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Article

Efficient Bioreduction of Cr(VI) by a Halotolerant Acinetobacter sp. ZQ-1 in High-Salt Environments: Performance and Metabolomic Mechanism

by
Lei Yu
1,
Qi Zhou
2 and
Jing Liang
2,*
1
The Open University of Jilin, Changchun 130022, China
2
College of Life Science, Jilin Agricultural University, Changchun 130118, China
*
Author to whom correspondence should be addressed.
Processes 2025, 13(11), 3423; https://doi.org/10.3390/pr13113423 (registering DOI)
Submission received: 25 September 2025 / Revised: 22 October 2025 / Accepted: 22 October 2025 / Published: 24 October 2025
(This article belongs to the Section Chemical Processes and Systems)
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Abstract

Bioreduction is an effective method to reduce Cr(VI) for bioremediation. In this study, a hexavalent chromium-reducing bacterium with salt tolerant abilities, Acinetobacter ZQ-1, was isolated, which could efficiently reduce Cr(VI) under a wide range of pH (6.0–9.0), temperatures (28–42 °C) and coexisting heavy metals (Mn2+, Pb2+ and Fe3+). It is worth mentioning that the strain ZQ-1 could reduce Cr(VI) containing 15% (w/v) NaCl, showing strong salt tolerance. Under optimal culture conditions, strain ZQ-1 was able to completely reduce 50 mg/L of Cr(VI) in 24 h. The metabolic data of ZQ-1 showed that salt stress significantly altered the composition of metabolites, in which the accumulation of compatible solutes such as Arginine, Leucine, Lysine and Proline contributed to the alleviation of high salt stress for strain ZQ-1. Meanwhile, the increased content of alginate and betaine also helped to maintain the normal function of strain ZQ-1 in a high-salt environment. This is of great significance for the development, utilization and mechanism of action of salt-tolerant hexavalent chromium-reducing bacteria in the future.

1. Introduction

Large amounts of heavy metals such as Cr(VI) have been released into the environment as a result of improper treatment [1]. Cr(VI) can migrate into the environment and accumulate in the food chain, with carcinogenic, mutagenic and teratogenic impacts, and a resulting risk to the health of human beings, animals and plants [2]. Therefore, effective methods to reduce Cr(VI) have been important issues for research. Compared with physical and chemical methods, bioremediation presents the advantages of low cost and high removal efficiency. Many microorganisms that are capable of reducing Cr(VI) have been isolated from polluted environments, such as Exiguobacterium sp., Bacillus sp., Rhodococcus sp., Aeribacillus sp., Cellulosimicrobium sp. and Arthrobacter sp. [3,4,5,6,7,8]. These microorganisms can utilize their ecological advantages to efficiently reduce Cr(VI), yielding Cr(III) with a weaker toxicity [9,10].
However, Cr(VI)-containing wastewater is usually from chromite mining, tannery, and metal manufacturing, which typically contain high concentrations of salts [11]. The existence of salts leads to the inefficient microbial reduction of Cr(VI) [12]. In a high-salt environment, microorganisms are unable to maintain the balance of osmotic pressure inside and outside their cells, resulting in their dehydration and death [13]. In addition, salt ions may bind to enzymes and affect their normal performance. Therefore, the isolation and application of microorganisms with salt tolerance, which are capable of reducing Cr(VI), are in great demand. Microbacterium sp. M5 is able to reduce 400 mg/L Cr(VI) with the efficiency of 75% and 50%, in the presence of 2% (w/v) and 4.0% (w/v) NaCl, respectively [14]. In addition, it has been reported that Nesterenkonia sp. MF2 can completely reduce 104 mg/L Cr(VI) in the presence of 5.85% (w/v) NaCl [15]. Thus, salt-tolerant bacteria are expected to play a role in the bioremediation of contamination when high-salt and Cr(VI) concentrations coexist. Due to the adaptive evolution in high-salt environments, salt-tolerant bacteria have established special genetic mechanisms, fabricated proper physiological structures and metabolic types, as well as having salt-tolerant genes. In some cases, they have also produced unique metabolites, such as compatible substances, including amino acids, alginate, betaine and sugars [16]; these can be synthesized by the microorganisms themselves or accumulated inside the cells to resist externally high osmotic pressures, maintaining intra- and extracellular homeostasis, and thus adapt to high-salt environments. Currently, there is scant research about the use of salt-tolerant bacteria to reduce Cr (VI). The use of metabolites to explain the salt tolerance mechanisms during the process of bacteria reducing hexavalent chromium has been rarely reported [17,18,19].
In this study, the Cr(VI) reduction and salt tolerance of Acinetobacter ZQ-1 were investigated from multiple perspectives: (1) isolation and identification of the strain; (2) the impact of environmental factors on the biological reduction of hexavalent chromium; and (3) research on the mechanism of the salt tolerance of the strain.

