Pseudomonas sp. ZXY-1, a newly isolated and highly efficient atrazine-degrading bacterium, and optimization of biodegradation using response surface methodology

The Degradation Characteristics and Soil Remediation Capabilities of the Butachlor-Degrading Strain DC-1

Butachlor is a widely utilized acetamide herbicide noted for its systemic selectivity against pre-emergence grass weeds. Butachlor has negative effects on organisms and the environment, so it is necessary to screen degradation strains. In this investigation, Bacillus cereus strain DC-1 was isolated from soil persistently exposed to butachlor. Through rigorous single-factor and response surface analyses, strain DC-1 exhibited a notable 87.06% degradation efficiency under optimized conditions where the temperature was 32.89 °C, pH was 7.29, and inoculum concentration was 5.18%. It was further hypothesized by LC-MS that the degradation pathway of butachlor by strain DC-1 might be as follows: butachlor undergoes initial deoxygenation catalyzed by dioxygenases to form 2-chloro-N-(2,6-diethylphenyl)-N-methylacetamide, followed by N-demethylation yielding 2-chloro-N-(2,6-diethylphenyl) acetamide, and culminating in conversion to 2,6-diethylphenol. In addition, bioremediation experiments of butachlor-contaminated soil were conducted. The results show that strain DC-1 could degradable 99.23% of butachlor (100 mg·kg-1) from the soil within 12 d, and soil sucrase, cellulase, and urease activities are promoted by the bacteria. And through high-throughput sequencing, it was concluded that the strain DC-1 was able to influence the relative abundance of certain bacteria in the soil, and make the microbial community in the soil develop in a more stable and beneficial direction. DC-1 thus represents a valuable resource in the realm of butachlor degradation due to its robust efficacy, favorable characteristics, and ecological restorative capabilities, underscoring its promising role in the bioremediation of butachlor-contaminated soils.

Mitigating risks from atrazine drift to soybeans through foliar pre-spraying with a degrading bacterium

Herbicides play a crucial role in managing weeds in agriculture, ensuring the productivity and quality of crops. However, herbicide drift poses a significant threat to sensitive plants, necessitating the consideration of ecosystem-based solutions to address this issue. In this study, foliar pre-spraying of atrazine-degrading Paenarthrobacter sp. AT5 was proposed as a new approach to mitigate the risks associated with atrazine drift on soybeans. Exposure to atrazine reduced chlorophyll levels and disturbed the antioxidant system and metabolic processes in soybean leaves, ultimately causing leaves to turn yellow. However, by pre-spraying, strain AT5 successfully colonized the surface of soybean leaves and mitigated the harmful effects of atrazine. This was achieved by slowing down atrazine absorption, expediting its reduction (half-life decreased from 2.22 d to 0.86 d), altering its degradation pathway (enhancing hydroxylation while weakening alkylation), and enhancing the interaction within phyllosphere bacteria communities. This study introduces a new approach that is both eco-friendly and user-friendly for reducing the risks of herbicide drift to sensitive crops, hence promoting the development of mixed cropping.

Physiological and transcriptomic changes drive robust responses in Paenarthrobacter sp. AT5 to co-exposure of sulfamethoxazole and atrazine

Agricultural waterways are often contaminated with herbicide and antibiotic residues due to the widespread use of these chemicals in modern agriculture. The search for resistant bacterial strains that can adapt to and degrade these mixed contaminants is essential for effective in situ bioremediation. Herein, by integrating chemical and transcriptomic analyses, we shed light on mechanisms through which Paenarthrobacter sp. AT5, a well-known atrazine-degrading bacterial strain, can adapt to sulfamethoxazole (SMX) while degrading atrazine. When exposed to SMX and/or atrazine, strain AT5 increased the production of extracellular polymeric substances and reactive oxygen species, as well as the rate of activity of antioxidant enzymes. Atrazine and SMX, either alone or combined, increased the expression of genes involved in antioxidant responses, multidrug resistance, DNA repair, and membrane transport of lipopolysaccharides. Unlike atrazine alone, co-exposure with SMX reduced the expression of genes encoding enzymes involved in the lower part of the atrazine degradation pathway. Overall, these findings emphasize the complexity of bacterial adaptation to mixed herbicide and antibiotic residues and highlight the potential of strain AT5 in bioremediation efforts.

