Nickel resistance in Escherichia coli V38 is dependent on the concentration used for induction.

Strain Escherichia coli V38 resistant to 4 mM NiCl2 was isolated from the city sewage sludge. It showed low nickel accumulation by cells and nickel ion efflux. Cells were pregrown (induced) overnight in the presence of Ni2+, then the culture was kept on ice for 20-30 min and transferred to 37 degrees C for further incubation. When the Ni2+ concentration during growth was the same as during incubation, there was no noticeable accumulation of Ni2+. When the Ni2+ concentration during incubation was higher than that used for induction, uptake of 63Ni2+ and delayed efflux were seen. The uptake and delay of both efflux and growth were directly proportional to the difference between the concentrations used for induction and incubation. Active nickel ion uptake was seen in cells taken from cultures in the delayed efflux period.

Crystal protein formed by Bacillus subtilis cells.

Electron microscopic investigation of ultrathin sections of Bacillus subtilis Cgr4 cells revealed the presence of crystal-like inclusions which were formed of spheric homogeneous subunits. The frequency of cells with a crystal-like inclusion in the culture approached 1%. The appearance of the crystal protein in cells coincided in time with spore morphogenesis. However, the process of crystal protein formation and sporulation are two alternatives: the cells either form the crystal protein or continue spore morphogenesis. Fractionation of cells in the stationary growth phase on a Percoll density gradient showed that the cells containing the crystal protein accumulated in the fraction corresponding to a 1.14-g/ml Percoll density. The cells were disintegrated by sonication, and alkaline-extracted proteins were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. After sodium dodecyl sulfate-gel electrophoresis, the fraction enriched with crystal-containing cells showed practically a single band with a molecular weight of 47,000 that corresponded to the crystal-forming protein. The antigenic features and amino acid composition indicated certain similarities between the crystal-forming protein in B. subtilis Cgr4 cells and the spore coat protein.