Gene function and expression regulation of RuvRCAB in bacterial Cr(VI), As(III), Sb(III), and Cd(II) resistance

Adsorption capacity of Penicillium amphipolaria XK11 for cadmium and antimony

Heavy metal pollution is a global problem that affects both the environment and human health. Microorganisms play an important role in remediation. Most studies on the use of microorganisms for heavy metal remediation focus on single heavy metals. In this study, a strain of Penicillium amphipolaria, XK11 with high resistance to both antimony (Sb III) and cadmium (Cd II) was screened from the mineral slag. The strain also had a high phosphate solubilization capacity. The single-factor adsorption experiment results showed that the initial pH (pH₀), adsorption time (T), and initial solution concentration (C₀) all affected the adsorption of Sb and Cd by XK11. When the initial pH₀ (Cd = 6, Sb = 4) and adsorption time (T = 7 d) were constant, XK11 achieved the maximum removal rate of Cd (45.6%) and Sb (34.6%). These results confirm that XK11 has potential as a biomaterial or remediation of Sb and Cd pollution.

Chromium (VI) bioremoval from contaminated wastewater using Pseudomonas aeruginosa ATHA23 producing biofilm supported on clinoptilolite

More has yet to be investigated on the increased efficiency of microbes for the removal of heavy metals from industrial wastewaters. The objective was to determine the Cr (VI) bioabsorption and bioreduction ability of biofilm-producing bacteria supported on clinoptilolite from contaminated aqueous solutions. Chromium (VI)-tolerant bacteria, namely Pseudomonas aeruginosa ATHA23, were identified by biochemical methods and 16S rDNA sequencing and were deposited in NCBI (accession number: KF680991). Preparation of clinoptilolite, bacterial growth and isolation, biofilm production including extracellular polysaccharides (EPS) and Cr (VI) removal efficiency, affected by the experimental treatments, were investigated. The use of FTIR characterized clinoptilolite properties with and without biofilm in the presence and absence of Cr (IV). Higher Cr (VI) levels in the bacterial growth medium, increased EPS production with the highest value (0.171 mg L^-1), produced 18 h after treating the bacteria with Cr (VI) (100 mg L^-1). However, in the absence of Cr (VI), EPS significantly decreased to 0.117 mg L^-1. Plackett-Burman and Taguchi statistical analyses were used to optimize the experimental treatments affecting the removal efficiency of Cr (VI). Among the anions (nitrate, sulfate, and chloride), sulfate decreased Cr removal efficiency. The absorption data were best fitted to the pseudo-second order, and the data of Cr adsorption by clinoptilolite-biofilm were also better fitted to Freundlich isotherm model. The Cr (VI) bioremediation potential of P. aeruginosa ATHA23 by the production of biofilm supported on clinoptilolite has been shown for the first time, which is of significance for the environment and the industry.

In silico Structural and Functional Characterization of a Hypothetical Protein from Stenotrophomonas maltophilia SRM01

Stenotrophomonas maltophilia is a low-virulence opportunistic pathogen that causes human infections, especially in profound ill patients. Even if the bacterial genomes seem understood, the activities of many proteins are unknown. The purpose of our current research is to unravel the functional characteristics i.e. functional domain search and valuable regions of a hypothetical protein that would aid in the identification of potential drug targets in Stenotrophomonas maltophilia. The hypothetical protein of S.maltophilia was located and annotated using different in silico techniques. Our target protein was predicted to be Transcrip Reg superfamily YebC/PmpR based on motif and domain analysis by functional annotation tools. The regulator proteins of the YebC family are part of a vast collection of widely conserved hypothetical proteins with unclear functions. Examining and reviewing the function of YebC family protein, they repress Quorum sensing by directly binding to the promoter region of QS master regulator pqrS. It has also been reported that T3SS expression is regulated by YebC, to activate the virulence expression direct interaction with one of the T3SS promoters is needed.

Identification of a Novel Chromate and Selenite Reductase FesR in Alishewanella sp. WH16-1

A ferredoxin protein (AAY72_06850, named FesR) was identified to associate with chromate [Cr(VI)] resistance in Alishewanella sp. WH16-1. FesR and its similar proteins were phylogenetically separated from other reductase families. Unlike the reported Cr(VI) and selenite [Se(IV)] reductases, two 4Fe-4S clusters and one flavin adenine dinucleotide (FAD) -binding domain were found in the FesR sequence. The experiment in vivo showed that the mutant strain ΔfesR had lost partial Cr(VI) and Se(IV) reduction capacities compared to the wild-type and complemented strains. Furthermore, overexpression in Escherichia coli and enzymatic tests in vitro showed FesR were involved in Cr(VI) and Se(IV) reduction. 4Fe-4S cluster in purified FesR was detected by ultraviolet-visible spectrum (UV-VIS) and Electron Paramagnetic Resonance (EPR). The Km values of FesR for Cr(VI) and Se(IV) reduction were 1682.0 ± 126.2 and 1164.0 ± 89.4 μmol/L, and the Vmax values for Cr(VI) and Se(IV) reduction were 4.1 ± 0.1 and 9.4 ± 0.3 μmol min^–1 mg^–1, respectively. Additionally, site-directed mutagenesis and redox potential analyses showed that 4Fe-4S clusters were essential to FesR, and FAD could enhance the enzyme efficiencies of FesR as intracellular electron transporters. To the best of our knowledge, FesR is a novel Cr(VI) and Se(IV) reductase.

