Expression Changes in Metal-Resistance Genes in Microbacterium liquefaciens Under Nickel and Vanadium Exposure

Influence pathways of vanadium stress to microbial community in soil-tailings-groundwater systems

The large-scale exploitation of vanadium (V) bearing minerals has led to a massive accumulation of V tailings, of which V pollution poses severe ecological risks. Although the mechanisms of V stress to the microbial community have been reported, the influential pathways in a multi-medium-containing system, for example, the soil-tailings-groundwater system, are unknown. The dynamic redox conditions and substance exchange within the system exhibited complex V stress on the local microbial communities. In this study, the influence pathways of V stress to the microbial community in the soil-tailings-groundwater system were first investigated. High V contents were observed in groundwater (139.2 ± 0.15 µg/L) and soil (98.0-323.8 ± 0.02 mg/kg), respectively. Distinct microbial composition was observed for soil and groundwater, where soil showed the highest level of diversity and richness. Firmicutes, Proteobacteria, Actinobacteria, and Acidobacteria were dominant in soil and groundwater with a sum relative abundance of around 80 %. Based on redundancy analysis and structural equation models, V was one of the vital driving factors affecting microbial communities. Groundwater microbial communities were influenced by V via Cr, dissolved oxygen, and total nitrogen, while Fe, Mn, and total phosphorus were the key mediators for V to affect soil microbial communities. V affected the microbial community via metabolic pathways related to carbonaceous matter, which was involved in the establishment of survival strategies for metal stress. This study provides novel insights into the influence pathways of V on the microorganisms in tailings reservoir for pollution bioremediation.

A novel method for achieving ecological indicator based on vertical soil bacterial communities coupled with machine learning: A case study of a typical tropical site in China

Global industrialization has resulted in severe contamination of soil with heavy metals (HMs). Nevertheless, it is unclear if it affects the depth-resolved bacterial communities. Herein, we collected soil samples at different depths from a typical HM-contaminated site and used amplicon sequencing to determine the differences in depth-resolved bacterial communities and to assess the thresholds and ecological impacts of HMs. Results revealed that HM levels reduced markedly with soil depth. The bacteria in upper soil exhibited higher community diversity and a more complex and stable ecological network structure. As depth increased, the proportion of negative interactions gradually elevated, indicating more competitive interspecies behavior. Threshold analyses based on machine learning revealed that arsenic (As) and copper (Cu) exhibited nonlinear impacts on ecosystems. Cu demonstrated a low-threshold effect, with its ecological consequences manifested at extremely low concentrations. Our results highlighted the utility of microbial monitoring in assessing the adverse effects of HMs on soil health to support environmental management and ecological restoration.

Vanadium in the Environment: Biogeochemistry and Bioremediation

Vanadium(V) is a highly toxic multivalent, redox-sensitive element. It is widely distributed in the environment and employed in various industrial applications. Interactions between V and (micro)organisms have recently garnered considerable attention. This Review discusses the biogeochemical cycling of V and its corresponding bioremediation strategies. Anthropogenic activities have resulted in elevated environmental V concentrations compared to natural emissions. The global distributions of V in the atmosphere, soils, water bodies, and sediments are outlined here, with notable prevalence in Europe. Soluble V(V) predominantly exists in the environment and exhibits high mobility and chemical reactivity. The transport of V within environmental media and across food chains is also discussed. Microbially mediated V transformation is evaluated to shed light on the primary mechanisms underlying microbial V(V) reduction, namely electron transfer and enzymatic catalysis. Additionally, this Review highlights bioremediation strategies by exploring their geochemical influences and technical implementation methods. The identified knowledge gaps include the particulate speciation of V and its associated environmental behaviors as well as the biogeochemical processes of V in marine environments. Finally, challenges for future research are reported, including the screening of V hyperaccumulators and V(V)-reducing microbes and field tests for bioremediation approaches.

