Extremophiles

Permafrozen Anartic soils that experience extreme dryness and high salinity. Halophiles and xerophiles may be found here.

An Extremophile is an organism that experiences optimal growth in environments outside the realm of what is considered “normal” and may even require intense geochemical or physical conditions to survive [1]. Extremophiles associated with plants encompass all three domains of life: Archaea, Bacteria, and Eukarya. Within these domains, they can be found in different phylums and groups such as Actinobacteria, Ascomycota, Bacteroidetes, Basidiomycota, Crenarchaeota, Euryarchaeota, Firmicutes and Proteobacteria. Extremophilic microbes that benefit plant health and soil fertility are Arbuscular Mycorrhizal Fungi and bacteria found in the rhizosphere growing under abiotic stress conditions of temperature, salinity, pH and water deficiency. These microbes are said to be psychrophiles (-2°C to 20°C), thermophiles (60°C to 115°C), halophiles (2-5M), acidophiles (pH<4), alkaliphiles (pH>9) and xerophiles (water potential 0.75 kPa) [2]. Though not intensively studied until recently, extremophiles may have huge potential in the application of agriculture, biotechnology and bioremediation [3].

Plant Health and Agriculture

Penicillium chrysogenum, a rhizobacteria used both in penicillin production and a bio-fertilizer.

Extremophilic microbes found in soils and within plants present a of variety of benefits towards increasing overall plant health. They have ability to produce phytohormones, solubilize nutrients, and attack pathogens.

There has been success in applying these microbes as biofertilizers for crop improvement and soil health as a sustainable option[2]. Two rhizobacteria root endophytes that are found in Antarctica, Penicillium chrysogenum and Penicillium brevicompactum, increased fitness in cayenne, lettuce, onion, and tomato in high salinity environments by limiting the intake of salt. This has useful application in reduction of saline stress on plants that are not saline tolerant, such as lettuce [4].

In another study, endophytic mycorrhizae isolated from the roots of a tomato grown in intense drought and saline conditions was found to activate and stimulate defense mechanisms in plants through the use of phytohormones to achieve improved growth [5]. There is an extreme interest in extremophilic microbes found in cold environments due to their ability to thrive in what is often a high salinity and arid environment, but full potential of these microbes in agriculture is still being discovered and researched, for example the recent increase in the reports of acidophiles found in plants growing within acidic soil [2].

Bioremediation

The Atacama desert, subject of intensive research due to the diverse extremophilic organisms found residing there.

Aspergillus, a diverse fungi that contains many extremophiles.

Bioremediation refers to the use of an organism in degradation of contaminants that pose environmental and human risks. There has been a number of extremophilic organisms successful in remediation of contaminated soil [3].

Deinococcus radiodurans is a radiation-resistant bacteria occurring naturally in the cracks of rocks in Antarctica that has been genetically engineered by insertion of the mercuric reductase gene from Escherichia coli to be useful in remediation of heavy metals and radiation in nuclear waste sites. The gene combined with the bacteria's ability to tolerate radiation has made it a reliable option degrade mercury in radiation enriched soil environments [6].

Acidophiles have been successfully utilized in remediation of heavy metal soil sites. The fungi in Aspergillus, which also contains the species that causes black mold, and the bacteria A.ferrooxidans, have been used to remove nickel from contaminated soil and wastewater. Extremophilic bacteria B. thuringiensis have been shown to increase extraction of Cd and Zn from Cd-rich soil and soil polluted with effluent from metal industry [14]. Acidithiobacillus sp has been successful in removing sulfur from coal in order to help prevent acid rain [8]. The soil of the Atacama desert, noted for its similarity to mars, is now being heavily studied due to the vast variety of extremophilic organisms found there with high bioremediation potential [9].

Biotechnology

In a process known as bio-leaching, g, the removal of insoluble metal sulfides or oxides by using microorganisms, extremophiles are used as a sustainble option to mine ores, referred to as biomining. This is much more eco-friendly to soils and the surrounding environment. Biomining techniques have successfully been employed to mine metals such as gold, silver, copper, zinc, nickel, and uranium. The organisms used in this process are acidophiles such as Acidithiobacillus and Ferroplasma. In certain mining conditions there is extreme heat present, where thermophilic organisms Sulfolobus and Metallosphaera are utilized [15].

Waimangu Stream, an example of where the acidophilc algae Cyanidium caldarium can be found.

Extremophilic organisms have been increasingly researched as an option for a cleaner fuel source. Cyanidium caldarium and galdieria sulphuraria contain long chain hydrocarbons similar to those found in petroleum. They can be found in bogs and moist acidic soil all over the world and grown in open containers as the high salinity required for growth inhibits most other microbes [10].

