR. prowazekiigenome. For example,R. prowazekiiwas found to have a unique arrangement of genes upstream ofdnaAin a region that is highly conserved among other microbial genomes and thought to represent the origin of replication of a primordial replicon. The results presented in this paper support the hypothesis that theR. prowazekiigenome is a highly derived genome and provide examples of gene order structures that are unique for theRickettsia.