Characterization, real-time quantification and in silico modeling of arsenate reductase (arsC) genes in arsenic-resistant Herbaspirillum sp. GW103

Significance of Herbaspirillum sp. in biodegradation and biodetoxification of herbicides, pesticides, hydrocarbons and heavy metals - A review

In today's industrialized world, contamination of soil and water with various substances has emerged as a pressing concern. Bioremediation, with its advantages of degradation or detoxification, non-polluting nature, and cost-effectiveness, has become a promising method due to technological advancements. Among the bioremediation agents, bacteria have been highly explored and documented as a productive organism. Recently, few studies have reported on the significance of Herbaspirillum sp., a Gram-negative bacterium, in bioremediating herbicides, pesticides, polycyclic aromatic hydrocarbons, metalloids, and heavy metals, as well as its role in augmenting phytoremediation efforts. Herbaspirillum sp. GW103 leached 66% of Cu from ore materials and significantly enhanced the phytoaccumulation of Pb and Zn in plumule and radical tissues of Zea mays L. plants. Additionally, Herbaspirillum sp. WT00C reduced Se6+ into Se0, resulting in an increased Se0 content in tea plants. Also, Herbaspirillum sp. proved effective in degrading 0.6 mM of 4-chlorophenol, 92.8% of pyrene, 77.4% of fluoranthene, and 16.4% of trifluralin from aqueous solution and soil-water system. Considering these findings, this review underscores the need for further exploration into the pathways of pollutant degradation, the enzymes pivotal in the degradation or detoxification processes, the influence of abiotic factors and pollutants on crucial gene expression, and the potential toxicity of intermediate products generated during the degradation process. This perspective reframes the numerical data to underscore the underutilized potential of Herbaspirillum sp. within the broader context of addressing a significant research gap. This shift in emphasis aligns more closely with the problem-necessity for solution-existing unexplored solution framework.

The Effects of Paddy Cultivation and Microbiota Members on Arsenic Accumulation in Rice Grain

Access to safe food is one of the most important issues. In this context, rice plays a prominent role. Because high levels of arsenic in rice grain are a potential concern for human health, in this study, we determined the amounts of arsenic in water and soil used in the rice development stage, changes in the arsC and mcrA genes using qRT-PCR, and the abundance and diversity (with metabarcoding) of the dominant microbiota. When the rice grain and husk samples were evaluated in terms of arsenic accumulation, the highest values (1.62 ppm) were obtained from areas where groundwater was used as irrigation water, whereas the lowest values (0.21 ppm) occurred in samples from the stream. It was observed that the abundance of the Comamonadaceae family and Limnohabitans genus members was at the highest level in groundwater during grain formation. As rice development progressed, arsenic accumulated in the roots, shoots, and rice grain. Although the highest arsC values were reached in the field where groundwater was used, methane production increased in areas where surface water sources were used. In order to provide arsenic-free rice consumption, the preferred soil, water source, microbiota members, rice type, and anthropogenic inputs for use on agricultural land should be evaluated rigorously.

Arsenic (As) resistant bacteria with multiple plant growth-promoting traits: Potential to alleviate As toxicity and accumulation in rice

A currently serious agronomic concern for paddy soils is arsenic (As) contamination. Paddy soils are mostly utilized for rice cultivation. Arsenite (As(III)) is prevalent in paddy soils, and its high mobility and toxicity make As uptake by rice substantially greater than that by other food crops. Globally, interest has increased towards using As-resistant plant growth-promoting bacteria (PGPB) to improve plant metal tolerance, promote plant growth, and immobilize As to prevent its uptake and accumulation in the edible parts of rice as much as possible. This review focuses on the As-resistant PGPB characteristics influencing rice growth and the mechanisms by which they function to alleviate As toxicity stress in rice plants. Several recent examples of mechanisms responsible for decreasing the availability of As to rice and coping with As stresses facilitated by the PGPB with multiple PGP traits (e.g., phosphate and silicate solubilization, the production of 1-aminocyclopropane-1-carboxylate deaminase, phytohormones, and siderophore, N₂ fixation, sulfate reduction, the biosorption, bioaccumulation, methylation, and volatilization of As, and arsenite oxidation) are also reviewed. In addition, future research needs about the application of As-resistant PGPB with PGP traits to mitigate As accumulation in rice plants are described.

