Stress responses of linear plasmids from Debaryomyces hansenii

The triplet linear plasmids pDHL1/2/3 from the salt-tolerant yeast Debaryomyces hansenii TK are localized in the cytoplasm and characterized by a unique feature that they require environmental stressors (0.3 M NaCl or solutes such as sorbitol with equivalent osmolarity) for stable replication and maintenance. The degree of osmolarity dependence of pDHLs was greatly affected by growth temperature of the host cells: the stability of pDHLs was maintained in the absence of osmolarity in cells growing at 25 °C, and required osmorarity equivalent to 0.3–1.0 M NaCl on shifting to 30–35 °C. Although to less extent, similar osmolarity dependence at high temperatures was observed with another system of D. hansenii linear plasmids. Short-term conditioning of cells to heat or high osmolarity resulted in significant improvement in the plasmid stability, suggesting possible involvement of stress proteins and/or high glycerol level in the stabilization process.