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Article

Effects of Lanthanum-Modified Bentonite on Antibiotic Resistance Genes and Bacterial Communities in Tetracycline-Contaminated Water Environments

by
Wanzhong Wang
1,†,
Sijia Liang
1,†,
Shuai Zhang
2,
Daming Wei
3,*,
Xueting Xu
1 and
Peng Zhang
3,*
1
Nanjing Institute of Environmental Sciences, Ministry of Ecology and Environment, Nanjing 210042, China
2
Jiangsu Key Laboratory of Atmospheric Environment Monitoring and Pollution Control (AEMPC), Collaborative Innovation Center of Atmospheric Environment and Equipment Technology (CIC-AEET), School of Environmental Science and Engineering, Nanjing University of Information Science & Technology, Nanjing 210044, China
3
Chinese Academy of Environmental Planning, Ministry of Ecology and Environment, Beijing 100012, China
*
Authors to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Water 2025, 17(15), 2188; https://doi.org/10.3390/w17152188
Submission received: 26 June 2025 / Revised: 14 July 2025 / Accepted: 17 July 2025 / Published: 22 July 2025
(This article belongs to the Section Water Quality and Contamination)
Browse Figures
Versions Notes

Abstract

Water environments and sediments are important reservoirs for antibiotic resistance genes (ARGs). Under the pressure of antibiotics, ARGs can transform between microorganisms. Lanthanum-modified bentonite (LMB) is a phosphorus passivation material with good prospects in water environment restoration. After a treatment with LMB, the phosphorus forms in water and sediments will change, which may have an impact on microorganisms and the transmission of ARGs. To investigate the effects of LMB and antibiotics on ARGs and bacterial communities in sediment and aquatic environments, LMB and tetracycline (Tet) were added individually and in combination to mixed samples of sediment and water. The results showed that the addition of either LMB or Tet increased the abundance of intI1 and tetA genes in both the sediment and water, with the Tet addition increasing ARGs to more than 1.5 times the abundance in the control group. However, when LMB and Tet were present simultaneously, the abundance of ARGs showed no significant difference compared to the control group. Tet and LMB also affected the bacterial community structure and function in the samples and had different effects on the sediment and water. A correlation analysis revealed that the potential host bacteria of the intI1 and tetA genes were unclassified_Geobacteraceae, Geothrix, Flavobacterium, Anaeromyxobacter, and Geothermobacter. These findings indicate that Tet or LMB may increase the dissemination of ARGs by affecting microbial communities, while LMB may reduce the impact of Tet through adsorption, providing a reference for the safety of the LMB application in the environment and its other effects (alleviating antibiotic pollution) in addition to phosphorus removal.