Insight into universality and characteristics of nitrate reduction coupled with arsenic oxidation in different paddy soils

Nitrate reduction coupled with arsenic (As) oxidation strongly influences the bioavailability and toxicity of As in anaerobic environments. In the present study, five representative paddy soils developed from different parent materials were used to investigate the universality and characteristics of nitrate reduction coupled with As oxidation in paddy soils. Experimental results indicated that 99.8 % of highly toxic aqueous As(III) was transformed to dissolved As(V) and Fe-bound As(V) in the presence of nitrate within 2-8 d, suggesting that As was apt to be reserved in its low-toxic and nonlabile form after nitrate treatment. Furthermore, nitrate additions also significantly induced the higher abundance of 16S rRNA and As(III) oxidase (aioA) genes in the five paddy soils, especially in the soils developed from purple sand-earth rock and quaternary red clay, which increased by 10 and 3-5 times, respectively, after nitrate was added. Moreover, a variety of putative novel nitrate-dependent As(III)-oxidizing bacteria were identified based on metagenomic analysis, mainly including Aromatoleum, Paenibacillus, Microvirga, Herbaspirillum, Bradyrhizobium, Azospirillum. Overall, all these findings indicate that nitrate reduction coupled with As(III) oxidation is an important nitrogen-As coupling process prevalent in paddy environments and emphasize the significance of developing and popularizing nitrate-based biotechnology to control As pollution in paddy soils and reduce the risk of As compromising food security.

Influence of bioaugmentation in crude oil contaminated soil by Pseudomonas species on the removal of total petroleum hydrocarbon

This study aimed to carry out the bioaugmentation of crude oil/motor oil contaminated soil. The mixture of novel strains Pseudomonas aeruginosa PP3 and Pseudomonas aeruginosa PP4 were used in this bioaugmentation studies. The four different bioaugmentation systems (BS 1-4) were carried out in this experiment labelled as BS 1 (Crude oil contaminated soil), BS 2 (BS 1 + bacterial consortia), BS 3 (Motor oil sludge contaminated soil), and BS 4 (BS 3 + bacterial consortia). The total petroleum hydrocarbon (TPH) was investigated for monitor the effectiveness of bioaugmentation process. The highest TPH removal rate was recorded on BS 4 (9091 mg Kg ^-1) was about 67% followed by 52% on BS 2 (8584 mg Kg ^-1) respectively. The percentage of biodegradation efficiency (BE) of residual crude and motor oil contaminated soil were evaluated by GCMS analysis and the results showed that 65% (BS 2) and 83% (BS 4) respectively. Further the bioaugmented soil was subjected to the plant cultivation (Lablab purpureus) and the results revealed that the L. purpureus was rapidly grown in the systems BS 4 and BS 2 than the system BS 1 and BS 2 which was due to the lesser biodegradation of the crude oil contents. In resultant, it can be concluded that the soil was suitable for the cultivation of plant. Overall, this study revealed that the selected bacterial consortia were effectively degraded the hydrocarbon and act as a potential bioremediator in the hydrocarbon polluted soil in a short period.

Biosorption efficiency of nickel by various endophytic bacterial strains for removal of nickel from electroplating industry effluents: an operational study

Realising the hazardous effect of nickel on human health, microbes and plants are effectively used for bioremediation. The endophytic microorganisms have an important role in the phytoremediation of nickel using Vigna radiata. Therefore, in order to harness the potential of microbial strains, the present study was designed to examine the metal biosorption ability of endophytic bacterial strains isolated from plants growing in nickel-contaminated soil. A total of six endophytic nickel resistance bacteria were isolated from the plant Vigna radiata. The metal tolerant bacterial strains were identified following 16 S rRNA gene sequence analysis. Nickel biosorption estimation and plant growth-promoting (PGP) activities of isolated strains were performed and found high nickel biosorption efficiency of 91.3 ± 0.72% at 600 mg L^-1 using Bacillus safensis an isolated endophytic strain from Vigna radiata. Furthermore, high indole acetic acid (IAA) and exopolysaccharide (EPS) production were obtained in all the strains as compared to without nickel-containing medium used as control. Moreover, the production of high EPS suggests improved biosorption ability of isolated endophytic strains. In addition, a kinetic study was also performed to evaluate different adsorptions isotherms and support the nickel biosorption ability of endophytic strains. The treatment of nickel electroplating industrial effluent was also demonstrated by isolated endophytic strains. Among six (6) strains, B. cereus showed maximum 57.2 ± 0.62% biosorption efficiency of nickel which resulted in the removal of 1003.50 ± 0.90 mg L^-1 of nickel from the electroplating industry effluents containing initial 1791 ± 0.90 mg L^-1 of nickel. All other strains were also capable of significant nickel biosorption from electroplating industry effluents as well. Thus, isolated endophytic nickel tolerant strains can be further used at large-scale biosorption of nickel from electroplating industry effluent.

