Accumulation of the compatible solutes, glycine-betaine and ectoine, in osmotic stress adaptation and heat shock cross-protection in the biocontrol agent Pantoea agglomerans CPA-2

Aims: The effect of modifying the water activity (a(w)) of Pantoea agglomerans growth medium with the ionic solute NaCl on water stress resistance, heat-shock survival and intracellular accumulation of the compatible solutes glycine-betaine and ectoine were determined. Methods and Results: The bacterium was cultured in an unmodified liquid medium or that modified with NaCl to 0.98 and 0.97 a(w), and viability of cells evaluated on a 0.96 a(w)-modified solid media to check water stress tolerance. Cells grown under ionic stress had better water stress tolerance than control cells. These cells also had cross-protection to heat stress (30 min, 45 degrees C). The modified cells accumulated substantial amounts of the compatible solutes glycine-betaine and ectoine in contrast to the control cells, which contained little or none of these two compounds. Conclusions: Improvement in osmotic and thermal tolerance of cells of the biocontrol agent P. agglomerans by modifying growth media with the ionic solute NaCl was achieved. The compatible solutes glycine-betaine and ectoine play a critical role in environmental stress tolerance improvement. Significance and Impact of the Study: This approach provides a method for improving the physiological quality of inocula and could have implications for formulation and shelf-life of biocontrol agents.