1. Introduction

Antibiotics are secondary metabolites produced by microorganisms, and similar compounds are synthesized or semi-synthetic chemically, which can inhibit the growth and even survival of other microorganisms [1,2]. Although antibiotics are effective at combatting pathogenic bacterial infections in animals and improving their overall health, they have led to issues such as drug residues, resistance, and environmental pollution [3,4]. The resistance to antibiotics stems from the existence of antibiotic resistance genes (ARGs) [5]. Under the selective pressure of antibiotics, ARGs can be transferred vertically and horizontally in the environment [6]. Vertical gene transfer refers to the process in which ARGs are passed from parents to offspring, whereas horizontal gene transfer (HGT) via mobile genetic elements (MGEs), such as plasmids, integrons, and transposons, allows ARGs to spread between antibiotic resistance bacteria (ARB) and non-ARB [7,8]. Tetracycline (Tet) is widely used in human therapy, aquaculture, and animal husbandry due to its low production cost, high quality, and extremely high purity [9]. The production and usage of all kinds of Tet rank second worldwide, and rank first in China, which has also contributed to the widespread dissemination of Tet resistance genes [9]. In recent years, ARGs have been detected in aquatic ecosystems in all regions of the globe [10], and most rivers detected in China contain sulfonamide and Tet resistance genes. TetA and tetB are dominant among the Tet resistance genes [11,12]. For example, in the Pearl River system in China, the detection frequencies of tetA and tetB were 43% and 40%, respectively, among the Tet resistance genes [12]. Xu et al. [13] detected the abundance of ARGs in the urban rivers of Beijing and reported that the absolute abundance of ARGs ranged up to 5.9 × 106 copies/mL in water, while up to 2 × 108 copies/g in river sediments. Similarly, Chen et al. [14] reported that the concentrations of Tet resistance genes in sediments were at least 100 times greater than those in water. Evidence has demonstrated that the translocation of ARGs to the commensal microbiota and pathogenic bacteria within the human body compromises antibiotic efficacy, thereby presenting a substantial risk to human health [15].
Lanthanum-modified bentonite (LMB) is a kind of clay mineral modified with the lanthanum rare earth element as a sediment phosphorus passivation material, which has good prospects in water environment remediation [16,17]. LMB has been commercially used as Phoslock. Owing to its abundance and single oxidation state, La is the most promising rare earth element for binding phosphate in aquatic environments to replicate one or more of the minerals commonly found in the natural environment [18]. La3+ has a very strong binding ability with PO43− to produce LaPO4. After being treated with LMB, a decrease in PO43− in water and the transformation of phosphorus in sediments from mobile forms of P (Mobile-P), which can be converted into PO43− under certain conditions, to immobile forms of P (Immobile-P) were observed [19,20]. Thus, the growth of phytoplankton could be affected. Meis et al. [21] monitored the changes in the phytoplankton community before and after the application of LMB and reported that the number of cyanobacteria decreased significantly, whereas the numbers of dinoflagellates and green algae increased. Recently, Yin et al. [22,23] reported that other microorganisms could also be affected by LMB because the bacterial diversity and richness increased.
Some studies have indicated that clay minerals can inhibit the horizontal transfer of ARGs, thereby effectively reducing their abundance [24]. When antibiotics are present, clay minerals can reduce the spread of ARGs by adsorbing the antibiotics [24]. However, in complex environmental settings, clay minerals may also lead to a decrease in the degradation of ARGs [25]. Therefore, further research is required to explore the effects and mechanisms of clay minerals on ARGs. Currently, there is a paucity of research on the impact of bentonite on environmental ARGs, let alone the effects of LMB on ARGs and bacterial communities. Therefore, the response mechanisms of the bacterial community structure and ARGs to LMB were investigated in this study. Moreover, since Tet resistance genes are widely present in Chinese rivers, Tet was selected as an exogenous pollutant to study the changes in bacterial communities and resistance genes when Tet and LMB exist alone or simultaneously.

2. Materials and Methods

2.1. Reagents, Lake Water Samples, and Sediment Samples

Tetracycline hydrochloride was purchased from Beijing Belo Biotechnology Co., Ltd. (Beijing, China), lanthanum-modified bentonite (LMB) was obtained from Phoslock Water Solutions (Changxing) Ltd. (Huzhou, Zhejiang, China), and glucose and potassium dihydrogen phosphate were purchased from Sinopharm Chemical Reagent Co. (Shanghai, China) Water samples (6 L) and sediment (3 L) were taken from the lake on the campus of Nanjing University of Information Science and Technology (118.71162° E, 32.20238° N).

2.2. Culture Experiment

A total of 6 L of lake water and 3 L of sediment were mixed with 156.12 mg of potassium dihydrogen phosphate and 421.74 mg of glucose. The mixed sample was divided equally into 4 plastic containers and named as Con group, Tet group, LMB group, and TetLMB group. Con group was the control group, Tet group was dosed with 0.225 mg of Tet, LMB group was dosed with 9 g of LMB, and TetLMB group was dosed with 0.225 mg of Tet and 9 g of LMB. The 4 plastic containers were placed in a dark environment and shaken every 5 days for 5 min. Meanwhile, 46.86 mg/L glucose was added every 5 days. Samples were taken after 60 days of incubation [26], water samples (40 mL each time, 3 replicates) were taken from the middle layer, and sediment samples (10 mL each time, 3 replicates) were taken at different locations spatially distributed in the plastic containers. Individual water and sediment samples collected at each spatial/temporal point were homogenized separately and centrifuged at 8000 r/min for 5 min. The water and sediment samples were named WCon, WTet, WLMB, WTetLMB, SCon, STet, SLMB, and STetLMB, respectively, and the samples were stored in a refrigerator at −20 °C.

