Polyphasic evaluation of key cyanobacteria in biocrusts from the most arid region in Europe

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.

Isolation of biocrust cyanobacteria and evaluation of Cu, Pb, and Zn immobilisation potential for soil restoration and sustainable agriculture

Soil contamination by heavy metals represents an important environmental and public health problem of global concern. Biocrust-forming cyanobacteria offer promise for heavy metal immobilisation in contaminated soils due to their unique characteristics, including their ability to grow in contaminated soils and produce exopolysaccharides (EPS). However, limited research has analysed the representativeness of cyanobacteria in metal-contaminated soils. Additionally, there is a lack of studies examining how cyanobacteria adaptation to specific environments can impact their metal-binding capacity. To address this research gap, we conducted a study analysing the bacterial communities of cyanobacteria-dominated biocrusts in a contaminated area from South Sardinia (Italy). Additionally, by using two distinct approaches, we isolated three Nostoc commune strains from cyanobacteria-dominated biocrust and we also evaluated their potential to immobilise heavy metals. The first isolation method involved acclimatizing biocrust samples in liquid medium while, in the second method, biocrust samples were directly seeded onto agar plates. The microbial community analysis revealed Cyanobacteria, Bacteroidota, Proteobacteria, and Actinobacteria as the predominant groups, with cyanobacteria representing between 13.3 % and 26.0 % of the total community. Despite belonging to the same species, these strains exhibited different growth rates (1.1-2.2 g L-1 of biomass) and capacities for EPS production (400-1786 mg L-1). The three strains demonstrated a notable ability for metal immobilisation, removing up to 88.9 % of Cu, 86.2 % of Pb, and 45.3 % of Zn from liquid medium. Cyanobacteria EPS production showed a strong correlation with the removal of Cu, indicating its role in facilitating metal immobilisation. Furthermore, differences in Pb immobilisation (40-86.2 %) suggest possible environmental adaptation mechanisms of the strains. This study highlights the promising application of N. commune strains for metal immobilisation in soils, offering a potential bioremediation tool to combat the adverse effects of soil contamination and promote environmental sustainability.

Characteristics of Bacterial Community Structure and Function in Artificial Soil Prepared Using Red Mud and Phosphogypsum

The preparation of artificial soil is a potential cooperative resource utilization scheme for red mud and phosphogypsum on a large scale, with a low cost and simple operation. The characteristics of the bacterial community structure and function in three artificial soils were systematically studied for the first time. Relatively rich bacterial communities were formed in the artificial soils, with relatively high abundances of bacterial phyla (e.g., Cyanobacteria, Proteobacteria, Actinobacteriota, and Chloroflexi) and bacterial genera (e.g., Microcoleus_PCC-7113, Rheinheimera, and Egicoccus), which can play key roles in various nutrient transformations, resistance to saline-alkali stress and pollutant toxicity, the enhancement of various soil enzyme activities, and the ecosystem construction of artificial soil. There were diverse bacterial functions (e.g., photoautotrophy, chemoheterotrophy, aromatic compound degradation, fermentation, nitrate reduction, cellulolysis, nitrogen fixation, etc.), indicating the possibility of various bacteria-dominated biochemical reactions in the artificial soil, which can significantly enrich the nutrient cycling and energy flow and enhance the fertility of the artificial soil and the activity of the soil life. The bacterial communities in the different artificial soils were generally correlated with major physicochemical factors (e.g., pH, OM, TN, AN, and AP), as well as enzyme activity factors (e.g., S-UE, S-SC, S-AKP, S-CAT, and S-AP), which comprehensively illustrates the complexity of the interaction between bacterial communities and environmental factors in artificial soils, and which may affect the succession direction of bacterial communities, the quality of the artificial soil environment, and the speed and direction of the development and maturity of the artificial soil. This study provides an important scientific basis for the synergistic soilization of two typical industrial solid wastes, red mud and phosphogypsum, specifically for the microbial mechanism, for the further evolution and development of artificial soil prepared using red mud and phosphogypsum.

Molecular Screening for Cyanobacteria and Their Cyanotoxin Potential in Diverse Habitats

Cyanobacteria are adaptable and dominant organisms that exist in many harsh and extreme environments due to their great ecological tolerance. They produce various secondary metabolites, including cyanotoxins. While cyanobacteria are well studied in surface waters and some aerial habitats, numerous other habitats and niches remain underexplored. We collected 61 samples of: (i) biofilms from springs, (ii) aerial microbial mats from buildings and subaerial mats from caves, and (iii) water from borehole wells, caves, alkaline, saline, sulphidic, thermal, and iron springs, rivers, seas, and melted cave ice from five countries (Croatia, Georgia, Italy, Serbia, and Slovenia). We used (q)PCR to detect cyanobacteria (phycocyanin intergenic spacer-PC-IGS and cyanobacteria-specific 16S rRNA gene) and cyanotoxin genes (microcystins-mcyE, saxitoxins-sxtA, cylindrospermopsins-cyrJ), as well as amplicon sequencing and morphological observations for taxonomic identification. Cyanobacteria were detected in samples from caves, a saline spring, and an alkaline spring. While mcyE or sxtA genes were not observed in any sample, cyrJ results showed the presence of a potential cylindrospermopsin producer in a biofilm from a sulphidic spring in Slovenia. This study contributes to our understanding of cyanobacteria occurrence in diverse habitats, including rare and extreme ones, and provides relevant methodological considerations for future research in such environments.

