Some Effects of Rare Earth Elements and Yttrium on Microbial Growth

SUMMARY

Evidence supplied by growth responses on gradient plates indicates that yttrium and the rare earth elements are generally toxic to microbial growth. Bacteria are more sensitive to these elements than the fungi. Some species of the fungi are much more sensitive to these metals than other species.

Colonies of Aspergillus niger (and three other fungi) produce oxalic acid which combines with the rare earth elements and yttrium to form insoluble oxalates, resulting in an important detoxification mechanism permitting further growth.

Many hyphae of filamentous fungi develop abnormal morphological appearance in the presence of yttrium or rare earth elements. These changes include multiple terminal branching, swelling, lateral branching, and the rupture of hyphal strands by a process similar to plasmoptysis. These elements also inhibit the production of asexual spores.

A ranking in descending order of the relative toxicity of individual rare earth elements and yttrium to growth of four filamentous fungi on gradient plates generally follows the order of decreasing atomic number and increasing atomic radius.