2.3. Gene Sampling, Extraction, and Quantitative Analysis

The total DNA of the water and sediment samples was extracted via the soil genomic DNA extraction kit TIANNAMP Soil DNA Kit (TIANGEN Biotech, Beijing, China), and the specific extraction steps are explained in the instruction manual of the kit. Afterwards, the quality of the amplified products was assessed via agarose gel electrophoresis (1% concentration), and the sequencing library was established after passing the test.
The 16S rRNA, tetA, and class 1 integron-integrase (intI1) genes were quantified via a StepOnePlus™ Real-Time Polymerase Chain Reaction (PCR) system from Thermo Fisher Scientific (Wcgene Biotech, Inc., Shanghai, China). IntI1 is usually related to genes conferring resistance to antibiotics, disinfectants, and heavy metals [27]. The abundance of intI1 can change rapidly in response to environmental stress because it is present in different bacterial species and is usually located on MGEs that can be easily transferred between bacteria and can participate in the horizontal transfer of ARGs [27].
The qPCR volume was 10 μL, consisting of 5 μL of TB Green Premix Ex Taq II (Tli RNaseH Plus) (2×), 0.4 μL of Primer F, 0.4 μL of Primer R, 0.2 μL of ROX Reference Dye (50×), 1 μL of DNA sample, and 3 μL of double-distilled water. The specific reaction program for qPCR amplification was as follows: predenaturation phase: 95 °C for 30 s; cycling phase (40 cycles): 95 °C deformation for 5 s; annealing, 30 s; and extension at 60 °C for 30 s. Finally, the mixture was held at 60 °C for 1 min. During extension at 60 °C, the fluorescence signals emitted by the SYBR fluorescent dye were collected from the qPCR detection system. At the end of amplification, a melting curve was plotted for the system from 60 °C to 95 °C with an increase in temperature of 0.3 °C/min to determine the specificity of the amplification product with a single solubilization peak. Three technical replicates of each qPCR sample were performed, and amplification was considered successful when all the results were positive. Amplification of each target gene was accompanied by the generation of a standard curve (regression coefficient, R2 > 0.990) and a negative control. The cycle threshold (CT) was limited to 40, and the starting copy number of the target gene was calculated by comparing the CT value with the standard curve [28,29].

2.4. Bacterial Community Structure Analysis

After the DNA samples were extracted, the V3-V4 highly variable region of the 16S rRNA gene was amplified via the primers 314F (5′-CCTAYGGGRBGCASCAG-3′) and 806R (5′-GGACTACNNGGGGTATCTAAT-3′) to analyze the bacterial community composition of the samples collected. PCR amplification was performed via an ABI Gene Amp® 9700 PCR instrument (Applied Biosystems, Waltham, MA, USA), and the specific PCR system and operating conditions were based on the parameters and procedures provided in previous studies [30,31]. The PCR was carried out in a 25 µL system composed of 2.5 µL of buffer (10×), 0.8 µL of Primer F (10 µmol/L), 0.8 µL of Primer R (10 µmol/L), 2.5 µL of dNTPs (2 mmol/L), 2.0 µL of MgSO4 (25 mmol/L), 1.0 µL of KOD Plus (1.0 U/µL), 14.9 µL of PCR grade water, and 0.5 µL of template.
All PCR amplification samples were analyzed in triplicate. The amplification products were purified with the help of SigmaAldrich Nucleic Acid Purification Kit (St. Louis, MO, USA), and the genes were quantified via the StepOnePlus™ real-time fluorescence PCR detection system [32]. The 16S rRNA genes of the bacteria in the samples were sequenced via high-throughput sequencing via the Illumina HiSeq 2500 sequencing platform and analyzed via macrogenomics [33].
Clean reads were quality controlled via Trimmomatic v0.33 software on the analytics platform of Biomarker Technologies (Beijing, China). The primer sequences were then identified and removed via Cutadapt 1.9.1 software. Paired-ended sequences were spliced and filtered for each sample via Usearch v10 software. Chimeric sequences were identified and removed via UCHIME v4.2 software to obtain a dataset of valid sequences. All sequences were clustered via USEARCH 7.1 software and classified into operational taxonomic units (OTUs) on the basis of 97% sequence similarity.

2.5. Data Analysis and Statistical Analysis

Origin 2023 Pro was used to present gene abundance. The BMK microbial diversity analysis platform (www.biocloud.net) was used to create Venn diagrams, species abundance heatmaps, similarity dendrograms, and abundance histograms. Spearman correlation analyses, Mantel test analysis, and bubble plots were generated via the R packages “ggplot2,” “corrplot,” and “ggcor” in R version 3.5, respectively. Statistical significance for all analyses was determined by setting the significance level at a p-value less than 0.05 via an independent samples t-test.

