Maximum Tolerance Concentration Research Articles

Draft genome analysis for Enterobacter kobei, a promising lead bioremediation bacterium.

Lead pollution of the environment poses a major global threat to the ecosystem. Bacterial bioremediation offers a promising alternative to traditional methods for removing these pollutants, that are often hindered by various limitations. Our research focused on isolating lead-resistant bacteria from industrial wastewater generated by heavily lead-containing industries. Eight lead-resistant strains were successfully isolated, and subsequently identified through molecular analysis. Among these, Enterobacter kobei FACU6 emerged as a particularly promising candidate, demonstrating an efficient lead removal rate of 83.4% and a remarkable lead absorption capacity of 571.9mg/g dry weight. Furthermore, E. kobei FACU6 displayed a remarkable a maximum tolerance concentration (MTC) for lead reaching 3,000mg/L. To further investigate the morphological changes in E. kobei FACU6 in response to lead exposure, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed. These analyses revealed significant lead adsorption and intracellular accumulation in treated bacteria in contrast to the control bacterium. Whole-genome sequencing was performed to gain deeper insights into E. kobei's lead resistance mechanisms. Structural annotation revealed a genome size of 4,856,454bp, with a G + C content of 55.06%. The genome encodes 4,655 coding sequences (CDS), 75 tRNA genes, and 4 rRNA genes. Notably, genes associated with heavy metal resistance and their corresponding regulatory elements were identified within the genome. Furthermore, the expression levels of four specific heavy metal resistance genes were evaluated. Our findings revealed a statistically significant upregulation in gene expression under specific environmental conditions, including pH 7, temperature of 30°C, and high concentrations of heavy metals. The outstanding potential of E. kobei FACU6 as a source of diverse genes related to heavy metal resistance and plant growth promotion makes it a valuable candidate for developing safe and effective strategies for heavy metal disposal.

Bacterial bioremediation of textile effluent dyes contaminated sites

Water and soil pollution caused by industrial effluent has become an alarming threat to environmental safety. This is mainly because of the direct discharge of textile effluents into the water bodies, without any pre-treatments. To resolve this, microbial bioremediation is used for the effective removal of the dyes and toxic compounds present in textile effluents. The textile dye-degrading isolates (3A, 4A, 5B and 6B) were isolated from the soil samples collected at the dye contaminated sites. Synthetic textile dyes, Brill Red 3BN and Blue SE2R obtained from the textile dyeing units were used as positive control for this study. The genus of the dye degrading isolates was identified by morphological and biochemical characterization. Based on the results, the isolates were belonged to the genus Pseudomonas. All four strains are producing both pyomelanin (brown) and pyoverdine (green) pigments during their growth. Maximum tolerance concentration (MTC) test, growth kinetics, decolorization and degradation studies were performed to analyze the dye degrading potential of isolates. Strain 3A and 6B showed more than 80% of decolorization up to 2500 ppm dye mix within 5 days of incubation. Isolates used textile dye as their sole carbon source for their growth and development. The biodegraded dye was analysed by GC-MS to measure the dye degrading ability of isolates.

Arsenic pollution and arsenic-resistant bacteria of drying Urmia Salt Lake

Extensive arsenic contamination of groundwater, rivers, and agricultural farms has led to widespread arsenic poisoning and consequent problems associated with health and economy. In recent years, many studies have been performed to understand bacterial arsenic detoxification and metabolism which has paved the way for bioremediation applications. This study attempted to isolate and characterize arsenic-resistant bacteria from the drying Urmia lake. As a result of the 16S rDNA analysis, six arsenic-resistant strains were identified as the members of Shouchella, Salipaludibacillus, and Evansella genera. For some of the strains, the maximum tolerance concentration for either arsenate or arsenite was considerably high, 320 and 16 mM, respectively. All the strains harbored the arsenate reductase gene (arsC). The arsenate permease (arsB) gene was identified in all strains except in strains S1, S12, and E15. The metabolic genes of respiratory arsenate reductase (arrB) and arsenite oxidase (arxA) were identified in none of these strains. This feature of the strains with the arsC gene region can be exploited to bioremediate arsenic from contaminated areas by using a two-step process. The second step can be carried out by the adsorption of arsenite to iron oxide or by precipitation with sulfide. Today, more and more ecosystems are being destroyed due to anthropogenic pollution, and it is important to reveal the negative effects and solutions of this situation on the ecosystems. So, the current study provides a potential source of bacteria for such studies that implement bioremediation practices to prevent arsenic catastrophe in vicinal territories, and reveals arsenic pollution in Urmia lake.

