Introduction

Prometryne [2-(methylthio)-4,6-bis(isopropylamino)-s-triazine], an herbicide belonging to the group of s-triazines, is a nonionic, weakly polar hydrophobic (log Kow > 2) compound [1], with average solubility in water. It is stable in slightly acidic, slightly alkaline, and neutral environments [2]. Prometryne has been extensively used as a pre- or post-emergence control of annual grasses and broadleaf weeds [3, 4]. The half-lives for the biodegradation of prometryne in aerobic and anaerobic soil have been reported as 1–3 months, respectively, and its production and use as an herbicide is expected to result in its release to the environment, triggering direct harm to humans through the food chain [5, 6]. In view of that, prometryne has been listed as a reproductive and developmental toxin by the U.S. Environmental Protection Agency (EPA) on their toxic substance release list, and is also identified as an endocrine disruptor on the EU priority list [7]. However, this chemical is still used in large quantities in the rice, sugarcane, and soybean growing regions of China because of its broad spectrum of weed control and high potency [8]. Therefore, the removal of prometryne from soil is an important aspect of ecological restoration. Previous research shows that prometryne can be removed by photodegradation, herbicide adjuvants, physical adsorbents, and molecularly imprinted polymers [7, 9,10,11,12]. Photodegradation can decrease the content of prometryne in soil [10, 11], but this process takes a long time. Using herbicide adjuvants may affect the biodegradation of recalcitrant compounds [7]. Physical adsorbents can remove prometryne from water [9], and molecularly imprinted polymers have been used to analyze herbicides at trace levels in media [12]; however, none of these approaches can solve the problem of prometryne in soil.

Microbial biodegradation is one of the key processes of herbicides attenuation in the environment [13]. This process has gradually become a focus of research and captured the attention of government officials due to its low cost, efficiency, lack of secondary pollution and other advantages [14]. Despite having been banned in several countries, prometryne is a widely used herbicide in China. Therefore, biodegradation may be an ideal strategy for the detoxification of prometryne from the environment. Many microorganisms that can degrade prometryne have been isolated and characterized, including Leucobacter sp. JW-1 [15], Rhodococcus sp. FJ1117YT [16], Bacillus sp. JUN7 [17], Nicotinovorans sp. HIM [18], Nocardioides sp. DN36 [19], and Arthrobacter aurescens TC1 [20]. To the best of our knowledge, only a few prometryne biodegradation pathways have been reported in the literature. Therefore, studies related to prometryne degradation are essential for a better understanding of prometryne-degrading bacteria.

In the present study, a new bacterial strain, Pseudomonas sp. DY-1, was isolated from prometryne-contaminated rice paddies and characterized by its efficient degradation of prometryne. The objectives of this study were to describe the degradation-related characteristics of this strain and its use in the bioremediation of prometryne-contaminated soil. Furthermore, the detailed pathway of prometryne metabolism was also elucidated.

Materials and Methods

Chemicals and Media

Prometryne (C10H19N5S, 97%), simetryne (C8H15N5S, 97%), desmetryne (C8H15N5S, 98%), and metribuzin (C8H14N4SO, 97%) were purchased from Harbin LIMIN Agrochemical Technology Ltd. Ametryne (C9H17N5S, 97%) was purchased from Shanghai KALANG Technology Ltd. All of the other chemicals used in this study were analytical or HPLC-grade reagents that are available commercially.

Luria–Bertani (LB) medium contained 10.0 g L−1 tryptone, 5.0 gL−1 yeast extract, and 5.0 gL−1 NaCl, at pH 7.2. Minimal salt medium (MSM) contained 1 gL−1 K2HPO4, 1 gL−1 KH2PO4, 1 gL−1 NH4NO3, 0.2 gL−1 MgSO4‧7H2O, 0.2 gL−1 NaCl, and 1% trace element solution (TES), at pH 7.2. TES contained 0.4 gL−1 Na2B4O7⋅10H2O, 0.5 gL−1 Na2MoO4⋅2H2O, 0.8 gL−1 CuSO4⋅5H2O, 2 gL−1 FeSO4‧7H2O, 2 gL−1 MnSO4‧H2O, 10 gL−1 ZnSO4‧7H2O, and 5 gL−1 EDTA, at pH 7.2. Solid media plates received a concentration of 1.5% agar.

