Nitrogen source influences natural abundance 15N of Escherichia coli

Escherichia coli cells were forced to mineralize or assimilate nitrogen in vitro by manipulating substrate carbon and nitrogen availability. When grown on an organic nitrogen source, E. coli cells released NH4+ and were enriched in N-15 relative to the nitrogen source (1.6-3.1 parts per thousand). However, when cells were grown on an inorganic nitrogen source, the biomass was depleted (6.1-9.1 parts per thousand) relative to the source. By measuring N-15 enrichment of microorganisms relative to nitrogen pools, ecosystem ecologists may be able to determine if microorganisms are assimilating or mineralizing nitrogen.