Compartmentalization of gypsum and halite associated with cyanobacteria in saline soil crusts

Comparative analysis of marine and agricultural gypsum as nutrient sources: feasibility of marine gypsum as a substitute for acid sandy soils and sodic soil recovery

To minimize the environmental impact of sea salt production and promote agricultural sustainability, studies on the reuse of marine gypsum have piqued interest in semi-arid regions. This study aimed to (a) verify the characteristics of marine gypsum, (b) analyze its agronomic potential for replacing agricultural gypsum as a nutrient source in acidic sandy soils, and (c) assess its effectiveness in recreating sodic soils. The study comprised two experiments: acidic sandy soil (Red Latosol) and sodic clayey soil (Fluvic Neosol). Both experiments employed a completely randomized design with 14 treatments and three replications. The treatments included as follows: (1) soil without any additional treatment (Control-C); (2) agricultural gypsum (AG) (40 mesh-0.42 mm)-reference treatment; (3) 12 treatments involving marine gypsum (MG), with variations in recommended doses (50%, 100%, and 200%) and particle sizes (1.19, 0.84, 0.59, and 0.42 mm, corresponding to 16, 20, 30, and 40 mesh, respectively). MG exhibited higher levels of Ca2⁺, Mg2⁺, and S-SO4-2 and lower levels of Cd, Cr, Pb, and Ni, with a predominant mineralogy of gypsum. In sandy, acidic soils, adding marine gypsum (MG) increased the electrical conductivity (EC), Ca2⁺, Mg2⁺, K⁺, Na+, and S-SO4-2, especially in the first leaches. Thus, MG is recommended at a dose of 100%, with a granulometry of 0.59 or 0.42 mm, as it proves as efficient as agricultural gypsum in providing calcium and sulfur to the soil and facilitating the vertical translocation of cations and anions. Both gypsum types were essential to increasing base saturation in this soil type. However, high MG doses may induce deficiencies in Mg2⁺ and K⁺ due to leaching stimulation. In sodic soils, MG doses exceeding 50% of the recommended dose were more efficient than agricultural gypsum in lowering pH, increasing Mg2⁺ and K⁺ contents, and reducing exchangeable Na⁺ content in the soil. Thus, we recommend a 100% MG dose with a particle size of 0.42 mm. We conclude that marine gypsum should replace agricultural gypsum as a source of nutrients in acidic sandy soil and for the recovery of sodic soil.

Hard shell, soft blue-green core: Ecology, processes, and modern applications of calcification in terrestrial cyanobacteria

Cyanobacteria are the oldest photoautotrophic lineage that release oxygen during photosynthesis, an ability that possibly evolved as far as 3.5 billion years ago and changed the Earth's environment-both in water and on land. Linked to the mechanism of carbon accumulation by cyanobacteria during photosynthesis are their calcifying properties, a process of biologically mediated mineralization of CO2 by precipitation with calcium to CaCO3. In recent decades, scientific research has mainly focused on calcifying cyanobacteria from aquatic habitats, while their terrestrial relatives have been neglected. This review not only presents the ecology of terrestrial calcifying cyanobacteria in caves and biocrusts but also discusses recent biotechnological applications, such as the production of living building materials through microbial-induced carbonate precipitation for structural engineering, which has the potential to open a new and efficient pathway for mitigating climate change, e.g., as carbon capture and storage technology.

Kalidium cuspidatum colonization changes the structure and function of salt crust microbial communities

The changes of soil moisture, salinity, and nutrients by halophyte colonization in high-salinity environment profoundly affect the assembly and structure of microbial communities. However, salt marshes in arid region have received little attention. This study was conducted in Lianhuachi Lake, a typical inland salt marsh wetland in China, to determine the physicochemical characteristics of salt crusts in [Kalidium cuspidatum (Ung.-Sternb.) Grub.] colonization areas and bulk soil, respectively, and to analyze the microbial community structure of salt crusts by high-throughput sequencing. Kalidium cuspidatum colonization significantly decreased total salinity, soil water content, and water-soluble ions of salt crusts and increased total carbon, total nitrogen, and total phosphorus content. At the same time, changes in physicochemical properties caused by Kalidium cuspidatum colonization affect the ecological processes of bacterial, fungal, and archaeal community assemblies in salt crusts. In addition, cross-kingdom network analysis showed that Kalidium cuspidatum colonization increased the complexity and stability of microbial networks in salt crust soils. Functional projections further showed that bacterial diversity had a potential driving effect on the nitrogen cycle function of salt crust. Our study further demonstrated the different ecological strategies of microorganisms for halophyte colonization in extreme environments and contributed to the understanding of restoration and management of salt marsh wetlands in arid region.

