Summary: The selenate ion, a remarkably powerful competitive antagonist of the reduction of sulphate by (Hildenborough) suspensions, did not affect reduction of sulphite and thiosulphate. Cysteine, methionine and glutathione had no anti-selenate effect. Selenate also inhibited the growth of ; this effect was antagonized competitively by sulphate and non-competitively by sulphite. Repeated subculture in subinhibitory selenate + sulphate mixtures did not give rise to a selenate-resistant strain, though selenium was deposited in these conditions.

The monofluorophosphate ion behaved similarly: it was a competitive sulphate antagonist in growth and in sulphate reduction, though it had a lower specific anti-sulphate activity than selenate. It did not affect the metabolism of sulphite or thiosulphate. At high concentrations it showed non-competitive inhibition of sulphate reduction.

Of the other ‘analogues’ of sulphate tested, potassium tellurate suspensions and chromate inhibited growth and sulphate reduction, but were not competitive sulphate antagonists. High concentrations of perchlorate depressed sulphate reduction in a non-competitive manner, and methanesulphonate, β-hydroxyethanesulphonate, benzenesulphonate, ethylsulphate, sulphamate and dimethylsulphone were inactive.

An acridinium dye known to inhibit the growth of did not affect sulphate reduction, and, in growth, was not antagonized by sulphate or complex nitrogenous supplements. The organism was readily ‘trained’ to resist this dye.


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