MSM with different concentrations of prometryne was used in enrichment, isolation, and degradation experiments, while LB medium was used to purify and preserve the bacterial strains.

Enrichment and Isolation of Prometryne-Degrading Bacteria

Soil samples were collected from the top 0–20 cm of a rice paddy that had been treated with prometryne for over 5 years in northwestern Heilongjiang Province, China. All of the samples were stored at 4 °C for no more than 2 weeks after being passed through a 2.0-mm sieve.

For the whole experiment, bacterial cells were inoculated at 5% (v/v) into a 250-mL flask containing 100 mL of MSM unless otherwise stated. Soil samples were added to MSM supplemented with 50 mg L−1 prometryne as the sole carbon source. Initially, the liquid culture was incubated in the dark on a rotary shaker at 30 °C and 160 rpm for 7 days. After that the culture was transferred to fresh MSM containing 100 mg L–1 to start the second soil enrichment. This process was repeated four times until the prometryne concentration reached 200 mg L−1. Afterward, 100 μL of serial dilutions (10–4, 10–5, and 10–6) of the enrichment culture were spread onto LB agar plates and incubated in the dark for 48 h at 30 °C. On the basis of morphological features, different bacterial colonies were picked, purified, and tested for their prometryne-degrading ability. All of the above were implemented to identify favorable conditions for prometryne-degrading bacteria and a growth-limiting culture for other soil microorganisms. The final isolated strain was named DY-1, which was preserved at − 80 °C in LB medium with 30% sterile glycerol for further assay.

Identification of the Isolated Strain

Strain DY-1 was identified on the basis of its morphological, physiological, and biochemical properties [21] (with reference to Bergey’s Manual of Determinative Bacteriology) and its 16S rRNA gene sequence. The morphology of the strain was observed by electron microscopy, and the total genome was extracted using a Bacterial Genomic DNA Kit (Cat No. CW0552) according to the manufacturer's protocols. The extracted DNA was amplified using the universal primer set 27F (5′-AGAGTTTGATCCTGGCTCAG-3′) and 1492R (5′-GGTTACCTTGTTACGACTT-3′) of the bacterial 16S ribosomal RNA (rRNA) genes [22]. The PCR products were examined using 0.7% agarose gel electrophoresis and purified using an Axygen® AxyPrep DNA Gel Extraction Kit (Cat No. AP-GX-250). The purified products were sequenced by Jilin Comate Bioscience Co., Ltd. To align 16S rRNA gene sequences, a Basic Local Alignment Search Tool (BLAST) was used to identify sequences, Clustal X2 was used for alignment, and Molecular Evolutionary Genetics Analysis (MEGA) version 7.0 [23] was used to construct the phylogenetic tree with the maximum livelihood method and the Kimura two-parameter distance model to calculate each distance. In each case, bootstrap values were calculated based on 1000 replications.

Growth and Degradation Conditions of the Prometryne-Degrading Strain

Strain DY-1 was incubated in LB medium at 30 °C for 24 h, and then the bacteria were harvested by centrifugation at 8000 rpm for 5 min at room temperature. The supernatant was discarded, using sterilized water to suspend the bacteria. The optical density at 600 nm (OD600) of all the cultures was adjusted to 1.0 to determine the growth and biodegradation ability of strain DY-1. Following this, the samples that were already transferred into MSM were incubated in the dark at 30 °C and 160 rpm on a rotary shaker.

To investigate the effects of the concentrations of prometryne on the growth and prometryne biodegradation of strain DY-1, the concentrations were adjusted to 50, 100, 200, 300, 400, and 500 mg L−1 for different treatments, and the mixtures were incubated in the dark for 48 h at pH 7.0 and 30 °C. To determine the effects of temperature on strain DY-1, cultures containing 50 mg L−1 prometryne with a pH adjusted to 7.0 were incubated in the dark for 48 h at different temperatures of 15, 20, 25, 30, 35, 40, and 45 °C. The pH values of different cultures (containing 50 mg L−1 prometryne) were adjusted to 4–12 to analyze the effects of pH on strain DY-1 and incubated in the dark for 48 h at 30 °C. To study the effects of NaCl concentrations on strain DY-1, NaCl was added into different cultures (containing 50 mg L−1 prometryne) to final concentrations of 200, 400, 600, 800, and 1000 mg L−1, and the mixtures were incubated in the dark for 48 h at pH 7.0 and 30 °C. The cultures without NaCl were used as negative controls. All of the treatments were repeated three times.

