Resurrecting Van Leeuwenhoek's rotifers: a reappraisal of the role of disaccharides in anhydrobiosis

Effect of polystyrene nanoplastics on its toxicity and reproduction in Philodina roseola

Micro-nano plastics have emerged as a major ecological concern. The nanoplastics (NPs) pose a huge threat to microscopic animals. Our study aims to decipher the effect of polystyrene nanoplastics (PSNPs) of 50 and 100 nm sizes on a bdelloid rotifer (Philodina roseola). Both sizes of PSNPs were analyzed using field emission Scanning electron microscopy, Fourier transform Infrared spectroscopy, and Dynamic light scattering analyses. The LC50 values for 50 and 100 nm PSNPs at 48 h upon interaction with the rotifers were 16.36 and 22.94 mg/L respectively. The total protein and superoxide dismutase levels decreased with an increase in concentration in both PSNPs upon interaction at various concentrations (4, 8, 12, and 16 mg/L). Whereas the lipid peroxidase and reactive oxygen species levels increased with an increase in concentration for both PSNPs at similar concentrations. Further, both PSNPs were found to cause internal organ damage in rotifers. A delay in the hatching rate was observed when the rotifers interacted with both PSNPs in addition to the decrease in the hatching rate of F1 generation. Therefore, PSNPs pose a threat to the natural life cycle in the rotifers.

Disordered proteins interact with the chemical environment to tune their protective function during drying

The conformational ensemble and function of intrinsically disordered proteins (IDPs) are sensitive to their solution environment. The inherent malleability of disordered proteins, combined with the exposure of their residues, accounts for this sensitivity. One context in which IDPs play important roles that are concomitant with massive changes to the intracellular environment is during desiccation (extreme drying). The ability of organisms to survive desiccation has long been linked to the accumulation of high levels of cosolutes such as trehalose or sucrose as well as the enrichment of IDPs, such as late embryogenesis abundant (LEA) proteins or cytoplasmic abundant heat-soluble (CAHS) proteins. Despite knowing that IDPs play important roles and are co-enriched alongside endogenous, species-specific cosolutes during desiccation, little is known mechanistically about how IDP-cosolute interactions influence desiccation tolerance. Here, we test the notion that the protective function of desiccation-related IDPs is enhanced through conformational changes induced by endogenous cosolutes. We find that desiccation-related IDPs derived from four different organisms spanning two LEA protein families and the CAHS protein family synergize best with endogenous cosolutes during drying to promote desiccation protection. Yet the structural parameters of protective IDPs do not correlate with synergy for either CAHS or LEA proteins. We further demonstrate that for CAHS, but not LEA proteins, synergy is related to self-assembly and the formation of a gel. Our results suggest that functional synergy between IDPs and endogenous cosolutes is a convergent desiccation protection strategy seen among different IDP families and organisms, yet the mechanisms underlying this synergy differ between IDP families.

Disordered proteins interact with the chemical environment to tune their protective function during drying

The conformational ensemble and function of intrinsically disordered proteins (IDPs) are sensitive to their solution environment. The inherent malleability of disordered proteins combined with the exposure of their residues accounts for this sensitivity. One context in which IDPs play important roles that is concomitant with massive changes to the intracellular environment is during desiccation (extreme drying). The ability of organisms to survive desiccation has long been linked to the accumulation of high levels of cosolutes such as trehalose or sucrose as well as the enrichment of IDPs, such as late embryogenesis abundant (LEA) proteins or cytoplasmic abundant heat soluble (CAHS) proteins. Despite knowing that IDPs play important roles and are co-enriched alongside endogenous, species-specific cosolutes during desiccation, little is known mechanistically about how IDP-cosolute interactions influence desiccation tolerance. Here, we test the notion that the protective function of desiccation-related IDPs is enhanced through conformational changes induced by endogenous cosolutes. We find that desiccation-related IDPs derived from four different organisms spanning two LEA protein families and the CAHS protein family, synergize best with endogenous cosolutes during drying to promote desiccation protection. Yet the structural parameters of protective IDPs do not correlate with synergy for either CAHS or LEA proteins. We further demonstrate that for CAHS, but not LEA proteins, synergy is related to self-assembly and the formation of a gel. Our results suggest that functional synergy between IDPs and endogenous cosolutes is a convergent desiccation protection strategy seen among different IDP families and organisms, yet, the mechanisms underlying this synergy differ between IDP families.

Recombination in bdelloid rotifer genomes: asexuality, transfer and stress

Bdelloid rotifers constitute a class of microscopic animals living in freshwater habitats worldwide. Several strange features of bdelloids have drawn attention: their ability to tolerate desiccation and other stresses, a lack of reported males across the clade despite centuries of study, and unusually high numbers of horizontally acquired, non-metazoan genes. Genome sequencing is transforming our understanding of their lifestyle and its consequences, while in turn providing wider insights about recombination and genome organisation in animals. Many questions remain, not least how to reconcile apparent genomic signatures of sex with the continued absence of reported males, why bdelloids have so many horizontally acquired genes, and how their remarkable ability to survive stress interacts with recombination and other genomic processes.

Helicity of a tardigrade disordered protein contributes to its protective function during desiccation

To survive extreme drying (anhydrobiosis), many organisms, spanning every kingdom of life, accumulate intrinsically disordered proteins (IDPs). For decades, the ability of anhydrobiosis-related IDPs to form transient amphipathic helices has been suggested to be important for promoting desiccation tolerance. However, evidence empirically supporting the necessity and/or sufficiency of helicity in mediating anhydrobiosis is lacking. Here, we demonstrate that the linker region of CAHS D, a desiccation-related IDP from the tardigrade Hypsibius exemplaris, that contains significant helical structure, is the protective portion of this protein. Perturbing the sequence composition and grammar of the linker region of CAHS D, through the insertion of helix-breaking prolines, modulating the identity of charged residues, or replacement of hydrophobic amino acids with serine or glycine residues results in variants with different degrees of helical structure. Importantly, correlation of protective capacity and helical content in variants generated through different helix perturbing modalities does not show as strong a trend, suggesting that while helicity is important, it is not the only property that makes a protein protective during desiccation. These results provide direct evidence for the decades-old theory that helicity of desiccation-related IDPs is linked to their anhydrobiotic capacity.

