Gene Loss and Gene Conservation in Obligatory Intracellular Parasites of Human

Molecular characterization of various microbial genomes has revealed that many pathogenic and mutualistic intracellular bacterial species have smaller genomes than their free-living relatives. The flux, streamlining and elimination of genes in these genomes constitute a selective and ongoing process. Obligatory intracellular parasites display marked similarities in patterns of protein length and frequency distribution, with substantial sharing of a ‘backbone genome’. The results highlight that gene loss is function-dependent, but is independent of protein length. It is suggested that obligate genomes have greater proportion of overlapping genes, which may be a result of evolutionary pressure to minimize genome size. The differential loss of genes in these organisms is also reflected in their metabolic plasticity. Here, we present a review on gene loss and gene conservation in obligatory intracellular parasites. These data are essential for understanding of genome evolution and microbial pathogenesis of these organisms.