Glu-tRNA is either bound to elongation factor Tu to enter protein synthesis or is reduced by glutamyl-tRNA reductase (GluTR) in the first step of tetrapyrrole biosynthesis in most bacteria, archaea and in chloroplasts. Acidithiobacillus ferrooxidans, a bacterium that synthesizes a vast amount of heme, contains three genes encoding tRNA(Glu). All tRNA(Glu) species are substrates in vitro of GluRS1 from A. ferrooxidans.Glu-tRNA(3)(Glu), that fulfills the requirements for protein synthesis, is not substrate of GluTR. Therefore, aminoacylation of tRNA(3)(Glu) might contribute to ensure protein synthesis upon high heme demand by an uncoupling of protein and heme biosynthesis.