An environmentally important bacterium with versatile respiration, Shewanella oneidensis MR-1, displayed significantly different growth rates under three culture conditions: minimal medium (doubling time similar to 3 h), salt stressed minimal medium (doubling time similar to 6 h), and minimal medium with amino acid supplementation (doubling time similar to 1.5 h). C-13-based metabolic flux analysis indicated that fluxes of central metabolic reactions remained relatively constant under the three growth conditions, which is in stark contrast to the reported significant changes in the transcript and metabolite profiles under various growth conditions. Furthermore, 10 transposon mutants of S. oneidensis MR-1 were randomly chosen from a transposon library and their flux distributions through central metabolic pathways were revealed to be identical, even though such mutational processes altered the secondary metabolism, for example, glycine and C1 (5,10-Me-THF) metabolism. (c) 2009 American Institute of Chemical Engineers Biotechnol. Prog., 25: 1254-1259, 2009