Desiccation and radiation stress tolerance in cyanobacteria

The adaptation mechanism of desert soil cyanobacterium Chroococcidiopsis sp. to desiccation

Desiccation is a common stress for organisms living in desert soil. Chroococcidiopsis sp. is the dominant species in the soil microbial community of desert regions. Some species of Chroococcidiopsis sp. are highly tolerant to desiccation, making them a good biological system for soil restoration in desert regions, but their adaptation mechanisms to desiccation are not well understood. In this study, different desiccation levels of desert regions were simulated in terms of relative humidity to investigate the adaptation of desert cyanobacterium Chroococcidiopsis sp. ASB-02 to desiccation. Chroococcidiopsis sp. ASB-02 exhibited the ability to rapidly restore PSII activity under desiccation-rehydration conditions. Desiccation-induced oxidative stress is a common feature and the Chroococcidiopsis sp. ASB-02 activated diverse antioxidant genes to eliminate oxidative products. When exposed to desiccation-induced water stress, Chroococcidiopsis sp. ASB-02 can slow water loss and regulate osmotic pressure by enhancing the synthesis of exopolysaccharides and intracellular sucrose. However, under extreme desiccation stress, trehalose is crucial in regulating the osmotic potential of Chroococcidiopsis sp. ASB-02. When the relative humidity is ≤ 56%, with the continuous loss of cellular water, Chroococcidiopsis sp. ASB-02 responds to reduced metabolic activity in the cell by initiating energy-saving pathways and enhancing transcription mechanisms. This study provides a theoretical basis for understanding the adaptation mechanisms of desert cyanobacterium Chroococcidiopsis sp., which is important for soil restoration in desert regions.

Relationships between radiation, wildfire and the soil microbial communities in the Chornobyl Exclusion Zone

There is considerable uncertainty regarding radiation's effects on biodiversity in natural complex ecosystems typically subjected to multiple environmental disturbances and stresses. In this study we characterised the relationships between soil microbial communities and estimated total absorbed dose rates to bacteria, grassy vegetation and trees in the Red Forest region of the Chornobyl Exclusion Zone. Samples were taken from sites of contrasting ecological histories and along burn and no burn areas following a wildfire. Estimated total absorbed dose rates to bacteria reached levels one order of magnitude higher than those known to affect bacteria in laboratory studies. Sites with harsher ecological conditions, notably acidic pH and low soil moisture, tended to have higher radiation contamination levels. No relationship between the effects of fire and radiation were observed. Microbial groups that correlated with high radiation sites were mostly classified to taxa associated with high environmental stress habitats or stress resistance traits. Distance-based linear models and co-occurrence analysis revealed that the effects of radiation on the soil microbiome were minimal. Hence, the association between high radiation sites and specific microbial groups is more likely a result of the harsher ecological conditions in these sites, rather than due to radiation itself. In this study, we provide a starting point for understanding the relationship between soil microbial communities and estimated total absorbed radiation dose rates to different components of an ecosystem highly contaminated with radiation. Our results suggest that soil microbiomes adapted to natural soil conditions are more likely to be resistant to ionising radiation than expected from laboratory studies, which demonstrates the importance of assessing the impact of ionising radiation on soil microbial communities under field conditions.

Optimizing survival and growth of inoculated biocrust-forming cyanobacteria through native plant-based habitat amelioration

Low restoration success in degraded drylands has promoted research efforts towards recovery of pioneer components of these ecosystems such as biocrusts. Biocrusts can stabilize soils and improve nutrient cycling to assist vegetation establishment, but their natural recovery following a disturbance may be very slow. Soil inoculation with biocrust-forming components such as cyanobacteria is widely spread to foster biocrust formation. However, the growth of induced biocrust can be constrained under field conditions due to the harsh environmental conditions in drylands. Thus, strategies to reduce abiotic stresses have to be explored to improve cyanobacteria survival and growth. In this study, we performed an outdoor experiment to analyze the effect of plant-based ameliorating strategies in combination with cyanobacteria inoculum on biocrust formation and improvement of degraded arid soil properties. These ameliorants consisted of a plant mesh made of Macrochloa tenacissima and a Plantago ovata-based stabilizer. Application of ameliorating treatments improved cyanobacteria growth (higher chlorophyll a content, lower albedo and higher NDVI) compared to the application of cyanobacteria inoculum alone. Inoculated soils showed higher aggregate stability than non-inoculated ones, but the highest soil stability was found in the soils treated with P. ovata and was also significantly increased in the soils covered by the M. tenacissima mesh compared to uncovered soils. Both the mesh and the P. ovata stabilizer increased soil organic carbon content by up to 10% and 172%, respectively, compared to soils without habitat amelioration. Microbial community composition was similar between control and inoculated soils and between the mesh covered and uncovered soils, indicating that neither cyanobacteria inoculation nor the vegetal mesh had negative effects on the native soil community. In contrast, the soil with the P. ovata stabilizer alone displayed a different composition, with up to 95% of the bacteria's relative abundance represented by Firmicutes. This effect needs to be considered when applying this stabilizer to prevent a potential alteration of the indigenous soil microbial community. This study indicates the viability of using plant-based ameliorating strategies to optimize the establishment and growth of cyanobacteria inoculum and maximize their effects on soil properties, thus contributing to advancing in the application of nature-based solutions for the restoration of degraded dryland ecosystems.

