Sulphur requirements for growth of Acetivibrio cellulolyticus

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Abstract
The sulphur requirement for growth of Acetivibrio cellulolyticus was determined using a mineral salts basal medium reduced with titanium(III) citrate and supplemented with 1% (w/v) cellobiose and 0.05% (w/v) yeast extract. Inorganic sulphide (Na2S∙9H2O) in the range of 0.7–1.0 mM was found to support maximum growth whereas 8.0 mM sulphide caused complete inhibition. Of the other sulphur-containing compounds tested (cystine, sodium thioglycollate, methionine, glutathione, homocystine, S-methyl-L-cysteine, inorganic sulphate) cysteine-HCl at 10–15 mM concentration was the only one which supported maximum growth that was at least 80% of that obtained in the optimum sulphide medium. A modified medium incorporating the optimum inorganic sulphide concentration supported maximum growth that was about twice that obtained in a conventional medium reduced with cysteine-Na2S. The possible reasons for the inhibition of growth in defined media containing Na2S as the sole reducing agent and the sulphur source are discussed.