Cd immobilization mechanisms in a Pseudomonas strain and its application in soil Cd remediation

In this study, we isolated a highly cadmium (Cd)-resistant bacterium, Pseudomonas sp. B7, which immobilized 100% Cd(II) from medium. Culturing strain B7 with Cd(II) led to the change of functional groups, mediating extracellular Cd(II) adsorption. Proteomics showed that a carbonic anhydrase, CadW, was upregulated with Cd(II). CadW expression in Escherichia coli conferred resistance to Cd(II) and increased intracellular Cd(II) accumulation. Fluorescence assays demonstrated that CadW binds Cd(II) and the His123 residue affected Cd(II) binding activity, indicating that CadW participates in intracellular Cd(II) sequestration. Chinese cabbage pot experiments were performed using strain B7 and silicate [Si(IV)]. Compared with the control, Cd content in aboveground parts significantly decreased by 21.3%, 29.4% and 32.9%, and nonbioavailable Cd in soil significantly increased by 129.4%, 45.0% and 148.7% in B7, Si(IV) and B7 +Si(IV) treatments, respectively. The application of Si(IV) alone reduced chlorophyll content by 20.8% and arylsulfatase activity in soil by 33.9%, and increased malonaldehyde activity by 15.0%. The application of strain B7 alleviated the negative effect of Si(IV) on plant and soil enzymes. Overall, application of Si(IV) is most conducive to the decreased Cd accumulation in plant, and strain B7 is beneficial to maintaining soil and plant health.

Microbial Cd(II) and Cr(VI) resistance mechanisms and application in bioremediation

The heavy metals cadmium (Cd) and chromium (Cr) are extensively used in industry and result in water and soil contamination. The highly toxic Cd(II) and Cr(VI) are the most common soluble forms of Cd and Cr, respectively. They enter the human body through the food chain and drinking water and then cause serious illnesses. Microorganisms can adsorb metals or transform Cd(II) and Cr(VI) into insoluble or less bioavailable forms, and such strategies are applicable in Cd and Cr bioremediation. This review focuses on the highlighting of novel achievements on microbial Cd(II) and Cr(VI) resistance mechanisms and their bioremediation applications. In addition, the knowledge gaps and research perspectives are also discussed in order to build a bridge between the theoretical breakthrough and the resolution of Cd(II) and Cr(VI) contamination problems.

Elucidation of a Novel Role of YebC in Surface Polysaccharides Regulation of Escherichia coli bipA-Deletion

The BipA (BPI-inducible protein A) protein is ubiquitously conserved in various bacterial species and belongs to the translational GTPase family. Interestingly, the function of Escherichia coli BipA is not essential for cell growth under normal growth conditions. However, cultivation of bipA-deleted cells at 20°C leads to cold-sensitive growth defect and several phenotypic changes in ribosome assembly, capsule production, and motility, suggesting its global regulatory roles. Previously, our genomic library screening revealed that the overexpressed ribosomal protein (r-protein) L20 partially suppressed cold-sensitive growth defect by resolving the ribosomal abnormality in bipA-deleted cells at low temperature. Here, we explored another genomic library clone containing yebC, which encodes a predicted transcriptional factor that is not directly associated with ribosome biogenesis. Interestingly, overexpression of yebC in bipA-deleted cells diminished capsule synthesis and partially restored lipopolysaccharide (LPS) core maturation at a low temperature without resolving defects in ribosome assembly or motility, indicating that YebC may be specifically involved in the regulation of exopolysaccharide and LPS core synthesis. In this study, we collectively investigated the impacts of bipA-deletion on E. coli capsule, LPS, biofilm formation, and motility and revealed novel roles of YebC in extracellular polysaccharide production and LPS core synthesis at low temperature using this mutant strain. Furthermore, our findings suggest that ribosomal defects as well as increased capsule synthesis, and changes in LPS composition may contribute independently to the cold-sensitivity of bipA-deleted cells, implying multiple regulatory roles of BipA.

Understanding Stress Response to High-Arsenic Gold-Bearing Sulfide Concentrate in Extremely Metal-Resistant Acidophile Sulfobacillus thermotolerans

Biooxidation of gold-bearing arsenopyrite concentrates, using acidophilic microbial communities, is among the largest commercial biohydrometallurgical processes. However, molecular mechanisms of microbial responses to sulfide raw materials have not been widely studied. The goal of this research was to gain insight into the defense strategies of the acidophilic bacterium Sulfobacillus thermotolerans, which dominates microbial communities functioning in industrial biooxidation processes at >35 °C, against the toxic effect of the high-arsenic gold-bearing sulfide concentrate. In addition to extreme metal resistance, this acidophile proved to be one of the most As-tolerant microorganisms. Comparative proteomic analysis indicated that 30 out of 33 differentially expressed proteins were upregulated in response to the ore concentrate, while the synthesis level of the functional proteins required for cell survival was not negatively affected. Despite a high level of cellular metal(loid) accumulation, no specific metal(loid)-resistant systems were regulated. Instead, several proteins involved in the metabolic pathways and stress response, including MBL fold metallo-hydrolase, sulfide:quinone oxidoreductase, and GroEL chaperonin, may play crucial roles in resistance to the sulfide ore concentrate and arsenic, in particular. This study provides the first data on the microbial responses to sulfide ore concentrates and advances our understanding of defense mechanisms against toxic compounds in acidophiles.