Hormetic dose responses induced by antibiotics in bacteria: A phantom menace to be thoroughly evaluated to address the environmental risk and tackle the antibiotic resistance phenomenon

Effects of sulfamethazine on microbially-mediated denitrifying anaerobic methane oxidation in estuarine wetlands

Nitrite/nitrate-dependent anaerobic methane oxidation (n-DAMO) is an important methane (CH4) consumption and nitrogen (N) removal pathway in estuarine and coastal wetlands. Antibiotic contamination is known to affect microbially mediated processes; however, its influences on n-DAMO and the underlying molecular mechanisms remain poorly understood. In the present study, using 13CH4 tracer method combined with molecular techniques, we investigated the responses of n-DAMO microbial abundance, activity, and the associated microbial community composition to sulfamethazine (SMT, a sulfonamide antibiotic, with exposure concentrations of 0.05, 0.5, 5, 20, 50, and 100 µg L-1). Results showed that the effect of SMT exposure on n-DAMO activity was dose-dependent. Exposure to SMT at concentrations of up to 5 µg L-1 inhibited the potential n-DAMO rates (the average rates of nitrite- and nitrate-DAMO decreased by 92.9 % and 79.2 % relative to the control, respectively). In contrast, n-DAMO rates tended to be promoted by SMT when its concentration increased to 20-100 µg L-1 (the average rates of nitrite- and nitrate-DAMO increased by 724.1 % and 630.1 % relative to the low-doses, respectively). Notably, low-doses of SMT suppressed nitrite-DAMO to a greater extent than nitrate-DAMO, indicating that nitrite-DAMO was more sensitive to SMT than nitrate-DAMO. Molecular analyses suggest that the increased n-DAMO activity under high-doses SMT exposure may be driven by changes in microbial communities, especially because of the promotion of methanogens that provide more CH4 to n-DAMO microbes. Moreover, the abundances of n-DAMO microbes at high SMT exposure (20 and 50 µg L-1) were significantly higher than that at low SMT exposure (0.05-5 µg L-1). These results advance our understanding of the ecological effects of SMT on carbon (C) and N interactions in estuarine and coastal wetlands.

Low-dose zinc oxide nanoparticles trigger the growth and biofilm formation of Pseudomonas aeruginosa: a hormetic response

INTRODUCTION

Hormesis describes an inverse dose-response relationship, whereby a high dose of a toxic compound is inhibitory, and a low dose is stimulatory. This study explores the hormetic response of low concentrations of zinc oxide nanoparticles (ZnO NPs) toward Pseudomonas aeruginosa.

METHOD

Samples of P. aeruginosa, i.e. the reference strain, ATCC 27,853, together with six strains recovered from patients with cystic fibrosis, were exposed to ten decreasing ZnO NPs doses (0.78-400 µg/mL). The ZnO NPs were manufactured from Peganum harmala using a chemical green synthesis approach, and their properties were verified utilizing X-ray diffraction and scanning electron microscopy. A microtiter plate technique was employed to investigate the impact of ZnO NPs on the growth, biofilm formation and metabolic activity of P. aeruginosa. Real-time polymerase chain reactions were performed to determine the effect of ZnO NPs on the expression of seven biofilm-encoding genes.

RESULT

The ZnO NPs demonstrated concentration-dependent bactericidal and antibiofilm efficiency at concentrations of 100-400 µg/mL. However, growth was significantly stimulated at ZnO NPs concentration of 25 µg/mL (ATCC 27853, Pa 3 and Pa 4) and at 12.5 µg/mL and 6.25 µg/mL (ATCC 27853, Pa 2, Pa 4 and Pa 5). No significant positive growth was detected at dilutions < 6.25 µg/mL. similarly, biofilm formation was stimulated at concentration of 12.5 µg/mL (ATCC 27853 and Pa 1) and at 6.25 µg/mL (Pa 4). At concentration of 12.5 µg/mL, ZnO NPs upregulated the expression of LasB ( ATCC 27853, Pa 1 and Pa 4) and LasR and LasI (ATCC 27853 and Pa 1) as well as RhII expression (ATCC 27853, Pa 2 and Pa 4).

CONCLUSION

When exposed to low ZnO NPs concentrations, P. aeruginosa behaves in a hormetic manner, undergoing positive growth and biofilm formation. These results highlight the importance of understanding the response of P. aeruginosa following exposure to low ZnO NPs concentrations.

Occurrence and dissemination of antibiotics and antibiotic resistance in aquatic environment and its ecological implications: a review

The occurrence of antibiotics and antibiotic-resistant bacteria (ARBs), genes (ARGs), and mobile genetic elements (MGEs) in aquatic systems is growing global public health concern. These emerging micropollutants, stemming from improper wastewater treatment and disposal, highlight the complex and evolving nature of environmental pollution. Current literature reveals potential biases, such as a geographical focus on specific regions, leading to an insufficient understanding of the global distribution and dynamics of antibiotic resistance in aquatic systems. There is methodological inconsistency across studies, making it challenging to compare findings. Potential biases include sample collection inconsistencies, detection sensitivity variances, and data interpretation variability. Gaps in understanding include the need for comprehensive, standardized long-term monitoring programs, elucidating the environmental fate and transformation of antibiotics and resistance genes. This review summarizes current knowledge on the occurrence and dissemination of emerging micropollutants, their ecological impacts, and the global health implications of antimicrobial resistance. It highlights the need for interdisciplinary collaborations among researchers, policymakers, and stakeholders to address the challenges posed by antibiotic resistance in aquatic resistance in aquatic systems effectively. This review highlights widespread antibiotic and antibiotic resistance in aquatic environment, driven by human and agricultural activities. It underscores the ecological consequences, including disrupted microbial communities and altered ecosystem functions. The findings call for urgent measures to mitigate antibiotics pollution and manage antibiotic resistance spread in water bodies.