Thrive or survive: prokaryotic life in hypersaline soils

BACKGROUND

Soil services are central to life on the planet, with microorganisms as their main drivers. Thus, the evaluation of soil quality requires an understanding of the principles and factors governing microbial dynamics within it. High salt content is a constraint for life affecting more than 900 million hectares of land, a number predicted to rise at an alarming rate due to changing climate. Nevertheless, little is known about how microbial life unfolds in these habitats. In this study, DNA stable-isotope probing (DNA-SIP) with ¹⁸O-water was used to determine for the first time the taxa able to grow in hypersaline soil samples (EC_e = 97.02 dS/m). We further evaluated the role of light on prokaryotes growth in this habitat.

RESULTS

We detected growth of both archaea and bacteria, with taxon-specific growth patterns providing insights into the drivers of success in saline soils. Phylotypes related to extreme halophiles, including haloarchaea and Salinibacter, which share an energetically efficient mechanism for salt adaptation (salt-in strategy), dominated the active community. Bacteria related to moderately halophilic and halotolerant taxa, such as Staphylococcus, Aliifodinibius, Bradymonadales or Chitinophagales also grew during the incubations, but they incorporated less heavy isotope. Light did not stimulate prokaryotic photosynthesis but instead restricted the growth of most bacteria and reduced the diversity of archaea that grew.

CONCLUSIONS

The results of this study suggest that life in saline soils is energetically expensive and that soil heterogeneity and traits such as exopolysaccharide production or predation may support growth in hypersaline soils. The contribution of phototrophy to supporting the heterotrophic community in saline soils remains unclear. This study paves the way toward a more comprehensive understanding of the functioning of these environments, which is fundamental to their management. Furthermore, it illustrates the potential of further research in saline soils to deepen our understanding of the effect of salinity on microbial communities.

Interplay between abiotic and microbial biofilm-mediated processes for travertine formation: Insights from a thermal spring (Piscine Carletti, Viterbo, Italy)

Active hydrothermal travertine systems are ideal environments to investigate how abiotic and biotic processes affect mineralization mechanisms and mineral fabric formation. In this study, a biogeochemical characterization of waters, dissolved gases, and microbial mats was performed together with a mineralogical investigation on travertine encrustations occurring at the outflow channel of a thermal spring. The comprehensive model, compiled by means of TOUGHREACT computational tool from measured parameters, revealed that mineral phases were differently influenced by either abiotic conditions or microbially driven processes. Microbial mats are shaped by light availability and temperature gradient of waters flowing along the channel. Mineralogical features were homogeneous throughout the system, with euhedral calcite crystals, related to inorganic precipitation induced by CO₂ degassing, and calcite shrubs associated with organomineralization processes, thus indicating an indirect microbial participation to the mineral deposition (microbially influenced calcite). The microbial activity played a role in driving calcite redissolution processes, resulting in circular pits on calcite crystal surfaces possibly related to the metabolic activity of sulfur-oxidizing bacteria found at a high relative abundance within the biofilm community. Sulfur oxidation might also explain the occurrence of gypsum crystals embedded in microbial mats, since gypsum precipitation could be induced by a local increase in sulfate concentration mediated by S-oxidizing bacteria, regardless of the overall undersaturated environmental conditions. Moreover, the absence of gypsum dissolution suggested the capability of microbial biofilm in modulating the mobility of chemical species by providing a protective envelope on gypsum crystals.

