Effects of thermal acclimation and photoacclimation on lipophilic pigments in an invasive and a native cyanobacterium of temperate regions

The freshwater cyanobacterium Cylindrospermopsis raciborskii spreads from tropical to temperate regions worldwide. This entails acclimation to varied light and temperature conditions. We studied the thermal and light acclimation of the photosynthetic machinery of C. raciborskii by monitoring alteration of the chlorophyll a and carotenoid content in German strains of C. raciborskii, in African and Australian strains of C. raciborskii, and in German strains of Aphanizomenon gracile, a native cyanobacterium belonging to the same order (Nostocales). Our results showed that temperate and tropical C. raciborskii strains did not differ in pigment acclimation to light and temperature. In contrast, the ratio of photoprotective carotenoids (namely the carotenoid glycoside 4-hydroxymyxol glycoside [aphanizophyll]) to chlorophyll a increased significantly more in C. raciborskii in comparison with A. gracile (1) with decreasing temperatures from 20 to 10°C and a moderate light intensity of 80?µmol photons m^?2?s^?1 and (2) with increasing light intensities at a suboptimal temperature of 15°C, compared to 20°C. We conclude that below 20°C photoinhibition is avoided by greater photoprotection in the invasive species C. raciborskii compared to the native species A. gracile.     

CYLINDROSPERMOPSIS RACIBORSKII (CYANOBACTERIA) INVASION AT MID‐LATITUDES: SELECTION,WIDE PHYSIOLOGICAL TOLERANCE,ORGLOBALWARMING?1

The tropical bloom‐forming cyanobacterium Cylindrospermopsis raciborskii (Woloszynska) Seenaya et Subba Raju is causing increasing concern because of its potential toxicity and invasive behavior at mid‐latitudes. This species has recently been identified in several temperate areas and was first reported in France in 1994, but the mechanisms underlying this acclimation process remain to be elucidated. We performed a range of laboratory experiments in an attempt to identify the physiological characteristics that could account for this behavior. We investigated the three following hypotheses: 1) clones of C. raciborskii adapted to temperate climate have been selected as it advanced north, 2) C. raciborskii has high physiological tolerance that allows it to prosper in a wide range of conditions, and 3) changes inclimate (global warming) have favored the development of C. raciborskii in mid‐latitudes. Ten strains of C. raciborskii from Australia n=1), Brazil (2), France (2), Germany (1), Hungary (1), Mexico (1), and Senegal (2) were cultured at different temperatures and light intensities. The in vitro growth parameters (μ and T_opt) were the same for the tropical and temperate strains. All 10 strains displayed positive net growth in a wide range of temperatures (from 20 to 35°C) and light intensities (from 30 to 400 μmol photons·m^?2·s^?1), with maximum growth rates at around 30°C and 80 μmol photons·m^?2·s^?1. This suggests that the colonization of mid‐latitudes by C. raciborskii may result from a combination of its ability to tolerate a rather wide range of climatic conditions and the global warming phenomenon, which provides this species with better environmental conditions for its growth.     

Mesocosm experiments on nutrient and fish effects on shallow lake food webs in a Mediterranean climate

1. Nutrient and fish manipulations in mesocosms were carried out on food‐web interactions in a Mediterranean shallow lake in south‐east Spain. Nutrients controlled biomass of phytoplankton and periphyton, while zooplankton, regulated by planktivorous fish, influenced the relative percentages of the dominant phytoplankton species. 2. Phytoplankton species diversity decreased with increasing nutrient concentration and planktivorous fish density. Cyanobacteria grew well in both turbid and clear‐water states. 3. Planktivorous fish increased concentrations of soluble reactive phosphorus (SRP). Larger zooplankters (mostly Ceriodaphnia and copepods) were significantly reduced when fish were present, whereas rotifers increased, after fish removal of cyclopoid predators and other filter feeders (cladocerans, nauplii). The greatest biomass and diversity of zooplankton was found at intermediate nutrient levels, in mesocosms without fish and in the presence of macrophytes. 4. Water level decrease improved underwater light conditions and favoured macrophyte persistence. Submerged macrophytes (Chara spp.) outcompeted algae up to an experimental nutrient loading equivalent to added concentrations of 0.06 mg L^?1 PO₄‐P and 0.6 mg L^?1 NO₃‐N, above which an exponential increase in periphyton biomass and algal turbidity caused characean biomass to decline. 5. Declining water levels during summer favoured plant‐associated rotifer species and chroococcal cyanobacteria. High densities of chroococcal cyanobacteria were related to intermediate nutrient enrichment and the presence of small zooplankton taxa, while filamentous cyanobacteria were relatively more abundant in fishless mesocosms, in which Crustacea were more abundant, and favoured by dim underwater light. 6. Benthic macroinvertebrates increased significantly at intermediate nutrient levels but there was no relationship with planktivorous fish density. 7. The thresholds of nutrient loading and in‐lake P required to avoid a turbid state and maintain submerged macrophytes were lower than those reported from temperate shallow lakes. Mediterranean shallow lakes may remain turbid with little control of zooplankton on algal biomass, as observed in tropical and subtropical lakes. Nutrient loading control and macrophyte conservation appear to be especially important in these systems to maintain high water quality.     