2. Materials and Methods

2.1. Materials

K2Cr2O7, NaCl, diphenyl carbamide, MnCl2·4H2O, HgCl2, ZnCl2, Pb(NO3)2, CdCl2·2.5H2O, NaOH and HCl were obtained from National Pharmaceutical Group Corporation, Beijing, China. Tryptone and yeast extract were purchased from Hangzhou Best Bioscience Bio-technology Co., Ltd., Hangzhou, China. Agar was obtained from Beijing AOBOX Bio-technology Co., Ltd., Beijing, China.

2.2. Isolation and Identification of Strain

A sample was collected from soil contaminated with heavy metals from Jiaohe City, Jilin Province, China. The soil (1 g) was put into 100 mL of Luria-Bertani (LB) medium (tryptone 10 g/L, yeast extract 5 g/L, NaCl 10 g/L) containing 100 mg/L Cr(VI). Then, the soil suspension was incubated in a constant-temperature shaking incubator at 37 °C and 160 rpm) for 48 h. The bacterial solution was diluted to 10−2–10−10 and coated on LB solid medium with 200 mg/L Cr(VI), which was then incubated at 37 °C. Individual colonies were selected and purified on solid plates 3–5 times. The purified strains were inoculated into LB liquid medium containing 50 mg/L Cr(VI) and incubated at 37 °C and 160 rpm. The content of Cr(VI) was determined by the dibenzoyl dihydrazide method [20]. The biomass was determined using a turbidimetric method, and the optical density values (OD600) of the cell suspensions were determined using a UV-vis spectrophotometer.
The morphology of the strains was observed under an optical microscope. Bacterial smears were prepared and stained using the Gram staining method for initial morphological characterization. Physiological and biochemical characterization of the strains was carried out according to Berger’s Handbook of Bacteria. Genomic DNA of the Cr(VI)-reducing strain was extracted using a commercial DNA extraction kit (Hepeng Biotechnology Co., Ltd., Shanghai, China). The 16S rRNA gene was amplified using the universal primers 27F (5′-AGAGTTTGATCMTGGCTCAG-3′) and 1492R (5′-GGTTACCTTGTTACGACTT-3′), and the PCR product was sequenced. A phylogenetic analysis was conducted using the neighbor-joining method in MEGA 11. Strains with ≥97% sequence similarity in the 16S rRNA gene were considered to be closely related and potentially of the same species.

2.3. Influencing Factors of Bioreduction of Cr(VI)

The inoculum volume (1, 5, and 10%), temperature (15, 28, 32, 37 and 42 °C), pH (5, 6, 7, 8, and 9), and initial Cr (VI) concentration (50, 100, 150, 200, and 250) mg/L), co-existing heavy metals (Fe3+, Hg2+, Pb2+, Cd2+, Zn2+ and Mn2+, 50 mg/L) and NaCl concentrations (1, 3, 5, 7, 9, 11 and 15% (w/v)), according to previously reported studies [21,22], were selected to investigate their effects on Cr(VI) reduction. All experiments were repeated three times, unless specifically mentioned.

2.4. Detection of Metabolites

Strains were inoculated into LB medium with NaCl of 1%, 5% and 15% (w/v) and Cr(VI) content of 50 mg/L. After reaching the logarithmic growth stage, the strains were broken by an ultrasonic crusher for 10 min and then centrifuged at 8000 rpm for 10 min to collect the supernatant. An appropriate amount of sample was added to pre-cooled methanol/acetonitrile/water solution (2:2:1, v/v), vortexed and mixed, sonicated for 30 min at −40 °C, left to stand for 10 min at −20 °C, and then centrifuged at 14,000× g for 20 min at 4 °C. After that, the supernatant was dried under vacuum, and 100 μL of acetonitrile aqueous solution (acetonitrile: water = 1:1, v/v) was added, then vortexed and centrifuged at 14,000× g for 15 min at 4 °C. The supernatant was dried in a vacuum and then analyzed by mass spectrometry (MS). The composition and relative content of metabolites were analyzed by gas chromatography–mass spectrometry.

