Microbial remediation of fluoride-contaminated water via a novel bacterium Providencia vermicola (KX926492)

Biopriming of Pseudomonas aeruginosa Abates Fluoride Toxicity in Oryza sativa L. by Restricting Fluoride Accumulation, Enhancing Antioxidative System, and Boosting Activities of Rhizospheric Enzymes

Plant growth-promoting bacteria (PGPB) are free-living microorganisms that actively reside in the rhizosphere and affect plant growth and development. These bacteria employ their own metabolic system to fix nitrogen, solubilize phosphate, and secrete hormones to directly impact the metabolism of plants. Generating sustainable agricultural production under various environmental stresses requires a detailed understanding of mechanisms that bacteria use to promote plant growth. In the present study, Pseudomonas aeruginosa (MW843625), a PGP soil bacterium with a minimum inhibitory concentration (MIC) of 150 mM against fluoride (F), was isolated from agricultural fields of Chhattisgarh, India, and was assessed for remedial and PGP potential. This study concentrated on biomass accumulation, nutrient absorption, and oxidative stress tolerance in plants involving antioxidative enzymes. By determining MDA accumulation and ROS (O2•- and H2O2) in Oryza sativa L. under F (50 ppm) stress, oxidative stress tolerance was assessed. The results showed that inoculation with P. aeruginosa enhanced the ability of O. sativa L. seedlings to absorb nutrients and increased the amounts of total chlorophyll (Chl), total soluble protein, and biomass. In contrast to plants cultivated under F-stress alone, those inoculated with P. aeruginosa along with F showed considerably reduced concentrations of F in their roots, shoots, and grains. The alleviation of deleterious effects of F-stress on plants owing to P. aeruginosa inoculation has been associated with improved activity/upregulation of antioxidative genes (SOD, CAT, and APX) in comparison to only F-subjected plants, which resulted in lower O2•-, H2O2, and MDA content. Additionally, it has also been reflected from our study that P. aeruginosa has the potential to increase the activities of soil enzymes such as urease, phosphatase, dehydrogenase, nitrate reductase, and cellulase. Accordingly, the findings of the conducted study suggest that P. aeruginosa can be exploited not only as an ideal candidate for bioremediation but also for enhancing soil fertility and the promotion of growth and development of O. sativa L. under F contamination.

Insights of using microbial material in fluoride removal from wastewater: A review

Fluoride is an essential trace element for the human body, but excessive fluoride can cause serious environmental and health problems. Therefore, developing efficient fluoride removal technologies is crucial. This review summarizes the progress made in using microbial materials to remove fluoride from wastewater, covering strategies that involve pure cultures of bacteria, fungi, and algae, as well as modified microbial materials and bioreactors. Live microorganisms exhibit high efficiency in adsorbing low concentrations of fluoride, while modified microbial materials are more suitable for treating high concentrations of fluoride. The review discusses the adsorption mechanisms and influencing factors of these technologies, and evaluates their practical application potential through techno-economic analysis. Finally, future research directions are proposed, including the optimization of modification technologies and the selection of effective microbial species, providing theoretical guidance and a basis for future microbial defluoridation technologies.

Enhancement of Fluoride's Antibacterial and Antibiofilm Effects against Oral Staphylococcus aureus by the Urea Derivative BPU

