1 Microbial Life in Extreme Environments: Atacama Desert 2 Abstract The peculiarity of human beings has led them to discover many things. Things that they are attempting to make sense about since their discoveries. About the Atacama Desert, understanding the poly-extreme environment and the ecology behavior and reaction of the endolithic microbial communities is a motivation to conduct extensive studies to conceptualize perspective on environmental selection. These extreme habitats encompass physical extremes such as pressure, radiation, temperature, and geochemical height. For example, absolute redox potential or depletion of oxygen, pH, salinity, or extreme desiccation. It is vital to investigate such conditions or environments because the investigation of such habitats helps study the evolution associations, the surfacing of new organic species, and numerous relations of ecology among organisms that are essential in compensating various environmental externalities. The scope of the paper focuses on exploring the endolithic life, in particular, the phototrophic fraction, which supports the microbial habitats and the behavior to adapting and acclimatizing to the immediate environment. Introduction To affirm the recovery of microorganisms living in extremely arid environments or to answer their current existence and zeal to live is still a considerable debate, and it remains a mystery yet to be decrypted. Thriving in such extreme conditions requires microorganisms to have a high affinity to survival potential on the assessment of the atmospheric processes deposited on the environment. The provision of evidence to show a correlation of the indigenous microbial population presenting the temporal activeness in some environments such as hyperarid soils concerning the Atacama Desert. The region is dominated by high temperatures and low humidity and characterized by rare precipitation occurrences in areas receiving the most extreme aridity. The Atacama Desert found in Northern Chile is one of the identified deserts deemed to be the oldest in the history of extreme arid environments. With its extreme environmental responses and behavior, Atacama Desert has qualified as the hostile desert ever to exist. Water is limited in desert surroundings, but for the case of Atacama Desert, the situation is further threatened by the availability of liquid water, which results in significant inhibition of life to the extent of once referred to as an uninhabitable territory. However, through comprehensive studies, it is now possible to discuss various documentations offering insights on the soils, sediments, rock formation, and life holistically as it exists in the poly-extreme environment harbored at Atacama Deserts. It functions as a habitat for various microorganisms that depend on the pre-existing conditions to progress with microbial biological activities, including bacteria, protozoa, algae, protozoa, and viruses as well (Bull et al., 2018; Wierzchos, Casero, Artieda, & Ascaso, 2018). Endolithic microbial activities are a significant function in the life of microbial organisms concerning their community structure to adapt to extreme environments (Robinson et al., 2015). For an environment to be defined as a desert, there are particular indicative features to look to determine its aridity index. Aridity index (AI) refers to the ratio between the average annual rainfall amount and average annual evapotranspiration. With the subject environment being Atacama Desert in northern Chile, the mean annual temperature ranges at >18 °C as it 3 qualifies as the hottest desert on earth. Atacama Desert is an excellent example of hyper-arid deserts. According to Azua-Bustos, Urrejola & Vicuña (2012), “during a four-year period, the average air temperature had been 16.5 °C, with recorded extremes of −6 °C and 38 °C. Annual average sunlight was about 336 Wm−2 and winds averaged a few meters per second.” The structure of the rocks a preferential element for microbial organisms’ habitat, optimally the predominating habitat found in deserts. Rocks play an integral role in deserts to sustain life. Due to its intrinsic value and formation, the rocks act as a water reservoir drawn from the condensation of dew. Additionally, rocks can naturally prompt thermoregulation to caution the water from severe temperature regulations. Lithobionts are dominantly known to habitat within the rocks. At the same time, endolithic organisms live in the rocks are shielded from extreme solar radiation due to the volatility of the high ultra-violet (UV) radiation, which characterizes the desert environment (Wierzchos, Casero, Artieda, & Ascaso, 2018). Discussion of Evidence Types of Microbes and how they adapt to the Desert Environment For years, researchers have gained interest in exploring the extreme desert environments, therefore, they did diverse studies to demonstrate the existence of the conditions that offer habitat for different forms of life. The subject matter of the paper is founded on the case of Atacama Desert in the attempt to discuss the microbial life as it exists in the desert environment. There are a variety of microbial organisms found in the desert including bacteria, archaea, chlorophytes, cyanobacteria, and diatoms living at the edge of limited biological and extreme terrestrial conditions. However, the microorganisms have developed adaptation mechanisms to cope up with the harsh conditions for the purpose of survival. Noting the characterization of endolithic microbial population, numerous reports have documented the existence of Cyanobacteria, Proteobacteria, and Actinobacteria as the representatives. Another instrumental microbe in the discussion is the microalgae that displays higher level of tolerance to extreme conditions often referred to as Chlorella sorokiniana halite environments of the Atacama Desert. The microalgae display biochemical components attributed to its high tolerance level (Bull et al., 2018). Although the description of deserts is often perceived with low biological diversity, numerous studies show extensive microbial life with the environment functioning as a habitat and lodge for the microbe in the Atacama Desert. In particular, the Atacama Desert is a heterogeneous ecosystem surrounded by fragility since a notable change in environmental conditions could significantly alter the capacity to balance the microbial population which could affect the trophic levels. 