Reduction mechanisms of V5+ by vanadium-reducing bacteria in aqueous environments: Role of different molecular weight fractionated extracellular polymeric substances

Extracellular polymeric substances (EPS) are high-molecular polymers secreted by microbes and play essential roles in metallic biogeochemical cycling. Previous studies demonstrated the reducing capacity of the functional groups on EPS for metal reduction. However, the roles of different EPS components in vanadium speciation and their responsible reducing substances for vanadium reduction are still unknown. In this study, the EPS of Bacillus sp. PFYN01 was fractionated via ultrafiltration into six components with different kDa (EPS_>100, EPS_100-50, EPS_50-30, EPS_30-10, EPS_10-3, and EPS_<3). Batch reduction experiments of the intact cells, EPS-free cells, the pristine and fractionated EPS with V⁵⁺ were conducted and characterized. The results demonstrated that the extracellular reduction of V⁵⁺ into V⁴⁺ by EPS was the major reduction process. Among the functional groups in EPS, C=O/C-N of amide in protein/polypeptide and CO of carboxyl in fulvic acid-like substances might act as the reductants for V⁵⁺, while CO in polysaccharide molecules and PO in phosphodiester played a key role in the adsorption process. The intracellular reduction was via translocating V⁵⁺ into the cells and releasing V⁴⁺ by the intracellular reductases. The reducing capacity of the fractionated EPS followed a sequence of EPS_<3 > EPS_10-3 > EPS_50-30 > EPS_100-50 > EPS_30-10 > EPS_>100. The small molecules of fulvic acid-like substances and amino acids were responsible for the high reducing capacity of EPS_<3. EPS_>100 had the lowest reducing capacity due to its macromolecular structure decreasing the exposure of the reactive sites. In addition to reduction, those intermediate EPS components may also have supporting functions, such as connecting protein skeletons and increasing the specific surface area of EPS. Therefore, the diverse effects of the EPS components cannot be neglected in vanadium biogeochemical cycling.

Unraveling diverse survival strategies of microorganisms to vanadium stress in aquatic environments

Worldwide vanadium contamination is posing serious risks to ecosystems. Although abilities of microbial communities to cope with vanadium stress using specific survival strategies have been reported, little is known regarding their relative importance and the underlying detoxification/tolerance mechanisms. Herein, we investigated the potential survival strategies of microbial communities and associated pathways in aquatic environments based on geochemistry and molecular biology. High vanadium content was observed for both water (12.6 ± 1.15 mg/L) and sediment (1.18 × 10³ ± 10.4 mg/kg) in the investigated polluted stream. Co-occurrence network investigation implied that microbial communities showed cooperative interactions to adapt to the vanadium-polluted condition. Vanadium was also characterized as one of the vital factors shaping the community structure via redundancy analysis and structural equation models. Based on the metagenomic technology, three survival strategies including denitrification pathway, electron transfer, and metal resistance in innate microbes under the vanadium stress were revealed, with comprehensively summarized vanadium detoxification/tolerance genes. Remarkable role of electron transfer genes and the prevalent existence of resistance genes during detoxifying vanadium were highlighted. Overall, these findings provide novel insights into survival strategies under the vanadium contamination in aquatic environments, which can be of great significance for the identification, isolation, and application of vanadium reducing bacteria in vanadium bioremediation.

(NH4)2[Co(H2O)6]2V10O28·4H2O Vs. (NH4)2[Ni(H2O)6]2V10O28·4H2O: Structural, Spectral and Thermal Analyses and Evaluation of Their Antibacterial Activities