3. Results

3.1. Changes in 16S rRNA, intI1, and tetA Genes After Exogenous Input of Tet and LMB

The absolute abundances of the 16S rRNA, intI1, and tetA genes in the sediment samples and lake water samples after 60 days of incubation are shown in Figure 1. The absolute abundances of the them in sediment samples were an order of magnitude greater than those in lake water samples because sediment provides favorable conditions for microorganism growth and protection from sunlight inactivation and protozoan grazing [34]. Moreover, sediments with high levels of particles (clay and silt) can bind DNA and protect it from degradation [35].
The absolute abundance of the 16S rRNA in the sediment samples and lake water samples clearly increased significantly compared with that in the control samples after the dosing of Tet or LMB, respectively (Figure 1a,b). The abundance of the 16S rRNA after the addition of Tet (1.05 × 109 copies/mL in sediment and 5.73 × 107 copies/mL in water) was greater than that after the addition of LMB (8.56 × 108 copies/mL in sediment and 3.43 × 106 copies/mL in water). And the amount of added Tet was less than one-tenth of the amount of added LMB. Therefore, the addition of Tet had a more significant effect on the 16S rRNA of bacterial communities in the environment. When Tet and LMB were added simultaneously, they did not have an additive effect. In contrast, compared with those in the groups in which only Tet or LMB was added, the amount of 16S rRNA detected was lower and did not significantly differ from that in the control groups, indicating that Tet and LMB have antagonistic effects.
As shown in Figure 1c–f, after the addition of Tet, the abundances of intI1 increased from 2.84 × 106 to 4.38 × 106 copies/mL in sediment (p < 0.01) and from 0.75 × 105 to 5.67 × 105 copies/mL in water (p < 0.001). The abundances of tetA increased from 2.03 × 105 to 3.23 × 105 copies/mL in sediment (p < 0.01) and from 0.65 × 104 to 1.64 × 104 copies/mL in water (p < 0.001). After the addition of LMB, the abundance of intI1 and tetA increased to 3.37 × 106 and 2.95 × 105 in sediment and increased to 2.75 × 105 and 1.35 × 104 in the water (p < 0.01, except intI1 in sediment). Nevertheless, when Tet and LMB were added simultaneously, not only was there no significant difference in the abundance of 16S rRNA between the control groups but also there was no significant difference in the abundance of intI1 and tetA compared with the control groups.