Comparative analysis of cyanobacterial communities in gypsum outcrops: insights from sites in Israel and Poland

Today, the biodiversity of endolithic microbial colonisations are only partly understood. In this study, we used a combination of molecular community metabarcoding using the 16S rRNA gene, light microscopy, CT-scan analysis, and Raman spectroscopy to describe gypsum endolithic communities in 2 sites-southern Poland and northern Israel. The obtained results have shown that despite different geographical areas, climatic conditions, and also physical features of colonized gypsum outcrops, both of these sites have remarkably similar microbial and pigment compositions. Cyanobacteria dominate both of the gypsum habitats, followed by Chloroflexi and Pseudomonadota. Among cyanobacteria, Thermosynechococcaceae were more abundant in Israel while Chroococcidiopsidaceae in Poland. Interestingly, no Gloeobacteraceae sequences have been found in Poland, only in Israel. Some of the obtained 16S rRNA gene sequences of cyanobacteria matched previously detected sequences from endolithic communities in various substrates and geographical regions, supporting the hypothesis of global metacommunity, but more data are still needed. Using Raman spectroscopy, cyanobacterial UV-screening pigments-scytonemin and gloeocapsin have been detected alongside carotenoids, chlorophyll a and melanin. These pigments can serve as potential biomarkers for basic taxonomic identification of cyanobacteria. Overall, this study provides more insight into the diversity of cyanobacterial endolithic colonisations in gypsum across different areas.

Effects of ultraviolet and photosynthetically active radiation on morphogenesis, antioxidants and photoprotective defense mechanism in a hot-spring cyanobacterium Nostoc sp. strain VKB02

The continuous increase in global temperature and ultraviolet radiation (UVR) causes profound impacts on the growth and physiology of photosynthetic microorganisms. The hot-spring cyanobacteria have a wide range of mitigation mechanisms to cope up against current unsustainable environmental conditions. In the present investigation, we have explored the indispensable mitigation strategies of an isolated hot-spring cyanobacterium Nostoc sp. strain VKB02 under simulated ultraviolet (UV-A, UV-B) and photosynthetically active radiation (PAR). The adaptive morphological changes were more significantly observed under PAB (PAR, UV-A, and UV-B) exposure as compared to P and PA (PAR and UV-A) irradiations. PAB exposure also exhibited a marked decline in pigment composition and photosynthetic efficiency by multi-fold increment of free radicals. To counteract the oxidative stress, enzymatic and non-enzymatic antioxidants defense were significantly enhanced many folds under PAB exposure as compared to the control. In addition, the cyanobacterium has also produced shinorine as a strong free radicals scavenger and excellent UV absorber for effective photoprotection against UV radiation. Therefore, the hot-spring cyanobacterium Nostoc sp. strain VKB02 has unique defense strategies for survival under prolonged lethal UVR conditions. This study will help in the understanding of environment-induced defense strategies and production of highly value-added green photo-protectants for commercial applications.

Radiation-resistant bacteria in desiccated soil and their potentiality in applied sciences

A rich diversity of radiation-resistant (Rr) and desiccation-resistant (Dr) bacteria has been found in arid habitats of the world. Evidence from scientific research has linked their origin to reactive oxygen species (ROS) intermediates. Rr and Dr. bacteria of arid regions have the potential to regulate imbalance radicals and evade a higher dose of radiation and oxidation than bacterial species of non-arid regions. Photochemical-activated ROS in Rr bacteria is run through photo-induction of electron transfer. A hypothetical model of the biogeochemical cycle based on solar radiation and desiccation. These selective stresses generate oxidative radicals for a short span with strong reactivity and toxic effects. Desert-inhibiting Rr bacteria efficiently evade ROS toxicity with an evolved antioxidant system and other defensive pathways. The imbalanced radicals in physiological disorders, cancer, and lung diseases could be neutralized by a self-sustaining evolved Rr bacteria antioxidant system. The direct link of evolved antioxidant system with intermediate ROS and indirect influence of radiation and desiccation provide useful insight into richness, ecological diversity, and origin of Rr bacteria capabilities. The distinguishing features of Rr bacteria in deserts present a fertile research area with promising applications in the pharmaceutical industry, genetic engineering, biological therapy, biological transformation, bioremediation, industrial biotechnology, and astrobiology.

Effect of salinity on scytonemin yield in endolithic cyanobacteria from the Atacama Desert

Cyanobacteria inhabiting extreme environments constitute a promising source for natural products with biotechnological applications. However, they have not been studied in-depth for this purpose due to the difficulties in their isolation and mass culturing. The Atacama Desert suffers one of the highest solar irradiances that limits the presence of life on its hyperarid core to endolithic microbial communities supported by cyanobacteria as primary producers. Some of these cyanobacteria are known to produce scytonemin, a UV-screening liposoluble pigment with varied biotechnological applications in cosmetics and other industries. In this work we carried out a strain selection based on growth performance among 8 endolithic cyanobacteria of the genera Chroococcidiopsis, Gloeocapsa and Gloeocapsopsis isolated from non-saline rocks of the Atacama Desert. Then we investigated the influence of NaCl exposure on scytonemin production yield. Results in the selected strain (Chroococcidiopsis sp. UAM571) showed that rising concentrations of NaCl lead to a growth decrease while triggering a remarkable increase in the scytonemin content, reaching maximum values at 20 g L-1 of NaCl over 50-fold higher scytonemin contents than those obtained without NaCl. Altogether, these findings point out to cyanobacteria from the Atacama Desert as potentially suitable candidates for pilot-scale cultivation with biotechnological purposes, particularly to obtain scytonemin.

