Multiple-species hormetic phenomena induced by indole: A case study on the toxicity of indole to bacteria, algae and human cells

Adsorption enhanced biological treatment of hydrothermal liquefaction aqueous phase derived from municipal sludge

Hydrothermal liquefaction (HTL) is a promising method for municipal sludge valorization through waste minimization and biofuel production. The process wastewater, HTL aqueous, presents a significant challenge for scale-up due to recalcitrant compounds. In this study, granular activated carbon (GAC) was used to remove potential inhibitors from HTL aqueous through adsorption to enhance aerobic and anaerobic biological treatment. GAC removed up to 61 % chemical oxygen demand (COD), 50 % biochemical oxygen demand (BOD) and potential inhibitors, such as total phenolic compounds (87 %) and N-heterocycles (90 % of pyridines) at 100 g/L. Conversely, most volatile fatty acids remained in HTL aqueous. Subsequently, mesophilic and thermophilic specific methane potential increased by up to 97 % and 83 %, respectively. BOD increased by up to 50 %, which enhanced BOD/COD ratio from 81 % to 93 % before and after adsorption. This study established the groundwork for HTL aqueous adsorption, described mechanism for pollutant removal, and provided insights for biological treatment.

Exploring salivary metabolome alterations in people with HIV: towards early diagnostic markers

Background

The human immunodeficiency virus (HIV) remains a critical global health issue, with a pressing need for effective diagnostic and monitoring tools.

Methodology

This study explored distinctions in salivary metabolome among healthy individuals, individuals with HIV, and those receiving highly active antiretroviral therapy (HAART). Utilizing LC-MS/MS for exhaustive metabolomics profiling, we analyzed 90 oral saliva samples from individuals with HIV, categorized by CD4 count levels in the peripheral blood.

Results

Orthogonal partial least squares-discriminant analysis (OPLS-DA) and other analyses underscored significant metabolic alterations in individuals with HIV, especially in energy metabolism pathways. Notably, post-HAART metabolic profiles indicated a substantial presence of exogenous metabolites and changes in amino acid pathways like arginine, proline, and lysine degradation. Key metabolites such as citric acid, L-glutamic acid, and L-histidine were identified as potential indicators of disease progression or recovery. Differential metabolite selection and functional enrichment analysis, combined with receiver operating characteristic (ROC) and random forest analyses, pinpointed potential biomarkers for different stages of HIV infection. Additionally, our research examined the interplay between oral metabolites and microorganisms such as herpes simplex virus type 1 (HSV1), bacteria, and fungi in individuals with HIV, revealing crucial interactions.

Conclusion

This investigation seeks to contribute understanding into the metabolic shifts occurring in HIV infection and following the initiation of HAART, while tentatively proposing novel avenues for diagnostic and treatment monitoring through salivary metabolomics.

Quorum-sensing gene regulates hormetic effects induced by sulfonamides in Comamonadaceae

IMPORTANCE

Antibiotics can induce dose-dependent hormetic effects on bacterial cell proliferation, i.e., low-dose stimulation and high-dose inhibition. However, the underlying molecular basis has yet to be clarified. Here, we showed that sulfonamides play dual roles as a weapon and signal against Comamonas testosteroni that can modulate cell physiology and phenotype. Subsequently, through investigating the hormesis mechanism, we proposed a comprehensive regulatory pathway for the hormetic effects of Comamonas testosteroni low-level sulfonamides and determined the generality of the observed regulatory model in the Comamonadaceae family. Considering the prevalence of Comamonadaceae in human guts and environmental ecosystems, we provide critical insights into the health and ecological effects of antibiotics.