Oxidative stress is an essential factor for the induction of anhydrobiosis in the desiccation-tolerant midge, Polypedilum vanderplanki (Diptera, Chironomidae)

The sleeping chironomid (Polypedilum vanderplanki) is the only insect capable of surviving complete desiccation in an ametabolic state called anhydrobiosis. Here, we focused on the role of oxidative stress and we observed the production of reactive oxygen species (ROS) in desiccating larvae and in those exposed to salinity stress. Oxidative stress occurs to some extent in desiccating larvae, inducing carbonylation of proteins. Oxidative stress overcomes the antioxidant defenses of the larvae during the first hour following rehydration of anhydrobiotic larvae. It facilitates the oxidation of DNA and cell membrane lipids; however, these damages are quickly repaired after a few hours. In addition to its deleterious effects, we demonstrated that artificial exposure to oxidative stress could induce a response similar to desiccation stress, at the transcriptome and protein levels. Furthermore, the response of anhydrobiosis-related genes to desiccation and salinity stress was inhibited by antioxidant treatment. Thus, we conclude that oxidative stress is an essential trigger for inducing the expression of protective genes during the onset of anhydrobiosis in desiccating of P. vanderplanki larvae.

Antioxidant Response during the Kinetics of Anhydrobiosis in Two Eutardigrade Species

Anhydrobiosis, a peculiar adaptive strategy existing in nature, is a reversible capability of organisms to tolerate a severe loss of their body water when their surrounding habitat is drying out. In the anhydrobiotic state, an organism lacks all dynamic features of living beings since an ongoing metabolism is absent. The depletion of water in the anhydrobiotic state increases the ionic concentration and the production of reactive oxygen species (ROS). An imbalance between the increased production of ROS and the limited action of antioxidant defences is a source of biomolecular damage and can lead to oxidative stress. The deleterious effects of oxidative stress were demonstrated in anhydrobiotic unicellular and multicellular organisms, which counteract the effects using efficient antioxidant machinery, mainly represented by ROS scavenger enzymes. To gain insights into the dynamics of antioxidant patterns during the kinetics of the anhydrobiosis of two tardigrade species, Paramacrobiotus spatialis and Acutuncus antarcticus, we investigated the activity of enzymatic antioxidants (catalase, superoxide dismutase, glutathione peroxidase, and glutathione reductase) and the amount of non-enzymatic antioxidants (glutathione) in the course of rehydration. In P. spatialis, the activity of catalase increases during dehydration and decreases during rehydration, whereas in A. antarcticus, the activity of superoxide dismutase decreases during desiccation and increases during rehydration. Genomic varieties, different habitats and geographical regions, different diets, and diverse evolutionary lineages may have led to the specialization of antioxidant strategies in the two species.

Examples of Extreme Survival: Tardigrade Genomics and Molecular Anhydrobiology

Tardigrades are ubiquitous meiofauna that are especially renowned for their exceptional extremotolerance to various adverse environments, including pressure, temperature, and even ionizing radiation. This is achieved through a reversible halt of metabolism triggered by desiccation, a phenomenon called anhydrobiosis. Recent establishment of genome resources for two tardigrades, Hypsibius exemplaris and Ramazzottius varieornatus, accelerated research to uncover the molecular mechanisms behind anhydrobiosis, leading to the discovery of many tardigrade-unique proteins. This review focuses on the history, methods, discoveries, and current state and challenges regarding tardigrade genomics, with an emphasis on molecular anhydrobiology. Remaining questions and future perspectives regarding prospective approaches to fully elucidate the molecular machinery of this complex phenomenon are discussed.

Introduction to Bacterial Anhydrobiosis: A General Perspective and the Mechanisms of Desiccation-Associated Damage

Anhydrobiosis is the ability of selected organisms to lose almost all water and enter a state of reversible ametabolism. Such an organism dries up to a state of equilibrium with dry air. Unless special protective mechanisms exist, desiccation leads to damage, mainly to proteins, nucleic acids, and membrane lipids. A short historical outline of research on extreme dehydration of living organisms and the current state of research are presented. Terminological issues are outlined. The role of water in the cell and the mechanisms of damage occurring in the cell under the desiccation stress are briefly discussed. Particular attention was paid to damage to proteins, nucleic acids, and membrane lipids. Understanding the nature of the changes and damage associated with desiccation is essential for the study of desiccation-tolerance mechanisms and application research. Difficulties related to the definition of life and the limits of life in the scientific discussion, caused by the phenomenon of anhydrobiosis, were also indicated.

Multiomics study of a heterotardigrade, Echinisicus testudo, suggests the possibility of convergent evolution of abundant heat-soluble proteins in Tardigrada

Background

Many limno-terrestrial tardigrades can enter an ametabolic state, known as anhydrobiosis, upon desiccation, in which the animals can withstand extreme environments. Through genomics studies, molecular components of anhydrobiosis are beginning to be elucidated, such as the expansion of oxidative stress response genes, loss of stress signaling pathways, and gain of tardigrade-specific heat-soluble protein families designated CAHS and SAHS. However, to date, studies have predominantly investigated the class Eutardigrada, and molecular mechanisms in the remaining class, Heterotardigrada, still remains elusive. To address this gap in the research, we report a multiomics study of the heterotardigrade Echiniscus testudo, one of the most desiccation-tolerant species which is not yet culturable in laboratory conditions.

Results

In order to elucidate the molecular basis of anhydrobiosis in E. testudo, we employed a multi-omics strategy encompassing genome sequencing, differential transcriptomics, and proteomics. Using ultra-low input library sequencing protocol from a single specimen, we sequenced and assembled the 153.7 Mbp genome annotated using RNA-Seq data. None of the previously identified tardigrade-specific abundant heat-soluble genes was conserved, while the loss and expansion of existing pathways were partly shared. Furthermore, we identified two families novel abundant heat-soluble proteins, which we named E. testudo Abundant Heat Soluble (EtAHS), that are predicted to contain large stretches of disordered regions. Likewise the AHS families in eutardigrada, EtAHS shows structural changes from random coil to alphahelix as the water content was decreased in vitro. These characteristics of EtAHS proteins are analogous to those of CAHS in eutardigrades, while there is no conservation at the sequence level.

