<P> Microorganisms tend to have a relatively fast rate of evolution . Most microorganisms can reproduce rapidly, and bacteria are also able to freely exchange genes through conjugation, transformation and transduction, even between widely divergent species . This horizontal gene transfer, coupled with a high mutation rate and other means of transformation, allows microorganisms to swiftly evolve (via natural selection) to survive in new environments and respond to environmental stresses . This rapid evolution is important in medicine, as it has led to the development of multidrug resistant pathogenic bacteria, superbugs, that are resistant to antibiotics . </P> <P> A possible transitional form of microorganism between a prokaryote and a eukaryote was discovered in 2012 by Japanese scientists . Parakaryon myojinensis is a unique microorganism larger than a typical prokaryote, but with nuclear material enclosed in a membrane as in a eukaryote, and the presence of endosymbionts . This is seen to be the first plausible evolutionary form of microorganism, showing a stage of development from the prokaryote to the eukaryote . </P> <P> Archaea are prokaryotic unicellular organisms, and form the first domain of life, in Carl Woese's three - domain system . A prokaryote is defined as having no cell nucleus or other membrane bound - organelle . Archaea share this defining feature with the bacteria with which they were once grouped . In 1990 the microbiologist Woese proposed the three - domain system that divided living things into bacteria, archaea and eukaryotes, and thereby split the prokaryote domain . </P> <P> Archaea differ from bacteria in both their genetics and biochemistry . For example, while bacterial cell membranes are made from phosphoglycerides with ester bonds, archaean membranes are made of ether lipids . Archaea were originally described as extremophiles living in extreme environments, such as hot springs, but have since been found in all types of habitats . Only now are scientists beginning to realize how common archaea are in the environment, with Crenarchaeota being the most common form of life in the ocean, dominating ecosystems below 150 m in depth . These organisms are also common in soil and play a vital role in ammonia oxidation . </P>

Where are large amounts of micro-organisms found in animals