Isolation and identification of a high-efficiency hexavalent uranium adsorption strain and preliminary study of the influencing factors and adsorption mechanism

doi:10.21203/rs.3.rs-3453909/v1

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Isolation and identification of a high-efficiency hexavalent uranium adsorption strain and preliminary study of the influencing factors and adsorption mechanism

https://doi.org/10.21203/rs.3.rs-3453909/v1

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published 16 Mar, 2024

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In this study, a bacterial strain WK-3 with high adsorption efficiency of hexavalent uranium U(VI) was isolated from the rhizosphere soil of a uranium (U) tailings in southern China, with an adsorption rate of 92.3%, and was identified as Chryseobacterium bernardetii. The influence of different environmental conditions on the adsorption rate of Chryseobacterium bernardetii was investigated, and the adsorption mechanism was preliminarily discussed by scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS). The results showed that: 1) The optimal adsorption conditions for Chryseobacterium bernardetii were pH = 5, temperature 30 ℃, NaCl concentration 1%, and inoculation volume 10%; 2) Under the condition of initial concentration of 50 mg/L U(VI), the maximum adsorption rate of Chryseobacterium Bernardetii was reached and maintained in equilibrium within 24 h; Under the condition of initial concentration of 50 ~ 150 mg/L U(VI), the time for Chryseobacterium bernardii to reached its maximum adsorption rate and maintained equilibrium was extended to 48 h; 3) Under the condition of initial concentration of ≥ 200 mg/L U(VI), Chryseobacterium bernardii did not grow and had no adsorption capacity; 4) Under the condition of coexistence of 2 mmol/l Zn(II) and 50 mg/L U(VI), the adsorption of Chryseobacterium bernardii to U(VI) was significantly inhibited. ESM-EDS results show that phosphorus in cells participates in the interaction of uranyl ions, which may indicate that phosphate is produced during cell metabolism and is further combined to form U(VI)-phosphate minerals. Meanwhile, the possibility of complexation between cell surface groups and U(VI) cannot be ruled out.

Rhizosphere

Isolation

Identification

Adsorption

Hexavalent uranium

Chryseobacterium bernardetii

Uranium (U), atomic number 92, relative atomic mass of 238.03, is an actinide metal and is the heaviest metallic substance found in nature (Xu et al. 2014). There are three natural isotopes of U, ²³⁴U, ²³⁵U and ²³⁸U, respectively, all of which are radioactive, and their half-lives are extremely long, reaching 2.35×10⁵, 7.09×10⁸ and 4.51×10⁹ years, respectively (Todorov et al. 2006). As an important nuclear fuel, U is an indispensable resource for the development of the nuclear industry. However, U is chemically toxic and radioactive at the same time, and with the development of human activities such as mining and milling, U gradually accumulates in groundwater, soil and other environments, causing the occurrence of U pollution, which seriously threatens the ecological environment and human health (Fathi et al. 2014; Pattison et al. 2013), which has been reported in many countries around the world (Carvalho et al. 2009; Choiniere et al. 2009). For example, the U content of a U-contaminated farmland is up to 390 mg/kg (Yao et al. 2016), which indicates that the soil has been seriously polluted by U. It can be seen that the current situation of soil U-contaminated is severe and needs to be remediated, and what kind of technology to take to remediate is the key to the problem. Studies have reported that microbes (such as bacteria, fungi, algae) can adsorb metal elements (Ma et al. 2015), because of their rapid growth, non-chemical toxicity and will not cause secondary pollution to the environment, it can be developed into one of the environmentally friendly and efficient U pollution remediation materials (Chen et al. 2021; Merroum et al. 2008; Stylo et al. 2013). Therefore, the screening and isolation of U resistant microbes is a prerequisite for remediation. In recent years, many microbes that can remove U have been reported, such as Pseudomonas MGF-48 can adsorb 86% of U within 5 min (Malekazadeh et al. 2002), Rahnella sp. has a mineralization rate of 95% to U (Beazley et al. 2007), and Desulfovibrio vulgaris has a reduction rate of 80% to U(VI) (Zhou et al. 2014), etc. Rhizosphere is a narrow and sensitive soil micro-regions where plant roots interact with plant-microbe-soil, its physical, chemical, and biological characteristics are significantly different from the bulk soil (Hinsinger et al. 2009). On the one hand, the rhizosphere effect can promote soil nutrient cycling, enhance the diversity of soil animals and microbes, and the degradation of pollutants (Zverev et al. 2016; Liu et al. 2022; Bonkowski et al. 2000). On the other hand, selective enrichment and genetic variation may also occur in microbes exposed to U-contaminated environments for a long time (Guo et al. 2011). In view of this, it may be a feasible way to isolate and screen microbes that are resistant to U and can adsorb U in the rhizosphere soil of a U tailings.

