Effects of Polyamine on the Growth ofAcidiphilium facilis24R under Acidic Conditions

A mutant unable to grow under acidic conditions was isolated from the acidophilic heterotrophic bacterium Acidiphilium facilis 24R. The growth of the mutant could be fully restored by the addition of spermidine or lysine at the concentration of 100 μm. The HPLC analysis of polyamine composition showed that spermidine and putrescine were major polyamine components in the parental strain. In the mutant strain, putrescine was replaced by cadaverine. It was found that some polyamines in the cells were conjugated with the other cell components. The growth of the bacterium in the medium below pH 4.5 was inhibited in the presence of α-methylornithine or methylglyoxal-bis(guanylhydrazone), which are inhibitors of rate-limiting enzymes involved in the biosynthesis of polyamines. The growth of the bacterium that had been inhibited in the presence of inhibitors could be fully restored by the addition of putrescine or spermidine. On the basis of these results, it was concluded that polyamines have a significant role in the growth of Acidiphilium facilis 24R under acidic conditions.