Interplay between desiccation and oxidative stress responses in iron-oxidizing acidophilic bacteria

Variations in water availability represent a foremost stress factor affecting the growth and survival of microorganisms. Acidophilic bioleaching bacteria are industrially applied for releasing metals from mineral sulphides, and they are considered extremely tolerant to oxidative conditions prevailing in acidic bioleaching environments. Such processes usually are performed in heaps and thus these microorganisms are also exposed to intermittent desiccations or high osmolarity periods that reduce the water availability. However, the tolerance to water stress and the molecular basis of adaptation to it are still largely unknown. The aim of this work was to determine the cellular response to desiccation stress and establish its relationship to oxidative stress response in the acidophilic iron-oxidizing bacteria Acidithiobacillus ferrooxidans ATCC 23270 and Leptospirillum ferriphilum DSM 14647. Results showed that the exposure of cell cultures to desiccation (0-120 min) led to a significant reduction in cell growth, and to an increase in content in reactive oxygen species in both bacteria. However, Leptospirillum ferriphilum turned out to be more tolerant than Acidithiobacillus ferrooxidans. In addition, the pre-treatment of the cell cultures with compatible solutes (trehalose and ectoine), and antioxidants (glutathione and cobalamin) restored all stress parameters to levels exhibited by the control cultures. To evaluate the role of the osmotic and redox homeostasis mechanisms in coping with desiccation stress, the relative expression of a set of selected genes was approached by RT-qPCR experiments in cells exposed to desiccation for 30 min. Results showed a generalized upregulation of genes that code for mechanosensitive channels, and enzymes related to the biosynthesis of compatible solutes and oxidative stress response in both bacteria. These data suggest that acidophiles show variable tolerance to desiccation and allow to establish that water stress can trigger oxidative stress, and thus anti-oxidative protection capability can be a relevant mechanism when cells are challenged by desiccation or other anhydrobiosis states.

Trichocoleus desertorum isolated from Negev desert petroglyphs: Characterization, adaptation and bioerosion potential

The Negev petroglyphs are considered valuable cultural heritage sites, but unfortunately, they are exposed to deterioration processes caused by anthropogenic and natural forces. Despite the many studies that have already pointed to the role of cyanobacteria in biogenic rock weathering, the knowledge involved in the process is still lacking. In this study, a cyanobacterial strain was isolated from the Negev Desert petroglyphs aiming to reveal its involvement in geochemical cycles and in the weathering processes of the rock substrate. The strain was characterized using morphological, molecular, and microscopic studies. The morphological research revealed a green-bluish, bundle-forming filamentous strain characterized by trichomes embedded in a common sheath. A combination of Nanopore and Illumina sequencing technologies facilitated the assembly of a near-complete genome containing 5,458,034 base pairs. A total of 5027 coding sequences were revealed by implementing PROKKA software. Annotation of five replicas of the 16S ribosomal RNA genes revealed that the Negev cyanobacteria isolate is closely (99.73 %) related to Trichocoleus desertorum LSB90_MW403957 isolated from the Sahara Desert, Algeria. The local strain was thus named Trichocoleus desertorum NBK24 CP116619. Several gene sequences that code for possible environmental adaptation mechanisms were found. Our study also identified genes for membrane transporters involved in the exchange of chemical elements, suggesting a possible interaction with rock minerals. Microscopic observations of T. desertorum NBK24 CP116619 infected onto calcareous stone slabs under laboratory conditions demonstrated the effect of the isolated cyanobacteria on stone surface degradation. In conclusion, the findings of this study further our understanding of terrestrial cyanobacterial genomes and functions and highlight the role of T. desertorum NBK24 CP116619 in stone weathering processes. This information may contribute to the creation of efficient restoration strategies for stone monuments affected by cyanobacteria.

Biochar-Associated Free Radicals Reduce Soil Bacterial Diversity: New Insight into Ecoenzymatic Stoichiometry

The toxicity of environmentally persistent free radicals (EPFRs), often generated during biochar production, on soil bacteria is still not truly reflected when considering the conditions in real soil. Herein, the influence of free radicals within biochar on soil bacteria was investigated from the perspectives of enzyme activity, community structure, and ecoenzymatic stoichiometry. Biochar addition enhanced the contents of EPFRs and derived hydroxyl radicals (•OH) in the soil, while it reduced bacterial alpha diversity by 5.06-35.44%. The results of redundancy analysis and inhibition experiments collectively demonstrated the key role of EPFRs and •OH in reducing the bacterial alpha diversity. Specifically, EPFRs and •OH increased the stoichiometric imbalance by promoting the release of dissolved organic carbon and ammonium N, thus aggravating the P limitation in soil. This was further confirmed by increased alkaline phosphatase activity from 702 to 874 nmol g-1 h-1. The P limitation induced by EPFRs and •OH decreased the bacterial alpha diversity, as evidenced by the negative correlation between P limitation and bacterial alpha diversity (r2 = -0.931 to -0.979, P < 0.01) and the structural equation model. The obtained results demonstrate a ubiquitous but previously overlooked mechanism for bacterial toxicity of biochar-associated free radicals, providing scientific guidance for safe utilization of biochar.