2.5. Measurements

A L5S UV-vis spectrophotometer from Shanghai Yidian Analytical Instrument Co., Ltd., Shanghai, China was used to measure the content of Cr(VI) and the biomass of the strains. LC-MS/MS analysis using an AB Triple TOF 6600 mass spectrometer (AB SCIEX, Tokyo, Japan) and an Agilent 1290 Infinity LC ultra-high-performance liquid chromatography system (Waldbronn, Germany). The experimental results are presented as mean ± standard deviation (Mean ± SD).

3. Results and Discussion

3.1. Isolation and Identification of Strain ZQ-1

The microorganisms used unique detoxification mechanisms for Cr(VI), such as changing the Cr(VI) to Cr(III) [23]. However, the reduction ability of Cr(VI) by bacteria isolated from polluted environments is different. Therefore, the isolation of strains for the efficient bioremediation of Cr(VI) is of great significance. After a series of isolation and purification processes, a strain with a high reduction ability of Cr(VI) was obtained. The colonies of the strain were milky white, opaque and smooth, and identified as a Gram-negative bacteria (Figure S1). The physiological and biochemical results of the strain are shown in Table S1, which is consistent with the physiological and biochemical characteristics of Acinetobacter. After that, a phylogenetic analysis was used for comparison with 16S rRNA gene sequences. As shown in Figure 1, the isolated strain was identified as Acinetobacter, named as ZQ-1. The control without the addition of strain ZQ-1 showed that a very small amount of Cr(VI) was reduced (Figure S2) due to the existence of -NH2 and -OH groups in the LB medium. As shown in Figure 1b, the increase of Cr(VI) concentration led to a low reduction efficiency.