In this study, we carried out the following work: (1) Screened and isolated 12 U resistant bacterial strains including strain WK-3 from the rhizosphere soil of a U tailings in southern China, and U(VI) adsorption experiments were carried out; (2) Strain WK-3, which is resistant to U(VI) and highly efficient adsorption of U(VI), was identified; (3) Experiments were carried out on the influence of different environmental conditions (such as pH, temperature, NaCl concentration, etc.) on the adsorption of U(VI) by strain WK-3; (4) The U(VI) adsorption mechanism of strain WK-3 was analyzed by a scanning electron microscope equipped with energy dispersive X-ray spectroscopy (SEM-EDS).

1.1 Materials

1.1.1 Sample collection

A total of 9 species of luxuriant plants (Imperata cylindrica, Erigeron canadensis, Erigeron annuus, Rhus chinensis, Setaria viridis, Macleaya cordata, Eleusine indica, Solanum nigrum, Equisetum ramosissimum) were selected from a U tailings in southern China. The plants were lifted completely with roots with a spade, shaking off lager chunks of soil, and the soil attached to the roots of the plants was carefully brushed off, which was regarded as rhizosphere soil samples to be collected. The samples were divided into two parts (one for experimentation and one for retention), placed in a sterile bag and stored on ice pack, and immediately transported to the laboratory for strain isolation and purification.

1.1.2 Culture medium

Luria-Bertani (LB) medium (g/L): Casein Tryptone, 10 g; Yeast Extract Powder, 5 g; NaCl, 10 g; and then added in 1000 mL of distilled water, pH 7.0 ± 0.2, sterilized at 121°C for 20 min (Baev et al. 2006). LB agar medium is added 1.5 ~ 2% agar in the same formula as the above LB medium. R2A medium (g/L): Yeast Extract Powder, 0.5 g; Peptone, 0.5 g; casein peptone, 0.5 g; C₆H₁₂O₆, 0.5 g; (C₆H₁₀O₅)n, 0.5 g; KH₂PO₄, 0.3 g; MgSO₄, 0.024 g; C₃H₃NaO₃, 0.3 g and then added in 1000 mL of distilled water, pH 7.2 ± 0.2, sterilized at 115°C for 30 min (Massa et al. 1998).

1.1.3 U(VI) stock solution

An aqueous stock solution of U(VI) (1 g/L) was prepared by dissolving 2.1092 g uranyl nitrate [UO₂(NO₃)₂·6H₂O], 10 mL of HNO₃ was used to help dissolve, and the solution volume was made up to 1000 mL (Ma et al. 2015). Other concentrations of U(VI) solution were obtained by dilution. The pH of U(VI) stock solution was adjusted with 0.1 mol/L HNO₃ or Ca₂CO₃. In addition, unless otherwise specified, the remaining chemical reagents are of commercially available analytical grade.

1.1.4 Main test instruments

Constant temperature shaking incubator (ZHWY-2112B, Langbo Instrument Manufacturing, China); pH meter (PHS-3C, Precision Scientific Instrument, China); Desktop high-speed centrifuge (TG16-WS, Xiangyi Centrifuge Instrument, China); Ultraviolet spectrophotometer (UV759, Precision Scientific Instrument, China); Optical microscope (VHX-7000N, KEYENCE, China); Polymerase chain reaction (PCR) amplifier (T100, BIO-RAD, USA); SEM (SU8100, Hitachi, Japen); SEM fitted with Oxford EDS detector and Gatan CCD camera (X-MaxN, Oxford, United Kingdom).

