Extreme makeover: the incredible cell membrane adaptations of extremophiles to harsh environments.

The existence of life beyond Earth has long captivated humanity, and the study of extremophiles-organisms surviving and thriving in extreme environments-provides crucial insights into this possibility. Extremophiles overcome severe challenges such as enzyme inactivity, protein denaturation, and damage of the cell membrane by adopting several strategies. This feature article focuses on the molecular strategies extremophiles use to maintain the cell membrane's structure and fluidity under external stress. Key strategies include homeoviscous adaptation (HVA), involving the regulation of lipid composition, and osmolyte-mediated adaptation (OMA), where small organic molecules protect the lipid membrane under stress. Proteins also have direct and indirect roles in protecting the lipid membrane. Examining the survival strategies of extremophiles provides scientists with crucial insights into how life can adapt and persist in harsh conditions, shedding light on the origins of life. This article examines HVA and OMA and their mechanisms in maintaining membrane stability, emphasizing our contributions to this field. It also provides a brief overview of the roles of proteins and concludes with recommendations for future research directions.

The Undeniable Potential of Thermophiles in Industrial Processes.

Extremophilic microorganisms play a key role in understanding how life on Earth originated and evolved over centuries. Their ability to thrive in harsh environments relies on a plethora of mechanisms developed to survive at extreme temperatures, pressures, salinity, and pH values. From a biotechnological point of view, thermophiles are considered a robust tool for synthetic biology as well as a reliable starting material for the development of sustainable bioprocesses. This review discusses the current progress in the biomanufacturing of high-added bioproducts from thermophilic microorganisms and their industrial applications.

Adaptation at the Extremes of Life: Experimental Evolution with the Extremophile Archaeon Sulfolobus acidocaldarius.

The archaeon Sulfolobus acidocaldarius has emerged as a promising thermophilic model system. Investigating how thermophiles adapt to changing temperatures is a key requirement, not only for understanding fundamental evolutionary processes but also for developing S. acidocaldarius as a chassis for bioengineering. One major obstacle to conducting experimental evolution with thermophiles is the expense of equipment maintenance and energy usage of traditional incubators for high-temperature growth. To address this challenge, a comprehensive experimental protocol for conducting experimental evolution in S. acidocaldarius is presented, utilizing low-cost and energy-efficient bench-top thermomixers. The protocol involves a batch culture technique with relatively small volumes (1.5 mL), enabling tracking of adaptation in multiple independent lineages. This method is easily scalable through the use of additional thermomixers. Such an approach increases the accessibility of S. acidocaldarius as a model system by reducing both initial investment and ongoing costs associated with experimental investigations. Moreover, the technique is transferable to other microbial systems for exploring adaptation to diverse environmental conditions.

Hot, dry, and salty: The present and future of an Extremophile model lizard from Argentina.

Global warming poses a threat to lizard populations by raising ambient temperatures above historical norms and reducing thermoregulation opportunities. Whereas the reptile fauna of desert systems is relatively well studied, the lizard fauna of saline environments has not received much attention and-to our knowledge-thermal ecology and the effects of global warming on lizards from saline environments have not been yet addressed. This pioneer study investigates the thermal ecology, locomotor performance and potential effects of climate warming on Liolaemus ditadai, a lizard endemic to one of the largest salt flats on Earth. We sampled L. ditadai using traps and active searches along its known distribution, as well as in other areas within Salinas Grandes and Salinas de Ambargasta, where the species had not been previously recorded. Using ensemble models (GAM, MARS, RandomForest), we modeled climatically suitable habitats for L. ditadai in the present and under a pessimistic future scenario (SSP585, 2070). L. ditadai emerges as an efficient thermoregulator, tolerating temperatures near its upper thermal limits. Our ecophysiological model suggests that available activity hours predict its distribution, and the projected temperature increase due to global climate change should minimally impact its persistence or may even have a positive effect on suitable thermal habitat. However, this theoretical increase in habitat could be linked to the distribution of halophilous scrub in the future. Our surveys reveal widespread distribution along the borders of Salinas Grandes and Salinas de Ambargasta, suggesting a potential presence along the entire border of both salt plains wherever halophytic vegetation exists. Optimistic model results, extended distribution, and no evidence of flood-related adverse effects offer insights into assessing the conservation status of L. ditadai, making it and the Salinas Grandes system suitable models for studying lizard ecophysiology in largely unknown saline environments.

