Soil acidification enhancing the growth and metabolism inhibition of PFOS and Cr(VI) to bacteria involving oxidative stress and cell permeability

Soil amendments reduce PFAS bioaccumulation in Eisenia fetida following exposure to AFFF-impacted soil

The efficacy of RemBind® 300 to immobilize per- and polyfluoroalkyl substances (PFAS) in aqueous film forming foam (AFFF)-impacted soil (∑28 PFAS 1280-8130 ng g-1; n = 8) was assessed using leachability (ASLP) and bioaccumulation (Eisenia fetida) endpoints as the measure of efficacy. In unamended soil, ∑28 PFAS leachability ranged from 26.0 to 235 μg l-1, however, following the addition of 5% w/w RemBind® 300, ∑28 PFAS leachability was reduced by > 99%. Following exposure of E. fetida to unamended soil, ∑28 PFAS bioaccumulation ranged from 18,660-241,910 ng g-1 DW with PFOS accumulating to the greatest extent (15,150-212,120 ng g-1 DW). Biota soil accumulation factors (BSAF) were significantly (p < 0.05) higher for perfluoroalkyl sulfonic acids (PFSA; 13.2-50.9) compared to perfluoroalkyl carboxylic acids (PFCA; 1.2-12.7) while for individual PFSA, mean BSAF increased for C4 to C6 compounds (PFBS: 42.6; PFPeS: 52.7; PFHxS: 62.4). In contrast, when E. fetida were exposed to soil amended with 5% w/w RemBind® 300, significantly lower PFAS bioaccumulation occurred (∑28 PFAS: 339-3397 ng g-1 DW) with PFOS accumulation 23-246 fold lower compared to unamended soil. These results highlight the potential of soil amendments for reducing PFAS mobility and bioavailability, offering an immobilization-based risk management approach for AFFF-impacted soil.

Transcriptomic and biochemical analysis of metabolic remodeling in Bacillus subtilis MSC4 under Benzo[a]pyrene stress

Polyaromatic benzo[a]pyrene (B[a]P) is a toxic carcinogenic environmental pollutant, and the use of microorganisms to remediate B[a]P contamination is considered to be one of the most effective strategies. However, there is still a gap in studying the metabolic remodeling of microorganisms under B[a]P stress. In this study, our systematically investigated the effects of B[a]P on the metabolism of Bacillus subtilis MSC4 based on transcriptomic, molecular and biochemical analyses. The results showed that in response to B[a]P stress, MSC4 formed more biofilm matrix and endospores, the structure of the endospores also was changed, which led to a reduction in their resistance and made them more difficult to germinate. In addition to an increase in glycolysis activity, the activities of tricarboxylic acid cycle, pentose phosphate pathway and the electron transport chain were decreased. B[a]P stress forced MSC4 to strengthen arginine synthesis, urea cycle, and urea decomposition, meanwhile, synthesize more ribonucleotides. The activity of DNA replication, transcription activities and the expression of multiple ribosomal protein genes were reduced. Moreover, all of the reported enzymes involved in B[a]P degradation showed decreased transcript abundance, and the degradation of B[a]P caused significant up-regulation of the gene expression of the acid inducible enzyme OxdC and the synthesis of acetoin. In addition, the cytotoxicity of B[a]P to bacteria was directly displayed in four aspects: increased intracellular level of reactive oxygen species (ROS), elevated cell membrane permeability, up-regulation of the cell envelope stress-sensing two-component system LiaRS, and downregulation of siderophores biosynthesis. Finally, B[a]P also caused morphological changes in the cells, with some cells exhibiting significant deformation and concavity. These findings provide effective research directions for targeted improvement the cellular activity of B[a]P-degrading strains, and is beneficial for further application of microorganisms to remediate B[a]P -contaminated soils.

Uptake and cellular responses of Microcystis aeruginosa to PFOS in various environmental conditions

Although PFOS has been banned as a persistent organic pollutant, it still exists in large quantities within the environment, thus impacting the health of aquatic ecosystems. Previous studies focused solely on high PFOS concentrations, disregarding the connection with environmental factors. To gain a more comprehensive understanding of the PFOS effects on aquatic ecosystems amidst changing environmental conditions, this study investigated the cellular responses of Microcystis aeruginosa to varying PFOS concentrations under heatwave and nutrient stress conditions. The results showed that PFOS concentrations exceeding 5.0 µg/L had obvious effects on multiple physiological responses of M. aeruginosa, resulting in the suppression of algal cell growth and the induction of oxidative damage. However, PFOS concentration at levels below 20.0 µg/L has been found to enhance the growth of algal cells and trigger significant oxidative damage under heatwave conditions. Heatwave conditions could enhance the uptake of PFOS in algal cells, potentially leading to heightened algal growth when PFOS concentration was equal to or less than 5.0 µg/L. Conversely, deficiency or limitation of nitrogen and phosphorus significantly decreased algal abundance and chlorophyll content, inducing severe oxidative stress that could be mitigated by exposure to PFOS. This study holds significance in managing the impact of PFOS on algal growth across diverse environmental conditions.