Conclusions

Our results suggest that Heterotardigrada have partly shared but distinct anhydrobiosis machinery compared with Eutardigrada, possibly due to convergent evolution within Tardigrada. (276/350).

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-08131-x.

Genome-Wide Role of HSF1 in Transcriptional Regulation of Desiccation Tolerance in the Anhydrobiotic Cell Line, Pv11

The Pv11, an insect cell line established from the midge Polypedilum vanderplanki, is capable of extreme hypometabolic desiccation tolerance, so-called anhydrobiosis. We previously discovered that heat shock factor 1 (HSF1) contributes to the acquisition of desiccation tolerance by Pv11 cells, but the mechanistic details have yet to be elucidated. Here, by analyzing the gene expression profiles of newly established HSF1-knockout and -rescue cell lines, we show that HSF1 has a genome-wide effect on gene regulation in Pv11. The HSF1-knockout cells exhibit a reduced desiccation survival rate, but this is completely restored in HSF1-rescue cells. By comparing mRNA profiles of the two cell lines, we reveal that HSF1 induces anhydrobiosis-related genes, especially genes encoding late embryogenesis abundant proteins and thioredoxins, but represses a group of genes involved in basal cellular processes, thus promoting an extreme hypometabolism state in the cell. In addition, HSF1 binding motifs are enriched in the promoters of anhydrobiosis-related genes and we demonstrate binding of HSF1 to these promoters by ChIP-qPCR. Thus, HSF1 directly regulates the transcription of anhydrobiosis-related genes and consequently plays a pivotal role in the induction of anhydrobiotic ability in Pv11 cells.

Stabilization of Dry Sucrose Glasses by Four LEA_4 Proteins from Arabidopsis thaliana

Cells of many organisms and organs can withstand an (almost) total water loss (anhydrobiosis). Sugars play an essential role in desiccation tolerance due to their glass formation ability during dehydration. In addition, intrinsically disordered LEA proteins contribute to cellular survival under such conditions. One possible mechanism of LEA protein function is the stabilization of sugar glasses. However, little is known about the underlying mechanisms. Here we used FTIR spectroscopy to investigate sucrose (Suc) glass stability dried from water or from two buffer components in the presence of four recombinant LEA and globular reference proteins. Buffer ions influenced the strength of the Suc glass in the order Suc < Suc/Tris < Suc/NaP. LEA proteins strengthened the sugar H-bonded network and the molecular structure in the glassy state. The position of νOH peak and the wavenumber–temperature coefficient (WTC_g) provided similar information about the H-bonded network. Protein aggregation of LEA proteins was reduced in the desiccation-induced Suc glassy state. Detailed knowledge about the role of LEA proteins in the stabilization of dry sugar glasses yields information about their role in anhydrobiosis. This may open the possibility to use such proteins in biotechnical applications requiring dry storage of biologicals such as proteins, cells or tissues.

An Animal Able To Tolerate D2 O

It is possible to gain a deeper insight into the role of water in biology by using physicochemical variant molecules, such as deuterium oxide (D₂ O); however, D₂ O is toxic to multicellular organisms in high concentrations. By using a unique desiccation-rehydration process, we demonstrate that the anhydrobiotic nematode Panagrolaimus superbus is able to tolerate and proliferate in 99 % D₂ O. Moreover, we analysed P. superbus' water-channel protein (aquaporin; AQP), which is associated with dehydration/rehydration, by comparing its primary structure and modelling its tertiary structure in silico. Our data evidence that P. superbus' AQP is an aquaglyceroporin, a class of water channel known to display a wider pore; this helps to explain the rapid and successful organismal influx of D₂ O into this species. This is the first demonstration of an animal able to withstand high D₂ O levels, thus paving a way for the investigation of the effects D₂ O on higher levels of biological organization.

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.

Kramers’ Theory and the Dependence of Enzyme Dynamics on Trehalose-Mediated Viscosity

The disaccharide trehalose is accumulated in the cytoplasm of some organisms in response to harsh environmental conditions. Trehalose biosynthesis and accumulation are important for the survival of such organisms by protecting the structure and function of proteins and membranes. Trehalose affects the dynamics of proteins and water molecules in the bulk and the protein hydration shell. Enzyme catalysis and other processes dependent on protein dynamics are affected by the viscosity generated by trehalose, as described by the Kramers’ theory of rate reactions. Enzyme/protein stabilization by trehalose against thermal inactivation/unfolding is also explained by the viscosity mediated hindering of the thermally generated structural dynamics, as described by Kramers’ theory. The analysis of the relationship of viscosity–protein dynamics, and its effects on enzyme/protein function and other processes (thermal inactivation and unfolding/folding), is the focus of the present work regarding the disaccharide trehalose as the viscosity generating solute. Finally, trehalose is widely used (alone or in combination with other compounds) in the stabilization of enzymes in the laboratory and in biotechnological applications; hence, considering the effect of viscosity on catalysis and stability of enzymes may help to improve the results of trehalose in its diverse uses/applications.

Panagrolaimus superbus tolerates hypoxia within Gallium metal cage: implications for the understanding of the phenomenon of anhydrobiosis

Panagrolaimus superbus nematodes are able to tolerate desiccation by entering into a peculiar state of suspended animation known as anhydrobiosis. When desiccated, anhydrobiotic organisms are also able to tolerate other physical stresses, as high and low levels of temperature and pressure. Here, we decided to investigate the tolerance of desiccated P. superbus to an unprecedented double stress - hypoxia within 99.99% Gallium (Ga) metal cage. The authors observed that regardless of the external relative humidity, desiccated P. superbus tolerated 7 d confined within the metal cage, displaying no negative effects on its survival and population growth rates over 40 d. The results evidence that anhydrobiosis also renders nematodes tolerant to otherwise lethal concentrations of Ga, in an oxygen-poor environment; thus, expanding its polyextremotolerance profile.

Panagrolaimus superbus nematodes are able to tolerate desiccation by entering into a peculiar state of suspended animation known as anhydrobiosis. When desiccated, anhydrobiotic organisms are also able to tolerate other physical stresses, as high and low levels of temperature and pressure. Here, we decided to investigate the tolerance of desiccated P. superbus to an unprecedented double stress – hypoxia within 99.99% Gallium (Ga) metal cage. The authors observed that regardless of the external relative humidity, desiccated P. superbus tolerated 7 d confined within the metal cage, displaying no negative effects on its survival and population growth rates over 40 d. The results evidence that anhydrobiosis also renders nematodes tolerant to otherwise lethal concentrations of Ga, in an oxygen-poor environment; thus, expanding its polyextremotolerance profile.