Comparison of the Photosynthetic Yield of Cyanobacteria and Green Algae: Different Methods Give Different Answers

The societal importance of renewable carbon-based commodities and energy carriers has elicited a particular interest for high performance phototrophic microorganisms. Selection of optimal strains is often based on direct comparison under laboratory conditions of maximal growth rate or additional valued features such as lipid content. Instead of reporting growth rate in culture, estimation of photosynthetic efficiency (quantum yield of PSII) by pulse-amplitude modulated (PAM) fluorimetry is an often applied alternative method. Here we compared the quantum yield of PSII and the photonic yield on biomass for the green alga Chlorella sorokiniana 211-8K and the cyanobacterium Synechocystis sp. PCC 6803. Our data demonstrate that the PAM technique inherently underestimates the photosynthetic efficiency of cyanobacteria by rendering a high F₀ and a low F_M, specifically after the commonly practiced dark pre-incubation before a yield measurement. Yet when comparing the calculated biomass yield on light in continuous culture experiments, we obtained nearly equal values for both species. Using mutants of Synechocystis sp. PCC 6803, we analyzed the factors that compromise its PAM-based quantum yield measurements. We will discuss the role of dark respiratory activity, fluorescence emission from the phycobilisomes, and the Mehler-like reaction. Based on the above observations we recommend that PAM measurements in cyanobacteria are interpreted only qualitatively.     

REEVALUATION OF THE NITROGEN FIXATION BEHAVIOR IN THE MARINE NON‐HETEROCYSTOUS CYANOBACTERIUM LYNGBYA MAJUSCULA1

Lyngbya majuscula Harvey ex Gomont is a common marine cyanobacterium in tropical and subtropical near‐shore waters. A few reports have indicated that L. majuscula fixes nitrogen only in the light. Because this feature is uncommon among non‐heterocystous cyanobacteria, we attempted a reevaluation. Nitrogenase activity, regulation, and localization were examined over diel cycles on natural populations of L. majuscula growing in subtidal zones off Zanzibar in the western Indian Ocean. The data show that L. majuscula fixed nitrogen and synthesized nitrogenase in all cells during the dark phase of a diel cycle. During the light phase, nitrogenase was degraded to undetectable levels.     

Production,by filamentous,nitrogen-fixing cyanobacteria,of a bacteriocin and of other antibiotics that kill related strains

Colonies of sixty-five filamentous cyanobacteria were screened for the production of temperate phages and/or antibiotics on solid medium. None of them was observed to release phages. However, seven N₂-fixing strains were found to produce antibiotics very active against other cyanobacteria. The antibiotic produced by Nostoc sp. 78-11 A-E represents a bacteriocin of low molecular weight. Nostoc sp. ATCC 29132 appears to secrete, together with an antibiotic, a protein that inhibits its action.     

Effects of intensity and quality of light on phycocyanin production by a marine cyanobacterium Synechococcus sp. NKBG 042902

Among 150 strains, including marine cyanobacteria isolated from coastal areas of Japan and a freshwater cyanobacterium from the IAM collection, Spirulina platensis IAM M-135, the marine cyanobacterium Synechococcus sp. NKBG 042902 contained the highest amount of phycocyanin (102 mg/g dry cell weight). We have proposed that the cyanobacterium could be an alternative producer for phycocyanin. The effects of light intensity and light quality on the phycocyanin content in cells of Synechococcus sp. NKBG 042902 were investigated. When the cyanobacterium was cultured under illumination of 25 mol m^–2 s^–1 using a cool-white fluorescent lamp, the phycocyanin content was highest, and the phycocyanin and biomass productivities were 21 mg 1^–1 day^–1 and 100 mg 1^–1 day^–1 respectively. Red light was essential for phycocyanin production by this cyanobacterium. Phycocyanin and biomass production were carried out by the cyanobacterium cultures grown under only red light (peak wavelength at 660 nm) supplied from light-emitting diodes (LED). Maximum phycocyanin and biomass productivities were 24 mg 1^–1 day^–1 and 130 mg 1^–1 day^–1 when the light intensity of the LED was 55 mol m^–2 s^–1.     

