Comparison of Ni-sensitive and Ni-resistant strains of Nostoc muscorum

A wild-type Ni-sensitive (Ni^s) strain of Nostoc muscorum ISU spontaneously yielded mutants resistant to inhibition by 40 M Ni with a frequency of about 10^-7. A Ni-resistant (Ni^r) mutant was deficient in the activities of urease and uptake hydrogenase. Cellular Ni uptake in the Ni^s strain was dependent on concentration (40 to 120 M) and time (0 to 30 min) (V_max=0.51 nmol/g protein.min; K_m=92 M). The Ni bioconcentration factor for such cells ranged between 0.95×10³ and 1.89×10³. Ni uptake in spheroplast preparations from Ni^s cells followed almost the same trend as intact cells except that the bioconcentration factor was slightly less (0.82 to 1.39)×10³]. In contrast, Ni uptake in the Ni^r intact cells was not concentration dependent and also the uptake was saturated, even at 40 M, within 10 min. Spheroplasts from the Ni^r strain showed a Ni bioconcentration factor of 1.19×10³ compared with 4.41×10³ for intact cells. The invariably lower Ni uptake by spheroplasts was attributed to altered membrane transport properties.R.K. Asthana, A.L. Singh and S.P. Singh are with the Algal Research Laboratory, Centre of Advanced Study in Botany, Banaras Hindu University, Varanasi-221 005, India.