Relative importance of amino acids, glycine-betaine and ectoine synthesis in the biocontrol agent Pantoea agglomerans CPA-2 in response to osmotic, acidic and heat stress

Aims The objective of this work was to determine the role of different compatible solutes in adaptation of Pantoea agglomerans CPA-2 at different stages of growth to solute (0.98, 0.97, 0.96 a(w)), heat (35 and 40 degrees C) and acidic (pH 4.0, 5.0, 6.0) stress. Methods and results: Solute stress was imposed by using NaCl, glucose or glycerol, and pH was imposed with malic and citric acids. The accumulation of glycine-betaine, ectoine and amino acids in bacterial cells was quantified using high performance liquid chromathography (HPLC). There was a significant (P < 0.05) accumulation of glycine-betaine (NaCl modified, 100-150 mu mol g(-1) dry weight of cells) and ectoine (glucose modified media, > 340 mu mol g(-1) dry weight of cells) in the cells over a 48 h incubation period when compared with controls (< 10 mu mol g(-1) dry weight of cells). Chromatographic profile of amino acids was different with respect to control when NaCl or glucose was used as osmolyte. Conclusions: Pantoea agglomerans CPA-2 cells synthesised significant amounts of glycine-betaine and ectoine in response to imposed solute stress. However, these compounds and tested amino acids were not involved in cellular adaptation to either heat or pH stress. Significance and Impact of the study: This type of information can be effectively applied to improve ecophysiological quality of cells of bacterial biocontrol agents for better survival and biocontrol efficacy in the phyllosphere of plants.