Browsing by Author "Swartwood, Suzanne Christine"

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    The evolution of hydrogen sulfide by Gluconobacter species
    Swartwood, Suzanne Christine (Virginia Tech, 1995)
    Previous studies demonstrate that members of the strictly aerobic genus Gluconobacter produce detectable quantities of hydrogen sulfide (H₂S) when incubated in SYP medium (5% sorbitol, 1% yeast extract, and 1% peptone) containing thiosulfate. This finding is puzzling, since the microbial evolution of H₂S is characteristic of anaerobic or facultative bacteria. The goal of this research was to determine the physiological role of H₂S evolution for the gluconobacters. A methylene blue method was used to quantify the amount of H₂S evolved from cultures grown aerobically for 3 days at 28°C. Five of the six tested strains of gluconobacter evolved from 6 to 68 μg of H₂S. Strains which grew to a higher density (> 300 μg cell protein/ml ) evolved between 10 and 68 μg of H₂S. Strains which grew to a lesser extent (< 140 μg cell protein/ml ) evolved no more than 6 μg of H₂S. Uninoculated SYP medium containing 1% thiosulfate showed no evidence of H₂S evolution; however, sterile SYP medium with decreasing concentrations of yeast extract and peptone showed increasing amounts of H₂S evolved. When SYP medium was exhausted by gluconobacter growth for 72 hours, then supplemented with thiosulfate, filter sterilized, and incubated for 3 days at 28°C, these sterile solutions evolved over 400 μg of H₂S. A drop in pH. similar to that which occurs during gluconobacter growth, is not sufficient to evolve H₂S. My results to date suggest that H₂S evolution results not from gluconobacter metabolism, but rather from spontaneous decomposition of thiosulfate and the depletion of media components during growth.