Abstract EANA2026-101

In the absence of host cells, viral particles must persist in environments that can be chemically heterogeneous, physically structured, and subject to fluctuating conditions. Understanding how viral structure mediates survival under these conditions is essential for predicting viral persistence and potential biosignatures beyond Earth. Here, we investigate how adaptive mutations affecting host entry influence extracellular stability in the RNA bacteriophage Qβ. Experimental evolution under low host density at 37 °C led to the fixation of multiple non-synonymous mutations in the readthrough domain of the minor capsid protein A1 (positions Q195R, T222N, F224L, and F224S). These mutations enhance infection efficiency under host-limited conditions but consistently reduce viral replication at 43 °C, revealing a temperature-dependent trade-off.

To probe the basis of this trade-off, we developed an assay to measure viral inactivation in membrane-free bacterial lysates, used here as a chemically complex proxy for heterogeneous extracellular environments. All single mutants displayed accelerated loss of infectivity relative to the wild type, with a consistent hierarchy of sensitivity (F224S > F224L > T222N > Q195R > WT), and with inactivation rates increasing with temperature. These results suggest that mutations in the externally exposed A1 domain enhance susceptibility to non-specific interactions or environmentally induced conformational changes. Ongoing work aims to quantify how environmental complexity shapes this phenotype by systematically varying lysate concentration and temperature, and by extending the analysis to defined systems, including macromolecular crowding agents, complex organic mixtures, and mineral substrates.

Our findings support a model in which viral adaptation toward efficient host entry generates localized structural vulnerabilities that become critical during extracellular exposure. In environments characterized by host scarcity and prolonged abiotic stress—conditions expected in many planetary settings—such trade-offs may govern viral survival, accumulation, and long-term detectability.