Diversity of Microorganisms in Biocrusts Surrounding Highly Saline Potash Tailing Piles in Germany

Potash tailing piles located in Germany represent extremely hypersaline locations that negatively affect neighbouring environments and limit the development of higher vegetation. However, biocrusts, as cryptogamic covers, inhabit some of these areas and provide essential ecological functions, but, nevertheless, they remain poorly described. Here, we applied high-throughput sequencing (HTS) and targeted four groups of microorganisms: bacteria, cyanobacteria, fungi and other eukaryotes. The sequencing of the 16S rRNA gene revealed the dominance of Proteobacteria, Cyanobacteria and Actinobacteria. Additionally, we applied yanobacteria-specific primers for a detailed assessment of the cyanobacterial community, which was dominated by members of the filamentous orders Synechococcales and Oscillatoriales. Furthermore, the majority of reads in the studied biocrusts obtained by sequencing of the 18S rRNA gene belonged to eukaryotic microalgae. In addition, sequencing of the internal rDNA transcribed spacer region (ITS) showed the dominance of Ascomycota within the fungal community. Overall, these molecular data provided the first detailed overview of microorganisms associated with biocrusts inhabiting highly saline potash tailing piles and showed the dissimilarities in microbial diversity among the samples.

Poly-γ-glutamic acid bioproduct improves the coastal saline soil mainly by assisting nitrogen conservation during salt-leaching process

Salt-leaching is considered to be a major method for soil desalting in agriculture. Therefore, conservation of soil nutrition is significant to soil fertility and environment protection during the salt-leaching process. The effect of poly-γ-glutamic acid bioproduct (PGAB), which was manufactured by solid-state fermentation with the bacteria producing glutamic acid (GA) and poly-γ-glutamic acid (γ-PGA) and organic waste, on keeping nitrogen (N) during salt-leaching was investigated in this study. The isolated bacteria producing GA and γ-PGA were identified as Brevibacterium flavum and Bacillus amyloliquefaciens, respectively. After the saline soil was leached for 90 days, compared to the control, soil salinity (0-30 cm) in the PGAB treatment was decreased by 39.9%, while soil total N was significantly (P < 0.05) higher than other treatments. Furthermore, the microbial biomass N (0-30 cm) in PGAB treatment was increased by 119.5%; populations of soil total bacteria, fungi, actinomyces, nitrogen-fixing bacteria, ammonifying bacteria, nitrifying bacteria, and denitrifying bacteria and soil algae biomass were also significantly (P < 0.05) increased. In terms of physical properties, the percentage of soil aggregates with diameter > 0.25 mm was increased by 293.5%, and the soil erosion-resistance coefficient was increased by 50.0%. In conclusion, the PGAB can effectively conserve soil N during the process of salt-leaching and therefore offer a sustainable way to improve coastal saline soil.

Uncovering Unique Green Algae and Cyanobacteria Isolated from Biocrusts in Highly Saline Potash Tailing Pile Habitats, Using an Integrative Approach

Potash tailing piles caused by fertilizer production shape their surroundings because of the associated salt impact. A previous study in these environments addressed the functional community "biocrust" comprising various micro- and macro-organisms inhabiting the soil surface. In that previous study, biocrust microalgae and cyanobacteria were isolated and morphologically identified amongst an ecological discussion. However, morphological species identification maybe is difficult because of phenotypic plasticity, which might lead to misidentifications. The present study revisited the earlier species list using an integrative approach, including molecular methods. Seventy-six strains were sequenced using the markers small subunit (SSU) rRNA gene and internal transcribed spacer (ITS). Phylogenetic analyses confirmed some morphologically identified species. However, several other strains could only be identified at the genus level. This indicates a high proportion of possibly unknown taxa, underlined by the low congruence of the previous morphological identifications to our results. In general, the integrative approach resulted in more precise species identifications and should be considered as an extension of the previous morphological species list. The majority of taxa found were common in saline habitats, whereas some were more likely to occur in nonsaline environments. Consequently, biocrusts in saline environments of potash tailing piles contain unique microalgae and cyanobacteria that will possibly reveal several new taxa in more detailed future studies and, hence, provide new data on the biodiversity, as well as new candidates for applied research.