GROWTH,PHYSIOLOGY, AND ULTRASTRUCTURE OF A DIAZOTROPHIC CYANOBACTERIUM,CYANOTHECE SP. STRAIN ATCC 51142, IN MIXOTROPHIC AND CHEMOHETEROTROPHIC CULTURES1

The growth, physiology, and ultrastructure of the marine, unicellular, diazotrophic cyanobacterium, Cyanothece sp. strain ATCC 51142, was examined under mixotrophic and chemoheterotrophic conditions. Several organic substrates were tested for the capacity to support heterotrophic growth. Glycerol was the only substrate capable of enhancing mixotrophic growth in the light and supporting chemoheterotrophic growth in the dark. Dextrose enhanced mixotrophic growth but could not support chemoheterotrophic growth. Chemoheterotrophic cultures in continuous darkness grew faster and to higher densities than photoautotrophic cultures, thus demonstrating the great respiratory capacity of this cyanobacterial strain. Only small differences in the pigment content and ultrastructure of the heterotrophic strains were observed in comparison to photoautotrophic control strains. The chemoheterotrophic strain grown in continuous darkness and the mixotrophic strain grown in light/dark cycles exhibited daily metabolic oscillations in N₂ fixation and glycogen accumulation similar to those manifested in photoautotrophic cultures grown in light/dark cycles or continuous light. This “temporal separation” helps protect O₂-sensitive N₂ fixation from photosynthetic O₂ evolution. The rationale for cyclic glycogen accumulation in cultures with an ample source of organic carbon substrate is unclear, but the observation of similar daily rhythmicities in cultures grown in light/dark cycles, continuous light, and continuous dark suggests an underlying circadian mechanism.     

Effects of toxic and non-toxic cyanobacteria on the life history of tropical and temperate cladocerans

1. This study compares the effects of four toxic strains of Microcystis aeruginosa on tropical and temperate Cladocera. Survival was tested in acute toxicity experiments using Microcystis alone or in mixtures with the edible green algae Ankistrodesmus falcatus. The effect of chronic exposure on population growth was estimated in life‐table experiments by varying the proportion of Microcystis and the green alga. Nutritional deficiency was assessed using a non‐toxic cyanobacterium in a zooplankton growth experiment. Feeding inhibition was tested using a C‐labelled green alga as a tracer in mixtures with toxic Microcystis.
2. Toxicity varied consistently between Microcystis strains, while sensitivity varied consistently between cladoceran species. However, no relationship was found between sensitivity and geographical origin or cladoceran body size. Two small‐bodied cladocerans from the same tropical lake, Ceriodaphnia cornuta and Moinodaphnia macleayi, were the least sensitive and most sensitive species, respectively.
3. Surprisingly, two small tropical cladocerans survived longer without food than did three large Daphnia species and a third small tropical species.
4. Each of the three tropical Microcystis strains strongly reduced the population growth rate (little ‘r’) and reproductive output of each cladoceran, this reduction being proportional to the percentage of toxic cells in the diet.
5. As the sole food source, the non‐toxic cyanobacterium, Synechococcus elongatus, supported poor growth in M. macleayi. The nutritional deficiency was overcome when Synechococcus was mixed with either Ankistrodesmus or an emulsion rich in omega‐3 fatty acids.
6. Microcystis inhibited the feeding rate of two cladocerans, even when it comprised only 5% of a mixture with the green algae A. falcatus.
7. Differences in sensitivity to the toxic cyanobacterium appear to be associated with differences in life history between the cladoceran species rather than differences between tropical and temperate taxa. Slow‐growing species that are resistant to starvation appear less sensitive to toxic Microcystis than fast‐growing species, which also tend to die more quickly in the absence of food.     