Prometryne extraction was done accordance with Liu et al. [15] with minor modifications. Samples from the cultures were collected in sterilized centrifuge tubes every 4 h. An equal volume of dichloromethane was added to the tubes and shaken to mix well, and the tubes were centrifuged at 10,000 rpm for 5 min and incubated for 20 min at room temperature. After the samples were delaminated, the supernatant was discarded, and the organic phase was transferred into the round-bottom flasks. Then, all of the flasks were evaporated in a rotary evaporator and dissolved in 1 mL of methanol.

The growth of DY-1 was analyzed using a spectrophotometer (U-2910; HITACHI, Japan) to measure the absorbance at 600 nm of the cultures, while HPLC (Waters 600; Waters, USA) was used to quantify the concentration of prometryne. An Agilent TC-C18 separation column (4.6 × 250 mm, 5 μm) (Cat No. 518925-902) was used at the stationary phase. The mobile phase was methanol: water (80:20, v/v), the flow rate was 1.0 mL min−1, and the UV detection was set to 216 nm.

Identification of the Metabolites Products

To analyze the intermediate metabolites during prometryne degradation by strain DY-1, 10 mL of the cell suspension (OD600, 1.0) was added to 200 mL of MSM containing 50 mg L−1 prometryne with the pH adjusted to seven and incubated in the dark for 48 h at 30 °C and 160 rpm on a rotary shaker. Then, prometryne was extracted using the method described in the previous section.

The metabolite products were determined by liquid chromatography tandem-mass spectrometry (LC–MS/MS, LCQ Deca XP; Thermo Finnigan, USA). A Waters BEH C18 column (3.9 mm × 100 mm × 1.7 μm) was used to separate the transformation products. The sample injection volume was 25 μL. The mass spectrometry mobile phase consisted of acetonitrile and water, and the flow rate was 0.1 mL min−1. Gradient elution was performed under the following conditions successively: 0–2 min, 10% acetonitrile, and 90% water; 2–24 min, 70% acetonitrile, and 30% water; and 24–36 min, 10% acetonitrile, and 90% water. The mass spectrometry mode was SIR ion scanning with an ESI (+) source voltage of 3.5 kV, and capillary voltage of 24 V, capillary temperature of 25 °C.

Determination of the Ability of Strain DY-1 to Degrade Other 3-Triazine Herbicides

The cell suspension (OD600, 1.0) was added to the four MSM containing 50 mg L−1 simetryne, ametryne, desmetryne, and metribuzin. All of the cultures were incubated in the dark for 48 h at 30 °C and 160 rpm on a rotary shaker, and then herbicides were extracted for analysis. The degradation dynamics were determined by HPLC, with a noninoculated suspension as a control.

Bioremediation of the Prometryne-Contaminated Soil

Soil samples were collected from the top 0–20 cm of the experimental farm at Northeast Agricultural University, which had not experienced contamination by prometryne or other s-triazine herbicides in the past 5 years. The samples were air-dried and passed through a 2.0-mm sieve. The prometryne (97%) was dissolved in methanol to obtain a 1 mg mL−1 solution. Then, to get 50 mg kg−1 of prometryne, the right amount of the solution was added to the dry soil and mixed. After the methanol was completely volatilized at room temperature, the treated soil was stored at 4 °C. Strain DY-1 was incubated in the two LB media until the number of living bacteria was 1 × 106 and 1 × 108 colony forming units (CFU) mL−1, and then the bacteria were harvested from the liquid culture by centrifugation at 8000 rpm for 5 min. The bacteria were suspended in sterile water to a density of approximately 1 × 106 and 1 × 108 CFU mL−1, and then immediately sprayed onto the contaminated soil.

