Shewanella oneidensis MR-1 has conventionally been considered unable to use glucose as a carbon substrate for growth. The genome sequence of S. oneidensis MR-1 however suggests the ability to use glucose. Here, we demonstrate that during initial glucose exposure, S. oneidensis MR-1 quickly and frequently gains the ability to utilize glucose as a sole carbon source, in contrast to wild-type S. oneidensis, which cannot immediately use glucose as a sole carbon substrate. High-performance liquid chromatography and 14C glucose tracer studies confirm the disappearance in cultures and assimilation and respiration, respectively, of glucose. The relatively short time frame with which S. oneidensis MR-1 gained the ability to use glucose raises interesting ecological implications.