1.2 Methods

1.2.1 Isolation and purification of U resistant strains

5 g of rhizosphere soil samples were taken from each of 9 plants and added into a shake flask filled with 45 mL sterile water, and oscillated at 30 ℃ and 180 r/min for 30 min. The sample was diluted by a 10-fold series gradient dilution method, and then 1 mL of 10^− 6 dilution was added to R2A medium (50 mL) contained 20 mg/L U(VI), and incubated at 30°C and 180 r/min in a constant temperature shaking incubator for 3 ~ 5 days to obtain the first generation enrichment solution. The same method was operated until the fourth generation enrichment solution, in which the second, third and fourth generation enrichment solutions contained 50, 100 and 150 mg/L U(VI), respectively. Taken 1 mL of the fourth generation enrichment solution was evenly spread on LB agar medium without U, sealed with parafilm and incubated upside down in a constant temperature incubator at 30°C for 1 ~ 2 d. Finally, single colonies with incomplete morphology, size and color were selected, purified by plate scribing more than 3 times, and the purified U resistant strains was stored at 4°C on the inclined slope.

1.2.2 Adsorption capacity of U resistant strains to U(VI)

The method of drawing uranium standard curve according to reference (Xu et al. 2013), regression equation: y = 0.1977 x + 0.0013, R² = 0.9995. The 12 strains obtained were prepared into bacterial suspensions with OD₆₀₀ ≈ 0.6, and inoculated into LB medium with 50 mg/L U(VI) at an inoculation volume of 1%, and cultured with shaking at 30°C and 180 r/min for 10 h, assumed 3 groups of repetitions. An equal volume of sterile water was used as a control. After the culture is completed, 1 mL of supernatant was taken for standby (centrifugation at 12000 r/min for 3 min), and the control was treated in the same way. The U concentration of each supernatant was determined by azosine III method (Liu et al. 2010). Adsorption rate (R)=(C₀-C_t)/C₀×100%. Among them, C₀ is the U concentration in the control supernatant (mg/L), and C_t is the U concentration in the supernatant after adsorption (mg/L).

1.2.3 16S rDNA species identification of strain WK-3 that efficiently adsorbs U(VI)

The colony morphological characteristics of strain WK-3 on LB agar medium were observed, and the bacterial morphological characteristics were observed under optical microscope after Gram staining for preliminary identification. Bacterial genome extraction kit was used to extract the DNA of the strain, and PCR was performed using universal primers 27F (5' -AGTTTGATCMTGGCTCAG- 3') and 1492R (5' -GGTTACCTTGTTACGACTT- 3'). The size of the target DNA fragment was about 1500 bp. Amplification system (40 µL): 2×T8 high-fidelity master mix, 20 µL; 27F, 2 µL; 1492R, 2 µL; template DNA, 1 µL; ddH₂O, 15 µL. Amplification procedure: 98°C for 2 min; 98°C for 10 s, 57°C for 10 s, 72°C for 45 s, total 35 cycles; 72°C 5 min; and then held at 4°C. After the amplification product electrophoresis is qualified, the sequencing is completed by Shanghai Tsingke Biotech Co., Ltd. The spliced sequence of the sequenced 16S rDNA was submitted to NCBI GenBank, the accession number was obtained, the 16S rDNA sequence similar strains were downloaded, and the phylogenetic tree was constructed using the Neighbor-Joining method with MEGA 7.0 and Figtree 1.4.3, with a bootstrap value of 1000.

1.2.4 Effects of different culture conditions on adsorption rate of strain WK-3

pH: The pH of LB medium containing 50 mg/L U(VI) was adjusted to 5.0, 5.5, 6.0, 6.5 and 7.0, the bacteria were removed by 0.22 µm filtration membrane (the same below), and the bacterial suspension (OD₆₀₀ ≈ 0.6, the same below) was inoculated at 1%, and cultured at 30°C, 180 r/min for 24 h, respectively.

Temperature: The pH of LB medium containing 50 mg/L U(VI) was adjusted to 5, the bacteria were removed by filtration membrane, and the bacterial suspension was inoculated at 1%, and cultured at 16, 25, 30, 37, and 42°C, 180 r/min for 24 h, respectively.

