Infodoc : Sciences, Techniques et Culture

In the absence of A1 the lower limit for multiplication by Rhizobium trifolii strain HP3 was pH 4.8-5.0 and for BEL was pH 4.4-4.6. 50uM Al caused inhibition of multiplication of both strains in the range pH 4.6-5.6 despite precipitation of Al at pH values greater than 4.6. An increase in phosphate concentration from 10 to 100 uM for cells which had been exposed to Al for 14 days at pH 4.5 and 5.5 did not remove the inhibitory effect of Ai. Transfer of these cells to fresh Al medium caused a further decrease in numbers although transfer to non-stress medium allowed multiplication to occur. Equilibration of Al medium for 18 months or centrifugation of the medium before inoculation did not reduce the inhibitory effect of Al. Data from these experiments indicate that Rhizobium cells exp[...]

In the absence of A1 the lower limit for multiplication by Rhizobium trifolii strain HP3 was pH 4.8-5.0 and for BEL was pH 4.4-4.6. 50uM Al caused inhibition of multiplication of both strains in the range pH 4.6-5.6 despite precipitation of Al at pH values greater than 4.6. An increase in phosphate concentration from 10 to 100 uM for cells which had been exposed to Al for 14 days at pH 4.5 and 5.5 did not remove the inhibitory effect of Ai. Transfer of these cells to fresh Al medium caused a further decrease in numbers although transfer to non-stress medium allowed multiplication to occur. Equilibration of Al medium for 18 months or centrifugation of the medium before inoculation did not reduce the inhibitory effect of Al. Data from these experiments indicate that Rhizobium cells exposed to Al suffer an initial irreversible toxic effect and cells which survive this stage, perhaps due to environmental variation, then suffer a bacteriostatic effect. Calculation of ion activity products pAl + 3pOH and pAl + pPO4 successfully predicted the precipitation of Al in the medium, but not the conditions under which Al was toxic to Rhizobium. Therefore, both the toxic from of Al and the mechanism(s) of toxicity remain unclear.