Abstract
Genomes of the month microbial genome evolution
Eight microbial genomes have been published in the four weeks since the last Genome Update was written (Ussery et al., 2004). They represent five bacterial and three eukaryotic organisms, and provide several interesting aspects of genome evolution. A very brief overview of the new genomes will be presented below; this is meant merely to wet the appetite of the reader and to provide pointers to the relevant recent literature.
Two spirochaete genomes have been published this month, bringing the total number of genomes from three to five for this phylum. The genome of Treponema denticola strain ATCC 35405 (Seshadri et al., 2004) is more than twice the size of the previously sequenced genome of Treponema pallidum (2·8 Mbp vs 1·1 Mbp), although the number of tRNAs and rRNAs are about the same in both genomes. The difference in genome size appears to be the result of a combination of three types of evolution: genome reduction, lineage-specific recombination and horizontal gene transfer (Seshadri et al., 2004). The other newly sequenced spirochaete genome, of Leptospira interrogans serovar Copenhageni strain Fiocruz L1-130 (Nascimento et al., 2004), has two chromosomes and encodes 3728 genes, two rRNA operons and 37 tRNAs, as shown in Table 1. This genome is nearly identical in size to that of L. interrogans serovar Lai (Ren et al., 2003), which has 4727 annotated genes, or nearly 1000 extra genes. This is perhaps due to the difference in cut-off values for gene-finding from the two different groups.