Background: The oral cavity is an important but often overlooked reservoir for Staphylococcus aureus. The effective control and prevention of S. aureus colonization and infection in the oral and maxillofacial regions are crucial for public health. Fluoride is widely used in dental care for its remineralization and antibacterial properties. However, its effectiveness against S. aureus has not been thoroughly investigated. Objectives: This study aimed to evaluate the potential of combining sodium fluoride (NaF) with compounds to enhance its antibacterial and antibiofilm effects against S. aureus. Method: We found that a urea derivative significantly enhances the efficacy of fluoride by promoting the retention of fluoride ions within the cells. The synergistic antibacterial and antibiofilm effects of BPU with NaF were confirmed through various assays, including checkerboard assays, time-kill assays, and growth curve analysis. These findings were further supported by additional methods, including transmission electron microscopy (TEM), in silico simulations, and gene overexpression studies. Results: These findings suggest that targeting fluoride ion membrane exporters could enhance antibacterial efficacy. When combined with fluoride, 1,3-Bis [3,5-bis(trifluoromethyl)phenyl]urea (BPU) showed increased effectiveness in inhibiting S. aureus growth and reducing established biofilms. Conclusions: This novel combination represents a promising therapeutic strategy for treating biofilm-associated S. aureus infections, offering a new strategy in oral healthcare. To fully evaluate the clinical potential of this synergistic therapy, further in vivo studies are essential.

The link between ancient microbial fluoride resistance mechanisms and bioengineering organofluorine degradation or synthesis

Fluorinated organic chemicals, such as per- and polyfluorinated alkyl substances (PFAS) and fluorinated pesticides, are both broadly useful and unusually long-lived. To combat problems related to the accumulation of these compounds, microbial PFAS and organofluorine degradation and biosynthesis of less-fluorinated replacement chemicals are under intense study. Both efforts are undermined by the substantial toxicity of fluoride, an anion that powerfully inhibits metabolism. Microorganisms have contended with environmental mineral fluoride over evolutionary time, evolving a suite of detoxification mechanisms. In this perspective, we synthesize emerging ideas on microbial defluorination/fluorination and fluoride resistance mechanisms and identify best approaches for bioengineering new approaches for degrading and making organofluorine compounds.

Tomato seed bio-priming with Pseudomonas aeruginosa strain PAR: a study on plant growth parameters under sodium fluoride stress

The primary goal of this experiment is to examine the effectiveness of Pseudomonas aeruginosa strain PAR as a rhizobacterium that promotes plant growth in mitigating the negative effects of fluoride-induced stress in tomato (Lycopersicon esculentum Mill.) plants. A total of 16 rhizobacterial strains were tested for plant growth-promoting (PGP) attributes, with isolates S1, S2, and S3 exhibiting different characteristics. Furthermore, growth kinetics studies revealed that these isolates were resilient to fluoride stress (10, 20, 40, and 80 ppm), with isolate S2 exhibiting notable resilience compared to the other two strains. Phylogenetic analysis revealed isolate S2 as P. aeruginosa strain PAR. Physiological analyses demonstrated that P. aeruginosa strain PAR had a beneficial impact on plant properties under fluoride stress, comprising seed germination, root length, shoot height, relative water content, and leaf area, the strain also impacted the buildup of glycine betaine, soluble sugar, and proline, demonstrating its significance in enhancing plant stress tolerance. In P. aeruginosa strain PAR-treated plants, chlorophyll content increased while malondialdehyde (MDA) levels decreased, indicating enhanced photosynthetic efficiency and less oxidative stress. The strain modified antioxidant enzyme action (catalase, ascorbate, glutathione reductase, peroxidase, and superoxide dismutase), which contributed to improved stress resilience. Mineral analysis revealed a decrease in sodium and fluoride concentrations while increasing magnesium, potassium, phosphorus, and iron levels, emphasizing the strain's significance in nutrient management. Correlation and principal component analysis revealed extensive correlations between physiological and biochemical parameters, underscoring P. aeruginosa strain PAR's multifaceted impact on plant growth and stress response. This study offers valuable information on effectively utilizing PGPR, particularly P. aeruginosa strain PAR, in fluoride-contaminated soils for sustainable agriculture. It presents a promising biological strategy to enhance crop resilience and productivity.