3.2. Changes in the Bacterial Community and Bacterial Functions After the Addition of Exogenous Tet or LMB

The structure of the bacterial community at the phylum level is illustrated in Figure 2. Proteobacteria dominated in all the sediment samples and lake water samples (34.19–65.50%). Desulfobacterota, Bacteroidota, Acidobacteriotaa, and Actinobacteriota also account for a large proportion of bacteria. After 60 days of incubation, the results revealed that the Tet or LMB dosing affected the community structure at the phylum level (Figure 2a). For example, in sediment samples, the relative abundance of Proteobacteria increased from 34.19% to 40.23% after the addition of LMB or the addition of a mixture of Tet and LMB compared with the control. However, the change in the abundance of Proteobacteria was not significant after the addition of Tet, ranging from 34.19% to 35.16%. Correspondingly, the relative abundance of Desulfobacterota decreased from 19.33% to 18.32% after the LMB dosing compared with the control and decreased significantly from 19.33% to 14.49% after the addition of a mixture of Tet and LMB compared with the control, while the relative abundance of Desulfobacterota did not change significantly from 19.33% to 19.06% after the addition of Tet. In the water samples, the proportion of Proteobacteria was greater than that in the sediment samples and exceeded 50%. There was a small decrease in the relative abundance of Proteobacteria from 51.79% to 50.41% after the addition of LMB compared with the control, while the relative abundance of Proteobacteria increased significantly from 51.79% to 65.50% after the addition of Tet and increased from 51.79% to 59.28% after the addition of a mixture of Tet and LMB.
Figure 2b,c show the similarity and overlap of the bacterial communities at the genus level in the sediment and water samples. Among the sediment samples, the number of genera in the SLMB group was the greatest, at 299; the next highest number was 289 in the SCon group, while the number in the STet group was the lowest, at 269 (Figure 2b). Among the water samples, the number of genera in the WCon group was the greatest at 322, whereas the WTet group and WLMB group presented the lowest number of 308 (Figure 2c).
The composition of the bacterial community at the genus level in the different samples is shown in Figure 3a. In the sediment samples, the bacterial community in the control group was dominated by Anaeromyxobacter, unclassified_Saccharimonadales, and unclassified_Xanthomonadaceae. After the addition of Tet, LMB, or both, the abundance of Anaeromyxobacter decreased. Specifically, after the addition of Tet or LMB, respectively, the abundance of unclassified_Xanthomonadaceae clearly decreased, whereas after they were added simultaneously, the abundance of unclassified_Xanthomonadaceae did not decrease, possibly because the interaction between LMB and Tet had an inhibitory effect on each material. In the lake water samples, the major genera were unclassified_Saccharimonadales and unclassified_Xanthomonadaceae. When Tet, LMB, or both were added, their abundances decreased. Similarly, in the water samples and sediment samples, after the addition of Tet and/or LMB, the proportions of other bacteria increased, indicating that they interfered with the overall survival of the originally dominant community and were conducive to the overall survival of the originally weak community. In addition, when LMB was added, the abundance of Tolumonas in both the water and sediment samples increased significantly, indicating that LMB promoted the growth of these bacterial genera. The UPGMA cluster analysis based on the unweighted UniFrac distance revealed that the eight samples were grouped into five classes (Figure 3a), where cluster I included WTetLMB and STetLMB, cluster II included WTet and STet, cluster III included SLMB and SCon, cluster IV included WLMB, and cluster V included WCon. The results showed that the addition of Tet or the addition of Tet and LMB caused the bacterial genera in the sediment samples and water samples to tend to be similar.
To analyze the effects of the Tet and LMB inputs on bacterial community functions, BugBase phenotypic predictions of the bacterial community in our samples were analyzed, and functional changes at the metabolic pathway and genus levels in bacteria were predicted, as shown in Figure 3b. After 60 days of incubation, in the sediment samples, compared with those in the SCon group, when Tet or LMB was dosed, the function of the Form_Biofilms was enhanced. In contrast, in the water samples, compared with those in the WCon group, after Tet or LMB was dosed, the function of the Forms_Biofilms weakened, indicating that these two substances had different functions in the sediment and water. In the water samples, the addition of LMB increased the Potential_Pathogenic function, and the pathogenicity of the bacteria increased. In contrast, the addition of Tet weakened the Potentially_Pathogenic function, indicating that Tet had antibacterial effects. This effect was not obvious in the sediments, possibly because of the protective effect of the sediments on bacteria. In addition to the Potentially_Pathogenic function, the addition of Tet altered multiple functions of bacteria in the water samples, increasing Faculatively_Anaerobic, Stress_Tolerant, Aerobic, and Gram_Positive functions while decreasing the Gram_Negative function. Notably, the samples with both LMB and Tet added were more similar to the control samples in the sediment and water in terms of the predicted bacterial community function (the connecting line at the top of Figure 3b). As previously indicated, the interactions between LMB and Tet have inhibitory effects on each material.

3.3. Correlations Between ARGs and the Bacterial Community

The dominant bacteria for constructing community networks were identified to explore the interactions between the bacterial community at the genus level (Figure 4a). The nodes with strong correlations included unclassified_Bacteria, Geothrix, Geothermobacter, Anaeromyxobacter, C39, OLB12, unclassified_Cyanobacteriales, Ellin6067, and unclassified_Geobacteraceae. Among them, C39 had a negative correlation with all the other eight genera; unclassified_Bacteria, Geothermobacter, Anaeromyxobacter, OLB12, Ellin6067, and unclassified_Geobacteraceae had positive correlations with all the other genera except C39; and Geothrix and unclassified_Cyanobacteriales had positive correlations with all the other genera except C39.
To explore the relationships between 16S rRNA, intI1, and tetA and the bacterial communities, a correlation analysis and Mantel tests were performed (Figure 4b). The correlation relationships between the bacterial genera were the same as those shown in Figure 4a. For example, C39 was negatively correlated with other genera. With respect to the relationships between bacterial genera and nucleic acids, 16S rRNA was significantly correlated with unclassified_Geobacteraceae, Geothrix, unclassified_Bacteria, Flavobacterium, Anaeromyxobacter, and Geothermobacter (p < 0.05). The intI1 gene was positively correlated with Geothrix, unclassified_Bacteria, Flavobacterium, Anaeromyxobacter, and Geothermobacter (p < 0.05), indicating that these genes may be potential hosts for intI1. The tetA gene was positively correlated with (p < 0.05) unclassified_Geobacteraceae, Geothrix, unclassified_Bacteria, Flavobacterium, Anaeromyxobacter, and Geothermobacter.

