New insights into Acinetobacter baumannii pathogenesis revealed by high-density pyrosequencing and transposon
Michael G Smith1, Tara A Gianoulis, Stefan Pukatzki
1Department of Molecular Cellular and Developmental Biology, Yale University, New Haven, Connecticut 06520, USA.
Abstract:
Acinetobacter baumannii has emerged as an important and problematic human pathogen as it is the causative agent of several types of infections including pneumonia, meningitis, septicemia, and urinary tract infections. We explored the pathogenic content of this harmful pathogen using a combination of DNA sequencing and insertional mutagenesis. The genome of this organism was sequenced using a strategy involving high-density pyrosequencing, a novel, rapid method of high-throughput sequencing. Excluding the rDNA repeats, the assembled genome is 3,976,746 base pairs (bp) and has 3830 ORFs. A significant fraction of ORFs (17.2%) are located in 28 putative alien islands, indicating that the genome has acquired a large amount of foreign DNA. Consistent with its role in pathogenesis, a remarkable number of the islands (16) contain genes implicated in virulence, indicating the organism devotes a considerable portion of its genes to pathogenesis. The largest island contains elements homologous to the Legionella/Coxiella Type IV secretion apparatus. Type IV secretion systems have been demonstrated to be important for virulence in other organisms and thus are likely to help mediate pathogenesis of A. baumannii. Insertional mutagenesis generated avirulent isolates of A. baumannii and verified that six of the islands contain virulence genes, including two novel islands containing genes that lacked homology with others in the databases. The DNA sequencing approach described in this study allows the rapid elucidation of the DNA sequence of any microbe and, when combined with genetic screens, can identify many novel genes important for microbial pathogenesis.
Insights
Acinetobacter baumannii pathogenesis was investigated using whole-genome sequencing and insertional mutagenesis. This study identified novel virulence genes within alien genomic islands, offering new targets for combating this critical human pathogen.
Area of Science:
- Microbiology
- Genomics
- Pathogenesis Research
Background:
- Acinetobacter baumannii is a significant human pathogen causing severe infections like pneumonia and septicemia.
- Understanding its pathogenic mechanisms is crucial for developing effective treatments.
Purpose of the Study:
- To explore the pathogenic content of Acinetobacter baumannii.
- To identify novel virulence genes and genomic islands contributing to pathogenesis.
Main Methods:
- Whole-genome sequencing using high-density pyrosequencing.
- Insertional mutagenesis to identify essential virulence genes.
- Bioinformatic analysis of genomic islands and open reading frames (ORFs).
Main Results:
- The assembled genome is 3,976,746 bp with 3830 ORFs.
- 17.2% of ORFs are located in 28 putative alien islands, with 16 islands containing virulence genes.
- Insertional mutagenesis confirmed six islands, including two novel ones, harbor virulence genes, with one island containing a Type IV secretion system.
Conclusions:
- Acinetobacter baumannii possesses a significant number of virulence genes within acquired genomic islands.
- The identified novel virulence factors provide potential targets for therapeutic intervention.
- Rapid DNA sequencing combined with genetic screens is effective for discovering microbial virulence genes.
