Microbial diversity and geochemistry of groundwater impacted by steel slag leachates

Amendments affect the community assembly and co-occurrence network of microorganisms in Cd and Pb tailings of the Eucalyptus camaldulensis rhizosphere

Mining tailings containing large amounts of Pb and Cd cause severe regional ecosystem pollution. Soil microorganisms play a regulatory role in the restoration of degraded ecosystems. The remediation of heavy metal-contaminated tailings with amendments and economically valuable Eucalyptus camaldulensis is a research hotspot due to its cost-effectiveness and sustainability. However, the succession and co-occurrence patterns of these microbial communities in this context remain unclear. Tailing samples of five kinds of Cd and Pb were collected in E. camaldulensis restoration models. Physicochemical properties, the proportions of different Cd and Pb forms, microbial community structure, and the co-occurrence network of rhizosphere tailings during different restoration process (organic bacterial manure, organic manure, inorganic fertilizer, bacterial agent) were considered. Organic and organic bacterial manures significantly increased pH, cation exchange capacity, and the proportion of residual Pb. Still, there was a significant decrease in the proportion of reducible Pb. The changes in microbial communities were related to physicochemical properties and the types of amendments. Organic and organic bacterium manures decreased the relative abundance of oligotrophic groups and increased the relative abundance of syntrophic groups. Inorganic fertilizers and bacterial agents decreased the relative abundance of saprophytic fungi. B. subtilis would play a better role in the environment improved by organic manure, increasing the relative abundance of beneficial microorganism and reducing the relative abundance of pathogenic microorganism. pH, cation exchange capacity, and the proportion of different forms of Pb were the main factors affecting the bacterial and fungi variation. All four amendments transformed the main critical groups of the microbial network structure from acidophilus and pathogenic microorganisms to beneficial microorganisms. Heavy metal-resistant microorganisms, stress-resistant microorganisms, beneficial microorganisms that promote nutrient cycling, and copiotrophic groups have become critical to building stable rhizosphere microbial communities. The topological properties and stability of the rhizosphere co-occurrence network were also enhanced. Adding organic and organic bacterium manures combined with E. camaldulensis to repair Cd and Pb tailings improved (1) pH and cation exchange capacity, (2) reduced the biological toxicity of Pb, (3) enhanced the stability of microbial networks, and (4) improved ecological network relationships. These positive changes are conducive to the restoration of the ecological functions of tailings.

Biostimulation of indigenous microbes for uranium bioremediation in former U mine water: multidisciplinary approach assessment

Characterizing uranium (U) mine water is necessary to understand and design an effective bioremediation strategy. In this study, water samples from two former U-mines in East Germany were analysed. The U and sulphate (SO42-) concentrations of Schlema-Alberoda mine water (U: 1 mg/L; SO42-: 335 mg/L) were 2 and 3 order of magnitude higher than those of the Pöhla sample (U: 0.01 mg/L; SO42-: 0.5 mg/L). U and SO42- seemed to influence the microbial diversity of the two water samples. Microbial diversity analysis identified U(VI)-reducing bacteria (e.g. Desulfurivibrio) and wood-degrading fungi (e.g. Cadophora) providing as electron donors for the growth of U-reducers. U-bioreduction experiments were performed to screen electron donors (glycerol, vanillic acid, and gluconic acid) for Schlema-Alberoda U-mine water bioremediation purpose. Thermodynamic speciation calculations show that under experimental conditions, U(VI) is not coordinated to the amended electron donors. Glycerol was the best-studied electron donor as it effectively removed 99% of soluble U, 95% of Fe, and 58% of SO42- from the mine water, probably by biostimulation of indigenous microbes. Vanillic acid removed 90% of U, and no U removal occurred using gluconic acid.

Distinct microbial structure and metabolic potential shaped by significant environmental gradient impacted by ferrous slag weathering

Alkaline ferrous slags pose global environmental issues and long-term risks to ambient environments. To explore the under-investigated microbial structure and biogeochemistry in such unique ecosystems, combined geochemical, microbial, ecological and metagenomic analyses were performed in the areas adjacent to a ferrous slag disposal plant in Sichuan, China. Different levels of exposure to ultrabasic slag leachate had resulted in a significant geochemical gradient of pH (8.0-12.4), electric potential (-126.9 to 437.9 mV), total organic carbon (TOC, 1.5-17.3 mg/L), and total nitrogen (TN, 0.17-1.01 mg/L). Distinct microbial communities were observed depending on their exposure to the strongly alkaline leachate. High pH and Ca2+ concentrations were associated with low microbial diversity and enrichment of bacterial classes Gamma-proteobacteria and Deinococci in the microbial communities exposed to the leachate. Combined metagenomic analyses of 4 leachate-unimpacted and 2-impacted microbial communities led to the assembly of one Serpentinomonas pangenome and 81 phylogenetically diversified metagenome assembled genomes (MAGs). The prevailing taxa in the leachate-impacted habitats (e.g., Serpentinomonas and Meiothermus spp.) were phylogenetically related to those in active serpentinizing ecosystems, suggesting the analogous processes between the man-made and natural systems. More importantly, they accounted for significant abundance of most functional genes associated with environmental adaptation and major element cycling. Their metabolic potential (e.g., cation/H+ antiporters, carbon fixation on lithospheric carbon source, and respiration coupling sulfur oxidization and oxygen or nitrate reduction) may support these taxa to survive and prosper in these unique geochemical niches. This study provides fundamental understandings of the adaptive strategies of microorganisms in response to the strong environmental perturbation by alkali tailings. It also contributes to a better comprehension of how to remediate environments affected by alkaline industrial material.

Insights into the relationship between denitrification and organic carbon release of solid-phase denitrification systems: Mechanism and microbial characteristics

Solid-phase denitrification is a promising alternative denitrification technology when facing a shortage of carbon sources. Nevertheless, it is still unclear whether there is a certain interaction between the denitrification process and the carbon release process in a solid-phase denitrification system. In this study, the concept of "Self-adaptation" was proposed for the relationship between denitrification and carbon release. At various influent nitrate loads, the PCL-supported denitrification system achieved an average nitrate removal rate of over 90.59 ± 7.01 % and a maximum denitrification rate of 0.67 ± 0.06 gN/(L·d). Microorganisms can spontaneously regulate the carbon release rate of PCL in response to changes in influent nitrate load, demonstrating "self-adaptation" of the PCL-supported solid-phase denitrification system. Regulation of carbon release rate via the "Self-adaptation" was achieved by changes in extracellular depolymerase activity. Acidovorax_sp. played a key role in "Self-adaptation", for its function of both denitrification and PCL degradation.