Metabolic Flux Analysis using <sup>13</sup>C Isotopes: III. Significance for System Biology and Metabolic Engineering
At present, <sup>13</sup>C-MFA is a primary method for the quantitative characterization of the intracellular carbon fluxes in vivo distribution under steady-state cell conditions. During more than twenty-year long history of application, the method has been used successfully for both investigations of the fundamental characteristics of the prokaryotic and eukaryotic cell metabolism and improvement of producing strain properties. Present publication is the final in a set of reviews describing various aspects of the method. Here, the authors highlight the recent achievements in the bacterial metabolism investigation reached with the <sup>13</sup>C-MFA assistance. Analysis of the well-characterized bacteria model strains revealed the central metabolism robustness provided by a set of the alternative metabolic pathways, and helped understand physiological meaning and find previously unknown functions of the well-studied metabolic pathways. Several good examples of the <sup>13</sup>C-MFA-based fundamental investigations of the poorly characterized bacteria are also analyzed. In applied investigations, the flux analysis in strains producing amino acids, vitamins and antibiotics permitted to determine targets for further modifications, to suggest unconventional metabolic engineering approaches, and which is most important, to confirm their helpfulness. In the final section of this article, the <sup>13</sup>C-MFA prospects including the monitoring of the dynamics of metabolic fluxes distribution during the culture growth are discussed.