RESUMEN
Bordetella pertussis, Bordetella parapertussis and Bordetella bronchiseptica are closely related Gram-negative beta-proteobacteria that colonize the respiratory tracts of mammals. B. pertussis is a strict human pathogen of recent evolutionary origin and is the primary etiologic agent of whooping cough. B. parapertussis can also cause whooping cough, and B. bronchiseptica causes chronic respiratory infections in a wide range of animals. We sequenced the genomes of B. bronchiseptica RB50 (5,338,400 bp; 5,007 predicted genes), B. parapertussis 12822 (4,773,551 bp; 4,404 genes) and B. pertussis Tohama I (4,086,186 bp; 3,816 genes). Our analysis indicates that B. parapertussis and B. pertussis are independent derivatives of B. bronchiseptica-like ancestors. During the evolution of these two host-restricted species there was large-scale gene loss and inactivation; host adaptation seems to be a consequence of loss, not gain, of function, and differences in virulence may be related to loss of regulatory or control functions.
Asunto(s)
Bordetella bronchiseptica/genética , Bordetella pertussis/genética , Bordetella/genética , Genoma Bacteriano , Secuencia de Bases , Bordetella/metabolismo , Bordetella/patogenicidad , Bordetella bronchiseptica/metabolismo , Bordetella bronchiseptica/patogenicidad , Bordetella pertussis/metabolismo , Bordetella pertussis/patogenicidad , ADN Bacteriano , Datos de Secuencia Molecular , Análisis de Secuencia de ADN , Especificidad de la EspecieRESUMEN
The African trypanosome, Trypanosoma brucei, causes sleeping sickness in humans in sub-Saharan Africa. Here we report the sequence and analysis of the 1.1 Mb chromosome I, which encodes approximately 400 predicted genes organised into directional clusters, of which more than 100 are located in the largest cluster of 250 kb. A 160-kb region consists primarily of three gene families of unknown function, one of which contains a hotspot for retroelement insertion. We also identify five novel gene families. Indeed, almost 20% of predicted genes are members of families. In some cases, tandemly arrayed genes are 99-100% identical, suggesting an active process of amplification and gene conversion. One end of the chromosome consists of a putative bloodstream-form variant surface glycoprotein (VSG) gene expression site that appears truncated and degenerate. The other chromosome end carries VSG and expression site-associated genes and pseudogenes over 50 kb of subtelomeric sequence where, unusually, the telomere-proximal VSG gene is oriented away from the telomere. Our analysis includes the cataloguing of minor genetic variations between the chromosome I homologues and an estimate of crossing-over frequency during genetic exchange. Genetic polymorphisms are exceptionally rare in sequences located within and around the strand-switches between several gene clusters.
Asunto(s)
Cromosomas/genética , ADN Protozoario/genética , Genes Protozoarios/genética , Trypanosoma brucei brucei/genética , Animales , Mapeo Cromosómico , ADN Protozoario/química , Repeticiones de Microsatélite/genética , Datos de Secuencia Molecular , Polimorfismo Genético , Recombinación Genética , Análisis de Secuencia de ADN , Glicoproteínas Variantes de Superficie de Trypanosoma/genéticaRESUMEN
African trypanosomes cause human sleeping sickness and livestock trypanosomiasis in sub-Saharan Africa. We present the sequence and analysis of the 11 megabase-sized chromosomes of Trypanosoma brucei. The 26-megabase genome contains 9068 predicted genes, including approximately 900 pseudogenes and approximately 1700 T. brucei-specific genes. Large subtelomeric arrays contain an archive of 806 variant surface glycoprotein (VSG) genes used by the parasite to evade the mammalian immune system. Most VSG genes are pseudogenes, which may be used to generate expressed mosaic genes by ectopic recombination. Comparisons of the cytoskeleton and endocytic trafficking systems with those of humans and other eukaryotic organisms reveal major differences. A comparison of metabolic pathways encoded by the genomes of T. brucei, T. cruzi, and Leishmania major reveals the least overall metabolic capability in T. brucei and the greatest in L. major. Horizontal transfer of genes of bacterial origin has contributed to some of the metabolic differences in these parasites, and a number of novel potential drug targets have been identified.
