Research on the decomposition mechanisms of lithium silicate ores with different crystal structures by autotrophic and heterotrophic bacteria.

Ores serve as energy and nutrient sources for microorganisms. Through complex biochemical processes, microorganisms disrupt the surface structure of ores and release metal elements. However, there is limited research on the mechanisms by which bacteria with different nutritional modes act during the leaching process of different crystal structure ores. This study evaluated the leaching efficiency of two types of bacteria with different nutritional modes, heterotrophic bacterium Bacillus mucilaginosus (BM) and autotrophic bacterium Acidithiobacillus ferrooxidans (AF), on different crystal structure lithium silicate ores (chain spodumene, layered lepidolite and ring elbaite). The aim was to understand the behavioral differences and decomposition mechanisms of bacteria with different nutritional modes in the process of breaking down distorted crystal lattices of ores. The results revealed that heterotrophic bacterium BM primarily relied on passive processes such as bacterial adsorption, organic acid corrosion, and the complexation of small organic acids and large molecular polymers with metal ions. Autotrophic bacterium AF, in addition to exhibiting stronger passive processes such as organic acid corrosion and complexation, also utilized an active transfer process on the cell surface to oxidize Fe2+ in the ores for energy maintenance and intensified the destruction of ore lattices. As a result, strain AF exhibited a greater leaching effect on the ores compared to strain BM. Regarding the three crystal structure ores, their different stacking modes and proportions of elements led to significant differences in structural stability, with the leaching effect being highest for layered structure, followed by chain structure, and then ring structure. These findings indicate that bacteria with different nutritional modes exhibit distinct physiological behaviors related to their nutritional and energy requirements, ultimately resulting in different sequences and mechanisms of metal ion release from ores after lattice damage.

Lithium extraction from typical lithium silicate ores by two bacteria with different metabolic characteristics: Experiments, mechanism and significance.

Microorganisms obtain inorganic nutrients or energy from specific minerals to selectively weather minerals, but few studies on the differences in metabolic components of different functional bacteria lead to different weathering effects. This study evaluated the leaching effects of two bacteria with distinct metabolic characteristics on lithium silicate minerals with different structures. We aimed to understand the microscopic mechanism of crystal destruction of lithium silicate minerals with different structures under the action of microorganisms. The results showed that the metabolites produced by an acid producing silicate strain Raoultella sp. Z107 (strain Z107) had a high content of organic acids, among which lactic acid was up to about 11 g/L. Bacillus mucilaginosus 21,699 (strain BM) secreted capsular polysaccharide with a high content of 14.84 mg/L. The metabolic activities of the two strains were significantly different. Through the analysis of the leaching residue, it was found that the lithium silicate minerals were acid etched, interlayer domains expanded, crystallinity decreased, and metal bonds were broken under the action of bacteria. The dissolution of lithium silicate minerals by bacteria is a combination of bacterial adsorption, organic acid corrosion, and complexation of small molecular organic acids and macromolecular polymers with metal ions. The acid erosion and complexation effects of organic acids are greater than the single complexation of capsular polysaccharides, and the layered lepidolite is more likely to be decomposed by the weathering of bacterial metabolites than the chain structure spodumene. These results indicate that the diversity of metabolic activity of bacteria from different sources and the sequence and decomposition mechanism of metal ions released from minerals after lattice destruction are also different. Microorganisms decompose minerals for energy and nutrients, and eventually become the main players in the transformation of elements in biogeology.

[Microbial Community Composition and Diversity in Metal Sulfide Mine Water Systems].

To understand the characteristics of heavy metal pollution and physicochemical properties caused by mining activities in mine water systems and the response of the microbial community to habitats with different contamination levels, this study selected different types of water (mining area wastewater, spoil heap area wastewater, dressing area wastewater, mine seepage water, and pond water) as the variables related to the mining activities in the water system of the Shizishan mining area in Tongling, Anhui Province. The pollution characteristics and physicochemical properties were compared, and the relationship between environmental factors and the microbial communities were analyzed. The results showed that the content of heavy metals, the physicochemical properties, and the structure and diversity of the microbial community of different types of water were significantly different in different mine areas, among which the most seriously polluted areas were the mining area, the spoil heap area, and the dressing area. There were significant differences in microbial community structure among different functional types of wastewaters, and the diversity and abundance of the microbial community in DW with the heaviest heavy metal pollution were weaker than those in the other four regions. PcoA analysis showed that samples of similar water types had similar clustering. Spearman correlation heat map analysis and canonical correlation analysis (CCA) indicated that heavy metal pollution, pH, electrical conductivity (EC), SO2-4, and chemical oxygen demand (COD) had the greatest effect on the microbial communities in the mine water systems. Moreover, this study found that Proteobacteria, Euryarchaeota, and Bacteroidetes dominated in mine water systems, and their potential use could be explored in the future. Our results provide a better understanding of the different types of water pollution characteristics in mine water systems and the key factors that determine the microbial community structure.