4 Source: Astrobiology Web Atacama Desert rocks are renowned habitats for the fungal population that espouses a consolidated diverse lifestyle. The organisms comprised in this group include the saprobes, symbionts, man and crop pathogens, endophytes, and species producing a mycotoxin (GomezSilva, 2018; Schulze-Makuch et al., 2018). Clearly, the included samples for this supposition explains the natural features of the endolithic organisms represented by halite fungi, elucidated in the ecological niches of the rock environment through bioactive enzymatic compounds. The rare existence of the cultivable fungal population documented in the Atacama Desert reports on the limited conceptualization of the environment in the pretext of the environment shown through the description of the protozoa and fungi biodiversity. It places the vitality of the contributing knowledge and utilizing the available literature exploring the poly-extreme ecosystems, although not fully exhausted. 5 There are extensive studies providing information to contribute to the increasing knowledge and understanding of the endolithic microbiology activities at the Atacama Desert. The point of focus is mainly on the structure of the halites community, although further research is still encouraged. The lack of extensive research on the proliferation of the eukaryotic microbes is a vital element in the exploitation of the biotechnological potential which is underexplored. Additionally, the diversity of microbiology life documented in the Atacama Desert leads to the description of the consolidated biodiversity and fungi ecology in halites classification. The halite endolithobiont population is revered as a representation of unique systemic models that assist in the comprehension of the ecology. At the same time, other research sources point on the need to explore comprehensively the diversity, ecological functions, and the potential to facilitate the exploitation of biotechnology in the manifestation of the microbial activities living in the rock habitats. 6 Source Wierzchos, Casero, Artieda, & Ascaso (2018): The diagram indicates the possible lithobiontic habitats of microorganisms. epilithic (rock surface); hypolithic (rock underside in contact with the soil); endolithic (the main habitats of hyper-arid deserts, and further divided into cryptoendolithic, chasmoendolithic and hypoendolithic The literature offers a claim of extremophile and the temperature is the variable factor often used as a parameter to determine the status of the environment by using the case for the Atacama Desert. Temperature as a critical element is claimed to affect the enzymatic activities in organisms. To support scientific claims, an experiment is set out at the top of cold mountains 7 where temperatures are shallow (Gomez-Silva, 2018). The analysis reveals that, indeed, low temperatures lower the enzymatic activities and also influence the membrane activity. In regards to high temperatures, the structure of biomolecules is altered irreversibly and also increases the enzyme activity. Using sugar in the experiment and the appearance of bubbles is sufficient evidence that life can exist in extreme environments. The Atacama Desert is an excellent example showing the wonder of nature and fascination in the vast array of life forms. The study and exploration conducted to understand the extremophiles shows there is a higher possibility of finding other planets where life can exist. Extremophiles are a genuine fascination providing positivity in further exploration of the future. The discovery of bizarre organisms is a central pointer confirming the quest to understand where life can be supported and even find a new home for humanity. One also wonders how the Earth came to be and question if it could have originated from a hydrothermal vent. The extremophile offers an opportunity to determine the possibility of Mars being habitable to support other life forms. This is supported by the diversity of life regarding microorganisms found in the extreme depths of oceans. To contextualize the extremity of Atacama Deserts and the response of the endolithic micro-organisms, research has followed a proposal to explore claims of Mars harboring subsurface according to research exploration activities which is likened to natural hydrothermal communities that exist on planet Earth. The broad composition of Mars is carbon dioxide which is the primary raw material that supports photosynthesis in plants. However, oxygen is unavailable. On the other hand, life exists which even extends to the surface of the rock structures in the deepest regions of the Earth in deep oceans. Life exists in extreme environments on Earth and a wide range of temperature, pressure, acidity, and salinity. Simplest organisms (prokaryotes) occupy the extremes environments. However, others have a complicated life (eukaryotes) that are diverse. The Discovery of life in extreme environments on Earth provides insight on possible niches for growth in other planets. Following the suppositions put forward by scholars Wierzchos, Casero, Artieda, & Ascaso, (2018), halites often regarded as salt rocks comprise of evaporitic stones made up of 95% Sodium Chloride. The rock habitats are described as poly-extreme environments due to the prevalence of exposure to extremely high temperatures and radiation which leading to increased affinity to salinity. The features of halites are caused by a continuous photosynthetic result of this photosynthetic activity. A carbohydrate-based productive nutrient environment exists with these rocks which is capable of sustaining microbial life (Schulze-Makuch et al., 2018). Drawing from research sources, halites can be termed as micro-scaled salterns developed through colonization caused by poly-extremophiles microbial activities (Bull et al., 2015). Special attention is granted to lithic habitats through the observation of the shelters that support life forms that function as a protection element in the environments that are exposed to extreme environments that cause the process of desiccation and high levels of UV and solar 8 irradiation on earth and other planets such as