Native Biocrust Cyanobacteria Strains Showing Antagonism against Three Soilborne Pathogenic Fungi

The biocontrol potential of three native soil cyanobacteria from biological soil crusts (Nostoc commune, Scytonema hyalinum, and Tolypothrix distorta) was tested by means of in vitro mycelial growth inhibition assays for eighteen cyanobacteria-based products against three phytopathogenic soilborne fungi (Phytophthora capsici, Pythium aphanidermatum, and Fusarium oxysporum f. sp. radicis-cucumerinum). Three cyanobacteria-based production factors were considered: (i) cyanobacterium strain, (ii) cyanobacterial culture growth phase, and (iii) different post-harvest treatments: raw cultures, cyanobacterial filtrates, and cyanobacterial extracts. Results showed that any of the factors considered are key points for successfully inhibiting fungal growth. N. commune showed the highest growth inhibition rates for the three phytopathogens; stationary phase treatments produced higher inhibition percentages than logarithmic ones; and all the post-harvest treatments of N. commune at the stationary phase inhibited the growth of P. capsici, up to 77.7%. Thus, N. commune products were tested in planta against P. capsici, but none of the products showed efficacy in delaying the onset nor reducing the damage due to P. capsici, demonstrating the complexity of the in planta assay's success and encouraging further research to design an appropriate scaling up methodology.

Organizing a global list of cyanobacteria and algae from soil biocrusts evidenced great geographic and taxonomic gaps

Biocrusts determine soil stability and resiliency, with a special role played by oxygenic photoautotrophic microorganisms in these communities. We evaluated temporal and geographic trends in studies focused on these microorganisms in biocrusts. Two databases were surveyed to obtain scientific articles published from 1998 to 2020 containing the terms 'biocrusts,' 'algae,' and 'cyanobacteria.' Although interest in biocrusts has increased recently, their ecological importance is still little explored. The scientific articles that mentioned a species list of cyanobacteria and/or algae revealed a very heterogeneous geographic distribution of research. Biocrusts have not been explored in many regions and knowledge in the tropics, where these communities showed high species richness, is limited. Geographic gaps were detected and more detailed studies are needed, mainly where biocrust communities are threatened by anthropogenic impacts. Aiming to address these knowledge gaps, we assembled a taxonomic list of all algae and cyanobacteria found in these articles, including information on their occurrence and ecology. This review is an updated global taxonomic survey of biocrusts, which importantly reveals their high species richness of oxygenic photoautotrophic microorganisms. We believe this database will be useful to future research by providing valuable taxonomic and biogeographic information regarding algae and cyanobacteria in biocrusts.

Nitrogen-fixing bacterial communities differ between perennial agroecosystem crops

Biocrusts, common in natural ecosystems, are specific assemblages of microorganisms at or on the soil surface with associated microorganisms extending into the top centimeter of soil. Agroecosystem biocrusts have similar rates of nitrogen (N) fixation as those in natural ecosystems, but it is unclear how agricultural management influences their composition and function. This study examined the total bacterial and diazotrophic communities of biocrusts in a citrus orchard and a vineyard that shared a similar climate and soil type but differed in management. To contrast climate and soil type, these biocrusts were also compared with those from an apple orchard. Unlike natural ecosystem biocrusts, these agroecosystem biocrusts were dominated by proteobacteria and had a lower abundance of cyanobacteria. All of the examined agroecosystem biocrust diazotroph communities were dominated by N-fixing cyanobacteria from the Nostocales order, similar to natural ecosystem cyanobacterial biocrusts. Lower irrigation and fertilizer in the vineyard compared with the citrus orchard could have contributed to biocrust microbial composition, whereas soil type and climate could have differentiated the apple orchard biocrust. Season did not influence the bacterial and diazotrophic community composition of any of these agroecosystem biocrusts. Overall, agricultural management and climatic and edaphic factors potentially influenced the community composition and function of these biocrusts.