First characterization of cultivable extremophile Chroococcidiopsis isolates from a solar panel

Introduction

Microorganisms colonize a wide range of natural and artificial environments. Even though most of them are unculturable in laboratory conditions, some ecosystems are ideal niches for bioprospecting extremophiles with unique properties. Up today, there are few reports concerning microbial communities found on solar panels, a widespread, artificial, extreme habitat. Microorganisms found in this habitat belong to drought-, heat- and radiation-adapted genera, including fungi, bacteria, and cyanobacteria.

Methods

Here we isolated and identified several cyanobacteria from a solar panel. Then, some strains isolated were characterizated for their resistance to desiccation, UV-C exposition, and their growth on a range of temperature, pH, NaCl concentration or diverse carbon and nitrogen sources. Finally, gene transfer to these isolates was evaluated using several SEVA plasmids with different replicons to assess their potential in biotechnological applications.

Results and discussion

This study presents the first identification and characterization of cultivable extremophile cyanobacteria from a solar panel in Valencia, Spain. The isolates are members of the genera Chroococcidiopsis, Leptolyngbya, Myxacorys, and Oculatella all genera with species commonly isolated from deserts and arid regions. Four of the isolates were selected, all of them Chroococcidiopsis, and characterized. Our results showed that all Chroococcidiopsis isolates chosen were resistant up to a year of desiccation, viable after exposition to high doses of UV-C, and capable of being transformed. Our findings revealed that a solar panel is a useful ecological niche in searching for extremophilic cyanobacteria to further study the desiccation and UV-tolerance mechanisms. We conclude that these cyanobacteria can be modified and exploited as candidates for biotechnological purposes, including astrobiology applications.

The two-component response regulator OrrA confers dehydration tolerance by regulating avaKa expression in the cyanobacterium Anabaena sp. strain PCC 7120

The cyanobacterium Anabaena sp. strain PCC 7120 exhibits dehydration tolerance. The regulation of gene expression in response to dehydration is crucial for the acquisition of dehydration tolerance, but the molecular mechanisms underlying dehydration responses remain unknown. In this study, the functions of the response regulator OrrA in the regulation of salt and dehydration responses were investigated. Disruption of orrA abolished or diminished the induction of hundreds of genes in response to salt stress and dehydration. Thus, OrrA is a principal regulator of both stress responses. In particular, OrrA plays a crucial role in dehydration tolerance because an orrA disruptant completely lost the ability to regrow after dehydration. Moreover, in the OrrA regulon, avaKa encoding a protein of unknown function was revealed to be indispensable for dehydration tolerance. OrrA and AvaK are conserved among the terrestrial cyanobacteria, suggesting their conserved functions in dehydration tolerance in cyanobacteria.

Membrane composition and successful bioaugmentation. Studies of the interactions of model thylakoid and plasma cyanobacterial and bacterial membranes with fungal membrane-lytic enzyme Lecitase ultra

Cyanobacterial/bacterial consortia are frequently inoculated to soils to increase the soil fertility and to accelerate the biodegradation of organic pollutants. Moreover, such consortia can also be successfully applied in landfills especially for the biodegradation of plastic wastes. However, the bioaugmentation techniques turn out frequently inefficient due to the competition of the indigenous microorganisms attacking directly these inoculated or secreting to their surroundings cell wall and membrane-lytic enzymes. It can be hypothesized that the resistance of the microbial membrane to the enzymatic degradation is correlated with its lipid composition. To verify this hypothesis glycolipid and phospholipid Langmuir monolayers were applied as models of thylakoid and plasma cyanobacterial and bacterial membranes. Hybrid fungal enzyme Lecitase ultra joining the activity of lipase and phospholipase A1 was applied as the model of fungal membrane-lytic enzyme. It turned out that anionic thylakoid lipids sulfoquinovosyldiacylglycerol and phosphatidylglycerols were the main targets of Lecitase ultra in the model multicomponent thylakoid membranes. The resistance of the model plasma bacterial membranes to enzymatic degradation depended significantly to their composition. The resistance increased generally when the unsaturated lipids were exchanged to their saturated counterparts. However, most resistant turned out the membranes composed of unsaturated phosphatidylamine and saturated anionic phospholipids.

Salty Twins: Salt-Tolerance of Terrestrial Cyanocohniella Strains (Cyanobacteria) and Description of C. rudolphia sp. nov. Point towards a Marine Origin of the Genus and Terrestrial Long Distance Dispersal Patterns

The ability to adapt to wide ranges of environmental conditions coupled with their long evolution has allowed cyanobacteria to colonize almost every habitat on Earth. Modern taxonomy tries to track not only this diversification process but also to assign individual cyanobacteria to specific niches. It was our aim to work out a potential niche concept for the genus Cyanocohniella in terms of salt tolerance. We used a strain based on the description of C. rudolphia sp. nov. isolated from a potash tailing pile (Germany) and for comparison C. crotaloides that was isolated from sandy beaches (The Netherlands). The taxonomic position of C. rudolphia sp. nov. was evaluated by phylogenetic analysis and morphological descriptions of its life cycle. Salt tolerance of C. rudolphia sp. nov. and C. crotaloides was monitored with cultivation assays in liquid medium and on sand under salt concentrations ranging from 0% to 12% (1500 mM) NaCl. Optimum growth conditions were detected for both strains at 4% (500 mM) NaCl based on morpho-anatomical and physiological criteria such as photosynthetic yield by chlorophyll a fluorescence measurements. Taking into consideration that all known strains of this genus colonize salty habitats supports our assumption that the genus might have a marine origin but also expands colonization to salty terrestrial habitats. This aspect is further discussed, including the ecological and biotechnological relevance of the data presented.

