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Industrial development has caused significant environmental pollution by discharging chromium (Cr) contaminated hazardous effluents into the ecosystem. The main goal of this study was to isolate, characterize, and assess the Cr(VI) resistance potential of indigenous naturally occurring chromate-resistant bacteria from the Uttar Dinajpur region of West Bengal. Based on the maximum tolerable concentration (MTC) to Cr(VI), a potent indigenous bacterial isolate with an MTC of 400 µg mL − 1 was selected for a detailed assessment of its Cr(VI) tolerance and reducing abilities. Molecular identification and phylogenetics revealed the isolate as a strain of Bacillus wiedmannii . Cr(VI) resistance ability of the isolate in different pH was analyzed, and a Fourier-transform infrared spectroscopy analysis under different pH in the presence of Cr(VI) was performed to capture the preliminary variation in the metabolic fingerprints. The isolate demonstrated Cr(VI) removal efficiency of 70.27% Cr(VI) at pH 8. The expression of chromate reductase enzyme in constitutive and Cr(VI) induced conditions was measured using different electron donors, and a detailed statistical analysis was performed to determine whether there exists a significant difference in the specific activity of chromate reductase in constitutive and induced conditions. The extracellular chromate reductase had a 98.42% Cr(VI) reduction rate using glucose as an electron donor and it was significantly higher than that of other electron donors, indicating glucose as the preferred electron source for Cr(VI) reduction. The genes responsible for coding enzymes responsible for chromate reduction viz., azoreductase, FMN-dependent NADH-azoreductase type1, and chromate reductase were also detected in the studied isolate. The findings of this study may contribute to the pool of indigenous isolates in countering chromate toxicity and their efficient utilization in chromate detoxification and bioremediation.

Chromate induced dermatitis is a significant occupational health concern. Chromate (Cr) resistant Lacticaseibacillus rhamnosus strains were isolated from commercial probiotic sachets PREPRO and HiFLORA. Among 13 Cr-resistant bacterial isolates, six were selected based on high chromate resistance at 500 ug/ml. Selected isolates were subjected to biochemical and molecular characterization and in vivo analyses. DPC assay was conducted under controlled conditions in order to determine the reduction potential of the isolated bacteria. The selected isolates were identified as L. rhamnosus -L1 (PP493917), L. rhamnosus -L2 (PP493918), L. rhamnosus -L3 (PP493921) L. rhamnosus -L4 (PP493920) L. rhamnosus -L8 (PP493922) and L. rhamnosus -L12 (PP493923). Lacticaseibacillus rhamnosus L1showed highest resistance against Cr (VI) with reduction potential 56%. In vivo experiments were performed to assess the healing effects of isolated bacterial strains on mice skin, with Hematoxylin and Eosin (H&E) staining used to identify severe dermatitis in skin tissue and evaluate therapeutic effects of probiotic strains. The structural determination of flavin reductase protein of L. rhamnosus was carried out using bioinformatics tools. These tools predicted the structural-based functional homology of flavin reductase protein in bacterial Cr (VI)-detoxification system. Lacticaseibacillus rhamnosus can be effectively used against chromate-induced dermatitis due to its high chromate resistance and reduction potential.

Chromium pollution is a problem that affects different areas worldwide and, therefore, must be solved. Bioremediation is a promising alternative to treat environmental contamination, but finding bacterial strains able to tolerate and remove different contaminants is a major challenge, since most co-polluted sites contain mixtures of organic and inorganic substances. In the present work, Bacillus sp. SFC 500-1E, isolated from the bacterial consortium SFC 500-1 native to tannery sediments, showed tolerance to various concentrations of different phenolic compounds and heavy metals, such as Cr(VI). This strain was able to efficiently remove Cr(VI), even in the presence of phenol. The detection of the chrA gene suggested that Cr(VI) extrusion could be a mechanism that allowed this strain to tolerate the heavy metal. However, reduction through cytosolic NADH-dependent chromate reductases may be the main mechanism involved in the remediation. The information provided in this study about the mechanisms through which Bacillus sp. SFC 500-1E removes Cr(VI) should be taken into account for the future application of this strain as a possible candidate to remediate contaminated environments.

Thiacalix[4]arenes as a family of promising ligands have been widely used to construct polynuclear metal clusters, but scarcely employed in silver nanoclusters. Herein, an anion-templated Ag 88 nanocluster (SD/Ag88a) built from p -tert-butylthiacalix[4]arene (H 4 TC4A) is reported. Single-crystal X-ray diffraction reveals that C 4 -symmetric SD/Ag88a resembles a metal-organic super calix comprised of eight TC4A 4− as walls and 88 silver atoms as base, which can be deconstructed to eight [CrO 4 @Ag 11 (TC4A)(EtS) 4 (OAc)] secondary building units arranged in an annulus encircling a CrO 4 2− in the center. Local and global anion template effects from chromates are individually manifested in SD/Ag88a. The solution stability and hierarchical assembly mechanism of SD/Ag88a are studied by using electrospray mass spectrometry. The Ag 88 nanocluster represents the highest nuclearity metal cluster capped by TC4A 4− . This work not only exemplify the specific macrocyclic effects of TC4A 4− in the construction of silver nanocluster but also realize the shape heredity of TC4A 4− to overall silver super calix. The assembly of giant silver clusters by using macrocylic multidentate ligand remains a challenge. Here, the authors synthesize a chromate-templated 88-nuclei silver super calix and reveal the role of anion templating effects and a hierarchical assembly mechanism.