4. Discussion

4.1. Effect of Tet and/or LMB on 16S rRNA, intI1, and tetA Genes

The results demonstrate that both exogenous Tet and LMB significantly impacted the microbial ecosystem and ARGs in the simulated lake environment. The addition of Tet or LMB individually led to an increase in the abundance of 16S rRNA, intI1, and tetA genes in both sediment and water samples (Figure 1). The stimulatory effect of Tet was more pronounced than that of LMB, despite the lower dosage of Tet, suggesting a strong selective pressure favoring bacterial proliferation or survival under antibiotic stress. Previous studies have shown that antibiotics may exert selective pressure on environmental microorganisms and effectively promote the dissemination of ARGs [36,37]. However, studies have shown that bentonite reduced the abundance of ARGs during the composting process, possibly due to the combined effect of the high-temperature killing of bacteria in composting and the absorption ability of bentonite [38].
The increase in the intI1 abundance under the Tet stress aligns with its known role in facilitating the HGT of ARGs via MGEs under selective pressure [27]. The concurrent rise in the tetA abundance confirms the specific induction of Tet resistance under Tet pressure, and intI1 is positively correlated with Tet resistance genes [39]. While tetA was not identified as a gene cassette within intI1, it co-occurred with intI1 on conjugative plasmids that enabled their co-transfer into recipient bacteria [40]. The increase in the abundance of 16S rRNA when Tet was added may be due to the transfer and expression of ARGs among bacteria under Tet stress. In fact, the spread of Tet resistance genes via the conjugation among bacteria and pathogens (including E. coli, Acinetobacter, Aeromonas, Chryseobacterium, Pseudomonas, and Serratia) has been reported in urban watersheds, and intI1 is largely attributed to the dissemination of ARGs through HGT [41,42]. The increase in 16S rRNA, intI1, and tetA genes upon the LMB addition alone may be attributed to the physical properties of bentonite. Similarly to natural sediments, LMB can create protective microhabitats that shield bacteria from adverse conditions [43]. Under the protection of LMB, ARGs could be transferred between bacteria.
Notably, a critical finding is the antagonistic interaction observed when Tet and LMB were added together. Their combined application negated the individual increases in 16S rRNA, intI1, and tetA gene abundances observed, resulting in levels statistically indistinguishable from the control (Figure 1). The previous literature demonstrated the adsorption capacity of both natural and modified bentonites for tetracycline antibiotics [44,45], which suggests that LMB adsorbed Tet, thereby mitigating its bioavailability and the consequent selective pressure.

4.2. Effect of Tet and/or LMB on Bacterial Community and Bacterial Functions

The analysis of the bacterial community structure revealed distinct effects of Tet and LMB, often differing between sediment and water compartments. Proteobacteria dominated across all samples, which is consistent with findings in various aquatic sediments. Zhang et al. [46] reported that the dominant bacteria in four marine sediment samples were Bacteroidota, Actinobacteriota, Desulfobacterota, Myxococcota, and Firmicute. Lin et al. [47] reported that the percentages of Proteobacteria and Actinobacteria were 21.99–27.32% and 18.10–23.23%, respectively. The LMB addition increased the relative abundance of Proteobacteria in sediments (from 34.19% to 40.23%) and correspondingly decreased the Desulfobacterota abundance. In contrast, Tet alone had negligible effects on these phyla in the sediment (Figure 2a). This disparity likely arises because the added LMB primarily settled into the sediment, exerting a more direct physicochemical influence (e.g., altering microenvironments or phosphorus speciation) [19,20], whereas the effect of Tet may have been partially masked or attenuated by the sediment matrix [44,45]. In the water column, Tet boosted the Proteobacteria abundance (from 51.79% to 65.50%), while LMB caused a minor decrease (to 50.41%) (Figure 2a). This contrasting effect further highlights the compartment-specific actions, possibly related to the LMB precipitation reducing its direct interaction with bacteria. Conversely, Tet in the water column is not shielded by other substances, making it easier to exert an impact on bacteria.
The genus-level analysis showed that both Tet and LMB interfered with the originally dominant communities (e.g., reducing unclassified_Saccharimonadales, unclassified_Xanthomonadaceae) and favored the proliferation of initially less abundant taxa (Figure 3a). Tet consistently reduced the bacterial genus richness in both the sediment (SCon: 289 vs. STet: 269) and water (WCon: 322 vs. WTet: 308) (Figure 2b,c), which is indicative of its inhibitory or selective action against susceptible bacteria. LMB increased the genus richness in the sediment (SLMB: 299), potentially by creating organic-matter-rich microenvironments conducive to microbial diversity [48], but decreased it in water (WLMB: 308), possibly due to coprecipitation effects [49,50]. The cluster analysis indicated that the Tet addition (alone or with LMB) drove the convergence in the bacterial community composition between sediment and water samples (Figure 3a), possibly due to the selective effect of antibiotics.
Functional predictions revealed differential effects of Tet and LMB on bacterial phenotypes, also varying by compartment (Figure 3b). LMB increased the potential pathogenicity of bacteria in water but decreased biofilm formation. Tet reduced the potential pathogenicity and biofilm formation in water because of its antibacterial effect [51]. In the sediment, both compounds enhanced the biofilm-forming capability. Notably, samples receiving both Tet and LMB exhibited bacterial functional profiles much closer to the controls than samples receiving either alone (Figure 3b), reinforcing the notion that the LMB adsorption counteracts the functional perturbations induced by Tet.