A critical review of soil algae as a crucial soil biological component of high ecological and economic significance

Aero-terrestrial algae are ecologically and economically valuable bioresources contributing to carbon sequestration, sustenance of soil health, and fertility. Compared to aquatic algae, the literature on subaerial algae is minimal, including studies of distinctive habitats such as forest soils, agricultural fields, deserts, polar regions, specific subaerial zones, artificial structures, and tropical soils. The primary goal here was to identify the gaps and scope of research on such algae. Accordingly, the literature was analyzed per sub-themes, such as the "nature of current research data on terrestrial algae," "methodological approaches," "diversity," "environmental relationships," "ecological roles," and "economic significance." The review showed there is a high diversity of algae in soils, especially members belonging to the Cyanophyta (Cyanobacteria) and Chlorophyta. Algal distributions in terrestrial environments depend on the microhabitat conditions, and many species of soil algae are sensitive to specific soil conditions. The ecological significance of soil algae includes primary production, the release of biochemical stimulants and plant growth promoters into soils, nitrogen fixation, solubilization of minerals, and the enhancement and maintenance of soil fertility. Since aero-terrestrial habitats are generally stressed environments, algae of such environments can be rich in rare metabolites and natural products. For example, epilithic soil algae use wet adhesive molecules to fix them firmly on the substratum. Exploring the ecological roles and economic utility of soil and other subaerial algae could be helpful for the development of algae-based industries and for achieving sustainable soil management.

Ecophysiological and genomic approaches to cyanobacterial hardening for restoration

Cyanobacteria inhabit extreme environments, including drylands, providing multiple benefits to the ecosystem. Soil degradation in warm drylands is increasing due to land use intensification. Restoration methods adapted to the extreme stress in drylands are being developed, such as cyanobacteria inoculation to recover biocrusts. For this type of restoration method to be a success, it is crucial to optimize the survival of inoculated cyanobacteria in the field. One strategy is to harden them to be acclimated to stressful conditions after laboratory culturing. Here, we analyzed the genome and ecophysiological response to osmotic desiccation and UVR stresses of an Antarctic cyanobacterium, Stenomitos frigidus ULC029, which is closely related to other cyanobacteria from warm and cold dryland soils. Chlorophyll a concentrations showed that preculturing ULC029 under moderate osmotic stress improved its survival during an assay of desiccation plus rehydration under UVR. Additionally, its sequential exposure to these stress factors increased the production of exopolysaccharides, carotenoids, and scytonemin. Desiccation, but not osmotic stress, increased the concentrations of the osmoprotectants trehalose and sucrose. However, osmotic stress might induce the production of other osmoprotectants, for which the complete pathways were observed in the ULC029 genome. In total, 140 genes known to be involved in stress resistance were annotated. Here, we confirm that the sequential application of moderate osmotic stress and dehydration could improve cyanobacterial hardening for soil restoration by inducing several resistance mechanisms. We provide a high-quality genome of ULC029 and a description of the main resistance mechanisms (i.e., production of exopolysaccharides, osmoprotectants, chlorophyll, and carotenoids; DNA repair; and oxidative stress protection).

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.

Enhancing Biocrust Development and Plant Growth through Inoculation of Desiccation-Tolerant Cyanobacteria in Different Textured Soils

In recent years, there has been a burgeoning interest in the utilization of cyanobacteria for the purpose of land rehabilitation via enhancements in soil fertility, prevent erosion, and counter desertification. This study evaluated the ability of Nostoc calcicola BOT1, Scytonema sp. BOT2, and their consortia to form biocrusts on the substrate of coarse sand, fine sand, and loamy soil. A nutrient- and water-deficient substrate was inoculated with cyanobacteria to facilitate biocrust formation and evaluate their impact on agriculture. Cyanobacteria inoculation resulted in significant improvements in soil fertility, especially in coarse and fine sand, which initially had the lowest fertility. The findings of this investigation underscore that the consortium of cyanobacteria exhibited greater efficacy than individual strains in enhancing soil fertility and stimulating plant growth. The loamy soil treated with the consortium had the highest plant growth across all soil types, in contrast to the individual strains. The consortium of cyanobacteria showed promising results in promoting biocrust formation and fostering rice seedling growth in fine sand. This study provides empirical evidence supporting the potential utility of cyanobacterial consortia as a valuable tool for the rehabilitation of degraded land. Furthermore, the results indicate that cyanobacterial species can persist in soil environments even following prolonged periods of desiccation.

