EVIDENCE FOR THE INTERFERENCE OF ALUMINUM WITH BACTERIAL PORPHYRIN BIOSYNTHESIS

Aluminum (0.74 mM) was found to retard bacterial growth, and enhance p orphyrin formation and excretion in Arthrobacter aurescens RS-2. Copro porphyrin III was shown to be the main porphyrin excreted by aluminum- exposed A. aurescens RS-2 cultures and by RS-2 cultures grown under an oxic conditions. Synthesis and excretion of porphyrins in A. aurescens RS-2 increased in a dose-dependent manner when the bacteria were expo sed to increasing aluminum concentrations. Incubation of A. aurescens RS-2 with delta-aminoevulinic acid (delta-ALA, 1.2 mM) brought about t he intense formation and excretion of porphyrins by the cells, in the presence or absence of aluminum. delta-ALA slightly enhanced the toxic ity of aluminum towards RS-2 bacteria. Furthermore, the intracellular concentration of heme was reduced by 63.9 +/- 8.67% in aluminum-expose d RS-2 bacteria when compared with control cultures. The results are d iscussed in light of the recent finding concerning aluminum toxicity a nd porphyrin biosynthesis in microorganisms.