Inoculation volume: The pH of LB medium containing 50 mg/L U(VI) was adjusted to 5, the bacteria were removed by filtration membrane, and the bacterial suspension was inoculated at 1, 5, 10, 15, and 20%, and cultured at 30°C, 180 r/min for 24 h, respectively.

NaCl concentration: The pH of LB medium containing 50 mg/L U(VI) was adjusted to 5, 1, 2, 3, 4, and 5% NaCl were added respectively. The bacteria were removed by filtration membrane, and the bacterial suspension was inoculated at 1%, and cultured at 30°C, 180 r/min for 24 h.

U initial concentration: 1 g/L of U stock solution was diluted to the required concentration, and it was added to LB medium, so that LB medium contained U(VI) 50, 75, 100, 125, 150, and 200 mg/L, respectively. The pH was adjusted to 5, and the bacterial suspension was inoculated at 1%, and cultured at 30°C, 180 r/min for 48 h.

Coexisting ions: LB medium was mixed with K(I), Mg(II), Na(I), Mn(II), NH(IV), Ca(II) and Zn(II) solutions respectively, and the pH was adjusted to 5. Then, the solution contained 50 mg/L U(VI), the concentration of coexisting ions was 2 mmol/L, and the bacterial suspension was inoculated at 1%, and cultured at 30°C, 180 r/min for 24 h.

1.2.5 SEM-EDS analysis

SEM-EDS techniques were used to analyze bacterial cells before and after exposure to U bacterial cells were recovered by centrifugation (5000 r/min, 20 min), washed twice in 0.2 mol/L phosphate buffered saline (PBS) (pH 7). The bacterial samples were fixed overnight (at 4°C) in 2.5% glutaraldehyde and then washed three times with the same buffer. Then, cell pellets were dehydrated with a graded series of ethanol (30, 50, 70, 85, and 100%) for 20 min. Finally, the pellets were lyophilized in a freeze dryer, coated with platinum (Pt) and analyzed by using SEM (Sharma et al. 2018). EDS analyses were performed at 3 kV with the SEM fitted with Oxford EDS detector and Gatan CCD camera.

2.1 Isolation and purification of U resistant strains

12 bacterial strains were isolated and purified by Gram staining and microscopic examination. The purified strains were re-inserted into LB medium (150 mg/L U(VI)) at 1% inoculation volume, and the biomass (OD₆₀₀) was measured. Three groups of repeats were set up, and the results were averaged. The test results showed that the 12 strains grew well and were able to tolerate at least 150 mg/L U (VI) (Table 1).

Table 1

Biomass (DO₆₀₀) and U tolerance of 12 bacterial strains
Strain NO.	Sample Source	Tolerable U Concentration	Biomass (OD₆₀₀)	Biomass (OD₆₀₀) Rank
WJ	Equisetum ramosissimum	150 mg/L U(VI)	2.384	1
WK-4	Solanum nigrum		2.305	2
WK-3	Solanum nigrum		2.232	3
WYY-1	Erigeron annuus		2.199	4
WM	Imperata cylindrica		2.190	5
WL-1	Macleaya cordata		2.147	6
WL	Macleaya cordata		2.100	7
WYY-2	Erigeron annuus		1.900	8
WM-1	Imperata cylindrica		1.888	9
WK-2	Solanum nigrum		1.850	10
WP	Erigeron canadensis		1.844	11
WK-1	Solanum nigrum		1.840	12

2.2 Adsorption capacity of U resistant strains to U(VI)

The adsorption rate of U(VI) by 12 U resistant strains is shown in Fig. 1. It can be seen from Fig. 1 that all 12 strains had adsorption effect on U(VI), but the adsorption capacity was significantly different, and the adsorption capacity of WK-3 and WYY-1 ranked first and second, reaching 92.3% and 80.24%, respectively. Combined with Table 1, it can be seen that strain biomass (OD₆₀₀) does not show a positive correlation with adsorption capacity, which is similar to the results of Liu et al. (1996). WK-3, the strain with the strongest adsorption capacity, was subsequently selected as the study object.

