The¹⁵N isotope effect inEscherichia coli: A neutron can make the difference

Abstract

Several techniques based on stable isotope labeling are used for quantitative MS. These include stable isotope metabolic labeling methods for cells in culture as well as live organisms with the assumption that the stable isotope has no effect on the proteome. Here, we investigate the (15) N isotope effect on Escherichia coli cultures that were grown in either unlabeled ((14) N) or (15) N-labeled media by LC-ESI-MS/MS-based relative protein quantification. Consistent protein expression level differences and altered growth rates were observed between (14) N and (15) N-labeled cultures. Furthermore, targeted metabolite analyses revealed altered metabolite levels between (14) N and (15) N-labeled bacteria. Our data demonstrate for the first time that the introduction of the (15) N isotope affects protein and metabolite levels in E. coli and underline the importance of implementing controls for unbiased protein quantification using stable isotope labeling techniques.

Isotopic Resonance Hypothesis: Experimental Verification by Escherichia coli Growth Measurements

“…Preliminary experiments showed that the growth rate of E. coli is retarded at a significant enrichment of 15 N, which is in line with literature data12. For instance, at 50% enrichment, the lag time was extended by 0.53%, the growth rate decreased by 0.77%, and the maximum density was reduced by 0.94% (Figure S1).…”

“…The heavy isotopes of C, N and O are currently considered “safe”10, although recently Turck et al have reported that mice growth on 15 N diet exhibit systematic behavioural differences11. They also found that E. Coli grow slower in a media highly enriched with 15 N12. These examples demonstrate that the effects of heavy isotopic substitution on biology are still insufficiently understood13.…”

On the Effect of Planetary Stable Isotope Compositions on Growth and Survival of Terrestrial Organisms

“…They also found that the growth of the bacterium Escherichia coli ( E . coli ) is slowed down in a media highly enriched with 15 N[8]. …”

Kinetic 15N-isotope effects on algal growth

“…Heavier isotopes form stronger bonds that require higher energy to break them, which ultimately slows down the chemical reaction rate910. Slower reactions for organisms, in the context of isotopic labeling, can result in changing metabolic fluxes11 and decreased growth and development712. A few studies have addressed effects of externally supplied heavy isotopes on the growth and morphology of algae.…”