4.3. Potential Hosts of ARGs

Correlation and Mantel test analyses identified specific bacterial genera as potential hosts for the studied ARGs (Figure 4). The intI1 gene showed significant positive correlations with Geothrix, Flavobacterium, Anaeromyxobacter, and Geothermobacter. The tetA gene correlated positively with unclassified_Geobacteraceae, Geothrix, Flavobacterium, Anaeromyxobacter, and Geothermobacter, suggesting these genera could be the potential hosts of the ARGs. Similarly, Ding et al. and Li et al. found Flavobacteriales as one of the potential hosts of ARGs [52,53]. Xu et al. found Anaeromyxobacter as one of the potential hosts of ARGs [54]. Zhang et al. also found that Anaeromyxobacter is one of the potential hosts of tetA [55]. The overlap in potential hosts (Geothrix, Flavobacterium, Anaeromyxobacter, Geothermobacter) for both intI1 and tetA is consistent with the recognized role of intI1 in potentiating the spread of ARGs like tetA via the HGT among diverse microbes in aquatic environments [56,57,58,59]. The correlation of the 16S rRNA abundance with these same genera further supports their ecological relevance under the experimental conditions.

5. Conclusions

The addition of Tet or LMB to the lake water and sediment samples resulted in the spread of ARGs in the samples and a change in the bacterial community. Tet or LMB could increase the abundance of intI1 and tetA. However, LMB inhibited the spread of intI1 and tetA in the Tet-contaminated samples. Proteobacteria, Desulfobacterota, Bacteroidota, and Acidobacteriota were the dominant bacteria in the samples, and Tet or LMB had different effects on the water and sediment samples. In the sediment samples, LMB significantly increased the relative abundance of Proteobacteria, whereas after the addition of Tet, the change in the abundance of Proteobacteria was not significant. In the water samples, the changes in the abundance of Proteobacteria caused by LMB and Tet were opposite. This might be because LMB easily accumulated in the sediments, while the effect of Tet in the sediments was concealed. In addition, Tet and LMB caused changes in the number of bacterial genera and community functions in the samples. Like the spread of ARGs, whether in terms of community structures or functions, LMB would inhibit the impact produced by Tet. According to Mantel tests, unclassified_Geobacteraceae, Geothrix, Flavobacterium, Anaeromyxobacter, and Geothermobacter could be potential hosts for intI1 and tetA. The results of this study show that LMB could inhibit the spread of ARGs and changes in microbial communities caused by Tet in sediment and water, indicating that, in addition to being a phosphorus removal agent, LMB may also play a role in alleviating antibiotic pollution, which is worthy of further research.

Author Contributions

Investigation, W.W.; writing—original draft preparation, W.W.; writing—review and editing, S.L. and P.Z.; methodology, S.L.; formal analysis, S.L.; visualization, S.Z.; data curation, S.Z.; resources, D.W.; conceptualization, D.W.; supervision, X.X.; project administration, P.Z.; funding acquisition, W.W. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the innovation team project of the Nanjing Institute of Environmental Sciences, Ministry of Ecology and Environment (ZX2023QT017) and the Open Fund of the State Key Laboratory of Lake and Watershed Science for Water Security (2024SKL006).

Data Availability Statement

The data presented in this study are available upon request from the corresponding author.

Acknowledgments

The authors would like to acknowledge the postgraduate studies of Nanjing University of Information Science and Technology.

Conflicts of Interest

The authors declare no conflicts of interest.

