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Heavy metals have been severely polluting the environment. However, the response mechanism of microbial communities to short-term heavy metals stress remains unclear. In this study, metagenomics (MG) and metatranscriptomics (MT) was performed to observe the microbial response to short-term Cr(VI) stress. MG data showed that 99.1% of species were similar in the control and Cr(VI) treated groups. However, MT data demonstrated that 83% of the microbes were active in which 58.7% increased, while the relative abundance of 41.3% decreased after short-term Cr(VI) incubation. The MT results also revealed 9% of microbes were dormant in samples. Genes associated with oxidative stress, Cr(VI) transport, resistance, and reduction, as well as genes with unknown functions were 2–10 times upregulated after Cr(VI) treatment. To further confirm the function of unknown genes, two genes (314 and 494) were selected to detect the Cr(VI) resistance and reduction ability. The results showed that these genes significantly increased the Cr(VI) remediation ability of Escherichia coli. MT results also revealed an increase in the expression of some rare genera (at least two times) after Cr(VI) treatment, indicating these rare species played a crucial role in microbial response to short-term Cr(VI) stress. In summary, MT is an efficient way to understand the role of active and dormant microbes in specific environmental conditions. [ABSTRACT FROM AUTHOR]

Serum uric acid elevation has been found in long-term nickel (Ni) exposure occupational workers, but the mechanism is unclear. In this study, the relationship between Ni exposure and uric acid elevation was explored in a cohort of 109 participants composed of a Ni-exposed workers group and a control group. The results showed that Ni concentration (5.70 ± 3.21 μg/L) and uric acid level (355.95 ± 67.87 μmol/L) in the serum were increased in the exposure group with a significant positive correlation (r = 0.413, p < 0.0001). The composition of gut microbiota and metabolome revealed that the abundance of uric acid-lowering bacteria, such as Lactobacillus , Lachnospiraceae _Unclassfied and Blautia were reduced while pathogenic bacteria including Parabacteriadies and Escherichia-Shigella were enriched in Ni group, accompanied by impaired intestinal degradation of purines and upregulated biosynthesis of primary bile acids. Consistent with human results, the mice experiments showed that Ni treatment significantly promotes uric acid elevation and systemic inflammation. Lactobacillus and Blautia in gut microbiota were reduced and inflammation-related taxa Alistipes and Mycoplasma were enriched in the Ni treatment. In addition, LC-MS/MS metabolomic analysis indicated that purine nucleosides were accumulated in mice feces, which increased purine absorption and uric acid elevation in the serum. In summary, this study provides evidence that UA elevation was correlated with heavy metals exposure and highlighted the role of gut microbiota in intestinal purine catabolism and in the pathogenesis of heavy metal-induced hyperuricemia. [Display omitted] • Serum uric acid level positively correlates with nickel exposure. • Abundances of uric acid-lowering bacteria are diminished upon nickel exposure. • Intestinal degradation of purine to uric acid is disturbed by nickel exposure. • Excessive nickel exerts toxic effects by disrupting gut microbiota. [ABSTRACT FROM AUTHOR]

The phytoremediated plant contains rich carbon resources, but the anaerobic digestion (AD) process can be inhibited due to high Heavy metals (HMs). In this study, the phytoremediated Halogeton glomeratus (H. glomeratus) was utilized in AD. Results showed that suitable HMs improved the AD efficiency, and the HMs were positively correlated to methane production and microbiota. Compared to CK (without HMs contaminated), H. glomeratus containing HMs (TG) enhanced methane production (increased 85.5%). Also, the highest VS removal rate of 66.5% were achieved. Furthermore, the increased of hydrolytic and acidogenic Acinetbacter and Hydrogenophaga improved substrates degradation. Besides, the methanogenic Methanosarcina increased from 6.5 to 89.5%, and the methanogenic pathway shifted from hydrogenotrophic methanogenesis to aceticlastic methanogenesis. Thus, substrates conversion to methane was improved. Finally, the HMs in digestion slurry were successfully removed and decreased its secondary pollution. This study provided a potential for the resourceful utilization of the phytoremediated plants with suitable HMs concentration. [Display omitted] [ABSTRACT FROM AUTHOR]