Bio-Characterization and Liquid Chromatography-Mass Spectrometry Analysis of Exopolysaccharides in Biofilm-Producing Cyanobacteria Isolated from Soil Crust: Exploring the Potential of Microalgal Biomolecules

Exopolysaccharide-producing cyanobacterial strains in biological soil crusts are described, in addition to their chemical properties and antioxidant and flocculation activities. The EPSs from Pudukkottai blackish biological soil crusts (PBBSCs) showed significant amounts of total soluble proteins (0.1687 mg/mL) and carbohydrates (0.8056 mg/mL) compared with the Ariyalur blackish biological soil crusts (ABBSCs). LC-MS analysis of the cyanobacterial polysaccharides revealed the presence of natural sugars such as ribose and glucose/mannose, and uronic acids. The FTIR spectrum showed specific peak for OH and -NH stretching, C-H stretching, and carboxylic acids as the dominant groups in EPS. The in vitro DPPH assay of EPSs from PBBSCs showed 74.3% scavenging activity. Furthermore, the reducing power was determined to be 0.59 ata 500 mg/mL concentration, respectively. The extracted EPSs from the biological soil crust flocculated Kaolin clay suspension maximum at 500 mg/mL. Consequently, the cyanobacterial strain and exopolysaccharide characterization from the sacred forest's biological soil crust were analyzed for their bioactive potential, bio-crust diversity, and distribution.

Impact of dehydration on the physiochemical properties of Nostoc calcicola BOT1 and its untargeted metabolic profiling through UHPLC-HRMS

The global population growth has led to a higher demand for food production, necessitating improvements in agricultural productivity. However, abiotic and biotic stresses pose significant challenges, reducing crop yields and impacting economic and social welfare. Drought, in particular, severely constrains agriculture, resulting in unproductive soil, reduced farmland, and jeopardized food security. Recently, the role of cyanobacteria from soil biocrusts in rehabilitating degraded land has gained attention due to their ability to enhance soil fertility and prevent erosion. The present study focused on Nostoc calcicola BOT1, an aquatic, diazotrophic cyanobacterial strain collected from an agricultural field at Banaras Hindu University, Varanasi, India. The aim was to investigate the effects of different dehydration treatments, specifically air drying (AD) and desiccator drying (DD) at various time intervals, on the physicochemical properties of N. calcicola BOT1. The impact of dehydration was assessed by analyzing the photosynthetic efficiency, pigments, biomolecules (carbohydrates, lipids, proteins, osmoprotectants), stress biomarkers, and non-enzymatic antioxidants. Furthermore, an analysis of the metabolic profiles of 96-hour DD and control mats was conducted using UHPLC-HRMS. Notably, there was a significant decrease in amino acid levels, while phenolic content, fatty acids, and lipids increased. These changes in metabolic activity during dehydration highlighted the presence of metabolite pools that contribute to the physiological and biochemical adjustments of N. calcicola BOT1, mitigating the impact of dehydration to some extent. Overall, present study demonstrated the accumulation of biochemical and non-enzymatic antioxidants in dehydrated mats, which could be utilized to stabilize unfavorable environmental conditions. Additionally, the strain N. calcicola BOT1 holds promise as a biofertilizer for semi-arid regions.

Carbonate precipitation and nitrogen fixation in AMG (Artificial Martian Ground) by cyanobacteria

This article describes experiments performed to study the survival, growth, specific adaptations and bioremediation potential of certain extreme cyanobacteria strains within a simulation of the atmospheric composition, temperature and pressure expected in a future Martian greenhouse. Initial species have been obtained from Mars-analogue sites in Georgia. The results clearly demonstrate that specific biochemical adaptations allow these autotrophs to metabolize within AMG (Artificial Martian Ground) and accumulate biogenic carbon and nitrogen. These findings may thus contribute to the development of future Martian agriculture, as well as other aspects of the life-support systems at habitable Mars stations. The study shows that carbonate precipitation and nitrogen fixation, performed by cyanobacterial communities thriving within the simulated Martian greenhouse conditions, are cross-linked biological processes. At the same time, the presence of the perchlorates (at low concentrations) in the Martian ground may serve as the initial source of oxygen and, indirectly, hydrogen via photo-Fenton reactions. Various carbonates, ammonium and nitrate salts were obtained as the result of these experiments. These affect the pH, salinity and solubility of the AMG and its components, and so the AMG's scanty biogenic properties improved, which is essential for the sustainable growth of the agricultural crops. Therefore, the use of microorganisms for the biological remediation and continuous in situ fertilization of Artificial Martian Ground is possible.

Cyanobacterial diversity of biological soil crusts and soil properties in karst desertification area