For reference, a blank control without prometryne or bacteria was used. Two of the experimental treatments contained 500 g of contaminated soil and 10 mL of strain DY-1 with different densities: (1) 1 × 106 CFU mL−1 and (2) 1 × 108 CFU mL−1. Another treatment contained 500 g of the contaminated soil and 10 mL of sterile water. For each treatment, the soil moisture content was kept at 20%, and the temperature was kept at 25 °C. All the treatments were repeated three times.

Samples were collected from each group every 3 days, a double volume of methanol was added, and the mixture was stirred for 2 h, and then incubated for 12 h at room temperature. Next, the cultures were incubated for 1 h at room temperature on a rotary shaker and centrifuged at 8000 rpm for 10 min. Then the herbicide was extracted from the supernatant for determination of the concentration of prometryne by HPLC.

Pot Experiment

Methanol was used to dissolve the prometryne (97%). Soil samples from the previous section were added to the right amount of prometryne solution to obtain a concentration of 80 μg kg−1. Strain DY-1 was incubated in LB medium until the number of living bacteria was 1 × 108 CFU mL−1, and then the bacteria were harvested from the liquid culture by centrifugation at 8000 rpm for 5 min. The bacteria were suspended in sterile water to match the original volume and sprayed onto the contaminated soil immediately. Six kilograms of the treated soil was transferred into a pot (23 × 16.5 × 20 cm). Corn seeds were soaked at a constant temperature at 45 °C for 4 h; thereafter, their surfaces of them were disinfected. Subsequently, the germinated plants were wrapped in sterile gauze and sprayed with sterile water three times a day for 3 days at 28 °C. Each of the pots contained three germinated plants. Each group was cultured for 10 days at 28 °C and a 16 h/8 h light/dark cycle (1000 lx) in phytotron and sprayed with sterile water two times a day. After 10 days of cultivation, the morphological parameters of corn plants in every treatment group were measured, including the length and fresh weight of seedlings and roots.

To determine the influence of strain DY-1 and prometryne on the growth of corn, three treatments were applied: soil containing prometryne (experimental group, EG1), soil containing prometryne and strain DY-1 (EG2), and soil without prometryne or strain DY-1 (control group, CG). Each treatment group included six replicates to ensure accuracy.

Statistical Analysis

The data of pot experiment were carried out with six independent experiments, while of others were carried out with three. Each result shown in this paper is represented as the mean ± standard deviation (SD) or percentage of at least three replicated treatments. Statistical analysis was carried out with one-way analysis of variance (ANOVA) using SPSS software (version 25.0; IBM SPSS, Armonk, NY, USA) [24]. In addition, least significant differences (LSDs) were calculated or Games-Howell test was used for testing treatment effects at P < 0.05 [25].

Accession Number

The sequences of 16S rDNA of Pseudomonas DY-1 was submitted to the GenBank under the accession number KU054384.

Results and Discussion

Isolation and Identification of Prometryne-Degrading Strains

A strain (named DY-1) was isolated from soil after enrichment culturing. The cells of strain DY-1 were gram negative, and colonies on LB agar plates were convex, cream-to-white, nontransparent and had a smooth surface and regular edges. Strain DY-1 tested negative in the methyl red, starch hydrolysis, liquefaction of gelatin, and Voges-Proskauer tests and tested positive in the oxidase and nitrate reductase tests. On the basis of the 16S rRNA gene sequence of strain DY-1, a phylogenetic tree was constructed, as shown in Fig. 1, which indicated that strain DY-1 showed 98.66% similarity with Pseudomonas resinovorans ATCC14235T (NR 112062). The isolated strain, DY-1, was identified as a species of Pseudomonas in accordance with all the above.