Nascent transcription reveals regulatory changes in extremophile fishes inhabiting hydrogen sulfide-rich environments.

Regulating transcription allows organisms to respond to their environment, both within a single generation (plasticity) and across generations (adaptation). We examined transcriptional differences in gill tissues of fishes in the Poecilia mexicana species complex (family Poeciliidae), which have colonized toxic springs rich in hydrogen sulfide (H2S) in southern Mexico. There are gene expression differences between sulfidic and non-sulfidic populations, yet regulatory mechanisms mediating this gene expression variation remain poorly studied. We combined capped-small RNA sequencing (csRNA-seq), which captures actively transcribed (i.e. nascent) transcripts, and messenger RNA sequencing (mRNA-seq) to examine how variation in transcription, enhancer activity, and associated transcription factor binding sites may facilitate adaptation to extreme environments. csRNA-seq revealed thousands of differentially initiated transcripts between sulfidic and non-sulfidic populations, many of which are involved in H2S detoxification and response. Analyses of transcription factor binding sites in promoter and putative enhancer csRNA-seq peaks identified a suite of transcription factors likely involved in regulating H2S-specific shifts in gene expression, including several key transcription factors known to respond to hypoxia. Our findings uncover a complex interplay of regulatory processes that reflect the divergence of extremophile populations of P. mexicana from their non-sulfidic ancestors and suggest shared responses among evolutionarily independent lineages.

Taxonomic diversity of extremophilic prokaryotes adapted to special environmental parameters in Hungary: a review.

The taxonomic and metabolic diversity of prokaryotes and their adaptability to extreme environmental parameters have allowed extremophiles to find their optimal living conditions under extreme conditions for one or more environmental parameters. Natural habitats abundant in extremophilic microorganisms are relatively rare in Hungary. Nevertheless, alkaliphiles and halophiles can flourish in shallow alkaline lakes (soda pans) and saline (solonetz) soils, where extreme weather conditions favor the development of unique bacterial communities. In addition, the hot springs and thermal wells that supply spas and thermal baths and provide water for energy use are suitable colonization sites for thermophiles and hyperthermophiles. Polyextremophiles, adapted to multiple extreme circumstances, can be found in the aphotic, nutrient-poor and radioactive hypogenic caves of the Buda Thermal Karst, among others. The present article reviews the organization, taxonomic composition, and potential role of different extremophilic bacterial communities in local biogeochemical cycles, based on the most recent studies on extremophiles in Hungary.

Susceptibility of extremophiles to far-UVC light for bioburden reduction in spacecraft assembly facilities.

The prevention and reduction of microbial species entering and leaving Earth's biosphere is a critical aspect of planetary protection research. While various decontamination methods exist and are currently utilized for planetary protection purposes, the use of far-UVC light (200-230 nm) as a means for microbial reduction remains underexplored. Unlike conventional germicidal ultraviolet at 254 nm, which can pose a health risk to humans even with small exposure doses, far-UVC light poses minimal health hazard making it a suitable candidate for implementation in occupied areas of spacecraft assembly facilities. This study investigates the efficacy of far-UVC 222-nm light to inactivate bacteria using microbial species which are relevant to planetary protection either in vegetative cell or spore form. All the tested vegetative cells demonstrated susceptibility to 222-nm exposure, although susceptibility varied among the tested species. Notably, Deinococcus radiodurans, a species highly tolerant to extreme environmental conditions, exhibited the most resistance to far-UVC exposure with a dose of 112 mJ/cm2 required for a 1-log reduction in survival. While spore susceptibility was similar across the species tested, Bacillus pumilus spores were the most resistant of the tested spores when analyzed with a bi-exponential cell killing model (D90 of 6.8 mJ/cm2). Overall, these results demonstrate the efficacy of far-UVC light for reducing microbial bioburden to help ensure the success and safety of future space exploration missions.

Extremophiles in a changing world.

