Sulfate-reducing bacteria comprise a diverse and ecologically interactive group of anaerobic prokaryotes which share an extraordinary trait: growth by sulfate respiration with hydrogen sulfide as a major end-product. Sulfate-reducers are found in diverse environments ranging from estuaries to geological oil-bearing formations. They have attracted considerable scientific and commercial interest. These organisms have been actively investigated by researchers in microbial energetics, protein chemistry, ecology and more recently molecular biology. This interest has increased greatly over the past...