Microbial characterization of heavy metal resistant bacterial strains isolated from an electroplating wastewater treatment plant

Unravelling the mechanism of arsenic resistance and bioremediation in Stenotrophomonas maltophilia: A molecular approach

The mechanism of arsenic resistance in bacteria is under studied and still lacks a clear understanding despite of wide research work. The advanced technologies can help in analysing the arsenic bioremediating bacteria at a molecular level. With this line of idea, highly efficient arsenic bioremediating S. maltophilia was subjected to extensive analysis to understand the mechanism of arsenic resistance and bioremediation. The cell surface analysis revealed that S. maltophilia induces only slight changes in cell surface in the presence of arsenic. Whereas, TEM analysis has indicated the bioaccumulation of arsenic in S. maltophilia. Also, arsenic was found to generate ROS in a concentration dependant manner, and in response, S. maltophilia activated SOD, catalase, thioredoxin reductase etc. to manage oxidative stress which is very much crucial in managing arsenic toxicity. S. maltophilia was found to possess genes such as arsC, aoxB, aoxC and aioA. These genes are involved in arsenic reduction and oxidation. Transcriptomics and proteomics analysis have shown that S. maltophilia detoxifies arsenic by upregulating ars operon, arsH, BetB etc. which are responsible for arsenic reduction, efflux methylation, oxidation etc. A detailed molecular mechanism of arsenic bioremediation in S. maltophilia was put forth.

Microbial Contributions to Heavy Metal Phytoremediation in Agricultural Soils: A Review

Phytoremediation is a sustainable technique that employs plants to reinforce polluted environments such as agroecosystems. In recent years, new strategies involving the plant microbiome as an adjuvant in remediation processes have been reported. By leveraging this microbial assistance to remediate soils contaminated with heavy metals such As, Pb, Cd, Hg, and Cr, plants can sequester, degrade, or stabilize contaminants more efficiently. Remarkably, some plant species are known for their hyper-accumulative traits in synergy with their microbial partners and can successfully mitigate heavy metal pollutants. This sustainable biotechnology based on plant-microbe associations not only aids in environmental cleanup but also enhances biodiversity, improves soil structure, and promotes plant growth and health, making it a promising solution for addressing agro-pollution challenges worldwide. The current review article emphasizes the potential of synergistic plant-microbe interactions in developing practical and sustainable solutions for heavy metal remediation in agricultural systems, which are essential for food security.

Biosorption of copper, nickel, and manganese as well as the production of metal nanoparticles by Bacillus species isolated from soils contaminated with electronic wastes

Improper electronic waste management in the world especially in developing countries such as Iran has resulted in environmental pollution. Copper, nickel, and manganese are from the most concerned soil contaminating heavy metals which found in many electronic devices that are not properly processed. The aim of this study was to investigate the biological removal of copper, nickel, and manganese by Bacillus species isolated from a landfill of electronic waste (Zainal Pass hills located in Isfahan, Iran) which is the and to produce nanoparticles from the studied metals by the isolated bacteria. The amounts of copper, nickel, and manganese in the soil was measured as 1.9 × 104 mg/kg, 0.011 × 104 mg/kg and 0.013 × 104 mg/kg, respectively based on ICP-OES analysis, which was significantly higher than normal (0.02 mg/kg, 0.05 mg/kg, and 2 mg/kg, respectively. The minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) of metals on the bacterial isolates was determined. The biosorption of metals by the bacteria was evaluated by inductively coupled plasma optical emission spectroscopy (ICP-OES). The metal nanoparticles were synthetized utilizing the isolates in culture media containing the heavy metals with the concentrations to which the isolates had shown resistance. X ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) were used for the evaluation of the fabrication of the produced metal nanoparticles. Based on the findings of this study, a total of 15 bacterial isolates were obtained from the soil samples. The obtained MICs of copper, nickel, and manganese on the isolates were 40-300 mM, 4-10 mM, and 60-120 mM, respectively. The most resistant isolates to copper were FM1 and FM2 which were able to bio-remove 79.81% and 68.69% of the metal, respectively. FM4 and FM5 were respectively the most resistant isolate to nickel and manganese and were able to bio-remove 86.74% and 91.96% of the metals, respectively. FM1, FM2, FM4, and FM5 was molecularly identified as Bacillus cereus, Bacillus thuringiensis, Bacillus paramycoides, and Bacillus wiedmannii, respectively. The results of XRD, SEM and EDS showed conversion of the copper and manganese into spherical and oval nanoparticles with the approximate sizes of 20-40 nm. Due to the fact that the novel strains in this study showed high resistance to copper, nickel, and manganese and high adsorption of the metals, they can be used in the future, as suitable strains for the bio-removal of these metals from electronic and other industrial wastes.

A systematic review of antibiotics and antibiotic resistance genes (ARGs) in mariculture wastewater: Antibiotics removal by microalgal-bacterial symbiotic system (MBSS), ARGs characterization on the metagenomic

Antibiotic residues in mariculture wastewater seriously affect the aquatic environment. Antibiotic Resistance Genes (ARGs) produced under antibiotic stress flow through the environment and eventually enter the human body, seriously affecting human health. Microalgal-bacterial symbiotic system (MBSS) can remove antibiotics from mariculture and reduce the flow of ARGs into the environment. This review encapsulates the present scenario of mariculture wastewater, the removal mechanism of MBSS for antibiotics, and the biomolecular information under metagenomic assay. When confronted with antibiotics, there was a notable augmentation in the extracellular polymeric substances (EPS) content within MBSS, along with a concurrent elevation in the proportion of protein (PN) constituents within the EPS, which limits the entry of antibiotics into the cellular interior. Quorum sensing stimulates the microorganisms to produce biological responses (DNA synthesis - for adhesion) through signaling. Oxidative stress promotes gene expression (coupling, conjugation) to enhance horizontal gene transfer (HGT) in MBSS. The microbial community under metagenomic detection is dominated by aerobic bacteria in the bacterial-microalgal system. Compared to aerobic bacteria, anaerobic bacteria had the significant advantage of decreasing the distribution of ARGs. Overall, MBSS exhibits remarkable efficacy in mitigating the challenges posed by antibiotics and resistant genes from mariculture wastewater.

