Types of Anaerobic and Microaerophilic Bacteria

Abstract

The earliest days of Earth were devoid of oxygen gas. Four thousand million years ago, degassing of the rocks by condensation and physiochemical action led to the formation of oceans containing organic compounds, carbonate and reduced mineral salts with an atmosphere consisting mainly of nitrogen, but also containing significant amounts of carbon dioxide, hydrogen sulphide and hydrogen. Life forms appeared about this time, and the nutrients available imply a fermentative mode of metabolism for utilization of the organic compounds. The limitations of this as an energy source may have soon led to the development of anaerobic respiration involving fumarate to improve energy yield, but the major steps of obtaining energy by methanogenesis from the consumption of carbon dioxide and hydrogen, and energy from photosynthesis and sulphide oxidation, must have occurred relatively early. These developments would cause new competitive balances having further evolutionary consequences. Carbon dioxide and hydrogen would continue to be supplied from geophysical sources, but the competition for organic compounds would ’ increase, even though the increased variety of forms would themselves produce more organic compounds. Limitation of soluble nitrogen suggests that nitrogen fixation would evolve, and the formation of sulphate by photosynthetic bacteria encouraged the appearance of sulphate-reducing bacteria and additional cytochrome functions.