Interplays between cyanobacterial blooms and antibiotic resistance genes

Cyanobacterial harmful algal blooms (cyanoHABs), which are a form of microbial dysbiosis in freshwater environments, are an emerging environmental and public health concern. Additionally, the freshwater environment serves as a reservoir of antibiotic resistance genes (ARGs), which pose a risk of transmission during microbial dysbiosis, such as cyanoHABs. However, the interactions between potential synergistic pollutants, cyanoHABs, and ARGs remain poorly understood. During cyanoHABs, Microcystis and high microcystin levels were dominant in all the nine regions of the river sampled. The resistome, mobilome, and microbiome were interrelated and linked to the physicochemical properties of freshwater. Planktothrix and Pseudanabaena competed with Actinobacteriota and Proteobacteria during cyanoHABs. Forty two ARG carriers were identified, most of which belonged to Actinobacteriota and Proteobacteria. ARG carriers showed a strong correlation with ARGs density, which decreased with the severity of cyanoHAB. Although ARGs decreased due to a reduction of ARG carriers during cyanoHABs, mobile gene elements (MGEs) and virulence factors (VFs) genes increased. We explored the relationship between cyanoHABs and ARGs for potential synergistic interaction. Our findings demonstrated that cyanobacteria compete with freshwater commensal bacteria such as Actinobacteriota and Proteobacteria, which carry ARGs in freshwater, resulting in a reduction of ARGs levels. Moreover, cyanoHABs generate biotic and abiotic stress in the freshwater microbiome, which may lead to an increase in MGEs and VFs. Exploration of the intricate interplays between microbiome, resistome, mobilome, and pathobiome during cyanoHABs not only revealed that the mechanisms underlying the dynamics of microbial dysbiosis but also emphasizes the need to prioritize the prevention of microbial dysbiosis in the risk management of ARGs.

Ethylenediurea protects against ozone phytotoxicity not by adding nitrogen or controlling stomata in a stomata-unresponsive hybrid poplar

Ozone (O₃) pollution is a persistent environmental issue worldwide, which causes widespread damage to vegetation, deteriorating plant health and reducing plant productivity. Ethylenediurea (EDU) is a synthetic chemical that has been widely applied in scientific studies as a protectant against O₃ phytotoxicities. Despite four decades of active research, the exact mechanisms to explain its mode of action remain unclear. Here, we aimed to reveal whether EDU's phytoprotective property is due to its control over stomatal regulation and/or its action as a nitrogen (N) fertilizer, utilizing stomatal-unresponsive plants of a hybrid poplar (Populus koreana × trichocarpa cv. Peace) grown in a free-air O₃-concenctration enrichment (FACE) facility. Plants were treated with water (WAT), EDU (400 mg L^-1), or EDU's constitutive amount of N every nine days, and exposed to ambient (AOZ) or elevated (EOZ) O₃ during a growing season (June-September). EOZ led to extensive foliar injuries (but protected against rust disease), lower photosynthetic rate (A), impaired dynamics of responses of A to changes in light intensity, and smaller total plant leaf area. EDU protected against common phytotoxicities caused by EOZ without inducing stomatal closure, since stomatal conductance (g_s) was generally unresponsive to the experimental treatments. EDU also modulated the dynamic response of A to light fluctuations under O₃ stress. N addition acted as a fertilizer but did not satisfactorily protect plants against O₃ phytotoxicities. The results suggest that EDU protects against O₃ phytotoxicity not by adding N or controlling stomata, which provides a new insight into our understanding of the mode of action of EDU as a protectant against O₃ phytotoxicity.

Inhibitory effects of Ipomoea cairica extracts on the harmful algae Phaeocystis globosa

Ipomoea cairica (L.) Sweet is an invasive plant that cause serious invasion and damage in South China. Phaeocystis globosa is a common harmful algal bloom species on the southeast coast of China. Both species cause great environmental disturbances and serious economic damage to the localregion. This study explored the potential inhibitory effects of I. cairica leaf extracts on P. globosa. The results showed that solitary cells growth was inhibited at extract concentrations higher than 0.25 % (v/v). Although the colony diameter did not change, and the colony number increased rapidly in the first 36 h, we found that cells in the colonies had been damaged using scanning electron microscope and SYTOX-Green staining at 48 h. In addition, the rapid light-response curve of cells treated with extracts decreased, along with down-regulation of photosynthesis-related genes (psbA, psbD, and rbcL), suggesting damage to the photosynthetic system. Finally, the activities of antioxidant enzymes including superoxide dismutase, peroxidase, and catalase increased with increasing treatment time, indicating that cells activate antioxidant enzyme defense systems to alleviate the production of reactive oxygen species (ROS). Increased ROS levels disrupt cell membranes, alter cellular ultrastructures, and ultimately lead to cell death. This study not only achieved the reuse of invasive plant resources, but also demonstrated that I. cairica leaf extract has potential value as an algaecide.

