Superoxide Dismutage (sod) is Regulared by Environmental Stress in Bacterial System

Abstract

Oxygen, which has been present in only trace amounts for 2.5 billion years, begins to build-up in the atmosphere. Some oxygen is formed through photodissociation of water vapour. However most of the oxygen was probably produced as a by-product of photosynthetic autotrophs using light energy, to split water molecules and so build organic compounds. Primitive unicellular forms resembling modern blue-green algae (cyanobacteria) released oxygen, which accumulated in the atmosphere and was deposited in iron oxide beds on the floor of the ocean. Recent research has suggested that that non-oxygen producing bacteria species such as the purple and green bacteria are the most ancient photosynthetic bacteria. Another group of non-oxygen-producing bacteria, known as heliobacteria, evolved later and appear to have been the precursors of the forms that produce oxygen as a byproduct. Relatives of cyanobacteria appear to have given rise to chloroplasts in algae and green plants - the chloroplasts are the small bodies in plant cells that carry out photosynthesis in algae and other plants. This occurred through a process of engulfment where these primitive cyanobacteria were captured, engulfed and enslaving by other cells to become the solar driven carbohydrate factories within the cells. Chloroplasts contain their own RNA and are thought to have been derived fromcells, which were once independent. A similar process is thought to have involved the engulfing and enslavement of other bacteria to form mitochondria - the energy powerhouses of cells using oxidative phosphorylation to use oxygen and carbohydrate to release energy, carbon dioxide and water. These complex cells with organelles entrapped within them, and nuclei became the 'eukaryotes' - the next stages in evolution of unicellular organisms. In some ways these forms can be regarded as the first type of 'multi-cellular organism' - though they are not generally recognized as such. The organelles represent cells within cells. The final phase of development of the modern atmosphere was the removal of the last remnants carbon dioxide (from 1-5% down to 0.04% today) and the build-up of oxygen to modern day proportions (from about 10% to 21% today). The oxygen that was produced was toxic to most forms present at the time and its build-up may have caused the first mass extinction on the planet opening up new habitats and opportunities for eukaryotes respiring oxygen. Anaerobic organism also exist today and must have followed a kind of evolutionary “adaptation” to the increasing atmospheric oxygen levels by restricting themselves to extreme environments where oxygen cannot penetrate in poisonous concentrations. Other organisms generated antioxidant defenses to tolerate oxygen and to use it for metabolic purpose, such as energy production gained by electron transport chains with oxygen a terminal acceptor.