Biocathode application in microbial fuel cell has been developed as a sustainable technology for heavy metal reduction. However, most biocathodes require pretreatment with acclimatization inversion. Here, a biocathode MFC based on strain Corynebacterium vitaeruminis LZU47-1 without acclimatization inversion was constructed for hexavalent chromium reduction. The maximum power generation by the biocathode MFC with C. vitaeruminis LZU47-1 increased by 24.5% and 53.4% in inversion and abiotic cathode groups, respectively. Compared with the inversion (72.52%) and abiotic cathode groups (64.75%), the biocathode group achieved a Cr(VI) removal efficiency of 98.63%. Furthermore, electrochemical analysis such as SEM-EDS, XPS and CV test were conducted to elucidate the adsorption-reduction mechanism for Cr(VI) reduction. MiSeq sequencing revealed that Geobacter (51.28%) was enriched on the anode biofilm in the biocathode group than inversion (38.52%) and abiotic cathode groups (31.74%). Therefore, this study provides a convenient and highly effective method for enhancing power output and Cr(VI) reduction in biocathode MFCs. Image 1 • A Cr(VI) reduction strain LZU47-1 can form biofilm in electrode for current output. • A biocathode MFC was fabricated by strain LZU47-1 without acclimatization inversion. • High Cr(VI) reduction (98.63%) and power generation (252.36 mW/m2) were obtained. • Simultaneous treatment of combined pollutants with organic matters and heavy metals. [ABSTRACT FROM AUTHOR]

• The modified SA-kaolin carrier can be used in the aerobic activated-sludge system. • Immobilization help strain LZ-4 colonize in activated sludge. • Bioaugmentation protect denitrifiers from Cr(VI) toxicity. • Change of microbial community is the major reason for protection of denitrification. The inhibition of denitrification by heavy metals is a problem in nitrogen wastewater treatment, but the solutions are rarely studied. In this study, Pseudomonas brassicacearum LZ-4, immobilized in sodium alginate-kaolin, was applied in an activated-sludge reactor to protect denitrifiers from hexavalent chromium (Cr(VI)). Q-PCR result showed that the strain LZ-4 was incorporated into activated sludge under the help of immobilization. In the non-bioaugmentation system, the removal efficiency of nitrate was decreased by 86.07% by 30 mg/L Cr(VI). Whereas, denitrification was protected and 95% of nitrate was removed continuously in immobilized-cell bioaugmentation system. Miseq sequencing data showed that bioaugmentation decreased the impact of Cr(VI) on microbial communities and increased the abundance of denitrifiers. Based on the results of biomass and extracellular polymers, activated sludge was protected from Cr(VI) toxicity. This discovery will provide a feasible technique for nitrogen wastewater treatment in the presence of distressing heavy metals. [ABSTRACT FROM AUTHOR]

Abstract Heavy metals (HMs), which accumulate in digestion substrates, such as plant residues and livestock manure, can affect biogas yields during anaerobic digestion (AD). Low concentration of Cu2+ (0–100 mg/L), Fe2+ (50–4000 mg/L), Ni2+ (0.8–50 mg/L), Cd2+ (0.1–0.3 mg/L), and Zn2+ (0–5 mg/kg) promote biogas production, while high concentrations inhibit AD. Trace amounts of HMs are necessary for the activity of some enzymes. For example, Cu2+ and Cd2+ serve as cofactors in the catalytic center of cellulase and stimulate enzyme activity. High contents of Cd2+ and Cu2+ inhibit enzyme activity by disrupting protein structures. Trace amounts of HMs stimulate the growth and activity of methanogens, while high levels have toxic effects on methanogens. HMs affect the hydrolysis, acidification, and other biochemical reactions of organics in AD by changing the enzyme structure and they also impact methanogen growth. A better understanding of the impact of HMs on AD can provide valuable insights for improving the digestion of poultry manure and plant residues contaminated with HMs, as well as help mitigate HMs pollution. Although several studies have been conducted in this field, few comprehensive reviews have examined the effect of many common HMs on AD. This review summarizes the effects of HMs on the biogas production efficiency of AD and also discusses the effects of HMs on the activities of enzymes and microbial communities. Graphical abstract Image 10243 Highlights • Heavy metals reduce cellulase activity by altering the enzyme spatial structure. • Heavy metals inhibit methanogens growth and reduce their activities. • Heavy metals have minor effects on pH and VFA concentration in anaerobic digestion. [ABSTRACT FROM AUTHOR]