Effects of low-level deuterium enrichment on bacterial growth

Using very precise (up to 0.05%) measurements of the growth parameters for bacteria E. coli grown on minimal media, we aimed to determine the lowest deuterium concentration at which the adverse effects that are prominent at higher enrichments start to become noticeable. Such a threshold was found at 0.5% D, a surprisingly high value, while the ultralow deuterium concentrations (up to 0.25% D) showed signs of the opposite trend. Bacterial adaptation for 400 generations in isotopically different environment confirmed preference for ultralow (up to 0.25% D) enrichment. This effect appears to be similar to those described in sporadic but multiple earlier reports. Possible explanations include hormesis and isotopic resonance phenomena, with the latter explanation being favored.Comment: Accepted to PLoS One. Press embargo applie

Origin of life : testing the isotopic resonance hypothesis

The Miller-Urey (MU) experiment provided evidence supporting the abiogenesis theory, and is considered to be the seminal experiment in the context of origin of life. The MU mixture produced in the experiment is assumed to be an essential raw material for life emergence on the primitive Earth or beyond. However, there was no direct experimental evidence that this primordial soup supports life. In this thesis, we provided a proof that the abiotically produced MU mixture can support the growth of primitive living organisms, such as bacteria Escherichia coli. The recent Isotopic Resonance hypothesis suggests that the rates of chemical and biochemical reactions are not monotonous upon the enrichment degree of isotopic composition of reactants. Instead, at some “resonance” isotopic conditions with certain compositions of CHON, the kinetics increases or decreases compared to the “off-resonance” conditions. To test the predictions of this hypothesis, we designed a precise (standard error ±0.05%) method to explore the bacterial growth behaviour under different isotopic compositions. A number of predicted resonances including the terrestrial resonance and several other non-terrestrial resonances were tested, with significant enhancements in kinetics discovered at most of these conditions. The terrestrial resonance was intensively studied with multiple living organisms including prokaryotic bacteria Escherichia coli, eukaryotic yeast, mammalian RKO cells, grass seeds and shrimp. All obtained results strongly confirm the preference of living organisms for the terrestrial resonance and support the validity of isotopic resonance phenomena. Our study confirmed that the MU-type process created hospitable environment for early life, which further benefited from the presence of the terrestrial isotopic resonance

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

Isotopic compositions of reactants affect the rates of chemical and biochemical reactions. Usually it is assumed that heavy stable isotope enrichment leads to progressively slower reactions. Yet the effect of stable isotopes may be nonlinear, as exemplified by the "isotopic resonance" phenomenon. Since the isotopic compositions of other planets of Solar system, including Mars and Venus, are markedly different from terrestrial (e.g., deuterium content is ≈5 and ≈100 times higher, respectively), it is far from certain that terrestrial life will thrive in these isotopic conditions. Here we found that Martian deuterium content negatively affected survival of shrimp in semi-closed biosphere on a year-long time scale. Moreover, the bacterium Escherichia coli grows slower at Martian isotopic compositions and even slower at Venus's compositions. Thus, the biological impact of varying stable isotope compositions needs to be taken into account when planning interplanetary missions

Shrimp survival in BYOES under the period of 20 months.

<p>(A) The median number of shrimp in BYOES over the observation period of 20 months as well as the Student’s t-test (two-tailed, unpaired) results for each deuterium content. 150 ppm corresponds to normal terrestrial deuterium content. (B) The survival plots after 3-point smoothing. The number of shrimp that were still alive after 20 months was subtracted for each D content and the obtained value renormalized to day 1.</p

Stock solutions and their corresponding D content in the final samples.

<p>Stock solution (column one) was prepared by mixing M9 minimal media and heavy water at a certain ratio that resulted in the final D content in the sample (column four). For each sample, stock solution for its corresponding standards (below it is called stock solution of standard X) was prepared in the same way but using Milli-Q water instead of heavy water.</p

Maximum growth rate, lag time and maximum density of aged <i>E. coli</i>.

<p>(<b>A</b>) Maximum growth rate of aged <i>E. coli</i> grown in M9 minimal media with ultralow composition of deuterium. * denotes p<0.05. (<b>B</b>) Lag time of aged <i>E. coli</i> grown in M9 minimal media with ultralow composition of deuterium. (<b>C</b>) Maximum density of aged <i>E. coli</i> grown in M9 minimal media with ultralow composition of deuterium. * denotes p<0.05.</p

The results of <i>E</i>. <i>coli</i> growth parameter measurements at 25°C summarizing two independent experiments, each on a separate 100-well plate.

<p>(A) Maximum growth rate. (B) Maximum density. (C) Lag time. Usually, more advantageous growth conditions result in faster growth, higher maximum density and shorter lag time.</p

Typical growth curve and the three growth parameters derived from the curve.

<p>Typical growth curve and the three growth parameters derived from the curve.</p

Maximum growth rate, lag time, maximum density of <i>E. coli</i> grown in minimal media.

<p>(<b>A</b>) Blue circles: maximum growth rate of <i>E. coli</i> grown in M9 minimal media normalized by that at normal deuterium content of 156 ppm. * denotes p<0.05, ** - p<0.005, etc. Brown squares: predicted maximum growth rate calculated according to the maximum growth rate of <i>E. coli</i> grown in 50% of deuterium. (<b>B</b>) Blue circles: lag time of <i>E. coli</i> grown in M9 minimal media normalized by that at terrestrial content of deuterium from 156 ppm (terrestrial value) to 8%. Inset shows a zoom-in of the ultralow enrichment region. Brown squares: predicted lag time calculated according to the lag time of <i>E. coli</i> grown in 50% of deuterium. (<b>C</b>) Blue circles: maximum density of <i>E. coli</i> grown in M9 minimal media normalized by that at terrestrial deuterium content from 156 ppm (terrestrial value) to 8%. Inset shows a zoom-in of the ultralow enrichment region. Brown squares: predicted maximum density calculated according to maximum density of <i>E. coli</i> grown in 50% of deuterium.</p