As important components of the biological soil crusts (BSCs) and of the primary stage of crust succession, cyanobacterial communities occupy an important ecological niche and play an important ecological role in desertification areas. In this study, we focused on the karst desertification area, which also belongs to the same category of desertification, and selected three study areas, Guanling-Zhenfeng Huajiang (HJ), Bijie Salaxi (SLX), and Shibing (SB), in the Guizhou Plateau, which represents the overall ecological environment of South China karst, to conduct surveys on the diversity of BSC species and soil properties. Analysis of the cyanobacterial communities and physicochemical properties using the Shannon-Wiener diversity index, principal component analysis, and redundancy analysis revealed that: (1) The three study areas had common cyanobacterial species, with a total of 200 species distributed across 22 genera, 2 classes, 5 orders, and 6 families belonging to the Oscillatoriales (39%), Scytonematales (24.5%), Chroococcales (23%), Nostocales (11.5%), and Rivulariales (2%), (2) The number of species increased with the intensity of karst desertification—while Oscillatoriaceae was the dominant family in HJ and moderate–severe desertification areas, Chroococcaceae and Scytonemataceae were dominant in the mild and potential desertification areas SLX and SB, (3) The Shannon-Wiener diversity indices followed the trend: SLX (3.56) > SB (3.08) > HJ (3.01), indicating that the species were more evenly distributed in mild desertification, (4) In the carbonate background, shrubland harbored the largest number of cyanobacterial species compared to grassland, bare land, and arbor woodland; however, the highest number was documented in arbor woodland in dolomite karst, (5) The soil is weathered limestone or yellow soil in all three areas, with pH ranging from 5.73 to 6.85, fine sand dominated, and soil nutrients increased with the intensity of desertification, and (6) Redundancy analysis showed that organic carbon, soil moisture content (0–5 cm), and total nitrogen substantially influenced cyanobacterial diversity. These results reveal that differences in soil nutrient content play an important role in regulating the cyanobacterial diversity and composition, thereby establishing a foundation for further research and application of soil ecological restoration of cyanobacteria in BSCs of karst desertification areas.

Characterization of a novel thermophilic cyanobacterium within Trichocoleusaceae, Trichothermofontia sichuanensis gen. et sp. nov., and its CO2-concentrating mechanism

Thermophiles from extreme thermal environments have shown tremendous potential regarding ecological and biotechnological applications. Nevertheless, thermophilic cyanobacteria remain largely untapped and are rarely characterized. Herein, a polyphasic approach was used to characterize a thermophilic strain, PKUAC-SCTB231 (hereafter B231), isolated from a hot spring (pH 6.62, 55.5°C) in Zhonggu village, China. The analyses of 16S rRNA phylogeny, secondary structures of 16S-23S ITS and morphology strongly supported strain B231 as a novel genus within Trichocoleusaceae. Phylogenomic inference and three genome-based indices further verified the genus delineation. Based on the botanical code, the isolate is herein delineated as Trichothermofontia sichuanensis gen. et sp. nov., a genus closely related to a validly described genus Trichocoleus. In addition, our results suggest that Pinocchia currently classified to belong to the family Leptolyngbyaceae may require revision and assignment to the family Trichocoleusaceae. Furthermore, the complete genome of Trichothermofontia B231 facilitated the elucidation of the genetic basis regarding genes related to its carbon-concentrating mechanism (CCM). The strain belongs to β-cyanobacteria according to its β-carboxysome shell protein and 1B form of Ribulose bisphosphate Carboxylase-Oxygenase (RubisCO). Compared to other thermophilic strains, strain B231contains a relatively low diversity of bicarbonate transporters (only BicA for HCO₃^- transport) but a higher abundance of different types of carbonic anhydrase (CA), β-CA (ccaA) and γ-CA (ccmM). The BCT1 transporter consistently possessed by freshwater cyanobacteria was absent in strain B231. Similar situation was occasionally observed in freshwater thermal Thermoleptolyngbya and Thermosynechococcus strains. Moreover, strain B231 shows a similar composition of carboxysome shell proteins (ccmK1-4, ccmL, -M, -N, -O, and -P) to mesophilic cyanobacteria, the diversity of which was higher than many thermophilic strains lacking at least one of the four ccmK genes. The genomic distribution of CCM-related genes suggests that the expression of some components is regulated as an operon and others in an independently controlled satellite locus. The current study also offers fundamental information for future taxogenomics, ecogenomics and geogenomic studies on distribution and significance of thermophilic cyanobacteria in the global ecosystem.

Towards large scale biocrust restoration: Producing an efficient and low-cost inoculum of N-fixing cyanobacteria

Dryland soil degradation is increasing due to global change and traditional restoration methods are not successful due to water scarcity. Thus, an alternative technology based on inoculating biocrust-forming cyanobacteria on degraded soils has emerged. Biocrusts are communities of mosses, lichens, cyanobacteria or fungi that colonize soil surface forming a stable and fertile layer. Previous studies have shown the benefits of inoculating cyanobacteria to restore soils at a small scale. However, to face field restoration projects, it is necessary to produce high quantities of biomass at an affordable cost. In this work, we analyze if the previously tested cyanobacteria Scytonema hyalinum, Tolypothrix distorta (heterocystous strains) and Trichocoleus desertorum (a bundle-forming one) can be produced with agricultural fertilizers. Different culture media were used: two containing pure chemicals (BG11 and BG11₀, this N-free medium was used just for heterocystous strains) and two containing fertilizers (BG11-F and MM-F). The performance of the cultures was monitored by measuring the biomass concentration and photosynthetic stress. Afterwards, we analyzed their capacity to induce biocrusts and improve soil properties by inoculating the biomass on a mine substrate indoors and measuring, three months later, the albedo, chlorophyll a and organic carbon content. Results show that the bundle-forming cyanobacterium was unable to grow in the media tested, whereas both heterocystous cyanobacteria grew in all of them and induced the formation of biocrusts improving the organic carbon substrate content. The best results for S. hyalinum were found using the MM-F medium, and for T. distorta using a medium containing pure chemicals (BG11). However, results were also positive when using a medium containing fertilizers (BG11-F). Thus, agricultural fertilizers can be used to undertake the production of heterocystous cyanobacteria for large scale restoration in drylands. On the other hand, more research is needed to find sustainable techniques to produce biomass of bundle-forming cyanobacteria.