Unravelling the mechanisms of antibiotic and heavy metal resistance co-selection in environmental bacteria

The co-selective pressure of heavy metals is a contributor to the dissemination and persistence of antibiotic resistance genes in environmental reservoirs. The overlapping range of antibiotic and metal contamination and similarities in their resistance mechanisms point to an intertwined evolutionary history. Metal resistance genes are known to be genetically linked to antibiotic resistance genes, with plasmids, transposons, and integrons involved in the assembly and horizontal transfer of the resistance elements. Models of co-selection between metals and antibiotics have been proposed, however, the molecular aspects of these phenomena are in many cases not defined or quantified and the importance of specific metals, environments, bacterial taxa, mobile genetic elements, and other abiotic or biotic conditions are not clear. Co-resistance is often suggested as a dominant mechanism, but interpretations are beset with correlational bias. Proof of principle examples of cross-resistance and co-regulation has been described but more in-depth characterizations are needed, using methodologies that confirm the functional expression of resistance genes and that connect genes with specific bacterial hosts. Here, we comprehensively evaluate the recent evidence for different models of co-selection from pure culture and metagenomic studies in environmental contexts and we highlight outstanding questions.

Effects of simulated acid rain on hydrochemical factors and microbial community structure in red soil aquifers

Acid rain can lower the pH of groundwater and affect its hydrogeochemistry and microbial ecology. However, the effects of acid rain on the hydrogeochemistry and microbial ecology of red soil groundwater systems in southern China are poorly understood. Previous research had mainly investigated the sources and patterns of groundwater acidification, but not the microbial mechanisms that contribute to this process and their associations with hydrochemical factors. To address this knowledge gap, we conducted a soil column experiment to simulate the infiltration of acid rain through various filter materials (coarse, medium, and fine sand) and to examine the hydrochemical and microbial features of the infiltrate, which can reveal how simulated acid rain (pH 3.5-7.0) alters the hydrochemistry and microbial community composition in red soil aquifers. The results showed that the pH of the leachate decreased due to simulated acid rain, and that the leaching efficiency of nitrogen and metal ions was influenced by the particle size of the filter media. Illumina 16S rRNA gene sequencing revealed that the leachate was dominated by Proteobacteria, Patescibacteria, Actinobacteria, and Acidobacteria, with Proteobacteria accounting for 67.04-74.69% of the bacterial community and containing a high proportion of nitrifying and denitrifying bacteria. Additionally, several genera with heavy metal tolerance, such as Burkholderia-Caballeronia-Paraburkholderia, Delftia, Methylversatilis, Aquicella, and Ralstonia, were widely distributed in the leachate, indicating the strong adaptive capacity of the microbial population. A correlation analysis between the hydrochemical factors and the microbial community structure revealed that pH was the most influential factor, followed by NO2--N, Fe, Al, Cu, Mn, and others. These results indicate that acidification modifies the hydrochemical conditions of the aquifer, creating an environment that is unfavorable for microbial growth and survival. However, some microorganisms may acquire resistance genes to cope with environmental changes.

Antibiotic and Heavy Metal Co-Resistant Strain Isolated from Enrichment Culture of Marine Sediments, with Potential for Environmental Bioremediation Applications

Antibiotics and heavy metals have caused serious contamination of the environment and even resulted in public health concerns. It has therefore become even more urgent to adopt a sustainable approach to combating these polluted environments. In this paper, we investigated the microbial community of marine sediment samples after 255 days of enrichment culture under Cu (II) and lincomycin stress and ZC255 was the most resistant strain obtained. The 16S rRNA gene sequence confirmed that it belonged to the genus Rossellomorea. Strain ZC255 was resistant to 12 kinds of antibiotics, and had a superior tolerance to Cu (II), Pb (II), Ni (II), Zn (II), Cr (III), and Cd (II). Moreover, it exhibits strong bioremoval ability of Cu and lincomycin. The removal efficiency of Cu (II) and lincomycin can achieve 651 mg/g biomass and 32.5 mg/g biomass, respectively. Strain ZC255 was a promising isolate for pollution bioremediation applications.

Whole Genome Sequence Analysis of Cupriavidus necator C39, a Multiple Heavy Metal(loid) and Antibiotic Resistant Bacterium Isolated from a Gold/Copper Mine

Here a multiple heavy metal and antibiotic resistant bacterium Cupriavidus necator C39 (C. necator C39) was isolated from a Gold-Copper mine in Zijin, Fujian, China. C. necator C39 was able to tolerate intermediate concentrations of heavy metal(loid)s in Tris Minimal (TMM) Medium (Cu(II) 2 mM, Zn(II) 2 mM, Ni(II) 0.2 mM, Au(III) 70 μM and As(III) 2.5 mM). In addition, high resistance to multiple antibiotics was experimentally observed. Moreover, strain C39 was able to grow on TMM medium containing aromatic compounds such as benzoate, phenol, indole, p-hydroxybenzoic acid or phloroglucinol anhydrous as the sole carbon sources. The complete genome of this strain revealed 2 circular chromosomes and 1 plasmid, and showed the closest type strain is C. necator N-1^T based on Genome BLAST Distance Phylogeny. The arsenic-resistance (ars) cluster GST-arsR-arsICBR-yciI and a scattered gene encoding the putative arsenite efflux pump ArsB were identified on the genome of strain C39, which thereby may provide the bacterium a robust capability for arsenic resistance. Genes encoding multidrug resistance efflux pump may confer high antibiotic resistance to strain C39. Key genes encoding functions in degradation pathways of benzene compounds, including benzoate, phenol, benzamide, catechol, 3- or 4-fluorobenzoate, 3- or 4-hydroxybenzoate and 3,4-dihydroxybenzoate, indicated its potential for degrading those benzene compounds.