Asunto(s)
Genoma de Protozoos , Glutatión/análogos & derivados , Proteínas Protozoarias/genética , Análisis de Secuencia de ADN , Espermidina/análogos & derivados , Trypanosoma brucei brucei/genética , Aminoácidos/metabolismo , Animales , Variación Antigénica , Antígenos de Protozoos/química , Antígenos de Protozoos/genética , Antígenos de Protozoos/inmunología , Metabolismo de los Hidratos de Carbono , Cromosomas/genética , Citoesqueleto/química , Citoesqueleto/genética , Citoesqueleto/fisiología , Ergosterol/biosíntesis , Genes Protozoarios , Glutatión/metabolismo , Glicosilfosfatidilinositoles/biosíntesis , Humanos , Metabolismo de los Lípidos , Datos de Secuencia Molecular , Transporte de Proteínas , Proteínas Protozoarias/química , Proteínas Protozoarias/metabolismo , Seudogenes , Purinas/metabolismo , Pirimidinas/biosíntesis , Recombinación Genética , Espermidina/metabolismo , Trypanosoma brucei brucei/química , Trypanosoma brucei brucei/inmunología , Trypanosoma brucei brucei/metabolismo , Tripanosomiasis Africana/parasitologíaRESUMEN
Mycobacterium bovis is the causative agent of tuberculosis in a range of animal species and man, with worldwide annual losses to agriculture of $3 billion. The human burden of tuberculosis caused by the bovine tubercle bacillus is still largely unknown. M. bovis was also the progenitor for the M. bovis bacillus Calmette-Guérin vaccine strain, the most widely used human vaccine. Here we describe the 4,345,492-bp genome sequence of M. bovis AF2122/97 and its comparison with the genomes of Mycobacterium tuberculosis and Mycobacterium leprae. Strikingly, the genome sequence of M. bovis is >99.95% identical to that of M. tuberculosis, but deletion of genetic information has led to a reduced genome size. Comparison with M. leprae reveals a number of common gene losses, suggesting the removal of functional redundancy. Cell wall components and secreted proteins show the greatest variation, indicating their potential role in host-bacillus interactions or immune evasion. Furthermore, there are no genes unique to M. bovis, implying that differential gene expression may be the key to the host tropisms of human and bovine bacilli. The genome sequence therefore offers major insight on the evolution, host preference, and pathobiology of M. bovis.
Asunto(s)
Genoma Bacteriano , Modelos Biológicos , Modelos Genéticos , Datos de Secuencia Molecular , Mycobacterium bovis/genética , Mycobacterium tuberculosis/genética , Análisis de Secuencia de ADN , Especificidad de la EspecieRESUMEN
Staphylococcus aureus is an important nosocomial and community-acquired pathogen. Its genetic plasticity has facilitated the evolution of many virulent and drug-resistant strains, presenting a major and constantly changing clinical challenge. We sequenced the approximately 2.8-Mbp genomes of two disease-causing S. aureus strains isolated from distinct clinical settings: a recent hospital-acquired representative of the epidemic methicillin-resistant S. aureus EMRSA-16 clone (MRSA252), a clinically important and globally prevalent lineage; and a representative of an invasive community-acquired methicillin-susceptible S. aureus clone (MSSA476). A comparative-genomics approach was used to explore the mechanisms of evolution of clinically important S. aureus genomes and to identify regions affecting virulence and drug resistance. The genome sequences of MRSA252 and MSSA476 have a well conserved core region but differ markedly in their accessory genetic elements. MRSA252 is the most genetically diverse S. aureus strain sequenced to date: approximately 6% of the genome is novel compared with other published genomes, and it contains several unique genetic elements. MSSA476 is methicillin-susceptible, but it contains a novel Staphylococcal chromosomal cassette (SCC) mec-like element (designated SCC(476)), which is integrated at the same site on the chromosome as SCCmec elements in MRSA strains but encodes a putative fusidic acid resistance protein. The crucial role that accessory elements play in the rapid evolution of S. aureus is clearly illustrated by comparing the MSSA476 genome with that of an extremely closely related MRSA community-acquired strain; the differential distribution of large mobile elements carrying virulence and drug-resistance determinants may be responsible for the clinically important phenotypic differences in these strains.