Dinitrogen fixation (C2H2 reduction) by bacterial strains at various temperatures

Acetylene-reducing activities (ARA) of strains ofEnterobacter agglomerans, Azospirillum brasilense, Azotobacter chroococcum, and Bacillus, isolated from temperate or tropical soils, were compared at different temperatures to study temperature adaptability. All Enterobacter strains and Bacillus strain C-11-25 reduced C₂H₂ at temperatures as low as 5°C. ARA by Enterobacter strains declined sharply above 30°C but ARA by Bacillus strain C-11-25 continued to increase with an increase in temperature.A. brasilense strain sp 245, isolated from wheat roots in Brazil, reduced more C₂H₂ at lower temperatures than strain Cd, isolated from a Californian soil. Similarly, the temperate strain ofA. chroococcum was a better N₂ fixer than the tropicalA. chroococcum strain at lower temperatures. Tropical strains ofA. brasilense andA. chroococcum reduced more C₂H₂ than temperate strains at higher temperatures. Therefore, it appears that temperate and tropical N₂-fixing organisms adapt themselves to their particular environment and should have more potential to benefit crops grown at the particular temperatures favorable to them. Only Bacillus strain C-11-25 has potential to benefit both temperate and tropical crops because it reduced significant acetylene over a wide temperature range.     

Phylogenetic relationships between geographically separate Phormidium cyanobacteria: is there a link between north and south polar regions?

We present a phytogeographical comparison between polar (Arctic and Antarctic) and non-polar strains of the cyanobacterial genus Phormidium, which plays a key role in Arctic and Antarctic ecosystems as primary producer. A total of 26 Phormidium strains were studied using a polyphasic approach, 18 from Arctic (Svalbard, Ellesmere Island and Scandinavian Arctic—Abisko) and Antarctic (Antarctic Peninsula—King George and James Ross Island) regions, and 8 from temperate sites (mostly situated in Central Europe). A phylogenetic tree was constructed and compared with similar 16S rRNA sequences retrieved from Genbank. Within the Phormidium autumnale cluster, genetic similarity of 16S rDNA was more related to geographical proximity of strain origin than to morphological similarity. No genetic identity of Phormidium strains from north and south polar regions was found. The cluster Phormidium autumnale apparently belongs to generic entities in which geographical limitation plays a prominent role. However, the cyanobacterial strains found in Europe suggest that the distribution areas of some Phormidium cyanobacteria overlap. The Phormidium autumnale cluster is evidently a very characteristic type and represents an isolated clade within the traditional genus Phormidium. According to morphological features and the structure of trichomes, it is most similar and thus probably belongs to the genus Microcoleus.     

Heterotrophic eubacteria isolated from cultures of the cyanobacterium,spirulina maxima

Three distinct heterotrophic eubacterial strains were isolated from mixotrophic cultures of the filamentous cyanobacterium, Spirulina maxima (Gom) Geitl. Spirulina spp. are considered to be prime candidates for the phototrophic production of biomass protein, particularly in developing countries. These cyanobacteria are extreme alkaliphiles and halophiles, making their production in arid regions promising. Most previous studies on the eubacteria which live in Spirulina culture systems have focused on determining the possible presence of pathogenic species in biomass protein. Little has been done to understand the symbiotic relationships between the cyanobacterium and its eubacterial cosymbionts. From the perspective of a heterotrophic eubacterium, autotrophic cultural systems of Spirulina have limited carbon and energy resources, being limited to cyanobacterial exudates. In this study, three eubacterial strains were isolated and studied. One strain, a Gram-negative, non-sporing, motile rod, grew exceptionally well in a mineral salts medium where only a small amount of a single low molecular weight organic compound (e.g., acetate) was supplied as sole energy source. This strain was also extremely euryresponsive with respect to salinity and alkalinity as well. Two less well-adapted eubacterial strains are also described.     

