RESUMO
Single-stranded (ss)RNA viruses are thought to evolve rapidly due to an inherently high mutation rate. However, it remains unclear how ssRNA viruses adapt to novel environments and/or how many and what types of substitutions are needed to facilitate this evolution. In this study, we followed the adaptation of the ssRNA bacteriophage Qß using thermally adapted Escherichia coli as a host, which can efficiently grow at temperatures between 37.2 and 45.3 °C. This made it possible to evaluate Qß adaptation to the highest known temperature that supports growth, 45.3 °C. We found that Qß was capable of replication at this temperature; within 114 days (~1260 generations), we detected more than 34 novel point mutations in the genome of the thermally adapted Qß population, representing 0.8% of the total Qß genome. In addition, we returned the 45.3 °C-adapted Qß populations to 37.2 °C and passaged them for 8 days (~124 generations). We found that the reverse-adapted Qß population showed little to no decrease in fitness. These results indicate that Qß can evolve in response to increasing temperatures in a short period of time with the accumulation of point mutations.
