Metabolic profiling of Klebsiella oxytoca: evaluation of methods for extraction of intracellular metabolites using UPLC/Q-TOF-MS.

The global pool of intracellular metabolites is a reflection of all the metabolic functions of an organism. In the absence of in situ methods capable of directly measuring metabolite pools, intracellular metabolite measurements need to be performed after an extraction procedure. In this study, we evaluated the optimization of technologies for generation of a global metabolomics profile for intracellular metabolites in Klebsiella oxytoca. Intracellular metabolites of K. oxytoca were extracted at the early stationary phase using six different common extraction procedures, including cold methanol, boiling ethanol, methanol/chloroform combinations, hot water, potassium hydroxide, and perchloric acid. The metabolites were subsequently collected for further analysis, and intracellular metabolite concentration profiles were generated using ultra-performance liquid chromatography/quadrupole time-of-flight mass spectrometry. During analysis, the stability of metabolites extracted using cold methanol was clearly higher than that obtained by other extraction methods. For the majority of metabolites, extracts generated in this manner exhibited the greatest recovery, with high reproducibility. Therefore, the use of cold ethanol was the best extraction method for attaining a metabolic profile. However, in another parallel extraction method, perchloric acid may also be required to maximize the range of metabolites recovered, particularly to extract glucose 1-phosphate and NADPH.