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Water 17 02188 g001
Figure 1. Absolute abundance of 16S rRNA, intI1, and tetA in sediment samples and water samples. (a) Absolute abundance of 16S rRNA in sediment samples; (b) Absolute abundance of 16S rRNA in water samples; (c) Absolute abundance of intI1 in sediment samples; (d) Absolute abundance of intI1 in waterr samples; (e) Absolute abundance of tetA in sediment samples; (f) Absolute abundance of tetA in waterr samples (** p < 0.01, and *** p < 0.001).
Figure 1. Absolute abundance of 16S rRNA, intI1, and tetA in sediment samples and water samples. (a) Absolute abundance of 16S rRNA in sediment samples; (b) Absolute abundance of 16S rRNA in water samples; (c) Absolute abundance of intI1 in sediment samples; (d) Absolute abundance of intI1 in waterr samples; (e) Absolute abundance of tetA in sediment samples; (f) Absolute abundance of tetA in waterr samples (** p < 0.01, and *** p < 0.001).
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Figure 2. The bacterial community structure of sediment samples and lake water samples. (a) Species abundance bars of lake water samples and sediment samples at the phylum level. (b) Venn diagrams of sediment samples at the genus level. (c) Venn diagrams of lake water samples at the genus level.
Figure 2. The bacterial community structure of sediment samples and lake water samples. (a) Species abundance bars of lake water samples and sediment samples at the phylum level. (b) Venn diagrams of sediment samples at the genus level. (c) Venn diagrams of lake water samples at the genus level.
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Figure 3. Bacterial similarity and bacterial community functions of sediment samples and lake water samples. (a) Similarity dendrograms of bacterial genus-level communities based on UPGMA clustering analysis of unweighted UniFrac distances. (b) Functional thermograms of bacterial communities in lake water samples and sediment samples.
Figure 3. Bacterial similarity and bacterial community functions of sediment samples and lake water samples. (a) Similarity dendrograms of bacterial genus-level communities based on UPGMA clustering analysis of unweighted UniFrac distances. (b) Functional thermograms of bacterial communities in lake water samples and sediment samples.
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Figure 4. The correlation analysis. (a) The correlation network analysis at the phylum level. Bacterial relationship pairs with Spearman correlation coefficients greater than 0.1 between the relative abundances of bacteria and a correlation of p < 0.05 were selected. The node size indicates the relative abundance of bacteria, the red line indicates a significant positive correlation, and the green line indicates a significant negative correlation. (b) The correlation analysis (upper right diagram) and Mantel test (bottom left diagram) showing the correlations among 16S rRNA, intI1, tetA, and the dominant genera.
Figure 4. The correlation analysis. (a) The correlation network analysis at the phylum level. Bacterial relationship pairs with Spearman correlation coefficients greater than 0.1 between the relative abundances of bacteria and a correlation of p < 0.05 were selected. The node size indicates the relative abundance of bacteria, the red line indicates a significant positive correlation, and the green line indicates a significant negative correlation. (b) The correlation analysis (upper right diagram) and Mantel test (bottom left diagram) showing the correlations among 16S rRNA, intI1, tetA, and the dominant genera.
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Wang, W.; Liang, S.; Zhang, S.; Wei, D.; Xu, X.; Zhang, P. Effects of Lanthanum-Modified Bentonite on Antibiotic Resistance Genes and Bacterial Communities in Tetracycline-Contaminated Water Environments. Water 2025, 17, 2188. https://doi.org/10.3390/w17152188

AMA Style

Wang W, Liang S, Zhang S, Wei D, Xu X, Zhang P. Effects of Lanthanum-Modified Bentonite on Antibiotic Resistance Genes and Bacterial Communities in Tetracycline-Contaminated Water Environments. Water. 2025; 17(15):2188. https://doi.org/10.3390/w17152188

Chicago/Turabian Style

Wang, Wanzhong, Sijia Liang, Shuai Zhang, Daming Wei, Xueting Xu, and Peng Zhang. 2025. "Effects of Lanthanum-Modified Bentonite on Antibiotic Resistance Genes and Bacterial Communities in Tetracycline-Contaminated Water Environments" Water 17, no. 15: 2188. https://doi.org/10.3390/w17152188

APA Style

Wang, W., Liang, S., Zhang, S., Wei, D., Xu, X., & Zhang, P. (2025). Effects of Lanthanum-Modified Bentonite on Antibiotic Resistance Genes and Bacterial Communities in Tetracycline-Contaminated Water Environments. Water, 17(15), 2188. https://doi.org/10.3390/w17152188

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