Low Levels of Contaminants Stimulate Harmful Algal Organisms and Enrich Their Toxins

A widespread increase in intense phytoplankton blooms has been noted in lakes worldwide since the 1980s, with the summertime peak intensity amplifying in most lakes. Such blooms cause annual economic losses of multibillion USD and present a major challenge, affecting 11 out of the 17 United Nations Sustainable Development Goals. Here, we evaluate recent scientific evidence for hormetic effects of emerging contaminants and regulated pollutants on Microcystis sp., the most notorious cyanobacteria forming harmful algal blooms and releasing phycotoxins in eutrophic freshwater systems. This new evidence leads to the conclusion that pollution is linked to algal bloom intensification. Concentrations of contaminants that are considerably smaller than the threshold for toxicity enhance the formation of harmful colonies, increase the production of phycotoxins and their release into the environment, and lower the efficacy of algaecides to control algal blooms. The low-dose enhancement of microcystins is attributed to the up-regulation of a protein controlling microcystin release (McyH) and various microcystin synthetases in tandem with the global nitrogen regulator Ycf28, nonribosomal peptide synthetases, and several ATP-binding cassette transport proteins. Given that colony formation and phycotoxin production and release are enhanced by contaminant concentrations smaller than the toxicological threshold and are widely occurring in the environment, the effect of contaminants on harmful algal blooms is more prevalent than previously thought. Climate change and nutrient enrichment, known mechanisms underpinning algal blooms, are thus joined by low-level pollutants as another causal mechanism.

Effect of halogenated indoles on biofilm formation, virulence, and root surface colonization by Agrobacterium tumefaciens

Agrobacterium tumefaciens is a plant pathogen that causes crown gall disease in several plant species by transferring its T-DNA to the host genome. Its chemotactic response to a range of chemical compounds released by hosts facilitates its colonization to host surfaces, and thus, novel anti-agrobacterium compounds are needed to prevent its biofilm formation. Here, we investigated 83 indole derivatives against A. tumefaciens, and based on the screening, 4-chloroindole, 6-iodoindole, and 5-chloro-2-methyl indole were selected as candidates that at 50 μg mL^-1 significantly inhibited the adherence and biofilm formation of A. tumefaciens to abiotic (nitrocellulose and polystyrene) and biotic (roots of Brassica juncea) surfaces. Furthermore, they reduced bacterial growth in a time and concentration-dependent manner and significantly reduced log CFU mL^-1 and survival (%). Changes in biofilm morphologies and biomasses, thicknesses, and substratum coverages were determined, and 2-D and 3-D analyses were performed using a crystal violet assay and bright field, CLSM, and SEM microscopies. Virulence factors such as swimming motility, exopolysaccharide, and exo-protease production, and cell surface hydrophobicity were markedly inhibited by the three compounds. Transcriptional analysis showed multi-fold downregulation of biofilm, virulence, motility, and stress-related genes; however, the degrees of these downregulations were variably affected. B. juncea seed germination was only severely affected by 4-chloroindole. This study demonstrates the promising antibiofilm and antivirulence activities of the three indole derivatives tested and their potentials for targeting and curbing A. tumefaciens infections.

