Host-virus coevolutionary interactions between Sulfolobus islandicus and Sulfolobus SpindleShaped viruses
Maria A. Bautista, Nicole Held, Jeffrey Kremer, Alfa Herrera, Jessica Kelliher, Sarah Reinhart, Whitney
England, Angela Kouris and Rachel J. Whitaker
Department of Microbiology, University of Illinois, Urbana-Champaign, Urbana, IL 61801,
USA.
Coevolutionary interactions with viral parasites play a key role in defining population structure
for all organisms. Because viruses are agents of gene flow in Sulfolobus we hypothesize that coevolutionary interactions with proviruses may also define the genetic structure of microbial
populations. The crenarchaeon Sulfolobus has served as a model organism for the study of cell
biology, biochemistry, and genetics of hyperthermophilic Archaea. Looking at the core and
variable genome components of the chronic integrative Sulfolobus Spindle-Shaped virus (SSV)
we have confirmed previous observations showing that the core genome displays a
biogeographic pattern. However the variable genome lacks this pattern suggesting that there is
gene flow between geographically isolated populations. These observations together with
signatures of coevolutionary interactions between geographically structured populations of
Sulfolobus islandicus and SSV recorded by CRISPR (Clustered regularly interspaced short
palindromic repeats) sequences have led to the hypothesis that SSV is locally adapted to its host
S.islandicus. We have screened S. islandicus strains from Yellowstone National Park and the
Mutnovsky Volcano for SSV. Using quantitative PCR we have characterized seven of these
strains and we have observed strain-specific differences in viral production on native hosts
ranging from very low production (10 SSV genome copies/cell) to hundreds of viral genome
copies per cell detected at different stages of host growth. Through cross-infection assays using
a panel of 45 S. islandicus hosts, representing different points in time and space, we tested
whether there are differences in host susceptibility to infection from local or foreign viruses.
Based on the pattern resolved through these preliminary crosses, we suggest that resistance to
infection with SSV is widespread among S.islandicus populations.