This paper presents the synthesis of two cluster compounds {(NH4)2[Co(H2O)6]2V10O28·4H2O (C1) and (NH4)2[Ni(H2O)6]2V10O28·4H2O (C2)} which were obtained as single crystals suitable for XRD analysis that revealed their crystallization in the monoclinic (C2/c) and triclinic (P-1) space groups, respectively. Additionally, C1 and C2 were characterized using CHN analysis and FT-IR spectroscopy and their thermal decomposition mechanisms were investigated. The antibacterial activities of both compounds were determined against three human pathogenic bacterial strains {Bacillus cereus ATCC 33,018, Escherichia coli O157:H7 and Pseudomonas aeruginosa ATCC 9027} and one phytopathogenic bacterial strain {Ralstonia solanacearum}, while drug standards {chloramphenicol and streptomycin} were used as control. The inhibitory activity and the minimum inhibitory concentration (MIC) values of the tested compounds clearly indicated higher antibacterial activities of the nickel compound against B. cereus ATCC 33,018, E. coli O157 and R. solanacearum with MIC values of 3.150, 3.150 and 6.300 mg/ml, respectively. On the other hand, (NH4)2[Co(H2O)6]2V10O28·4H2O exhibited higher antibacterial activity against P. aeruginosa ATCC 9027 (MIC value of 6.300 mg/ml) in comparison to the nickel analog. In general, the measured activities are lower than that obtained for the standards except for the higher activity given by C2 in comparison to streptomycin against the R. solanacearum strain.

Characterization of cadmium biosorption by inactive biomass of two cadmium-tolerant endophytic bacteria Microbacterium sp. D2-2 and Bacillus sp. C9-3

In this study, two cadmium-tolerant endophytic bacteria (Microbacterium sp. D2-2 and Bacillus sp. C9-3) were employed as biosorbents to remove Cd(II) from aqueous solutions. The influence of initial pH, initial Cd(II) concentration, adsorbent biomass, temperature and contact time on Cd(II) removal were investigated. Results showed that the Langmuir isotherms were found to best fit the equilibrium data, and the maximum biosorption capacities were found to be 222.22 and 163.93 mg/g at a solution pH of 5.0 for Microbacterium sp. D2-2 and Bacillus sp. C9-3, respectively. The biosorption kinetics followed well pseudo-second-order kinetics. Fourier transform infrared spectroscopic analysis suggested that the hydroxyl, carboxyl, carbonyl and amino groups on Microbacterium sp. D2-2 and Bacillus sp. C9-3 biomass were the main binding sites for Cd(II). The results presented in this study showed that Microbacterium sp. D2-2 and Bacillus sp. C9-3 are potential and promising adsorbents for the effective removal of Cd(II) from aqueous solutions.

Metagenomic sequencing reveals detoxifying and tolerant functional genes in predominant bacteria assist Metaphire guillelmi adapt to soil vanadium exposure

Due to extensive vanadium (V) mining and processing, an increasing amount of V has accumulated in soil, which poses a threat to public health. Consequently, we used earthworm (Metaphire guillelmi) incubation trials in V-contaminated soil (0-300 mg kg^-1) to explore the response of soil indigenous bacteria and earthworm intestinal bacteria to V stress. Metagenomic analysis revealed that V exposure changed the bacterial composition in the soil and the worm gut. However, although the core species varied between soil and worm gut, the two systems shared the predominant bacteria, including Staphylococcus, Nocardioides, Streptococcus, and Nitrosopumilales. Two functional genotypes were detected in the shared core species, i.e., reductive genes and resistant genes. The reductive genes mainly consisted of those involved in glutathione, cysteine, methionine, sulfur, and nitrogen metabolisms. The resistant genes included those encoding the oxidation damage repair system, the outer membrane protein, the antioxidant enzyme system, the metal-binding, and the heavy-metal efflux. Therefore, the shared core species exert a comprehensive strategy to survive V stress involving the alliance of heavy metal detoxifying and tolerant genes. This study provides novel information about the detoxification mechanisms of bacterial populations in soil and worm gut to survive V stress.