Metagenomic and proteomic insights into the self-adaptive cell surface hydrophobicity of Sphingomonas sp. strain PAH02 reducing the migration of cadmium-phenanthrene co-pollutant in rice

Cell surface hydrophobicity (CSH) dominates the interactions between rhizobacteria and pollutants at the soil-water interface, which is critical for understanding the dissipation of pollutants in the rhizosphere microzone of rice. Herein, we explored the effects of self-adaptive CSH of Sphingomonas sp. strain PAH02 on the translocation and biotransformation behaviour of cadmium-phenanthrene (Cd-Phe) co-pollutant in rice and rhizosphere microbiome. We evidenced that strain PAH02 reduced the adsorption of Cd-Phe co-pollutant on the rice root surface while enhancing the degradation of Phe and adsorption of Cd via its self-adaptive CSH in the hydroponic experiment. The significant upregulation of key protein expression levels such as MerR, ARHDs and enoyl-CoA hydratase/isomerase, ensures self-adaptive CSH to cope with the stress of Cd-Phe co-pollutant. Consistently, the bioaugmentation of strain PAH02 promoted the formation of core microbiota in the rhizosphere soil of rice (Oryza sativa L.), such as Bradyrhizobium and Streptomyces and induced gene enrichment of CusA and PobA that are strongly associated with pollutant transformation. Consequently, the contents of Cd and Phe in rice grains at maturity decreased by 17.2% ± 0.2% and 65.7% ± 0.3%, respectively, after the bioaugmentation of strain PAH02. These findings present new opportunities for the implementation of rhizosphere bioremediation strategies of co-contaminants in paddy fields.

Oxidative stress-induced DNA damage and DNA repair mechanisms in mangrove bacteria exposed to climatic and heavy metal stressors

Bacteria thriving in the mangrove ecosystem are major drivers of elemental cycles. Climate change and environmental stressors (heavy metals) influence the performance of these microorganisms, thereby affecting the biogeochemical cycle. The present study reports the genotoxic effect of climatic and heavy metal stressors on mangrove bacteria and their adaptation strategies. Comparative analysis between two bacterial strains, Bacillus stercoris GST-03 and Pseudomonas balearica DST-02 isolated from the Bhitarkanika mangrove ecosystem, Odisha, India, showed cellular injuries in response to various stressors as evident by declined growth, elevated levels of reactive oxygen species (ROS) and resulted DNA damage. B. stercoris GST-03 showed more tolerance towards acidic pH, whereas P. balearica DST-02 showed higher tolerance towards UV exposure and heavy metals (Lead and Cadmium). The adaptation strategies of the strains revealed a significant role of GST in ROS scavenging activity and the involvement of Nucleotide excision repair or SOS response pathways. However, irreparable DNA damage was observed at pH 9 and 200 ppm Cd in B. stercoris GST-03, and at pH 4, 1000 ppm of Pb and 200 ppm of Cd in P. balearica DST-02. The current findings provide a broad overview of bacterial response and adaptability concerning future climate and environmental changes.

Exploration of the mechanism of 2-CP degradation by Acinetobacter sp. stimulated by Lactobacillus plantarum fermentation waste: A bio-waste reuse

Green and economical pollution management methods which reusing bio-waste as biostimulant to effectively improve the removal of target pollutants are receiving more and more attention. In this study, Lactobacillus plantarum fermentation waste solution (LPS) was used to investigate its facilitative effect and the stimulation mechanisms on the degradation of 2-chlorophenol (2-CP) by strain Acinetobacter sp. Strain ZY1 in terms of both cell physiology and transcriptomics. The degradation efficiency of 2-CP was improved from 60% to >80% under LPS treatment. The biostimulant maintained the morphology of strain, reduced the level of reactive oxygen species, and recovered the cell membrane permeability from 39% to 22%. It also significantly increased the level of electron transfer activity and extracellular polymeric substances secretion and improved the metabolic activity of the strain. The transcriptome results revealed the stimulation of LPS to promote biological processes such as bacterial proliferation, metabolism, membrane structure composition, and energy conversion. This study provided new insights and references for the reuse of fermentation waste streams in biostimulation methods.

