The extremely high Al resistance of Penicillium janthineleum F-13 is not caused by internal or external sequestration of Al

Abstract

Penicillium janthinellum F-13 has been isolated in previous work as a fungus tolerating the presence of high concentrations of Al (as high as 100 mM AlCl₃). Here its growth rate and yield in three acidic (pH 3.0) media of different composition with varying concentrations of Al are reported. The presence of Al did not affect these parameters, except that the growth yield was somewhat lower in GM (a glucose/peptone/yeast extract-containing medium) with the highest concentration tested (100 mM AlCl₃). The amount of Al found in the mycelium was so low that it cannot lead to a significant decrease in the medium for the higher Al concentrations applied. Although citric acid was excreted at growth on GM, and the presence of Al even promoted this, the concentration of this was far too low to diminish (by chelation) the high Al concentrations in the medium to a non-toxic level, i.e. the level (of approx. 1 mM) that is tolerated by low-resistance fungi. At growth on SLBM (a peptone/yeast extract/soil extract-containing medium), a rise in pH occurred. The same was found for SM (a glucose/mineral salts-containing medium), although in this case the picture was more complicated because the initial rise in pH was followed by a lowering due to the excretion of oxalic acid. Although both phenomena can diminish Al toxicity (by decreasing the external concentration of monomeric Al, regarded to be the toxic species), again the decrease is far too low to attain a non-toxic level when high Al concentrations are applied. Therefore, although in principal the metabolic phenomena observed for P. janthinellum F-13 at growth on different media can diminish Al toxicity, the tolerance of this organism for high external Al concentrations must be caused by another mechanism.