Metabonomics Study Ongluconacetobacterxylinusfrom Different Micro-Environments

The growth, metabolism and biosynthesis of end-products in micro-organisms could be significantly influenced by micro-environment. Revealing the metabolic mechanism of micro-organisms to specific micro-environment, would contribute to illustrate physiological response to environmetal stress. The yield and structure of bacterial cellulose synthesized by Gluconacetobacter xylinus were quite different as cultural miro-environments changed, which may be closely related to corresponding cells growth and metabolism.In the current work, G. xylinus was cultured in two different micro-environments. Metabonomics based on gas chromatography-mass spectrometer (GC-MS) and multivariate statistical analysis was applied to reveal the metabolic profiles and mechanism of G. xylinus responsing to different cultural environments.When G. xylinus was grown under static or agitated culture, changes in the level of oxygen transfer rate obviously influenced cell growth and metabolism. In this work, a total of 79 intracellular metabolites were identified and quantified using GC-MS, including amino acids, sugars, organic acids, nucleic acids, sugar alcohol, amine and others. Potential biomarkers were found by the principal component analysis as well as partial least squares, including trehalose, gluconic acid, phosphate and xylose. Analysis on metabolic profiles and metablic network showed that cells from high rotational speeds represented high activity of glycolysis and TCA cycle pathway, for example, the glucose consumption increased by 75.84%. Gluconic acid, the main by product of bacterial cellulose production from glucose, decreased by 65.09%, which was responsible for the correspondingly low yield of bacterial cellulose. In addition, the increase of shear stress accompanied with high liquid flow rate from agitated culture induced the accumulation of metabolites that protected cells from damaging, including trehalso, proline and glutamic acid. Relative contents of the three metabolites increased by 1866.91%,382.84% and 1576.95% at 2-day point, respectively. As cells adapted to environmental changes when cultured for 3 days, the levels of the three metabolites decreased to 18.17%,18.14% and6.76%, respectively, compared to that cultured for 2 days.Another alteration of micro-environment was realized by the addition of weak direct-current electric field to static culture of G. xylinus. Results showed that cells concentration increased on cathode, but cells viability decreased on anode after 18 h. A total of 104 intracellular metabolites were identified and quantified by GC-MS, including sugars, sugar alcohols, organic acids, animo acids, amine and others. Multivariate statistical analysis showed that lactic acid, gluconic acid, hexadecanoic acid and ornithine were potential biomarkers. Activity of glycolysis and TCA cycle pathway in cells from cathode increased by 28.97% and 80.47% compared to anode and that without electric field. Amino acids shunt pathways or others branched little flux from the glycolysis or TCA cycle, which was benefit for cells growth and eneygy metabolism. For anode, cells viability was quite high at 6-h time point, increasing by 48.42% compared to control group, while cells concentration didn’t show up to be any superior than that without electric field, which was mostly due to the low activity of TCA cycle. When cells were cultured for 18 h under direct current electric field at anode, significantly changes of metabolic profiles were obtained in cells from anode, the accumulation of intra-cellular lactic acid and gluconic acid increase by 1.26-fold and 6.49-fold than 12 h, respectively, due to the decrease of extracellular pH. At the same time, metabolites for self-defense, glutamic acid, proline, ethanolamine, fatty acids and ornithine cylce, accumulated remarkably. Even though, they didn’t make cells survive, cells was found to be dead at 24-h.It was illustrated from this work that the regulation of amino acids and organic acids metabolism work as the main roles, when G. xylinus responded to changes of cultural environment. Fatty acids mainly worked for regulation of cell membrane fluidity and integrity response to environmental stress.