Current progress on fluoride occurrence in the soil environment: Sources, transformation, regulations and remediation

Fluorine is a halogen element widely distributed in nature, but due to excessive emissions from industrial manufacturing and agricultural production, etc., the soil is over-enriched with fluoride and the normal growth of plants is under stress, and it also poses a great threat to human health. In this review, we summarized the sources of fluoride in soil, and then analyzed the potential mechanisms of fluoride uptake in soil-plant systems. In addition, the main influences of soil ecosystems on plant fluoride uptake were discussed, soil management options to mitigate fluoride accumulation in plants were also summarized. The bioremediation techniques were found to be a developmental direction to improve fluoride pollution. Finally, we proposed other research directions, including fluoride uptake mechanisms in soil-plant systems at the molecular expression levels, development of visualization techniques for fluoride transport in plants, interactions mechanisms between soil microhabitats and plant metabolism affecting fluoride uptake, as well as combining abiotic additives, nanotechnology and biotechnology to remediate fluoride contamination problems.

Applications of biomass-based materials to remove fluoride from wastewater: A review

Fluoride is one of the essential trace elements for the human body, but excessive fluoride will cause serious environmental and health problems. This paper summarizes researches on the removal of fluoride from aqueous solutions using newly developed or improved biomass materials and biomass-like organic materials in recent years. These biomass materials are classified into chitosan, microorganisms, lignocellulose plant materials, animal attribute materials, biological carbonized materials and biomass-like organic materials, which are explained and analyzed. By comparing adsorption performance and mechanism of adsorbents for removing fluoride, it is found that carbonizing materials and modifying adsorbents with metal ions are more beneficial to improving adsorption efficiency and the adsorption mechanisms are various. The adsorption capacities are still considerable after regeneration. This paper not only reviews the properties of these materials for fluoride removal, but also focuses on the comparison of materials performance and fluoride removal mechanism. Herein, by discussing the improved adsorption performance and research technology development of biomass materials and biomass-like organic materials, various innovative ideas are provided for adsorbing and removing contaminants.

Potential of a novel facultative anaerobic denitrifying Cupriavidus sp. W12 to remove fluoride and calcium through calcium bioprecipitation

This study focused on a novel denitrifying Cupriavidus sp. W12, which can perform microbial induced calcium precipitation (MICP) to remove fluoride (F^-) under aerobic and anaerobic conditions. Under anaerobic condition, the removal ratios of F^-, calcium (Ca²⁺), and nitrate (NO₃^--N) reached 87.52%, 65.03%, and 96.06%, respectively, which were higher than that under aerobic condition (50.17%, 88.21%, and 67.33%, respectively). Higher pH of 8.26 was obtained after 120 h of the strain W12 growth under anaerobic condition than that under aerobic condition (7.77). The F^- removal ratio of 98.20% was predicted by the response surface methodology (RSM). Scanning electron microscopy (SEM) images of anaerobic precipitation were dense and porous. CaCO₃, Ca₅(PO₄)₃OH, Ca₅(PO₄)₃F, and CaF₂ were determined by X-ray diffraction (XRD) and energy dispersive spectrometer (EDS). Self-aggregation of bacteria and adsorption of biological crystal seeds were the determinant of the precipitates formation. The results of infrared spectrometer (FTIR) and excitation-emission matrix (EEM) showed that anaerobic extracellular polymeric substances (EPS) expression led the proportion of hydroxylapatite in the precipitates increased. As the first report on the anaerobic MICP to remove F^-, it provides a theoretical basis for the remediation of F^-, Ca²⁺, and NO₃^--N in groundwater.

Isolation and identification of high fluoride resistant bacteria from water samples of Dindigul district, Tamil Nadu, South India

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High Fluoride (F⁻) resistant bacteria (200-300 mM) isolated from water samples of Dindigul district, Tamil Nadu, South India.High F⁻ (4.7 and 11 ppm) concentration was detected at Odukampatty and Chellapanaikenpatti villages of Dindigul district. They exhibited β and γ-haemolytic activities on blood agar plates. F⁻ resistant isolates showed their salt tolerances ranged from 4% to 7% NaCl.

