Cultivation techniques to study lanthanide metal interactions in the haloalkaliphilic Type I methanotroph "Methylotuvimicrobium buryatense" 5GB1C.

Abstract

Lanthanide metals are commonly used in technological devices including batteries, computers, catalysts and magnets. Despite their important properties, mining difficulties and pollution concerns limit the number of mines worldwide. Because of these concerns, biometallurgy is an attractive possibility for lanthanide extraction from recycled materials or from contaminated sites. Methylotrophs, bacteria that grow on reduced carbon substrates like methane and methanol, utilize lanthanides for a central reaction in their metabolisms. They must have some mechanism for uptake or trafficking, and are therefore excellent candidates for applying small molecules or proteins for selective lanthanide metal recycling. The haloalkaliphilic methanotroph "Methylotuvimicrobium buryatense" 5GB1C is the fastest growing methanotroph isolated to date, and thus has great industrial potential. The MxaFI enzyme complex uses calcium as a Lewis acid in conjunction with the pyroquinoline quinone cofactor to oxidize methanol, while the alternative enzyme XoxF uses lanthanide metals (e.g. lanthanum and cerium) for the same function. Lanthanide metals, abundant in the earth's crust, strongly repress the transcription of mxaF yet activate the transcription of xoxF, implying that XoxF may be the predominant methanol dehydrogenase in the bacterium's native environment. It may be that lanthanum interaction mechanisms are different from those in other microorganisms. In addition, the facile genetics in this strain and existing background information make it a good study organism for biological lanthanum uptake. The interesting physiology of this organism required empirical work to develop cultivation methods that allow robust assays of gene expression and measurement of lanthanum associated with cell biomass. In this chapter, we show that altering the metal chelator increased the availability of lanthanum to the cell as measured by the specific gene expression response. We also made further alterations to prevent lanthanum precipitation in medium for the growth of haloalkaliphiles.