Pseudomonas aeruginosa based concurrent degradation of beta-cypermethrin and metabolite 3-phenoxybenzaldehyde, and its bioremediation efficacy in contaminated soils

Beta-cypermethrin is one of the widely used pyrethroid insecticides, and problems associated with the accumulation of its residues have aroused public attention. Thus, there is an urgent need to effectively remove the beta-cypermethrin that is present in the environment. Biodegradation is considered a cost-effective and environmentally friendly method for removing pesticide residues. However, the beta-cypermethrin-degrading microbes that are currently available are not optimal. In this study, Pseudomonas aeruginosa PAO1 was capable of efficiently degrading beta-cypermethrin and its major metabolite 3-phenoxybenzaldehyde in water/soil environments. Strain PAO1 could remove 91.4% of beta-cypermethrin (50 mg/L) in mineral salt medium within 120 h. At the same time, it also possesses a significant ability to metabolize 3-phenoxybenzaldehyde-a toxic intermediate of beta-cypermethrin. The Andrews equation showed that the maximum substrate utilization concentrations of beta-cypermethrin and 3-phenoxybenzaldehyde by PAO1 were 65.3558 and 49.6808 mg/L, respectively. Box-Behnken design-based response surface methodology revealed optimum conditions for the PAO1 strain-based degradation of beta-cypermethrin as temperature 30.6 °C, pH 7.7, and 0.2 g/L inoculum size. The results of soil remediation experiments showed that indigenous micro-organisms helped to promote the biodegradation of beta-cypermethrin in soil, and beta-cypermethrin half-life in non-sterilized soil was 6.84 days. The bacterium transformed beta-cypermethrin to produce five possible metabolites, including 3-phenoxybenzyl alcohol, methyl 2-(4-hydroxyphenoxy)benzoate, diisobutyl phthalate, 3,5-dimethoxyphenol, and 2,2-dimethyl-1-(4-phenoxyphenyl)propanone. Among them, methyl 2-(4-hydroxyphenoxy)benzoate and 3,5-dimethoxyphenol were first identified as the intermediate products during the beta-cypermethrin degradation. In addition, we propose a degradation pathway for beta-cypermethrin that is metabolized by strain PAO1. Beta-cypermethrin could be biotransformed firstly by hydrolysis of its carboxylester linkage, followed by cleavage of the diaryl bond and subsequent metabolism. Based on the above results, P. aeruginosa PAO1 could be a potent candidate for the beta-cypermethrin-contaminated environmental bioremediation.

Core bacteria carrying the genes associated with the degradation of atrazine in different soils

Atrazine residues can pose serious threats to soil ecology and human health. Currently, the underlying relationship between soil microbial communities and the degradation genes associated with atrazine degradation remains unclear. In this study, the degradation characteristics of atrazine was investigated in ten different soil types. Further, diversity and abundance of degradation genes and succession of the bacterial community were also studied. The degradation of 10 mg/kg atrazine in different soil types exhibited an initial rapid trend followed by a gradual slowdown, adhering to the first-order kinetic equation. Atrazine significantly increased the absolute abundance of atz degradation genes. The increase in the absolute abundance of atzC gene was the largest, whereas that of atzA gene was the smallest, and the trzD gene was only detected in the Binzhou loam soil. Co-occurrence network analysis showed that the number of potential bacterial hosts of atzC was the highest compared with the other atz genes. Atrazine also altered the structural composition of the soil microbial community. The relative abundances of Ochrobactrum, Nocardiopsis, Lactobacillus, and Brevibacterium was increased in the atrazine-treated soils, while those of Conexibate, Solirubacter, and Micromonospora was decreased significantly compared with the control. Additionally, four atrazine-degrading bacterial strains Rhizobium AT1, Stenotrophomonas AT2, Brevibacterium AT3, and Bacillus AT4 were isolated from the atrazine-treated soils. After 14 d for inoculation, their degradation rate for 10 mg/L atrazine ranged from 17.56 % to 30.55 %. Moreover, the relative abundances of the bacterial genera, including these four isolates, in the atrazine-treated soil were significantly higher than those in the control, indicating that they were involved in the synergistic degradation of atrazine in the soil. This study revealed the degradation characteristics of atrazine, distribution of degradation genes, and succession of microbial communities, and explored the internal relationship between microbial community structure and atrazine degradation mechanisms in different soil types.

Investigation of the Persistence, Toxicological Effects, and Ecological Issues of S-Triazine Herbicides and Their Biodegradation Using Emerging Technologies: A Review

S-triazines are a group of herbicides that are extensively applied to control broadleaf weeds and grasses in agricultural production. They are mainly taken up through plant roots and are transformed by xylem tissues throughout the plant system. They are highly persistent and have a long half-life in the environment. Due to imprudent use, their toxic residues have enormously increased in the last few years and are frequently detected in food commodities, which causes chronic diseases in humans and mammals. However, for the safety of the environment and the diversity of living organisms, the removal of s-triazine herbicides has received widespread attention. In this review, the degradation of s-triazine herbicides and their intermediates by indigenous microbial species, genes, enzymes, plants, and nanoparticles are systematically investigated. The hydrolytic degradation of substituents on the s-triazine ring is catalyzed by enzymes from the amidohydrolase superfamily and yields cyanuric acid as an intermediate. Cyanuric acid is further metabolized into ammonia and carbon dioxide. Microbial-free cells efficiently degrade s-triazine herbicides in laboratory as well as field trials. Additionally, the combinatorial approach of nanomaterials with indigenous microbes has vast potential and considered sustainable for removing toxic residues in the agroecosystem. Due to their smaller size and unique properties, they are equally distributed in sediments, soil, water bodies, and even small crevices. Finally, this paper highlights the implementation of bioinformatics and molecular tools, which provide a myriad of new methods to monitor the biodegradation of s-triazine herbicides and help to identify the diverse number of microbial communities that actively participate in the biodegradation process.

