Bacterial Metabolism Shapes the Host-Pathogen Interface.

Why do organisms “eat”? This core question drives the study of biochemistry—specifically metabolism. The short answer to this seemingly simple question is 2-fold: first, eating provides cells with the physical building blocks for the generation of cellular components (i.e., growth of the physical cell; something must come from something); second, eating is the way to extract energy to do cellular work (i.e., powering the process of growth; work is never done for free). These two processes—catabolism and anabolism—are inextricably linked. The pathways of catabolism, such as glycolysis and the tricarboxylic acid (TCA) cycle, which break down molecules for energy metabolism, also branch off into anabolic pathways that generate building blocks for the cell. Bacterial metabolism is dynamic and flexible, with different bacterial species encoding different metabolic capacities within their genomes. Thus, the canonical TCA cycle may function fully in one bacterial species, while another bacterium, missing a key enzyme of the cycle now uses the other TCA enzymes in branched oxidative and reductive pathways. Moreover, depending on the availability of carbon sources or oxygen, even if a bacterium encodes all of the enzymes for respiration, with its high-energy yield, the less energy-efficient but faster process of fermentation may predominate. Thus, the flexible metabolic space of rapidly evolving bacterial genomes enables many different ways for bacteria to take advantage of nutrients in complex environments for robust replication.