Divergence of the hyperthermophilic archaea Pyrococcus furiosus and P. horikoshii inferred from complete genomic sequences

Divergence of the hyperthermophilic Archaea, Pyrococcus furiosus and Pyroco ccus horikoshii, was assessed by analysis of complete genomic sequences of both species. The average nucleotide identity between the genomic sequences is 70-75% within ORFs. The P. furiosus genome (1.908 mbp) is 170 kbp large r than the P. horikoshii genome (1.738 mbp) and the latter displays signifi cant deletions in coding regions, including the trp, his, a ro, leu-ile-val , arg; pro, cys, thr, and mab operons. P. horikoshii is auxotrophic for try ptophan and histidine and is unable to utilize maltose, unlike P. furiosus. In addition, the genomes differ considerably in gene order, displaying dis placements and inversions. Six allelic intein sites are common to both Pyro coccus genomes, and two intein insertions occur in each species and not the other. The bacteria-like methylated chemotaxis proteins form a functional group in P. horikoshli, but are absent in P. furiosus. Two paralogous famil ies of ferredoxin oxidoreductases provide evidence of gene duplication prec eding the divergence of the Pyrococcus species.