Abstract
Tupanviruses are giant viruses recently discovered in Brazil from extreme environments: Tupanvirus soda lake (TPV-SL) and Tupanvirus deep ocean (TPV-DO). Unexpected features in Tupanviruses is the cytotoxic effect observed during infection, where the virus degrades the ribosomal RNA (rRNA) of its amoebal host. Interestingly, only TPV-SL causes this rRNA shutdown. We performed a genomic comparison of the two strains to determine potential modifications explaining the absence of rRNA degradation by TPV-DO. Whole genome comparisons were performed as well as more in-depth analysis at the gene level. We also calculated selective pressure on the orthologous genes between the two viruses. Our computational and evolutionary investigations revealed a potential target: a ribonuclease T2. These enzymes are known to be involved in cellular RNA catabolism such as in lysosomal degradation of rRNA. Our results suggest a functional ribonuclease localized in acid compartment closely related to ribonuclease T2 from eukaryotes. Silencing of the RNAse T2 gene of TPV-SL abolished its rRNA shutdown ability thereby correlating in silico assumption to the experimental evidence. In conclusion, all our results pointed to RNAse T2 as a target for explaining the difference for rRNA degradation ability between both strains.
Highlights
The giant viruses revolutionized the field of virology
Tupanvirus strain soda lake was co-cultured with A. castellanii strain Neff in peptone-yeast extract glucose (PYG) medium
Cell culture flasks containing 7 × 106 A. castellanii were infected with tupanvirus at an multiplicity of infection (M.O.I) of 0.1 and incubated at 32◦C
Summary
The giant viruses revolutionized the field of virology. Their isolation redefined the structural morphology and the size of the virion abolishing the small size parameter of viruses (inferior to 200 nm) (La Scola et al, 2003; Boyer et al, 2009; Reteno et al, 2015; Andreani et al, 2016; Levasseur et al, 2016). Tupanvirus is one of the most complex giant viruses discovered at this time. Two strains: Tupanvirus soda lake (TPV-SL) and Tupanvirus deep ocean (TPV-DO), were isolated respectively from soda lake and marine sediments at a depth of 3000 m (Abrahão et al, 2018).
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