Elevated antimony concentration stimulates rare taxa of potential autotrophic bacteria in the Xikuangshan groundwater

Groundwater arsenic and antimony mobility from an antimony mining area: Controls of sulfide oxidation, carbonate and silicate weathering, and secondary mineral precipitation

Sulfide mineral oxidation has been recognized as the key driver of arsenic (As) and antimony (Sb) mobility in mining-impacted groundwater. However, the role of carbonate and silicate weathering and secondary mineral precipitation in this process remain unknown. A comprehensive geochemical study of groundwater was conducted in an Sb-mining area, Hunan, China, with samples collected from aquifers of the Xikuangshan Formation (D3x), the Shetianqiao Formation (D3s ), and the Lower Carboniferous Formation (C1y). Results show co-enrichment of dissolved As and Sb with concentrations reaching up to 28.8 and 22.1 mg/L, respectively. The significant positive correlation between SO42- and As or Sb concentrations, coupled with the similarity of δ34S-SO4 to δ34S signature of sulfide minerals (e.g., arsenopyrite and stibnite), indicate sulfide mineral oxidation as the primary mobilization mechanism. The significantly higher SO42- concentrations support more extensive sulfide mineral oxidation in the D3s aquifer than those in the D3x and C1y aquifers, which was responsible for its significantly higher As and Sb concentrations. The SO42-/Σ+ against Ca2+/Σ+ cross plot suggests that, in addition to sulfide mineral oxidation, silicate weathering was more prevalent in the D3s groundwater, which may contribute to enhance As and Sb mobility. However, carbonate dissolution triggered by sulfide mineral oxidation dominated in the C1y groundwater with significantly higher Ca2+/Σ+, favoring the precipitation of pharmacolite (CaHAsO4:2H2O) and Ca2Sb2O7, which acted as important sinks for dissolved As and Sb. This study highlights that, in addition to sulfide mineral oxidation, the carbonate and silicate weathering and precipitation of As and Sb-bearing minerals are also pivotal in influencing the As and Sb mobility in groundwater from a mining area.

Inhibition of denitrification and enhancement of microbial interactions in the AGS system by high concentrations of quinoline

Quinoline represents a highly toxic and structurally stable nitrogen-containing heterocyclic compound in coking wastewater, posing a potential threat to human beings and the ecological environment. In this study, we investigated the impact of gradually elevating quinoline concentration on pollutant removal efficiency, sludge characteristics, microbial community and their interactions in the aerobic granular sludge (AGS) system. The results demonstrated that AGS was capable of effectively degrading quinoline, with a final removal rate of 90 mg/L quinoline reaching 98.54 ± 0.28%. Notably, the denitrification process was significantly impeded in the presence of 90 mg/L quinoline, with the Phase D effluent displaying a notably high NO3--N concentration of 37.09 ± 21.81 mg/L, primarily attributed to the reduced abundance of norank_f_A4b bacteria. As the quinoline concentration increased, the sludge particle size diminished from 3.46 to 2.60 mm, while the settling performance deteriorated significantly, escalating from 31.29 ± 1.63 mL/g to 62.32 ± 2.87 mL/g. Meanwhile, the protein (PN) content in EPS gradually increased (from 19.87 ± 0.88 mg/g MLVSS to 51.22 ± 3.21 mg/g MLVSS), while the polysaccharide (PS) content fluctuated. Quinoline profoundly modified microbial community composition and structure, with deterministic processes dominating community assembly. Network analysis indicated intensified and complex microbial interactions at 90 mg/L quinoline, characterized by significantly higher positive correlations. In addition, rare taxa (RT) dominated the network nodes, with 74 of 93 key species belonging to RT, highlighting their pivotal roles in sustaining system functions and strengthening microbial connections. This study provides new insights into the effects of quinoline on microbial community structure and interactions in AGS system.

