Genome sequence of Actinobacillus actinomycetemcomitans

The genome sequence and annotation of the human pathogen Actinobacillus actinomycetemcomitans (for obvious reasons, often abbreviated as Aa) were recently completed by the Laboratory for Genomics and Bioinformatics at OUHSC. This project was funded by a grant from NIDCR at NIH with Dr. David Dyer as the Principal Investigator, in collaboration with Dr. Bruce Roe of the Department of Chemistry and Biochemistry on the OU-Norman campus.

Aa is an important dental pathogen capable of causing several forms of periodontitis, a severe infection of the soft tissues and bony structures supporting the teeth. We sequenced and annotated the genome of strain HK1651, an Aa clinical isolate from an adolescent African male diagnosed with localized juvenile periodontitis.

The complete Aa genome is 2,105,503 bp and is predicted to encode 2,345 open reading frames (ORFs). The %G+C is 44.4%, similar to other previously sequenced members of the Pasteurellaceae family. Six complete copies of the ribosomal RNA operons, tRNAs representing each of the 20 amino acids have been identified. Annotation of the genome resulted in only 47.8% of the total predicted ORFs with a functional assignment, the remaining being comprised of conserved hypothetical proteins (32%) and hypothetical proteins (20.2%).

In addition, whole genome comparisons of the three completed Pasteurellaceae, Aa, Haemophilus influenzae and Pasteurella multocida were done to examine phylogenetic relationships among members of this family. Although 16s sequence data shows that these three organisms are closely related, whole genome comparisons show that there is little or no colinearity among the three organisms. Furthermore, comparison at the protein level demonstrates that Aa is most closely related to the sequenced Pasteurella multocida strain Pm70, with over 50% of the proteins being at least 30% identical between the two genomes. This is interesting since Aa was once taxonomically classified as a member of the Haemophilus genus.

The data collected from the Aa genome project suggests that further comparative analysis may help to elucidate minor genetic differences that may play a role in host tropism and disease. The data for this project is hosted on Dr. Roe's website and can be found here.