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Category: Bacterial Pathogenesis; Microbial Genetics and Molecular Biology
The Contribution of Pathogenicity Islands to the Evolution of Bacterial Pathogens, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555815622/9781555813000_Chap05-1.gif /docserver/preview/fulltext/10.1128/9781555815622/9781555813000_Chap05-2.gifAbstract:
Pathogenicity islands (PAIs) have been defined as (i) large genomic regions that (ii) carry one or more virulence associated gene, (iii) have a G+C content different from that of the rest of the chromosome, (iv) are frequently associated with tRNA genes, (v) are often flanked by repeat structures, (vi) contain mobility genes such as integrase genes and transposases, and (vii) are often unstable. This chapter discusses the role of PAIs in the evolution of bacterial virulence. It focuses on features of PAIs, and other mobile genetic elements. Insertion sequence (IS) elements contribute to genome variability by several means. First, they mediate DNA rearrangements by transpositional events as well as by homologous recombination between multiple copies of the same insertion sequence (IS) element within one genome. Second, IS elements can modulate fast changes in gene activity by reversible excision and integration events into target sequences within coding regions. Finally, they are involved in the mobilization of genetic information due to association and dissociation of chromosomal DNA segments to and from natural vectors such as plasmids. Genomic island (GEIs) have been described for more than 30 microbial species, and the ongoing discussion of their properties and definition as well as their significance for microbial evolution is reflected in the chapter. GEIs represent formerly transferred or still mobile genetic entities that have evolved from horizontal gene transfer and DNA recombination events. They are important factors for bacterial evolution and will contribute to an ongoing evolution of bacterial variants, including bacterial pathogens.
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General mechanisms in evolution of bacterial pathogens. Genome evolution is based on loss (indicated by shaded areas) and acquisition of genetic information. Mobile genetic elements such as plasmids, bacteriophages, and PAIs encoding virulence traits (fimbriae, secreted toxins, etc.) that are horizontally transferred by transformation, transduction, and conjugation play an important role in gene acquistion. For more details, see text.
Features of pathogenicity islands (PAIs). The model illustrates the main features of PAIs that are listed in the box. Island-associated genes are shown as shaded boxes and the bacterial chromosome as a line (top). G+C content of the PAI and the core genome often differ from each other (bottom). Abbreviations: int, integrase gene; vir, virulence-associated gene; Δmob, truncated mobility gene; IS, insertion sequence. Modified from reference 49 .
Properties of mobile genetic elements
Pathogenicity islands (PAIs) or PAI-like structures of pathogenic enterobacteria”a
PAIs of other gram-negative bacteria
PAIs of gram-positive bacteria
Genomic islands (GEIs) and their encoded functionsa