Molecular mechanisms of rare earth element utilization by methane-oxidizing bacteria and protease-producing bacteria

概要

Rare earth elements (REEs) form a chemically uniform group and include scandium (Sc),
yttrium (Y), and 15 lanthanides. Despite the name, their abundance in the earth's crust is not
low. Their bioavailability had long been overlooked until their discovery as a co-factor in the
active site of alcohol dehydrogenases, such as XoxF-type methanol dehydrogenase (REEMDH), whereas their well-characterized counterparts MxaF-type (Ca-MDH) are Ca-dependent.
Since then, the response in various methane/methanol-oxidizing bacteria to REEs has been
researched and it showed REEs can readily enhance and suppress the expressions of Xox-MDH
and Mxa-MDH, respectively. This regulation, the so-called REE switch has only been
investigated in a limited number of species. Furthermore, most REEs exist in the natural
environment as insoluble oxide forms. However, the utilization mechanism of such REEs is
remaining unclear. In addition, there are no known cases of REEs being used by enzymes other
than alcohol dehydrogenases.
In this study, REE switch and the differences from other species were confirmed in one of the
model strains of less studied gamma-proteobacterial methane-oxidizing bacterium
Methylococcus capsulatus Bath. Moreover, the molecular mechanisms of their utilization of
insoluble REE were investigated. Besides, as a Ca-containing enzyme, protease has drawn
attention. The REE effect on protease-producing bacteria is examined. ...

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