Variations in the Behaviour, Survival, Haematology, and Biochemistry of Ctenopharyngodon idella (Grass Carp) After Exposure to Commercial Grade Atrazine

The current study assessed the harmful effects of Atrazine (ATZ) herbicide on haematology and biochemistry of the freshwater fish Ctenopharyngodon idella, a commercially significant fish in Pakistan. C. idella (13 ± 8.4 cm; 132 ± 5.6 g) was exposed to graded levels of ATZ, and its 96-hour LC₅₀ value at 25°C was calculated to be 150.5 µl/L. After exposure to ATZ, fish displayed rapid movements, a loss of balance in position and equilibrium, anxious swimming patterns, colour changes, and increased mucous production. The MCHC, MCH, RBCs, and Hb in C. idella decreased significantly (P < 0.05), whereas the MCV, Ht, and WBCs were significantly increased (P < 0.05). At different time intervals (24, 48, 72, and 96 h) following ATZ administration (50, 100, 150, and 200 µl/L), biochemical analysis significantly decreased (P < 0.05) triglyceride, total protein, cholesterol, and albumin levels, whereas glucose levels significantly increased (P < 0.05). We concluded that ATZ is toxic to C. idella, altering their haematology and blood biochemistry even after only a brief exposure.

Treatment of atrazine-containing wastewater by algae-bacteria consortia: Signal transmission and metabolic mechanism

Atrazine is a toxic endocrine disruptor. Biological treatment methods are considered to be effective. In the present study, a modified version of the algae-bacteria consortia (ABC) was established and a control was simultaneously set up to investigate the synergistic relationship between bacteria and algae and the mechanism by which atrazine is metabolized by those microorganisms. The total nitrogen (TN) removal efficiency of the ABC reached 89.24% and the atrazine concentration was reduced to below the level recommended by the Environment Protection Agency (EPA) regulatory standards within 25 days. The protein signal released from the extracellular polymeric substances (EPS) secreted by the microorganisms triggered the resistance mechanism of the algae, and the conversion of humic acid to fulvic acid and electron transfer constituted the synergistic mechanism between the bacteria and algae. The mechanism by which atrazine is metabolized by the ABC mainly consists of hydrogen bonding, H-pi interactions, and cation exchange with atzA for hydrolysis, followed by a reaction with atzC for decomposition to non-toxic cyanuric acid. Proteobacteria was the dominant phylum for bacterial community evolution under atrazine stress, and the analysis revealed that the removal of atrazine within the ABC was mainly dependent on the proportion of Proteobacteria and the expression of degradation genes (p < 0.01). EPS played a major role in the removal of atrazine within the single bacteria group (p < 0.01).

Responses of straw foam-based aerobic granular sludge to atrazine: Insights from metagenomics and microbial community variations

Atrazine (ATZ) has caused serious environmental pollution, but the biodegradation of ATZ is relatively slow and inefficient. Herein, a straw foam-based aerobic granular sludge (SF-AGS) was developed, the spatially ordered architectures of which could greatly improve the drug tolerance and biodegradation efficiency of ATZ. The results showed that, in the presence of ATZ, chemical oxygen demand (COD), ammonium nitrogen (NH₄⁺-N), total phosphorus (TP), and total nitrogen (TN) were effectively removed within 6 h, and the removal efficiencies were as high as 93.37%, 85.33%, 84.7%, and 70%, respectively. Furthermore, ATZ stimulated microbial consortia to secrete three times more extracellular polymers compared to without ATZ. Illumina MiSeq sequencing results showed that bacterial diversity and richness decreased, leading to significant changes in microbial population structure and composition. ATZ-resistant bacteria including Proteobacteria, Actinobacteria, and Burkholderia laid the biological basis for the stability of aerobic particles, efficient removal of pollutants, and degradation of ATZ. The study demonstrated that SF-AGS is feasible for ATZ-laden low-strength wastewater treatment.