Fig. 1
figure 1

Phylogenetic analysis of strain DY-1 constructed based on the 16S rDNA sequences with maximum livelihood method. The bootstrap values were calculated based on 1000 replications

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Optimization of the Growth and Degradation Conditions of Strain DY-1

The effects of different substrate concentrations on the growth and degradation ability of strain DY-1 are shown in Fig. 2a. In previous studies, Liu et al. [15] chose 50, 200, and 400 mg L−1 as initial prometryne concentrations to determine the degradation rate of prometryne, while Zhang et al. [26] used 10, 20, 50, 80, and 100 mg L−1 to analyze the degradation characteristics of atrazine. To study the prometryne degradation characteristics of strain DY-1 more clearly, the initial concentration range of prometryne was further expanded on the basis of previous studies. At initial prometryne concentrations of 50 and 100 mg L−1, the removal efficiencies were 100 and 85% after 48 h, respectively. However, it is worth mentioning that the growth rate was rose considerably at 100 mg L−1, being slightly higher than that under the former. This result demonstrated that the low concentration of prometryne may not be capable of providing enough both energy and carbon to allow the bacteria to grow normally. Furthermore, strain DY-1 could efficiently degrade over 50% of prometryne within 48 h at a concentration of 300 mg L−1. When the initial prometryne concentrations reached 400 and 500 mg L−1, both the growth and degradation ability of strain DY-1 were less pronounced, which indicated that high concentrations of prometryne inhibited the growth of strain DY-1, giving rise to a decrease in the degradation ability of strain DY-1. Although the initial prometryne concentration was high, the strain did show a positive effect on degradation. Similar trends were observable in studies of Bacillus sp. reported previously: Wang et al. [27] suggested that the biodegradation ability of HB-6 declines from 90 to 20% when the atrazine concentration is 500 mg  L−1 and that only 100 mg L−1 is beneficial for biodegradation; Wang et al. [28] showed that a lower buprofezin concentration can promote the degradation of BF-5; and Lu et al. [29] concluded that the nicosulfuron capability degradation of YB1 is significantly higher at 0.5–2.0 mg L−1 than at 5–10 mg L−1. In China, a strict maximum residue limit of prometryne is set at 0.02 mg kg−1 for various agricultural products [30]. Strain DY-1 could degrade prometryne at a concentration of 500 mg L−1, which is much higher than at 0.02 mg kg−1. Moreover, only a few strains could degrade herbicides at a concentration of 500 mg L−1, indicating that strain DY-1 had good tolerance to prometryne and excellent application prospects.

Fig. 2
figure 2

The effects of environmental factors on prometryne degradation by stain DY-1 after 48 h incubation (n = 3). a Prometryne concentration, b temperature, c pH, and d NaCl concentration. Optical density at 600 nm indicate OD600. Asterisk and double asterisk denote significant effect of environmental factors at P < 0.05 and P < 0.01, respectively

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The efficiency of microbial bioremediation depends on the temperature and pH of the contaminated areas [31]. As shown in Fig. 2b, the optimal temperature for prometryne degradation of strain DY-1 was 30 °C, a with degradation efficiency reaching 100%. Moreover, the degradation rates of prometryne were very similar at 25 and 35 °C with over 90% degradation within 48 h of cultivation. At 15, 20, 40, and 45 °C, the rates decreased compared with those at the above temperatures. Furthermore, strain DY-1 could hardly grow when the temperature was below 20 °C or above 40 °C, suggesting that temperature affected the cell concentration of bacteria, which in turn affected the degradation rate of prometryne. Previous studies of s-triazine herbicide biodegradation have drawn similar conclusions. For instance, Wang et al. [32] found that the atrazine degradation rate of Arthrobacter sp. DAT-1 increases with temperature in a range from 10 to 35 °C, and the results of Zhao et al. [33] and Zhang et al. [26] indicate that the rates of Pseudomonas sp. ZXY-1 and Klebsiella variicola FH-1 reached their maximum levels at 25–35 and 25–30 °C, respectively.

The degradation of prometryne by strain DY-1 under a series of pH values is illustrated in Fig. 2c. The degradation efficiency reached 100% at pH 7.0 and 8.0 and was 87, 68, 60, 43, and 37% at pH 9.0, 10.0, 6.0, 11.0, and 15.0, respectively. The results indicated that the prometryne degradation efficiency of strain DY-1 was higher under neutral or weakly alkaline conditions than under strongly acidic or alkaline conditions. Liu et al. [15] reported that a neutral pH was the most favorable for prometryne degradation by Leucobacter sp. JW-1, which was similar to our results.

