Time-dependent distribution of silicon in intact cells and cell-free extracts of Proteus mirabilis as a model of bacterial silicon transport

Proteus mirabilis cells were incubated in Si-containing media, and the distribution of silicon into the cell walls, the cell extract, and in alcohol-ether-insoluble and insoluble fraction was followed analytically. It was found that the silicon is first stored in the cell walls and then slowly transferred to the cell fluid. In both the cell walls and fluid, organic Si components are synthesized. Infrared spectra of Si-incubated P. mirabilis cells revealed that COSi, CSi, NSi, and SiH bonds are present. The distribution of the various compounds in cell walls and extract was determined. The occurrence of certain organo-silicates in the bacteria and their possible function in the process of Si transport are discussed. Cell-free extracts of these bacteria are enabled to fix silicon in organic binding. The influence of ATP, ADP, AMP, and DPNH on the Si uptake was examined, and it was shown that DPNH activates the reaction, whereas the liberated P i of the nucleotides inhibits the uptake of Si. The primary binding, storage, translocation, and final fixation are discussed with respect to the accompanying energy-linked reactions.