Synergistic remediation of lead pollution by biochar combined with phosphate solubilizing bacteria.

Pb(II) is extreme toxic to biological cells, which limits the restoration of Pb(II) by functional strains. This study examined a Pb(II)-tolerant phosphate solubilizing bacteria(PSB) Ochrobactrum sp. J023 combined with corn stover biochar to enhance the immobilization of Pb(II). The results showed that the removal rate of Pb(II) by biochar combined with phosphate-solubilizing bacteria was as high as 71.30 %. SEM-EDS showed that more disordered crystals appeared on the surface of biochar treated with bacteria. XRD analysis indicated that the mineralization products of Pb(II) in biochar combined strain system were mainly in Pb5(PO4)3OH and Pb5(PO4)3Cl. FT-IR analysis revealed that there were more phosphate groups involved in the mineralization process when biochar was added. XPS verified the formation of PbO or lead-containing precipitates in this system, and the amount of lead precipitates was larger. The mechanism of lead fixation by strain combined with biochar can be regarded that the strain regulates the microenvironment of the biochar surface, enhances the release of phosphate and promotes the generation of stable pyroxite. Moreover, biochar composition and porous structure not only provide nutrient elements for strains, but also protect and promote the metabolism of strains. Biochar adsorption also reduces the loss of available phosphorus, which helps PSB to fix Pb sustainably and effectively. This suggests that the synergistic effect of PSB-biochar can not only effectively reduce the mobility and bioavailability of Pb(II), but also increase the sustainability of remediation. Therefore, the combination of phosphate solubilizing bacteria and biochar is a promising approach to the remediation of heavy metal pollution.

Effect of the phosphate solubilization and mineralization synergistic mechanism of Ochrobactrum sp. on the remediation of lead.

Phosphate-solubilizing bacteria (PSB) promotes the formation of mineralized precipitation through phosphorous dissolution and mineralization, forming stable lead (Pb(II)) minerals and reducing the migration of Pb(II) in the environment. In this study, a Pb-tolerant strain Ochrobactrum sp. J023 from a contaminated soil around a battery factory in Jiangsu Province, China, was screened for experiments to investigate the phosphate solubilization and mineralization mechanism of this strain. The organic acids and the acid phosphatase produced by the bacteria have a synergistic effect on phosphate dissolution. When the pH of the culture medium decreased to the lowest 4.55, the amount of soluble phosphate and the activity of acid phosphatase reached the maximum 161.29 mg L-1 and 61.98 U mL-1, and there was a significant correlation between the concentration of soluble phosphate and the activity of acid phosphatase (R = 0.832**, P < 0.05). It was found that acetic acid played the most important role in the secreted organic acids. During the mineralization reaction, the extracellular polymeric substances (EPS) chelates part of the Pb(II) on the surface of the cell wall, preventing the metal Pb from penetrating into the cell, thus providing protection to the strain. Meanwhile, due to the nucleation sites provided by cell surface groups (carboxyl and phosphate groups), a large number of metal ions are absorbed to promote the formation of crystallization. The final mineralized product of Pb(II) by strain J023 was pyroxite (Pb5(PO4)3X, where X = Cl, OH). The mechanism of phosphate dissolution and mineralization proposed by us is that the organic acids and acid phosphatases secreted by phosphate-solubilizing bacteria promote the increase of PO43- concentration in the solution, the complexation of metal cations and cell surface groups will induce the formation of mineralized precipitation under the catalysis of enzyme. Therefore, it is a promising strategy for bioremediation of lead pollution by screening functional strains with strong abilities of phosphate solubility and mineralization.

Ecological Effects of Heavy Metal Pollution on Soil Microbial Community Structure and Diversity on Both Sides of a River around a Mining Area.

The objectives of this study were to understand the characteristics of heavy metal pollution caused by mining activities on the two sides of the Shun'an river and the response of soil microorganisms to the habitats by different contamination levels and vegetation. This paper selected soil samples from the banks of the Shun'an River near the Shizishan mining area, which is at the left of the river, in Tongling, Anhui Province, China. Using Illumina MiSeq 2500 technology, we analyzed the relationship between environmental factors and microbial communities. As the distance from the mining area increased, the heavy metal comprehensive pollution and potential risk value decreased. Additionally, the pollution severity and risk value of the left bank, where the mining area lies, were generally higher than those of the right bank. Because the symmetric sampling points on both banks of the river had similar planting types, their environmental factors and microbial community structure were similar and clustered. However, under different vegetation, the paddy soils tended to have a higher nutrient content and community richness and diversity than the vegetable fields or the abandoned land. It was found that soil microbial communities in this area were mostly affected by pH and Nemerow pollution index (PN). The pH significantly affected the abundance and structure of most microorganisms. In addition, Proteobacteria, Acidobacteria, and Bacteroidetes had significant tolerance to Zn, Pb, and Cd. By exploring the potential use of these tolerant microorganisms, we seek to provide strains and the theoretical basis for the bioremediation of areas contaminated by heavy metal.