Process parameters and biological mechanism of efficient removal of Cd(II) ion from wastewater by a novel Bacillus subtilis TR1

The safe treatment of heavy metals in wastewater is directly related to the human health and social development. In this paper, a new biological strain has been isolated from electroplating wastewater, which can effectively remove metal ions in wastewater. The results of 16 S rDNA sequencing analysis and NCBI GenBank database comparison show that the strain belongs to a novel Bacillus genus and names Bacillus subtilis TR1 with the accession number of OL441606. The removal rate of Cd(II) reaches to 85.68% with the conditions of pH = 7, C_0Cd(II) = 20 mg L^-1, t = 48 h, m = 0.1 g, and T = 35 °C. The biological removal mechanism of Cd(II) is in-depth studied by FTIR and XRD combined with third-generation sequencing. The results indicate that Bacillus subtilis TR1 removes Cd(II) mainly through two synergistic pathways, namely, extracellular chemisorption and intracellular bioaccumulation: 1) The groups carried on the surface of the strain, such as -COOH, -NH, -OH and C-H, have good chemisorption properties for Cd(II) and easily form cadmium containing chelation (-COO-Cd(II), -N-Cd(II), etc.) with these groups. The appearance of TR1 strain changes from cylindrical to spherical after Cd(II) adsorption, which is due to the biotoxicity of Cd(II); 2) Cd(II) exchanges on the surface of TR1 strain with K and Na ions released from the intracellular cytoplasm and enters the cytoplasm under the transfer of biological transport medium. This part of Cd(II) is converted into its own components by anabolic enzymes and accumulates in the cytoplasm. These data provide a new biological agent for the efficient treatment of heavy metal ions in wastewater and enrich relevant theoretical knowledge.

Impact of lead (Pb2+) on the growth and biological activity of Serratia marcescens selected for wastewater treatment and identification of its zntR gene-a metal efflux regulator

Microorganisms isolated from contaminated areas play an important role in bioremediation processes. They promote heavy metal removal from the environment by adsorbing ions onto the cell wall surface, accumulating them inside the cells, or reducing, complexing, or precipitating these substances in the environment. Microorganism-based bioremediation processes can be highly efficient, low-cost and have low environmental impact. Thus, the present study aimed to select Pb²⁺-resistant bacteria and evaluate the growth rate, biological activity, and the presence of genes associated with metal resistance. Serratia marcescens CCMA 1010, that was previously isolated from coffee processing wastewater, was selected since was able to growth in Pb²⁺ concentrations of up to 4.0 mM. The growth rate and generation time did not differ from those of the control (without Pb²⁺), although biological activity decreased in the first hour of exposure to these ions and stabilized after this period. The presence of the zntR, zntA and pbrA genes was analysed, and only zntR was detected. The zntR gene encodes a protein responsible for regulating the production of ZntA, a transmembrane protein that facilitates Pb²⁺ extrusion out of the cell. S. marcescens CCMA 1010 demonstrated a potential for use as bioindicator that has potential to be used in bioremediation processes due to its resistance to high concentrations of Pb²⁺, ability to grow until 24 h of exposure, and possession of a gene that indicates the existence of mechanisms associated with resistance to lead (Pb²⁺).

Investigating the effects of biodegradable microplastics and copper ions on probiotic (Bacillus amyloliquefaciens): Toxicity and application

Currently, microplastic pollution is more serious and complicates the toxic effects of other co-existing pollutants in the environment. However, the effect and mechanism of biodegradable plastics on the growth and metabolism of probiotic remain unclear. This work selected Bacillus amyloliquefaciens as model bacterium for a three-day exposure experiment to probe the issues. The results showed that 100 mg/L polylactic acid microplastics (PLA MPs) (3-4 mm, flake shape) caused oxidative damage to cell membranes, disrupted cell wall composition and inhibited cell growth by 21.2-27.5 %. The toxicity was not simply additive or synergistic effects when PLA MPs (100 mg/L) and copper ions (10 mg/L) coexisted. PLA MPs did not significantly increase the toxicity of copper to bacteria, instead triggered some mechanisms to resist the toxicity of copper. The bacteria formed spores to resist PLA MPs, while the copper ions toxicity was weaken by chelation and efflux. It is worth noting that copper ions instead increased the expression of genes related fengycin and iturin then improving the bacteriostatic activity of the probiotic. This paper deeply analyzes the toxicity mechanism of combined pollution on Bacillus amyloliquefacien, and also provides new perspective for helping to inhibit pathogenic bacteria under biodegradable microplastics and metal stress.