Leveraging arsenic resistant plant growth-promoting rhizobacteria for arsenic abatement in crops

Arsenic is a toxic metalloid categorized under class 1 carcinogen and is detrimental to both plants and animals. Agricultural land in several countries is contaminated with arsenic, resulting in its accumulation in food grains. Increasing global food demand has made it essential to explore neglected lands like arsenic-contaminated lands for crop production. This has posed a severe threat to both food safety and security. Exploration of arsenic-resistant plant growth-promoting rhizobacteria (PGPR) is an environment-friendly approach that holds promise for both plant growth promotion and arsenic amelioration in food grains. However, their real-time performance is dependent upon several biotic and abiotic factors. Therefore, a detailed analysis of associated mechanisms and constraints becomes inevitable to explore the full potential of available arsenic-resistant PGPR germplasm. Authors in this review have highlighted the role and constraints of arsenic-resistant PGPR in reducing the arsenic toxicity in food crops, besides providing the details of arsenic transport in food grains.

Activated multi-walled carbon nanotubes decorated with zero valent nickel nanoparticles for arsenic, cadmium and lead adsorption from wastewater in a batch and continuous flow modes

Nickel nanoparticles (NiNPs) supported on activated multi-walled carbon nanotubes (MWCNTs) were used as an adsorbent applied towards Pb(II), As(V) and Cd(II) remediation from industrial wastewater. The result revealed the hydrophilic surface of MWCNTs-KOH was enhanced with the incorporation of NiNPs enabling higher surface area, functional groups and pore distribution. Comparatively, the removal of Pb(II), As(V) and Cd(II) on the various adsorbents was reported as NiNPs (58.6 ± 4.1, 46.8 ± 3.7 and 40.5 ± 2.5%), MWCNTs-KOH (68.4 ± 5.0, 65.5 ± 4.2 and 50.7 ± 3.4%) and MWCNTs-KOH@NiNPs (91.2 ± 8.7, 88.5 ± 6.5 and 80.6 ± 5.8%). Using MWCNTs-KOH@NiNPs, the maximum adsorption capacities of 481.0, 440.9 and 415.8 mg/g were obtained for Pb(II), As(V) and Cd(II), respectively. The experimental data were best suited to the Langmuir isotherm and pseudo-second order kinetic model. The fitness of experimental data to the kinetic models in a fixed-bed showed better fitness to Thomas model. The mechanism of metal ion adsorption onto MWCNTs-KOH@NiNPs show a proposed electrostatic attraction, surface adsorption, ion exchange, and pore diffusion due to the incorporated NiNPs. The nanocomposite was highly efficient for 8 adsorption cycles. The results of this study indicate that the synthesized nanocomposite is highly active with capacity for extended use in wastewater treatment.

Simultaneous removal of chromate and arsenite by the immobilized Enterobacter bacterium in combination with chemical reagents

Simultaneous chromate [Cr(VI)] reduction and arsenite [As(III)] oxidation is a promising pretreatment process for Cr and As removal. Here, a facultative anaerobic bacterium, Enterobacter sp. Z1, presented capacities of simultaneous Cr(VI) reduction and As(III) oxidation during anoxic cultivation in a wild range of temperature (20-45 °C) and pH (Cerkez et al., 2015; Chen et al., 2015; China Environmental Prote, 1996; Fan et al., 2008, 2019) conditions. Strikingly, strain Z1 could simultaneously contribute up to 92.8% of the reduction of Cr(VI) and 45.8% of the oxidation of As(III) in wastewater. The cells of strain Z1 were embedded with sodium alginate to produce biobeads, and the biobeads exhibited stable ratio of Cr(VI) reduction (91.8%) and As(III) oxidation (29.6%) even in the 5 continuous cycles of wastewater treatment. Moreover, in a process pretreated with the Z1 biobeads followed a precipitation with Ca(OH)₂ and FeCl₃, the removal efficiencies in wastewater were 98.9% and 98.3% for total Cr and As, respectively, which were 44.1% and 9.8% higher than those of using Ca(OH)₂ and FeCl₃, only. The residual amounts of Cr and As met the national standard levels of wastewater discharge. Proteomics analysis showed that cysteine, sulfur and methionine metabolisms, As resistance and oxidoreductase (CysH, CysI, CysJ, NemA and HemF) were induced by Cr(VI) and As(III). Moreover, the addition of cysteine to the medium also significantly improved bacterial Cr(VI) reduction rate. Our results provide a novel microbial pretreatment approach for enhancing remediation of Cr(VI) and As(III) pollution in wastewater, and reveal the evident that cysteine, sulfur and methionine metabolisms, As resistance and oxidoreductases are associated with the redox conversion of Cr(VI) and As(III).