Microbial bioreporters offer excellent potentialities for the detection of the bioavailable portion of pollutants in contaminated environments, which currently cannot be easily measured. This paper describes the construction and evaluation of two microbial bioreporters designed to detect the bioavailable chromate in contaminated water samples. The developed bioreporters are based on the expression of gfp under the control of the chr promoter and the chrB regulator gene of TnOtChr determinant from Ochrobactrum tritici 5bvl1. pCHRGFP1 Escherichia coli reporter proved to be specific and sensitive, with minimum detectable concentration of 100 nM chromate and did not react with other heavy metals or chemical compounds analysed. In order to have a bioreporter able to be used under different environmental toxics, O. tritici type strain was also engineered to fluoresce in the presence of micromolar levels of chromate and showed to be as specific as the first reporter. Their applicability on environmental samples (spiked Portuguese river water) was also demonstrated using either freshly grown or cryo-preserved cells, a treatment which constitutes an operational advantage. These reporter strains can provide on-demand usability in the field and in a near future may become a powerful tool in identification of chromate-contaminated sites.

Contamination of soil by toxic chromium (Cr) is a rising health issue due to over-exploitation and industrial production. Toxicity can be decreased by bioremediation because some microorganisms are able to convert highly toxic hexavalent chromium Cr(VI) into less toxic trivalent chromium Cr(III) by secreting chromate reductase. Moreover, microorganisms are able to remove Cr by adsorption on microbial cell walls. Plants can also be used for phytoremediation by uptaking Cr from soil into plant organs. Here, we review the speciation of Cr in soil, remediation methods to remove Cr, bioremediation challenges, and remaining ecological impacts after bioremediation. We present the mechanisms of microbial remediation, phytoremediation and plant–microbial combined remediation and applications.

In the past decades, chromium contamination of agricultural land has become an emerging concern. For land reclamation, several strategies including bioremediation have been used. Owing the potential of hyperaccumulators, the current project aims to enhance the phytoremediation potential of Brassica campestris L. with the application of chromate tolerant endophytic fungus Aspergillus niger CSR3. when B. campestris was watered with chromate concentration (300, 500, and 1000 ppm) in the form of potassium chromate (K 2 CrO 4 ), seed germination, hypocotyl length, root shoot length, and leaf area were severely reduced ( p  < 0.05). However, reproductive parts of the plants remained viable once initiated. Inoculation of the selected endophyte stimulated host growth, reducing the severity of the chromate stress. Interestingly, CSR3-inoculated plants accumulated 1.82-, 1.51-, and 2.16-fold greater quantities of chromate than the un-inoculated plants. To cope better with the stress, endophyte-associated host had stronger antioxidant system supported by enhanced production of nonenzymatic antioxidants (flavonoids, phenolics, and proline) and enzymatic antioxidants (SOD, CAT, APX, and POD) than the non-endophytes host plants. It may be concluded that hyperaccumulator B. campestris accumulates even higher quantities of chromate in the presence of endophytic A. niger CSR3 and tolerates elevated levels of chromate with boosted antioxidant system. Thus, hyperaccumulator host associated with heavy metal tolerant endophytic fungi can be the possible efficient way to reclaim the contaminated site from the heavy metals effectively in a short time period.

Chromate has been shown to dysregulate epigenetic mechanisms such as DNA methylation, leading to changes in gene expression and genomic instability. However, most in vitro studies are limited to short incubation periods, although chronic exposure may be more relevant for both environmental and occupational exposure. In this study, human adenocarcinoma A549 cells were treated with 1, 2 or 5 µM chromate for 24 h and compared with incubations with 0.2, 0.5 or 1 µM chromate for 1 to 5 weeks. Chromium accumulated in a pronounced time- and concentration-dependent manner after short-term treatment, whereas a plateau of intracellular chromium content was observed after long-term treatment. While short-term treatment induced a G2 arrest of the cell cycle, this effect was not observed after long-term treatment at lower concentrations. The opposite was observed for global DNA methylation: while short-term treatment showed no effect of chromate, significant dose-dependent hypomethylation was observed in the long-term experiments. Time-dependent effects were also observed in a high-throughput RT-qPCR gene expression analysis, particularly in genes related to the inflammatory response and DNA damage response. Taken together, the results suggest specific differences in toxicity profiles when comparing short-term and long-term exposure to chromate in A549 cells.

The Escherichia coli ChrR enzyme is an obligatory two-electron quinone reductase that has many applications, such as in chromate bioremediation. Its crystal structure, solved at 2.2 Å resolution, shows that it belongs to the flavodoxin superfamily in which flavin mononucleotide (FMN) is firmly anchored to the protein. ChrR crystallized as a tetramer, and size exclusion chromatography showed that this is the oligomeric form that catalyzes chromate reduction. Within the tetramer, the dimers interact by a pair of two hydrogen bond networks, each involving Tyr128 and Glu146 of one dimer and Arg125 and Tyr85 of the other; the latter extends to one of the redox FMN cofactors. Changes in each of these amino acids enhanced chromate reductase activity of the enzyme, showing that this network is centrally involved in chromate reduction.

Spherical black carbon aggregates were frequently observed in dust dry deposition in Daejeon, Korea. They were tens of micrometers in diameter and presented a mixture of black carbon and several mineral phases. Transmission electron microscopy (TEM) observations with energy-dispersive X-ray spectroscopy (EDS) and selected area diffraction pattern (SADP) analyses confirmed that the aggregates were compact and included significant amounts of lead chromate (PbCrO 4 ). The compositions and morphologies of the nanosized lead chromate particles suggest that they probably originated from traffic paint used in roads and were combined as discrete minerals with black carbon. Based on Pb isotope analysis and air-mass backward trajectories, the dust in Daejeon received a considerable input of anthropogenic pollutants from heavily industrialized Chinese cities, which implies that long-range transported aerosols containing PbCrO 4 were a possible source of the lead and hexavalent chromium levels in East Asia. Lead chromate should be considered to be a source of global atmospheric Pb and Cr(VI) pollution, especially given its toxicity.