Repairing of rutin to the toxicity of combined F-53B and chromium pollution on the biofilm formed by Pseudomonas aeruginosa

The wastewater discharge from the process of chrome plating, which contains 6:2 chlorinated polyfluorinated ether sulfonate (F-53B) and chromium (Cr), may be toxic to biofilm. In this study we found that the biofilm formed by Pseudomonas aeruginosa PAO1 was inhibited by exposure to a combination of F-53B and Cr(VI). The combined pollution damaged the cell membranes and the structure of the biofilm, and inhibited the production of the Pseudomonas quinolone-based signal, which affected biofilm formation. Moreover, the secretion of extracellular polymeric substances decreased as a result of this combined exposure. Exposure to F-53B and Cr(VI) individually or in combination could induce the excessive accumulation of intracellular reactive oxygen species (ROS), and the ROS positive rate of the bacteria increased under the treatment with 0.2 mmol/L of Cr(VI) and 250 nmol/L of F-53B, respectively. In addition, the activities of superoxide dismutase (SOD) and catalase (CAT) were enhanced for scavenging ROS in the bacteria that were exposed to Cr(VI) and F-53B. As an antioxidant, rutin was used to repair the toxicity of Cr(VI) and F-53B towards the biofilm formed by the bacteria. When rutin was added to the bacteria medium, with either Cr(VI) or F-53B as pollutant, or with the combined pollutants, the extracellular protein content of the bacteria recovered to 0.84, 0.94, and 0.85 times that of the control, respectively. Meanwhile, the accumulation of ROS and the activities of SOD and CAT decreased, which indicated that the addition of rutin can alleviate the oxidative stress and promote the antioxidant stress system.

Hormetic Effect of Pyroligneous Acids on Conjugative Transfer of Plasmid-mediated Multi-antibiotic Resistance Genes within Bacterial Genus

Spread of antibiotic resistance genes (ARGs) by conjugation poses great challenges to public health. Application of pyroligneous acids (PA) as soil amendments has been evidenced as a practical strategy to remediate pollution of ARGs in soils. However, little is known about PA effects on horizontal gene transfer (HGT) of ARGs by conjugation. This study investigated the effects of a woody waste-derived PA prepared at 450°C and its three distillation components (F1, F2, and F3) at different temperatures (98, 130, and 220°C) on conjugative transfer of plasmid RP4 within Escherichia coli. PA at relatively high amount (40-100 μL) in a 30-mL mating system inhibited conjugation by 74-85%, following an order of PA > F3 ≈ F2 ≈ F1, proving the hypothesis that PA amendments may mitigate soil ARG pollution by inhibiting HGT. The bacteriostasis caused by antibacterial components of PA, including acids, phenols, and alcohols, as well as its acidity (pH 2.81) contributed to the inhibited conjugation. However, a relatively low amount (10-20 μL) of PA in the same mating system enhanced ARG transfer by 26-47%, following an order of PA > F3 ≈ F2 > F1. The opposite effect at low amount is mainly attributed to the increased intracellular reactive oxygen species production, enhanced cell membrane permeability, increased extracellular polymeric substance contents, and reduced cell surface charge. Our findings highlight the hormesis (low-amount promotion and high-amount inhibition) of PA amendments on ARG conjugation and provide evidence for selecting an appropriate amount of PA amendment to control the dissemination of soil ARGs. Moreover, the promoted conjugation also triggers questions regarding the potential risks of soil amendments (e.g., PA) in the spread of ARGs via HGT.

Contributions of Beneficial Microorganisms in Soil Remediation and Quality Improvement of Medicinal Plants

Medicinal plants (MPs) are important resources widely used in the treatment and prevention of diseases and have attracted much attention owing to their significant antiviral, anti-inflammatory, antioxidant and other activities. However, soil degradation, caused by continuous cropping, excessive chemical fertilizers and pesticide residues and heavy metal contamination, seriously restricts the growth and quality formation of MPs. Microorganisms, as the major biota in soil, play a critical role in the restoration of the land ecosystem. Rhizosphere microecology directly or indirectly affects the growth and development, metabolic regulation and active ingredient accumulation of MPs. Microbial resources, with the advantages of economic efficiency, harmless to environment and non-toxic to organisms, have been recommended as a promising alternative to conventional fertilizers and pesticides. The introduction of beneficial microbes promotes the adaptability of MPs to adversity stress by enhancing soil fertility, inhibiting pathogens and inducing systemic resistance. On the other hand, it can improve the medicinal quality by removing soil pollutants, reducing the absorption and accumulation of harmful substances and regulating the synthesis of secondary metabolites. The ecological and economic benefits of the soil microbiome in agricultural practices are increasingly recognized, but the current understanding of the interaction between soil conditions, root exudates and microbial communities and the mechanism of rhizosphere microecology affecting the secondary metabolism of MPs is still quite limited. More research is needed to investigate the effects of the microbiome on the growth and quality of different medicinal species. Therefore, the present review summarizes the main soil issues in medicinal plant cultivation, the functions of microbes in soil remediation and plant growth promotion and the potential mechanism to further guide the use of microbial resources to promote the ecological cultivation and sustainable development of MPs.

