Lanthanide utilization in bacteria

What comes to your mind when you think about lanthanides aka rare earth elements? We all carry them around in our smartphones, and you might know that industry needs them for numerous high-tech products including optical glas, superconductors, and batteries (Figure 1). Maybe you also know that China produces most of them - demands are high and global production is limited.

While it was hypothesized for years that lanthanides would be powerful enzymatic co-factors due to their strong Lewis acidity, lanthanide-dependent enzymes were only discovered a few years ago in methylotrophic bacteria (bacteria that utilize organic compounds without carbon-carbon bonds as energy and carbon source). Lanthanides are the most recently described life metals. The relevance of lanthanides goes beyond microbiology as positive effects of lanthanides on crop growing and livestock are known for a long time, while the underlying mechanisms are not understood.

In methylotrophic bacteria, lanthanides function as co-factors in methanol dehydrogenase, the key enzyme of methanol oxidation. Taking into account the ecological role of methylotrophs, lanthanides are of high relevance with respect to microbial carbon cycling.

The ability of certain methylotrophic taxa to solubilize lanthanides might facilitate the development of bio-inspired methods to recover and recycle these valuable metals for instance by coupling lanthanide enrichment to the consumption of waste and inexpensive feedstocks such as methane and methanol. In that sense, understanding lanthanide utilization better can contribute to a more sustainable economy, especially regarding the ongoing decarbonisation and green-energy transition.

Motivation & selected findings

Research dedicated to lanthanide-dependent metabolism is severely limited to few model organisms that do not represent the taxonomic and expected functional diversity of microbes utilizing lanthanides. I'm working on establishing a new, lanthanide-dependent methylotroph of the family Beijerinckiaceae, strain AL1 (Figure 2), as platform to win a more comprehensive understanding about lanthanide-dependent metabolism (Wegner et al., 2020; Wegner et al., 2021). Strain AL1 was isolated from soft coal slags enriched in lanthanides (Wegner and Liesack, 2017) and in comparison to methylotrophic model organisms it only posseses lanthanide-dependent methanol dehydrogenases and multiple other lanthanide-dependent enzymes with unknown substrate spectra. We could show periplasmic storage of lanthanides in strain AL1, something that was so far not seen in other methylotrophs (Figure 3).

Based on advanced electron microscopy, RNAseq-based gene expression analysis, and high-resolution elemental analysis, we have increasing evidence that Beijerinckiaceae bacterium RH AL1 can sense, distinguish, and selectively take up and store lanthanides. Changes in lanthanide supplementation reach into many metabolic aspects in strain RH AL1 - way beyond methylotrophy (Gornial et al., 2023) (Figure 4).