Biodegradation of diuron by endophytic Bacillus licheniformis strain SDS12 and its application in reducing diuron toxicity for green algae

Comprehensive toxicological, metabolomic, and transcriptomic analysis of the biodegradation and adaptation mechanism by Achromobacter xylosoxidans SL-6 to diuron

Biodegradation was considered a promising and environmentally friendly method for treating environmental pollution caused by diuron. However, the mechanisms of biodegradation of diuron required further research. In this study, the degradation process of diuron by Achromobacter xylosoxidans SL-6 was systematically investigated. The results suggested that the antioxidant system of strain SL-6 was activated by adding diuron, thereby alleviating their oxidative stress response. In addition, degradation product analysis showed that diuron in strain SL-6 was mainly degraded by urea bridge cleavage, dehalogenation, deamination, and ring opening, and finally cis, cis-muconic acid was generated. The combined analysis of metabolomics and transcriptomics revealed the biodegradation and adaptation mechanism of strain SL-6 to diuron. Metabolomics analysis showed that after the strain SL-6 was exposed to diuron, metabolic pathways such as tricarboxylic acid cycle (cis, cis-muconic acid), glutathione metabolism (oxidized glutathione), and urea cycle (arginine) were reprogrammed in the cells. Furthermore, diuron could induce the production of membrane transport proteins in strain SL-6 cells and overexpress antioxidant enzyme genes, finally ultimately promoting the up-regulation of genes encoding amide hydrolases and dioxygenases, which was revealed by transcriptomics studies. This work enriched the biodegradation mechanism of phenylurea herbicides and provided guidance for the removal of diuron residues in the environment and promoting agriculture sustainable development.

Mechanistic insights into the effects of diuron exposure on Alexandrium pacificum

Diuron (N-(3,4-dichlorophenyl)-N,N‑dimethylurea, DCMU), a ureic herbicide, is extensively used in agriculture to boost crop productivity; however, its extensive application culminates in notable environmental pollution, especially in aquatic habitats. Therefore, the present study investigated the effect of diuron on the dinoflagellate Alexandrium pacificum, which is known to induce harmful algal blooms (HAB), and its potential to biodegrade DCMU. Following a four-day DCMU exposure, our results revealed that A. pacificum proficiently assimilated DCMU at concentrations of 0.05 mg/L and 0.1 mg/L in seawater, attaining a complete reduction (100 % efficiency) after 96 h for both concentrations. Moreover, evaluations of paralytic shellfish toxins content indicated that cells subjected to higher DCMU concentrations (0.1 mg/L) exhibited reductions of 73.4 %, 86.7 %, and 75 % in GTX1, GTX4, and NEO, respectively. Exposure to DCMU led to a notable decrease in A. pacificum's photosynthetic efficacy, accompanied by increased levels of reactive oxygen species (ROS) and suppressed cell growth, with a growth inhibition rate of 41.1 % at 72 h. Proteomic investigations pinpointed the diminished expression levels of specific proteins like SxtV and SxtW, linked to paralytic shellfish toxins (PSTs) synthesis, as well as key proteins associated with Photosystem II, namely PsbA, PsbD, PsbO, and PsbU. Conversely, proteins central to the cysteine biosynthesis pathways exhibited enhanced expression. In summary, our results preliminarily resolved the molecular mechanisms underlying the response of A. pacificum to DCMU and revealed that DCMU affected the synthesis of PSTs. Meanwhile, our data suggested that A. pacificum has great potential in scavenging DCMU.

Assessment of Phenanthrene Degradation Potential by Plant-Growth-Promoting Endophytic Strain Pseudomonas chlororaphis 23aP Isolated from Chamaecytisus albus (Hacq.) Rothm

Polycyclic aromatic hydrocarbons (PAHs) are common xenobiotics that are detrimental to the environment and human health. Bacterial endophytes, having the capacity to degrade PAHs, and plant growth promotion (PGP) may facilitate their biodegradation. In this study, phenanthrene (PHE) utilization of a newly isolated PGP endophytic strain of Pseudomonas chlororaphis 23aP and factors affecting the process were evaluated. The data obtained showed that strain 23aP utilized PHE in a wide range of concentrations (6-100 ppm). Ethyl-acetate-extractable metabolites obtained from the PHE-enriched cultures were analyzed by gas chromatography-mass spectrometry (GC-MS) and thin-layer chromatography (HPTLC). The analysis identified phthalic acid, 3-(1-naphthyl)allyl alcohol, 2-hydroxybenzalpyruvic acid, α-naphthol, and 2-phenylbenzaldehyde, and allowed us to propose that the PHE degradation pathway of strain 23aP is initiated at the 1,2-, 3,4-carbon positions, while the 9,10-C pathway starts with non-enzymatic oxidation and is continued by the downstream phthalic pathway. Moreover, the production of the biosurfactants, mono- (Rha-C8-C8, Rha-C10-C8:1, Rha-C12:2-C10, and Rha-C12:1-C12:1) and dirhamnolipids (Rha-Rha-C8-C10), was confirmed using direct injection-electrospray ionization-mass spectrometry (DI-ESI-MS) technique. Changes in the bacterial surface cell properties in the presence of PHE of increased hydrophobicity were assessed with the microbial adhesion to hydrocarbons (MATH) assay. Altogether, this suggests the strain 23aP might be used in bioaugmentation-a biological method supporting the removal of pollutants from contaminated environments.