Novel insights into antimony mobilization in different high- antimony aquifers from the molecular signatures of dissolved organic matter

The crucial role of the fluorescent components of dissolved organic matter (DOM) in controlling antimony (Sb) mobilization in groundwater has been confirmed. However, the molecular signatures contributing to Sb enrichment in DOM remain unknown. This study aims to investigate the origins and molecular compositions of DOM in different high-Sb aquifers (Sb-mining and no-Sb-mining aquifer), as well as compare different molecular signatures of DOM and mechanisms for Sb migration. The findings showed that Sb concentrations in Sb-mining aquifer exhibited a positive correlation with lignin- and tannin-like molecules characterized by high O/C and low H/C ratios, indicating an increased abundance of aromatic components with higher Humification Index and SUV-absorbance at 254 nm, compared to no-Sb-mining aquifer. Correspondingly, the complexation and competitive adsorption were considered as the predominate formation mechanisms on Sb enrichment in Sb-mining aquifer. In addition, high abundances of bioreactivity DOM may facilitated the migration of Sb via electron transfer and competitive adsorption in native no-Sb-mining aquifer. The outcomes of this investigation offer novel insights into the mechanism on Sb enrichment influenced by DOM at the molecule level.

Stibnite dissolution and Sb oxidation by Paraccocus versutus XT0.6 via direct and indirect contact

In this study Paraccocus versutus XT0.6 was employed to address the mechanism of microbial dissolution and oxidation of stibnite. Results showed that with the growth of XT0.6, pH increased to 9.0 in both microbe-mineral contact (MM) and microbe-mineral non-contact groups (M[M]). Dissolved Sb(III) was released from stibnite, which was subsequently quickly oxidized to Sb(V) completely in MM and partially in M[M] groups. On the contrast, the final pH decreased to 6.5 and 4.9, respectviely, in system amended with extracellular secretion (EM) of XT0.6 and abiotic groups. Dissolution of stibnite and oxidation of Sb(III) were also observed in EM group, suggesting a potential contribution of extracellular enzyme in Sb(III) oxidation. The dissolution and oxidation rates were the highest in MM group, followed by those in M[M], EM and abiotic groups. To be noted, Sb(V) concentration decreased in MM group on the fifth day, which might indicate the formation of Sb(V)-bearing secondary mineral. Genome of XT0.6 consisted of two chromosomes and one plasmid, and most genes responsible for antimony oxidation and antimony resistance were located on the chromosomes. Proteomics analysis of the extracellular secretions indicated the up-regulated proteins were mainly related to electron-transfer, suggesting their potential role in Sb(III) oxidation.

Ecological and functional differences of abundant and rare sub-communities in wastewater treatment plants across China

The microbial community in activated sludge is composed of a small number of abundant sub-community with high abundance and a large number of rare sub-community with limited abundance. Our knowledge regarding the ecological properties of both abundant and rare sub-communities in activated sludge is limited. This article presented an analysis of functional prediction, assembly mechanisms, and biogeographic distribution characteristics of abundant and rare sub-communities in 211 activated sludge samples from 60 wastewater treatment plants across China. Moreover, this study investigated the dominant factors influencing the community structure of these two microbial groups. The results showed that the functions associated with carbon and nitrogen cycling were primarily detected in abundant sub-community, while rare sub-community were primarily involved in sulfur cycling. Both microbial groups were mainly influenced by dispersal limitation, which, to some extent, resulted in a distance-decay relationship in their biogeographic distribution. Moreover, a higher spatial turnover rate of rare sub-communities (0.0887) suggested that spatial differences in microbial community structure among different WWTPs may mainly result from rare sub-community. Moreover, SEM showed that geographic locations affected rare sub-communities greatly, which agreed with their higher dispersal limitation and turnover rate. In contrast, influent characteristics showed stronger correlations with abundant sub-communities, suggesting that abundant sub-community may contribute more to the removal of pollutants. This study enhanced our understanding of abundant and rare microorganisms in activated sludge especially the role of rare species and provided scientific evidence for precise regulation and control of wastewater treatment plants.

