the early stage of bacterial genome-reductive evolution in the host细菌genome-reductive进化的早期阶段的主机.pdf

The Early Stage of Bacterial Genome-Reductive Evolution in the Host 1. 1. 1. 2 3 3,4 Han Song , Junghyun Hwang , Hyojeong Yi , Ricky L. Ulrich , Yan Yu , William C. Nierman , Heenam Stanley Kim1* 1 Department of Medicine, College of Medicine, Korea University, Anam-Dong, Seongbuk-Gu, Seoul, Korea, 2 US Army Medical Research Institute of Infectious Diseases (USAMRIID), Fort Detrick, Maryland, United States of America, 3 J. Craig Venter Institute, Rockville, Maryland, United States of America, 4 The George Washington University School of Medicine, Department of Biochemistry and Molecular Biology, Washington, D.C., United States of America Abstract The equine-associated obligate pathogen Burkholderia mallei was developed by reductive evolution involving a substantial portion of the genome from Burkholderia pseudomallei, a free-living opportunistic pathogen. With its short history of divergence (,3.5 myr), B. mallei provides an excellent resource to study the early steps in bacterial genome reductive evolution in the host. By examining 20 genomes of B. mallei and B. pseudomallei, we found that stepwise massive expansion of IS (insertion sequence) elements ISBma1, ISBma2, and IS407A occurred during the evolution of B. mallei. Each element proliferated through the sites where its target selection preference was met. Then, ISBma1 and ISBma2 contributed to the further spread of IS407A by providing secondary insertion sites. This spread increased genomic deletions and rearrangements, which were predominantly mediated by IS407A. There were also nucleotide-level disruptions in a large number of genes.