Pesticide-tolerant microbial consortia: Potential candidates for remediation/clean-up of pesticide-contaminated agricultural soil

Reclamation of pesticide-polluted lands has long been a difficult endeavour. The use of synthetic pesticides could not be restricted due to rising agricultural demand. Pesticide toxicity has become a pressing agronomic problem due to its adverse impact on agroecosystems, agricultural output, and consequently food security and safety. Among different techniques used for the reclamation of pesticide-polluted sites, microbial bioremediation is an eco-friendly approach, which focuses on the application of resilient plant growth promoting rhizobacteria (PGPR) that may transform or degrade chemical pesticides to innocuous forms. Such pesticide-resilient PGPR has demonstrated favourable effects on soil-plant systems, even in pesticide-contaminated environments, by degrading pesticides, providing macro-and micronutrients, and secreting active but variable secondary metabolites like-phytohormones, siderophores, ACC deaminase, etc. This review critically aims to advance mechanistic understanding related to the reduction of phytotoxicity of pesticides via the use of microbe-mediated remediation techniques leading to crop optimization in pesticide-stressed soils. The literature surveyed and data presented herein are extremely useful, offering agronomists-and crop protectionists microbes-assisted remedial strategies for affordably enhancing crop productivity in pesticide-stressed soils.

Environmental behaviors of emerging contaminants in freshwater ecosystem dominated by submerged plants: A review

Persistent exposure of emerging contaminants (ECs) in freshwater ecosystem has initiated intense global concerns. Freshwater ecosystem dominated by submerged plants (SP-FES) has been widely constructed to control eutrophic water. However, the environmental behaviors (e.g. migration, transformation, and degradation) of ECs in SP-FES have rarely been concerned and summarized. This review briefly introduced the sources of ECs, the pathways of ECs entering into SP-FES, and the constituent elements of SP-FES. And then the environmental behaviors of dissolved ECs and refractory solid ECs in SP-FES were comprehensively summarized, and the feasibility of removing ECs from SP-FES was critically evaluated. Finally, the challenges and perspectives on the future development for ECs removal from SP-FES were prospected, giving possible research gaps and key directions. This review will provide theoretical and technical support for the effective removal of ECs in freshwater ecosystem, especially in SP-FES.

Bacterial community are more susceptible to nanoplastics than algae community in aquatic ecosystems dominated by submerged macrophytes

As a ubiquitous emerging pollutant, microplastics can interact with algal and bacterial communities in aquatic ecosystems. Currently, knowledge on how microplastics influence algae/bacteria is mostly limited to toxicity tests using either monocultures of algae/bacteria or specific algal-bacterial consortium. However, information on the effect of microplastics on algal and bacterial communities in natural habitats is not easily available. Here, we conducted a mesocosm experiment to test the effect of nanoplastics on algal and bacterial communities in aquatic ecosystems dominated by different submerged macrophytes. The community structure of algae and bacteria suspended in the water column (planktonic) and attached to the surface of submerged macrophytes (phyllospheric) were identified, respectively. Results showed that both planktonic and phyllospheric bacteria were more susceptible to nanoplastics, and these variations driven by decreased bacterial diversity and increased abundance of microplastic-degrading taxa, especially in aquatic systems dominated by V. natans. The community composition of both algae and bacteria were influenced to varying degrees by nanoplastics and/or plant types, but RDA results showed that only bacterial community composition was strongly correlated with environmental variables. Correlation network analysis showed that nanoplastics not only reduced the intensity of associations between planktonic algae and bacteria (average degree reduced from 4.88 to 3.24), but also reduced proportion of positive correlations (from 64% to 36%). Besides, nanoplastics also decreased the algal/bacterial connections between planktonic and phyllospheric habitats. Our study elucidates the potential interactions between nanoplastics and algal-bacterial community in natural aquatic ecosystems. These findings suggest that in aquatic ecosystems, bacterial community are more vulnerable to nanoplastics and may serve as a protective barrier for algae community. Further research is needed to reveal the protective mechanism of bacteria against algae at the community level.