Perfluorooctane sulfonate (PFOS) enhanced polystyrene particles uptake by human colon adenocarcinoma Caco-2 cells

As microplastics and nanoplastics (MNPs) are widely distributed in the environment and can be transferred to human body through food chain, their potential impact on human health is of great concern. Perfluorooctane sulfonate (PFOS) is persistent, bioaccumulative and can be adsorbed by MNPs. However, there are few studies on the combined human health effects of MNPs with PFOS. In this study, the effects of polystyrene (PS) particles and PFOS on human colon adenocarcinoma cell Caco-2 were investigated in vitro to explore the combined toxicity from cellular level, and the toxic mechanism was further illustrated. Results showed that the presence of PFOS significantly increased the cell uptake of PS nanoparticles by >30 %, which is related to variations of the surface properties of PS particles, including the decrease of hydration kinetic diameter, the rise of surface potential and the adsorption of hydrophobic PFOS molecules. The toxic effect of PFOS was weakened in the presence of PS particles under low PFOS concentration (10 μg/mL), which is because the bioavailability of PFOS was reduced after adsorption. PS particles with small particle size (20 nm) showed higher cell uptake and ROS production, while PS particles with large particle size (1 μm) led to higher lipid oxidation degree and related membrane damage as well as mitochondrial stress. This study provides the first evaluation of combined toxicity of MNPs and PFOS on human intestinal cells, in order to support the risk assessment of combined pollution of MNPs and PFOS on human health.

The toxicity of hexavalent chromium to soil microbial processes concerning soil properties and aging time

Chromium (Cr) pollution has attracted much attention due to its biological toxicity. However, little is known regarding Cr toxicity to soil microorganisms. The present study assesses the toxicity of Cr(VI) on two microbial processes, potential nitrification rate (PNR) and substrate-induced respiration (SIR), in a wide range of agricultural soils and detected the abundance of soil bacteria, fungi, ammonia-oxidizing bacteria and archaea. The toxicity thresholds of 10% and 50% effective concentrations (EC₁₀ and EC₅₀) for PNR varied by 32.18- and 38.66-fold among different soils, while for SIR they varied by 391.21- and 16.31-fold, respectively. Regression model analysis indicated that for PNR, CEC as a single factor explained 27% of the variation in EC₁₀, with soil clay being the key factor explaining 47.3% of the variation in EC₅₀. For SIR, organic matter and pH were found to be the most vital predictors for EC₁₀ and EC₅₀, explaining 34% and 61.1% of variation, respectively. In addition, extended aging time was found to significantly attenuate the toxicity of Cr on PNR. SIR was mainly driven by total bacteria rather than fungi, while PNR was driven by both AOA and AOB. These results were helpful in deriving soil Cr toxicity threshold based on microbial processes, and provided a theoretical foundation for ecological risk assessments and establishing a soil environmental quality criteria for Cr.

Chemically induced oxidative stress improved bacterial laccase-mediated degradation and detoxification of the synthetic dyes

To alleviate the risk of textile effluent, the development of highly effective bioremediation strategies for synthetic dye removal is needed. Herein, we aimed to assess whether intensified bioactivity of Bacillus pumilus ZB1 by oxidative stress could improve the removal of textile dyes. Methyl methanesulfonate (MMS) induced oxidative stress significantly promoted laccase expression of B. pumilus ZB1. Both the level of hydrogen dioxide and superoxide anion showed a significant positive correlation with laccase activity (RSQ = 0.963 and 0.916, respectively) along with the change of MMS concentration. The regulation of laccase expression was closely related to oxidative stress. The overexpressed laccase in the supernatant improved the decolorization of synthetic dyes (16.43% for Congo Red, 54.05% for Crystal Violet, and 41.61% for Reactive Blue 4). Laccase was subsequently expressed in E. coli. Investigation of the potential of bacterial laccase in dye remediation using Congo Red showed that an effective degradation of azo dye could be achieved with laccase treatment. Laccase remediation alleviated the cytotoxicity of Congo Red to human hepatocytes. In silico study identified eight amino acid residues of laccase involved in binding with Congo Red. Overall, regulation of oxidative stress towards bacterium can be used as a promising approach for the improvement of bacterial bioactivity in synthetic dye remediation.