Characterization of an antimony-resistant fungus Sarocladium kiliense ZJ-1 and its potential as an antimony bio-remediator

Antimony (Sb) is a toxic metalloid widely distributed in the natural environments. Microorganisms, especially fungi, could serve as ideal biomaterials for bioremediation of Sb-polluted soils and waters. In this study, we isolated an antimony-resistant fungus, Sarocladium kiliense ZJ-1, from a slag sample collected in Xikuangshan Sb mine in P. R. China. ZJ-1 showed an extremely high resistance to Sb, with a MIC level of > 175 mM for arsenite [Sb(Ⅲ)] and 40 mM for arsenate [Sb(V)]. Whole genomic analysis identified multiple Sb (Ⅲ)- and/or As(Ⅲ)-resistant genes on ZJ-1's genome, which may partially explain its hyper-resistance to Sb. The potential of ZJ-1 in removing Sb from Sb(Ⅲ) or Sb(V) solutions was also quantified. The average biosorption capacity of ZJ-1 for Sb(Ⅲ) and Sb(V) is 635.14 mg/g and 149.65 mg/g, respectively, in Sb aqueous solutions with an initial concentration of 2000 mg/L (16.43 mM). Besides, almost 99% of Sb(Ⅲ) in the growing system was removed with an initial concentration of 500 mg/L (4.11 mM). Furthermore, Fourier transformation infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS) were used to probe the Sb adsorption mechanism on ZJ-1, and -OH, -NH2, -COOH, C-O and C-O-C were found to be the main surface functional groups of ZJ-1 cells to adsorb Sb.

Archaea are better adapted to antimony stress than their bacterial counterparts in Xikuangshan groundwater

Archaea are important ecological components of microbial communities in various environments, but are currently poorly investigated in antimony (Sb) contaminated groundwater particularly on their ecological differences in comparison with bacteria. To address this issue, groundwater samples were collected from Xikuangshan aquifer along an Sb gradient and subjected to 16S rRNA gene amplicon sequencing and bioinformatic analysis. The results demonstrated that bacterial communities were more susceptibly affected by elevated Sb concentration than their archaeal counterparts, and the positive stimulation of Sb concentration on bacterial diversity coincided with the intermediate disturbance hypothesis. Overall, the balance of environmental variables (Sb, pH, and EC), competitive interactions, and stochastic events jointly regulated bacterial and archaeal communities. Linear fitting analysis revealed that Sb significantly drove the deterministic process (heterogeneous selection) of bacterial communities, whereas stochastic process (dispersal limitation) contributed more to archaeal community assembly. In contract, the assembly of Sb-resistant bacteria and archaea was dominated by the stochastic process (undominated), which implied the important role of diversification and drift instead of selection. Compared with Sb-resistant microorganisms, bacterial and archaeal communities showed lower niche width, which may result from the constraints of Sb concentration and competitive interaction. Moreover, Sb-resistant archaea had a higher niche than that of Sb-resistant bacteria via investing on flexible metabolic pathways such as organic metabolism, ammonia oxidation; and carbon fixation to enhance their competitiveness. Our results offered new insights into the ecological adaptation mechanisms of bacteria and archaea in Sb-contaminated groundwater.

Rhizobacterial compositions and their relationships with soil properties and medicinal bioactive ingredients in Cinnamomum migao

Introduction

Rhizobacterial communities and their metabolites can affect plant growth, development, and stress resistance, as well as the biosynthesis and accumulation of bioactive compounds in medicinal plants. This relationship has been well-characterized in many medicinal herbs, although much less commonly in medicinal trees.

Methods

Here, we analyzed the composition and structure of Cinnamomum migao rhizobacterial communities across nine growing regions in Yunnan, Guizhou and Guangxi, China, as well as differences in soil properties and fruit bioactive compounds.

Results

Results showed that the C. migao rhizobacterial communities exhibited high species richness, but location-specific differences in structure. Site-specific differences in soil properties and bioactive compounds were also observed. Furthermore, rhizobacterial community compositions were correlated with both soil properties and fruit bioactive compounds, metabolism-related functions were most common in C. migao rhizobacteria.

Discussion

Several bacterial genera, including Acidothermus, Acidibacter, Bryobacter, Candidatus_Solibacter, and Acidimicrobiales, potentially promote the biosynthesis and accumulation of 1,8-cineole, cypressene, limonene, and α-terpineol, Nitrospira and Alphaproteobacteria may play an inhibitory role. Finally, our results emphasized the critical role that soil pH and nitrogen levels play in driving rhizobacterial community structure, and specific functional bacteria can also counteract with soil properties, Acidibacter and Nitrospira can affect soil pH and nitrogen effectiveness. Overall, this study provides additional insight into the complex correlation of rhizosphere microorganisms with bioactive ingredients and soil properties of medicinal plants.