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The selected F⁻ resistant bacteria were identified as Enterobacter cloacae strain 3, E. hormaechei strain 14, Enterobacter sp. strain 21, E. hormaechei strain 22, E. coli strain S2-9, Aeromonas caviae strain 31, A. caviae strain 32, A. caviae strain 34.

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F⁻ resistant Aeromonas species are pathogens and exhibited β-haemolytic activity. E. coli S2-9 is a fluoride resistant, non-pathogenic and thermotolerant bacteria.

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The ‘crcB’ involved in bacterial fluoride resistance was amplified from Aeromonas, E. coli, and Enterobacter species.

Fluoride (F⁻) pollution is one of the major issues in India and worldwide. Water samples were collected, and analyse the physicochemical characteristics. From the results, acceptable limit pH ranges, low and high electrical conductivity (EC) values, high-level of TDS (total dissolved solids) and chloride (Cl⁻) values, less than desirable and higher than permissible F⁻ concentrations (4.7 and 11 ppm) were found. At first, ninety-three colonies were screened using rapid hicoliform agar plates. After that, sixty-six F⁻ resistant colonies were picked up from 50  mM NaF (Sodium fluoride) containing LB agar plates. Finally, eight isolates were showing a high degree of F⁻ resistance (200–-300 mM NaF) and selected for further studies. High F⁻ resistance isolates exhibited β and γ-haemolytic activities were determined in blood agar plates. F⁻ resistant isolates showed their salt tolerances ranged from 4% to 7% NaCl and resistant to multiple antibiotics. Biochemical and 16S rRNA sequencing results showed that the F⁻ resistant isolates were identified as Enterobacter cloacae strain 3, E. hormaechei strain 14, Enterobacter sp. strain 21, E. hormaechei strain 22, E. coli strain S2-9, Aeromonas caviae strain 31, A. caviae strain 32, A. caviae strain 34. All strains were submitted in the NCBI database with the accession numbers (MW131637, MW131639; MW131650-655). The F⁻ resistant gene ‘crcB’ gene was successfully amplified from the resistant isolates using gene-specific primers. These results have demonstrated that fluoride resistant bacteria would be useful for bacterial fluoride bioremediation near future.

Bioaccumulation of Fluoride in Plants and Its Microbially Assisted Remediation: A Review of Biological Processes and Technological Performance

Fluoride is widely found in soil–water systems due to anthropogenic and geogenic activities that affect millions worldwide. Fluoride ingestion results in chronic and acute toxicity, including skeletal and dental fluorosis, neurological damage, and bone softening in humans. Therefore, this review paper summarizes biological processes for fluoride remediation, i.e., bioaccumulation in plants and microbially assisted systems. Bioremediation approaches for fluoride removal have recently gained prominence in removing fluoride ions. Plants are vulnerable to fluoride accumulation in soil, and their growth and development can be negatively affected, even with low fluoride content in the soil. The microbial bioremediation processes involve bioaccumulation, biotransformation, and biosorption. Bacterial, fungal, and algal biomass are ecologically efficient bioremediators. Most bioremediation techniques are laboratory-scale based on contaminated solutions; however, treatment of fluoride-contaminated wastewater at an industrial scale is yet to be investigated. Therefore, this review recommends the practical applicability and sustainability of microbial bioremediation of fluoride in different environments.

Comprehensive and critical appraisal of plant-based defluoridation from environmental matrices

Fluoride is recognized as one of the global environmental threats because of its non-biodegradable nature and long-term persistence in the environment. This has created the dire need to explore various defluoridation techniques (membrane process, adsorption, precipitation, reverse osmosis, ion exchange, and electrocoagulation). Owing to their cost ineffectiveness and high operational costs, these technologies failed to find any practical utility in fluoride remediation. Comparatively, defluoridation techniques involving the use of low-cost plant-derived adsorbents and fluoride phytoremediators are considered better alternatives. Through this review, an attempt has been made to critically synthesize information about various plant-based bioadsorbents and hyperaccumulators from existing literature. Moreover, mechanisms underlying the fluoride adsorption and accumulation by plants have been thoroughly discussed that will invigorate the researchers to develop novel ideas about process/product modifications to further enhance the removal potential of the adsorbents and plants. Literature survey unravels that various low-cost plant-derived adsorbents have shown their efficacy in defluoridation, yet there is an urgent need to explore their pragmatic application on a commercial scale.