Draft genome of Raoultella planticola, a high lead resistance bacterium from industrial wastewater

Isolation of heavy metals-resistant bacteria from their original habitat is a crucial step in bioremediation. Six lead (Pb) resistant bacterial strains were isolated and identified utilizing 16S rRNA to be Enterobacter ludwigii FACU 4, Shigella flexneri FACU, Microbacterium paraoxydans FACU, Klebsiella pneumoniae subsp. pneumonia FACU, Raoultella planticola FACU 3 and Staphylococcus xylosus FACU. It was determined that all these strains had their Minimum inhibitory concentration (MIC) to be 2500 ppm except R. planticola FACU 3 has a higher maximum tolerance concentration (MTC) up to 2700 ppm. We evaluated the survival of all six strains on lead stress, the efficiency of biosorption and lead uptake. It was found that R. planticola FACU 3 is the highest MTC and S. xylosus FACU was the lowest MTC in this evaluation. Therefore, transmission electron microscopy (TEM) confirmed the difference between the morphological responses of these two strains to lead stress. These findings led to explore more about the genome of R. planticola FACU 3 using illumine Miseq technology. Draft genome sequence analysis revealed the genome size of 5,648,460 bp and G + C content 55.8% and identified 5526 CDS, 75 tRNA and 4 rRNA. Sequencing technology facilitated the identification of about 47 genes related to resistance to many heavy metals including lead, arsenic, zinc, mercury, nickel, silver and chromium of R. planticola FACU 3 strain. Moreover, genome sequencing identified plant growth-promoting genes (PGPGs) including indole acetic acid (IAA) production, phosphate solubilization, phenazine production, trehalose metabolism and 4-hydroxybenzoate production genes and a lot of antibiotic-resistant genes.

Aeromonas sobria as a potential candidate for bioremediation of heavy metal from contaminated environments.

The uncontrolled discharge of industrial wastes causes the accumulation of high heavy metal concentrations in soil and water, leading to many health issues. In the present study, a Gram-negative Aeromonas sobria was isolated from heavily contaminated soil in the Tanjaro area, southwest of Sulaymaniyah city in the Kurdistan Region of Iraq; then, we assessed its ability to uptake heavy metals. A. sobria was molecularly identified based on the partial amplification of 16S rRNA using novel primers. The sequence was aligned with 33 strains to analyze phylogenetic relationships by maximum likelihood. Based on maximum tolerance concentration (MTC), A. sobria could withstand Zn, Cu, and Ni at concentrations of 5, 6, and 8mM, respectively. ICP-OES data confirmed that A. sobria reduced 54.89% (0.549mM) of the Cu, 62.33% (0.623mM) of the Ni, and 36.41% (0.364mM) of the Zn after 72h in the culture medium. Transmission electron microscopy (TEM) showed that A. sobria accumulated both Cu and Ni, whereas biosorption was suggested for the Zn. These findings suggest that metal-resistant A. sobria could be a promising candidate for heavy metal bioremediation in polluted areas. However, more broadly, research is required to assess the feasibility of exploiting A. sobria in situ.

Bioaccumulation characteristics and acute toxicity of uranium in Hydrodictyon reticulatum: An algae with potential for wastewater remediation

The bioaccumulation characteristics and acute toxicity of uranium (U) to Hydrodictyon reticulatum were studied to provide reference for further mechanism and application research. According to an analysis using visual MINTEQ software, the pH change caused by the photosynthesis of H. reticulatum leads to U remaining mainly in the species of UO2(OH)3-. Fourier transform infrared spectrometer (FTIR) and transmission electron microscope (TEM) analysis showed that the bioaccumulation of U was related to the amino and carboxyl groups, resulting in cell wall damage. Using innovative cell staining microscopic observation techniques, U was mainly compartmentalized in vacuoles and pyrenoid; chlorophyll, soluble protein, dehydrogenase activity, and other physiological responses were closely related to the U stress concentration. Especially here, the change trend of the specific activity and specific growth rate of dehydrogenase was consistent, showing low concentration promotion and high concentration inhibition. Combined with the toxic response of the two, the half inhibitory dose for 72 h was determined to be about 30 mg L−1. When bioaccumulation equilibrium is reached at 72 h, the maximum tolerance concentration of U without affecting the easy collection characteristics of the algae is 30 mg L−1, and the maximum U bioaccumulation capacity was able to reach 24.47 ± 0.86 mg g−1 by dry biomass.