Microbiome enrichment from contaminated marine sediments unveils novel bacterial strains for petroleum hydrocarbon and heavy metal bioremediation

Petroleum hydrocarbons and heavy metals are some of the most widespread contaminants affecting marine ecosystems, urgently needing effective and sustainable remediation solutions. Microbial-based bioremediation is gaining increasing interest as an effective, economically and environmentally sustainable strategy. Here, we hypothesized that the heavily polluted coastal area facing the Sarno River mouth, which discharges >3 tons of polycyclic aromatic hydrocarbons (PAHs) and ∼15 tons of heavy metals (HMs) into the sea annually, hosts unique microbiomes including marine bacteria useful for PAHs and HMs bioremediation. We thus enriched the microbiome of marine sediments, contextually selecting for HM-resistant bacteria. The enriched mixed bacterial culture was subjected to whole-DNA sequencing, metagenome-assembled-genomes (MAGs) annotation, and further sub-culturing to obtain the major bacterial species as pure strains. We obtained two novel isolates corresponding to the two most abundant MAGs (Alcanivorax xenomutans strain-SRM1 and Halomonas alkaliantarctica strain-SRM2), and tested their ability to degrade PAHs and remove HMs. Both strains exhibited high PAHs degradation (60-100%) and HMs removal (21-100%) yield, and we described in detail >60 genes in their MAGs to unveil the possible genetic basis for such abilities. Most promising yields (∼100%) were obtained towards naphthalene, pyrene and lead. We propose these novel bacterial strains and related genetic repertoire to be further exploited for effective bioremediation of marine environments contaminated with both PAHs and HMs.

Ecophysiological and genomic analyses of a representative isolate of highly abundant Bacillus cereus strains in contaminated subsurface sediments

Bacillus cereus strain CPT56D-587-MTF (CPTF) was isolated from the highly contaminated Oak Ridge Reservation (ORR) subsurface. This site is contaminated with high levels of nitric acid and multiple heavy metals. Amplicon sequencing of the 16S rRNA genes (V4 region) in sediment from this area revealed an amplicon sequence variant (ASV) with 100% identity to the CPTF 16S rRNA sequence. Notably, this CPTF-matching ASV had the highest relative abundance in this community survey, with a median relative abundance of 3.77% and comprised 20%-40% of reads in some samples. Pangenomic analysis revealed that strain CPTF has expanded genomic content compared to other B. cereus species-largely due to plasmid acquisition and expansion of transposable elements. This suggests that these features are important for rapid adaptation to native environmental stressors. We connected genotype to phenotype in the context of the unique geochemistry of the site. These analyses revealed that certain genes (e.g. nitrate reductase, heavy metal efflux pumps) that allow this strain to successfully occupy the geochemically heterogenous microniches of its native site are characteristic of the B. cereus species while others such as acid tolerance are mobile genetic element associated and are generally unique to strain CPTF.

Biosorption of heavy metals by microorganisms: Evaluation of different underlying mechanisms

Globally, ecotoxicologists, environmental biologists, biochemists, pathologists, and other experts are concerned about environmental contamination. Numerous pollutants, such as harmful heavy metals and emerging hazardous chemicals, are pervasive sources of water pollution. Water pollution and sustainable development have several eradication strategies proposed and used. Biosorption is a low-cost, easy-to-use, profitable, and efficient method of removing pollutants from water resources. Microorganisms are effective biosorbents, and their biosorption efficacy varies based on several aspects, such as ambient factors, sorbing materials, and metals to be removed. Microbial culture survival is also important. Biofilm agglomerates play an important function in metal uptake by extracellular polymeric molecules from water resources. This study investigates the occurrence of heavy metals, their removal by biosorption techniques, and the influence of variables such as those indicated above on biosorption performance. Ion exchange, complexation, precipitation, and physical adsorption are all components of biosorption. Between 20 and 35 °C is the optimal temperature range for biosorption efficiency from water resources. Utilizing living microorganisms that interact with the active functional groups found in the water contaminants might increase biosorption efficiency. This article discusses the negative impacts of microorganisms on living things and provides an outline of how they affect the elimination of heavy metals.

Transcriptome analysis provides new insights into the tolerance and aerobic reduction of Shewanella decolorationis Ni1-3 to bromate

As a possible human carcinogen, bromate is easily formed in drinking water and wastewater treatments using advanced oxidation technology. Microbial reduction is a promising method to remove bromate, but little is known about aerobic bromate reduction as well as the molecular mechanism of tolerance and reduction to bromate in bacteria. Herein, bromate reduction by isolate under aerobic conditions was reported for the first time. Shewanella decolorationis Ni1-3, isolated from an activated sludge recently, was identified to reduce bromate to bromide under both aerobic and anaerobic conditions. RNA-Seq together with differential gene expression analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis was performed to identify that bromate triggered the expression of genes for oxidative stress protection (e.g., ohr, msrQ, dsbC, gpo, gorA, and gst), DNA damage repair (e.g., dprA, parA, and recJ), and sulfur metabolism (e.g., cysH, cysK, and cysP). However, the genes for lactate utilization (e.g., lldF and dld), nitrate reduction (e.g., napA and narG), and dissimilatory metal reduction (e.g., mtrC and omcA) were down-regulated in the presence of bromate. The results contribute to revealing the molecular mechanism of resistance and reduction in S. decolorationis Ni1-3 to bromate under aerobic conditions and clarifying the biogeochemical cycle of bromine. KEY POINTS: • Aerobic bromate reduction by pure culture was observed for the first time • Strain Ni1-3 effectively reduced bromate under both aerobic and anaerobic conditions • ROS and SOS response genes were strongly induced in the presence of bromate.