Mineral Matrix Effects on Pyrolysis Products of Kerogens Infer Difficulties in Determining Biological Provenance of Macromolecular Organic Matter at Mars

Ancient martian organic matter is likely to take the form of kerogen-like recalcitrant macromolecular organic matter (MOM), existing in close association with reactive mineral surfaces, especially iron oxides. Detecting and identifying a biological origin for martian MOM will therefore be of utmost importance for life-detection efforts at Mars. We show that Type I and Type IV kerogens provide effective analogues for putative martian MOM of biological and abiological (meteoric) provenances, respectively. We analyze the pyrolytic breakdown products when these kerogens are mixed with mineral matrices highly relevant for the search for life on Mars. We demonstrate that, using traditional thermal techniques as generally used by the Sample Analysis at Mars and Mars Organic Molecule Analyser instruments, even the breakdown products of highly recalcitrant MOM are transformed during analysis in the presence of reactive mineral surfaces, particularly iron. Analytical transformation reduces the diagnostic ability of this technique, as detected transformation products of both biological and abiological MOM may be identical (low molecular weight gas phases and benzene) and indistinguishable. The severity of transformational effects increased through calcite < kaolinite < hematite < nontronite < magnetite < goethite. Due to their representation of various habitable aqueous environments and the preservation potential of organic matter by iron, it is not advisable to completely avoid iron-rich strata. We conclude that hematite-rich localities, with evidence of extensive aqueous alteration of originally reducing phases, such as the Vera Rubin Ridge, may be relatively promising targets for identifying martian biologically sourced MOM.

Comprehensive Metabolic and Taxonomic Reconstruction of an Ancient Microbial Mat From the McMurdo Ice Shelf (Antarctica) by Integrating Genetic, Metaproteomic and Lipid Biomarker Analyses

Paleobiological reconstructions based on molecular fossils may be limited by degradation processes causing differential preservation of biomolecules, the distinct taxonomic specificity of each biomolecule type, and analytical biases. Here, we combined the analysis of DNA, proteins and lipid biomarkers using 16S and 18S rRNA gene metabarcoding, metaproteomics and lipid analysis to reconstruct the taxonomic composition and metabolisms of a desiccated microbial mat from the McMurdo Ice Shelf (MIS) (Antarctica) dated ~1,000 years BP. The different lability, taxonomic resolution and analytical bias of each biomolecule type led to a distinct microbial community profile. DNA analysis showed selective preservation of DNA remnants from the most resistant taxa (e.g., spore-formers). In contrast, the proteins profile revealed microorganisms missed by DNA sequencing, such as Cyanobacteria, and showed a microbial composition similar to fresh microbial mats in the MIS. Lipid hydrocarbons also confirmed Cyanobacteria and suggested the presence of mosses or vascular plant remnants from a period in Antarctica when the climate was warmer (e.g., Mid-Miocene or Eocene). The combined analysis of the three biomolecule types also revealed diverse metabolisms that operated in the microbial mat before desiccation: oxygenic and anoxygenic photosynthesis, nitrogen fixation, nitrification, denitrification, sulfur reduction and oxidation, and methanogenesis. Therefore, the joint analysis of DNA, proteins and lipids resulted in a powerful approach that improved taxonomic and metabolic reconstructions overcoming information gaps derived from using individual biomolecules types.

Acclimation response and ability of growth and photosynthesis of terrestrial cyanobacterium Cylindrospermum sp. strain FS 64 under combined environmental factors

This investigation tested the hypothesis that the native cyanobacteria can acclimatize and grow under the combination of environmental factors and/or how does their process change with the age of culture? Here, we tried to combine multiple factors to simulated what happens in natural ecosystems. We analyzed the physiological response of terrestrial cyanobacterium, Cylindrospermum sp. FS 64 under combination effect of different salinity (17, 80, and 160 mM) and alkaline pHs (9 and 11) at extremely limited carbon dioxide concentration (no aeration) up to 96 h. Our evidence showed that growth, biomass, photosystem II, and phycobilisome activity significantly increased under 80 mM salinity and pH 11. In addition, this combined condition led to a significant increase in maximum light-saturated photosynthesis activity and photosynthetic efficiency. While phycobilisomes and photosystem activity decreased by increasing salinity (160 mM) which caused decreased growth rates after 96 h. The single-cell study (CLMS microscopy) which illustrated the physiological state of the individual and active-cell confirmed the efficiency and effectiveness of both photosystems and phycobilisome under the combined effect of 80 mM salinity and pH 11.