Differences in bioaccumulation of Ni and Zn by microalgae in the presence of fulvic acid

In the presence of dissolved organic matter, the mechanism of algal bioaccumulation of different metals is complex, and its significance goes far beyond the alga-metal binary system. In the presence of 10 and 20 mg L−1 fulvic acid (FA), the maximum tolerance concentrations of Chlorella pyrenoidosa to Ni were 0.25 and 0.26 mmol L−1, and to Zn were 0.62 and 0.68 mmol L−1, respectively. Within the maximum tolerance concentration ranges, the bioaccumulation behaviors of Ni and Zn were systematically compared in the presence of FA. The presence of FA shortened the adsorption equilibrium time and decreased the maximum bioaccumulation capacity of Ni and Zn. The bioaccumulation mechanism of Ni by C. pyrenoidosa was more inclined to monolayer adsorption, while the bioaccumulation mechanism of Zn was more inclined to multilayer adsorption. More details were revealed after the bioaccumulated metals were separated into adsorption and internalization states by 0.01 M EDTA elution. The presence of FA decreased more adsorbed Zn than the adsorbed Ni, due to the different competitive roles of FA in the ternary system of Ni and Zn, but the presence of FA increased the internalized Ni might due to the stronger complexation of Ni-FA. This research indicated that algae had unique bioaccumulation mechanisms for different metals in the presence of FA, which is of great significance to accurately evaluate the ecological risk posed by heavy metals.

Mechanism of recombinant bacteria adsorb UO22+ under culture condition

Research on the ability and mechanism of genetically recombinant E. coli DH5α containing DSR A gene to enrich uranium under culture conditions provides a theoretical basis for the application of the bacteria in the treatment of uranium pollution. By exploring the influence of factors such as the initial concentration of uranium, culture time, and inoculation amount on the characteristics of uranium enrichment in genetically recombinant E. coli, using FTIR, SEM-EDS, XPS and XRD explore the mechanism of uranium-enriched bacteria. The results showed that when initial UO22+ concentration reach 600 mg/L, E. Coli D1 could not survived, indicated that the maximum tolerance concentration is lower than 600 mg/L. While concentration between 0∼500 mg/L, strains D1 can grow normally and has the ability to enrich uranium. In the prime stage, strains D1 resist toxics through release inorganic phosphates to precipitate UO22+ on cell wall, after 96 h, most UO22+ were transferred into cytoplasm and metabolized into U(IV) which is less toxic. In the metabolize process, all groups involved in metabolizing UO22+, especially protein contain groups like hydroxyl, amine and carboxyl paly a huge role. It shows that within a certain concentration rage, strains D1 has a good enrichment effect on uranium under culture conditions.

Genomic and Physiological Investigation of Heavy Metal Resistance from Plant Endophytic Methylobacterium radiotolerans MAMP 4754, Isolated from Combretum erythrophyllum.

Combretum erythrophyllum is an indigenous southern African tree species, a metal hyperaccumulator that has been used as a phytoextraction option for tailing dams in Johannesburg, South Africa. In hyperaccumulators, metal detoxification has also been linked or attributed to the activities of endophytes, and, in this regard, metal detoxification can be considered a form of endophytic behavior. Therefore, we report herein on the identification of proteins that confer heavy metal resistance, the in vitro characterization of heavy metal resistance, and the production of plant growth-promoting (PGP) volatiles by Methylobacterium radiotolerans MAMP 4754. Multigenome comparative analyses of M. radiotolerans MAMP 4754 against eight other endophytic strains led to the identification of zinc, copper, and nickel resistance proteins in the genome of this endophyte. The maximum tolerance concentration (MTC) of this strain towards these metals was also investigated. The metal-exposed cells were analyzed by transmission electron microscopy (TEM). The ethyl acetate and chloroform extracts (1:1 v/v) of heavy metal untreated M. radiotolerans MAMP 4754 were also screened for the production of PGP compounds by Gas Chromatography–Mass Spectroscopy (GC/MS). The MTC was recorded at 15 mM, 4 mM, and 12 mM for zinc, copper, and nickel, respectively. The TEM analysis showed the accumulation of metals in the intracellular environment of M. radiotolerans MAMP 4754, while the GC/MS analysis revealed several plant growth-promoting compounds, including alcohols, phthalate esters, alkenes, ketones, sulfide derivatives, phenols, and thiazoles. Our findings suggest that the genetic makeup of M. radiotolerans MAMP 4754 encodes heavy metal resistant proteins that indicate hyperaccumulator-specific endophytic behavior and the potential for application in bioremediation. The production of plant growth-promoting volatiles in pure culture by M. raditotolerans MAMP 4754 is a characteristic feature for plant growth-promoting bacteria.