Enhanced Bioremediation Potential of Shewanella decolorationis RNA Polymerase Mutants and Evidence for Novel Azo Dye Biodegradation Pathways

Bioremediation has been considered as a promising method for recovering chemical polluted environments. Here Shewanella decolorationis strain Ni1-3 showed versatile abilities in bioremediation. To improve the bioremediation activity, RNA polymerase (RNAP) mutations of strain Ni1-3 were screened. Eleven mutants were obtained, of which mutant #40 showed enhanced Amaranth (AMR) degradation capacity, while mutant #21 showed defected capacity in AMR degradation but greatly enhanced capacity in cathodic metal leaching which is three to four times faster than that of the wild-type (WT) strain Ni1-3, suggesting that different pathways were involved in these two processes. Transcriptional profiling and gene co-expression networks between the mutants (i.e., #40 and #22) and the WT strain disclosed that the non-CymA-Mtr but cytochrome b- and flavin-oxidoreductase-dominated azo dye degradation pathways existed in S. decolorationis, which involved key proteins TorC, TorA, YceJ, YceI, Sye4, etc. Furthermore, the involvement of TorA was verified by trimethylamine N-oxide reduction and molybdenum enzyme inhibitory experiments. This study clearly demonstrates that RNAP mutations are effective to screen active microbial candidates in bioremediation. Meanwhile, by clarifying the novel gene co-expression network of extracellular electron transfer pathways, this study provides new insights in azo dye degradation and broadens the application of Shewanella spp. in bioremediation as well.

Sustainable approaches for nickel removal from wastewater using bacterial biomass and nanocomposite adsorbents: A review

In this article, the nickel (Ni²⁺) ions removal from the wastewater is reviewed. Adsorption is widely used to remove Ni²⁺ ions from waters and wastewaters. The usage of biomass is becoming more common for Ni²⁺ ions removal, while the commercial activated carbon from different agriculture wastes is preferred as an adsorbent for Ni²⁺ ion removal. The present review aimed to organise the available information regarding sustainable approaches for Ni²⁺ ions removal from water and wastewaters. These include adsorption by nanoparticles, bacterial biomass, and activated carbon from agriculture wastes, since they are the most common used for the Ni²⁺ ions removal. The bacterial and agricultural waste adsorbents exhibited high efficiency with a renewable source of biomass for Ni²⁺ ion removal. The biosorption capacity of the Ni²⁺ ions by the bacterial biomass range from 5.7 to 556 mg/g, while ranging from 5.8 to 150 mg/g by the activated carbon from different organic materials. The biosorption capacity of the nanocomposite adsorbents might reach to 400 mg/g. It appeared that the elimination of nickel ions need a selective biomass adsorbent such as the tolerant bacterial cells biomass which acts as a store for Ni²⁺ ion accumulations as a results for the active and passive transportation of the Ni²⁺ ions through the bacterial cell membrane.

Evidence of Resistance of Heavy Metals from Bacteria Isolated from Natural Waters of a Mining Area in Mexico

This study focuses on identifying relationships between the content of heavy metals in water and the resistance patterns of different bacteria. Samples from watercourses in one of the most important mining areas in Mexico were collected. Seventy-one bacteria were isolated, and their resistance to Cr, Zn, Cu, Ag, Hg, and Co was studied. The Minimum Inhibitory Concentration range was determined, and a Multiple Metal Resistant index was calculated. After that, 11 isolated bacteria were chosen to estimate kinetic parameters. The obtained results show differences in the behavior of the studied bacteria concerning the presence of heavy metals in the media: (1) without effect, (2) inhibited growth; and (3) considerable inhibited growth. Finally, a Performance Index was proposed to select adequate bacteria for heavy metals removal; five bacteria were selected. Among them, Pseudomonas koreensis was identified as a good candidate for a future biosorption system since these bacteria can stimulate growth in the presence of all the metals tested.

The first complete genome sequence of species Shewanella decolorationis, from a bioremediation competent strain Ni1-3

Shewanella decolorationis are Gram-negative γ-Proteobacteria with environmental bioremediation potential because they can perform anaerobic respiration using various types of pollutants as terminal electron acceptors. So far, three isolated and cultured strains of S. decolorationis have been reported. However, no complete S. decolorationis genome has been published yet, which limited exploring their metabolism and feasibility in application. Here, S. decolorationis Ni1-3 isolated from an electroplating wastewater treatment plant showed strong reduction capabilities on azo dyes and oxidized metals. In order to construct the complete genome, high-quality whole-genome sequencing of strain Ni1-3 were performed by using both Nanopore MinION and Illumina NovaSeq platforms, from which the first complete genome of S. decolorationis was obtained by hybrid assembly. The genome of strain Ni1-3 contains a megaplasmid and a circular chromosome which encodes more proteins than that of the strains LDS1 and S12 belonging to the same species. In addition, more Clustered Regularly Interspaced Short Palindromic Repeats (CRISPRs) are identified in strain Ni1-3 genome. Importantly, 32 cytochrome-c and AzoR azoreductase coding genes are identified in the genome, which make strain Ni1-3 competent to degrade the azo dyes and versatile to bioremediate some other environmental pollution. The complete genome sequence of strain Ni1-3 can expand our knowledge toward its metabolic capabilities and potential, meanwhile, provide a reference to reassemble genomes of other S. decolorationis strains.