2.3 Morphology and species identification of strain WK-3

2.3.1 Morphology of strain WK-3

The morphology of strain WK-3 on LB agar plate, Gram staining, and cell morphology observed by SEM are shown in Fig. 2. The round edges of the colonies are regular and neat, yellow, the surface is smooth and moist, shiny, easy to pick, opaque, and soft in texture (Fig. 2a); Gram staining was negative (Fig. 2b), and rod-shaped (Fig. 2c).

2.3.2 16S rDNA sequence analysis of strain WK-3

Agarose gel electrophoresis results of strain WK-3 showed that its DNA fragment size was about 1500 bp (Fig. 3). The obtained splicing sequences were BLAST aligned on NCBI (https://www.ncbi.nlm.nih.gov/) and strain WK-3 was found to be more than 99% similar to multiple Chryseobacterium bernardetii 16S rDNA sequences. The accession number obtained after submission to GenBank is: OR527924. Download the reported 16S rDNA similar sequences in GenBank to construct a phylogenetic tree (Fig. 4). The results showed that strain WK-3 was polymerized with Chryseobacterium bernardetii strain G229. Therefore, combined with strain morphology and developmental evolutionary analysis, strain WK-3 was identified as Chryseobacterium bernardetii.

2.4 Effects of different culture conditions on adsorption of U(VI) by strain WK-3

2.4.1 pH

pH has a significant effect on the adsorption of heavy metals (Liu et al. 2022), because pH can change the form of uranium present in solution, the charge on the surface of bacteria, and the binding point (Wang et al. 2022). However, the pH is too low, which can lead to problems such as equipment corrosion in practical applications, and the pH is too high, and UO₂²⁺ is easily hydrolyzed and precipitated resulting in data distortion (Wu et al. 2022). The soil pH range of the sampling site was about 5.0 ~ 6.0 (Huang et al. 2013), in order to simulate the real pH environment, the pH range of this experiment was set to 5.0 ~ 7.0.

The effect of pH on the adsorption of U(VI) by strain WK-3 is shown in Fig. 5. It can be seen from Fig. 5 that when the pH is 5, WK-3 has the highest adsorption rate of U, reaching 92.34%. The reasons may be: on the one hand, when the pH is 5, U(VI) mainly exists in the form of UO₂CO₃ in the aqueous solution (Yan et al. 2010), because the surface of the UO₂CO₃ molecule has no charge, which will make the charge repulsion between U(VI) and microbes smaller, making it easier to adsorb (Zhang et al. 2012); on the other hand, when the pH is 5, the activity of various active groups of microbes is stronger (Mar et al. 2012). As the pH increases, the adsorption rate shows a downward trend, which may be due to: when the pH greater than 5, uranyl ions exist in the solution in other forms, and the negative charge on the surface of the bacteria produces electrostatic repulsion, which is not conducive to adsorption, especially when the pH greater than 7, U will hydrolyze and precipitate, forming complex hydrolysis products, such as UO₂(CO₃)₂²⁻, UO₂(CO₃)₃⁴⁻ (Liu et al. 2012), causing the adsorption rate to further decrease (Chen et al. 2015). Most scholars believe that pH 5 is a suitable adsorption environment (Zhang et al. 2012; Liu et al. 2012; Hu et al. 2014), and this study is consistent with the view of most scholars.

2.4.2 Temperature

The effect of temperature on WK-3 adsorption U(VI) is shown in Fig. 6. As can be seen from Fig. 6, with the increase of temperature, the adsorption of WK-3 on U(VI) increases first and then decreases, reaching a maximum adsorption rate of 93.34% at 30°C. The reason may be that the biological enzyme activity and kinetic energy of the solution medium of strain WK-3 were enhanced under suitable temperature conditions (Wang et al. 2010).

2.4.3 Inoculation volume

Larger inoculation volumes can shorten the time it takes for bacteria to multiply to a stable growth phase and reduce the chance of miscellaneous bacterial growth (Li et al. 2015). The effect of inoculation volume on WK-3 adsorption U(VI) is shown in Fig. 7. It can be seen from Fig. 7 that with the increase of inoculation volume, the adsorption of WK-3 to U (VI) first increased and then decreased, and the inoculation volume was 10%, reaching a maximum adsorption rate of 94.92%. The reason may be the larger inoculation volume, the more bacterial metabolites, and the stronger the inhibitory and poisoning effect of metabolites on bacteria (Shi et al. 2002).

