Mechanism & significance
What changes in the microbe, and why
- A methanol dehydrogenase from Methylacidiphilum fumariolicum SolV was tested with lanthanides from La to Lu, excluding radioactive promethium. Earlier members supported higher activity than later ones. The study combined kinetic assays with calculations to investigate consequences of decreasing ionic size across the series. [1]
- SolV grown with europium yielded an enzyme with Eu in its active site. The overall protein structure remained similar to previously characterized forms, but catalytic efficiency was lower. Europium-supported growth and an isolated active enzyme are stronger evidence than metal binding alone. [2]
- In separate samarium experiments, Saccharomyces cerevisiae, Pseudomonas fluorescens, and Bacillus subtilis first adsorbed Sm and subsequently developed samarium-phosphate particles on their surfaces. Mineral formation occurred more rapidly at higher pH within the tested acidic range. [3]
The broader picture
Samarium, europium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium belong in the atlas, but their evidence is uneven. Comparative enzyme assays cover the series; europium also has direct structural and growth evidence, and samarium has experimental biomineralization evidence. No single “rare-earth effect” should be assigned to every member. [1][2][3]
Experiments worth knowing
Methylacidiphilum fumariolicum SolV
A direct europium enzyme example
Study design. Eu-supported culture growth followed by enzyme purification, metal analysis, crystallography, and kinetic assays.
What they found. Eu occupied the methanol dehydrogenase active site, with reduced catalytic efficiency relative to lighter-lanthanide forms. [2]
How to read it. A small change in metal chemistry can alter performance without a large visible structural change.
Yeast and two bacterial species
Samarium moves from solution to mineral
Study design. Time-resolved sorption and mineral characterization at starting pH 3, 4, and 5.
What they found. Sm-phosphate particles formed after an initial adsorption stage. [3]
How to read it. A disappearance from solution can reflect successive binding and precipitation rather than uptake into metabolism.
Community & host evidence
These studies concern environmental microbial cultures, cell surfaces, and purified enzymes. They do not establish individual human microbiome functions for the listed elements. For Tb, Dy, Ho, Er, Tm, Yb, and Lu, the evidence highlighted here remains comparative enzyme behavior, not a shared requirement for growth. [1]
Exposure & chemical form
Trivalent ions in an enzyme assay differ from mineral-bound metals. In the samarium study, changing pH altered the timing of surface mineral formation. In the europium study, the growth medium and enzyme preparation were controlled to determine the active-site assignment. [2][3]
What the evidence does not establish
Series membership is not a substitute for direct measurement. A metal can bind a protein without supporting efficient catalysis, and catalysis in vitro does not guarantee uptake or growth. Promethium was not tested in the comparative work and is not assigned a microbial role by analogy. [1]
Open research questions
Questions suggested by the evidence and its limits.
Selected research
Sources supporting the numbered statements and study summaries above. Publication status is identified where a source reports trial results outside a peer-reviewed paper. This is a curated entry point, not a systematic review.
- Lumpe H, Pol A, Op den Camp HJM, Daumann LJ (2018). Impact of the lanthanide contraction on the activity of a lanthanide-dependent methanol dehydrogenase – a kinetic and DFT study. View source↩↩↩↩↩
- Jahn B, Pol A, Lumpe H et al. (2018). Similar but Not the Same: First Kinetic and Structural Analyses of a Methanol Dehydrogenase Containing a Europium Ion in the Active Site. View source↩↩↩↩
- Jiang M, Ohnuki T, Utsunomiya S (2018). Biomineralization of Middle Rare Earth Element Samarium in Yeast and Bacteria Systems. View source↩↩↩↩↩