The Connection between Czc and Cad Systems Involved in Cadmium Resistance in Pseudomonas putida

Heavy metal pollution is widespread and persistent, and causes serious harm to the environment. Pseudomonas putida, a representative environmental microorganism, has strong resistance to heavy metals due to its multiple efflux systems. Although the functions of many efflux systems have been well-studied, the relationship between them remains unclear. Here, the relationship between the Czc and Cad systems that are predominantly responsible for cadmium efflux in P. putida KT2440 is identified. The results demonstrated that CzcR3, the response regulator of two-component system CzcRS3 in the Czc system, activates the expression of efflux pump genes czcCBA1 and czcCBA2 by directly binding to their promoters, thereby helping the strain resist cadmium stress. CzcR3 can also bind to its own promoter, but it has only a weak regulatory effect. The high-level expression of czcRS3 needs to be induced by Cd²⁺, and this relies on the regulation of CadR, a key regulator in the Cad system, which showed affinity to czcRS3 promoter. Our study indicates that the Cad system is involved in the regulation of the Czc system, and this relationship is important for maintaining the considerable resistance to cadmium in P. putida.

Assessment of resistance and biosorption ability of Lactobacillus paracasei to remove lead and cadmium from aqueous solution

Since heavy metals have been regarded as ubiquitous environmental pollutants, the exploitation of bacterial biosorption has been suggested as an applicable method for being employed for heavy metal depletion. The present study aimed to characterize the function of Lactobacillus paracasei in the presence of Pb (II) and Cd (II). The simultaneous effect of pH, initial metal concentration, and inoculum size demonstrated the Pb (II) removal of 85.77% at the lowest pH, while the inoculum size was enhanced to 45 CFU/100 ml. The maximum Cd (II) removal was obtained at a high level of pH and inoculum size, while the metal concentration was reduced to 30 ppb. The addition of Cd (II) concentration in access led to the 10% drop in Cd (II) removal efficiency attributed to the metal toxicity and pH. Additionally, the slight variation in the amount of inoculum size caused the decreasing trend in the Cd (II) removal. According to the obtained results, the benefit of L. paracasei in the biosorption of heavy metals was well-recognized, which could be suggested as an alternative candidate. PRACTITIONER POINTS: Strain of Lactobacillus paracasei as potential probiotics was tested for biosorption. A successful response surface method was proposed. L. paracasei showed a good efficiency for the lead and cadmium biosorption. Biosorption process was effective in removing low metal level from drinking water. The maximum biosorption was found to be 85.77% for Pb (II) obtained from the experiment.

Ureolytic bacteria from electronic waste area, their biological robustness against potentially toxic elements and underlying mechanisms

Ureolytic bacteria can be a promising mediator used for the immobilization of potentially toxic elements via microbially-induced carbonate precipitation (MICP) process from biodegradable ions to carbonate form. Electronic waste (E-waste) environment is very complex compared to general metal contaminated soil, however, MICP has not been studied under such an environment. In this study, three bacterial strains were successfully isolated from an E-waste area in Guiyu, China, and indicated to have positive ureolytic behavior with significant heavy metal resistance (specific to Cu and Pb), among which, a strain of Lysinibacillus sp. was proven to show a great persistence in heavy metal immobilization. This featured strain can tolerate up to 100 ppm copper and 1000 ppm lead according to minimal inhibitory concentration (MIC) results, and its urease activity was well-adapted to metal effects. Results also revealed the positive correlation (R² = 0.9819) between metal concentrations and surface layer protein content present in bacterial cells. The underlying mechanism on the role of S-layer protein in heavy metal immobilization during biocalcification was elucidated. The metabolic system of heavy metal resistance for these E-waste derived isolates is novel and represents a point of interest for possible environmental applications to immobilize toxic heavy metals from electronic waste sites.

Pollutants affect algae-bacteria interactions: A critical review

With increasing concerns on the ecological risks of pollutants, many efforts have been devoted to revealing the toxic effects of pollutants on algae or bacteria in their monocultures. However, how pollutants affect algae and bacteria in their cocultures is still elusive but crucial due to its more environmental relevance. The present review outlines the interactions between algae and bacteria, reveals the influential mechanisms of pollutants (including pesticides, metals, engineered nanomaterials, pharmaceutical and personal care products, and aromatic pollutants) to algae and bacteria in their coexisted systems, and puts forward prospects for further advancing toxic studies in algal-bacterial systems. Pollutants affect the physiological and ecological functions of bacteria and algae by interfering with their relationships. Cell-to-cell adhesion, substrate exchange and biodegradation of organic pollutants, enhancement of signal transduction, and horizontal transfer of tolerance genes are important defense strategies in algal-bacterial systems to cope with pollution stress. Developing suitable algal-bacterial models, identifying cross-kingdom signaling molecules, and deciphering the horizontal transfer of pollutant resistant genes between algae and bacteria under pollution stress are the way forward to fully exploit the risks of pollutants in natural aquatic environments.

Improvement of the Cu and Cd phytostabilization efficiency of perennial ryegrass through the inoculation of three metal-resistant PGPR strains

To explore a novel strategy for the remediation of soils polluted with Cu and Cd, three strains of plant-growth-promoting rhizobacteria (PGPRs) isolated from contaminated mines and two grass species (perennial ryegrass and tall fescue) were selected in this study. The performance of PGPR strains in metal adsorption, maintaining promotion traits under stress, and ameliorating phytostabilization potential was evaluated. Cd²⁺ exerted a stronger deleterious effect on microbial growth than Cu²⁺, but the opposite occurred for grass seedlings. Adsorption experiment showed that the growing PGPR strains were able to immobilize maximum 79.49% Cu and 81.35% Cd owing to biosorption or bioaccumulation. The strains exhibited the ability to secrete indole-3-acetic acid (IAA) and dissolve phosphorus in the absence and presence of metals, and IAA production was even enhanced in the presence of low Cu²⁺ (5 mg L^-1). However, the siderophore-producing ability of the isolates was strongly suppressed under Cu and Cd exposure. Ryegrass was further selected for pot experiments owing to its higher germination rate and tolerance under Cu and Cd stress than fescue. Pot-experiment results revealed that PGPR addition significantly increased the shoot and root biomasses of ryegrass by 11.49%-44.50% and 43.53%-90.29% in soil co-contaminated with 800 mg Cu kg^-1 and 30 mg Cd kg^-1, respectively. Metal uptake and translocation in inoculated ryegrass significantly decreased owing to the reduced diethylenetriamine pentaacetic acid-extractable metal content and increased residual metal-fraction percentage mediated by PGPR. Interestingly, stress mitigation was observed in these inoculated plants; in particular, their malondialdehyde content and superoxide dismutase activity were even significantly lower than those of ryegrass under normal conditions. Therefore, PGPR could be a promising option to enhance the phytostabilization efficiency of Cu and Cd in heavily polluted soils.

