Colorless Sulfur Bacteria

Since its recognition in the late nineteenth century, the ability to gain metabolically useful energy from the oxidation of reduced sulfur compounds by bacteria has been regarded as of such significance that it has been used as a primary characteristic in taxonomy. Essentially, any Gram-negative rod that could grow with a reduced sulfur compound as its primary energy source was automatically called "Thiobacillus." Similar bacteria with a spiral shape became "Thiomicrospira," and so on. As research progressed over the years, this approach has become steadily less satisfactory, and the development of genetic methods for identification has finally confirmed that the ability to metabolize reduced sulfur compounds is of no more taxonomic significance than the utilization of any other specialized substrate.

This chapter describes the scientific stages taken to reach this point, reviews the reorganization that has been necessary among the colorless sulfur bacteria, and considers the fact that while the metabolic trait is of less taxonomic significance than previously believed, this grouping is important ecologically and should be retained.