Reduced uptake based zinc resistance in Azospirillum brasilense sp7

Zinc resistant Azospirillum brasilense sp7 exhibited a low affinity for the metal. A zinc-sensitized, streptomycin-resistant variant and a sensitive mutant of the parent strain showed an increased affinity for zinc. Both the affinity for, and uptake of the metal were in the order of parent strain < sensitised variant < sensitive mutant, suggesting reduced uptake as the mechanism of resistance to zinc. Neither magnesium nor manganese could bestow any protection against zinc toxicity in the sensitive mutant, suggesting a specific pathway for the entry of the metal.