Bioremediation of Petroleum Hydrocarbons Using Acinetobacter sp. SCYY-5 Isolated from Contaminated Oil Sludge: Strategy and Effectiveness Study

Biodegradation has been considered as an ideal technique for total petroleum hydrocarbon (TPH) contamination, but its efficiency is limited by its application in the field. Herein, an original TPH-degrading strain, SCYY-5, was isolated from contaminated oil sludge and identified as Acinetobacter sp. by 16S rDNA sequence analysis. The biological function of the isolate was investigated by heavy metal tolerance, carbon, and nitrogen source and degradation tests. To enhance its biodegradation efficiency, the response surface methodology (RSM) based on a function model was adopted to investigate and optimize the strategy of microbial and environmental variables for TPH removal. Furthermore, the performance of the system increased to 79.94% with the further addition of extra nutrients, suggesting that the RSM and added nutrients increased the activity of bacteria to meet the needs of the co-metabolism matrix during growth or degradation. These results verified that it is feasible to adopt the optimal strategy of combining bioremediation with RSM to improve the biodegradation efficiency, for contaminated oil sludge.

Critical flocculation concentration for polyvalent ions using silica nanoparticles; a new version of Schulze-Hardy rule

Critical Flocculation Concentration (CFC) is an important quantity because allows to know the optimal amount of flocculant required to remove (adsorb) specific quantities of metal ions in aqueous solution allowing to reduce both, the flocculation time and the excess of unreacted flocculant; this unreacted material produces, by itself, an additional contamination. The results reported here show that the standard Schulze-Hardy-Rule (SHR), based only in the valence z, is not longer valid to obtain the right values of CFC. In this work it is reported a correct determination of CFC for di- and tri-valent ions using different types of silica nanoparticles. Both, the initial pH slope (-pHo) and the valence z are required to determine correctly the CFC. The proposed modified version for CFC is CFC ∝ [(-pHo)z]−1.

Resistance, removal, and bioaccumulation of Ni (II) and Co (II) and their impacts on antioxidant enzymes of Anoxybacillus mongoliensis

In this study, it was hypothesis that A. mongoliensis could be used as bioindicator for Ni (II) and Co (II). Thus, Ni (II) and Co (II) resistance, removal, bioaccumulation, and the impacts of them on antioxidant enzyme systems of thermophilic Anoxybacillus mongoliensis were investigated in details. The bioaccumulation of Ni (II) and Co (II) on the cell membrane of thermophilic A. mongoliensis, variations on surface macrostructure and functionality by FT-IR and SEM, and determination of antioxidant enzyme activities were also tested. The highest bioaccumulation values of Co (II) and Ni (II) were detected as 102.0 mg metal/g of dry bacteria at 10 mg/L for the 12th h and 90.4 mg metal/g of dry bacteria for the 24th h, respectively, and the highest Ni (II) and Co (II) cell membrane bioaccumulation capacities of A. mongoliensis were determined as 268.5 and 274.9 mg metal/g wet membrane, respectively at the 24th h. In addition, increasing on SOD and CAT activities were observed on depend of concentration of Ni (II) and Co (II) with respect to control. The antioxidant enzyme activity results also indicated that A. mongoliensis might be used as a bioindicator for Ni (II) and Co (II) pollution in environmental water specimens.

Draft Genome Sequences of Pseudomonas koreensis Strain UASWS1668, Bacillus megaterium Strain UASWS1667, and Paenibacillus sp. Strain UASWS1643, Considered Potential Plant Growth-Promoting Rhizobacteria

Plant growth-promoting rhizobacteria (PGPR) include species in the genera Bacillus, Paenibacillus, and Pseudomonas. We report here the draft genome sequences of the strains Pseudomonas koreensis UASWS1668 and Bacillus megaterium UASWS1667, isolated from a horse chestnut tree, and Paenibacillus sp. strain UASWS1643, isolated from a tomato stem. Auxin production and phosphate solubilization were biochemically confirmed.

Plant growth-promoting rhizobacteria (PGPR) include species in the genera Bacillus, Paenibacillus, and Pseudomonas. We report here the draft genome sequences of the strains Pseudomonas koreensis UASWS1668 and Bacillus megaterium UASWS1667, isolated from a horse chestnut tree, and Paenibacillus sp. strain UASWS1643, isolated from a tomato stem. Auxin production and phosphate solubilization were biochemically confirmed.