Role of endocrine disruption in toxicity of 6-benzylaminopurine (6-BA) to early-life stages of Zebrafish

6-benzylaminopurine (6-BA), classified as a "plant hormone", is an important ingredient in production of "toxic bean sprouts". Although there is no direct evidence of adverse effects, its hazardous effects have received some attention and aroused furious debate between proponents and environmental regulators. In this study, potential adverse effects of 6-BA were investigated by exposing zebrafish in vivo to 0.2 - 25 mg 6-BA/L. Results indicated that, when exposure was limited to early-life stage (4-36 hpf), 20 mg 6-BA/L caused early hatching, abnormal spontaneous movement, and precocious hyperactivity in zebrafish embryos/larvae. While under a continuous exposure regime, 6-BA at 0.2 mg/L was able to cause hyperactive locomotion and transcription of genes related to neurogenesis (gnrh3 and nestin) and endocrine systems (cyp19a and fshb) in 5 dpf larvae. Quantification by use of LC/MS indicated bioaccumulation of 6-BA in zebrafish increased when exposed to 0.2 or 20 mg 6-BA/L. These results suggested that 6-BA could accumulate in aquatic organisms and disrupt neuro-endocrine systems. Accordingly, exposure to 0.2 mg 6-BA/L increased production of estradiol (E2) and consequently E2/T ratio in zebrafish larvae, which directly indicated 6-BA is estrogenic. In silico simulations demonstrated potential for binding of 6-BA to estrogen receptor alpha (ERa) and cytochrome P450 aromatase (CYP19A). Therefore, induction of estrogenic effects, via potential interactions with hormone receptors or disturbance of downstream transcription signaling, was possible mechanism underlying the toxicity of 6-BA. Taken together, these findings demonstrate endocrine disrupting properties of 6-BA, which suggest concerns about risks posed to endocrine systems.

Investigation of indole biodegradation by Cupriavidus sp. strain IDO with emphases on downstream biotransformation and indigo production

Indole, as a typical N-heterocyclic aromatic pollutant, poses risks to living things; however, indole-biotransformation mechanisms remain under-discussed, especially those related to its downstream biotransformation. Here, we systematically investigated the characteristics of indole degradation by strain Cupriavidus sp. IDO. We found that Cupriavidus sp. IDO could utilize 25 to 150 mg/L indole within 40 h and identified three intermediates (2-oxindole, indigo, and isatin). Additionally, integrated genomics and proteomics analysis of the indole biotransformation mechanism in strain IDO revealed 317 proteins showing significant changes (262 upregulated and 55 downregulated) in the presence of indole. Among these, three clusters containing indole oxidoreductase, CoA-thioester ligase, and gentisate 1,2-oxidoreductase were identified as potentially responsible for upstream and downstream indole metabolism. Moreover, HPLC-MS and -omics analysis offered insight into the indole-degradation pathway in strain IDO. Furthermore, the indole oxidoreductase IndAB, which initiates indole degradation, was heterologously expressed in Escherichia coli BL21(DE3). Optimization by the response surface methodology resulted in a maximal production of 135.0 mg/L indigo by the recombination strains in tryptophan medium. This work enriches our understanding of the indole-biodegradation process and provides new insights into multiple indole-degradation pathways in natural environments.

Antibiotic-accelerated cyanobacterial growth and aquatic community succession towards the formation of cyanobacterial bloom in eutrophic lake water

