Evolutionary adaptation of Escherichia coli to nitrogen limitation

Organisms often face nitrogen limitation in the natural environment and they can adapt to it
through different  ways. Comparisons of existing taxa suggest that organisms tend to adapt to nitrogen
limitation by nitrogen conservation, but evolutionary experiments suggest that increased nitrogen acquisition
led to adaptation. These two types of studies have methodological drawbacks.Therefore we designed a more
synthetic evolutionary experiment. We used Escherichia coli to evolveint wo different nitrogen environments
 for 1300 generations and analyzed their adaptation to these environments. After 1300 generations, the fitness
 of all evolved lines in the two environments was significantly increased. The lines evolved in low  nitrogen
 environment had more fitness gains than the lines evolved in high nitrogen environment. Compared with their
ancestors, the lines evolved in low nitrogen environment showed significantly increased N%  and DNA%, but
decreased biomass C∶N ratio. While lines evolved in high nitrogen environment showed significantly increased
RNA%.These data suggest that E.coliad apts to nitrogen limitation by stronger ability to acquire nitrogen
but notnitrogen conservation.