Selective Isolation of Heavy Metals Resistant Bacteria From Waste Water

The current study was conducted to isolate bacteria resistant to heavy metals lead, chromium and cadmium from waste water. The concentration of lead, chromium and cadmium was measured in the waste water samples collected from different sites in Baghdad city using a flame atomic spectrometry. The results showed a significant increase in metals concentration in some sites compared to the standard determinants, as well as a significant variation between the concentration of the three metals, and nil values were recorded in some sites.The primary isolation of lead, chromium and cadmium tolerant bacteria from five sites which recorded the highest concentration of these metals showed 25 bacterial isolates distributed between 9 bacterial isolates tolerating 300 mg/l lead, 9 isolates tolerant to 100 mg/l chromium and 7 isolates tolerant to 100 mg/l of cadmium. Well diffusion method was used to choose resistant bacterial isolates, and the results showed a difference in the resistance of bacterial isolates to metals, and the bacterial isolates Pb1, Pb4, Cr8, Cr9, Cd5 were chosen which recorded resistance to high concentrations of heavy metals and more than one metal at the same time. The maximum tolerance concentration of the bacterial isolates was determined using liquid medium, and the bacterial isolate Pb1 recorded a maximum tolerance concentration of 1300, 700, 350 mg/l for lead, chromium and cadmium respectively, while the isolate Pb4 recorded the maximum tolerance concentration of 2300 mg/l for lead, and 700 mg/l for chromium, 300 mg/l for cadmium. The isolate Cr8 showed a maximum tolerance concentration of 700, 650, and 450 mg/l for lead, chromium and cadmium respectively, while the bacterial isolate Cr9 showed a maximum tolerance concentration of 700 mg/l for both lead and chromium and 500 mg/l for cadmium, while the bacterial isolate Cd5 recorded the highest maximum cadmium tolerance 650 mg/l among bacterial isolates, with a maximum tolerance concentration 800 mg/l for lead and 550 mg/l for chromium. Primary identification showed that all five bacterial isolates were Gram negative bacteria.

Evaluation of antifungal activity of Bacillus spp. against Fusarium oxysporum and Rhizoctonia solani in Chick pea (Cicer arietinum L.)

Bacillus isolates were evaluated for their antagonistic activities against Fusarium oxysporum and Rhizoctonia solani from chick pea rhizosphere and their compatibility with Fusarium oxysporum and Rhizoctonia solani.Bacillus B1 isolate showed 53.3% inhibition and Bacillus N2(2) showed 41.7% inhibition against R. solani. Compatibility of fungicides with B1 and N2(2), Bacillus isolates was checked using turbidometric method, disc method and poisoned food method. Both isolates were found compatible with different fungicides concentration. Both isolates when incorporated as seed treatment, increased germination percentage, root/shoot length and vigour index. Out of 5 fungicides, maximum tolerance concentration and maximum inhibition centration was found to be more concentration by Carbendazim.

Isolation and characterization of chromium(VI)-reducing bacteria from tannery effluents and solid wastes.