Antibiotics can stimulate the growth of model cyanobacterial species under pure culture conditions, but their influence on cyanobacterial blooms in natural aquatic ecosystems remains unclear. In this study, three commonly detected antibiotics (sulfamethoxazole, tetracycline, and ciprofloxacin) and their ternary mixture were proved to selectively stimulate (p < 0.05) the growth and photosynthetic activity of cyanobacteria in an aquatic microcosm at an environmentally relevant exposure dose of 300 ng/L under both oligotrophic and eutrophic conditions. Under the eutrophic condition, cyanobacteria reached a bloom density of 1.61 × 10⁶ cells/mL in 15 days without antibiotics, while the cyanobacteria exposed to tetracycline, sulfamethoxazole, ciprofloxacin, and their ternary mixture exceeded this bloom density within only 10, 8, 7, and 6 days, respectively. Principal coordinate analysis indicated that the antibiotic contaminants accelerated the prokaryotic community succession towards the formation of a cyanobacterial bloom by promoting the dominance of Microcystis, Synechococcus, and Oscillatoria under the eutrophic condition. After 15 days of culture, the antibiotic exposure increased the density of cyanobacteria by 1.38-2.31-fold and 2.28-3.94-fold under eutrophic and oligotrophic conditions, respectively. Antibiotic exposure generated higher stimulatory effects on cyanobacterial growth under the oligotrophic condition, but the antibiotic(s)-treated cyanobacteria did not form a bloom due to nutrient limitation. Redundancy analysis indicated that the three target antibiotics and their ternary mixture affected the prokaryotic community structure in a similar manner, while tetracycline showed some differences compared to sulfamethoxazole, ciprofloxacin, and the ternary antibiotic mixture with regard to the regulation of the eukaryotic community structure. This study demonstrates that antibiotic contaminants accelerate the formation of cyanobacterial blooms in eutrophic lake water and provides insights into the ecological effects of antibiotics on aquatic microbial communities.

Diverse roles of microbial indole compounds in eukaryotic systems

Indole and its derivatives are widespread across different life forms, functioning as signalling molecules in prokaryotes and with more diverse roles in eukaryotes. A majority of indoles found in the environment are attributed to bacterial enzymes converting tryptophan into indole and its derivatives. The involvement of indoles among lower organisms as an interspecies and intraspecies signal is well known, with many reports showing that inter‐kingdom interactions involving microbial indole compounds are equally important as they influence defence systems and even the behaviour of higher organisms. This review summarizes recent advances in our understanding of the functional properties of indole and indole derivatives in diverse eukaryotes. Furthermore, we discuss current perspectives on the role of microbial indoles in human diseases such as diabetes, obesity, atherosclerosis, and cancers. Deciphering the function of indoles as biomarkers of metabolic state will facilitate the formulation of diet‐based treatments and open unique therapeutic opportunities.

Insights into the role of energy source in hormesis through diauxic growth of bacteria in mixed cultivation systems

Hormesis, a biphasic dose-response relationship characterized by low-dose stimulation and high-dose inhibition, has been reported to be closely related to energy sources in cultivation systems. However, few studies have clarified how the energy source influences hormesis. In this study, based on the typical diauxic patterns of Escherichia coli (E. coli) growth in mixed cultivation media containing 1.0 g L^-1 glucose and Luria-Bertani broth, the hormetic response of sulfonamides (SAs) to E. coli growth was investigated under this diauxic growth condition to thoroughly explain the close relationship between hormesis and energy sources in cultivation systems. The results indicated that SAs trigger time-dependent hormetic effects on E. coli growth over the span of 24 h, in which the biphasic dose-response occurs only during the second lag and the earlier stage of the second log phase of diauxic growth. Mechanistic exploration reveals that SAs can bind with adenylate cyclase at a low dose and dihydropteroate synthase at a high dose, respectively, activating the stimulatory and inhibitory signaling pathway to influence carbon catabolite repression in diauxic growth, which can interfere with the metabolism of tryptone and yeast extract to ultimately trigger hormesis. Moreover, the stimulatory and inhibitory effects of SAs are changed by the variations in metabolic status at different growth phases, resulting in time-dependent hormesis. This study proposes an induced mechanistic explanation of hormesis in mixed cultivation media based on the energy source's metabolism, which may not only reflect the generalizability of hormesis but also further promote its application in production activities.

