Comparative Genomics Of Aggregatibacter actinomycetemcomitans Isolates From Primates and Humans

Objective: It is widely recognized that non-human primates are the most appropriate model for studying Aa-induced human periodontal disease. Our aim was to study the natural distribution of Aa in primates and then to perform comparative genomic analysis of Aa isolates from old world and new world monkeys as compared to humans. Methods: 11 Aa isolates (serotypes: f=5, b=3, c=1 and d=1) from monkeys (9 rhesus and 1 marmoset), in addition to 2 human isolates, were selected for whole genome sequencing. One monkey Aa isolate was subject to 454 pyrosequencing, while all others were sequenced by Illumina HiSeq 2000 system. A coverage of 75´ and 40´ was achieved for 454 data and Illumina data, respectively. Genome sequence from each strain was aligned and mapped to reference Aa strains HK1651 or D11S-1 using Newbler or DNAnexus.

Results: The average size of monkey Aa genomes was 2.4 Mbp (GC=44.4%), and that of human Aa was 2.2 Mbp (GC=44.2%). Annotation using the tools RAST and GLIMMER v3.02 revealed on average 2416 genes for monkey Aa and 2123 genes for human Aa. Except for one rhesus isolate, all 11 monkey Aa isolates and two human isolates possessed genes coding for major virulence factors of Aa, leukotoxin, CDT, tad operon, and adhesins ApiA and Aae. All Aa isolates had a non-JP2 leukotoxin promoter. Each of the above sequences when aligned with corresponding sequences from human Aa isolates exhibited 90-95% identity. Furthermore, genomic islands coding for O-antigen and Lipooligosaccharide, in addition to 3 uncharacterized genomic islands, were found in all isolates. Extensive analyses of genome sequences of the Aa isolates is under progress. Conclusion: Comparative genomics might help elucidate evolutionary significance of genome level differences among Aa isolates, and perhaps also to translate those differences into Aa’s role in periodontitis in humans and in monkeys.