Holmium has no known essential biological function. Some species of
Aspergillus and Penicillium form crystals of holmium oxalate when
grown on solid media containing holmium (Talburt and Johnson, 1967). Aspergillus niger
biomass binds Ho3+ in solution (Talburt and Johnson, 1972).
For more information:
Medline for holmium AND bacteria
Talburt DE, Johnson GT. Some effects of rare earth elements and yttrium on
microbial growth. Mycologia 1967;59:492-503.