  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.
