Interchange of L polymerase protein between two strains of viral hemorrhagic septicemia virus (VHSV) genotype IV alters temperature sensitivities in vitro

• Genotype IV strains from warm water grow at 23 °C in contrast to cold-water strains.
• The L protein plays an important role in temperature sensitivity of VHSV genotype IV.

Viral hemorrhagic septicemia virus (VHSV) has four genotypes (I–IV) and sub-lineages within genotype I and IV. Using a reverse genetics approach, we explored the importance of the L gene for growth characteristics at different temperatures following interchange of the L gene within genotype IV (IVa and IVb) strains. VHSV strains harboring heterologous L gene were recovered and we show that the L gene determines growth characteristics at different temperatures in permissive cell lines.