Metabolome profile of osmotolerant rhizobacteria under osmotic stress

An osmotolerant rhizobacteria (Enterococcus flavescens), isolated from the weed rhizosphere, has been subjected to osmotic stress in broth media supplemented with varied concentrations of glucose and sodium chloride (NaCl). The aims of this work was to evaluate the cells’ response and obtain a comprehensive view of metabolites profiles under osmotic stress. Cells were grown in rich medium (Luria Bertani, LB) supplemented with NaCl at varying concentrations (0.5 M – 1.8 M NaCl) and glucose (5% – 20%), both as a single or double stress condition. Physiological response was observed by measuring rhizobacterial growth and analysing metabolite synthesised using GC-MS. The results of this study demonstrated that different concentration of salt and glucose resulted in different metabolite profiles. It was also observed that cells cultivated in LB + 1,6 M NaCl and LB + 1,8 M NaCl medium resulted in only two different compounds detected, i.e amide and fatty acid. Under double stress, however, concentration of hexadecanoic acid, hexadecenoic acid, proline and glycerin was found increased, while under single-salt and glucose stress, hexadecanoic acid and 9octadecenoic acidmethyl ester were detected. Those two acid were absent from the cells’ metabolites under double stress. The results of this study thus suggested that osmotic stress provokes different pathway of fatty acid metabolism. The metabolome profile of the rhizobacteria under stress condition may also reveal specific mechanism of microbial tolerance to osmotic stress under different condition. The possible mechanism and pathway of osmotic stress in microorganisms will be discussed.