Isotope tracer coupled with mass spectrometry emerges as a powerful tool in metabolic research. Herein we reported our research advances that applied this new methodology in analyzing the metabolic potential of cyanobacteria, a group of model photosynthetic bacteria. Cyanobacteria are able to harness solar energy and convert atmospheric CO2 to biomass and bio-products and are capable of assimilating organic carbon sources as well. In this study, we generated a series of cyanobacterial strains capable of utilizing D-xylose, a major component of plant cell wall, by co-expression of exogenous E. coli xylA and xylB genes that encodes xylose isomerase and xylulose kinase, respectively. To investigate how xylose metabolism operates in engineered strains, mass spectroscopy (MS) analysis were applied to 13C-labeled cells. Engineered strains were first fed by stable 13C isotopes including 13C-bicarbonate or uniformly and positionally labeled xylose till reaching the labeling steady state. The labeling patterns of cyanobacterial biomass and bioproducts were then quantitatively measured by GC-MS and LC-MS. This method detected isotopes that are derived from labeled substrate, thus indicating the consequences of co-expression of xylA and xylB. Our data supports that xylAB engineered strains were enabled to assimilate D-xylose and the productivity of commodity chemicals including ethylene, α-ketoglutaric acid, and pyruvic acid was correspondingly enhanced. Using genetic and analytical tools as above, we quantified the fluxes throughout global metabolic network and identified an uncharacterized pathway in cyanobacteria metabolizing xylose.

Isotope tracer and mass spectrometry reveal engineered xylose metabolism in cyanobacteria

249th National Meeting (2015)

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