Estudo do metabolismo de Salmonella typhimurium : da abordagem tradicional à análise dos fluxos metabólicos

Abstract

The genus Salmonella spp. has been extensively investigated because these bacteria are important pathogens that frequently cause severe diseases and gastrointestinal infections in humans and animals. Moreover, in recent years, Salmonella has called attention due to the excellent results in the production and in vivo delivery of various substances with potential application in Vaccinology. However, there is still little information available concerning aspects of its metabolism, which hampers both the development of new attenuated strains and the large-scale production of live cells and cellular components. Thus, this work aimed to study the S. typhimurium LT2 metabolism, using traditional and innovative approaches to investigate different carbon sources as well as different bioreactor operation modes and aeration conditions (aerobic and anaerobic). Results obtained in batch and chemostat cultivations indicated that S. typhimurium metabolism differs significantly from E. coli metabolism, closely related bacteria species with regard to the central carbon metabolism. The main difference observed between these bacteria was the high level of acetate production exhibited by S. typhimurium LT2 cells, which, differently from E. coli, occurred even at the lowest dilution rate evaluated. Currently, genome scale metabolic models are important tools for better understanding the phenotypic behavior of many organisms. Therefore the model STM_v1.0 reconstructed for S. typhimurium LT2 was evaluated, comparing experimental data, obtained in chemostat cultivations, with model predictions. Since this model was derived from E. coli model, the simulated results for biomass formation were overestimated and, consequently, predicted acetate fluxes were lower than those obtained experimentally. Therefore, to obtain experimental data useful to improve the model and to reach a better comprehension of S. typhimurium metabolism, the technique of metabolic flux analysis using isotopic labeled substrate was adopted, allowing determination of the fluxes for the main pathways of central carbon metabolism of Salmonella. This analysis revealed different preferred metabolic pathways depending on the specific growth rate. At the lowest dilution rate evaluated, D = 0.24 h-1, glucose was catabolized predominantly by the pentose phosphate and glycolysis pathways, while at the dilution rate of 0.48 h-1, the major pathway of glucose oxidation was Entner-Doudoroff. In addition, a relatively high flux through the citric acid cycle at the higher dilution rate studied was observed.