Comparative And Phylogenetic Analysis Of Streptomyces Coelicolor A3(2) And Streptomyces Avermitilis

As the complete genome sequences of S.coelicolor and S.avermitilis have been sequenced, we compared the DNA sequence of the two genomes to each other by using MUMmer and Mauve. In addition, we aligned DNA sequences of them against their own sequences with MUMmer. The global DNA sequence alignment showed a large number of DNA duplications and inversions between the two genomes with high-order synteny and a great many of DNA sequence duplications in their own genome. The distribution of the number and size of the inverted sequences between the two genomes showed that most of the DNA inversions fell in the region of 1-5 kb. This may reveal that 1-5kb can just be appropriate length to form a complete gene, so as to respond flexibly to the changes of the environment, and retain easily in the long evolutionary history. The inverted regions with large fragments were analyzed to further study the inverting sites and inverting model of gene inversions. The distribution of the number and size of the duplicated sequences between the two genomes revealed that the content of DNA duplications in the genome of S.avermitilis was much larger than that of S.coelicolor, suggesting that duplication might be one factor contributing to larger size of S.avermitilis genome than that of S.coelicolor. In addition, the frequency of short duplicated sequences (20-25bp) in S.coelicolor was much higher than that between the two genomes. This demonstrated that most of duplications in the genome of S.coelicolor were much older than that between the genomes of S.coelicolor and S.avermilitis. There were many larger duplicated sequences (>200bp) in the genome of S.coelicolor, while only 7 such duplicated sequences between S.coelicolor and S.avermilitis, indicating that large duplications had occurred in the S.coelicolor after the duplications between S.coelicolor and S.avermilitis. In order to further study the evolutionary history of gene duplications, 34 duplicated genes of S.coelicolor were selected to analyze their DNA sequences similarity against orthologous DNA sequences from closely related species. The analysis revealed that 26 (～77%) of the gene duplications represent type A relationship, which indicated that a copy of the duplicate pair from S.coelicolor was more related to its orthologue from the S.avermilitis than to its paralogue. It was also demonstrated that the proportion of A-type genes decreased as the genetic distance between S.coelicolor and its closely related species became greater.