Figure 2d shows the effects of different NaCl concentrations on the prometryne degradation capability of strain DY-1. In the control group without NaCl, the prometryne removal percentage was 82.1% after 48 h. Concentrations of 200, 400, and 600 mg L−1 were more effective for removing prometryne than the control group. When the concentrations were 200 and 400 mg L−1, both of the removal percentages were 100%, while at 600 mg L−1 it was 91.4%. However, the prometryne removal percentages were 73.3 and 44.7% under NaCl concentrations of 800 and 1000 mg L−1, respectively, rates lower than those of the control. The results showed that an appropriate concentration of salt in the culture was helpful to improve the degradation efficiency of prometryne by strain DY-1. Similar to our results, Shir et al. [34] reported that the atrazine biodegradation rate of Ochrobactrum oryzae was decreased without NaCl, and Zhao et al. [35] indicated that atrazine degradation by Arthrobacter sp. ZXY-2 was improved with a proper salt concentration.

Degradation Spectrum of Strain DY-1

Table 1 indicates that strain DY-1 could grow on the screening media with simetryne, ametryne, desmetryne, and metribuzin at a concentration of 50 mg L−1, proving that strain DY-1 could degrade the above s-triazine herbicides containing methylthio (–SCH3). This substrate specificity may be related to the structures of the methylthio group, and the same conclusion was reached in previously for Rhodococcus sp. FJ1117YT [16], Bacillus cereus JUN7 [17], Leucobacter sp. JW-1 [15], and Nocardioides sp. C190 [36].

Table 1 Degradation of s-triazine compounds by strain DY-1
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Biodegradation of Prometryne by Strain DY-1

The products of prometryne degradation by strain DY-1 were identified by LC–MS/MS, and the liquid quality of the culture medium samples at different times was determined by total ion chromatogram (TIC). The mass-to-charge ratios (m/z) of the metabolites are shown in Fig. 3. The structure of prometryne was confirmed at m/z 242.1429 (Fig. 3a) on the basis of its protonated molecular ion [M + H]+ and the National Institute of Standards and Technology (NIST) library identification program (Fig. 3e) [37]. Based on the mass spectra, the major fragments of metabolite I exhibited at m/z 216.0916, 183.0693, and 170.1030 (Fig. 3b), and the formula of metabolite I was presumed to be C10H19N5SO. In addition, compared with prometryne, the peaks of the [M + H]+ of metabolite II (Fig. 3c) at m/z 274.1061 implied that an additional oxygen atom emerged on the parent molecule. The same phenomenon could be observed between metabolites I and II, and then the latter was hydrolyzed rapidly, resulting in metabolite III, the formula of which might be C9H17N5O (Fig. 3d).

Fig. 3
figure 3figure 3

LC–MS/MS identification of the products of prometryne degradation by strain DY-1. a Prometryne, b sulfoxide prometryne, c sulfone prometryne, d 2-hydroxy prometryne, and e mass spectra of prometryne from NIST database [37]

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In general, the molecular formulas of the three metabolites could be C10H19N5SO with a retention time (RT) of 8.0655 min, C10H19N5SO2 (RT = 12.9335 min), and C9H17N5O (RT = 8.4012 min). Combined with the chemical structure of prometryne, the results indicated that the three substances were sulfoxide prometryne, sulfone prometryne, and 2-hydroxy prometryne. Nevertheless, the accumulation of 2-hydroxy prometryne was observed, suggesting that strain DY-I might not be capable of metabolizing 2-hydroxy prometryne. It is possible claimed that at the beginning, strain DY-1 modifies prometryne by oxidation, and then the methylthio group is substituted by the hydroxy group, according to the molecular ion (M+) peaks of metabolites I (Fig. 3b) and metabolite III (Fig. 3c).

Figure 4 shows a schematic diagram of the degradation pathway of strain DY-1 based on these metabolites. Similar to strain DY-1, strains FJ1117YT [16] and JUN7 [17] degrade methylthio s-triazine by oxidation and hydrolysis.