Effects of soil heavy metal pollution on microbial activities and community diversity in different land use types in mining areas.

Microbial activities and community structures play crucial roles in the soil environment and can be served as effective indicators to assess the ecological influence of heavy metal pollution in soil. This article selected soil samples from five land use types (mining area, mineral processing area, heap mining area, tailing area, and vegetable area) in the Shizishan mining area in Tongling, Anhui Province, China. The physicochemical properties, pollution characteristics, enzyme activities (catalase, urease, alkaline phosphatase, neutral phosphatase, cellulase, and sucrase), microbial biomass carbon (MBC), basal respiration (SBR), and metabolic entropy (qCO2) in soil were determined and compared, and the relationship between environmental factors and the microbial activities and community diversity was analyzed. The results showed that, according to the Nemerow's Pollution Index (PN), the values were the heap mining area (24.47) > mineral processing area (12.55) > mining area (9.81) > tailings area (6.02) > vegetable area (4.51). With the increase of heavy metal contamination in the sampling area, the six enzyme activities, MBC and SBR decreased, but the qCO2 increased. Principal coordinate analysis (PCoA) and canonical correlation analysis (CCA) showed that the land use types, soil moisture content (MC), heavy metal content, pH, MBC, SBR, and qCO2 were significantly affected by the microbial community. The most dominant phyla were Proteobacteria (34.73%), Bacteroidetes (9.25%), Acidobacteria (8.99%), and Chloroflexi (8.68%) at the phylum (0.01) level by a total of 18 phyla. It was also found that Firmicutes and Phormidium were more tolerant to heavy metals. These results contributed to an insight into key environmental variables shaping the microbial activities, community structure, and diversity under various land use types in mining area.

[Effects of Different Land Use Types on Microbial Community Diversity in the Shizishan Mining Area].

Soil microorganisms play an important role in ecosystem function. Soil microbial community structure can be used to feed back the status of heavy metal pollution in soil at different functional areas of mines related to mining activities. Samples of four different land use types (vegetable garden, tailings reservoir, heap mining area, and dressing area) were collected in the Shizishan mining area, Tongling, Anhui Province, to determine the effect of heavy metal pollution on microbial community structure. Soil physical and chemical properties and heavy metal contents of the four different land use types were measured, and soil microbial community abundance and structure diversity were analyzed by Illumina MiSeq high-throughput sequencing technology. The results show that there are significant differences in physical and chemical properties between different regions. The comprehensive pollution index of Nemerow is heap mining area (7.28) > dressing area (6.99) > tailings reservoir (6.55) > vegetable garden (5.92). The distribution of microbial community abundance and structure diversity was tailings reservoir > dressing area > vegetable garden > heap mining area. In addition, principal coordinates analysis (PCoA), canonical correspondence analysis (CCA), and correlation analysis showed that land use type, soil pH and heavy metal content had significant effects on the microbial community. The dominant soil microbial communities at the phylum level were Proteobacteria, Bacteroidetes, Acidobacteria, and Actinobacteria, at the class level were ß-Proteobacteria, α-Proteobacteria, and γ-Proteobacteria, and at the genus level were Flavobacterium, Kaistobacter, and Ramlibacter. The bacteria that are more tolerant to heavy metals are Proteobacteria, Firmicutes, ß-Proteobacteria, and Kaistobacter. These results have deepened our understanding of microbial changes and aggregation patterns in soils of heavy-metal-contaminated mining areas. This study can provide bacterial species and theoretical basis for bioremediation of heavy metal mining areas.

Study on the Remediation of Cd Pollution by the Biomineralization of Urease-Producing Bacteria.

