The Chemolithotrophic Prokaryotes
Such was Winogradsky’s (1887) description of the ability of certain bacteria to use energy from inorganic chemicals. Winogradsky’s (1887) name for such organisms was “Anorgoxydanten” (literally “inorganic oxidizers”). Today the term chemolithotrophy is us
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Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 275 Inorganic Oxidations as Sources of Energy . . . . . . . . . . . . . . . . 276 Energy Yields from Inorganic Oxidations . . . . . . . . . . . . . . . . . 276 Chemolithotrophy and Autotrophy Among Heterotrophs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 277 The Overlap of Autotrophy, Methylotrophy, and Chemolithotrophy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279 Chemoorganotrophic Potential among Obligate Chemolithotrophs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 279 Some Novel Chemolithotrophic Reactions and Some ‘‘New’’ Chemolithotrophs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 280 Evolutionary Aspects of the Origin of Chemolithotrophy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 282
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Ihre Lebensprozesse spielen sich nach einem viel einfacheren Schema ab; durch einen rein anorganischen chemischen Prozess. . .werden alle ihre Lebensbewegungen im Gange erhalten. [‘‘Their life processes are played out in a very simple fashion; all their life activities are driven by a purely inorganic chemical process.’’] —Winogradsky, 1887
Introduction Such was Winogradsky’s (1887) description of the ability of certain bacteria to use energy from inorganic chemicals. Winogradsky’s (1887) name for such organisms was ‘‘Anorgoxydanten’’ (literally ‘‘inorganic oxidizers’’). Today the term chemolithotrophy is used to describe the energy metabolism of bacteria that use the oxidation of inorganic substances, in the absence of light, as a source of energy for cell biosynthesis and maintenance (Rittenberg 1969; Brock and Schlegel 1989; Kelly 1990). Chemolithotrophs exhibit extraordinary diversity of substrates, modes of carbon nutrition, morphology, and habitat. Grouping chemolithotrophs into some kind of
homogeneous taxonomic unit is thus at least as artificial as grouping by most taxonomic devices in that virtually every possible morphology and physiology among bacteria (including the archaebacteria) is represented. Such taxonomic ‘‘lumping’’ does have value because some fundamental aspects of carbon and energy metabolism unify many of the chemolithotrophs into groups that are useful for physiological comparison. The fundamental process in energy-conserving metabolism and in all respiratory processes is the transfer of hydrogen from a state more electronegative than that of the H+/H2O couple to that of water. Classically, ‘‘heterotrophs’’ or ‘‘chemoorganotrophs’’ obtain reducing potential from the dehydrogenation of organic compounds. Although a great variety of organic substrates are available and many are oxidized by heterotrophs, only a few principal metabolic processes exist whereby the hydrogen equivalents are fed into energy-conserving electron transport. Chief among these are processes that use the dehydrogenases of sugar phospha
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