Extremophiles and their products have been a major focus of research interest for over 40 years. Through this period, studies of these organisms have contributed hugely to many aspects of the fundamental and applied sciences, and to wider and more philosophical issues such as the origins of life and astrobiology. Our understanding of the cellular adaptations to extreme conditions (such as acid, temperature, pressure and more), of the mechanisms underpinning the stability of macromolecules, and of the subtleties, complexities and limits of fundamental biochemical processes has been informed by research on extremophiles. Extremophiles have also contributed numerous products and processes to the many fields of biotechnology, from diagnostics to bioremediation. Yet, after 40 years of dedicated research, there remains much to be discovered in this field. Fortunately, extremophiles remain an active and vibrant area of research. In the third decade of the twenty-first century, with decreasing global resources and a steadily increasing human population, the world's attention has turned with increasing urgency to issues of sustainability. These global concerns were encapsulated and formalized by the United Nations with the adoption of the 2030 Agenda for Sustainable Development and the presentation of the seventeen Sustainable Development Goals (SDGs) in 2015. In the run-up to 2030, we consider the contributions that extremophiles have made, and will in the future make, to the SDGs.

Tokorhabditis n. gen. (Rhabditida, Rhabditidae), a comparative nematode model for extremophilic living.

Life in extreme environments is typically studied as a physiological problem, although the existence of extremophilic animals suggests that developmental and behavioral traits might also be adaptive in such environments. Here, we describe a new species of nematode, Tokorhabditis tufae, n. gen., n. sp., which was discovered from the alkaline, hypersaline, and arsenic-rich locale of Mono Lake, California. The new species, which offers a tractable model for studying animal-specific adaptations to extremophilic life, shows a combination of unusual reproductive and developmental traits. Like the recently described sister group Auanema, the species has a trioecious mating system comprising males, females, and self-fertilizing hermaphrodites. Our description of the new genus thus reveals that the origin of this uncommon reproductive mode is even more ancient than previously assumed, and it presents a new comparator for the study of mating-system transitions. However, unlike Auanema and almost all other known rhabditid nematodes, the new species is obligately live-bearing, with embryos that grow in utero, suggesting maternal provisioning during development. Finally, our isolation of two additional, molecularly distinct strains of the new genus-specifically from non-extreme locales-establishes a comparative system for the study of extremophilic traits in this model.

Psychrophiles: A journey of hope.

Psychrophiles are organisms living in extremely cold conditions within the temperature range of -20°C to +10°C. These organisms survive in harsh environment by modulating their genetic make-up to thrive in extremely cold conditions. These cold-adaptations are closely associated with changes in the life forms, gene expression, and proteins, enzymes, lipids, etc. This review gives a brief description of the life and genetic adaptations of psychrophiles for their survival in extreme conditions as well as the bioactive compounds that are potential antimicrobials.

Experimental evolution of extremophile resistance to ionizing radiation.

A growing number of known species possess a remarkable characteristic - extreme resistance to the effects of ionizing radiation (IR). This review examines our current understanding of how organisms can adapt to and survive exposure to IR, one of the most toxic stressors known. The study of natural extremophiles such as Deinococcus radiodurans has revealed much. However, the evolution of Deinococcus was not driven by IR. Another approach, pioneered by Evelyn Witkin in 1946, is to utilize experimental evolution. Contributions to the IR-resistance phenotype affect multiple aspects of cell physiology, including DNA repair, removal of reactive oxygen species, the structure and packaging of DNA and the cell itself, and repair of iron-sulfur centers. Based on progress to date, we overview the diversity of mechanisms that can contribute to biological IR resistance arising as a result of either natural or experimental evolution.

Characterisation of a synthetic Archeal membrane reveals a possible new adaptation route to extreme conditions.

It has been proposed that adaptation to high temperature involved the synthesis of monolayer-forming ether phospholipids. Recently, a novel membrane architecture was proposed to explain the membrane stability in polyextremophiles unable to synthesize such lipids, in which apolar polyisoprenoids populate the bilayer midplane and modify its physico-chemistry, extending its stability domain. Here, we have studied the effect of the apolar polyisoprenoid squalane on a model membrane analogue using neutron diffraction, SAXS and fluorescence spectroscopy. We show that squalane resides inside the bilayer midplane, extends its stability domain, reduces its permeability to protons but increases that of water, and induces a negative curvature in the membrane, allowing the transition to novel non-lamellar phases. This membrane architecture can be transposed to early membranes and could help explain their emergence and temperature tolerance if life originated near hydrothermal vents. Transposed to the archaeal bilayer, this membrane architecture could explain the tolerance to high temperature in hyperthermophiles which grow at temperatures over 100 °C while having a membrane bilayer. The induction of a negative curvature to the membrane could also facilitate crucial cell functions that require high bending membranes.

