Viruses preserved in ancient materials provide snapshots of past
viral diversity and a means to trace viral evolution through time.
Here, we use a metagenomics approach to identify filterable and
nuclease-resistant nucleic acids preserved in 700-y-old caribou
feces frozen in a permanent ice patch. We were able to recover
and characterize two viruses in replicated experiments performed
in two different laboratories: a small circular DNA viral genome
(ancient caribou feces associated virus, or aCFV) and a partial RNA
viral genome (Ancient Northwest Territories cripavirus, or aNCV).
Phylogenetic analysis identifies aCFV as distantly related to the
plant-infecting geminiviruses and the fungi-infecting Sclerotinia
sclerotiorum hypovirulence-associated DNA virus 1 and aNCV as
within the insect-infecting Cripavirus genus. We hypothesize that
these viruses originate from plant material ingested by caribou or
from flying insects and that their preservation can be attributed to
protection within viral capsids maintained at cold temperatures.
To investigate the tropism of aCFV, we used the geminiviral reverse
genetic system and introduced a multimeric clone into the
laboratory model plant Nicotiana benthamiana. Evidence for infectivity
came from the detection of viral DNA in newly emerged
leaves and the precise excision of the viral genome from the multimeric
clones in inoculated leaves. Our findings indicate that viral
genomes may in some circumstances be protected from degradation
for centuries
