Rare earth metals are essential for methanotrophic life in volcanic mudpots

Abstract

Summary Growth of M ethylacidiphilum fumariolicum S olV , an extremely acidophilic methanotrophic microbe isolated from an I talian volcanic mudpot, is shown to be strictly dependent on the presence of lanthanides, a group of rare earth elements ( REEs ) such as lanthanum ( Ln ), cerium ( Ce ), praseodymium ( Pr ) and neodymium ( Nd ). After fractionation of the bacterial cells and crystallization of the methanol dehydrogenase ( MDH ), it was shown that lanthanides were essential as cofactor in a homodimeric MDH comparable with one of the MDHs of M ethylobacterium extorquens AM 1. We hypothesize that the lanthanides provide superior catalytic properties to pyrroloquinoline quinone ( PQQ )‐dependent MDH , which is a key enzyme for both methanotrophs and methylotrophs. Thus far, all isolated MxaF ‐type MDH s contain calcium as a catalytic cofactor. The gene encoding the MDH of strain SolV was identified to be a xoxF ‐ortholog, phylogenetically closely related to mxaF . Analysis of the protein structure and alignment of amino acids showed potential REE ‐binding motifs in XoxF enzymes of many methylotrophs, suggesting that these may also be lanthanide‐dependent MDHs . Our findings will have major environmental implications as metagenome studies showed (lanthanide‐containing) XoxF ‐type MDH is much more prominent in nature than MxaF ‐type enzymes.

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