Carbon to nitrogen ratios influence the removal performance of calcium, fluoride, and nitrate by Acinetobacter H12 in a quartz sand-filled biofilm reactor

This study investigated the influence of different carbon to nitrogen (C/N) ratios on the bio-removal efficiency of aquatic pollutants like calcium (Ca²⁺), fluoride (F^-), and nitrate (NO₃-N) in a quartz sand-filled biofilm reactor (QSBR) to treat the low C/N wastewater using Acinetobacter sp. H12 at pH 6.50. The simultaneous bio-removal rate of Ca²⁺, F^-, and NO₃^- reached 56.31%, 96.33, and 96.95 respectively. Nitrogen gas (N₂) was produced with no evidence of N₂O emission. Moreover, the morphological study of strain H12 and biological precipitates through SEM revealed that strain H12 provides the nucleation sites for microbially induced calcium precipitation to remove Ca²⁺ and F^-. Besides, XPS and XRD peak spectra implicated that Ca²⁺ and F^- were removed as CaF₂ and Ca₅(PO₄)₃F co-precipitates. The 16S rRNA sequencing analyses revealed that H12 belongs to Acinetobacter and has stronger MICP and denitrification potential as compared with other strains under low C/N conditions.

Bioaccumulation of fluoride from aqueous system and genotoxicity study on Allium cepa using Bacillus licheniformis

Removal of fluoride (F^-) was performed using a novel bacterium isolated from F^- contaminated soil collected from Pappireddipatti block of Dharmapuri District in Tamil Nadu, India. Impact of changing variables for the removal of F^- from synthetic medium at different concentrations of carbon and nitrogen sources (0.5, 1.0 and 1.5 g) was studied with bio inoculants of the bacterial strain (PPR8). The effects of different environmental parameters viz., pH (5.0-9.0) and temperature (25-45 °C) on the biosorption of F^- biosorption were also evaluated. The strain PPR8 was identified as Bacillus licheniformis through 16S rRNA sequencing and phylogenetic analysis. Bioaccumulation of F^- in the bacterial cells was confirmed by FTIR, SEM and TEM-EDAX and almost 97% of F^- removal was established. To test the potential applicability of the bacterium, the bioreactor study was carried out with F^- contaminated groundwater collected from the contaminated area. Furthermore, the treated and untreated F^- contaminated waters were used to evaluate the genotoxicity on the root cells of onion (Allium cepa) by root tip assay. The experimental results proved that the significant removal of F^- by Bacillus licheniformis PPR8 (KX646393) and it could be used as a potential adsorbent in removing F^- from contaminated ground waters.

Study on the simultaneous removal of fluoride, heavy metals and nitrate by calcium precipitating strain Acinetobacter sp. H12

The removal properties and mechanisms of fluoride (F^-) and nickel (Ni²⁺) were studied by biomineralizing bacteria (Acinetobacter sp. H12). The results showed that the removal ratio of F^-, Ca²⁺ and Ni²⁺ reached 75% (0.031 mg·L^-1·h^-1), 84.96% (2.123 mg·L^-1·h^-1), and 56.67% (0.024 mg·L^-1·h^-1) after 72 h, respectively. The removal ratio of nitrate (NO₃^-) reached 100% (0.686 mg·L^-1·h^-1) after 24 h. SEM and XRD images indicated that bioprecipitation of CaF₂, Ca₅(PO₄)₃F, Ca₅(PO₄)₃(OH), NiCO₃, CaCO₃ and Ni were formed, and some of these precipitation used bacteria as nucleation sites to form biological crystal seeds. N₂ was the primary product in gas chromatography analysis. Meanwhile, both the fluorescence spectroscopy and fourier transform near-infrared spectroscopy analysis proved that strain H12 had good ability to remove fluoride and nickel ions simultaneously.

