Discovery of a novel retrovirus sequence in an Australian native rodent (Melomys burtoni): a putative link between gibbon ape leukemia virus and koala retrovirus

Abstract

Gibbon ape leukaemia virus (GALV) and koala retrovirus (KoRV) share a remarkably close sequence identity despite the fact that they occur in distantly related mammals on different continents. It has previously been suggested that infection of their respective hosts may have occurred as a result of a species jump from another, as yet unidentified vertebrate host. To investigate possible sources of these retroviruses in the Australian context, DNA samples were obtained from 42 vertebrate species and screened using PCR in order to detect proviral sequences closely related to KoRV and GALV. Four proviral partial sequences totalling 2880 bases which share a strong similarity with KoRV and GALV were detected in DNA from a native Australian rodent, the grassland melomys, Melomys burtoni. We have designated this novel gammaretrovirus Melomys burtoni retrovirus (MbRV). The concatenated nucleotide sequence of MbRV shares 93% identity with the corresponding sequence from GALV-SEATO and 83% identity with KoRV. The geographic ranges of the grassland melomys and of the koala partially overlap. Thus a species jump by MbRV from melomys to koalas is conceivable. However the genus Melomys does not occur in mainland South East Asia and so it appears most likely that another as yet unidentified host was the source of GALV.

Figure 1. Relative positions of MbRV fragments with respect to GALV genome.

Schematic showing the relative positions of the four MbRV fragments (dark bars) and the positions in which they align against the GALV genome. MbRV sequenced fragments are labeled 1–4 starting from the 5′ end the genome.

Figure 2. Phylogenetic tree for concatenated pol sequences.

Bayesian inference tree for the concatenated pol sequences of MbRV and related sequences available on Genbank. Numbers given at nodes represent Bayesian posterior probabilities; scale bar represents 0.2 substitutions per site. The tree was midpoint rooted. Taxa abbreviations are described in Table 3.

Figure 3. Phylogenetic tree for concatenated env sequences.

Bayesian inference tree for the concatenated env sequences of MbRV and related sequences available on Genbank. Numbers at nodes represent Bayesian posterior probabilities; scale bar represents 0.2 substitutions per site. The tree was midpoint rooted. Abbreviations described in Table 3.