Hydrogen sulfide production by Pseudomonas aeruginosa. II. Qualitative substrate studies.

To determine the substrates from which hydrogen sulfide is evolved by Pseudomonas aeruginosa and to characterize the enzyme or enzymes involved, a study was made utilizing 40 strains of P. aeruginosa and 31 organic sulfur-containing compounds. Hydrogen sulfide sources were first determined with dried-cell preparations of one strain. Wet-cell preparations of 40 strains designated P. aeruginosa were then tested for their ability to liberate hydrogen sulfide from the positive substrates. All but three of the strains were isolated from human sources (feces, urine, eyes, throats, skin lesions) and all were capable of producing the blue pigment, pyocyanine, on one or more media. Two lots of dried-cell material of one strain of P. aeruginosa were used. One lot was prepared by washing the 24-hr growth from Trypticase Soy Agar (BBL) with distilled water. The second batch was obtained by culturing in Trypticase Soy Broth (BBL), with continuous forced aeration, and removing by centrifugation. Both batches were washed three times with distilled water and dried in vacuo at 37 C over Drierite. The dried materials were ground with mortar and pestle and stored at room temperature in screw-cap tubes. No difference in enzyme activity between the two preparations has been observed. Wet-cell preparations were prepared by washing cell masses from large Trypticase Soy Agar slants, washing once, and resuspending in distilled water. Screening of the organic sulfur compounds was accomplished by the following procedure: buffer [1 M tris(hydroxymethyl)aminomethane, pH 8.1 or 9.11, 1 ml; substrate (0.1 M), 0.2 ml; cells (10 mg dry wt/ml), 0.5 ml; distilled water, 0.3 ml; in 150 X 20 mm tubes; lead acetate paper held in tubes with rubber stopper; incubated in water bath at 37 C for up to 6 hr. Substrates positive with the dried-cell preparations were tested with wet-cell preparations of 40 strains of P. aeruginosa in a similar manner, substituting 0.5 ml of resuspended cells for the dried preparation. The results (Table 1) would'seem to indicate an activity in P. aeruginosa comparable with the TABLE 1. H2S evolution from organic sulfurcontaining compounds by Pseudomonas aeruginosa*