In the present investigation, five novel Cr(VI) reducing bacteria were isolated from tannery effluents and solid wastes and identified as Kosakonia cowanii MKPF2, Klebsiella pneumonia MKPF5, Acinetobacter gerneri MKPF7, Klebsiella variicola MKPF8 and Serratia marcescens MKPF12 by 16S rDNA gene sequence analysis. The maximum tolerance concentration of Cr(VI) as K2Cr2O7 of the bacterial isolates was varying up to 2000mg/L. Among the investigated bacterial isolates, A. gerneri MKPF7 was best in terms of reduction rate. The optimum temperatures for growth and Cr(VI) reduction by the bacterial isolates were 35 and 40°C, respectively except A. gerneri MKPF7 which grew and reduced Cr(VI) optimally at 40°C. The optimum pH for growth and Cr(VI) reduction by K. cowanii MKPF2, A. gerneri MKPF7 and S. marcescens MKPF12 was 7.0 whereas the optimum pH for growth and Cr(VI) reduction by K. pneumoniae MKPF5 and K. variicola MKPF8 were 7.0, 8.0 and 6.0, 7.0, respectively. All the bacterial isolates showed maximum tolerance against Ni2+ and Zn2+ whereas minimum tolerance was observed against Hg2+ and Cd2+. The bacteria isolated in the present study thus can be used as eco-friendly biological expedients for the remediation and detoxification of Cr(VI) from the contaminated environments.

Bioremediation of Lead by lead resistant bacterial isolates isolated from Contaminated soils of Chhattisgarh

The present study deals with isolation and identification of lead resistant bacteria from contaminated soil of Chhattisgarh, India. From morphological, biochemical analysis and 16S rRNA sequencing, one lead resistant bacteria isolate was identified as Brevibacillus brevis. Maximum tolerance concentration (MTC) was shown against the lead acetate at different levels. The higher MTC was observed 1500 µg/ml concentration of lead acetate. The present study reveals that the lead resistant bacterial isolate can be used for bioremediation of lead.

Iron (II) and other heavy-metal tolerance in bacteria isolated from rock varnish in the arid region of Al-Jafer Basin, Jordan

Alnaimat S, Shattal SA, AlthunibatO, Alsbou E, Amasha R. 2017. Iron (II) and other heavy-metal tolerance in bacteria isolated from rock varnish in the arid region of Al-Jafer Basin, Jordan. Biodiversitas 18: 1250-1257. This study deals with enumeration, identification and molecular characterization of bacterial species tolerant of iron (II) and other heavy metals that isolated from rock varnish collected from the arid region of Al-Jafer Basin, Jordan. Based on conventional culture-dependent methods, six isolates exhibited a high degree of tolerance to iron (II) and other heavy metals with a minimum inhibitory concentration (550–600 mg/L) to iron, (500-550 mg/L) to lead, (350 mg/L) to copper, (400-450 mg/L) to chromium, (150-200 mg/L) to silver, and (150-200 mg/L) to mercury, in solid media. The results showed that all isolates could tolerate 2000 mg/L Fe2+ expressed as maximum tolerance concentration (MTC). The multiple metal resistances of these isolates were also associated with multiple antibiotic resistances. These iron tolerant isolates were shown to be capable of growth at temperatures ranging from 30 to 40°C and pH values ranging from 5 to 9 with some differences between the six isolates. On the basis of morphology and of 16S rDNA gene sequencing and phylogeny analysis, the iron-tolerant isolates were identified as Bacillus zhangzhouensis (DVCr1), Staphylococcus warneri (DVCr6), Bacillus cereus (DVCr7), Staphylococcus pasteuri (DVCu2), Brevibacterium frigoritolerans (DVPb) and Bacillus altitudinis (DVCr10). The 16S rDNA sequences from five of the six strains were submitted to GenBank and are available under the accession numbers KX781139, KX781140, KX781141, KX781145 and KX781148. The results highlight the high potential of a non-polluted habitat like rock varnish to provide new microbial communities that could be used for enhanced bioremediation of heavy metals from a contaminated site.

Characterization of MAR and heavy metal-tolerant E. coli O157:H7 in water sources: a suggestion for behavioral intervention