Heterotrophic nitrification and biomineralization potential of Pseudomonas sp. HXF1 for the simultaneous removal of ammonia nitrogen and fluoride from groundwater

Pseudomonas sp. HXF1, a strain capable of heterotrophic nitrification, aerobic denitrification (HNAD), and biomineralization was identified and employed for the simultaneous removal of ammonia nitrogen (NH₄⁺-N) and fluoride (F^-). It removed 99.2% of NH₄⁺-N without accumulation of nitrous nitrogen (NO₂^--N) and nitrate nitrogen (NO₃^--N), while removed 87.3% of F^-. Response surface methodology (RSM) was used to study the best removal conditions for NH₄⁺-N and F^-. The results of nitrogen balance experiments with NH₄Cl, NaNO₂, and NaNO₃ as single nitrogen sources and amplification experiments of denitrification genes proved that the bacterial strains may remove NH₄⁺-N through HNAD. The experimental results of Scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffractometer (XRD) indicated that the way of F^- removal may be adsorption and co-precipitation. The results demonstrated that the strain HXF1 has great potential in the biological denitrification and F^- removal of groundwater.

Exemplifying an archetypal thorium-EPS complexation by novel thoriotolerant Providencia thoriotolerans AM3

It is the acquisition of unique traits that adds to the enigma of microbial capabilities to carry out extraordinary processes. One such ecosystem is the soil exposed to radionuclides, in the vicinity of atomic power stations. With the aim to study thorium (Th) tolerance in the indigenous bacteria of such soil, the bacteria were isolated and screened for maximum thorium tolerance. Out of all, only one strain AM3, found to tolerate extraordinary levels of Th (1500 mg L⁻¹), was identified to be belonging to genus Providencia and showed maximum genetic similarity with the type strain P. vermicola OP1T. This is the first report suggesting any bacteria to tolerate such high Th and we propose to term such microbes as ‘thoriotolerant’. The medium composition for cultivating AM3 was optimized using response surface methodology (RSM) which also led to an improvement in its Th-tolerance capabilities by 23%. AM3 was found to be a good producer of EPS and hence one component study was also employed for its optimization. Moreover, the EPS produced by the strain showed interaction with Th, which was deduced by Fourier Transform Infrared (FTIR) spectroscopy.

A new technology for simultaneous calcium-nitrate and fluoride removal in the biofilm reactor

In this study, a biofilm reactor containing Acinetobacter sp.H12 was established to investigate the simultaneous denitrification, the removal of calcium and fluoride performance. The main precipitation components in the reactor were determined by SEM, XPS and XRD. The effects of HRT (6 h, 9 h and 12 h), pH (6.0, 7.0, 8.0), influent F^- concentration (3 mg/L, 5 mg/L, 10 mg/L) on synchronously removal of nitrate and F^- and Ca²⁺ during reactor operation were studied. Optimum operating conditions were achieved with a nitrate removal ratio of 100%, F^- removal ratio of 81.91% and Ca²⁺ removal ratio of 67.66%. Nitrogen was the main gaseous product analyzed by gas chromatography. Extracellular polymers (proteins) were also identified as sites for biological precipitation nucleation by fluorescence spectroscopy. Moreover, microbial distribution and community structure analysis showed that strain H12 was the dominat strain in the biofilm reactor. And combined with the performance prediction of the reactor, strain H12 played a major role in the process of simultaneous denitrification, F^- and Ca²⁺ removal.