Impact of atrazine on soil microbial properties: A meta-analysis

Atrazine is a biotoxic long-residing herbicide whose toxic effects on soil microorganisms have attracted widespread attention. However, previous studies on the effects of atrazine on soil microorganisms have yielded highly variable results. Therefore, a meta-analysis using a database containing 1141 data points from 39 peer-reviewed papers was conducted to illustrate the response of soil microorganisms to the application of atrazine. The results showed that the application of atrazine significantly increased soil microbial biomass and respiration by 8.9% and 26.77%, respectively, and decreased soil microbial diversity and enzyme activity by 4.87% and 24.04%, respectively. In addition, mixed-effect models were used to explain the influence of moderator variables, including water holding capacity, temperature, pH, organic carbon content, atrazine concentration, duration, and soil texture, on the results to help account for inconsistent conclusions. It was found that soil microbial biomass was significantly positively correlated with temperature, organic carbon content, atrazine concentration, clay content and silt content, while it was negatively correlated with pH and sand content. Soil microbial respiration was negatively correlated with pH and positively correlated with atrazine concentration. Soil microbial diversity was positively correlated with water holding capacity, pH, silt content and sand content, and negatively correlated with organic carbon content and clay content. Soil enzyme activity, the indicator that showed the largest decrease after atrazine application, was significantly positively correlated with water holding capacity, temperature, organic carbon content, and herbicide concentration; it was negatively correlated with soil pH. On the basis of these analysis results, we recommend that atrazine should not be allowed to persist in alkaline sandy soil for long periods of time, as this can result in atrazine having a significant negative impact on soil microorganisms.

Characterization and novel pathway of atrazine catabolism by Agrobacterium rhizogenes AT13 and its potential for environmental bioremediation

Agrobacterium rhizogenes AT13, a novel bacterial strain that was isolated from contaminated soil, could utilize atrazine as the sole nitrogen, thereby degrading it. Optimization of the degradation reaction using a Box-Behnken design resulted in 99.94% atrazine degradation at pH 8.57, with an inoculum size of 3.10 × 10⁹ CFU/mL and a concentration of 50 mg/L atrazine. Ultra-high performance liquid chromatography-electrospray ionization-high resolution mass spectrometry (UPLC-ESI-HRMS), liquid chromatography tandem mass spectrometry (LC-MS/MS) and high performance liquid chromatography (HPLC) analyses identified and quantified six reported metabolites and a novel metabolite (2-hydroxypropazine) from atrazine degradation by AT13. On the basis of these metabolites, we propose an atrazine degradation pathway that includes dichlorination, hydroxylation, deamination, dealkylation and methylation reactions. The toxicity of the degradation products was evaluated by Toxicity Estimation Software Tool (T.E.S.T). Bioaugmentation of atrazine-polluted soils/water with strain AT13 significantly improved the atrazine removal rate. Thus, AT13 has potential applications in bioremediation.

Immobilization of bacterial mixture of Klebsiella variicola FH-1 and Arthrobacter sp. NJ-1 enhances the bioremediation of atrazine-polluted soil environments

In this study, the effects of the immobilized bacterial mixture (IM-FN) of Arthrobacter sp. NJ-1 and Klebsiella variicola strain FH-1 using sodium alginate-CaCl2 on the degradation of atrazine were investigated. The results showed that the optimal ratio of three types of carrier materials (i.e., rice straw powder, rice husk, and wheat bran) was 1:1:1 with the highest adsorption capacity for atrazine (i.e., 3774.47 mg/kg) obtained at 30°C. On day 9, the degradation efficiency of atrazine (50 mg/L) reached 98.23% with cell concentration of 1.6 × 108  cfu/ml at pH 9 and 30°C. The Box-Behnken method was used to further optimize the culture conditions for the degradation of atrazine by the immobilized bacterial mixture. The IM-FN could be reused for 2-3 times with the degradation efficiency of atrazine maintained at 73.0% after being stored for 80 days at 25°C. The population dynamics of IM-FN was explored with the total soil DNA samples specifically analyzed by real-time PCR. In 7 days, the copy numbers of both PydC and estD genes in the IM-FN were significantly higher than those of bacterial suspensions in the soil. Compared with bacterial suspensions, the IM-FN significantly accelerated the degradation of atrazine (20 mg/kg) in soil with the half-life shortened from 19.80 to 7.96 days. The plant heights of two atrazine-sensitive crops (wheat and soybean) were increased by 14.99 and 64.74%, respectively, in the soil restored by immobilized bacterial mixture, indicating that the IM-FN significantly reduced the phytotoxicity of atrazine on the plants. Our study evidently demonstrated that the IM-FN could significantly increase the degradation of atrazine, providing a potentially effective bioremediation technique for the treatment of atrazine-polluted soil environment and providing experimental support for the wide application of immobilized microorganism technology in agriculture.

Biodegradation of 4-nitroaniline by novel isolate Bacillus sp. strain AVPP64 in the presence of pesticides

In this study, Bacillus sp. strain AVPP64 was isolated from diuron-contaminated soil. It showed 4-nitroaniline (4-NA) degradation, pesticide tolerance, and self-nutrient integration via nitrogen (N)-fixation and phosphate (P)-solubilization. The rate constant (k) and half-life period (t_1/2) of 4-NA degradation in the aqueous medium inoculated with strain AVPP64 were observed to be 0.445 d^-1 and 1.55 d, respectively. Nevertheless, in the presence of chlorpyrifos, profenofos, atrazine and diuron pesticides, strain AVPP64 degraded 4-NA with t_1/2 values of 2.55 d, 2.26 d, 2.31 d and 3.54 d, respectively. The strain AVPP64 fixed 140 μg mL^-1 of N and solubilized 103 μg mL^-1 of P during the presence of 4-NA. In addition, strain AVPP64 produced significant amounts of plant growth-promoting metabolites like indole 3-acetic acid, siderophores, exo-polysaccharides and ammonia. In the presence of 4-NA and various pesticides, strain AVPP64 greatly increased the growth and biomass of Vigna radiata and Crotalaria juncea plants. These results revealed that Bacillus sp. strain AVPP64 can be used as an inoculum for bioremediation of 4-NA contaminated soil and sustainable crop production even when pesticides are present.

