The formation and activity of nitrogenase2 in Azotobacter vinelandii OP was examined using a cell-free assay system. A lag period of about 30 min occurred between the exhaustion of the combined nitrogen source and growth on N2. Cells grown on ammonium acetate or potassium nitrate had no detectable nitrogenase activity. Nitrogenase activity appeared in cells, grown under a flowing gas phase of 20% O2 – 60% He, about 45 min after the exhaustion of ammonia. Nitrogenase formation was inhibited in a closed system with an atmosphere containing 40% O2 but not by one containing 20% O2. Hydrogen did not inhibit enzyme formation. The question of whether N2 is required for the formation of the enzyme could not be answered as this gas could not be completely eliminated from the growth system. Chloramphenicol prevented the formation of the enzyme and inhibited nitrogen fixation in whole cells, but had no effect on cell-free enzyme activity. A brief rise in turbidity which occurred during nitrogenase formation appeared to be due to a color change in the cells from reddish brown to dark brown. Spectrophotometric examination of extracts from ammonia- and N2-grown cells did not reveal any components responsible for this color difference, but this result may reflect only the presence of interfering substances in the crude extract.

Uranium accumulated extracellularly on the surfaces of Saccharomyces cerevisiae celLs. The rate and extent of accumulation were subject to environmental parameters, such as pH, temperature, and interference by certain anions and cations. Uranium accumulation by Pseudomonas aeruginosa occurred intracellularly and was extremely rapid (<10 s), and no response to environmental parameters could be detected. Metabolism was not required for metal uptake by either organism. Cell-bound uranium reached a concentration of 10 to 15% of the dry cell weight, but only 32% of the S. cerevisiae cells and 44% of the P. aeruginosa cells within a given population possessed visible uranium deposits when examined by electron microscopy. Rates of uranium uptake by S. cerevisiae were increased by chemical pretreatment of the cells. Uranium could be removed chemically from S. cerevisiae cells, and the cells could then be reused as a biosorbent.

No abstract

Several different strains of fungi have been shown to solubilize some types of low-ranked coal, apparently by an extracellular process. Oxidative pretreatment enhances the microbial action, allowing the use of a variety of coal feedstocks. The resulting product, which is primarily a mixture of polar organic compounds with moderate to high molecular weights and a high degree of aromaticity, is water-soluble. Possible processing concepts include the use of continuous bioreactors configured as either fixed or fluidized beds.