Thioacetamide as a source of hydrogen sulfide for colony growth of purple sulfur bacteria

Abstract

Thioacetamide (TAA), CH₃CSNH₂, is an unstable sulfur compound which upon addition of acid decomposes into acetic acid, ammonia, and hydrogen sulfide (H₂S). This characteristic may be taken advantage of when doing plate counts or isolation streaks of phototrophic purple sulfur bacteria. We have performed plate counts and isolation streaks of these bacteria in Gas-Pak anaerobic jars (BBL) supplemented with a test tube containing 0.05 g or 0.10 g TAA dissolved in 1.0 ml of 0.2 N or 0.5 N HCl. It may be demonstrated in a Warburg respirometer that the gas is released over a period of at least 1 week. Colony growth may be observed in 5–10 days. One advantage of this technique is that sodium sulfide (Na₂S·9H₂O) need not be added to the agar medium, which, therefore, may be prepared and stored for future use. This technique has been used successfully for the isolation ofAmoebobacter, Chromatium, Ectothiorhodospira, Lamprocystis, Thiocapsa, andThiocystis.