Metabolism of volatile compounds by microorganisms

Graduation date: 1968Single-strain cultures of Streptococcus cremoris, Streptococcus\ud lactis, Streptococcus diacetilactis, and Leuconostoc citrovorum produced\ud little or no acetone and no dimethyl sulfide when grown in milk\ud culture. These organisms had little or no ability to decarboxylate\ud antexogenous source of acetoacetic acid nor were they capable of\ud producing dimethyl sulfide from methyl methionine sulfonium chloride.\ud The dimethyl sulfide content of milk was increased by heating\ud which indicated that a heat labile dimethyl sulfide precursor was\ud present in milk. The precursor remained in the skimmilk fraction\ud and was dialyzable. The precursor was identified as a methyl methionine\ud sulfonium salt on the basis of its thin-layer chromatographic\ud mobility and the heat instability of the compound. Heating of samples\ud caused the disappearance of the precursor compound with a\ud subsequent increase in the content of homoserine and dimethyl sulfide.\ud Single strain cultures of Pseudomonas fragi, Pseudomonas fluorescens, Pseudomonas putrefaciens, and two marine Pseudomonas\ud species reduced acetaldehyde, propionaldehyde, and butyraldehyde\ud to the corresponding alcohols at 21°C. All species studied\ud reduced propionaldehyde at 6°C. P. fragi and the marine species\ud reducted butanone and/or acetone at both 6 and 21°C. Under aerobic\ud conditions a strain of P. fragi quantitatively reduced added\ud propionaldehyde to n-propanol.\ud The quantities of acetaldehyde and ethanol produced by single-strain\ud cultures of Lactobacillus brevis, Lactobacillus casei, Lactolactis,\ud and Lactobacillus plantarum differed significantly both between\ud species and between strains of a species on incubation at both\ud their optimum growth temperature and 8°C. Growth and production of\ud these Compounds were very slow at 8°C. All organisms studied were\ud capable of reducing acetaldehyde and propionaldehyde to the corresponding\ud alcohol. L. brevis strains alone reduced added butanone\ud to 2-butanol. A strain of L. brevis produced n-propanol as a normal\ud metabolite when grown in milk culture.\ud Single-strain cultures of L. casei and L. plantarum accumulated\ud diacetyl when grown in milk culture at both 8 and 30°C, but\ud strains of L. lactis and L. brevis did not. Diacetyl reductase activity\ud was demonstrated in single-strain cultures of L. casei, L. brevis,\ud and L. lactis. Diacetyl reductase could be induced in L. plantarum\ud by growth in the presence of citrate. Growth in milk medium supplemented with citrate resulted in a stimulation of diacetyl reductase activity with L. casei