Biodegradation efficacy of soil inherent novel sp. Bacillus tropicus (MK318648) onto low density polyethylene matrix

The biodegradation of low density polyethylene (LDPE) was studied by employing a microbial strain isolated from the dumping site soil. The bacterium strain was identified as Bacillus tropicus (Gen Bank Accession no: MK318648) by 16S rRNA sequencing. The growth of the strain was observed on virgin LDPE during the biodegradation process. The change in properties of LDPE films before and after bacterial strain incubation was observed by FTIR, SEM, AFM, contact angle, mechanical and optical testing. Loss in mechanical properties and changes in optical properties of the polymer matrix was observed. Weight reduction by 10.15% and fall in the value of tensile strength, elongation at break, tear strength, Young’s Modulus, hardness and stiffness to 8.59 MPa, 10.85 mm, 69.18 N, 272.36, 37.6 Shor D and 10,672.21 N/m respectively were observed after 40 days of incubation. The transparency and haze percentage were also changed to 93.7% and 18.6% respectively after the study period. The pH of the media was measured during incubation to evaluate the change due to formation of different extracellular and intracellular enzymes excreted by the strain. Hence, Bacillus tropicus could be an efficient microorganism to degrade 10-micron thickness LDPE films, thereby preventing its harmful impacts in the environment.

Removal of fluoride in aqueous medium under the optimum conditions through intracellular accumulation in Bacillus flexus (PN4)

The removal of fluoride is essential for water contaminated with fluoride before being utilized since the unsafe concentration of fluoride with respect to the permissible limits. In the present study, there are 61 bacterial strains belonging to fluoride tolerance were isolated from the contaminated soil of Dharmapuri District, Tamil Nadu, India and they were evaluated for different characterization. Among the strains isolated, the strain PN4 showed a high tolerance to fluoride ranging from 500 to 2500 ppm under different stress conditions. The strain PN4 was selected as a possible organism for the degradation and removal of fluoride in an aqueous medium. Based on the morphology, biochemical characteristics and the 16S rRNA sequencing, the bacterium PN4 was identified as Bacillus flexus. In batch mode studies, the glucose was showed the maximum removal of fluoride (86%) followed by beef extract (82%) and a significant level of defluoridation was observed at pH 7.0 and the temperature at 35°C. In the antibiotic-resistance pattern, the strain Bacillus flexus PN4 was shown sensitive to three different antibiotics. Intracellular accumulation of fluoride by the bacterial cell was characterized by SEM- EDAX, TEM and FTIR analysis.

Biological approaches of fluoride remediation: potential for environmental clean-up

Fluoride (F), anion of fluorine which is naturally present in soil and water, behaves as toxic inorganic pollutant even at lower concentration and needs immediate attention. Its interaction with flora, fauna and other forms of life, such as microbes, adversely affect various physiochemical parameters by interfering with several metabolic pathways. Conventional methods of F remediation are time-consuming, laborious and cost intensive, which renders them uneconomical for sustainable agriculture. The solution lies in cracking down this environmental contaminant by adopting economic, eco-friendly, cost-effective and modern technologies. Biological processes, viz. bioremediation involving the use of bacteria, fungi, algae and higher plants that holds promising alternative to manage F pollution, recover contaminated soil and improve vegetation. The efficiency of indigenous natural agents may be enhanced, improved and selected over the hazardous chemicals in sustainable agriculture. This review article emphasizes on various biological approaches for the remediation of F-contaminated environment, and exploring their potential applications in environmental clean-up. It further focuses on thorough systemic study of modern biotechnological approaches such as gene editing and gene manipulation techniques for enhancing the plant-microbe interactions for F degradation, drawing attention towards latest progresses in the field of microbial assisted treatment of F-contaminated ecosystems. Future research and understanding of the molecular mechanisms of F bioremediation would add on to the possibilities of the application of more competent strains showing striking results under diverse ecological conditions.