Biocrust Amendments to Topsoils Facilitate Biocrust Restoration in a Post-mining Arid Environment

Soil cryptogamic biocrusts provide many ecological functions in arid zone ecosystems, though their natural reestablishment in disturbed areas is slow. Accelerating reestablishment of biocrusts may facilitate the establishment of vascular plant communities within the timeframes of restoration targets (typically 5–15 years). One technique is to inoculate the soil surface using slurries of biocrust material harvested from another site. However, this is destructive to donor sites, and hence the potential to dilute slurries will govern the feasibility of this practice at large spatial scales. We conducted a replicated experiment on a disturbed mine site to test the individual and combined effects of two strategies for accelerating soil cryptogamic biocrust reestablishment: (1) slurry inoculation using biocrust material harvested from native vegetation; and (2) the use of psyllium husk powder as a source of mucilage to bind the soil surface, and to potentially provide a more cohesive substrate for biocrust development. The experiment comprised 90 experimental plots across six treatments, including different dilutions of the biocrust slurries and treatments with and without psyllium. Over 20 months, the reestablishing crust was dominated by cyanobacteria (including Tolypothrix distorta and Oculatella atacamensis), and these established more rapidly in the inoculated treatments than in the control treatments. The inoculated treatments also maintained this cover of cyanobacteria better through prolonged adverse conditions. The dilute biocrust slurry, at 1:100 of the biocrust in the remnant vegetation, performed as well as the 1:10 slurry, suggesting that strong dilution of biocrust slurry may improve the feasibility of using this technique at larger spatial scales. Psyllium husk powder did not improve biocrust development but helped to maintain a soil physical crust through hot, dry, and windy conditions, and so the potential longer-term advantages of psyllium need to be tested.

Insights from cyanobacterial genomic and transcriptomic analyses into adaptation strategies in terrestrial environments

Phylogenomic analysis of Nostoc sp. MG11, a terrestrial cyanobacterium, and some terrestrial and freshwater Nostoc strains showed that the terrestrial strains grouped together in a distinctive clade, which reveals the effect of habitat on shaping Nostoc genomes. Terrestrial strains showed larger genomes and had higher predicted CDS contents than freshwater strains. Comparative genomic analysis demonstrated that genome expansion in the terrestrial Nostoc is supported by an increase in copy number of the core genes and acquisition of shared genes. Transcriptomic profiling analysis under desiccation stress revealed that Nostoc sp. MG11 protected its cell by induction of catalase, proteases, sucrose synthase, trehalose biosynthesis and maltodextrin utilization genes and maintained its normal metabolism during this condition by up-regulation of genes related to phycobilisomes and light reactions of photosynthesis, CO₂ fixation and protein metabolism. These results provide insights into the strategies related to survival and adaptation of Nostoc strains to terrestrial environments.

Soil microbiota as game-changers in restoration of degraded lands

Land degradation reduces soil functioning and, consequently, the services that soil provides. Soil hydrological functions are critical to combat soil degradation and promote soil restoration. Soil microorganisms affect soil hydrology, but the role of soil microbiota in forming and sustaining soil is not well explored. Case studies indicate the potential of soil microorganisms as game-changers in restoring soil functions. We review the state of the art of microorganism use in land restoration technology, the groups of microorganisms with the greatest potential for soil restoration, knowledge of the effect of microorganisms on soil physical properties, and proposed strategies for the long-term restoration of degraded lands. We also emphasize the need to advance the emerging research field of biophysical landscape interactions to support soil-plant ecosystem restoration practices.

