Sulfur (and selenium) bacteria

Abstract

As an example of chemosynthesis, the sulfur bacteria of the non-photosynthetic type play a unique role, particularly in that among them there are forms amenable to experimental attack and for which data specifically relating to the process of chemosynthesis are available. The term "chemosynthesis" is here taken to mean the synthesis of the entire cell body from CO2 by way of energy derived from inorganic sources, particularly sulfur, and without the intervention of the energy of light. The term "chemolithotrophy" has been introduced to cover this aspect of chemosynthesis1. At the outset, one may eliminate the selenium bacteria from further consideration since, while there have been reports of their existence (BRENNER 1916, LIPMAN and WAKSMAN 1923), these are essentially derived from an uncritical era and there have been no modern studies which have been related to them. By the same token, nothing is known of the mechanisms of chemosynthesis (if any) in these forms. Of course, there are many organisms capable of reducing selenates and selenites, and some are capable of methylating selenium compounds (for example, CHALLENGER, LISLE and DRANSFIELD 1953), but these do not derive energy from the reactions. Selellium bacteria capable of oxidizing selenides, or even selenium itself, are not at present within the knowledge of contemporary biological science. The chemoautotrophic sulfur bacteria are essentially the following: Sulfur oxidizing group -limited to inorganic sulfur. Acid type: Thiobacillus thiooxidans. Alkaline type: Thiobacillus thioparus, etc., including Th. denitrificans capable of using nitrate as an oxidant rather than oxygen pe1' se as required by the others. These are restricted to sulfur (in a range of inorganic forms) which is oxidized to provide energy, the end product being sulfate. Sulfur oxidizing group - limite(l to inorganics. Thiobacillus fe1'TOXidans (TEMPLE and COLMER 1951), an acid-type organism capable of oxidizing and living autotrophically on either thiosulfate or ferrous iron. Th. thiocyanoxidans (HAPPOLD, JOHNSTONE and ROGERS 1952, HAPPOLD, JOHNSTONE, ROGERS and YOUATT 1954, YOUATT 1954) is an organism capable of gro'wing autotrophically on sulfide, thiosulfate or thiocyanate. Higher forms of sulfur bacteria. These are related to the l\'Iyxophyceae and myxobacteria and are elsewhere classified as depositing sulfur within the cell. The taxonomy of the chemosynthetic sulfur group, and indeed, the essential information on other aspects of their growth and metabolism will be found in recent reviews on the subject of autotrophic bacteria as follows: Soc. Gen. JvIicrobiol. Symposia (1954) and LEES (1955). These largely replace the earlier revie'ws.