Isolation and characterization of strontium resistant mutant of Neurospora crassa

Abstract

Strontium is a trace element that has no known essential biological role. The divalent cation, Sr 2+, displays physicochemical properties similar to those of the abundant and biologically essential cations Ca 2+ and Mg 2+. Abundant release of strontium is known to be the effect of radionuclide explosions. As there is no special strain for the removal of strontium from the effected environments, a strontium-resistant strain of Neurospora crassa (SRR) was obtained by repeated subculturing of the wild type on strontium containing agar medium. Neurospora crassa SRR was obtained by repeated subculturing, then the stability of the mutant was compared with wild type in terms of uptake, cellular partitioning and cross-resistant to other metals. Neurospora crassa SRR is twelve fold more resistant to strontium ions compared with the wild type. Resistance was stable on repeated subculturing of SRR on strontium-free media. Neurospora crassa SRR is also cross-resistant to calcium (fourfold). Higher concentrations of calcium ions are required to reverse growth inhibition due to strontium toxicity in Neurospora crassa SRR, compared with the wild type. The mechanism of strontium uptake is shown to be primarily due to binding of strontium to mycelia and cell walls. Efflux of mycelial strontium was also observed in wild type and strontium-resistant Neurospora crassa. The characteristics of SRR in comparison with wild type Neurospora crassa are discussed in relation to the mechanisms of strontium resistance.