Comprehensive effects of salt stress and peanut cultivars on the rhizosphere bacterial community diversity of peanut

Plant rhizosphere bacterial communities are central to plant growth and stress tolerance, which differ across cultivars and external environments. The goal of this study was to assess the comprehensive effects of salt stress and peanut cultivars on rhizosphere bacterial community diversity. In this study, we investigated the effects of salt stress on peanut morphology and pod yield and the associated rhizosphere bacterial diversity using statistical analysis and 16S rRNA gene sequencing, respectively. Statistical analysis exhibited that salt stress indeed affected peanut growth and pod yield, and various peanut cultivars showed divergences. Taxonomic analysis showed that the bacterial community predominantly consisted of phyla Actinobacteria, Proteobacteria, Chloroflexi, Acidobacteria, and Cyanobacteria in peanut rhizosphere soils. Among these bacteria, numbers of beneficial bacteria Cyanobacteria and Proteobacteria increased, especially in the salt-resistant cultivars, while that of Acidobacteria decreased after salt treatment. Nitrogen-fixing bacterium Rhizobium closely related to peanut nodulation was significantly improved in rhizosphere soils of salt-resistant cultivars after salt treatment. Metabolic function prediction showed that the percentages of reads categorized to signaling transduction and inorganic ion transport and metabolism were higher in the salt-treated soils, which may be conducive to peanut survival and salt tolerance to some extent. The study is, therefore, crucially important to develop the foundation for improving the salt tolerance of various peanut cultivars via modifying the soil bacterial community.

Transformation of Cyanobacterial Biomolecules by Iron Oxides During Flash Pyrolysis: Implications for Mars Life-Detection Missions

Answering the question of whether life ever existed on Mars is a key goal of both NASA's and ESA's imminent Mars rover missions. The obfuscatory effects of oxidizing salts, such as perchlorates and sulfates, on organic matter during thermal decomposition analysis techniques are well established. Less well studied are the transformative effects of iron oxides and (oxy)hydroxides, which are present in great abundances in the martian regolith. We examined the products of flash pyrolysis-gas chromatography-mass spectrometry (a technique analogous to the thermal techniques employed by past, current, and future landed Mars missions) which form when the cyanobacteria Arthrospira platensis are heated in the presence of a variety of Mars-relevant iron-bearing minerals. We found that iron oxides/(oxy)hydroxides have transformative effects on the pyrolytic products of cyanobacterial biomolecules. Both the abundance and variety of molecular species detected were decreased as iron substrates transformed biomolecules, by both oxidative and reductive processes, into lower fidelity alkanes, aromatic and aryl-bonded hydrocarbons. Despite the loss of fidelity, a suite that contains mid-length alkanes and polyaromatic hydrocarbons and/or aryl-bonded molecules in iron-rich samples subjected to pyrolysis may allude to the transformation of cyanobacterially derived mid-long chain length fatty acids (particularly unsaturated fatty acids) originally present in the sample. Hematite was found to be the iron oxide with the lowest transformation potential, and because this iron oxide has a high affinity for codeposition of organic matter and preservation over geological timescales, sampling at Mars should target sediments/strata that have undergone a diagenetic history encouraging the dehydration, dihydroxylation, and oxidation of more reactive iron-bearing phases to hematite by looking for (mineralogical) evidence of the activity of oxidizing, acidic/neutral, and either hot or long-lived fluids.

Transcriptome and metabolome analyses of response of Synechocystis sp. PCC 6803 to methyl viologen

The toxicity of methyl viologen (MV) to organisms is mainly due to the oxidative stress caused by reactive oxygen species produced from cell response. This study mainly investigated the response of Synechocystis sp. PCC 6803 to MV by combining transcriptomic and metabolomic analyses. Through transcriptome sequencing, we found many genes responding to MV stress, and analyzed them by weighted gene co-expression network analysis (WGCNA). Meanwhile, many metabolites were also found by metabolomic analysis to be regulated post MV treatment. Based on the analysis results of Kyoto encyclopedia of genes and genomes (KEGG) of the differentially expressed genes (DEGs) in the transcriptome and the differential metabolites in the metabolome, the dynamic changes of genes and metabolites involved in ten metabolic pathways in response to MV were analyzed. The results indicated that although the oxidative stress caused by MV was the strongest at 6 h, the proportion of the upregulated genes and metabolites involved in these ten metabolic pathways was the highest. Photosynthesis positively regulated the response to MV-induced oxidative stress, and the regulation of environmental information processing was inhibited by MV. Other metabolic pathways played different roles at different times and interacted with each other to respond to MV. This study comprehensively analyzed the response of Synechocystis sp. PCC 6803 to oxidative stress caused by MV from a multi-omics perspective, with providing key data and important information for in-depth analysis of the response of organisms to MV, especially photosynthetic organisms. KEY POINTS: • Methyl viologen (MV) treatment caused regulatory changes in genes and metabolites. • Proportion of upregulated genes and metabolites was the highest at 6-h MV treatment. • Photosynthesis and environmental information processing involved in MV response.

Exposure of cyanobacterium Nostoc sp. to the Mars-like stratosphere environment

During the HH-19-2 flight mission of the Chinese Scientific Experimental System, dried Nostoc sp. cells were exposed to the stratosphere environment (32,508 m altitude) for 3 h and 22 min. The atmospheric pressure, temperature, relative humidity, and ionizing and non-ionizing radiation levels at that altitude are similar to those on the surface of Mars. Although analyses revealed decreased photosynthetic activity, a decline in autofluorescence, and damage to the cellular morphology in the flight-exposed sample, the death rate was low (28%). Physiological changes were not obvious after the exposure to the Mars-like vacuum conditions. The ground-exposed samples showed a similar trend to the flight-exposed samples, but the damage was relatively slight. RNA-sequencing data revealed a number of affected metabolic pathways: photosynthetic system and CO₂ fixation function, activation of antioxidant systems, heat shock protein, DNA repair, and protein synthesis. Results suggest that Nostoc sp. has the potential to survive in a Mars-like environment and that it may be a suitable pioneer species to colonize Mars in the future in closed life-support systems (base) or in localities with relatively suitable conditions for life, such as localities with water available.