Design Optimization of Biocrust-Plant Spatial Configuration for Dry Ecosystem Restoration Using Water Redistribution and Erosion Models

Land degradation is one of the main threats to dryland sustainability in the next decades, hence restoration of the degraded land from drylands is an urgent need to maintain ecosystem functionality and their ability to provide ecosystem services. To achieve this goal, restoration practices should pursue the recovery of the main ground components, arranged in an optimal spatial configuration, to mimic undisturbed natural conditions. Drylands function as complex ecohydrologically coupled systems in which interplant source areas, frequently covered by biocrusts, act as sources of runoff and nutrients to adjacent vegetation, which act as sinks for these resources. Thus, one way to increase dryland restoration success is through an optimal spatial configuration of biocrusts and plants that maximizes an efficient use of the limited resources within the system. In this study, we selected a degraded slope from a limestone quarry located in Almería province (SE Spain) and modeled how active restoration of the biocrust through soil inoculation with cyanobacteria and its combination with different spatial configurations of vegetation affected runoff redistribution and erosion. For that, we applied the spatially distributed Limburg Soil Erosion Model (LISEM) which was able to predict the erosion measured on the slope during the study period with low error (RMSE = 17.8%). Modeling results showed that the introduction of vegetation on the degraded slope reduced runoff between 2 and 24% and erosion between 4 and 17% for the scenario with plants compared to the one without restoration management. Of all the vegetation spatial configurations tested, the one that provided better results was the scenario in which plants were located in the areas of higher water accumulation (higher topographic wetness index). Moreover, we found that active biocrust restoration by cyanobacteria inoculation significantly reduced erosion by 70–90%, especially during the first stages of plant development, while maintaining water supply to vegetation. These findings highlight the potential of water redistribution and erosion simulation models to identify the most optimal spatial configuration of ground covers that maximizes water and nutrient supply to vegetation, while minimizes water, sediment, and nutrient losses by erosion, thus serving as an efficient tool to plan restoration actions in drylands.

Cyanobacterial community composition and their functional shifts associated with biocrust succession in the Gurbantunggut Desert

Cyanobacteria, as key biocrust components, provide a variety of ecosystem functions in drylands. In this study, to identify whether a cyanobacterial community shift is involved in biocrust succession and whether this is linked to altered ecological functions, we investigated cyanobacterial composition, total carbon and nitrogen contents of biocrusts in the Gurbantunggut Desert. Our findings showed that the biocrust cyanobacteria in the Gurbantunggut desert were mostly filamentous, coexisting with abundant unicellular colonial Chroococcidiopsis. Heterocystous Nostoc, Scytonema and Tolypothrix always represented the majority of biocrust nitrogen-fixing organisms, comprising an average of 92% of the nifH gene reads. Community analysis showed a clear shift in prokaryotic community composition associated with biocrust succession from cyanobacteria- to lichen- and moss-dominated biocrusts, and filamentous non-nitrogen-fixing cyanobacteria-dominated communities were gradually replaced by nitrogen-fixing and unicellular colonial communities. Along the succession, there were concomitant reductions in cyanobacterial relative abundance, whereas Chl-a, total carbon and nitrogen contents increased. Concurrently, distinct carbon and nitrogen stores shifts occurred, implying that the main ecological contribution of cyanobacteria in biocrusts changes from carbon- to nitrogen-fixation along with the succession. Our results suggest that any activity that reverses biocrust succession will influence cyanobacterial community composition and eventually lead to large reductions in soil carbon and nitrogen stores.

Reading and surviving the harsh conditions in desert biological soil crust: The cyanobacterial viewpoint

Biological soil crusts (BSCs) are found in drylands, cover ∼12% of the Earth's surface in arid and semi-arid lands and their destruction is considered an important promoter of desertification. These crusts are formed by the adhesion of soil particles to polysaccharides excreted mostly by filamentous cyanobacteria, which are the pioneers and main primary producers in BSCs. Desert BSCs survive in one of the harshest environments on Earth, and are exposed to daily fluctuations of extreme conditions. The cyanobacteria inhabiting these habitats must precisely read the changing conditions and predict, for example, the forthcoming desiccation. Moreover, they evolved a comprehensive regulation of multiple adaptation strategies to enhance their stress tolerance. Here we focus on what distinguishes cyanobacteria able to revive after dehydration from those that cannot. While important progress has been made in our understanding of physiological, biochemical and omics aspects, clarification of the sensing, signal transduction and responses enabling desiccation tolerance are just emerging. We plot the trajectory of current research and open questions ranging from general strategies and regulatory adaptations in the hydration/desiccation cycle, to recent advances in our understanding of photosynthetic adaptation. The acquired knowledge provides new insights to mitigate desertification and improve plant productivity under drought conditions.