2.4.4 NaCl concentration

The effect of NaCl concentration on WK-3 adsorption U(VI) is shown in Fig. 8. It can be seen from Fig. 8 that when the NaCl concentration was 1%, the maximum adsorption rate is 92.16%; When the NaCl concentration was greater than1%, the adsorption rate decreased significantly, indicating that the suitable NaCl concentration of strain WK-3 was 1%. The reason may be that the concentration of NaCl is too high and the osmotic pressure of the solution will increase, resulting in microbial dehydration and cell protoplasm separation, which will affect the growth and tolerance of the bacteria (Guo et al. 2010).

2.4.5 U initial concentration

High uranium concentrations have a significant inhibitory effect on the growth of microbes (Li et al. 2015). It is important to find out the range of U concentrations to which microbes are adapted. The effect of U initial concentration on WK-3 adsorption U(VI) is shown in Fig. 9. It can be seen from Fig. 9 that when C₀ = 50 mg/L, the adsorption rate of strain WK-3 within 24 h reached more than 90% and remained equilibrium. As C₀ rises to 75 ~ 150 mg/L, the toxic effect of U on strain WK-3 increases, and the adsorption rate reaches more than 90% and the time to maintain equilibrium is correspondingly prolonged (after 40 h, the adsorption rate reaches about 90% and gradually maintains equilibrium). This shows that the initial concentration of U is directly proportional to the toxic effect and inversely proportional to the adsorption rate; When C₀ = 200 mg/L, strain WK-3 stopped growing and had no adsorption capacity.

2.4.6 Coexisting ions

U-containing environments (U wastewater, U tailings, etc.) created by human activities usually contain other coexisting ions that often affect the capacity of microbes to adsorb U (Liu et al. 2004). The effect of coexisting ions on the adsorption of U(VI) by strain WK-3 is shown in Fig. 10. It can be seen from Fig. 10 that when Zn(II) and U(VI) coexist, the adsorption of strain WK-3 can be significantly inhibited (the adsorption rate is only 41.77%), and other coexisting ions have no obvious effect on the adsorption rate of strain WK-3.

2.5 SEM-EDS analysis

Cell morphology changes of WK-3 treated with or without U(VI) were revealed by a set of SEM images (Fig. 11), and the cell morphology showed obvious differences. Initially, the cell morphology was spindle-shaped, uniformly full, and intact shape (Fig. 11a, b); After interacting with U(VI), the cell morphology showed distortion, adhesion, and contraction to a certain extent, and some cells appeared cavitated and damaged (Fig. 11c, d).

The EDS results before and after the reaction of strain WK-3 with U(VI) were shown in Fig. 12. After the interacting with U(VI), the absorption peak of U element appeared on the cell surface, the binding energy was 2.0 ~ 4.0 KeV, and the content was 9.98%. At the same time, the content of element phosphorus (P) increased, indicating that P in cells participated in the interaction of uranyl ions, which may indicate that P was produced in the process of cell metabolism, and phosphate further combined with U(VI) to form phosphate minerals. However, the surface of microorganisms is rich in carboxyls, hydroxyl groups and amino groups, which can bind nuclides by complexation (Li et al. 2014), so the possibility of complexation with U(VI) by the cell surface group of strain WK-3 cannot be ruled out.

In this study, a total of 12 U resistant bacterial strains were isolated from the rhizosphere soil of a U tailings in southern China. The results showed that strain WK-3 had the strongest adsorption capacity for U(VI), with an adsorption rate of 92.3%. Combining morphology and 16S rDNA sequence analysis, strain WK-3 was identified as Chryseobacterium bernardetii. Referring to Holmes et al (2013) research, Chryseobacterium bernardetii has been isolated and identified from other countries and regions such as the United Kingdom, but this is the first time that Chryseobacterium bernardetii has been isolated and identified from this U tailings.

