Iridium has no known biological function. Some bacteria and fungi have been shown
to leach iridium from igneous rock and meteorites and to accumulate
iridium ions from solution. These
phenomena are one proposed explanation for the presence of anomalous iridium deposits in some sedimentary
rock layers (Dyer et al, 1989).
For more information:
Medline for iridium AND bacteria
Dyer BD, Lyalikova NN, Murray D, Doyle M, Kolesov GM, Krumbein WE. Role for microorganisms in the formation of
iridium anomalies. Geology 1989;17:1036-39.