THE DIVERSITY OF METABOLISM IN PROCARYOTES

Introduction
A lot of hoopla is made about microbial diversity.  Based on superficial inspection, the bacteria and archea hardly seem diversified. There are but a few basic morphologies, the possibilities of motility and resting cells (spores), and a major differential stain (the Gram stain) to distinguish the procaryotes microscopically. In the eukaryotes, there may be more structural diversity within a single genus of organisms. So what is all the hoopla about? It is about biochemical or metabolic diversity, especially as it relates to energy-generating metabolism and biosynthesis of secondary metabolites. The procaryotes, as a group, conduct all the same types of basic metabolism as eukaryotes, but, in addition, there are several types of energy-generating metabolism among the procaryotes that are non existent in eukaryotic cells or organisms. The diversity of procaryotes is expressed by their great variation in modes of energy production and metabolism.
Even within a procaryotic species, there may be great versatility in metabolism. Consider Escherichia coli. The bacterium can produce energy for growth by fermentation or respiration. It can respire aerobically using O2 as a final electron acceptor, or it can respire under anaerobic conditions, using NO3 or fumarate as a terminal electron acceptor. E. coli can use glucose or lactose as a sole carbon source for growth, with the metabolic ability to transform the sugar into all the necessary amino acids, vitamins and nucleotides that make up cells. A relative of E. coli, Rhodospirillum rubrum, has all the heterotrophic capabilities as E. coli,plus the ability to grow by photoautotrophic, photoheterotrophic or lithotrophic means. It does require one growth factor, however; biotin must be added to its growth media.
Fundamentally, most eukaryotes produce energy (ATP) through alcohol fermentation (e.g. yeast), lactic acid fermentation (e.g. muscle cells, neutrophils), aerobic respiration (e.g. molds, protozoa, animals) or oxygenic photosynthesis (e.g. algae, plants). These modes of energy-generating metabolism exist among procaryotes, in addition to all following types of energy production which are virtually non existent in eukaryotes.
Unique fermentations proceeding through the Embden-Meyerhof pathway
Other fermentation pathways such as the phosphoketolase (heterolactic) and Entner-Doudoroff pathways
Anaerobic respiration: respiration that uses substances other than 02 as a final electron acceptor
Lithotrophy: use of inorganic substances as sources of energy
Photoheterotrophy: use of organic compounds as a carbon source during bacterial photosynthesis
Anoxygenic photosynthesis: photophosphorylation in the absence of O2
Methanogenesis: an ancient type of archaeon metabolism that uses H2 as an energy source and produces methane
Light-driven nonphotosynthetic photophosphorylation: unique archaeon metabolism that converts light energy into chemical energy
In addition, among autotrophic procaryotes, there are three ways to fix CO2, two of which are unknown among eukaryotes, the CODH (acetyl CoA pathway) and the reverse TCA cycle.