Dry biobanking as a conservation tool in the Anthropocene

Species are going extinct at an alarming rate, termed by some as the sixth mass extinction event in the history of Earth. Many are the causes for this but in the end, all converge to one entity - humans. Since we are the cause, we also hold the key to making the change. Any change, however, will take time, and for some species this could be too long. While working on possible solutions, we also have the responsibility to buy time for those species on the verge of extinction. Genome resource banks, in the form of cryobanks, where samples are maintained under liquid nitrogen, are already in existence but they come with a host of drawbacks. Biomimicry - innovation inspired by Nature, has been a huge source for ideas. Searching methods that Nature utilizes to preserve biological systems for extended periods of time, we realize that drying rather than freezing is the method of choice. We thus argue here in favor of preserving at least part of the samples from critically endangered species in dry biobanks, a much safer, cost-effective, biobanking approach.

Carbonylation accumulation of the Hypsibius exemplaris anhydrobiote reveals age-associated marks

Together with nematodes and rotifers, tardigrade belong to micrometazoans that can cope with environmental extremes such as UV and solar radiations, dehydration, supercooling or overheating. Tardigrade can resist the harshest conditions by turning to cryptobiosis, an anhydrobiotic state that results from almost complete dehydration and is characterized by an ametabolic status. Although reports have challenged the molecular basis of the mechanisms underlying genomic injury resistance, little is yet known regarding the possible involvement of other tardigrade macromolecules in injury during a stress experience. In this report, we show that the tardigrade Hypsibius exemplaris can accumulate molecular damages by means of in situ detection of carbonyls. Furthermore, we demonstrate that living tardigrade can accumulate carbonylation. Finally, we reveal that anhydrobiotic tardigrade can be constitutively affected by carbonylation that marks aging in other metazoans.

Insects With Survival Kits for Desiccation Tolerance Under Extreme Water Deficits

The year 2002 marked the tercentenary of Antonie van Leeuwenhoek's discovery of desiccation tolerance in animals. This remarkable phenomenon to sustain 'life' in the absence of water can be revived upon return of hydrating conditions. Today, coping with climate change-related factors, especially temperature-humidity imbalance, is a global challenge. Under such adverse circumstances, desiccation tolerance remains a prime mechanism of several plants and a few animals to escape the hostile consequences of fluctuating hydroperiodicity patterns in their habitats. Among small animals, insects have demonstrated impressive resilience to dehydration and thrive under physiological water deficits without compromising on revival and survival upon rehydration. The focus of this review is to compile research insights on insect desiccation tolerance, gathered over the past several decades from numerous laboratories worldwide working on different insect groups. We provide a comparative overview of species-specific behavioral changes, adjustments in physiological biochemistry and cellular and molecular mechanisms as few of the noteworthy desiccation-responsive survival kits in insects. Finally, we highlight the role of insects as potential mechanistic models in tracking global warming which will form the basis for translational research to mitigate periods of climatic uncertainty predicted for the future.

Combined effects of osmotic and hydrostatic pressure on multilamellar lipid membranes in the presence of PEG and trehalose

We studied the interaction of lipid membranes with the disaccharide trehalose (TRH), which is known to stabilize biomembranes against various environmental stress factors. Generally, stress factors include low/high temperature, shear, osmotic and hydrostatic pressure. Small-angle X-ray-scattering was applied in combination with fluorescence spectroscopy and calorimetric measurements to get insights into the influence of trehalose on the supramolecular structure, hydration level, and elastic and thermodynamic properties as well as phase behavior of the model biomembrane DMPC, covering a large region of the temperature, osmotic and hydrostatic pressure phase space. We observed distinct effects of trehalose on the topology of the lipid's supramolecular structure. Trehalose, unlike osmotic pressure induced by polyethylene glycol, leads to a decrease of lamellar order and a swelling of multilamellar vesicles, which is attributable to direct interactions between the membrane and trehalose. Our results revealed a distinct biphasic concentration dependence of the observed effects of trehalose. While trehalose intercalates between the polar head groups at low concentrations, the effects after saturation are dominated by the exclusion of trehalose from the membrane surface.

Caenorhabditis elegans Tolerates Hyperaccelerations up to 400,000 x g

One of the most important laboratory animal species is the nematode Caenorhabditis elegans, which has been used in a range of research fields such as neurobiology, body development, and molecular biology. The scientific progress obtained by employing C. elegans as a model in these areas has encouraged its use in new fields. One of the new potential applications concerns the biological responses to hyperacceleration stress (g-force), but only a few studies have evaluated the response of multicellular organisms to extreme hypergravity conditions at the order of magnitude 10⁵ x g, which is the theorized force experienced by rocks ejected from Mars (or similar planets). Therefore, we subjected the nematode C. elegans to 400,000 x g (equivalent to that force) and evaluated viability, general morphology, and behavior of C. elegans after exposure to this stress. The metabolic activity of this nematode in response to the gravitational spectrum of 50-400,000 x g was also evaluated by means of the MTT assay. Surprisingly, we found that this organism showed no decrease in viability, no changes in behavior and development, and no drastic metabolic depression after hyperacceleration. Thus, we demonstrated for the first time that this multicellular research model can withstand extremely high g-forces, which prompts the use of C. elegans as a new model for extreme hypergravity. Key Words: Caenorhabditis elegans-Hypergravity-Ultracentrifugation-Acceleration-Panspermia-Astrobiology. Astrobiology 18, 825-833.

Multiple genes contribute to anhydrobiosis (tolerance to extreme desiccation) in the nematode Panagrolaimus superbus

The molecular basis of anhydrobiosis, the state of suspended animation entered by some species during extreme desiccation, is still poorly understood despite a number of transcriptome and proteome studies. We therefore conducted functional screening by RNA interference (RNAi) for genes involved in anhydrobiosis in the holo-anhydrobiotic nematode Panagrolaimus superbus. A new method of survival analysis, based on staining, and proof-of-principle RNAi experiments confirmed a role for genes involved in oxidative stress tolerance, while a novel medium-scale RNAi workflow identified a further 40 anhydrobiosis-associated genes, including several involved in proteostasis, DNA repair and signal transduction pathways. This suggests that multiple genes contribute to anhydrobiosis in P. superbus.

