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The pH-dependent inhibition of 22 metal salts was systematically examined for the yeast Saccharomyces cerevisiae. It was observed that the inhibition of growth by Cu, Co or Ni salts is substantially increased by histidine auxotrophy and by increasing the pH of the medium. Deletion of the high-affinity histidine permease Hip1p in His- strains caused greater sensitivity to Cu, Co and Ni and the requirement of a higher level of histidine to reverse the inhibition. It was concluded that intracellular histidine reduces the pH-dependent toxicity of Cu, Co and Ni.

A study was conducted to determine the effects of adding nickel and cobalt to methylotrophic-metanogenic biomass. Using on-line CH4 monitoring, it was observed that nickel and cobalt introduction hastens the increase in initial exponential and final arithmetic rates of methane production while curtailing temporary decrease in the rate. It was also noted that the continuous addition of nickel and cobalt facilitated the elimination of the temporary decrease stage, and thus, accelerating exponential production rate.

A bacterial chromate sensor was developed to characterize the determinants encoding inducible resistance to chromate and to cobalt and nickel in Alcaligenes eutrophus CH34. A cloned part of plasmid pMOL28, which contains both determinants, was mutated with Tn5-lacZ to develop metal-sensing bacterial strains. Results showed that A. eutrophus AE104(pEBZ141) could be used as a biosensor for chromate when cultivated in glycerol as an optimal carbon source.

The purification and characterization of a cobaltochelatase, an enzyme that catalyzes cobalt insertion during coenzyme B12 biosynthesis in Pseudomonas denitrificans, were described. It was shown that hydrogenobyrinic acid a,c-diamide is the substrate of cobaltochelatase and that the product of this enzyme's activity is cob(II)yrinic acid a, c-diamide. The complex enzyme consists of three proteins of M(sub r) 140,000 (CobN), 38,000 (CobS) and 80,000 (CobT), and the reaction is ATP dependent.