Astragaloside IV Extends Lifespan of Caenorhabditis elegans by Improving Age-Related Functional Declines and Triggering Antioxidant Responses

Astragaloside IV (AS-IV) is a representative component of astragaloside saponins in dried roots of Astragali Radix. Astragaloside possesses a broad spectrum of pharmacological activities, including antibacterial, anti-fibrosis, antioxidant, anti-inflammatory, and neuroprotective effects. However, the role of AS-IV in antiaging remains unclear. In this article, we studied the function of AS-IV in antiaging by using the Caenorhabditis elegans (C. elegans) model. We showed that AS-IV can prolong the lifespan of C. elegans in a natural aging model, a paraquat injury model, and a heat stress model and improve the movement capacity of nematodes. ¹H-NMR data indicate an improvement of glutamate content and a decrease in glucose in the AS-IV treatment group compared with the control. Further investigation revealed that AS-IV can induce the mRNA expression of superoxide dismutase (SOD) and catalase (CAT) genes and increase the activities of SOD and CAT in the nematode. Interestingly, AS-IV could not extend the lifespan of sod-1, sod-2, sod-3, sod-4, sod-5, ctl-1, ctl-2, ctl-3, and daf-16 mutants. These data indicate that AS-IV prevents aging via mainly improving age-related functional declines, the antioxidant capacity of nematodes and partially modulating the insulin/insulin growth factor 1 signaling pathway activity. Our results provide new insights into how AS-IV prevents and treats aging.

Similarities between the Yin/Yang Doctrine and Hormesis in Toxicology and Pharmacology

Hormesis is a generalizable dose-response relationship characterized by low-dose stimulation and high-dose inhibition. Despite debate over this biphasic dose-response curve, hormesis is challenging central beliefs in the evaluation of chemicals or drugs and has influenced biological model selection, concentration range, study design, and hypothesis testing. We integrate the traditional Chinese philosophy - Yin/Yang doctrine - into the representation of the Western hormetic dose-response relationship and review the Yin/Yang historical philosophy contained in the hormesis concept, aiming to promote general acceptance and wider applications of hormesis. We suggest that the Yin/Yang doctrine embodies the hormetic dose-response, including the relationship between the opposing components, curve shape, and time-dependence, and may afford insights that clarify the hormetic dose-response relationship in toxicology and pharmacology.

Elimination of the hormesis phenomenon by the use of synthetic sea water in a toxicity test towards Aliivibrio fischeri

Hormesis is an ecotoxicological phenomenon referred to as the biphasic dose-response effect. At a low concentration of toxic substances, a hormetic stimulating effect occurs, while an inhibitory effect occurs at higher concentrations. The phenomenon of hormesis may hinder the interpretation of toxicity test results and lower the actual toxicity of test samples. In this study, a hormesis phenomenon was observed and analysed during toxicity tests of wastewater from constructed wetlands containing two pharmaceutical substances, diclofenac (DCF) and sulfamethoxazole (SMX), against the marine bacteria Aliivibrio fischeri. To eliminate the hormesis phenomenon, a change in the diluent (ISO 11348-3:2007) to synthetic sea water (ISO 10253:2006) is proposed. The hormesis phenomenon was observed only during the analysis of wastewater toxicity with the standard toxicity test (with the diluent). The use of synthetic sea water eliminated the hormetic effects because of the presence of additional components in the sea water, such as MgCl₂, Na₂SO₄, CaCl₂, KCl, NaHCO₃, and H₃BO₃, which increased the sensitivity of A. fischeri to the pharmaceutical substances. The use of different media in toxicity tests may have significant effects on the toxicity classification of the tested compounds or wastewater. Additionally, the toxicity of tested pharmaceuticals towards A. fischeri was analysed. The IC₅₀ values of DCF were 8.7 ± 1.1 mg L^-1 (for diluent) and 13.9 ± 0.9 mg L^-1 (for synthetic sea water) whereas those of SMX were 50.5 ± 2.3 and 55.3 ± 1.6 mg L^-1, respectively.

