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Minimization of the Legionella pneumophila genome reveals chromosomal regions involved in host range expansion
Tamara J. O'Connor, Yewande Adepoju, Dana Boyd and Ralph R. Isberg
Proceedings of the National Academy of Sciences of the United States of America
Vol. 108, No. 36 (September 6, 2011), pp. 14733-14740
Published by: National Academy of Sciences
Stable URL: http://www.jstor.org/stable/27979370
Page Count: 8
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Legionella pneumophila is a bacterial pathogen of amoebae and humans. Intracellular growth requires a type IVB secretion system that translocates at least 200 different proteins into host cells. To distinguish between proteins necessary for growth in culture and those specifically required for intracellular replication, a screen was performed to identify genes necessary for optimal growth in nutrient-rich medium. Mapping of these genes revealed that the L. pneumophila chromosome has a modular architecture consisting of several large genomic islands that are dispensable for growth in bacteriological culture. Strains lacking six of these regions, and thus 18.5% of the genome, were viable but required secondary point mutations for optimal growth. The simultaneous deletion of five of these genomic loci had no adverse effect on growth of the bacterium in nutrient-rich media. Remarkably, this minimal genome strain, which lacked 31% of the known substrates of the type IVB system, caused only marginal defects in intracellular growth within mouse macrophages. In contrast, deletion of single regions reduced growth within amoebae. The importance of individual islands, however, differed among amoebal species. The host-specific requirements of these genomic islands support a model in which the acquisition of foreign DNA has broadened the L. pneumophila host range.
Proceedings of the National Academy of Sciences of the United States of America © 2011 National Academy of Sciences