Fig. 4
figure 4

Proposed degradation pathway of prometryne degradation by strain DY-1 based on the presumed metabolites

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Soil-Bioremediation and Detoxification by Strain DY-1

The degradation dynamics of prometryne at 50 mg kg−1 in soil are shown in Fig. 5. It could be seen that 94.3 and 98.1% of the prometryne was removed by treatment with 1 × 106 and 1 × 108 CFU mL−1 of strain DY-1, respectively, after incubation at 25 °C for 21 days, and for the blank control, chemical hydrolysis might be the reason why approximately 15.5% of the prometryne was dissipated. There was little difference in degradation between the two bacterial concentrations after 21 days, which indicated that the bacterial concentration was not important, but that bacteria were present. Therefore, this might be due to the synergistic effect between the low bacterial concentration and the microorganisms contained in the soil, which accelerated the degradation process of prometryne in the soil. Previous studies have resulted in similar conclusions, for instance, Arthrobacter sp. DNS10 can degrade 67.7% of atrazine (20 mg kg−1) after 20 days [38], and Arthrobacter sp. LY-1, 98.3% of atrazine (100 mg kg−1) after 14 days [39]. In China, overuse of herbicides in agriculture led to the accumulation of s-triazine at approximately 2.89–3.81 mg kg−1 [40], prompting the search for a method to address this phenomenon. This is the first step to remedy this trend. The concentration of prometryne in the field is much lower than that used in this study (50 mg L−1). Therefore, it is practically feasible to remove prometryne residues in nature using strain DY-1.

Fig. 5
figure 5

The degradation rate of prometryne in the soil by different colony numbers of strain DY-1 after incubation for 7, 14, and 21 days at 25 °C (n = 3). Blank noun, A 1 × 106 CFU mL−1, and B 1 × 108 CFU mL−1. Colony forming units indicate CFU. Asterisk and double asterisk denote significant effect of different colony numbers (compared to blank control) at P < 0.05 and P < 0.01, respectively

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The pot experiment used corn as an indicator to evaluate the detoxification ability of strain DY-1 for prometryne-contaminated soil. After cultivation for 14 days, corn growth data were obtained under different treatments, and the data are shown in Table 2. The data showed significant improvements in the seedling length, root length, seedling fresh weight and root fresh weight of corn of the EGs compared with the CG (P < 0.05). Moreover, compared with the CG, the measured morphological parameters of the EG1 decreased by 36.6, 33.8, 23.9, and 45.1%, respectively (P < 0.01). This signified that prometryne had toxic effect on corn growth, and it might become a pollutant of nontarget crops after decomposition. The measured morphological parameters in EG2 were higher than EG1, and were 96.8, 94.6, 80.4, and 96.7% of the control values (P < 0.05). The results highlighted that strain DY-1 had the ability to ameliorate the toxicity of prometryne to corn under laboratory conditions.

Table 2 The growth of corn in the soil treated with prometryne, the mixture of prometryne and strain DY-1, and the control soil (n = 6)
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Conclusions

In summary, Pseudomonas sp. strain DY-1, which offers superior remediation capability for soil contaminated by prometryne at 30 °C and pH 7.0, was obtained using enrichment culture. The prometryne degradation by DY-1 occurred at a wide range of prometryne concentrations, and appropriate amounts of NaCl addition could help improve the prometryne removal efficiency. Additionally, the LC–MS/MS data suggested that during degradation by strain DY-1, prometryne was oxidized and hydrolyzed in MSM, yielding sulfoxide prometryne, sulfone prometryne, and 2-hydroxy prometryne successively. A bioremediation trial with contaminated soil and pot experiments indicated that DY-1 could degrade over 94% of the prometryne contained in soil (50 mg kg−1) after incubation for 21 days at 30 °C. Moreover, the effects of strain DY-1 on crops during the degradation of prometryne were studied by a 21-day pot experiment, showing that strain DY-1 is capable of degrading prometryne into a form nontoxic to crops. The results of soil bioremediation and detoxification did not show a negative effect on soil and crops, which suggests that strain DY-1 is a promising candidate for the bioremediation of prometryne-contaminated environments, providing a new option for soil bioremediation and prometryne removal from crops. The experimental research results will hopefully prove useful for improvement of bioremediation, and provide a good starting point for discussion and further research.