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Evolution of sfbI encoding streptococcal fibronectin-binding protein I: horizontal genetic transfer and gene mosaic structure.

ABSTRACT: Streptococcal fibronectin-binding protein is an important virulence factor involved in colonization and invasion of epithelial cells and tissues by Streptococcus pyogenes. In order to investigate the mechanisms involved in the evolution of sfbI, the sfbI genes from 54 strains were sequenced. Thirty-four distinct alleles were identified. Three principal mechanisms appear to have been involved in the evolution of sfbI. The amino-terminal aromatic amino acid-rich domain is the most variable region and is apparently generated by intergenic recombination of horizontally acquired DNA cassettes, resulting in a genetic mosaic in this region. Two distinct and divergent sequence types that shared only 61 to 70% identity were identified in the central proline-rich region, while variation at the 3' end of the gene is due to deletion or duplication of defined repeat units. Potential antigenic and functional variabilities in SfbI imply significant selective pressure in vivo with direct implications for the microbial pathogenesis of S. pyogenes.

SUBMITTER: Towers RJ

PROVIDER: S-EPMC309019 | biostudies-literature | 2003 Dec

REPOSITORIES: biostudies-literature

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Evolution of sfbI encoding streptococcal fibronectin-binding protein I: horizontal genetic transfer and gene mosaic structure.

Towers Rebecca J RJ Fagan Peter K PK Talay Susanne R SR Currie Bart J BJ Sriprakash Kadaba S KS Walker Mark J MJ Chhatwal Gursharan S GS

Journal of clinical microbiology 20031201 12

Streptococcal fibronectin-binding protein is an important virulence factor involved in colonization and invasion of epithelial cells and tissues by Streptococcus pyogenes. In order to investigate the mechanisms involved in the evolution of sfbI, the sfbI genes from 54 strains were sequenced. Thirty-four distinct alleles were identified. Three principal mechanisms appear to have been involved in the evolution of sfbI. The amino-terminal aromatic amino acid-rich domain is the most variable region ...[more]

PMID: 14662917

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Project description:BackgroundShuffling and disruption of operons and horizontal gene transfer are major contributions to the new, dynamic view of prokaryotic evolution. Under the 'selfish operon' hypothesis, operons are viewed as mobile genetic entities that are constantly disseminated via horizontal gene transfer, although their retention could be favored by the advantage of coregulation of functionally linked genes. Here we apply comparative genomics and phylogenetic analysis to examine horizontal transfer of entire operons versus displacement of individual genes within operons by horizontally acquired orthologs and independent assembly of the same or similar operons from genes with different phylogenetic affinities.ResultsSince a substantial number of operons have been identified experimentally in only a few model bacteria, evolutionarily conserved gene strings were analyzed as surrogates of operons. The phylogenetic affinities within these predicted operons were assessed first by sequence similarity analysis and then by phylogenetic analysis, including statistical tests of tree topology. Numerous cases of apparent horizontal transfer of entire operons were detected. However, it was shown that apparent horizontal transfer of individual genes or arrays of genes within operons is not uncommon either and results in xenologous gene displacement in situ, that is, displacement of an ancestral gene by a horizontally transferred ortholog from a taxonomically distant organism without change of the local gene organization. On rarer occasions, operons might have evolved via independent assembly, in part from horizontally acquired genes.ConclusionsThe discovery of in situ gene displacement shows that combination of rampant horizontal gene transfer with selection for preservation of operon structure provides for events in prokaryotic evolution that, a priori, seem improbable. These findings also emphasize that not all aspects of operon evolution are selfish, with operon integrity maintained by purifying selection at the organism level.

Project description:BackgroundGenomes of Methanosarcina spp. are among the largest archaeal genomes. One suggested reason for that is massive horizontal gene transfer (HGT) from bacteria. Genes of bacterial origin may be involved in the central metabolism and solute transport, in particular sugar synthesis, sulfur metabolism, phosphate metabolism, DNA repair, transport of small molecules etc. Horizontally transferred (HT) genes are considered to play the key role in the ability of Methanosarcina spp. to inhabit diverse environments. At the moment, genomes of three Methanosarcina spp. have been sequenced, and while these genomes vary in length and number of protein-coding genes, they all have been shown to accumulate HT genes. However, previous estimates had been made when fewer archaeal genomes were known. Moreover, several Methanosarcinaceae genomes from other genera have been sequenced recently. Here, we revise the census of genes of bacterial origin in Methanosarcinaceae.ResultsAbout 5% of Methanosarcina genes have been shown to be horizontally transferred from various bacterial groups to the last common ancestor either of Methanosarcinaceae, or Methanosarcina, or later in the evolution. Simulation of the composition of the NCBI protein non-redundant database for different years demonstrates that the estimates of the HGT rate have decreased drastically since 2002, the year of publication of the first Methanosarcina genome. The phylogenetic distribution of HT gene donors is non-uniform. Most HT genes were transferred from Firmicutes and Proteobacteria, while no HGT events from Actinobacteria to the common ancestor of Methanosarcinaceae were found. About 50% of HT genes are involved in metabolism. Horizontal transfer of transcription factors is not common, while 46% of horizontally transferred genes have demonstrated differential expression in a variety of conditions. HGT of complete operons is relatively infrequent and half of HT genes do not belong to operons.ConclusionsWhile genes of bacterial origin are still more frequent in Methanosarcinaceae than in other Archaea, most HGT events described earlier as Methanosarcina-specific seem to have occurred before the divergence of Methanosarcinaceae. Genes horizontally transferred from bacteria to archaea neither tend to be transferred with their regulators, nor in long operons.

Dataset Information

Evolution of sfbI encoding streptococcal fibronectin-binding protein I: horizontal genetic transfer and gene mosaic structure.

Publications

Evolution of sfbI encoding streptococcal fibronectin-binding protein I: horizontal genetic transfer and gene mosaic structure.

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