Extremophilic microbes have also shown great promise in medical applications. Antimicrobial peptides have been found in halophiles belonging to numerous species that reside in soils. Peptides from halophiles are referred to as halocins, which have been shown to be effective at killing archaeal cells [11]. There has also been numerous research done showing the ability of extremophiles to assist canines in recovery from surgery [12]. Diketopiperazines, also found in halophiles, have shown to ability to reduce tumors and reduce blood clotting. An example of this is Naloterrigena hispanica, found in the soils of an extremely salty lake in Fuente de Piedra, Spain.

An extremely intriguing contribution from extremophiles may come from an alternative method for vaccines. Halobacterium, another organism found in extremely salty environments, produce internal gas vesicles and small gas-filled proteinaceous structures [13]. These structures have been engineered to show a recombinant form of an immunodeficiency virus on the external surface of the bacterium. These newly formed vesicles have shown a strong antibody response and long lasting immune memory when administered nasally to mice. The vaccine showed no toxicity in mice and is being further studied [13].

Refrences

[1] Rampelotto P. H. (2013). Extremophiles and extreme environments. Life (Basel, Switzerland), 3(3), 482–485. doi:10.3390/life3030482

[2] Yadav, Ajar Nath. (2017). Beneficial role of extremophilic microbes for plant health and soil fertility. Journal of Agricultural Science and Botany. 1. 1-4.

[3] Kristjánsson, J.K. & Hreggvidsson. (2017). G.O. World Journal of Microbiology & Biotechnology 11: 17. https://doi.org/10.1007/BF00339134

[4 ]Acuña-Rodríguez Ian S., Hansen Hermann, Gallardo-Cerda Jorge, Atala Cristian, Molina-Montenegro Marco A. (2019). Antarctic Extremophiles: Biotechnological Alternative to Crop Productivity in Saline Soils. Frontiers in Bioengineering and Biotechnology. 22.

[5] Khan, A.L., Waqas, M., Khan, A.R. et al. World J Microbiol Biotechnol (2013) 29: 2133. https://doi.org/10.1007/s11274-013-1378-1

[6] Rew, D. A (1 August 2003). "Deinococcus radiodurans". European Journal of Surgical Oncology (EJSO). 29 (6): 557–558. doi:10.1016/S0748-7983(03)00080-5

[7] Mohapatra, S.; Bohidar, S.; Pradhan, N.; Kar, R.N.; Sukla, L.B. (2007). "Microbial extraction of nickel from Sukinda chromite overburden by Acidithiobacillus ferrooxidans and Aspergillus strains".

[8] Rai, Charanjit; Reyniers, Jon P. (1988). "Microbial Desulfurization of Coals by Organisms of the Genus Pseudomonas". Biotechnology Progress. 4 (4): 225–30. doi:10.1002/btpr.5420040406.

[9] Orellana, R., Macaya, C., Bravo, G., Dorochesi, F., Cumsille, A., Valencia, R., … Seeger, M. (2018). Living at the Frontiers of Life: Extremophiles in Chile and Their Potential for Bioremediation. Frontiers in microbiology, 9, 2309. doi:10.3389/fmicb.2018.02309.

[10] Pulz O, Gross W.(2004).Valuable products from biotechnology of microalgae. Applied Microbiol Biotechnology;65(6):635–48. 10.1007/s00253-004-1647-x

[11] DasSarma P, Coker JA, Huse V, et al. : Halophiles, Industrial Applications. In: Encyclopedia of Industrial Biotechnology Hoboken, NJ, USA: John Wiley & Sons, Inc.2009.

[12] Shand RF, Leyva K: Archaeal antimicrobials: an undiscovered country. In: Paul Blum ed. Archaea: new models for prokaryotic biology Norfolk, UK: Caister Academic Press,2008;233–44.

[13] Stuart ES, Morshed F, Sremac M, et al. : Antigen presentation using novel particulate organelles from halophilic archaea. J Biotechnol. 2001;88(2):119–28. 10.1016/S0168-1656(01)00267-X

[14] G. U. Chibuike and S. C. Obiora,2014,“Heavy Metal Polluted Soils: Effect on Plants and Bioremediation Methods,” Applied and Environmental Soil Science, vol.article ID 752708, 12 pages, 2014. https://doi.org/10.1155/2014/752708.

[15] Coker J. A. (2016). Extremophiles and biotechnology: current uses and prospects. F1000Research, 5, F1000 Faculty Rev-396. doi:10.12688/f1000research.7432.1