Living in the Extreme: Extremophiles
Life on earth, as we know it today, developed through an evolutionary process of significant complexity over millions of years. The details are still contested in the scientific arena, but general consensus states life originated around 4.0 billion years ago on the ponds and oceans of a primitive Earth. Back then, our planet was bathed in lightning and ultraviolet light from the Sun; an extreme environment that helped kick-start the chemistry of life in a soup of complex molecules dispersed in the oceans gradually leading to the development of deoxyribonucleic acid or DNA.
It is difficult to imagine the environmental extremes of our planet’s past but the dawning of the twenty-first century has led to the discovery of many such environmental extremes that continue to exist on our planet as well as others in our Solar System. Equally marvelous has been the detection of life that seems to thrive in these extreme environments: Extremophiles.
Extreme Lovers
The word extremophile combines the Roman term extremus (“being on the outside”) with the Greek word philos (“lovers”) to describe organisms that thrive or love to thrive in extreme environments. Extremophiles include organisms that span all three domains of life. This three domain system is an evolutionary model that refers to the relationships between organisms where a common ancestral cell termed the last universal common ancestor (LUCA) is considered. These LUCAs evolved into three predominant cell types each representing a domain: Archaea, Bacteria, and Eukarya.
To keep it simple, archaea and bacteria are microbial organisms collectively known as prokaryotic cells where their DNA is not contained within a nucleus. Eukarya or eukaryotic cells are found in plants, animals, and fungi where their DNA is contained within a membrane-bound nucleus. While humans are composed of gobs of prokaryotic cells living inside or on us, we are categorically eukaryotic organisms. All human cells- including those in the brain, the heart, the muscles, and so on- are eukaryotic in nature.
Extremophiles have members within all three domains but to characterize these various organisms we must first begin by considering what we mean by extreme conditions.
Environmental extremes
To avoid human bias in defining what is “extreme,” a physical definition is usually favored where extremes are conditions that make it difficult for organisms to function. In the last few decades of the twentieth century, a library of extreme environments that play host to extremophilic activity have been identified.
These environments provide the essential environmental parameters that can be used to classify different categories of extremophiles: temperature, radiation, pressure, gravity, vacuum, desiccation, salinity, pH, oxygen tension, and other chemical extremes.
From heat-loving thermophiles to cold-loving psychrophiles, acidity loving acidophiles to alkali loving alkaliphiles, salty halophiles, pressure-loving piezophiles, and “everything in moderation” mesophiles, these extreme-loving organisms are largely prokaryotic in nature although several eukaryotes have been identified among their populace.
Humans and most animals fall in the mesophilic and neutrophilic ranges composed of moderate temperatures and neutral pH but depending on the criteria or context with which we distinguish extreme conditions, humans and animals can also be considered as extremophilic organisms. With that said, let us begin by looking at some popular representatives of the extremophilic community.
Meeting Extremophiles
Water bears or moss piglets as they are described popularly, Tardigrades are found everywhere from mountaintops to the deep sea, volcanoes, tropical rainforests, and the Antarctic, making them the promotional face of extremophile science.
Known for their extraordinary resilience, tardigrades are identified as poly-extremophiles for their ability to survive in various extremes including exposure to extreme temperatures and pressures, air deprivation, radiation, dehydration, starvation, and even the desolation of outer space. Short and plump, with four pairs of legs each with suction disks and claws, these micro-organisms are only 0.5 mm (0.02 in) long when fully grown. Their popularity largely stems from their characteristic abilities to survive diverse extrema as well as their prevalence in mosses and other easily accessible environments. When collected, tardigrades can be viewed easily under a low-power microscope, making them popular among students and amateur scientists.
Apart from the tardigrade, other well-known microbial species in the scientific arena include the thermophile Anaerobranca gottschalkii, the hyperthermophile Pyrococcus furiousus, and the psychrophile Lacinutrix algicola.
The personalized caricatures of these extremophiles is a callback to the fact that evolutionary responses, developed over several millenia, dictate why these organisms can do what they do. The basic tenet for an organism to maintain function in extreme environments involves finding a means to keep the external environment out. In the case of extremophiles, this is achieved either through spontaneous modification of bio-molecular function and structure (via DNA, proteins, or cellular fats or oils) or through evolutionary responses that signal protective mechanisms like altering physiology or enhanced repair capabilities.
Conclusion
Extremophiles are a unique window through which we can understand and predict evolutionary processes on Earth and other extreme environments. Commercially, extremophile research has potential applications in various industries including textiles (removal of textile stains and color maintenance), food science (production of lactose free milk, production of sugar syrup), biotechnology (amplification of DNA studies at high temperatures, biofuels or fuel from organic matter or waste such as bioethanol), and astrobiology (biological studies of life in planetary environments, planetary panspermia and terraforming). The existence of these tiny organisms puts into light the micro-machines that govern so many aspects of our lives and assist in the regulation of various phenomena in our biosphere. By studying nature at such extremes, we obtain an understanding of the expanded ranges of life on our own planet alongside greater insights into our evolutionary past and our possible future.
References
[1] Merino, Nancy et al. “Living at the Extremes: Extremophiles and the Limits of Life in a Planetary Context.” Frontiers in microbiology vol. 10 780. 15 Apr. 2019.
[2] Schokraie E, Warnken U, Hotz-Wagenblatt A, Grohme MA, Hengherr S, et al. (2012) Comparative proteome analysis of Milnesium tardigradum in early embryonic state versus adults in active and anhydrobiotic state. PLoS ONE 7(9): e45682.
[3] Schröder, Carola & Burkhardt, Christin & Antranikian, Garabed. (2020). What we learn from extremophiles. ChemTexts. 6. 8. 10.1007/s40828–020–0103–6.
[4] Rothschild, L., Mancinelli, R. Life in extreme environments. Nature 409, 1092–1101 (2001).
[5] Pereto, Juli. (2005). Controversies on the Origin of Life. International microbiology : the official journal of the Spanish Society for Microbiology. 8. 23–31.
[6] https://www.shmoop.com/study-guides/biology/biology-cells/all-eukaryotic-cells#:~:text=Despite%20the%20fact%20that%20we,so%20on%E2%80%94are%20also%20eukaryotic.
[7] https://www.visiblebody.com/learn/biology/cells/prokaryotes-vs-eukaryotes#:~:text=Prokaryotic%20cell&text=Prokaryotic%20cells%20comprise%20bacteria%20and%20archaea.&text=Eukaryotic%20cells%20are%20found%20in,are%20organisms%20containing%20eukaryotic%20cells.
Originally published at http://theprocrastinatingscientist.home.blog
