Abstract
Stable isotope labeling is a standard technique for tracing material transfer in molecular, ecological and biogeochemical studies. The main assumption in this approach is that the enrichment with a heavy isotope has no effect on the organism metabolism and growth, which is not consistent with current theoretical and empirical knowledge on kinetic isotope effects. Here, we demonstrate profound changes in growth dynamics of the green alga Raphidocelis subcapitata grown in 15N-enriched media. With increasing 15N concentration (0.37 to 50 at%), the lag phase increased, whereas maximal growth rate and total yield decreased; moreover, there was a negative relationship between the growth and the lag phase across the treatments. The latter suggests that a trade-off between growth rate and the ability to adapt to the high 15N environment may exist. Remarkably, the lag-phase response at 3.5 at% 15N was the shortest and deviated from the overall trend, thus providing partial support to the recently proposed Isotopic Resonance hypothesis, which predicts that certain isotopic composition is particularly favorable for living organisms. These findings confirm the occurrence of KIE in isotopically enriched algae and underline the importance of considering these effects when using stable isotope labeling in field and experimental studies.
Highlights
Stable isotope labeling is a standard technique for tracing material transfer in molecular, ecological and biogeochemical studies
The main assumption here is that the increased levels of a heavy isotope have no effect on the organism/cell growth and metabolism; i.e., the introduced isotopes do not modify the operation of the metabolic pathways, and the quantity and quality of the synthesized material are independent of the isotopic composition of the isotopic milieu
Cumulative enrichment of H, C, O and N with respective heavy isotopes resulted in a changed morphology and slower growth of the green alga Chlorella vulgaris[13], with strongest alterations attributed to enrichment with 2H and 18O isotopes
Summary
Stable isotope labeling is a standard technique for tracing material transfer in molecular, ecological and biogeochemical studies. The lag-phase response at 3.5 at% 15N was the shortest and deviated from the overall trend, providing partial support to the recently proposed Isotopic Resonance hypothesis, which predicts that certain isotopic composition is favorable for living organisms These findings confirm the occurrence of KIE in isotopically enriched algae and underline the importance of considering these effects when using stable isotope labeling in field and experimental studies. Cumulative enrichment of H, C, O and N with respective heavy isotopes resulted in a changed morphology and slower growth of the green alga Chlorella vulgaris[13], with strongest alterations attributed to enrichment with 2H and 18O isotopes In these studies, the focus was on algal cell size distribution, protein and nucleic acid content[13], while www.nature.com/scientificreports/. The full isotope labeling of autotrophic organisms for nuclear magnetic resonance spectroscopy (NMR) and mass spectrometry gained popularity since 13C and 15N isotopes were not found to affect algal growth measurably[14]
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