Full text loading...
Chapter 2 : Shigella Genomes: a Tale of Convergent Evolution and Specialization through IS Expansion and Genome Reduction
Category: Applied and Industrial Microbiology; Food Microbiology
Ebook: Choose a downloadable PDF or ePub file. Chapter is a downloadable PDF file. File must be downloaded within 48 hours of purchase
Shigella Genomes: a Tale of Convergent Evolution and Specialization through IS Expansion and Genome Reduction, Page 1 of 2< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555816902/9781555814571_Chap02-1.gif /docserver/preview/fulltext/10.1128/9781555816902/9781555814571_Chap02-2.gif
Although all Shigella species share similar pathogenic properties, each species exhibits peculiar epidemiological characteristics. S. dysenteriae, S. flexneri, and S. boydii are most common in developing countries, whereas S. sonnei is more prevalent in developed countries. A remarkable difference between Shigella and E. coli genomes is the presence of pseudogenes in the former. The second remarkable feature of the Shigella genome is the presence of enormous copies of IS elements, which are likely the cause of genomic rearrangements, including deletions, inversions, and translocations that may effectively disrupt the colinearity among different Shigella genomes. After the acquisition of the ancestral forms of the virulence plasmid by Shigella/enteroinvasive E. coli (EIEC), genome reduction by inactivation of the pathway-specific antivirulence loci (AVL) is vital for adaptation in the cytosolic niche. Similar to obligate pathogens, reduced selection pressure might have played an important role in Shigella genome reduction, which may have further accelerated terminal evolution and resulted in the increased host specificity. Numerous genes responsible for cell motility cell envelope, carbohydrate transport, and metabolism that are present in E. coli were frequently lost in Shigella. A combination of various strategies using the basic information provided by genomic research will be helpful in efficient control and prevention of Shigella infections.
Evolutionary path of Shigella/EIEC from diverse origins of E. coli. Acquisition of virulence plasmid and pathway-specific reductions are two decisive events in the pathoadaption path. Diverse genomewide reduction occurs because of reduced effectiveness of purifying selection in the cell cytosol. IS expansion and consequent genome rearrangements played a major role in both pathway-specific and genomewide reduction. Formation of pseudogenes is one other mechanism resulting in genome decay.
Summary of ongoing Shigella/EIEC genome sequencing projects (as of December 2008)
Characteristics of complete Shigella genome sequences
IS elements identified in Shigella genomes
Known and putative virulence factors in the Shigella genomesa
Inactivated genes relevant to biochemical reactions used in Shigella identification