High-throughput mass spectrometry analysis revealed a role for glucosamine in potentiating recovery following desiccation stress in Chironomus

Desiccation tolerance is an essential survival trait, especially in tropical aquatic organisms that are vulnerable to severe challenges posed by hydroperiodicity patterns in their habitats, characterized by dehydration-rehydration cycles. Here, we report a novel role for glucosamine as a desiccation stress-responsive metabolite in the underexplored tropical aquatic midge, Chironomus ramosus. Using high- throughput liquid chromatography quadrupole time-of-flight mass spectrometry (LC-QToF-MS) analysis, biochemical assays and gene expression studies, we confirmed that glucosamine was essential during the recovery phase in C. ramosus larvae. Additionally, we demonstrated that trehalose, a known stress-protectant was crucial during desiccation but did not offer any advantage to the larvae during recovery. Based on our findings, we emphasise on the collaborative interplay of glucosamine and trehalose in conferring overall resilience to desiccation stress and propose the involvement of the trehalose-chitin metabolic interface in insects as one of the stress-management strategies to potentiate recovery post desiccation through recruitment of glucosamine.

Enhanced flocculation of two bioflocculation-producing bacteria by secretion of Philodina erythrophthalma

Bdelloid rotifer are reported to play a promoting role in microbial aggregation and floc formation in activated sludge systems; however, the mechanisms involved in this process are unclear. This study explores the effect of a rotifer secretion (RS) from the species Philodina erythrophthalma on the flocculation and growth of two bioflocculation-producing bacteria isolated from activated sludge. Results show that although the secretion has weak bioflocculability in itself, it can significantly enhance the flocculability of bioflocculation-producing bacteria and promote formation of microbial aggregation and floc. The possible mechanism is that the RS causes an increase in the bacteria densities and extracellular polymeric substance contents. The improvement of flocculability using RS shows an S-curve changing tendency with collection time, and corresponds with the first-order model with secretion dosage. Chemical composition analysis shows that low contents of non-protein organic nitrogen and polysaccharides are found in the RS, which implies that RS acts more like a growth-promoting substance or infochemical than as a nutrient in the promotion of bacterial growth. In conclusion, the findings provide a novel and potential strategy for promoting sludge floc formation using the infochemical secreted by this rotifer.

RNA-Seq Analysis of the Antioxidant Status and Immune Response of Portunus trituberculatus Following Aerial Exposure

Desiccation tolerance has been long considered as an important trait for the life survival under acute environmental stress. One of the biggest problems for modern commercial crab farming is desiccation during transportation; high mortality could occur following the aerial exposure. In this regard, here, we utilized RNA-seq-based transcriptome profiling to characterize the molecular responses of swimming crab in response to aerial exposure. In present study, following aerial exposure, the gill samples were sequenced at 0, 6, 12, and 18 h. And the sequenced reads were assembled into 274,594 contigs, with average length of 735.59 bp and N50 size of 1262 bp. After differential expression analysis, a total of 1572 genes were captured significantly differentially expressed, and were categorized into antioxidant/oxidative stress response, chaperones/heat shock proteins, immune alteration, cell proliferation/apoptosis, and cytoskeletal. Our analysis revealed the dramatic tissue oxidant stress and the alteration of the tissue epithelial integrity, especially many genes that have not been reported in crab species. With the limited functional information in crab, further studies are needed and underway in our lab to further characterize the key cellular actors governing the crab tolerance to aerial exposure. Taken together, our results provide molecular resources for further identification of key genes for desiccation tolerance, and to facilitate the molecular selection and breeding of desiccation tolerant strain and family.

A New Physiological Role for the DNA Molecule as a Protector against Drying Stress in Desiccation-Tolerant Microorganisms

The DNA molecule is associated with the role of encoding information required to produce RNA which is translated into proteins needed by the cell. This encoding involves information transmission to offspring or to other organisms by horizontal transfer. However, despite the abundance of this molecule in both the cell and the environment, its physiological role seems to be restricted mainly to that of a coding and inheritance molecule. In this paper, we report a new physiological role for the DNA molecule as involved in protection against desiccation, in addition to its well-established main information transfer and other recently reported functions such as bio-film formation in eDNA form. Desiccation-tolerant microorganisms such as Microbacterium sp. 3J1 significantly upregulate genes involved in DNA synthesis to produce DNA as part of their defensive mechanisms to protect protein structures and functions from drying according to RNA-seq analysis. We have observed the intracellular overproduction of DNA in two desiccation-tolerant microorganisms, Microbacterium sp. 3J1 and Arthrobacter siccitolerans 4J27, in response to desiccation signals. In addition, this conclusion can be made from our observations that synthetic DNA protects two proteins from drying and when part of a xeroprotectant preparation, DNA from various organisms including desiccation-sensitive species, does the same. Removal of DNA by nuclease treatment results in absence of this additive protective effect. We validated this role in biochemical and biophysical assays in proteins and occurs in trans even with short, single chains of synthetically produced DNA.

Desiccation stress induces developmental heterochrony in Drosophila melanogaster

Stressful environments are known to perturb developmental patterns in insects. In the purview of desiccation as a stressor, relatively little is known about the developmental consequences linked with desiccation tolerance. In this study, we have particularly focused on the exploration of the temporal profile of postembryonic development in response to desiccation exposure in Drosophila melanogaster and the associated trade-offs. We document a correlation between variations in 20-hydroxyecdysone levels and the altered timing of metamorphic events during the life cycle. Following desiccation, we observed an extension in the larval longevity whereas the duration of the pupal and adult stages was significantly shortened. Alternately, feeding of 20-hydroxyecdysone apparently led to the restoration of the normal temporal pattern of development in the desiccated group. In spite of the desiccation-responsive heterochronic shifts in development, the overall lifespan post recovery remained almost unaltered among the desiccated and undesiccated groups suggesting plasticity in developmental control. This observation reminisces 'canalization-like' phenomenon that buffers alterations in the overall lifespan. We thus identified a desiccationresponsive period in the lifespan of D. melanogaster during which variations in ecdysone levels are capable to alter the temporal course of development.