Water Regulation in Cyanobacterial Biocrusts from Drylands: Negative Impacts of Anthropogenic Disturbance

Arid and semi-arid ecosystems are characterized by patchy vegetation and variable resource availability. The interplant spaces of these ecosystems are very often covered by cyanobacteria-dominated biocrusts, which are the primary colonizers of terrestrial ecosystems and key in facilitating the succession of other biocrust organisms and plants. Cyanobacterial biocrusts regulate the horizontal and vertical fluxes of water, carbon and nutrients into and from the soil and play crucial hydrological, geomorphological and ecological roles in these ecosystems. In this paper, we analyze the influence of cyanobacterial biocrusts on water balance components (infiltration-runoff, evaporation, soil moisture and non-rainfall water inputs (NRWIs)) in representative semiarid ecosystems in southeastern Spain. The influence of cyanobacterial biocrusts, in two stages of their development, on runoff-infiltration was studied by rainfall simulation and in field plots under natural rainfall at different spatial scales. Results showed that cover, exopolysaccharide content, roughness, organic carbon, total nitrogen, available water holding capacity, aggregate stability, and other properties increased with the development of the cyanobacterial biocrust. Due to the effects on these soil properties, runoff generation was lower in well-developed than in incipient-cyanobacterial biocrusts under both simulated and natural rainfall and on different spatial scales. Runoff yield decreased at coarser spatial scales due to re-infiltration along the hillslope, thus decreasing hydrological connectivity. Soil moisture monitoring at 0.03 m depth revealed higher moisture content and slower soil water loss in plots covered by cyanobacterial biocrusts compared to bare soils. Non-rainfall water inputs were also higher under well-developed cyanobacterial biocrusts than in bare soils. Disturbance of cyanobacterial biocrusts seriously affected the water balance by increasing runoff, decreasing soil moisture and accelerating soil water loss, at the same time that led to a very significant increase in sediment yield. The recovery of biocrust cover after disturbance can be relatively fast, but its growth rate is strongly conditioned by microclimate. The results of this paper show the important influence of cyanobacterial biocrust in modulating the different processes supporting the capacity of these ecosystems to provide key services such as water regulation or erosion control, and also the important impacts of their anthropic disturbance.

Accelerating the formation of biological soil crusts in the newly dried-up lakebeds using the inoculation-based technique

The disappearance of water bodies and the emergence of dry lakebeds have intensified global environmental challenges such as dust source regions and moving dunes. The rapid formation of biological soil crusts (biocrusts) in these new ecosystems can help to accelerate their sustainability. Thus, we assessed how an inoculation-based technique (IBT) could contribute to the formation of biocrusts in a simulated sandy soil profile collected from the dried region of Lake Urmia, in the northwest of Iran. To this end, a full factorial combination of native bacteria, cyanobacteria, and a combination of the two were inoculated onto an experimental soil. After 120 days, the soil surface properties were measured, and the differences between the treatments were tested. The results showed that microbial inoculation, especially cyanobacteria, accelerated the biocrusts formation and the soil surface stability. Inoculated micro-organisms improved the biocrusts indicators including carbon (225%; p < 0.01) and nitrogen (3200%; p < 0.01) content, available phosphorus (70%; p < 0.01) and potassium (19%; p < 0.05), cation exchange capacity (9.3%; p < 0.05), pH (-1.2%; p < 0.01), electrical conductivity (-23%; p < 0.01), soil moisture (15.7%; p < 0.05), bulk density (-2.5%; p < 0.05), surface roughness (34.8%; p < 0.01), and aggregate stability (133%; p < 0.01), as compared to the non-inoculated soil. Analysis of the scanning electron microscopy images obtained from the soil surface also confirmed the ability of cyanobacteria to create strong bonding between soil particles. Overall, the IBT could be considered as a fast and eco-friendly way for creating/restoring biocrusts in newly dried-up/degraded lands.

Spectral Response Analysis: An Indirect and Non-Destructive Methodology for the Chlorophyll Quantification of Biocrusts

Chlorophyll a concentration (Chla) is a well-proven proxy of biocrust development, photosynthetic organisms’ status, and recovery monitoring after environmental disturbances. However, laboratory methods for the analysis of chlorophyll require destructive sampling and are expensive and time consuming. Indirect estimation of chlorophyll a by means of soil surface reflectance analysis has been demonstrated to be an accurate, cheap, and quick alternative for chlorophyll retrieval information, especially in plants. However, its application to biocrusts has yet to be harnessed. In this study we evaluated the potential of soil surface reflectance measurements for non-destructive Chla quantification over a range of biocrust types and soils. Our results revealed that from the different spectral transformation methods and techniques, the first derivative of the reflectance and the continuum removal were the most accurate for Chla retrieval. Normalized difference values in the red-edge region and common broadband indexes (e.g., normalized difference vegetation index (NDVI)) were also sensitive to changes in Chla. However, such approaches should be carefully adapted to each specific biocrust type. On the other hand, the combination of spectral measurements with non-linear random forest (RF) models provided very good fits (R2 > 0.94) with a mean root mean square error (RMSE) of about 6.5 µg/g soil, and alleviated the need for a specific calibration for each crust type, opening a wide range of opportunities to advance our knowledge of biocrust responses to ongoing global change and degradation processes from anthropogenic disturbance.