Homology Modeling and Probable Active Site Cavity Prediction of Uncharacterized Arsenate Reductase in Bacterial spp

The arsC gene-encoded arsenate reductase is a vital catalytic enzyme for remediation of environmental arsenic (As). Microorganisms containing the arsC gene can convert pentavalent arsenate (As[V]) to trivalent arsenite (As[III]) to be either retained in the bacterial cell or released into the air. The molecular mechanism governing this process is unknown. Here we present an in silico model of the enzyme to describe their probable active site cavities using SCFBio servers. We retrieved the amino acid sequence of bacterial arsenate reductase enzymes in FASTA format from the NCBI database. Enzyme structure was predicted using the I-TASSER server and visualized using PyMOL tools. The ProSA and the PROCHECK servers were used to evaluate the overall significance of the predicted model. Accordingly, arsenate reductase from Streptococcus pyogenes, Oligotropha carboxidovorans OM5, Rhodopirellula baltica SH 1, and Serratia ureilytica had the highest quality scores with statistical significance. The plausible cavities of the active site were identified in our examined arsenate reductase enzymes which were abundant in glutamate and lysine residues with 6 to 16 amino acids. This in silico experiment may contribute greatly to the remediation of arsenic pollution through the utilization of microbial species.

Abundance and diversity of microbial arsenic biotransformation genes in the sludge of full-scale anaerobic digesters from a municipal wastewater treatment plant

Arsenic (As) is a potential contaminant in sewage sludge that may affect waste treatment and limit the use of these waste materials as soil amendments. Anaerobic digestion (AD) is an important and effective process for the treatment of sewage sludge and the chemical speciation of As is particularly important in sludge AD. However, the biotransformation genes of As in sludge during AD has not been fully explored. In this study, the influent and effluent sludge of anaerobic digester in a wastewater treatment plant (WWTP) was collected to investigate the species transformations of As, the abundance and diversity of As biotransformation genes was explored by real-time PCR (qPCR) and metagenomic sequencing, separately. The results showed that arsenite [As(III)] and arsenate [As(V)] were predominant in the influent sludge, whereas the relative abundance of monomethylarsenic acid (MMA) increased by 25.7% after digestion. As biotransformation genes were highly abundant, and the As(III) S-adenosylmethionine methyltransferase (arsM) gene was the predominant which significantly increased after AD by qPCR analysis. Metagenomic analysis indicated that the diversity of the arsM-like sequences also increased significantly after AD. Most of the arsM-like sequences in all the influent and effluent sludge samples were related to Bacteroidetes and Alphaproteobacteria. Furthermore, co-occurrence network analysis indicated a strong correlation between the microbial communities and As. This study provides a direct and reliable reference on As biotransformation genes and microbial community in the AD of sludge.

Efflux Transporter ArsK Is Responsible for Bacterial Resistance to Arsenite, Antimonite, Trivalent Roxarsone, and Methylarsenite

