The Genus Thermus

Abstract

The discovery of the genus Thermus (Brock and Freeze, 1969) provided our first impetus for detailed studies on the physiology of thermophilic bacteria. Its discovery was one of the simpler things we did, because enrichment and culture were so easy. We used a synthetic salts medium which had been shown to be suitable for growth of hot spring algae, added relatively low concentrations of organic compounds, and incubated at 70° C. The latter is of most importance. Before we began our work, the standard temperature for isolating and growing thermophilic bacteria had been 55°C, a temperature that the food microbiologists had used since the time of Cameron and Esty (Farrell and Campbell, 1969). At this temperature, and with the usual media, all one generally gets in culture is Bacillus stearothermophilus, a widespread, soil-borne sporeformer. Although this organism is of considerable importance in spoilage of canned foods, it is hardly of much importance in natural thermal environments, despite the fact that it can be routinely isolated (Fields, 1970). Microscopically, one never sees organisms resembling B. stearothermophilus. This organism is gram-positive; if one does gram stains of natural material, one never sees anything gram-positive, although gram-negative bacteria abound.