Development of Broad-Range Microbial Minimal Culture Medium for Lanthanide Studies

Rare Earth Elements (REE), also known as Lanthanides (Ln), are a group of 17 elements showing peculiar physical and chemical properties. Unlike technological applications, very little is known about the physiological role and toxicity of Ln on biological systems, in particular on microorganisms (e.g., bacteria), which represent the most abundant domains on our planet. Up to now, very limited studies have been conducted due to Ln precipitation with some anions commonly present in the culture media. Therefore, the development of a minimal medium is essential to allow the study of Ln-microbial interactions, limiting considerably the precipitation of insoluble salts. In this regard, a new minimal culture medium capable of solubilizing large amounts of Ln and allowing the growth of different microbial taxa was successfully developed. Assays have shown that the medium is capable of solubilizing Ln up to 100 times more than other common culture media and allowing the growth of 63 bacteria and 5 fungi. The kinetic growth of one yeast and one Gram-positive bacterium has been defined, proving to support superior growth and biomass compared to other commonly used minimal media. Moreover, the sensitivity and uptake/absorption of a strain were tested, highlighting its capability to tolerate concentrations up to 10 mM of either Cerium, Gadolinium or Lanthanum and accumulate different quantities of the three.