3.2. Bioreduction of Cr(VI)

The inoculation amount is an essential factor relating to the microbial remediation of Cr(VI)-containing wastewater. It determines the cell concentration at the initial stage of microbial remediation, which shows an impact on the bioreduction efficiency of Cr(VI) [24]. Herein, the effect of the inoculum amounts on the reduction of Cr(VI) by ZQ-1 was investigated, as shown in Figure 2a,b. There was no significant effect of the inoculum amount on the reduction of Cr(VI). Chen et al. found that the reduction efficiency of Cr(VI) by strain TJ-1 and TJ-5 was increased by an increase of initial inoculum. However, the reduction efficiency of Cr(VI) showed little change when the initial inoculum was greater than 5% [25]. From an economic cost point of view, 5% inoculum was selected for subsequent study. A suitable temperature is essential for the growth and metabolism of microorganisms [26]. In general, microorganisms can only grow within a certain range of temperatures beyond which they will not grow or even die [27]. In addition, the microbial reduction of Cr(VI) is an enzymatic process, which is also affected by temperature. Thus, an appropriate temperature can help the growth and metabolism of microorganisms and accelerate the bioreduction of Cr(VI) [28]. As shown in Figure 2, an increase in temperature was more favorable for the reduction of Cr(VI). From 28 °C to 37 °C, the reduction efficiency of Cr(VI) gradually increased to 100%. Notably, ZQ-1 was able to completely reduce 50 mg/L Cr(VI) within 24 h at 42 °C (Figure 2c). At 15 °C, the strains hardly reduced Cr(VI), which was mainly due to the fact that the microorganisms could not grow continuously at such a low temperature (Figure 2d). Temperature affects the rate of enzymatic reactions, which ultimately affects cellular synthesis. In addition, intracellular nucleic acids and other genetic material are more sensitive to temperature, and higher temperatures may destroy their structure [29]. Moreover, temperature affects nutrient uptake and metabolite secretion, as well as the solubility of substances. A high temperature enhances the mobility of cell membranes, which is favorable for the transportation of substances [30]. Compared with current reported works, strain ZQ-1 can reduce Cr(VI) across a wider temperature range [31,32,33], meaning it exhibits better adaptation to temperature changes in the environment.
pH increases the complexity and additional remediation costs in wastewater treatment [34]. Therefore, the effect of pH on the reduction of Cr(VI) by ZQ-1 was explored, as shown in Figure 3a. At pH of 7 and 6, the strains reduced Cr(VI) faster and could completely reduce 50 mg/L Cr(VI) at 28 h and 36 h, respectively. When the pH was increased to 8 and 9, the Cr(VI) reduction rate gradually decreased and the efficiency dropped to 94.24% and 69.96% at 48 h, respectively. Reductase activity is higher under neutral conditions, whereas lowering or raising the pH may alter reductase activity and thus reduce reduction efficiency [35]. Xiao et al. reported that the reduction of Cr(VI) by Bacillus sp. FY1 and Arthrobacter sp. WZ2 was best at pH 8 and 7, respectively, while the efficiency of Cr(VI) reduction was significantly decreased at lower or higher pH values [8]. pH values can have a strong influence on microbial growth. Too much acid or base can directly change the enzyme protein conformation and affect the binding of enzymes and substrates [36]. In addition, pH also affects the dissociated form of Cr(VI), further affecting the action of microorganisms or enzymes on Cr(VI) [37].
Co-existence of various heavy metal ions can lead to unsuccessful microbial remediation processes [38]. Therefore, the performance of microbial reduction of Cr(VI) in the presence of other heavy metal ions was explored. All the coexisting metals inhibited the bioreduction of Cr(VI) (Figure 3c). ZQ-1 showed good reduction of Cr(VI) in the presence of Fe3+, Mn2+ and Pb2+, while Hg2+, Cd2+ and Zn2+ were inhibitory. At 36 h, the reduction of Cr(VI) reached 100% in the presence of Fe3+, Mn2+ and Pb2+, which was 12 h slower than that of the CK group. The slight decrease of Cr(VI) under other metal ions conditions may have resulted from the abiotic reduction of the medium. Das et al. reported that strain CWB-54 showed a sharp decrease in Cr(VI) reduction efficiency in the presence of Cd2+ and Hg2+, whereas a lesser effect was seen with Mn2+ [6]. Heavy metals show strong complexation and affinity with enzymes and nucleic acid molecules, which can cause irreversible damage to microorganisms through a loss of function or inhibition of metabolic processes [39]. Microorganisms also have self-protective mechanisms against the toxicity of heavy metals, such as adsorption of metals on the cell surface and secretion of enzymes and extracellular polymers for the detoxification of metals [40].
