TDK conference 2010

Adenoviruses are double-stranded DNA viruses infecting vertebrate hosts, such as reptiles and amphibians. The different adenovirus types possess quite narrow host spectra, that is each animal species may have its own adenovirus, therefore these viruses are perfectly suitable for investigating co-evolution. According to previous results of the research group, Atadenovirus is supposed to be the genus co-evolved with Squamata from the five presently apporeved genera of Adenoviridae, though first members was found in ruminants and birds. Based on whole genome analysis and phylogenetic calculations, an isolate from a corn snake previously proved to belong to the atadenoviruses. Moreover, the analysis of several lizard and snake samples by PCR likewise pointed towards atadenoviruses. The only adenovirus ever detected in amphibians proved to be a Siadenovirus, which genus was supposed to be the lineage co-evolved with amphibians biginings.

The aim of my study was to uncover further evidence concerning the reptilian origin of atadenoviruses. I also analysed amphibian samples because of the lack of information on amphibian adenoviruses.Altogether 187 reptilian and 157 amphibian samples were screened by nested PCR, which amplifies a 300 bp long fragment of the viral DNA polymerase gene. Further sequences were aquired from the genomes of two Heloderma adenoviruses previously isolated in Germany. About 75% was sequenced of the genome of the Mexican beaded lizard (Heloderma horridum) adenovirus as well as 40% of the Gila monster (Heloderma suspectum) adenovirus. Both viruses were clearly atadenoviruses. Among the reptile samples 17, while only 4 amphibian samples proved to be positive in the PCR screening. Further evidences were uncovered of the high infection rate in bearded dragons (4 samples) and in colubrid snakes (2 samples). Two novel adenoviruses were revealed from the samples of one white-throated monitor (Varanus albigularis) and 10 short-tailed pygmy chameleons (Rampholeon brevicaudatus). Two identical viruses were detected in 4 amphibian samples (2 Dendrobates auratus, 2 Phyllobates vittatus) at both amino acid and nucleotide levels. The virus is not only supposed to be a novel one, but the 2nd amphibian adenovirus ever described. About 8,500 bp of its genome was sequenced on the basis of which can be assigned – similarly to the reptile viruses investigated – to the genus Atadenovirus.

Both the position of all the detected and sequenced reptile adenoviruses and the balanced G+C content of their genomes verify the reptilian origin of atadenoviruses. The adenovirus revealed from the poison-dart frogs clusters together with the ruminant atadenoviruses at the phylogenetic tree while having an extremly low G+C ratio of 38.4%. According to these facts, the atadenovirus infection in amphibians is presumed to be the result of a host switch.