Liquid-liquid phase separation promotes animal desiccation tolerance.

Proteinaceous liquid-liquid phase separation (LLPS) occurs when a polypeptide coalesces into a dense phase to form a liquid droplet (i.e., condensate) in aqueous solution. In vivo, functional protein-based condensates are often referred to as membraneless organelles (MLOs), which have roles in cellular processes ranging from stress responses to regulation of gene expression. Late embryogenesis abundant (LEA) proteins containing seed maturation protein domains (SMP; PF04927) have been linked to storage tolerance of orthodox seeds. The mechanism by which anhydrobiotic longevity is improved is unknown. Interestingly, the brine shrimp Artemia franciscana is the only animal known to express such a protein (AfrLEA6) in its anhydrobiotic embryos. Ectopic expression of AfrLEA6 (AWM11684) in insect cells improves their desiccation tolerance and a fraction of the protein is sequestered into MLOs, while aqueous AfrLEA6 raises the viscosity of the cytoplasm. LLPS of AfrLEA6 is driven by the SMP domain, while the size of formed MLOs is regulated by a domain predicted to engage in protein binding. AfrLEA6 condensates formed in vitro selectively incorporate target proteins based on their surface charge, while cytoplasmic MLOs formed in AfrLEA6-transfected insect cells behave like stress granules. We suggest that AfrLEA6 promotes desiccation tolerance by engaging in two distinct molecular mechanisms: by raising cytoplasmic viscosity at even modest levels of water loss to promote cell integrity during drying and by forming condensates that may act as protective compartments for desiccation-sensitive proteins. Identifying and understanding the molecular mechanisms that govern anhydrobiosis will lead to significant advancements in preserving biological samples.

MALDI-TOF analysis of a novel extremophile peptide purified from Halarchaeum acidiphilum ASDL78 with antiarchaeal and antibacterial activities.

In hypersaline environments, halophilic archaea synthesize antimicrobial substances called halocins. There is a promise to make new drugs for antibiotic-resistant strains. Here, we report the antibacterial activity of a new haloarchaea selected from Lut Desert, Iran. A total of 38 isolated halophilic bacteria and archaea were screened for the antagonistic activity test of each strain against other bacterial and archaeal strains. Finally, a strain, recognized as Halarchaeum acidiphilum, with a fast grown strain and high antagonistic potential against different strains was identified by morphological, physiological, and molecular characteristics. The halocin was produced in a semisolid submerge medium and partially purified by heat treatments and molecular weight ultrafiltration cutoff (3, 50, and 10 kDa). It was a cell-free, heat-resistant (85°C for 2 h) protein with a molecular mass near to 20 kDa produced at the endpoint of logarithmic growth. The molecular weight of halocin was 17 kDa, and indicated no apparent homology with known halocins, suggesting that this might be a new halocin. Therefore, a new strain belonging to Halarchaeum genus was isolated and characterized here that produced an antimicrobial and anti-haloarchaea halocin.

Haloarchaea swim slowly for optimal chemotactic efficiency in low nutrient environments.

Archaea have evolved to survive in some of the most extreme environments on earth. Life in extreme, nutrient-poor conditions gives the opportunity to probe fundamental energy limitations on movement and response to stimuli, two essential markers of living systems. Here we use three-dimensional holographic microscopy and computer simulations to reveal that halophilic archaea achieve chemotaxis with power requirements one hundred-fold lower than common eubacterial model systems. Their swimming direction is stabilised by their flagella (archaella), enhancing directional persistence in a manner similar to that displayed by eubacteria, albeit with a different motility apparatus. Our experiments and simulations reveal that the cells are capable of slow but deterministic chemotaxis up a chemical gradient, in a biased random walk at the thermodynamic limit.

Biotransformation of cladribine by a nanostabilized extremophilic biocatalyst.