Mars. Objectively, an analysis of scientific information regarding the lithobionts in the Atacama Desert, the substrate structure, and the adaptive features to survive through the extreme conditions resulting in desiccation, influenced by intense photosynthetic active radiation and UV radiations. The examination of the Chroococcidiopsis-like cells representing the microbial organisms displays the bacterial components taken from rock samples, and phylogenic research reveals their susceptibility and that of close genetic population affinity to Halothece genera (Schulze-Makuch et al., 2018). The structure of the gene sequence in regards to heterotrophic bacteria and archaea is indicative of its similarity to the hypersaline environments. The colonization forged by halites and formation of microbial activities through the interaction of the microbial aggregates. Following an exceptional of the features of porous halite rock structure with the environmental conditions that are specialized in promoting the rate of survival. Implications for life on Mars using Microbial Life in Atacama Desert Comparing Mars to Atacama Desert, the latter is a paradise as it has experienced minimal rainfall. However, for Mars, the planet has not received any drop of rainfall for millions of years. On the other hand, Atacama is a hellish environment in comparison to Earth standards. The prevalent dryness and considering salts have found their way to the environment, the accumulation has continued for century due to lack of sufficient water to wash them away. For that reason, the microbial life has developed adaptations to withstand the extreme saline conditions by dehydrating themselves and becoming inactive. The inactivity of the microorganisms renders them protection for deplorable damage although the natural repair mechanism does not work therefore risking their survival. Life forms develop adaptive mechanism to survive in hostile environments both physically and biochemically. For extreme dry deserts such as the Atacama, it offers researchers an excellent ground to explore the limits of life and understand the mechanisms used by microbe organisms to survive in such extreme environments. The studies accorded to examine the extreme microbial ecosystems have been cited to offer crucial clues of life in other planets. So, Atacama Desert has been described as a reservoirs of diversity. Scientists have pursued to find habitable planets in the last years and Mars has been earmarked with potent to support diverse life forms so far. Similar habitats found in the Atacama Deserts, such as the rock ecosystem which dominates as the habitat for microbe organism are found to be on Mars giving hope to the long scientific search. As microbial life conquers the habitat dominated by rock structure composed of chloride- and sulfate deposits, similar discoveries in Mars is sufficient evidence to suggest the capacity to support microbial life forms. Conclusion The extensive studies used for the discussion offer insights on the microbial life as it occurs in extreme environments, and the behavioral responses to the rock environment are functioning the ideal habitat for microbes. With a focus on the halite nodules in the Atacama Desert, the research presents the role of extreme environment towards the motivation to understand the proliferation of adaptation of the microbial population to the poly-extreme environment and the preexisting conditions. Forging a structural analysis of the microbes’ 9 population is indicative of the appearance and conduct of the halites to explore the biodiversity of micro-organisms in the Atacama Desert, although limited to some extent. The consideration of biogeochemical structures of the endolithobionts courses the continuous of the elemental cycles. Harsh conditions presented in the Atacama Desert case study characterized by drought, salinity, exploitation of the existing resources that are predominantly scarce like water and soils depicts the potential of the regions to support life for resilient organisms and microorganisms. However, it is evident that such environments offer limited opportunities to life and poses a threat to terrestrial life, such as animals and plants, which can also lead to migration and development of adaptive features. The progression of life is guided by the capacity of an environment to support life in correlation to adaptive behaviors espoused by the endolithic microbial organism documented in the Atacama Desert in pursuit of survival. References Azua-Bustos, A., Urrejola, C., & Vicuña, R. (2012). Life at the dry edge: microorganisms of the Atacama Desert. FEBS letters, 586(18), 2939-2945. Bull, A. T., Asenjo, J. A., Goodfellow, M., & Gomez-Silva, B. (2016). The Atacama Desert: technical resources and the growing importance of novel microbial diversity. Annual review of microbiology, 70, 215-234. Gómez-Silva, B. (2018). Lithobiontic life:“Atacama rocks are well and alive”. Antonie Van Leeuwenhoek, 111(8), 1333-1343. Schulze-Makuch, D., Wagner, D., Kounaves, S. P., Mangelsdorf, K., Devine, K. G., de Vera, J. P., ... & Galy, A. (2018). Transitory microbial habitat in the hyperarid Atacama Desert. Proceedings of the National Academy of Sciences, 115(11), 2670-2675. Robinson, C. K., Wierzchos, J., Black, C., Crits‐Christoph, A., Ma, B., Ravel, J., ... & Gómez Silva, B. (2015). Microbial diversity and the presence of algae in halite endolithic communities are correlated to atmospheric moisture in the hyper‐arid zone of the Atacama Desert. Environmental] microbiology, 17(2), 299-315. Wierzchos, J., Casero, M. C., Artieda, O., & Ascaso, C. (2018). Endolithic microbial habitats as refuges for life in poly-extreme environment of the Atacama Desert. Current opinion in microbiology, 43, 124-131. You have many undefined terms like Geochemical height. What does it mean? Also why do you think absolute reduction and lack of oxygen are limiting conditions in desert. I can not edit your paper word by word. I only pointed out a few examples in my last email. You have many more. You need to follow the directions in the guidelines which I attach here again. For example, you don't have any figure captions and don't label figure numbers (Fig. 1, 2, & 3). Why are you citing these figures and how do they support your argument??