Soil vanadium(V)-reducing related bacteria drive community response to vanadium pollution from a smelting plant over multiple gradients

The mining and smelting of navajoite has resulted in a serious vanadium pollution in regional geological environments and significant influence on soil microorganisms. However, the core microbiome responsible for adjusting community response to vanadium pollution and the driving pattern have been kept unclear. In this study, a suite of surface and profile soil samples over multiple gradients were collected in four directions and distances of 10-2000 m from a vanadium smelting plant in Panzhihua, China. The indigenous microbial communities and vanadium(V)-reducing related bacteria (VRB) were profiled by 16S rRNA gene high-throughput sequencing technique. Five VRB were detected in the original collected soil samples including Bacillus, Geobacter, Clostridium, Pseudomonas and Comamonadaceae based on high-throughput sequencing data analysis, and their abundances were significantly related with the content of vanadium. Low vanadium concentration promoted the growth of VRB, while high vanadium concentration would inhibit VRB multiplication. The Gaussian equation could be used to quantitatively describe the nonlinear relationship between VRB and vanadium. Network analysis demonstrated that the microbial communities were significantly influenced by VRB assemblage, and 1.32-52.77% of microbes in the community showed a close association with VRB. A laboratory incubation experiment also confirmed the core role of VRB to drive community response to vanadium pressure.

Microbial inoculant and garbage enzyme reduced cadmium (Cd) uptake in Salvia miltiorrhiza (Bge.) under Cd stress

The uptake and accumulation of cadmium (Cd) in Salvia miltiorrhiza (Bge.) negatively affects the quality of its harvested roots, and seriously threatens human health. This study investigates the effect of a microbial inoculant (MI) and garbage enzyme (GE) on Cd uptake, the accumulation of bioactive compounds, and the community composition of microbes in the rhizosphere soil of S. miltiorrhiza under Cd stress. S. miltiorrhiza seedlings were transplanted to Cd-contaminated pots and irrigated with an MI, GE, a combination of an MI and GE (MIGE) or water (control). The results indicated that treatments with an MI, GE or MIGE can reduce Cd uptake in S. miltiorrhiza. The MIGE treatment had greater efficiency in reducing Cd uptake than the control (reduction by 37.90%), followed by the GE (25.31%) and MI (5.84%) treatments. Treatments with an MI, GE and MIGE had no significant impact on fresh and dry root biomass. Relative to the control, the MI treatment had the highest efficiency in increasing the accumulation of total tanshinones (an increase of 40.45%), followed by the GE treatment (40.08%), with the MIGE treatment (9.90%) treatment not having a more favorable effect than the separate application of an MI or GE. The salvianolic acid content for all groups was higher than the standard prescribed by Chinese pharmacopoeia, notwithstanding a slightly lower level in the treated groups relative to the control. In addition, metagenomic analysis indicated changes in the relative abundance of soil microbes associated with the bioremediation of heavy metals. The relative abundances of Brevundimonas, Microbacterium, Cupriavidus and Aspergillus were significantly greater in the treated groups than in the Control. These results suggest that using MI and GE, either separately or together, may not only improve the quality of S. miltiorrhiza but may also facilitate the microbial remediation of soil contaminated with Cd.

The bacterial diversity on steam vents from Paricutín and Sapichu volcanoes

Vapor steam vents are prevailing structures on geothermal sites in which local geochemical conditions allow the development of extremophilic microorganisms. We describe the structure of the prokaryotic community able to grow on the walls and rocks of such microecosystems in two terrestrial Mexican volcanoes: Paricutín (PI and PII samples) and its satellite Sapichu (S sample). The investigated samples showed similar diversity indices, with few dominant OTUs (abundance > 1%): 21, 16 and 23, respectively for PI, PII and S. However, each steam vent showed a particular community profile: PI was dominated by photosynthetic bacteria (Cyanobacteria and Chloroflexia class), PII by Actinobacteria and Proteobacteria, and S by Ktedonobacteria class, Acidobacteria and Cyanobacteria phyla. Concerning the predicted metabolic potential, we found a dominance of cellular pathways, especially the ones for energy generation with metabolisms for sulfur respiration, nitrogen fixation, methanogenesis, carbon fixation, photosynthesis, and metals, among others. We suggest a different maturity stage for the three studied fumaroles, from the youngest (PI) to the oldest (S and PII), also influenced by the temperature and other geochemical parameters. Furthermore, four anaerobic strains were isolated, belonging to Clostridia class (Clostridium sphenoides, C. swellfunanium and Anaerocolumna cellulosilytica) and to Bacilli class (Paenibacillus azoreducens).