Further studies on environmental factors that modify the toxicity of nickel to microbes.

The toxicity of nickel (Ni) to mycelial growth of filamentous fungi and to replication of eubacteria, an actinomycete, and yeasts was influenced by various environmental abiotic factors. Sulfide and phosphate reduced the toxicity of Ni by the formation of insoluble salts. The clay minerals, montmorillonite and, to a much lesser extent, kaolinite, and the hydrous oxides of aluminum or manganese reduced the toxicity, presumably by the adsorption of cationic Ni to their net negatively charged surfaces. Amino acids, such as aspartic acid, complex organics, such as tryptone, casamino acids, and yeast extract, and chelating agents, such as citrate, 2,6-pyridine dicarboxylic acid, nitrilotriacetic acid, and ethylenediaminetetraacetic acid, significantly reduced the toxicity of Ni, presumably as the result of decreased attraction between the net negatively charged cell surfaces and the complexed Ni. The toxicity of Ni varied in different commercial media, with greater toxicities occurring in nutrient broth and MR-VP medium and lower toxicities occurring in lauryl tryptone, Elliker, microinoculum, and tryptic soy broths. Nickel had a lower toxicity in solid media gelled with Gelrite than with Bacto-agar.