Cladribine (2-chloro-2'-deoxy-ß-d-adenosine) is a 2'-deoxyadenosine analogue, approved by the FDA for the treatment of hairy cell leukemia and more recently has been proved for therapeutic against many autoimmune diseases as multiple sclerosis. The biosynthesis of this compound using Thermomonospora alba CECT 3324 as biocatalyst is herein reported. This thermophilic microorganism was successfully entrapped in polyacrylamide gel supplemented with nanoclays such as bentonite. The immobilized biocatalyst (T. alba-Ac-Bent 1.00 %), was able to biosynthesize cladribine with a conversion of 89 % in 1 h of reaction and retains its activity for more than 270 reuses without significantly activity loss, showing better operational stability and mechanical properties than the natural matrix. A microscale assay using the developed system, could allow the production of at least 181 mg of cladribine in successive bioprocesses.

Shared up-regulation and contrasting down-regulation of gene expression distinguish desiccation-tolerant from intolerant green algae.

Among green plants, desiccation tolerance is common in seeds and spores but rare in leaves and other vegetative green tissues. Over the last two decades, genes have been identified whose expression is induced by desiccation in diverse, desiccation-tolerant (DT) taxa, including, e.g., late embryogenesis abundant proteins (LEA) and reactive oxygen species scavengers. This up-regulation is observed in DT resurrection plants, mosses, and green algae most closely related to these Embryophytes. Here we test whether this same suite of protective genes is up-regulated during desiccation in even more distantly related DT green algae, and, importantly, whether that up-regulation is unique to DT algae or also occurs in a desiccation-intolerant relative. We used three closely related aquatic and desert-derived green microalgae in the family Scenedesmaceae and capitalized on extraordinary desiccation tolerance in two of the species, contrasting with desiccation intolerance in the third. We found that during desiccation, all three species increased expression of common protective genes. The feature distinguishing gene expression in DT algae, however, was extensive down-regulation of gene expression associated with diverse metabolic processes during the desiccation time course, suggesting a switch from active growth to energy-saving metabolism. This widespread downshift did not occur in the desiccation-intolerant taxon. These results show that desiccation-induced up-regulation of expression of protective genes may be necessary but is not sufficient to confer desiccation tolerance. The data also suggest that desiccation tolerance may require induced protective mechanisms operating in concert with massive down-regulation of gene expression controlling numerous other aspects of metabolism.

The extremophile Anoxybacillus sp. PC2 isolated from Brazilian semiarid region (Caatinga) produces a thermostable keratinase.

The aim of this study was to select and identify thermophilic bacteria from Caatinga biome (Brazil) able to produce thermoactive keratinases and characterize the keratinase produced by the selected isolate. After enrichment in keratin culture media, an Anoxybacillus caldiproteolyticus PC2 was isolated. This thermotolerant isolate presents a remarkable feature producing a thermostable keratinase at 60°C. The partially purified keratinase, identified as a thermolysin-like peptidase, was active at a pH range of 5.0-10.0 with maximal activity at a temperature range of 50-80°C. The optimal activity was observed at pH 7.0 and 50-60°C. These characteristics are potentially useful for biotechnological purposes such as processing and bioconversion of keratin.

Late embryogenesis abundant group3 protein (DrLEA3) is involved in antioxidation in the extremophilic bacterium Deinococcus radiodurans.

Deinococcus radiodurans is able to survive under extreme conditions, including high doses of ionizing radiation, desiccation and oxidative stress. In addition to enhanced DNA repair capabilities, an effective antioxidation system plays an important role in its robustness. Previous studies have linked the radiation resistance of D. radiodurans to its prolonged desiccation tolerance phenotype, which both cause DNA damage. In the current study, we investigated the roles of dr_1172 in D. radiodurans, the gene encoding a typical group 3 LEA protein (DrLEA3) conserved within Deinococcus species. In addition to the increased transcriptional level under oxidative stress, the inactivation of dr_1172-sensitized cells to H2O2 treatments and the reduced cellular antioxidation activities suggested that dr_1172 is involved in the cellular defense against oxidative stress. Moreover, DrLEA3 was enriched at the cell membrane and bound to various types of metal ions. Cells devoid of DrLEA3 showed a decreased intracellular Mn/Fe concentration ratio, indicating that DrLEA3 also plays a role in maintaining metal ion homeostasis in vivo.