Global Warming, Climate Change, and Environmental Pollution: Recipe for a Multifactorial Stress Combination Disaster

Global warming, climate change, and environmental pollution present plants with unique combinations of different abiotic and biotic stresses. Although much is known about how plants acclimate to each of these individual stresses, little is known about how they respond to a combination of many of these stress factors occurring together, namely a multifactorial stress combination. Recent studies revealed that increasing the number of different co-occurring multifactorial stress factors causes a severe decline in plant growth and survival, as well as in the microbiome biodiversity that plants depend upon. This effect should serve as a dire warning to our society and prompt us to decisively act to reduce pollutants, fight global warming, and augment the tolerance of crops to multifactorial stress combinations.

Responses of a hot spring cyanobacterium under ultraviolet and photosynthetically active radiation: photosynthetic performance, antioxidative enzymes, mycosporine-like amino acid profiling and its antioxidative potentials

This study summarizes the response of a hot spring cyanobacterium Fischerella sp. strain HKAR-14, under simulated light conditions of ultraviolet radiation (UVR), photosynthetically active radiation (PAR), PAR + UV-A (PA) and PAR + UV-A + UV-B (PAB). Exposure to UVR caused a decline in growth and Chl a while total carotene content increased under PA and PAB. Maximum photochemical efficiency of photosystem II (F v /F m) and relative electron transport rate decreased significantly in PA and PAB exposure. Higher non-photochemical quenching and lower photochemical quenching values were observed in UVR-exposed samples as compared to the control. Levels of intracellular reactive oxygen species (ROS) increased significantly in PAB and PA. Fluorescence microscopic images showed an increase in green fluorescence, indicating the generation of ROS in UVR. The antioxidant machinery including superoxide dismutase, catalase and peroxidase showed an increase of 1.76-fold and 2.5-fold superoxide dismutase, 2.4-fold and 3.7-fold catalase, 1.83-fold and 2.5-fold peroxidase activities under PA and PAB, respectively. High-performance liquid chromatography equipped with photodiode array detector, electrospray ionization mass spectrometry, Fourier-transform infrared spectroscopy and nuclear magnetic resonance spectroscopy analyses reveal the occurrence of a single mycosporine-like amino acid, shinorine (λ max 332.3 ± 2 nm, m/z 333.1), with a retention time of 1.157 min. The electrochemical characterization of shinorine was determined by cyclic voltammetry. The shinorine molecule possesses electrochemical activity and represents diffusion-controlled process in 0.1 M (pH 7.0) phosphate buffer. An antioxidant assay of shinorine showed its efficient activity as antioxidant which increased in a dose-dependent manner.

Cyanobacteria and Algae in Clouds and Rain in the Area of puy de Dôme, Central France

The atmosphere contains diverse living microbes, of which the heterotrophic community has been the best studied. Microbes with other trophic modes, such as photoautotrophy, have received much less attention. In this study, culture-independent and dependent methods were used to examine the presence and diversity of oxygenic photoautotrophic microbes in clouds and rain collected at or around puy de Dôme Mountain, central France. Cloud water was collected from the summit of puy de Dôme (1,465 m above sea level [a.s.l.]) for cultivation and metagenomic analysis. Cyanobacteria, diatoms, green algae, and other oxygenic photoautotrophs were found to be recurrent members of clouds, while green algae affiliated with the Chlorellaceae were successfully cultured from three different clouds. Additionally, rain samples were collected below the mountain from Opme meteorological station (680 m a.s.l.). The abundance of chlorophyll a-containing cells and the diversity of cyanobacteria and green algae in rain were assessed by flow cytometry and amplicon sequencing. The corresponding downward flux of chlorophyll a-containing organisms to the ground, entering surface ecosystems with rain, varied with time and was estimated to be between ∼1 and >300 cells cm^-2 day^-1 during the sampling period. Besides abundant pollen from Pinales and Rosales, cyanobacteria of the Chroococcidiopsidales and green algae of the Trebouxiales were dominant in rain samples. Certain members of these taxa are known to be ubiquitous and stress tolerant and could use the atmosphere for dispersal. Overall, our results indicate that the atmosphere carries diverse, viable oxygenic photoautotrophic microbes and acts as a dispersal vector for this microbial guild.IMPORTANCE Information regarding the diversity and abundance of oxygenic photoautotrophs in the atmosphere is limited. More information from diverse locations is needed. These airborne organisms could have important impacts upon atmospheric processes and on the ecosystems they enter after deposition. Oxygenic photoautotrophic microbes are integral to ecosystem functioning, and some have the potential to affect human health. A better understanding of the diversity and the movements of these aeolian dispersed organisms is needed to understand their ecology, as well as how they could affect ecosystems and human health.