Parthenium hysterophorus's Endophytes: The Second Layer of Defense against Biotic and Abiotic Stresses

Parthenium hysterophorus L. is considered an obnoxious weed due to its rapid dispersal, fast multiplications, and agricultural and health hazards. In addition to its physio-molecular and phytotoxic allelochemical usage, this weed most probably uses endophytic flora as an additional line of defense to deal with stressful conditions and tolerate both biotic and abiotic stresses. The aim of this article is to report the diversity of endophytic flora (fungi and bacteria) in P. hysterophorus and their role in the stress mitigation (biotic and abiotic) of other important crops. Various endophytes were reported from P. hysterophorus and their roles in crops evaluated under biotic and abiotic stressed conditions. These endophytes have the potential to alleviate different stresses by improving crops/plants growth, development, biomass, and photosynthetic and other physiological traits. The beneficial role of the endophytes may be attributed to stress-modulating enzymes such as the antioxidants SOD, POD and APX and ACC deaminases. Additionally, the higher production of different classes of bioactive secondary metabolites, i.e., flavonoids, proline, and glutathione may also overcome tissue damage to plants under stressed conditions. Interestingly, a number of medicinally important phytochemicals such as anhydropseudo-phlegmcin-9, 10-quinone-3-amino-8-O methyl ether 'anhydropseudophlegmacin-9, 10-quinone-3-amino-8-Omethyl ether were reported from the endophytic flora of P. hysterophorus. Moreover, various reports revealed that fungal and bacterial endophytes of P. hysterophorus enhance plant growth-promoting attributes and could be added to the consortium of biofertilizers.

A biochemical, physiological and molecular evaluation of how the herbicide 2, 4-dichlorophenoxyacetic acid intercedes photosynthesis and diazotrophy in the cyanobacterium Nostoc muscorum Meg 1

Among the non-target microorganisms residing in crop fields that are potentially vulnerable to herbicides are cyanobacteria. They contribute to the maintenance of soil quality and fertility and hence are considered to be an important component of soil microflora. Consequently, the present study was aimed to check the influence of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) on some major parameters of carbon (CO₂) and nitrogen (N₂) fixations of a cyanobacterium Nostoc muscorum Meg 1 isolated from a rice field in Cherrapunji, Meghalaya, India. These include various photosynthetic pigments, the oxygen-evolving complex activity of the PSII, the protein contents of RuBisCO, D1 protein, isocitrate dehydrogenase (IDH), nitrogenase and glutamine synthetase (GS) enzymes, the heterocyst percentage, nitrogenase and GS enzyme activities, and production of total proteins and carbohydrates in the cyanobacterium in a varying range of 50 to 125 ppm doses of 2,4-D. The mRNA levels of several proteins were also analyzed. Besides carotenoid concentration that enhanced at 50 ppm, all other parameters were compromised by 2,4-D in a dose-dependent manner resulting in a reduction in photosynthetic and N₂-fixing activities. The negative effect on N₂-fixation was partly due to compromised IDH activity. RT-PCR analysis further showed that these negative effects were initiated at transcription levels as mRNA contents of all enzymes studied were found compromised under 2,4-D exposure. The scanning and transmission electron microscopy further revealed herbicide induced adverse changes in the morphology and ultrastructure of the organism. The significance of the work lies in its detailed analysis of the effect of 2,4-D at biochemical, physiological, and molecular levels.

Emerging Strategies for the Bioremediation of the Phenylurea Herbicide Diuron

Diuron (DUR) is a phenylurea herbicide widely used for the effective control of most annual and perennial weeds in farming areas. The extensive use of DUR has led to its widespread presence in soil, sediment, and aquatic environments, which poses a threat to non-target crops, animals, humans, and ecosystems. Therefore, the removal of DUR from contaminated environments has been a hot topic for researchers in recent decades. Bioremediation seldom leaves harmful intermediate metabolites and is emerging as the most effective and eco-friendly strategy for removing DUR from the environment. Microorganisms, such as bacteria, fungi, and actinomycetes, can use DUR as their sole source of carbon. Some of them have been isolated, including organisms from the bacterial genera Arthrobacter, Bacillus, Vagococcus, Burkholderia, Micrococcus, Stenotrophomonas, and Pseudomonas and fungal genera Aspergillus, Pycnoporus, Pluteus, Trametes, Neurospora, Cunninghamella, and Mortierella. A number of studies have investigated the toxicity and fate of DUR, its degradation pathways and metabolites, and DUR-degrading hydrolases and related genes. However, few reviews have focused on the microbial degradation and biochemical mechanisms of DUR. The common microbial degradation pathway for DUR is via transformation to 3,4-dichloroaniline, which is then metabolized through two different metabolic pathways: dehalogenation and hydroxylation, the products of which are further degraded via cooperative metabolism. Microbial degradation hydrolases, including PuhA, PuhB, LibA, HylA, Phh, Mhh, and LahB, provide new knowledge about the underlying pathways governing DUR metabolism. The present review summarizes the state-of-the-art knowledge regarding (1) the environmental occurrence and toxicity of DUR, (2) newly isolated and identified DUR-degrading microbes and their enzymes/genes, and (3) the bioremediation of DUR in soil and water environments. This review further updates the recent knowledge on bioremediation strategies with a focus on the metabolic pathways and molecular mechanisms involved in the bioremediation of DUR.