Cadmium (Cd) is a highly toxic metal that can affect human health and environmental safety. The purpose of this study was to research the removal of Cd from an environmental perspective. In this article, four highly urease-active strains (CZW-2, CZW-5, CZW-9 and CZW-12) were isolated from an abandoned mine and their phylogenetic trees were analyzed. The maximum enzyme activities, the mineralized precipitate and the removal rates of these strains were compared. The results showed that CZW-2 had the highest urease activity at 51.6 U/mL, and the removal rates of CZW-2, CZW-5, CZW-9 and CZW-12 after 120 h were 80.10%, 72.64%, 76.70% and 73.40%, with an initial concentration of Cd of 2 mM in the Cd precipitation experiments. XRD (X-ray diffractometer), EDS (Energy dispersive spectrometer) and FTIR (Fourier transform infrared spectroscopy) analysis indicated that the mineralized precipitate was CdCO3. SEM (Scanning electron microscopy) analysis revealed that the diameter of the oval-shaped mineralized product ranked from 0.5 to 2 µm. These strains were used to remedy Cd-contaminated soil, and five different fractions of Cd were measured. Compared with the control, the results of spraying pre-cultured strains containing 2% urea to remove Cd from contaminated soils showed that the exchangeable fraction of Cd decreased by 53.30%, 27.78%, 42.54% and 53.80%, respectively, whereas the carbonate-bound fraction increased by 55.42%, 20.27%, 39.67% and 34.36%, respectively, after one month. These data show that these strains can effectively reduce the bioavailability and mobility of Cd in contaminated soils. The results indicate that biomineralization based on the decomposition of substrate urea can be applied to remedy heavy contaminated soil and water.

Study on the influence of soil microbial community on the long-term heavy metal pollution of different land use types and depth layers in mine.

To understand the importance of the response of soil microbial communities to the stress of heavy metals around mining areas by assessing the feedback of soil ecosystems in different soil habitats, this article selected different land use types (Mining area, Dressing area, Heap mine area, Tailings area and Vegetable field) and surface soil samples of different depths (0-10 cm, 10-20 cm, 20-30 cm) as the variables related to the mining activities in the Shizishan mining area in Tongling, Anhui Province, China. Soil physicochemical properties and heavy metal concentrations of the different land use types and soil depths were compared. Illumina MiSeq. 2500 Sequencing Technology was used to analyze the abundance and structural diversity of the microbial community in soil samples. The relationship between mine soil pollution characteristics and microbial community were investigated. The results showed that soil physicochemical properties and heavy metals significantly affected the microbial community. The microbial community structure was significantly variable in vertical soil depth-layer habitats. The relative abundance (1%) of the soil microbial community at the phylum level was represented by a total of 14 phyla, where the two most dominant phyla were Proteobacteria (41.71%) and Firmicutes (20.44%). The two bacteria were positively related with Cu, Zn, Pb, and pH but negatively associated with soil organic matter (SOM), available potassium (AK), and moisture content (MC). Therefore, Proteobacteria and Firmicutes were highly resistant to heavy metals. These results increased our understanding of microbial variation and assembly pattern under different land use types in heavy metals contaminated mining soils.

Characterization of depth-related microbial communities in lake sediment by denaturing gradient gel electrophoresis of amplified 16S rRNA fragments.

The characterization of microbial communities of different depth sediment samples was examined by a culture-independent method and compared with physicochemical parameters, those are organic matter (OM), total nitrogen (TN), total phosphorus (TP), pH and redox potential (Eh). Total genomic DNA was extracted from samples derived from different depths. After they were amplified with the GC-341f/907r primer sets of partial bacterial 16S rRNA genes, the products were separated by denaturing gradient gel electrophoresis (DGGE). The profile of DGGE fingerprints of different depth sediment samples revealed that the community structure remained relatively stable along the entire 45 cm sediment core, however, principal-component analysis of DGGE patterns revealed that at greater sediment depths, successional shifts in community structure were evident. The principle coordinates analysis suggested that the bacterial communities along the sediment core could be separated into two groups, which were located 0--20 cm and 21--45 cm, respectively. The sequencing dominant bands demonstrated that the major phylogenetic groups identified by DGGE belonged to Bacillus, Bacterium, Brevibacillus, Exiguobacterium, gamma-Proteobacterium, Acinetobacter sp. and some uncultured or unidentified bacteria. The results indicated the existence of highly diverse bacterial community in the lake sediment core.

[Vertical distribution of physicochemical characteristics and the microbial diversity in different spatial sediments samples in Lake Taihu].

The physicochemical characteristics, nutritions and the microbial community diversity of sediment core samples of three different space locations in the Lake Taihu were studied by fumigation-digestion and PCR-DGGE analysis respectively. The results indicated that below the surface of sediments Eh declined rapidly with increase of sediment depth and it was under anaerobic condition except the top layer of sediment. pH value changed silightly in the profile of sediments, which ranged from 7.2 to 7.8. TN and TP concentrations in sediments of Lake Taihu were high,and the maximum concentrations reached 2.436 mg/g and 0.731 mg/g, respectively. Their vertical profiles showed that TN and TP concentrations in surface sediments were much higher than in deeper layers and decreased with the increase of the depth of sediment layers. OM concentrations declined rapidly at the top 15 cm of sediment layers. There were prominent difference spatially in microbial diversity and the comparability and dynamics of community structure between different sediment samples of different space locations and different depth. The little significant correlation at alpha < or = 0.05 level was observed between the Eh, pH, percentage organic matter, TN concentration and TP concentration and microbial community structure diversity index except of TN concentration and percentage organic matter.