Extracellular Vesicles: An Overlooked Secretion System in Cyanobacteria

In bacteria, the active transport of material from the interior to the exterior of the cell, or secretion, represents a very important mechanism of adaptation to the surrounding environment. The secretion of various types of biomolecules is mediated by a series of multiprotein complexes that cross the bacterial membrane(s), each complex dedicated to the secretion of specific substrates. In addition, biological material may also be released from the bacterial cell in the form of vesicles. Extracellular vesicles (EVs) are bilayered, nanoscale structures, derived from the bacterial cell envelope, which contain membrane components as well as soluble products. In cyanobacteria, the knowledge regarding EVs is lagging far behind compared to what is known about, for example, other Gram-negative bacteria. Here, we present a summary of the most important findings regarding EVs in Gram-negative bacteria, discussing aspects of their composition, formation processes and biological roles, and highlighting a number of technological applications tested. This lays the groundwork to raise awareness that the release of EVs by cyanobacteria likely represents an important, and yet highly disregarded, survival strategy. Furthermore, we hope to motivate future studies that can further elucidate the role of EVs in cyanobacterial cell biology and physiology.

Simultaneous Metabarcoding of Eukaryotes and Prokaryotes to Elucidate the Community Structures within Tardigrade Microhabitats

Tardigrades are microscopic invertebrates that can withstand complete desiccation, but their interspecies interactions with prokaryotes and eukaryotes within their microhabitat remain relatively unexplored. Here, I utilized combined metabarcoding of eukaryotes and prokaryotes to simultaneously identify entire community structures within xeric and mesic mosses that harbor tardigrades. The populations of organisms within the microecosystems were successfully determined in 45 xeric moss samples and 47 mesic moss samples. Organismal composition was largely consistent regardless of the moss/lichen substrate, but significantly varied in the two tested locations, possibly because of the differences in environmental humidity. Xeric mosses containing xerophilic tardigrades and other anhydrobiotic invertebrates tended to have significantly limited biological diversity and prokaryotic population dominated by cyanobacteria, suggesting a selection due to extreme desiccation. A combined metabarcoding approach to identify both eukaryotes and prokaryotes can successfully elucidate community structures within microscopic ecosystems, and this can be a potential approach to study the microecology of meiofauna, including tardigrades.

Influence of salt stress on the rhizosphere soil bacterial community structure and growth performance of groundnut (Arachis hypogaea L.)

Soil salinity is regarded as severe environmental stress that can change the composition of rhizosphere soil bacterial community and import a plethora of harms to crop plants. However, relatively little is known about the relationship between salt stress and root microbial communities in groundnuts. The goal of this study was to assess the effect of salt stress on groundnut growth performance and rhizosphere microbial community structure. Statistical analysis exhibited that salt stress indeed affected groundnut growth and pod yield. Further taxonomic analysis showed that the bacterial community predominantly consisted of phyla Proteobacteria, Actinobacteria, Saccharibacteria, Chloroflexi, Acidobacteria, and Cyanobacteria. Among these bacteria, numbers of Cyanobacteria and Acidobacteria mainly increased, while that of Actinobacteria and Chloroflexi decreased after salt treatment via taxonomic and qPCR analysis. Moreover, Sphingomonas and Microcoleus as the predominant genera in salt-treated rhizosphere soils might enhance salt tolerance as plant growth-promoting rhizobacteria. Metagenomic profiling showed that series of sequences related to signaling transduction, posttranslational modification, and chaperones were enriched in the salt-treated soils, which may have implications for plant survival and salt tolerance. These data will help us better understand the symbiotic relationship between the dominant microbial community and groundnuts and form the foundation for further improvement of salt tolerance of groundnuts via modification of soil microbial community.

Effect of Drought Stress and Developmental Stages on Microbial Community Structure and Diversity in Peanut Rhizosphere Soil

Background: Peanut (Arachis hypogaea L.), an important oilseed and food legume, is widely cultivated in the semi-arid tropics. Drought is the major stress in this region which limits productivity. Microbial communities in the rhizosphere are of special importance to stress tolerance. However, relatively little is known about the relationship between drought and microbial communities in peanuts. Method: In this study, deep sequencing of the V3-V4 region of the 16S rRNA gene was performed to characterize the microbial community structure of drought-treated and untreated peanuts. Results: Taxonomic analysis showed that Actinobacteria, Proteobacteria, Saccharibacteria, Chloroflexi, Acidobacteria and Cyanobacteria were the dominant phyla in the peanut rhizosphere. Comparisons of microbial community structure of peanuts revealed that the relative abundance of Actinobacteria and Acidobacteria dramatically increased in the seedling and podding stages in drought-treated soil, while that of Cyanobacteria and Gemmatimonadetes increased in the flowering stage in drought-treated rhizospheres. Metagenomic profiling indicated that sequences related to metabolism, signaling transduction, defense mechanism and basic vital activity were enriched in the drought-treated rhizosphere, which may have implications for plant survival and drought tolerance. Conclusion: This microbial communities study will form the foundation for future improvement of drought tolerance of peanuts via modification of the soil microbes.

Terraforming: synthetic biology's final frontier

Synthetic biology, the design and synthesis of synthetic biological systems from DNA to whole cells, has provided us with the ultimate tools for space exploration and colonisation. Herein, we explore some of the most significant advances and future prospects in the field of synthetic biology, in the context of astrobiology and terraforming.