Complete Genome Sequence and Function Gene Identify of Prometryne-Degrading Strain Pseudomonas sp. DY-1

The genus Pseudomonas is widely recognized for its potential for environmental remediation and plant growth promotion. Pseudomonas sp. DY-1 was isolated from the agricultural soil contaminated five years by prometryne, it manifested an outstanding prometryne degradation efficiency and an untapped potential for plant resistance improvement. Thus, it is meaningful to comprehend the genetic background for strain DY-1. The whole genome sequence of this strain revealed a series of environment adaptive and plant beneficial genes which involved in environmental stress response, heavy metal or metalloid resistance, nitrate dissimilatory reduction, riboflavin synthesis, and iron acquisition. Detailed analyses presented the potential of strain DY-1 for degrading various organic compounds via a homogenized pathway or the protocatechuate and catechol branches of the β-ketoadipate pathway. In addition, heterologous expression, and high efficiency liquid chromatography (HPLC) confirmed that prometryne could be oxidized by a Baeyer-Villiger monooxygenase (BVMO) encoded by a gene in the chromosome of strain DY-1. The result of gene knock-out suggested that the sulfate starvation-induced (SSI) genes in this strain might also involve in the process of prometryne degradation. These results would provide the molecular basis for the application of strain DY-1 in various fields and would contribute to the study of prometryne biodegradation mechanism as well.

Zn2+-dependent enhancement of Atrazine biodegradation by Klebsiella variicola FH-1

Degradation efficiency of Atrazine by Klebsiella variicola FH-1 is improved by the addition of Zn²⁺. Both the chromosome and plasmid genomes of strain FH-1 were sequenced and annotated to identify genes involved in the degradation of Atrazine. Four open reading frames (ORFs) 1040, 2582, 3597, and 4043 encoding Zn²⁺-dependent hydrolases were knocked out to verify their predicted functions in the degradation of Atrazine. In the presence of Zn²⁺, the biodegradation efficiency of Atrazine by knockout mutant ∆ORF 3597 was 13.7% lower than that of wild type (WT) of strain FH-1 but still 9.4% higher than that of WT without Zn²⁺. These results indicated that ORF 3597 played a synergistic role but may not be the sole factor involved in the degradation of Atrazine. The enzymatic activities of pydC encoded by ORF 3597 were further characterized in the degradation of Atrazine. Results of fluorescence staining and flow cytometry analyses showed that the survival of bacterial cells and cell membrane permeability were increased in the presence of Zn²⁺ at different concentrations. Our study provided a scientific foundation for further investigation of the biological mechanisms of improving the degradation of Atrazine by strain FH-1 with the presence of Zn²⁺.

Isolation and Identification of Pseudomonas sp. Strain DY-1 from Agricultural Soil and Its Degradation Effect on Prometryne

Prometryne is a widely used herbicide in China to control annual grasses and broadleaf weeds. However, the stability of prometryne makes it difficult to be degraded, which poses a threat to human health. This study presents a bacterial strain isolated from soil samples with a prometryne application history, designated strain DY-1. Strain DY-1, identified as Pseudomonas sp., is capable of utilizing prometryne as a sole carbon source for growth and degrading 100% of prometryne within 48 h from an initial concentration of 50 mg L^-1. To further optimize the degradation of prometryne, the prometryne concentration, temperature, pH, and salt concentration were examined. The optimal conditions for degradation of prometryne by strain DY-1 were an initial prometryne concentration of 50 mg L^-1, 30 °C, pH 7-8, and NaCl concentration of 200 mg L^-1. The same strain also degraded other s-triazine herbicides, including simetryne, ametryne, desmetryne, and metribuzin, under the same conditions. The biodegradation pathway of prometryne was established by isolating sulfoxide prometryne as the first metabolite and by the identification of sulfone prometryne and 2-hydroxy prometryne by liquid chromatography-mass spectrometry (LC-MS/MS). The results illustrated that strain DY-1 achieved the removal of prometryne by gradually oxidizing and hydrolyzing the methylthio groups. A bioremediation trial with contaminated soil and pot experiments showed that after treating the prometryne-contaminated soil with strain DY-1, the content of prometryne was significantly reduced (P < 0.05). This study provides an efficient bacterial strain and approach that could be potentially useful for detoxification and bioremediation of prometryne analogs.

