Microorganisms and a new horizon of scientific discoveries
The simplest form of life is composed of single-celled microorganisms which are thought to have appeared around 3.5×109 years ago.1 Interestingly, evidence has shown that chloroplasts and mitochondria were once free-living microorganisms that became incorporated into eukaryotic cells and eventually became energy-producing organelles.1 Biodiversity enables microorganisms to survive in extreme environments all over the planet. In contrast to higher life forms, prokaryotes have had the transformative time to develop extraordinary hereditary uniqueness. But unlike metazoans, developmental change in prokaryotes is not reflected in morphological variety.
For whatever reasons, the morphology of microscopic organisms has generally changed very little over billions of years, in contrast to metazoans. Yet this does not mean that they have not evolved.2 Molecular sequencing demonstrates that they have developed, but the result of this change is invisible. Instead of significant changes in shape and appearance, developmental change in prokaryotes concentrated on metabolic changes and the ability to colonise every possible environment.3
Researchers are investigating prokaryotic genetic material to explore their phylogenetic diversity. And with advances in nucleic acid sequencing, the exploration of such magnificent life will open up a new world of biological discoveries.3 Such diversity in the metabolic activities of microbial life can be seen by the great divergence in its ability to withstand various unfavourable environmental conditions.4
Life forms with the capacity to survive and flourish in physically and/or geochemically harsh natural conditions unfavourable to most other life are called extremophiles.5,6 Most, but not all, extremophiles are single-celled organisms. Extremophiles are distributed in every one of the three domains – bacteria archaea, and eukaryotes. Over the past 20 years, researchers have discovered numerous life forms capable of surviving in incredibly inhospitable conditions under extremes of, for example, pH or temperature.7 Consequently, many scientists have concluded that life on Earth may have started in aqueous vents far beneath the sea.8
Astrophysicist Dr Steinn Sigurdsson supported such a theory when he suggested that bacterial spores had lived on Earth for 40m years, and that they are impervious to radiation.9 In February 2013, scientists discovered microscopic organisms living in an Antarctic lake covered by half a mile of ice, demonstrating another example of their extraordinary capacity to embrace conditions normally inadmissible for life.10 In the following month, researchers reported evidence that microorganisms were living in the Mariana Trench, the deepest place in the world’s oceans.11,12 Another group of scientists reported that microorganisms were flourishing inside rocks up to 580m beneath the sea floor under about 2.6km of water off the shore of the northwestern United States.11,13 It is not therefore surprising that other researchers concluded that organisms could be discovered in any niche.11 Polyextremophiles are organisms that live and flourish in more than one uninhabitable conditions normally unfavourable to living organisms.14