Arsenic-resistant bacteria have evolved various efflux systems for arsenic resistance. Five arsenic efflux proteins, ArsB, Acr3, ArsP, ArsJ, and MSF1, have been reported. In this study, comprehensive analyses were performed to study the function of a putative major facilitator superfamily gene, arsK, and the regulation of arsK transcriptional expression in Agrobacterium tumefaciens GW4. We found that (i) arsK is located on an arsenic gene island in strain GW4. ArsK orthologs are widely distributed in arsenic-resistant bacteria and are phylogenetically divergent from the five reported arsenic efflux proteins, indicating that it may be a novel arsenic efflux transporter. (ii) Reporter gene assays showed that the expression of arsK was induced by arsenite [As(III)], antimonite [Sb(III)], trivalent roxarsone [Rox(III)], methylarsenite [MAs(III)], and arsenate [As(V)]. (iii) Heterologous expression of ArsK in an arsenic-hypersensitive Escherichia coli strain showed that ArsK was essential for resistance to As(III), Sb(III), Rox(III), and MAs(III) but not to As(V), dimethylarsenite [dimethyl-As(III)], or Cd(II). (iv) ArsK reduced the cellular accumulation of As(III), Sb(III), Rox(III), and MAs(III) but not to As(V) or dimethyl-As(III). (v) A putative arsenic regulator gene arsR2 was cotranscribed with arsK, and (vi) ArsR2 interacted with the arsR2-arsK promoter region without metalloids and was derepressed by As(III), Sb(III), Rox(III), and MAs(III), indicating the repression activity of ArsR2 for the transcription of arsK These results demonstrate that ArsK is a novel arsenic efflux protein for As(III), Sb(III), Rox(III), and MAs(III) and is regulated by ArsR2. Bacteria use the arsR2-arsK operon for resistance to several trivalent arsenicals or antimonials.IMPORTANCE The metalloid extrusion systems are very important bacterial resistance mechanisms. Each of the previously reported ArsB, Acr3, ArsP, ArsJ, and MSF1 transport proteins conferred only inorganic or organic arsenic/antimony resistance. In contrast, ArsK confers resistance to several inorganic and organic trivalent arsenicals and antimonials. The identification of the novel efflux transporter ArsK enriches our understanding of bacterial resistance to trivalent arsenite [As(III)], antimonite [Sb(III)], trivalent roxarsone [Rox(III)], and methylarsenite [MAs(III)].

Mechanism of arsenic resistance in endophytic bacteria isolated from endemic plant of mine tailings and their arsenophore production

Arsenic contamination is an important environmental problem around the world since its high toxicity, and bacteria resist to this element serve as valuable resource for its bioremediation. Aiming at searching the arsenic-resistant bacteria and determining their resistant mechanism, a total of 27 strains isolated from roots of Prosopis laevigata and Spharealcea angustifolia grown in a heavy metal-contaminated region in Mexico were investigated. The minimum inhibitory concentration (MIC) and transformation abilities of arsenate (As⁵⁺) and arsenite (As³⁺), arsenophore synthesis, arsenate uptake, and cytoplasmatic arsenate reductase (arsC), and arsenite transporter (arsB) genes were studied for these strains. Based on these results and the 16S rDNA sequence analysis, these isolates were identified as arsenic-resistant endophytic bacteria (AREB) belonging to the genera Arthrobacter, Bacillus, Brevibacterium, Kocuria, Microbacterium, Micrococcus, Pseudomonas, and Staphylococcus. They could tolerate high concentrations of arsenic with MIC from 20 to > 100 mM for As⁵⁺ and 10-20 mM for As³⁺. Eleven isolates presented dual abilities of As⁵⁺ reduction and As³⁺ oxidation. As the most effective strains, Micrococcus luteus NE2E1 reduced 94% of the As⁵⁺ and Pseudomonas zhaodongensis NM2E7 oxidized 46% of As³⁺ under aerobic condition. About 70 and 44% of the test strains produced arsenophores to chelate As⁵⁺ and As³⁺, respectively. The AREB may absorb arsenate via the same receptor of phosphate uptake or via other way in some case. The cytoplasmic arsenate reductase and alternative arsenate reduction pathways exist in these AREB. Therefore, these AREB could be candidates for the bioremediation process.

Microbial Community Structure and Arsenic Biogeochemistry in Two Arsenic-Impacted Aquifers in Bangladesh

Long-term exposure to trace levels of arsenic (As) in shallow groundwater used for drinking and irrigation puts millions of people at risk of chronic disease. Although microbial processes are implicated in mobilizing arsenic from aquifer sediments into groundwater, the precise mechanism remains ambiguous. The goal of this work was to target, for the first time, a comprehensive suite of state-of-the-art molecular techniques in order to better constrain the relationship between indigenous microbial communities and the iron and arsenic mineral phases present in sediments at two well-characterized arsenic-impacted aquifers in Bangladesh. At both sites, arsenate [As(V)] was the major species of As present in sediments at depths with low aqueous As concentrations, while most sediment As was arsenite [As(III)] at depths with elevated aqueous As concentrations. This is consistent with a role for the microbial As(V) reduction in mobilizing arsenic. 16S rRNA gene analysis indicates that the arsenic-rich sediments were colonized by diverse bacterial communities implicated in both dissimilatory Fe(III) and As(V) reduction, while the correlation analyses involved phylogenetic groups not normally associated with As mobilization. Findings suggest that direct As redox transformations are central to arsenic fate and transport and that there is a residual reactive pool of both As(V) and Fe(III) in deeper sediments that could be released by microbial respiration in response to hydrologic perturbation, such as increased groundwater pumping that introduces reactive organic carbon to depth.IMPORTANCE The consumption of arsenic in waters collected from tube wells threatens the lives of millions worldwide and is particularly acute in the floodplains and deltas of southern Asia. The cause of arsenic mobilization from natural sediments within these aquifers to groundwater is complex, with recent studies suggesting that sediment-dwelling microorganisms may be the cause. In the absence of oxygen at depth, specialist bacteria are thought able to use metals within the sediments to support their metabolism. Via these processes, arsenic-contaminated iron minerals are transformed, resulting in the release of arsenic into the aquifer waters. Focusing on a field site in Bangladesh, a comprehensive, multidisciplinary study using state-of-the-art geological and microbiological techniques has helped better understand the microbes that are present naturally in a high-arsenic aquifer and how they may transform the chemistry of the sediment to potentially lethal effect.