Trifluralin and Atrazine Sensitivity to Selected Cereal and Legume Crops

Soil-applied herbicides can persist in sufficient concentrations to affect the growth of crops in rotations. The sensitivity of wheat, barley, oat, lucerne and lentil to trifluralin and atrazine residues were investigated with three glasshouse experiments in 2018 and 2019. Each bioassay crop species was tested against different concentrations of trifluralin and atrazine in sandy soil using a full factorial design. Shoot and root parameters of the tested crop species were fitted in logistic equations against herbicide concentrations to calculate effective doses for 50% growth inhibition (ED50). Results revealed that both shoot and root parameters of all the test crop species were significantly affected by trifluralin and atrazine. Trifluralin delayed crop emergence at the lower concentrations examined, while higher concentrations prevented emergence entirely. Low concentrations of atrazine did not affect emergence but significantly reduced plant height, soil–plant analyses development (SPAD) index, shoot dry weight, root length, root dry weight and number of nodules of all the crop species. At high concentration, atrazine resulted in plant death. Legumes were found to be more sensitive than cereals when exposed to both trifluralin and atrazine treatments, with lucerne being the most sensitive to both herbicides, ED50 ranging from 0.01 to 0.07 mg/kg soil for trifluralin; and from 0.004 to 0.01 mg/kg for atrazine. Barley was the most tolerant species observed in terms of the two herbicides tested. Lucerne can be used to develop a simple but reliable bioassay technique to estimate herbicide residues in the soil so that a sound crop rotation strategy can be implemented.

Bacterial catabolism of s-triazine herbicides: biochemistry, evolution and application

The synthetic s-triazines are abundant, nitrogen-rich, heteroaromatic compounds used in a multitude of applications including, herbicides, plastics and polymers, and explosives. Their presence in the environment has led to the evolution of bacterial catabolic pathways in bacteria that allow use of these anthropogenic chemicals as a nitrogen source that supports growth. Herbicidal s-triazines have been used since the mid-twentieth century and are among the most heavily used herbicides in the world, despite being withdrawn from use in some areas due to concern about their safety and environmental impact. Bacterial catabolism of the herbicidal s-triazines has been studied extensively. Pseudomonas sp. strain ADP, which was isolated more than thirty years after the introduction of the s-triazine herbicides, has been the model system for most of these studies; however, several alternative catabolic pathways have also been identified. Over the last five years, considerable detail about the molecular mode of action of the s-triazine catabolic enzymes has been uncovered through acquisition of their atomic structures. These structural studies have also revealed insights into the evolutionary origins of this newly acquired metabolic capability. In addition, s-triazine-catabolizing bacteria and enzymes have been used in a range of applications, including bioremediation of herbicides and cyanuric acid, introducing metabolic resistance to plants, and as a novel selectable marker in fermentation organisms. In this review, we cover the discovery and characterization of bacterial strains, metabolic pathways and enzymes that catabolize the s-triazines. We also consider the evolution of these new enzymes and pathways and discuss the practical applications that have been considered for these bacteria and enzymes. One Sentence Summary: A detailed understanding of bacterial herbicide catabolic enzymes and pathways offer new evolutionary insights and novel applied tools.

A Review on Recent Treatment Technology for Herbicide Atrazine in Contaminated Environment

Atrazine is a kind of triazine herbicide that is widely used for weed control due to its good weeding effect and low price. The study of atrazine removal from the environment is of great significance due to the stable structure, difficult degradation, long residence time in environment, and toxicity on the organism and human beings. Therefore, a number of processing technologies are developed and widely employed for atrazine degradation, such as adsorption, photochemical catalysis, biodegradation, etc. In this article, with our previous research work, the progresses of researches about the treatment technology of atrazine are systematically reviewed, which includes the four main aspects of physicochemical, chemical, biological, and material-microbial-integrated aspects. The advantages and disadvantages of various methods are summarized and the degradation mechanisms are also evaluated. Specially, recent advanced technologies, both plant-microbial remediation and the material-microbial-integrated method, have been highlighted on atrazine degradation. Among them, the plant-microbial remediation is based on the combined system of soil-plant-microbes, and the material-microbial-integrated method is based on the synergistic effect of materials and microorganisms. Additionally, future research needs to focus on the excellent removal effect and low environmental impact of functional materials, and the coordination processing of two or more technologies for atrazine removal is also highlighted.