High concentrations of Cr(VI) can more easily cause cell destruction [41]. Therefore, the effects of initial concentrations of Cr(VI) on reduction were investigated. As shown in Figure 4a, the results indicate that strain ZQ-1 could effectively reduce Cr(VI) from 50 to 200 mg/L of Cr(VI). The strain could completely reduce Cr(VI) within 24 h at 50 mg/L. With an increase of the initial concentration of Cr(VI), the reduction rate was gradually inhibited. However, strain ZQ-1 could still survive and reduce Cr(VI) at 200 mg/L, suggesting the potential applicability of the isolated strain [42]. Cr(VI) is highly toxic to strains and can cause oxidative stress and DNA damage. An important driving force for microbial reduction of Cr(VI) is detoxification. Strains actively and promptly reduce Cr(VI) to the non-toxic Cr(III) to protect their replication and growth from being disrupted during the growth period. After growth, the demand decreases for protecting key molecules such as DNA. Thus, the Cr(VI) reduction process also ceases. An increase in concentration lengthened the lag period of strain growth. Similarly, Banerjee et al. reported that Pseudomonas MF957286 could effectively reduce Cr(VI) in a relatively short time at the concentration of 1–20 mg/L, with the total biomass unchanged, although reduction was totally inhibited at 110 mg/L Cr(VI) [43,44]. Metal complexation can result in the cross-linking of DNA and mutagenic and carcinogenic effects, the generation of Cr(V) and Cr(IV), as well as reactive oxygen species (ROS) during the process of Cr (VI) reduction These phenomena cause damage to membrane structures, which is very unfavorable to the growth of bacteria.
Usually, Cr (IV)-containing wastewater have large amounts of salt when discharged into the environment. However, the growth of microorganisms can be inhibited in a high-salt environments resulting in a low efficiency of Cr(VI) reduction [45]. Therefore, the effect of NaCl concentration on the reduction of Cr(VI) by ZQ-1 was investigated. As shown in Figure 4c, ZQ-1 could efficiently reduce Cr(VI) below 15% NaCl (w/v). The strain could completely reduce Cr(VI) within 24 h at 1% NaCl (Figure 4c). The strain completely reduced Cr(VI) at 30 h without NaCl, which was due to the fact that the microbial growth process ingested a certain amount of salt to support development (Figure 4d). However, high amounts of salt inhibited the growth of the microorganisms. With an increase in NaCl concentration, the time for complete reduction of Cr(VI) was prolonged (Figure 4c), but Cr(VI) could still be completely reduced within 60 h, even at 7% NaCl. When the concentration of NaCl was further increased, the strain could partially reduce Cr(VI). Liu et al. applied strain BWL1061 for decolorization of sulfonated azo dyes and the reduction of Cr(VI) under high-salt conditions [46]. The strain showed good degradation and reduction of dyes and Cr(VI) at NaCl concentrations of 0–6%, but whose degradation and reduction were inhibited above 6% NaCl. Karthik et al. reported similar results that the efficiency of Cr(VI) reduction decreased by 11.63%, 29.90% and 48.90% through the use of strain AR8, when the NaCl concentration was increased from 1% to 3% [12]. From past studies of the microbial Cr(VI) reduction with salt tolerance, strain ZQ-1 currently shows the highest level of NaCl tolerance. Wang et al. have summarized the classification and salt-tolerance properties of salinophilic and salt-tolerant microorganisms [47]. Comparing with the reported studies, ZQ-1 tolerated salt concentrations up to 15% (2.6 M), exceeded general non-salinophilic, mildly salinophilic, and moderately salinophilic bacteria (0 to 2.5 M). In addition, growth of the strain was limited with an increase in NaCl concentration. In high-salt environments, microorganisms cannot maintain the balance of osmotic pressure inside and outside the cell, resulting in cell dehydration and cell death. In addition, salt ions bind with enzymes to further affect their functions.

