Enhanced desiccation tolerance of E. coli by overexpression of yjbJ and in vitro protective effects of YjbJ on enzyme and membrane

Escherichia coli, like other bacteria, maintains cellular viability under osmotic stress through multiple layers of molecular adaptation processes. Among various stress-induced responses, the accumulation of hydrophilic proteins has been suggested as a potential protective mechanism in stress tolerance. Here, we demonstrated that the overexpression of yjbJ enhanced desiccation tolerance of E. coli and its product, YjbJ, protected enzyme and membrane in vitro. Primarily, the expression of yjbJ was rapidly induced by various osmotic stressors (i.e., NaCl, desiccation, freezing). E. coli overexpressing yjbJ exhibited fast recovery of cell propagation and maintained cell viability following desiccation stress. yjbJ knocked-out E. coli showed no difference in desiccation tolerance compared to control E. coli, implying functional redundancies among desiccation responsive genes. YjbJ protein showed higher ability of water absorption than other proteins (i.e., BSA, gelatin, casein, gluten). In vitro, YjbJ preserved the activity of desiccation-sensitive enzyme (i.e., β-galactosidase) and maintained the membrane integrity of lipid vesicles under desiccation. Conclusively, based on direct experimental evidences using purified protein in vitro, we proposed that E. coli YjbJ protein potentially functioned as a protectant of macromolecules including enzymes, and membranes under stressed conditions.