A functional difference between native and horizontally acquired genes in bdelloid rotifers

The form of RNA processing known as SL trans-splicing involves the transfer of a short conserved sequence, the spliced leader (SL), from a noncoding SL RNA to the 5' ends of mRNA molecules. SL trans-splicing occurs in several animal taxa, including bdelloid rotifers (Rotifera, Bdelloidea). One striking feature of these aquatic microinvertebrates is the large proportion of foreign genes, i.e. those acquired by horizontal gene transfer from other organisms, in their genomes. However, whether such foreign genes behave similarly to native genes has not been tested in bdelloids or any other animal. We therefore used a combination of experimental and computational methods to examine whether transcripts of foreign genes in bdelloids were SL trans-spliced, like their native counterparts. We found that many foreign transcripts contain SLs, use similar splice acceptor sequences to native genes, and are able to undergo alternative trans-splicing. However, a significantly lower proportion of foreign mRNAs contains SL sequences than native transcripts. This demonstrates a novel functional difference between foreign and native genes in bdelloids and suggests that SL trans-splicing is not essential for the expression of foreign genes, but is acquired during their domestication.

Downregulation of dTps1 in Drosophila melanogaster larvae confirms involvement of trehalose in redox regulation following desiccation

As a survival strategy to environmental water deficits, desiccation-tolerant organisms are commonly known for their ability to recruit stress-protective biomolecules such as trehalose. We have previously reported the pivotal role of trehalose in larval desiccation tolerance in Drosophila melanogaster. Trehalose has emerged as a versatile molecule, serving mainly as energy source in insects and also being a stress protectant. While several recent reports have revealed the unconventional role of trehalose in scavenging reactive oxygen species in yeast and plants, this aspect has not received much attention in animals. We examined the status of desiccation-induced generation of reactive oxygen species in D. melanogaster larvae and the possible involvement of trehalose in ameliorating the harmful consequences thereof. Insect trehalose synthesis is governed by the enzyme trehalose 6-phosphate synthase 1 (TPS1). Using the ubiquitous da-GAL4-driven expression of the dTps1-RNAi transgene, we generated dTps1-downregulated Drosophila larvae possessing depleted levels of dTps1 transcripts. This resulted in the inability of the larvae for trehalose synthesis, thereby allowing us to elucidate the significance of trehalose in the regulation of desiccation-responsive redox homeostasis. Furthermore, the results from molecular genetics studies, biochemical assays, electron spin resonance analyses and a simple, non-invasive method of whole larval live imaging suggested that trehalose in collaboration with superoxide dismutase (SOD) is involved in the maintenance of redox state in D. melanogaster.

Transcriptome analysis of stress tolerance in entomopathogenic nematodes of the genus Steinernema

Entomopathogenic nematodes of the genus Steinernema are effective biological control agents. The infective stage of these parasites can withstand environmental stresses such as desiccation and heat, but the molecular and physiological mechanisms involved in this tolerance are poorly understood. We used 454 pyrosequencing to analyse transcriptome expression in Steinernema spp. that differ in their tolerance to stress. We compared these species, following heat and desiccation treatments, with their non-stressed counterparts. More than 98% of the transcripts found matched homologous sequences in the UniRef90 database, mostly nematode genes (85%). Among those, 60.8% aligned to the vertebrate parasites including Ascaris suum, Loa loa, and Brugia malayi, 23.3% aligned to bacteriovores, mostly from the genus Caenorhabditis, and 1% aligned to EPNs. Analysing gene expression patterns of the stress response showed a large fraction of down-regulated genes in the desiccation-tolerant nematode Steinernema riobrave, whereas a larger fraction of the genes in the susceptible Steinernema feltiae Carmiel and Gvulot strains were up-regulated. We further compared metabolic pathways and the expression of specific stress-related genes. In the more tolerant nematode, more genes were down-regulated whereas in the less tolerant strains, more genes were up-regulated. This phenomenon warrants further exploration of the mechanism governing induction of the down-regulation process. The present study revealed many genes and metabolic cycles that are differentially expressed in the stressed nematodes. Some of those are well known in other nematodes or anhydrobiotic organisms, but several are new and should be further investigated for their involvement in desiccation and heat tolerance. Our data establish a foundation for further exploration of stress tolerance in entomopathogenic nematodes and, in the long term, for improving their ability to withstand suboptimal environmental conditions.

Introduction to desiccation biology: from old borders to new frontiers

A special issue reviews the recent progress made in our understanding of desiccation tolerance across various plant and animal kingdoms. It has been known for a long time that seeds can survive near absolute protoplasmic dehydration through air drying and complete germination upon rehydration because of their desiccation tolerance. This property is present both in prokaryotes and eukaryotes across all life kingdoms. These dry organisms suspend their metabolism when dry, are extremely tolerant to acute environmental stresses and are relatively stable during long periods of desiccation. Studies aiming at understanding the mechanisms of survival in the dry state have emerged during the past 40 years, moving from in vitro to genomic models and comparative genomics, and from a view that tolerance is an all-or-nothing phenomenon to a quantitative trait. With the prospect of global climate change, understanding the mechanisms of desiccation tolerance appears to be a promising avenue as a prelude to engineering crops for improved drought tolerance. Understanding desiccation is also useful for seed banks that rely on dehydration tolerance to preserve plant genetic resources in the form of these propagules. Articles in this special issue explore the recent progress in our understanding of desiccation tolerance, including the evolutionary mechanisms that have been adopted across various plant (algae, lichens, seeds, resurrection plants) and animal model systems (Caenorhabditis elegans, brine shrimp). We propose that the term desiccation biology defines the discipline dedicated to understand the desiccation tolerance in living organisms as well as the limits and time constraints thereof.