3.3. Deciphering of Strain ZQ-1 on Salt-Tolerance

In a high-salt environment, microorganisms usually possess certain salt-adaptation mechanisms to maintain growth. Microorganisms maintain osmotic balance by accumulating large amounts of KCl or organic affinity solutes as osmoregulators or excreting excess Na+ from the cells through the Na+ export system to maintain low salt levels within cells [48]. In this study, the changes in the relative contents of ZQ-1 for differential metabolites under medium and high salt stress, were investigated. A total of 1190 organic compounds were detected, as shown in Figure 5. The relative contents of organic heterocyclic compounds, organic nitrogen, benzene, organic oxygen compounds, and alkaloids and their derivatives, gradually decreased with an increase in NaCl concentrations from 5% to 15%. This may be attributed to the general inhibition of metabolism associated with bacterial growth under high salt stress [49]. The relative content of lipid and lipid-like molecules were significantly increased at 5% NaCl but decreased at 15% NaCl. High osmotic pressure causes damage to membrane structures. At a moderate concentration of NaCl (5%), an increase in unsaturated fatty acid content in the membrane lipids maintains the normal fluidity of the membrane to resist cell damage. When the NaCl concentration gradually increased to 15%, the high osmotic pressure caused membrane damage, resulting in a decrease in lipid content and a loss of salt tolerance for ZQ-1 [50]. The relative content of organic acids and their derivatives at 15% NaCl was 1.5 times higher than at 1%. The large accumulation of organic acids such as malic acid, succinic acid, citric acid and gluconic acid was favorable for the strains to produce more energy and reducing agents, which can be attributed to the glycolysis process. In addition, organic acids can be used as precursors to provide a carbon skeleton for the synthesis of amino acids that can improve the salt tolerance of bacteria [51].
Herein, according to the type of metabolism, the metabolites were categorized into sugars, amino acids and fatty acids, as shown in Figure 6a. Compared with 1% NaCl, the content of sugars and amino acids were reduced, while the content of fatty acids was increased, under the stress of 5% and 15% NaCl for strain ZQ-1. An unfavorable survival environment affects the sugar metabolism pathway of microorganisms [52]. Thus, sugar metabolism can be used as an indicator of the degree of environmental stress on microorganisms, as well as the microbial adaptation to the stress. However, this study showed that the content of saccharides in strain ZQ-1 was decreased rather than increased under salt stress, which may be attributed to the imbalance of sugar metabolism under such high salt stress, and the non-protective ability of saccharides for strain ZQ-1 against salt stress. Fatty acids are not only important components of cell membrane lipids, but also the main form of energy storage in organisms. Under salt stress, the fatty acid content (21.8%) in the metabolites of strain ZQ-1 was highest at 5% NaCl, which may be due to the fact that the regulation of fatty acid metabolism is more suitable for ZQ-1 under moderate salt levels, while it was slightly insufficient at high-salt levels (15% NaCl). This was attributed to the ability of the microorganisms to maintain cell membrane fluidity through fatty acid degradation in adverse environments [53]; this may be one of the important mechanisms by which strain ZQ-1 resists salt stress.
Compatibility regulation mechanism refers to the accumulation of a high concentration of compatible substances in the cells to counteract a high external osmotic pressure. Compatible substances mainly include amino acids, betaine, alginate and other substances [54,55]. Therefore, the differences in the contents of amino acids, betaine and alginate were analyzed under salt stress, as shown in Table 1. The contents of most amino acids decreased with increasing salinity. However, the increase in arginine was more pronounced, from 0.124% to 4.564%. It has been reported that arginine can be used to produce the metabolite citrulline through the ADI pathway, which may play a role in balancing osmotic pressure and protecting cells against high salt stress [56]. Compared to 1% NaCl, strain ZQ-1 specifically accumulated lysine and proline to regulate the high osmotic environment under medium salt (5% NaCl) conditions. This is because negatively charged amino acids such as lysine may neutralize intracellular ions such as Na+ and K+, thus ensuring normal cell growth. Proline reduces the chemical potential energy caused by an increase in salt concentration, protects the integrity of membranes, and thus protects the cells from damage [57]. Therefore, one of the salt-tolerance mechanisms of ZQ-1 is the regulation of osmotic pressure through the metabolism of arginine to produce citrulline, and lysine and proline to neutralize ions to change the chemical potential. In addition, ZQ-1 increased the synthesis of the compatible substances alginate and betaine under high salt stress, as shown in Figure 6b. Compared with 1% salt concentration, with the elevation of the concentration of NaCl up to 15%, the levels of alginate and betaine were elevated by about 4.83-fold and 3.28-fold, respectively. It has been reported that alginate and betaine are widely present in bacteria, yeast, fungi and plants as protective agents for various stresses, which can rapidly accumulate in the cytoplasm to regulate cellular osmotic pressure and antioxidant pathways to alleviate the damage of salt stress and improve the salt-tolerance of bacteria [58,59]. Thus, another mechanism of strain ZQ-1 resisting high salt stress depended on the protection provided by alginate and betaine.

4. Conclusions

In summary, a halotolerant strain Acinetobacter ZQ-1 for Cr(VI) reduction was successfully isolated, showing a high reduction capacity at a wide range of pH, temperatures, and heavy metals, as well as a tolerance to high concentrations of NaCl. Salt stress affected the content of ZQ-1 metabolites, and the increased expression of arginine and proline; trehalose and betaine were important for ZQ-1 to exert its salt-tolerance mechanism. This study provides a green biological method for the treatment of high-salt, high-concentration chromium hexavalent wastewater, and lays a theoretical foundation for improving the salt tolerance of chromium hexavalent-reducing bacteria.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/pr13113423/s1, Figure S1: Growth of ZQ-1; Figure S2: Cr(VI) reduction with and without strain ZQ-1.; Table S1: Physiological and biochemical tests of strain ZQ-1.