Genetically engineering cyanobacteria to convert CO2, water,and light into the long-chain hydrocarbon farnesene

Genetically engineered cyanobacteria offer a shortcut to convert CO₂ and H₂O directly into biofuels and high value chemicals for societal benefits. Farnesene, a long-chained hydrocarbon (C₁₅H₂₄), has many applications in lubricants, cosmetics, fragrances, and biofuels. However, a method for the sustainable, photosynthetic production of farnesene has been lacking. Here, we report the photosynthetic production of farnesene by the filamentous cyanobacterium Anabaena sp. PCC 7120 using only CO₂, mineralized water, and light. A codon-optimized farnesene synthase gene was chemically synthesized and then expressed in the cyanobacterium, enabling it to synthesize farnesene through its endogenous non-mevalonate (MEP) pathway. Farnesene excreted from the engineered cyanobacterium volatilized into the flask head space and was recovered by adsorption in a resin column. The maximum photosynthetic productivity of farnesene was 69.1?±?1.8 μg·L^?1·O.D.^?1·d^?1. Compared to the wild type, the farnesene-producing cyanobacterium also exhibited a 60 % higher PSII activity under high light, suggesting increased farnesene productivity in such conditions. We envision genetically engineered cyanobacteria as a bio-solar factory for photosynthetic production of a wide range of biofuels and commodity chemicals.     

Genetic and eco-physiological differences of South American Cylindrospermopsis raciborskii isolates support the hypothesis of multiple ecotypes

The global distribution of the toxic cyanobacterium Cylindrospermopsis raciborskii has recently increased, and it has now been identified in tropical, subtropical and temperate freshwater bodies. The mechanisms underlying its success and expansion are still unknown. Several hypotheses have been proposed, including climate change, natural selection and physiological tolerance to different environmental conditions. In this study, we determined the phenotypic and genotypic characteristics of two recently isolated South American strains of C. raciborskii obtained from Uruguay. We analyzed the morphology, growth preferences, tolerance to low temperature (14 °C) and toxin production of the strains and performed phylogenetic analyses based on the ITS and nifH gene sequences. Both isolates showed significantly different morphology and growth behavior under different light intensities and phosphate supply. When genetic differences were assessed by BOX PCR, cluster analyses revealed that they could also be distinguished genotypically and were clearly distinct from C. raciborskii isolated from other continents. Phylogenetic analysis showed that the Uruguayan strains were closely affiliated to other C. raciborskii isolated from the Americas, especially to those from Brazil. Similar to previous studies, we found three solid clusters (Africa-Australia, Europe and America) according to the geographical origin of the isolates. Interestingly, based on nifH sequences, subclusters were identified in American populations indicating an early spread of the species within the continent. We propose that phenotypic and genetic variability of C. raciborskii populations is linked to the existence of different ecotypes whose success is subject to the local environmental conditions.     

Elainella gen. nov.: a new tropical cyanobacterium characterized using a complex genomic approach

Cyanobacteria represent an ancient, monophyletic lineage of bacteria with the ability to undertake oxygenic photosynthesis. Although they possess a relatively high degree of morphological variability compared with other prokaryotes and there is a wealth of molecular data, there are still significant gaps in our knowledge of cyanobacterial diversity, especially in tropical areas. Here, we present a novel, filamentous, tropical cyanobacterium, which could be classified as Pseudophormidium based on morphological criteria. A total evidence investigation employing ecological, morphological and genomic data, indicated that our strains form a new and ancient evolutionary lineage among cyanobacteria unrelated to Pseudophormidium. Based on this polyphasic assessment, our strains represent a novel, monospecific genus: Elainella. This new genus represents an example of phenotypic convergence, which seems to be a prevalent macroevolutionary pattern in cyanobacteria, a likely cause of the frequently cited polyphyly within a majority of genera.     

A comprehensive time‐course metabolite profiling of the model cyanobacterium Synechocystis sp. PCC 6803 under diurnal light:dark cycles

Cyanobacteria are a model photoautotroph and a chassis for the sustainable production of fuels and chemicals. Knowledge of photoautotrophic metabolism in the natural environment of day/night cycles is lacking, yet has implications for improved yield from plants, algae and cyanobacteria. Here, a thorough approach to characterizing diverse metabolites—including carbohydrates, lipids, amino acids, pigments, cofactors, nucleic acids and polysaccharides—in the model cyanobacterium Synechocystis sp. PCC 6803 (S. 6803) under sinusoidal diurnal light:dark cycles was developed and applied. A custom photobioreactor and multi‐platform mass spectrometry workflow enabled metabolite profiling every 30–120 min across a 24‐h diurnal sinusoidal LD (‘sinLD’) cycle peaking at 1600 μmol photons m^?2 sec^?1. We report widespread oscillations across the sinLD cycle with 90%, 94% and 40% of the identified polar/semi‐polar, non‐polar and polymeric metabolites displaying statistically significant oscillations, respectively. Microbial growth displayed distinct lag, biomass accumulation and cell division phases of growth. During the lag phase, amino acids and nucleic acids accumulated to high levels per cell followed by decreased levels during the biomass accumulation phase, presumably due to protein and DNA synthesis. Insoluble carbohydrates displayed sharp oscillations per cell at the day‐to‐night transition. Potential bottlenecks in central carbon metabolism are highlighted. Together, this report provides a comprehensive view of photosynthetic metabolite behavior with high temporal resolution, offering insight into the impact of growth synchronization to light cycles via circadian rhythms. Incorporation into computational modeling and metabolic engineering efforts promises to improve industrially relevant strain design.     