Against All Odds: Trehalose-6-Phosphate Synthase and Trehalase Genes in the Bdelloid Rotifer Adineta vaga Were Acquired by Horizontal Gene Transfer and Are Upregulated during Desiccation

The disaccharide sugar trehalose is essential for desiccation resistance in most metazoans that survive dryness; however, neither trehalose nor the enzymes involved in its metabolism have ever been detected in bdelloid rotifers despite their extreme resistance to desiccation. Here we screened the genome of the bdelloid rotifer Adineta vaga for genes involved in trehalose metabolism. We discovered a total of four putative trehalose-6-phosphate synthase (TPS) and seven putative trehalase (TRE) gene copies in the genome of this ameiotic organism; however, no trehalose-6-phosphate phosphatase (TPP) gene or domain was detected. The four TPS copies of A. vaga appear more closely related to plant and fungi proteins, as well as to some protists, whereas the seven TRE copies fall in bacterial clades. Therefore, A. vaga likely acquired its trehalose biosynthesis and hydrolysis genes by horizontal gene transfers. Nearly all residues important for substrate binding in the predicted TPS domains are highly conserved, supporting the hypothesis that several copies of the genes might be functional. Besides, RNAseq library screening showed that trehalase genes were highly expressed compared to TPS genes, explaining probably why trehalose had not been detected in previous studies of bdelloids. A strong overexpression of their TPS genes was observed when bdelloids enter desiccation, suggesting a possible signaling role of trehalose-6-phosphate or trehalose in this process.

Stone-dwelling actinobacteria Blastococcus saxobsidens, Modestobacter marinus and Geodermatophilus obscurus proteogenomes

The Geodermatophilaceae are unique model systems to study the ability to thrive on or within stones and their proteogenomes (referring to the whole protein arsenal encoded by the genome) could provide important insight into their adaptation mechanisms. Here we report the detailed comparative genome analysis of Blastococcus saxobsidens (Bs), Modestobacter marinus (Mm) and Geodermatophilus obscurus (Go) isolated respectively from the interior and the surface of calcarenite stones and from desert sandy soils. The genome-scale analysis of Bs, Mm and Go illustrates how adaptation to these niches can be achieved through various strategies including 'molecular tinkering/opportunism' as shown by the high proportion of lost, duplicated or horizontally transferred genes and ORFans. Using high-throughput discovery proteomics, the three proteomes under unstressed conditions were analyzed, highlighting the most abundant biomarkers and the main protein factors. Proteomic data corroborated previously demonstrated stone-related ecological distribution. For instance, these data showed starvation-inducible, biofilm-related and DNA-protection proteins as signatures of the microbes associated with the interior, surface and outside of stones, respectively.

The role of phospholipid headgroup composition and trehalose in the desiccation tolerance of Caenorhabditis elegans

Anhydrobiotic organisms have the remarkable ability to lose extensive amounts of body water and survive in an ametabolic state. Distributed to various taxa of life, these organisms have developed strategies to efficiently protect their cell membranes and proteins against extreme water loss. Recently, we showed that the dauer larva of the nematode Caenorhabditis elegans is anhydrobiotic and accumulates high amounts of trehalose during preparation to harsh desiccation (preconditioning). Here, we have used this genetic model to study the biophysical manifestations of anhydrobiosis and show that, in addition to trehalose accumulation, dauer larvae dramatically reduce their phosphatidylcholine (PC) content. The chemical composition of the phospholipids (PLs) has key consequences not only for their interaction with trehalose, as we demonstrate with Langmuir-Blodgett monolayers, but also, the kinetic response of PLs to hydration transients is strongly influenced as evidenced by time-resolved FTIR spectroscopy. PLs from preconditioned larvae with reduced PC content exhibit a higher trehalose affinity, a stronger hydration-induced gain in acyl chain free volume, and a wider spread of structural relaxation rates of their lyotropic transitions and sub-headgroup H-bond interactions. The different hydration properties of PC and phosphatidylethanolamine (PE) headgroups are crucial for the hydration-dependent rearrangement of the trehalose-mediated H-bond network. As a consequence, the compressibility modulus of PLs from preconditioned larvae is about 2.6-fold smaller than that from non-preconditioned ones. Thus, the biological relevance of reducing the PC:PE ratio by PL headgroup adaptation should be the preservation of plasma membrane integrity by relieving mechanical strain from desiccated trehalose-containing cells during fast rehydration.

The effects of a protein osmolyte on the stability of the integral membrane protein glycerol facilitator

Osmolytes are naturally occurring molecules used by a wide variety of organisms to stabilize proteins under extreme conditions of temperature, salinity, hydrostatic pressure, denaturant concentration, and desiccation. The effects of the osmolyte trimethylamine N-oxide (TMAO) as well as the influence of detergent head group and acyl chain length on the stability of the Escherichia coli integral membrane protein glycerol facilitator (GF) tetramer to thermal and chemical denaturation by sodium dodecyl sulphate (SDS) are reported. TMAO promotes the association of the normally tetrameric α-helical protein into higher order oligomers in dodecyl-maltoside (DDM), but not in tetradecyl-maltoside (TDM), lyso-lauroylphosphatidyl choline (LLPC), or lyso-myristoylphosphatidyl choline (LMPC), as determined by dynamic light scattering (DLS); an octameric complex is particularly stable as indicated by SDS polyacrylamide gel electrophoresis. TMAO increases the heat stability of the GF tetramer an average of 10 °C in the 4 detergents and also protects the protein from denaturation by SDS. However, it did not promote re-association to the tetramer when added to SDS-dissociated protein. TMAO also promotes the formation of rod-like detergent micelles, and DLS was found to be useful for monitoring the structure of the protein and the redistribution of detergent during thermal dissociation of the protein. The protein is more thermally stable in detergents with the phosphatidylcholine head group (LLPC and LMPC) than in the maltoside detergents. The implications of the results for osmolyte mechanism, membrane protein stability, and protein-protein interactions are discussed.

Impact of protective agents and drying methods on desiccation tolerance of Salix nigra L. seeds

Willow seeds are classified as orthodox, but they show some recalcitrant characteristics, as they lose viability in a few weeks at room temperature. The aim of this work was to improve the desiccation tolerance of willow seeds (Salix nigra L.), as a model of sensitive materials to dehydration, through imbibition in solutions and later vacuum (VD) or freeze-drying (FD). Imbibition was conducted with 45% w/v trehalose or polyethylene glycol 400 -PEG- or water prior to dehydration treatments. Water- and especially trehalose-imbibed seeds subjected to VD showed better germination capability with respect to the freeze-dried ones. Water crystallization was mainly responsible for the great loss of capability germination observed in water- or trehalose-imbibed seeds subjected to FD. PEG behavior was better when seeds were FD instead of VD. DSC thermograms of seeds allowed to identify two thermal transitions corresponding to lipids melting and to proteins denaturation. This last transition reveals information about proteins state/functionality. Dehydration of control and PEG- or water-imbibed seeds affected proteins functionality leading to lower germinability. In the case of trehalose-imbibed seeds subjected to VD, proteins maintained their native state along dehydration, and the seeds showed a great germination capacity for all the water content range. Germinated seeds showed higher luminosity (L*), greenness (a*) and yellowness (b*) values than not-germinated seeds independently of the employed agent. Present work reveals that the presence of adequate protective agents as well the dehydration method were the main critical factors involved in willow seed desiccation tolerance.