Author Contributions

Conceptualization, J.L. and L.Y.; methodology, L.Y. and Q.Z.; software, L.Y.; validation, L.Y. and Q.Z.; data curation, L.Y.; writing—original draft preparation, J.L. and L.Y.; writing—review and editing, J.L. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Data Availability Statement

The original contributions presented in this study are included in the article/Supplementary Material. Further inquiries can be directed to the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

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Figure 1. (a) 16S rRNA phylogenetic tree of strain ZQ-1 and (b) Cr(VI) reduction by strain ZQ-1. Data represent the mean ± standard deviation of three independent experiments.
Figure 1. (a) 16S rRNA phylogenetic tree of strain ZQ-1 and (b) Cr(VI) reduction by strain ZQ-1. Data represent the mean ± standard deviation of three independent experiments.
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Figure 2. The effect of inoculation amount on (a) Cr (VI) reduction and (b) strain concentration, and the effect of temperature on (c) Cr(VI) reduction and (d) strain concentration.
Figure 2. The effect of inoculation amount on (a) Cr (VI) reduction and (b) strain concentration, and the effect of temperature on (c) Cr(VI) reduction and (d) strain concentration.
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Figure 3. Effect of pH on (a) Cr (VI) reduction and (b) strain concentration, and the effect of heavy metal on (c) Cr(VI) reduction and (d) cell concentration. Data represent the mean ± standard deviation of three independent experiments.
Figure 3. Effect of pH on (a) Cr (VI) reduction and (b) strain concentration, and the effect of heavy metal on (c) Cr(VI) reduction and (d) cell concentration. Data represent the mean ± standard deviation of three independent experiments.
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Figure 4. Effect of Cr (VI) concentration on (a) Cr (VI) reduction and (b) strain concentration changes, and the effect of NaCl on (c) Cr(VI) concentration and (d) strain concentration.
Figure 4. Effect of Cr (VI) concentration on (a) Cr (VI) reduction and (b) strain concentration changes, and the effect of NaCl on (c) Cr(VI) concentration and (d) strain concentration.
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Figure 5. Effect of NaCl concentrations on the relative content of various metabolites of strain ZQ-1.
Figure 5. Effect of NaCl concentrations on the relative content of various metabolites of strain ZQ-1.
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Figure 6. Effect of salt concentration on the relative contents of (a) soluble sugars, fatty acids and amino acids; (b) alginate and betaine in strain ZQ-1.
Figure 6. Effect of salt concentration on the relative contents of (a) soluble sugars, fatty acids and amino acids; (b) alginate and betaine in strain ZQ-1.
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Table 1. The content of metabolized amino acids of ZQ-1 under different NaCl concentrations.
Table 1. The content of metabolized amino acids of ZQ-1 under different NaCl concentrations.
m/zrt (s)CompoundsRelative Content (% × 10−2)
1% NaCl5% NaCl15% NaCl
529.08175.12Arginine12.4514.15456.43
401.70146.04Glutamic acid39.4011.608.61
320.02145.06Glutamine0.960.820.24
401.43156.08Histidine50.1741.9620.69
247.27173.13Isoleucine0.611.380.17
330.15132.10Leucine4.7838.323.30
529.08147.11Lysine118.45137.97108.37
291.57150.06Methionine33.7926.0315.80
261.62166.09Phenylalanine0.590.480.26
318.31116.07Proline29.57164.5210.62
94.39102.05Threonine1.851.531.28
268.24205.10Tryptophan6.3420.7735.88
311.66182.08Tyrosine80.3277.9326.83
306.64118.08Valine23.854.403.43
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Yu, L.; Zhou, Q.; Liang, J. Efficient Bioreduction of Cr(VI) by a Halotolerant Acinetobacter sp. ZQ-1 in High-Salt Environments: Performance and Metabolomic Mechanism. Processes 2025, 13, 3423. https://doi.org/10.3390/pr13113423

AMA Style

Yu L, Zhou Q, Liang J. Efficient Bioreduction of Cr(VI) by a Halotolerant Acinetobacter sp. ZQ-1 in High-Salt Environments: Performance and Metabolomic Mechanism. Processes. 2025; 13(11):3423. https://doi.org/10.3390/pr13113423

Chicago/Turabian Style

Yu, Lei, Qi Zhou, and Jing Liang. 2025. "Efficient Bioreduction of Cr(VI) by a Halotolerant Acinetobacter sp. ZQ-1 in High-Salt Environments: Performance and Metabolomic Mechanism" Processes 13, no. 11: 3423. https://doi.org/10.3390/pr13113423

APA Style

Yu, L., Zhou, Q., & Liang, J. (2025). Efficient Bioreduction of Cr(VI) by a Halotolerant Acinetobacter sp. ZQ-1 in High-Salt Environments: Performance and Metabolomic Mechanism. Processes, 13(11), 3423. https://doi.org/10.3390/pr13113423

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