A critical review on the occurrence of resistomes in the environment and their removal from wastewater using apposite treatment technologies: Limitations, successes and future improvement

Recent reports are pointing towards the potential increasing risks of resistomes in human host. With no permissible limit in sight, resistomes are continually multiplying at an alarming rate in the ecosystem, with a disturbing level in drinking water source. The morphology and chemical constituent of resistomes afford them to resist degradation, elude membrane and counter ionic charge, thereby, rendering both conventional and advanced water and wastewater treatment inefficient. Water and wastewater matrix may govern the propagation of individual resistomes sub-type, co-selection and specific interaction towards precise condition may have enhanced the current challenge. This review covers recent reports (2011-2019) on the occurrence of ARB/ARGs and ease of spread of resistance genes in the aquatic ecosystem. The contributions of water matrix to the spread and mitigation, treatment options, via bulk removal or capture, and intracellular and extracellular DNA lysis were discussed. A complete summary of recent occurrences of ARB/ARGs, fate after disinfection and optimum conditions of individual treatment technology or in tandem, including process limitations, with a brief assessment of removal or degradation mechanism were highlighted.

A manganese-oxidizing bacterial consortium and its biogenic Mn oxides for dye decolorization and heavy metal adsorption

Manganese (Mn) contamination is a common environmental problem in the world and manganese oxidizing bacteria (MOB) play important roles in bioremediation of heavy metal and organic pollution. In this study, a novel MOB consortium AS containing core microbes of Sphingobacterium and Bacillus was acclimated from Mn-contaminated rivulet sediments. The MOB consortium AS presented good Mn(II) removal performance under 500-10,000 mg/L Mn(II), with Mn(II) removal capacities ranging from 481 to 3478 mg/L. In coexistence systems of Mn(II) and Fe(II), Ni(II), Cu(II), and Zn(II), the MOB consortium AS removed 98%, 91%, 99%, and 76% of Mn(II), respectively. Additionally, the MOB consortium AS could utilize multiple carbon sources (e.g., Chitosan, β-Cyclodextrin, and Phenanthrene) to remove Mn(II), with Mn(II) removal efficiencies ranging from 11% to 97%. Meanwhile, XRD, XPS, FTIR, SEM, and EDS analyses reflected that biogenic Mn oxides (bio-MnOx-C) contained C, O, Mn (Mn(II) and Mn(IV)) and embodied in rhodochrosite and birnessite. The bio-MnOx-C exhibited second-order kinetic reaction for removal of dye, with corresponding decolorization capacities of 22.0 mg/g for methylene blue and 23.8 mg/g for crystal violet. In addition, bio-MnOx-C showed adsorption capacities of 159.0 mg/g for Cu(II), 130.7 mg/g for Zn(II), and 123.3 mg/g for Pb(II). Overall, this study illustrates consortium AS and bio-MnOx-C have great potentials in remediation of pollution caused by heavy metals and organic pollutants.

Modified PVA (polyvinyl alcohol) biomaterials as carriers for simultaneous removal of nitrate, Cd (II), and Mn (II): performance and microbial community

The ecological toxicity and potential risks of heavy metals that coexist with nitrates in wastewater have aroused public attention. This study developed an immobilized Fe₃O₄@Cu/PVA mixotrophic reactor (Fe₃O₄@Cu/PVA-IMR) to investigate the effect of different Mn (II) concentrations (10 mg L^-1, 50 mg L^-1, and 90 mg L^-1), Cd (II) concentrations (10 mg L^-1, 20 mg L^-1, and 30 mg L^-1), and hydraulic retention time (HRT) (6 h, 8 h, and 10 h) on simultaneous nitrate, Cd (II), and Mn (II) removal. Using the advanced modified biomaterial Fe₃O₄@Cu/PVA as carrier to embed bacteria, the performance of the reactor was further improved. The surface morphology of Fe₃O₄@Cu/PVA was characterized by SEM as a rough surface three-dimensional skeleton structure. When the HRT was 10 h, Mn (II) and Cd (II) concentrations were 40 mg L^-1 and 10 mg L^-1, respectively, indicating that the immobilized Pseudomonas sp. H117 with Fe₃O₄@Cu/PVA achieved the highest nitrate, Cd (II), and Mn (II) removal efficiencies of 100% (1.64 mg L^-1 h^-1), 98.90% (0.92 mg L^-1 h^-1), and 92.26% (3.58 mg L^-1 h^-1), respectively. Compared with a reactor without Fe₃O₄@Cu/PVA addition, the corresponding removal ratio increased by 22.63%, 7.09%, and 15.96%. Gas chromatography (GC) identified nitrogen as the main gaseous product. Moreover, high-throughput sequencing showed that Pseudomonas sp. H117 plays a primary role in the denitrification process.

A WO3/PPy/ACF modified electrode in electrochemical system for simultaneous removal of heavy metal ion Cu2+ and organic acid

Heavy metal ions and organic acids are common pollutants in electroplating wastewater. Effective and economic treatment of such wastewater needs novel technologies. In this study, WO₃/PPy-1/ACF electrode was prepared using a hydrothermal modification method and it has large specific area (788.27 m² g^-1), high areal capacitance (2.58 F cm^-2 under 5 mA cm^-2 charge and discharge) and excellent conductivity. The modified electrode was used in an electrochemical system with activated carbon fiber felt (ACF) as counter electrode. The system simultaneously and successfully removed 97.8 % Cu²⁺ and 80.1 % citric acid (CA) from a simulated electroplating wastewater (typically 100 mg L^-1 Cu²⁺ and 800 mg L^-1 CA) in five- hour optimized operation. The influence of operating parameters (circulating inflow rate, applied voltage and influent pH) on the treatment performance was compared. There is interplay between Cu²⁺ reductive deposition and CA oxidation. The synergetic electrochemical treatment mechanism involves formation of hydrogen peroxide, free radicals, and catalytic effect of Cu species was proposed. This electrochemical system which is low-cost, easy to operate and highly efficient, may be applicable in treating acid-wash or electroplating wastewater, containing heavy-metal ions and organic acids.