The water sources in developing countries are usually contaminated with the members of enterobacteriaceae leading to gastrointestinal infections. There has been an increasing consumption of antibiotics during last decade in India. The development of multiple antibiotic resistance and heavy metal tolerance among waterborne bacteria has been coexisting traits. Keeping above features in view, 51 waterborne isolates of Escherichia coli O157:H7 have been characterized in the present study. The disk diffusion test for antibiotic sensitivity assay revealed that all the isolates were resistant to at least one or more antibiotics. Cephalosporins were least effective, while fluoroquinolones and aminoglycosides were most effective antibiotics. The isolates shared resistance pattern similarities regardless of their sources. The isolates were subjected to test maximum tolerance concentration of heavy metals such as arsenic, lead, chromium and mercury. About 98% isolates tolerated arsenic at 250 μg ml−1 or various above concentrations. Mercury >25 μg ml−1 was not tolerated by more than 90% isolates. In dug well, a commonly used water source in rural India, the isolates exhibited multiple antibiotic resistance index of 0.68 indicating it as high risk contaminating source. PCR–RFLP of 16S rDNA distinguished isolates into four groups with the smallest group represented by 3 isolates. Three isolates belonged to different sources but shared all the features of biochemical, serological, multiple antibiotic resistance and heavy metal tolerance test. 16S rDNA sequence analysis showed that the three selected isolates were closely related to each other. Based on the microbial and molecular findings, the study recommends to follow social cognitive theory to alter the behavior of the local communities for sustainable use of water resources.

Isolation, identification, and environmental adaptability of heavy-metal-resistant bacteria from ramie rhizosphere soil around mine refinery

Six bacteria strains from heavy-metal-polluted ramie rhizosphere soil were isolated through Cd2+ stress, which were numbered as JJ1, JJ2, JJ10, JJ11, JJ15, and JJ18. Sequence alignment and phylogenic analysis showed that strain JJ1 belonged to Pseudomonas, strain JJ2 belonged to Cupriavidus, strains JJ11 and JJ15 belonged to Bacillus, and strains JJ10 and JJ18 belonged to Acinetobacter. The tolerance capability of all the strains was the trend of Pb2+ > Zn2+ > Cu2+ > Cd2+, the maximum tolerance concentration to Cd2+ was 200 mg/L, to Pb2+ was 1600 mg/L, to Zn2+ was 600 mg/L, and to Cu2+ was 265 mg/L. Strains JJ1, JJ11, JJ15, and JJ18 could grow well under pH 9.0, and strains JJ2, JJ11, and JJ18 could grow well under 7% of NaCl. The results showed that as a whole these strains had high environmental adaptability. This is the first report that heavy-metal-tolerant bacteria were found from ramie rhizosphere soil, which could be as a foundation to discover the relationship between ramie, rhizosphere bacteria and heavy metals.

Evaluation of Heavy Metals Resistant Micrococcus sp. Isolated from Rivers in Basra, Iraq

The present study aims to isolation, identification and characterization of heavy metal resistant bacteria from six rivers in Basra Southern Iraq. Two species of Micrococcus (M. halobius and M. kristinae) were isolated on the basis of morphological and biochemical profiles and selected based on high levels of heavy metals (cadmium, lead, copper and nickel) resistance. The concentrations of dissolved heavy metals (Cd, Pb, Cu and Ni) in rivers were determined. The maximum tolerance concentration (MTC) of isolates against Pb, Cu, Cd and Ni was determined in solid media after 72 h incubation. All isolates were resistant to Pb (2200-2600) μg mL-1, Cu (400) μg mL-1, Cd (300-400) μg mL-1 and Ni (200-300) μg ml-1. Living biomass of M. halobius and M. kristinae were used for the removal of heavy metal ions at different concentrations (25, 50 and 100) μg mL-1 from aqueous metal solutions. The best concentration of removal was 25 μg mL-1 after 72 h incubation at 120 rpm. Percent removal efficiency of M. kristinae was 47.22, 26.26 for Cu and Pb respectively, and for M. halobius was 31.52, 27.87 for Cd and Ni respectively.

Heavy Metal tolerant Non endosymbiont PGPR’s; Psuedomonas spp. and Bacillus spp. associated with the roots of evergreen shrubs Casuarinas equisetifolia