Molecular analysis of the cold tolerant Antarctic nematode, Panagrolaimus davidi

Isolated and established in culture from the Antarctic in 1988, the nematode Panagrolaimus davidi has proven to be an ideal model for the study of adaptation to the cold. Not only is it the best-documented example of an organism surviving intracellular freezing but it is also able to undergo cryoprotective dehydration. As part of an ongoing effort to develop a molecular understanding of this remarkable organism, we have assembled both a transcriptome and a set of genomic scaffolds. We provide an overview of the transcriptome and a survey of genes involved in temperature stress. We also explore, in silico, the possibility that P. davidi will be susceptible to an environmental RNAi response, important for further functional studies.

Responses of invertebrates to temperature and water stress: A polar perspective

As small bodied poikilothermic ectotherms, invertebrates, more so than any other animal group, are susceptible to extremes of temperature and low water availability. In few places is this more apparent than in the Arctic and Antarctic, where low temperatures predominate and water is unusable during winter and unavailable for parts of summer. Polar terrestrial invertebrates express a suite of physiological, biochemical and genomic features in response to these stressors. However, the situation is not as simple as responding to each stressor in isolation, as they are often faced in combination. We consider how polar terrestrial invertebrates manage this scenario in light of their physiology and ecology. Climate change is also leading to warmer summers in parts of the polar regions, concomitantly increasing the potential for drought. The interaction between high temperature and low water availability, and the invertebrates' response to them, are therefore also explored.

Localization of trehalose in partially hydrated DOPC bilayers: insights into cryoprotective mechanisms

Trehalose, a natural disaccharide with bioprotective properties, is widely recognized for its ability to preserve biological membranes during freezing and dehydration events. Despite debate over the molecular mechanisms by which this is achieved, and that different mechanisms imply quite different distributions of trehalose molecules with respect to the bilayer, there are no direct experimental data describing the location of trehalose within lipid bilayer membrane systems during dehydration. Here, we use neutron membrane diffraction to conclusively show that the trehalose distribution in a dioleoylphosphatidylcholine (DOPC) system follows a Gaussian profile centred in the water layer between bilayers. The absence of any preference for localizing near the lipid headgroups of the bilayers indicates that the bioprotective effects of trehalose at physiologically relevant concentrations are the result of non-specific mechanisms that do not rely on direct interactions with the lipid headgroups.

Desiccation and heat tolerance of eggs of the Asian tadpole shrimp, Triops granarius

Triops granarius (Lucas) is a freshwater crustacean that is distributed from South Africa to the Eurasian continent. This species lives in temporary water pools and is exposed to desiccation and extreme temperatures after the water dries up in its habitat. To withstand this severe environment, Triops eggs enter anhydrobiosis when dehydrated. To clarify the physiological characteristics of T. granarius anhydrobiosis, we examined hatching rates after rehydration of eggs that were dehydrated at several humidity levels for 10 or 100 days. Lower humidity produced higher hatching rates when dehydration was continued for 100 days. These results suggest that drying at low humidity is required for long-term anhydrobiosis of T. granarius eggs. The eggs survived desiccation when dehydrated at the blastula, gastrula, and early organogenesis stages. The most dehydration-tolerant stage was early organogenesis. Non-dehydrated eggs hatched after temperature treatments of up to 50°C for 1 h, but did not hatch after exposure to 60°C for 1 h in air and under water. Similar results were obtained for dehydrated eggs exposed to high temperatures under water. In contrast, dehydrated eggs hatched after 1 h at 80°C in air but did not after 1 h at 90°C in air. Our results show that Triops eggs exhibit tolerance for desiccation and high temperature in a dried state, once they have entered anhydrobiosis.

Spatial and temporal escape from fungal parasitism in natural communities of anciently asexual bdelloid rotifers

Sexual reproduction is costly, but it is nearly ubiquitous among plants and animals, whereas obligately asexual taxa are rare and almost always short-lived. The Red Queen hypothesis proposes that sex overcomes its costs by enabling organisms to keep pace with coevolving parasites and pathogens. If so, the few cases of stable long-term asexuality ought to be found in groups whose coevolutionary interactions with parasites are unusually weak. In theory, antagonistic coevolution will be attenuated if hosts disperse among patches within a metapopulation separately from parasites and more rapidly. We examined whether these conditions are met in natural communities of bdelloid rotifers, one of the longest-lived asexual lineages. At any life stage, these microscopic invertebrates can tolerate the complete desiccation of their ephemeral freshwater habitats, surviving as dormant propagules that are readily carried by the wind. In our field experiments, desiccation and wind transport enabled bdelloids to disperse independently of multiple fungal parasites, in both time and space. Surveys of bdelloid communities in unmanipulated moss patches confirmed that fungal parasitism was negatively correlated with extended drought and increasing height (exposure to wind). Bdelloid ecology therefore matches a key condition of models in which asexuals persist through spatio-temporal decoupling from coevolving enemies.

Multiple roles of photosynthetic and sunscreen pigments in cyanobacteria focusing on the oxidative stress

Cyanobacteria have two types of sunscreen pigments, scytonemin and mycosporine-like amino acids (MAAs). These secondary metabolites are thought to play multiple roles against several environmental stresses such as UV radiation and desiccation. Not only the large molar absorption coefficients of these sunscreen pigments, but also their antioxidative properties may be necessary for the protection of biological molecules against the oxidative damages induced by UV radiation. The antioxidant activity and vitrification property of these pigments are thought to be requisite for the desiccation and rehydration processes in anhydrobiotes. In this review, the multiple roles of photosynthetic pigments and sunscreen pigments on stress resistance, especially from the viewpoint of their structures, biosynthetic pathway, and in vitro studies of their antioxidant activity, will be discussed.