Effects of drought and water pulses on microbial functionality and the role of Cyanoprokaryota in the rhizospheres of gypsophytes

In the rhizospheres of three gypsophytes and in non-rhizospheric soil, two samplings were carried out - the first during a summer drought and the second during spring - to detect the responses to the availability of water in the soil. Urease and protease showed higher values after the drought whereas β-glucosidase was highest in the spring. This pattern was the same for all the rhizospheres tested. However, the arylsulfatase and alkaline phosphatase did not change. Surprising results were obtained when water retention and water loss were studied, with the highest values being obtained for the dry season due to the association of Cyanoprokaryota with the rhizospheres. The results are also explained by two water pulses that occurred before the samplings. Several parameters, whose values changed markedly due to the microbiological activation just after the drought and water pulses, are proposed as indicators of this activation: microbial biomass carbon and basal respiration rate, together with urease and protease. However, it was the dehydrogenase activity in spring that best reflected the microbiology associated with the carbon cycle, together with β-glucosidase. The interrelationships between carbon and nitrogen were shown through the indices: water soluble nitrogen and water soluble carbon. We propose three functional adaptation mechanisms of these plants associated with the Cyanoprokaryota in their rhizospheres and related to the water availability as determined by drought and water pulse effects. Herniaria fruticosa is a pioneer with the greatest diversity of Cyanoprokaryota, in both summer and spring (10 species and 11 species, respectively), and with high-medium abundance (5-30%). Teucrium balthazaris exhibits an intermediate strategy, with greater diversity of Cyanoprokaryota in spring (7 species) and predominance of high-medium abundance (5-30%). Finally, Helianthemum squamatum has lower diversity, with one species in summer (with low abundance, <5%) and no species in spring.

Is soil microbial diversity affected by soil and groundwater salinity? Evidences from a coastal system in central Italy

Little is known about composition, diversity, and abundance of microbial communities in environments affected by primary soil salinization, such as coastal lagoon systems. The main objective of this study was to investigate the impact of lagoon salinity, soil type, and land-use on inland soil and groundwater quality, and soil microbial community structure, diversity, and gene abundance, as evaluated by T-RFLP (terminal-restriction fragment length polymorphism) and qPCR (quantitative polymerase-chain-reaction). For this purpose, four sites oriented along a groundwater salinity gradient (Fogliano lagoon, central Italy) were studied under different recreational, grazing, and land-use conditions. Spatial variability in groundwater attributes was observed depending on salinity and soil electrical conductivity, both influenced by salt intrusion. A comparison of community abundance and number of phylotypes of bacteria, archaea, and fungi across varying soil depths pointed out marked differences across soils characterized by different soil type, land-use, and salinity. The latter significantly affected the microbial population richness and diversity and showed a dominance in terms of bacteria species. Our study provides a comprehensive overview of the spatial relationship between soil microbial community and soil degradation processes along a relatively underexplored environmental gradient in a coastal system, coming to the conclusion that salinity acts differently as a driver of microbial community structure in comparison with other saline environments.

Epilithic and endolithic microorganisms and deterioration on stone church facades subject to urban pollution in a sub-tropical climate

Weathering of two church facades in Rio de Janeiro was caused substantially by salts, mainly halite and gypsum, detected by SEM and chemical analyses, which cause physical stresses by deposition within the rock. Biofilm populations, determined by SEM and as operational taxonomic units (OTUs), degraded stone by penetration, solubilization and redeposition of minerals on their surfaces. Endolithic cyanobacteria were associated with gypsum deposits. Microbiomes were typical for high-stress environments, high salt, intense insolation, low water and low nutrients (eg halophilic Rubrobacter, Salinicola, Sterigmatomyces). The main colonizers on the church most affected by traffic (Nossa Senhora da Candelária - CA) were Actinobacteria; Gammaproteobacteria (chiefly Pseudomonas) were predominant on the site situated in a leafy square (São Francisco de Paula - SF). Major Gammaproteobacteria on CA were halophilic Halomonas and Rhodobacteriaceae. Fungal OTUs on both churches were principally dimorphic, yeast-like basidiomycetes. Many OTUs of thermophilic microorganisms (eg the Thermomicrobia class, Chloroflexi) were present. This is the first use of next generation sequencing (NGS) to study microbial biofilm interactions with metamorphic and granite buildings in an intensely urban, sub-tropical climate.