Perceived Cost of Auxotrophic Amino Acids in Two Bacterial Species

Amino acid biosynthetic pathways are highly conserved throughout all domains of life. Biosynthesis of amino acid requires the diversion of resources from energy production to amino acid production. The consequent energy-cost of producing an individual amino acid is can be estimated by addingthe amount of ATP expended in production itself to the amount of potential energy lost. Some organisms lack the metabolic pathways required for the synthesis of some or all of their amino acids and must obtain them from their environment or their host organism. The energetic costs associated with this means of obtaining amino acids are largely a matter of speculation at the present time. This study examines the perceived cost of auxotrophic amino acids (amino acids an organism is unable to synthesize) in two bacteria (Bacillus cereus ATCC 10987 and Vibrio fischeri ES114). Auxotrophic amino acids in both organisms were found to be used preferentially in highly expressed genes and are therefore likely to be energetically inexpensive relative to those the organisms are capable of synthesizing themselves. A regression approach was used to computationally estimate the perceived costs to the organism.