Primary production in a tropical reservoir in Sri Lanka*

Primary production was measured every 2 weeks during 16 months (N = 33) in Tissawewa, a tropical shallow reservoir in the lowlands of south-east Sri Lanka. Results are interpreted in relation to selected environmental conditions such as oxygen concentrations, water temperature, Secchi-disc depth, wind force, conductivity, and morphoedaphic index and water level fluctuations. Because of regularly reoccurring high wind speeds the water column is well mixed. Daily gross primary production per unit area was plotted as a function of the algal biomass per unit area over the euphotic zone. Chlorophyll-a concentration in the euphotic zone was taken as measure for the algal biomass. The literature comparisons showed that the primary productivity in Tissawewa was in the same range as in 29 tropical lakes and reservoirs, of which 27 were from Africa. The productivity of these 30 tropical lakes and reservoirs was compared with: (a) 27 lakes of which 25 were temperate lakes, and (b) 49 North American temperate lakes. Firstly, comparisons were made on an annual basis for the tropical water bodies, but restricted to May–September, the growing season, for temperate water bodies. The gross primary productivity of tropical water bodies was ca. three times higher than that of temperate water bodies. These differences were even more dramatic if the two geographical regions are compared on an annual basis, i.e. the tropical systems are ca. six times more productive than their temperate counterpart.     

2,3 Butanediol production in an obligate photoautotrophic cyanobacterium in dark conditions via diverse sugar consumption

Cyanobacteria are under investigation as a means to utilize light energy to directly recycle CO₂ into chemical compounds currently derived from petroleum. Any large-scale photosynthetic production scheme must rely on natural sunlight for energy, thereby limiting production time to only lighted hours during the day. Here, an obligate photoautotrophic cyanobacterium was engineered for enhanced production of 2,3-butanediol (23BD) in continuous light, 12 h:12 h light-dark diurnal, and continuous dark conditions via supplementation with glucose or xylose. This study achieved 23BD production under diurnal conditions comparable to production under continuous light conditions. The maximum 23BD titer was 3.0 g L⁻¹ in 10 d. Also achieving chemical production under dark conditions, this work enhances the feasibility of using cyanobacteria as industrial chemical-producing microbes.     

Lithic cyanobacterial communities in the polyextreme Sahara Desert: implications for the search for the limits of life

The hyperarid Sahara Desert presents extreme and persistent dry conditions with a limited number of hours during which the moisture availability, temperature and light allow phototrophic growth. Some cyanobacteria can live in these hostile conditions by seeking refuge under (hypolithic) or inside (endolithic) rocks, by colonizing porous spaces (cryptoendoliths) or fissures in stones (chasmoendoliths). Chroococcidiopsis spp. have been reported as the dominant or even the only phototrophs in these hot desert lithic communities. However, the results of this study reveal the high diversity of and variability in cyanobacteria among the sampled habitats in the Sahara Desert. The chasmoendolithic samples presented high coccoid cyanobacteria abundances, although the dominant cyanobacteria were distinct among different locations. A high predominance of a newly described cyanobacterium, Pseudoacaryochloris sahariense, was found in hard, compact, and more opaque stones with cryptoendolithic colonization. On the other hand, the hypolithic samples were dominated by filamentous, non-heterocystous cyanobacteria. Thermophysiological bioassays confirmed desiccation and extreme temperature tolerance as drivers in the cyanobacterial community composition of these lithic niches. The results of the present study provide key factors for understanding life strategies under polyextreme environmental conditions. The isolated strains, especially the newly described cyanobacterium P. sahariense, might represent suitable microorganisms in astrobiology studies aimed at investigating the limits of life.