There is a lack in research related to association of non-endosymbiont bacteria with Casuarina sp. PGPR non-endosymbiont bacteria like pseudomonas sp. and Bacillus sp. are long associated with their properties of heavy metal accumulation and plant growth promoting activity. The present study focuses on heavy metal tolerant and accumulation potential of non endosymbiont PGPR isolated from rhizosphere of Casuarina equisetifolia . The plant growth promoting properties was studied by pot culture studies on fast growing Indian moth bean Vigna aconitifolia . In the pot culture study three bacterial isolates were found to be increasing the root and shoot length by Pseudomonas sp. RS-1 (7.4±0.64 and 21.7±1.42), Bacillus sp. RS-2 (6.5±0.93 21.2±2.09) and and Bacillus sp. RS-3 (6.4±0.73 19.1±1.83) respectively. The maximum tolerance concentration of Pseudomonas sp. RS-1 shows 200 mg/L towards Cr (VI), Pb (II) 150 mg/L whereas tolerance for Cd (II), and Zn (II) were 100mg/L. Maximum % removal was shown by Bacillus sp. RS-3 towards Cr, Pb and Zn (42.51, 26.35 and 26.65 % respectively), Pseudomonas sp. RS-1 towards Cd (36.52 %). As Frankia ecological interaction between non-endosymbiont bacteria and phytoremediation ability of Casuarina sp. is not fully understood. Further study in this area may lead to better prospect in application of Casuarina as a phytoremediation agent.

Characterization and Sorptivity of the Plesiomonas shigelloides Strain and Its Potential Use to Remove Cd2+ from Wastewater

In this study, the ability of adsorbing Cd2+ ions of Plesiomonas shigelloides was discovered. Herein, the method and mechanisms of adsorbing Cd2+ ions from aqueous solutions is discussed. The cadmium-resistant bacterium was collected from the sediment of Harbin section of the Songhua River in China, and then isolated, identified and characterized. The isolated strain was identified as Plesiomonas shigelloides H5 on the basis of morphological and biochemical characteristics, the sequencing of the 16SrDNA gene, and phylogeny analysis. P. shigelloides H5 was Gram-negative and bacillus. Maximum tolerance concentration (MTC) of the strain was 150 mg/L. The maximum adsorption rate and adsorption amounts was 42.71% ± 0.88% and 106.775 ± 2.325 mg/g when dried biomass was presented in a 50 mg/L Cd2+ solution. Dried biomass was in accordance with Lagergren pseudo-second-order models. A field emission scanning electron microscope (FE-SEM), an energy dispersive X-ray spectrometer (EDX), and Fourier transform infrared spectroscopy (FTIR) analyses were applied to identify the surface morphology and functional groups. Transmission electron microscope (TEM) results showed that Cd2+ was also absorbed into cells to form precipitates. The results revealed that the surface functional groups of P. shigelloides H5 can bind to heavy metal ions. To sum up, the ability of adsorbing cadmium ions of Plesiomonas shigelloides was discovered, which might be helpful in wastewater treatment in the future.

English

The presence of heavy metals in aquatic environments poses a serious environmental risk. The usage of heavy metal-tolerant bacteria may serve as a cost-effective tool for bioremediation of polluted water bodies. Thus, the present study aims at the isolation and characterization of heavy metal tolerant gram-negative bacteria collected from the polluted water of the river Yamuna, Delhi, India. The water samples were collected from the downstream river and enriched separately in the nutrient broth. Appropriate dilutions were then plated in eosin methylene blue (EMB) agar supplemented with cadmium (10 to 4000 µg/ml) and nickel (10 to 3000 µg/ml). The colonies having different morphologies that were formed in the EMB agar were selected, and their metal tolerance concentration (MTC) was determined. Based on their MTC values, two isolates were identified by using morphological, biochemical, and molecular (16S rRNA gene sequencing) methods. Besides, their growth kinetics, co-metal tolerance, and antibiotic resistance were also determined. The identified isolates 2 and 8 were tolerant to cadmium (3000 µg/ml) and nickle (2000 µg/ml), respectively. The isolates were found to be closely related to Pantoea agglomerans JCM 1236 (sample 2) and Enterobacter asburiae JCM 6051 (sample 8). They were not only co-tolerant to cadmium (3000 µg/ml) and nickle (2000 µg/ml) but also showed resistance to various antibiotics. Scanning electron microscopy (SEM) showed changes in surface morphology of nickle and cadmium-treated samples 2 and 8, and the energy dispersive X-ray spectroscopy (EDX) studies revealed the presence of cadmium and nickel in both the isolates after metal treatment. The results conclude that the identified heavy metal tolerant bacteria could be useful for the bioremediation of contaminated wastewater and industrial effluents. Key words: Heavy metal removal, gram-negative bacteria, 16S rRNA gene sequencing, maximum tolerance concentration, bioremediation.