Isolation, identification and characterization of arsenic transforming exogenous endophytic Citrobacter sp. RPT from roots of Pteris vittata

The aim of the present study was to assess the arsenic (As) transformation potential of endophytic bacteria isolated from roots of Pteris vittata plant. The endophytic bacterium was tested for minimal inhibitory concentration (MIC) against As. The endophytic strain RPT exhibited the highest resistance to As(V) (400 mg/l). Phylogenetic analysis of the 16S rRNA sequence suggested that strain RPT was a member of genus Citrobacter. The As transformation assay revealed As(III) oxidation and As(V) reduction potential of Citrobacter sp. RPT. The As resistance mechanism was further confirmed by amplification of arsC and aoxB genes. The growth kinetics of strain RPT was altered slightly in the presence of different concentration (100-400 mg/l) of As stress. Temperature and pH influenced the As removal rate. The maximum As removal was observed at pH 7.0 (74%) and 37 °C (70.9%). The results suggest that strain RPT can survive under the As stress and has been identified as a potential candidate for application in bioremediation of As in contaminated environments.

Significance of diazotrophic plant growth-promoting Herbaspirillum sp. GW103 on phytoextraction of Pband Zn by Zea mays L

Microbe-assisted phytoremediation has been considered a promising measure for the remediation of heavy metal-polluted soil. The aim of this study was to assess the effect of diazotrophic plant growth-promoting Herbaspirillum sp. GW103 on growth and lead (Pb) and zinc (Zn) accumulation in Zea mays L. The strain GW103 exhibited plant growth-promoting traits such as indole-3-acetic acid, siderophores, and 1-aminocyclopropane-1-carboxylic deaminase. Treatment of Z. mays L. plants with GW103 significantly increased 19, 31, and 52% of plant biomass and 10, 50, and 126% of chlorophyll a contents in Pb, Zn, and Pb + Zn-amended soils, respectively. Similarly, the strain GW103 significantly increased Pb and Zn accumulation in shoots and roots of Z. mays L., which were 77 and 25% in Pb-amended soil, 42 and 73% in Zn-amended soil, and 27 and 84% in Pb + Zn-amended soil. Furthermore, addition of GW103 increased 8, 12, and 7% of total protein content, catalase, and superoxide dismutase levels, respectively, in Z. mays L. plants. The results pointed out that isolate GW103 could potentially reduce the phytotoxicity of metals and increase Pb and Zn accumulation in Z. mays L. plant.

Bioremediation of heavy metals using an endophytic bacterium Paenibacillus sp. RM isolated from the roots of Tridax procumbens

The aim of the present study was to assess the bioremediation potential of endophytic bacteria isolated from roots of Tridax procumbens plant. Five bacterial endophytes were isolated and subsequently tested for minimal inhibitory concentration (MIC) against different heavy metals. Amongst the five isolates, strain RM exhibited the highest resistance to copper (750 mg/l), followed by zinc (500 mg/l), lead (450 mg/l), and arsenic (400 mg/l). Phylogenetic analysis of the 16S rDNA sequence suggested that strain RM was a member of genus Paneibacillus. Strain RM also had the capacity to produce secondary metabolites, indole acetic acid, siderophores, 1-aminocyclopropane-1-carboxylate (ACC) deaminase, and biosurfactant and solubilize phosphate. The growth kinetics of strain RM was altered slightly in the presence of metal stress. Temperature and pH influenced the metal removal rate. The results suggest that strain RM can survive under the high concentration of heavy metals and has been identified as a potential candidate for application in bioremediation of heavy metals in contaminated environments.