The performance and mechanism of simultaneous removal of fluoride, calcium, and nitrate by calcium precipitating strain Acinetobacter sp. H12

A calcium precipitating and denitrifying bacterium H12 was used to investigate the F^- removal performance and mechanism. The results showed that the strain H12 reduced 85.24% (0.036 mg·L^-1·h^-1) of F^-, 62.43% (0.94 mg·L^-1·h^-1) of Ca²⁺, and approximately 100% of NO₃^- over 120 h in continuous determination experiments. The response surface methodology analysis demonstrated that the maximum removal efficiency of F^- was 88.98% (0.062 mg·L^-1·h^-1) within 72 h under the following conditions: the initial Ca²⁺ concentration of 250.00 mg·L^-1, pH of 7.50, and the initial C₄H₄Na₂O₄·6H₂O concentration of 800.00 mg·L^-1. The scanning electron microscopy images, the X-ray photoelectron spectroscopy, and X-ray diffraction results suggested the following removal mechanism of F^-: (1) the bacteria, as the nucleation site, were encapsulated by bioprecipitation to form biological crystal seeds; (2) Biological crystal seeds adsorbed F^- to form Ca₅(PO₄)₃F and CaF₂; (3) Under the induction of bacteria, calcium, fluoride and phosphate coprecipitated to form Ca₅(PO₄)₃F and CaF₂. In addition, the gas chromatography data indicated that F^- had little or no effect on the gas composition during denitrification, and the fluorescence spectroscopy analysis also proved that the extracellular polymeric substance (protein) is the site of bioprecipitation nucleation.

Defluoridation of water using autochthonous bacterial isolates

Prolonged consumption of fluoride-contaminated water poses health problems like dental and skeletal fluorosis in many parts of the world including India. In regions with acute water scarcity, it demands immediate intervention like de-fluoridation of water before consumption. In the current study, fluoride-resistant bacteria were isolated from fluoride-contaminated groundwater and soil samples collected from Dungarpur district, India, for their potential use in defluoridation. Out of a total of 53 bacterial isolates that were recovered and screened for fluoride resistance, three highly fluoride-resistant isolates DWC1, DWC2 and DWB5, resistant to up to 9200 mg L^-1, 7200 mg L^-1 and 5200 mg L^-1 fluoride respectively, were characterized and identified as Aeromonas sp., Brevibacterium sp. and Paenibacillus sp. respectively. The fluoride removal capacity of isolates DWC1, DWC2, DWB5 and a consortium of all the three isolates was found to be 68.7%, 73.4%, 76.7 % and 70.1% respectively on nutrient broth supplemented with NaF (2000 mg L^-1) after 8 days of incubation. Defluoridation conditions for the strain showing the best result (Paenibacillus sp.) were optimized for real fluoride-rich water collected from Ajmer District, India, using the Taguchi design of experiment. A defluoridation of up to 73.3% was observed at 40 °C temperature and pH 8 with inoculum: water ratio of 2:1 after 8 days of incubation. To the best of our knowledge, the defluoridation capacity of Paenibacillus sp. is the highest reported in literature to date for real water samples and could be investigated in further detail for commercial application.

Advances in exopolysaccharides based bioremediation of heavy metals in soil and water: A critical review

Extracellular polysaccharides or Exopolysaccharides (EPS) are extensively studied bacterial byproducts with high molecular weight attributed to several applications. In spite of their application in the field of food, pharmaceutical, nutraceutical, herbicidal and cosmeceutical industries they were well known for their efficiency in the bioremediation of water and soil tainted with heavy metals. These heavy metals are comparatively high in density than water and are involved in several biological processes. But slight increase in levels can create toxicological bias. The techniques like electrodialysis, chemical precipitation, ion exchange and membrane separation have a lot of disadvantages akin to high energy consumption, high cost, partial exclusion, and creation of poisonous mire. In this context, EPS has a top role to play in the bioremediation of heavy metals. This review gives the critical assessment of the extensive work done to deal this issue by different groups in the last five years. It also explains how different natural circumstances have attributed to the advancement of EPS production, thereby increasing the capacity of bioremediation to deal the issue of heavy metal contamination in both soil and water. A detailed discussion of the EPS formation by bacteria and fungi with their applicability was reported.