RESUMO
The slow-growing Mycobacterium celatum is known to have two different 16S rRNA gene sequences. This study confirms the presence of two rrn operons and describes their organization. One operon (rrnA) was found to be located downstream from murA and the other (rrnB) was found downstream from tyrS. The promoter regions were sequenced, and also the intergenic transcribed spacer (ITS1 and ITS2) regions separating the 16S rRNA, 23S rRNA and 5S rRNA gene coding regions. Analysis of the RNA fraction revealed that rrnA is regulated by two (P1 and PCL1) promoters and rrnB is regulated by one (P1). These data show that the two rrn operons of M. celatum are organized in the same way as the two rrn operons of classical fast-growing mycobacteria. This information was incorporated into a phylogenetic analysis of the genus based on both 16S rRNA gene sequences and (where possible) the number of rrn operons per genome. The results suggest that the ancestral Mycobacterium possessed two (rrnA and rrnB) operons per genome and that subsequently, on two separate occasions, an operon (rrnB) was lost, leading to two clusters of species having a single operon (rrnA); one cluster includes the classical pathogens and the other includes Mycobacterium abscessus and Mycobacterium chelonae.
Assuntos
Evolução Molecular , Mycobacterium/genética , RNA Ribossômico/genética , Óperon de RNAr , Proteínas de Bactérias/genética , Proteínas de Bactérias/isolamento & purificação , Sequência de Bases , DNA Intergênico/genética , DNA Ribossômico/genética , Dados de Sequência Molecular , Mycobacterium/classificação , Mycobacterium/crescimento & desenvolvimento , Filogenia , Regiões Promotoras Genéticas , RNA Bacteriano/genética , Alinhamento de Sequência , Análise de Sequência de DNA , Homologia de Sequência do Ácido Nucleico , Sítio de Iniciação de TranscriçãoRESUMO
Using signature-tagged transposon mutagenesis, we isolated 23 Mycobacterium tuberculosis mutants, corresponding to 21 genes or genetic regions, attenuated in their ability to parasitize human macrophages. Mutants disrupted in the ABC transporter-encoding genes Rv0986 and Rv0987 were further characterized as being impaired in their ability to bind to host cells.