Carboxin and Diuron Adsorption Mechanism on Sunflower Husks Biochar and Goethite in the Single/Mixed Pesticide Solutions

The study focused on the adsorption mechanism of two selected pesticides: carboxin and diuron, on goethite and biochar, which were treated as potential compounds of mixed adsorbent. The authors also prepared a simple mixture of goethite and biochar and performed adsorption measurements on this material. The adsorbents were characterized by several methods, inter alia, nitrogen adsorption/desorption, Boehm titration, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The adsorption study included kinetics and equilibrium measurements, in the solution containing one or two pesticides simultaneously. The adsorption data were fitted to selected theoretical models (e.g., Langmuir, Freudlich, Redlich-Peterson, pseudo first-order and pseudo second-order equations). Based on the obtained results, it was stated that, among all tested adsorbents, biochar had the highest adsorption capacity relative to both carboxin and diuron. It equaled 0.64 and 0.52 mg/g, respectively. Experimental data were best fitted to the pseudo second-order and Redlich-Peterson models. In the mixed systems, the adsorption levels observed on biochar, goethite and their mixture were higher for diuron and lower for carboxin, compared to those noted in the single solutions. The presented results may enable the development of new mixed adsorbent for remediation of soils polluted with pesticides.

Pollutants affect algae-bacteria interactions: A critical review

With increasing concerns on the ecological risks of pollutants, many efforts have been devoted to revealing the toxic effects of pollutants on algae or bacteria in their monocultures. However, how pollutants affect algae and bacteria in their cocultures is still elusive but crucial due to its more environmental relevance. The present review outlines the interactions between algae and bacteria, reveals the influential mechanisms of pollutants (including pesticides, metals, engineered nanomaterials, pharmaceutical and personal care products, and aromatic pollutants) to algae and bacteria in their coexisted systems, and puts forward prospects for further advancing toxic studies in algal-bacterial systems. Pollutants affect the physiological and ecological functions of bacteria and algae by interfering with their relationships. Cell-to-cell adhesion, substrate exchange and biodegradation of organic pollutants, enhancement of signal transduction, and horizontal transfer of tolerance genes are important defense strategies in algal-bacterial systems to cope with pollution stress. Developing suitable algal-bacterial models, identifying cross-kingdom signaling molecules, and deciphering the horizontal transfer of pollutant resistant genes between algae and bacteria under pollution stress are the way forward to fully exploit the risks of pollutants in natural aquatic environments.

Disinfectant-like activity of lipopeptide biosurfactant produced by Bacillus tequilensis strain SDS21

Antiseptics and disinfectants are widely applied for eliminating microorganisms. However, microorganisms dwelling in the biofilm are less susceptible and in some cases resistant to biocide treatment. The present study describes isolation and characterization of lipopeptide biosurfactant exhibiting disinfectant-like activity. Biosurfactant was produced by an endo-rhizospheric bacterium Bacillus tequilensis strain SDS21. Biosurfactant reduced the surface tension of water from 72 to 30 mN/m with CMC of 40 mg/l. The Liquid Chromatography-Mass Spectrometry analysis of biosurfactant suggested it to be a mixture of C₁₄, C₁₅, C₁₆ and C₁₇ surfactin homologues. The lipopeptide biosurfactant exhibited bactericidal activity against planktonic cells and biofilm residing sessile cells. The biosurfactant treatment eradicated more than 99% of bacterial biofilm present on polystyrene, glass and stainless steel surface. The biosurfactant retained its bactericidal and biofilm eradicating activities even after exposure to extreme conditions like high temperate and extreme pH. Unlike some of the commonly used disinfectant, biosurfactant retained its bactericidal and biofilm removing activity even in the hard water containing Mg²⁺ and Ca²⁺ ions. Thus, suggesting that biosurfactant produced by strain SDS21 can be used as a disinfectant or in disinfectant-like formulations effective against both planktonic and biofilm residing bacteria.