Evaluation of the Strain Bacillus amyloliquefaciens YP6 in Phoxim Degradation via Transcriptomic Data and Product Analysis

Phoxim, a type of organophosphorus pesticide (OP), is widely used in both agriculture and fisheries. The persistence of phoxim has caused serious environmental pollution problems. In this study, Bacillus amyloliquefaciens YP6 (YP6), which is capable of promoting plant growth and degrading broad-spectrum OPs, was used to study phoxim degradation. Different culture media were applied to evaluate the growth and phoxim degradation of YP6. YP6 can grow rapidly and degrade phoxim efficiently in Luria-Bertani broth (LB broth) medium. Furthermore, it can also utilize phoxim as the sole phosphorus source in a mineral salt medium. Response surface methodology was performed to optimize the degradation conditions of phoxim by YP6 in LB broth medium. The optimum biodegradation conditions were 40 °C, pH 7.20, and an inoculum size of 4.17% (v/v). The phoxim metabolites, O,O-diethylthiophosphoric ester, phoxom, and α-cyanobenzylideneaminooxy phosphonic acid, were confirmed by liquid chromatography-mass spectrometry. Meanwhile, transcriptome analysis and qRT-PCR were performed to give insight into the phoxim-stress response at the transcriptome level. The hydrolase-, oxidase-, and NADPH-cytochrome P450 reductase-encoding genes were significantly upregulated for phoxim hydrolysis, sulfoxidation, and o-dealkylation. Furthermore, the phoxim biodegradation pathways by YP6 were proposed, for the first time, based on transcriptomic data and product analysis.

Bioaugmentation of atrazine removal in constructed wetland: Performance, microbial dynamics, and environmental impacts

Constructed wetland (CW) is an efficient technology to treat urban storm water runoff. However, the CW has limited capacity to degrade atrazine, a frequently detected herbicide in runoff. Bioaugmentation provides a feasible enhanced alternative; nevertheless, incorporating bioaugmentation into CW is likely to perpetuate the environmental consequences and incur complex trade-offs between environmental improvement and burdens. Since few efforts were made to improve above situation, the present work proposed the application of bioaugmentation, and tested the feasibility from both efficiency and sustainability dimensions. Results showed that bioaugmentation markedly enhanced atrazine degradation from 5 mg/L to below the threshold value within 43 day by increasing functional atrazine-degrading bacteria. Pseudomonas and Arthrobacter significantly proliferated among atrazine-degrading bacterial genera, indicating high adaptability and atrazine-degrading contribution. With life cycle assessment, enhancing 1 kg of atrazine degradation could decrease environmental burdens with 27.60 kg 1,4-DCB-Eq of freshwater-ecotoxicity reduction, and achieve shorter payback period compared to non-bioaugmented CW.

Biodegradation of Atrazine by the Novel Klebsiella variicola Strain FH-1

Bacterial strain FH-1 with high efficiency of degrading Atrazine is separated by means of enrichment culture from the soil applied with Atrazine for many years. FH-1, recognized as Klebsiella variicola based on phylogenetic analysis of 16S rDNA sequences, can grow with Atrazine which is the sole nitrogen source. In fluid inorganic salt medium, the optimal degradation temperature, pH value, and initial concentration of Atrazine are 25°C, 9.0, and 50 mg L^–1, respectively, and the degradation rate of Atrazine by strain FH-1 reached 81.5% in 11 d of culture. The degrading process conforms to the kinetics equation of pesticide degradation. Among the metal ions tested, Zn²⁺ (0.2 mM) has the most significant effect of facilitation on the degradation of Atrazine. In the fluid medium with Zn²⁺, the degradation rate of Atrazine is increased to 72.5%, while the Cu²⁺ (0.2 mM) inhibits the degradation of Atrazine. The degradation products of Atrazine by strain FH-1 were identified as HEIT (2-hydroxyl-4-ethylamino-6-isopropylamino-1,3,5-triazine), MEET (2-hydroxyl-4,6-bis(ethylamino)-1,3,5-triazine), and AEEO (4,6-bis(ethylamino)-1,3,5-triazin-2(1H)-one) by HPLC-MS/MS. Three genes (atzC, trzN, and trzD) encoding for Atrazine degrading enzymes were identified by PCR and sequencing in strain FH-1. This study provides additional theoretical support for the application of strain FH-1 in bioremediation of fields polluted by Atrazine.

Hexadecane biodegradation of high efficiency by bacterial isolates from Santos Basin sediments

The aim of the study was the investigation of bacterial diversity from sediments collected at Santos Estuarine System, regarding to their abilities for hexadecane biotransformation. Hexadecane is a medium-chain linear alkane, considered as a model molecule for hydrocarbon biodegradation studies. It is a component from aliphatic fraction of crude petroleum, commonly related to environmental contamination by diesel oil. Santos Basin is an area with historical petroleum contamination. In the present work, sediment samples from this area were inoculated in artificial seawater (ASW), containing hexadecane as carbon source. Six bacterial isolates were selected as resistant to hexadecane. Chromatographic results showed biodegradation indexes above 97%. After 48 h of culture, five of them could degrade >80% of the initial hexadecane added. These isolates were characterized by 16S rDNA gene sequencing analysis. The following species were found: Bacillus amyloliquefaciens, Staphylococcus epidermidis, Micrococcus luteus, Nitratireductor aquimarinus, and Bacillus pumilus.

