This article describes improved methods for isolating and cultivating sulphate-reducing bacteria, organisms that uniquely reduce sulfates to sulfides and play important roles in natural sulfur cycles and anaerobic corrosion. The authors isolated strains from diverse sources including soils, waters, and sediments using media based on mineral salts, lactate, and ferrous iron. A key innovation was adding 3% sodium sulphite to culture media, which selectively eliminated contaminating organisms and greatly facilitated purification of pure cultures. The authors demonstrated that sulphate-reducing bacteria are facultative autotrophs, capable of growing in mineral media using hydrogen oxidation as an energy source and sulfate, sulfite, thiosulfate, or elemental sulfur as hydrogen acceptors. Growth required only trace amounts of iron, with impurities in medium constituents providing sufficient quantities. The authors also clarified nomenclature issues, recommending Desulphovibrio as the proper genus name and noting evidence for multiple species rather than one. They established that sterile clay was superior to artificial media for maintaining stock cultures.

Key findings

• Addition of 3% sodium sulphite to culture media dramatically purifies mixed cultures by eliminating contaminants while allowing sulphate-reducers to proliferate, greatly simplifying isolation of pure cultures
• Sulphate-reducing bacteria are facultative autotrophs capable of growth in mineral media using hydrogen oxidation as energy and sulfate/sulfite/thiosulfate/elemental sulfur as electron acceptors
• Only trace amounts of iron from impurities in medium constituents are needed for growth; no growth occurs in biologically iron-free media
• Multiple strains with different temperature optima exist, and crude cultures can be obtained across a wide temperature range (30-55°C)
• Sterile clay is superior to artificial media for long-term maintenance of stock cultures, preserving original strain characteristics better than repeated subculturing