Adsorption of U(VI) by microbes is affected by different environmental conditions, such as pH, temperature, inoculation volume, NaCl concentration, U initial concentration and coexisting ions and so on. The experimental results showed that:

1) The optimal conditions for adsorption of U(VI) by Chryseobacterium bernardetii were: pH = 5, T = 30°C, NaCl concentration 1%, inoculation volume 10%;

2) Under the condition of 50 mg/L U(VI), Chryseobacterium bernardetii can reached the maximum adsorption rate and maintained equilibrium within 24 h; Under the condition of 50 ~ 150 mg/L U(VI), the adsorption rate by Chryseobacterium bernardetii can reached more than 90% and maintained equilibrium within 48 h, but the larger the U concentration, the longer the adsorption rate reached the maximum and maintained equilibrium; Under the condition of 200 mg/L U(VI), Chryseobacterium bernardetii stopped growing and had no adsorption capacity;

3) When 2 mmol/L Zn(II) and 50 mg/L U(VI) coexist, the adsorption capacity of Chryseobacterium bernardetii for U(VI) is significantly inhibited;

4) P in cells is involved in the interaction of uranyl ions, which may indicate the production of phosphate during cellular metabolism, which further combines with U(VI) to form U(VI)-phosphate minerals. However, the possibility of complexation between cell surface groups and U(VI) cannot be ruled out.

To our best knowledges, Chryseobacterium is a conditionally pathogenic bacterium (Bernardet et al. 2005; Holmes et al. 2015), and the academic research on this bacterium focuses on pathogenicity (He et al. 2019), infection (Chen et al. 2013), drug resistance (Cai et al. 2022), etc., and there are few studies involving heavy metal biosorption, especially U has hardly been reported. In view of this, Chryseobacterium bernardetii is expected to become a new strain that adsorbs U(VI). However, this study has the following shortcomings: 1) The environmental factors discussed are not comprehensive enough, such as pH range, types and concentrations of coexisting ions; 2) The adsorption mechanism was preliminarily analyzed only by SEM-EDS, without further analysis by transmission electron microscopy, proton induced X-ray emission, FT-IR spectroscopy and other analytical methods.Therefore, the adsorption mechanism of U(VI) by strain Chryseobacterium bernardetii and other factors affecting adsorption still need to be further study.

Author contributions Faming Wu, Xiang Li and Peng Wei participated in the material preparation, data collection, and analysis. The manuscript was written and revised by Faming Wu and Zhirong Liu. Zhirong Liu and Faming Wu conceived the idea, designed the experiment, and were involved in the data analysis.

Funding We gratefully acknowledge the generous support provided by the “National Natural Science Foundation of China (22266004, 11875105)”, and “General Project of Jiangxi Province Key Research and Development Program (20203BBFL63070)”.

Data availability The data used and analyzed during the current study are available from the corresponding author upon reasonable request.

Competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Ethics approval Not applicable.

Consent to participate Not applicable.

Consent for publication All the authors agreed to publish the data in this journal.

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published 16 Mar, 2024

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Isolation and identification of a high-efficiency hexavalent uranium adsorption strain and preliminary study of the influencing factors and adsorption mechanism

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Abstract

Figures

Introduction

Materials and methods

1.1 Materials

1.1.1 Sample collection

1.1.2 Culture medium

1.1.3 U(VI) stock solution

1.1.4 Main test instruments

1.2 Methods

1.2.1 Isolation and purification of U resistant strains

1.2.2 Adsorption capacity of U resistant strains to U(VI)

1.2.3 16S rDNA species identification of strain WK-3 that efficiently adsorbs U(VI)

1.2.4 Effects of different culture conditions on adsorption rate of strain WK-3

1.2.5 SEM-EDS analysis

Results and discussions

2.1 Isolation and purification of U resistant strains

2.2 Adsorption capacity of U resistant strains to U(VI)

2.3 Morphology and species identification of strain WK-3

2.3.1 Morphology of strain WK-3

2.3.2 16S rDNA sequence analysis of strain WK-3

2.4 Effects of different culture conditions on adsorption of U(VI) by strain WK-3

2.4.1 pH

2.4.2 Temperature

2.4.3 Inoculation volume

2.4.4 NaCl concentration

2.4.5 U initial concentration

2.4.6 Coexisting ions

2.5 SEM-EDS analysis

Conclusions

Declarations

References

Status:

Journal Publication

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