Isolation and identification of Pseudomonas from wastewater, its immobilization in cellulose biopolymer and performance in degrading Triclosan

Triclosan (TCS) is a well-known emerging contaminant got wide use in daily use products of domestic purpose, which provides the way to enter the ecological cycle, and is preferably detected in sewage treatment plants. In this study, TCS degrading bacteria (TDB) was isolated and identified from a wastewater treatment plant at the National Institute of Technology-Karnataka, Surathkal (NITK), India. The isolate was reported as Pseudomonas strain by performing 16S RNA Sequencing using BLAST analysis. Bacterial growth depends upon several environmental factors. Hence its growth optimization was carried out by response surface method (RSM) based central composite design (CCD) and validated by the artificial neural network (ANN). The Parameters or inputs used for optimization are pH, time (days), agitation (rpm) and sorbent dosage (μg/L). Experiments were conducted in batch mode to achieve optimum growth of bacteria based on RSM trial runs. The RSM model predictions were in better agreement with the experimental results and it was confirmed by ANN. The deviation lies within ±10% with experimental results compared to ANN for maximum trials. Hence optimized parameters were established and arrived at pH - 7, time - 13 days, agitation - 150 rpm, dosage - 1.5 μg/L presented 69% removal of TCS. Minimum inhibitory assay of isolated strain was conducted to identify the degradation capacity of TCS and it was found out to be lesser than 0.025 mg of TCS. Later the strain was immobilized in two different matrices. One is biopolymer extracted from cellulose (Water Hyacinth) along with sodium alginate and second is free bacteria with sodium alginate and was made in the form of beads. The removal of TCS by TDB-cellulose-alginate (BCA) and TDB-Alginate (BA) beads were 58% and 30% respectively. Hence it was concluded that BCA beads showed effective removal compared to BA beads. Therefore, isolate can degrade TCS when the concentration ranges from 0.025 mg/L to 5.5 ng/L.

Fluorinated waste and firefighting activities: biodegradation of hydrocarbons from petrochemical refinery soil co-contaminated with halogenated foams

Perfluorinated compounds, including fluorotelomers, are important constituents of firefighting foams to extinguish fuel fires in the petrochemical industry, airports, and at fire-training sites. In this study, we monitored the biodegradation process in a co-contamination scenario with monoaromatic hydrocarbons commonly found in fuels (benzene, toluene) and fluorotelomers. The CO₂ production rates were evaluated by a factorial design taking into account the effect of seasonality at in situ natural attenuation processes. Headspace analysis by gas chromatography with a thermal conductivity detector (GC-TCD) was applied to detect CO₂ production, whereas monoaromatics were analyzed by gas chromatography coupled to mass spectrometry (GC-MS). According to our results, seasonality had a detectable effect during summer, yielding different CO₂ production rates. Higher temperatures increased CO₂ production rate, while higher concentrations of fluorotelomer inhibited the biodegradation process. On average, benzene and toluene were depleted 17.5 days earlier in control assays without fluorotelomers. Toluene removal efficiency was also notably higher than benzene. The noticeable decrease in degradation rates of monoaromatics was caused by perfluorinated compounds that are possibly linked to metabolic inhibition mechanisms. Fluorotelomer diminished catabolism in all of our batch cultures. In addition to this, an alternative production of by-products could be detected. Thus, we propose that transient components of the benzene and toluene degradation may be differentially formed, causing the benzene, toluene, and perfluorinated co-contaminations to go through switched metabolic stages under the presence of fluoride in a contamination scenario.

Exploring bacterial communities and biodegradation genes in activated sludge from pesticide wastewater treatment plants via metagenomic analysis

Activated sludge (AS) has been regarded as the main driver in the removal of organic pollutants such as pesticides due to a high diversity and abundance of microorganisms. However, little is known about the biodegradation genes (BDGs) and pesticide degradation genes (PDGs) harbored in the AS from wastewater treatment plants (WWTPs). In this study, we explored the bacterial communities and BDGs/PDGs in the AS from five WWTPs affiliated with pesticide factories across four consecutive seasons based on high-throughput sequencing. The AS in pesticide WWTPs exhibited unique bacterial taxa at the genus level. Furthermore, a total of 17 BDGs and 68 PDGs were explored with a corresponding average relative abundance of 0.002-0.046% and 2.078-7.143% in each AS sample, respectively, and some BDGs/PDGs clusters were also identified in the AS. The bacterial communities and BDGs/PDGs were season-dependent, and the total variations of 50.4% and 76.8% were jointly explained by environmental variables (pesticide types, wastewater characteristics, and temperature). In addition, network analysis and distribution patterns suggested that the potential hosts of BDGs/PDGs were Thauera, Stenotrophomonas, Mycobacterium, Hyphomicrobium, Allochromatium, Ralstonia, and Dechloromonas. Our findings demonstrated the linkages of bacterial communities and BDGs/PDGs in the AS, and depended on the seasons and the pesticide wastewater characteristics.

Optimization of culturing conditions for isolated Arthrobacter sp. ZXY-2, an effective atrazine-degrading and salt-adaptive bacterium

The isolated strainArthrobactersp. ZXY-2 could biodegrade atrazine effectively with high salinity resistance.