Evidence for the interference of aluminum with bacterial porphyrin biosynthesis

Aluminum (0.74 m m) was found to retard bacterial growth, and enhance porphyrin formation and excretion in Arthrobacter aurescens RS-2. Coproporphyrin III was shown to be the main porphyrin excreted by aluminum-exposed A. aurescens RS-2 cultures and by RS-2 cultures grown under anoxic conditions. Synthesis and excretion of porphyrins in A. aurescens RS-2 increased in a dose-dependent manner when the bacteria were exposed to increasing aluminum concentrations. Incubation of A. aurescens RS-2 with δ-aminolevulinic acid (δ-ALA, 1.2 m m) brought about the intense formation and excretion of porphyrins by the cells, in the presence or absence of aluminum. δ-ALA slightly enhanced the toxicity of aluminum towards RS-2 bacteria. Furthermore, the intracellular concentration of heme was reduced by 63.9 ± 8.67% in aluminum-exposed RS-2 bacteria when compared with control cultures. The results are discussed in light of the recent finding concerning aluminum toxicity and porphyrin biosynthesis in microorganisms.