Inhibition of harmful algae Phaeocystis globosa and Prorocentrum donghaiense by extracts of coastal invasive plant Spartina alterniflora

Harmful algal blooms (HABs) and the invasion of smooth cordgrass (Spartina alterniflora) have become important environmental problems in intertidal zones of China, which caused serious damage on the coastal ecological systems. By using S. alterniflora as algaecide, this helps to utilize this invasive plant, in addition, is expected to help to control the expansion of S. alterniflora. The potential of S. alterniflora in HABs mitigation was investigated on controlling Phaeocystis globosa (haptophyceae) and Prorocentrum donghaiense (dinophyceae). The growth of both HABs species was significantly inhibited at high concentrations, and P. globosa was more sensitive than P. donghaiense. Furthermore, the extracts of S. alterniflora reduced the effective quantum yield, photosynthetic efficiency, and relative maximal electron transport rate of both algal species at high concentrations, which implies a disruption on their photosynthetic system. Flavonoids, which were previously known as antialgal chemicals, were found to be abundant in the extracts of S. alterniflora by UPLC-MS detection. Our results revealed that the potential of S. alterniflora as a novel antialgal agent for controlling HABs, simultaneously, resource utilization possibility for the invasive plant S. alterniflora.

An Evidence Synthesis of Pharmaceuticals and Personal Care Products (PPCPs) in the Environment: Imbalances among Compounds, Sewage Treatment Techniques, and Ecosystem Types

Pharmaceuticals and personal care products (PPCPs) garner increasing attention globally for both their usefulness as indicators of human waste and their potency as emerging organic toxicants. Three decades of rapid increase in PPCP study combined with an increasing number of PPCPs on the global market have created an opportunity (1) to review trends in diversity of compounds, sewage treatment techniques (STTs), and ecosystems investigated as well as (2) to identify knowledge gaps in the literature. We conducted a quantitative evidence synthesis of 6517 abstracts from primary articles in the environmental PPCP literature by examining relative abundance of specific PPCP classes, STTs, and ecosystem types. Our results demonstrate that non-prescription drugs and antibiotics dominated PPCP abstracts, appearing in 51% and 39% of reviewed abstracts, respectively, in comparison to hormones (18%), prescription drugs (18%), fragrances (0.3%), and antioxidants (0.0%), which can all elicit physiological and ecological responses even at low concentrations. References to centralized STTs (e.g., activated sludge, 37%) were more frequent than decentralized STTs (e.g., septic, 2%), despite decentralized STTs being common and frequently high impact sources of sewage pollution worldwide. Freshwater lotic systems (63%) were more prevalent than freshwater lentic (24%) and terrestrial (20%) systems. This discrepancy is notable because the longer residence times of lentic and terrestrial systems may enable PPCPs to concentrate and thus increase risk of biological consequences. These results highlight distinct opportunities to address knowledge gaps in the environmental PPCP literature, including underrepresented compounds (e.g., fragrances), sewage treatment techniques (e.g., septic systems), and ecosystem types (e.g., lakes).

A deep insight into the toxic mechanism for sulfonamides based on bacterial cell-cell communication

Sulfonamides (SAs), a kind of commonly used antibiotics, have been frequently detected in the environment. Due to their potential threat to the ecological environment, the toxicity of SAs to bacteria have been determined in depth, and the toxic mechanism is found to target dihydropteroate synthase (DHPS). However, other toxic mechanism may also exist for SAs, which is still unclear to us. In this paper, the toxic mechanism of sulfachloropyridazine (SCP, as a representative of SAs) was investigated thoroughly on Aliivibrio fischeri (A. fischeri) from the perspective of quorum sensing (QS). The results reveal that SCP may act on three signaling pathways, i.e., Pathway I, II and III, which triggers, maintains and destroys the homeostasis of A. fischeri respectively. In Pathway I, SCP changes the active form of LitR that regulates the expression of lux-related genes, inducing inhibition on bacterial growth while stimulation on luminescence; in Pathway II, SCP facilitates the production of C6HSL signaling molecules, maintaining the homeostasis in LitR and DHPS proteins; whereas in Pathway III, SCP typically combines with DHPS to inhibit the folate metabolism. This study can provide a deeper and more comprehensive understanding on the toxicity of SAs and help the environmental risk assessment of SAs.