Mechanism & significance
What changes in the microbe, and why
- Purified PedH from Pseudomonas putida KT2440 was active with Pr(III), as well as several other light lanthanides. Its calcium-dependent counterpart, PedE, acts on overlapping alcohol and aldehyde substrates. The two systems allow the bacterium to respond to different metal environments. [1]
- Comparative growth tests with Methylotenera mobilis and Methylomonas sp. included praseodymium among growth-supporting light lanthanides. Different XoxF enzyme types accepted different ranges of the series, showing why a result for one lanthanide or one enzyme cannot define all the others. [2]
The broader picture
Praseodymium has direct experimental support as a usable metal in bacterial alcohol oxidation. Evidence comes from a nonmethylotrophic soil bacterium and from comparative studies of methylotrophs. This is an element-specific experimental role, rather than an inference based only on the better-known lanthanum and cerium examples. [1][2]
Experiments worth knowing
Pseudomonas putida KT2440 PedH
Praseodymium supports a nonmethylotrophic enzyme
Study design. Purified PQQ-dependent alcohol dehydrogenase was assayed with different metals and substrates.
What they found. Pr(III) supported activity, whereas PedH and calcium-dependent PedE differed in metal requirement. [1]
How to read it. A lanthanide-dependent reaction can occur outside methane- and methanol-specialist bacteria.
Community & host evidence
These are environmental isolates and enzyme systems, not human microbiome experiments. The most immediate ecological question is how metal availability influences use of alcohol substrates and competition among environmental bacteria. [1][2]
Exposure & chemical form
Pr(III) supplied in a defined medium is the relevant experimental species. Purified-enzyme activity, whole-cell growth, and regulation were measured with different assays; in particular, a regulatory threshold established with lanthanum should not be relabeled as a praseodymium threshold. [1][2]
What the evidence does not establish
PedH activity confirms a biochemical capability but not an exclusive need for praseodymium. The comparative XoxF work also warns that artificial electron-acceptor assays do not fully reconstruct the natural electron-transfer chain. Metal preference may differ between an isolated enzyme and a living community. [1][2]
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.
- Wehrmann M, Billard P, Martin-Meriadec A et al. (2017). Functional Role of Lanthanides in Enzymatic Activity and Transcriptional Regulation of Pyrroloquinoline Quinone-Dependent Alcohol Dehydrogenases in Pseudomonas putida KT2440. View source↩↩↩↩↩↩↩
- Huang J, Yu Z, Chistoserdova L (2018). Lanthanide-Dependent Methanol Dehydrogenases of XoxF4 and XoxF5 Clades Are Differentially Distributed Among Methylotrophic Bacteria and They Reveal Different Biochemical Properties. View source↩↩↩↩↩↩