Morpholinium-based Ionic Liquids as Potent Antibiofilm and Sensitizing Agents for the Control of Pseudomonas aeruginosa

Rising antimicrobial resistance is a critical threat to worldwide public health. To address the increasing antibiotic tolerance, diverse antimicrobial agents are examined for their ability to decrease bacterial resistance. One of the most relevant and persistent human pathogens is Pseudomonas aeruginosa. Our study investigates the anti-biofilm and sensitizing activity of 12 morpholinium-based ionic liquids with herbicidal anions on four clinically relevant P. aeruginosa strains. Among all tested compounds, four ionic liquids prevented biofilm formation at sub-minimum inhibitory concentrations for all investigated strains. For the first time, we established a hormetic effect on biofilm formation for P. aeruginosa strains subjected to an ionic liquid treatment. Interestingly, while ionic liquids with 4,4-didecylmorpholinium [Dec2Mor]+ are more efficient against planktonic bacteria, 4-decyl-4-ethylmorpholinium [DecEtMor]+ showed more potent inhibition of biofilm formation. Ionic liquids with 4,4-didecylmorpholinium ([Dec2Mor]+) cations even induced biofilm formation by strain 39016 at high concentrations due to flocculation. Morpholinium-based ionic liquids were also shown to enhance the efficacy of commonly used antibiotics from different chemical groups. We demonstrate that this synergy is associated with the mode of action of the antibiotics.

Silversol® (a Colloidal Nanosilver Formulation) Inhibits Growth of Antibiotic-Resistant Staphylococcus aureus by Disrupting Its Physiology in Multiple Ways

Antibiotic-resistant strains of Staphylococcus aureus are being viewed as a serious threat by various public health agencies. Identifying novel targets in this important pathogen is crucial to the development of new effective antibacterial formulations. We investigated the antibacterial effect of a colloidal nanosilver formulation, Silversol®, against an antibiotic-resistant strain of S. aureus using appropriate in vitro assays. Moreover, we deciphered the molecular mechanisms underlying this formulation's anti-S. aureus activity using whole transcriptome analysis. Lower concentrations of the test formulation exerted a bacteriostatic effect against this pathogen, and higher concentrations exerted a bactericidal effect. Silversol® at sub-lethal concentration was found to disturb multiple physiological traits of S. aureus such as growth, antibiotic susceptibility, membrane permeability, efflux, protein synthesis and export, biofilm and exopolysaccharide production, etc. Transcriptome data revealed that the genes coding for transcriptional regulators, efflux machinery, transferases, β-lactam resistance, oxidoreductases, metal homeostasis, virulence factors, and arginine biosynthesis are expressed differently under the influence of the test formulation. Genes (argG and argH) involved in arginine biosynthesis emerged among the major targets of Silversol®'s antibacterial activity against S. aureus.

Time Is Ripe for Targeting Per- and Polyfluoroalkyl Substances-Induced Hormesis: Global Aquatic Hotspots and Implications for Ecological Risk Assessment

Globally implemented ecological risk assessment (ERA) guidelines marginalize hormesis, a biphasic dose-response relationship characterized by low-dose stimulation and high-dose inhibition. The present study illuminated the promise of hormesis as a scientific dose-response model for ERA of per- and polyfluoroalkyl substances (PFAS) represented by perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS). A total of 266 hormetic dose-response relationships were recompiled from 1237 observations, covering 30 species from nine representative taxonomic groups. The standardized hormetic amplitudes followed the log-normal probability distribution, being subject to the limits of biological plasticity but independent of stress inducers. The SHapley Additive exPlanations algorithm revealed that the target endpoint was the most important variable explaining the hormetic amplitudes. Subsequently, quantitative frameworks were established to incorporate hormesis into the predicted no-effect concentration levels, with a lower induction dose and a zero-equivalent point but a broader hormetic zone for PFOS. Realistically, 10,117 observed concentrations of PFOA and PFOS were gathered worldwide, 4% of which fell within hormetic zones, highlighting the environmental relevance of hormesis. Additionally, the hormesis induction potential was identified in other legacy and emerging PFAS as well as their alternatives and mixtures. Collectively, it is time to incorporate the hormesis concept into PFAS studies to facilitate more realistic risk characterizations.

Research progress on the origin, fate, impacts and harm of microplastics and antibiotic resistance genes in wastewater treatment plants

Previous studies reported microplastics (MPs), antibiotics, and antibiotic resistance genes (ARGs) in wastewater treatment plants (WWTPs). There is still a lack of research progress on the origin, fate, impact and hazards of MPs and ARGs in WWTPs. This paper fills a gap in this regard. In our search, we used "microplastics", "antibiotic resistance genes", and "wastewater treatment plant" as topic terms in Web of Science, checking the returned results for relevance by examining paper titles and abstracts. This study mainly explores the following points: (1) the origins and fate of MPs, antibiotics and ARGs in WWTPs; (2) the mechanisms of action of MPs, antibiotics and ARGs in sludge biochemical pools; (3) the impacts of MPs in WWTPs and the spread of ARGs; (4) and the harm inflicted by MPs and ARGs on the environment and human body. Contaminants in sewage sludge such as MPs, ARGs, and antibiotic-resistant bacteria enter the soil and water. Contaminants can travel through the food chain and thus reach humans, leading to increased illness, hospitalization, and even mortality. This study will enhance our understanding of the mechanisms of action among MPs, antibiotics, ARGs, and the harm they inflict on the human body.

Consumption and Informal Trade of Milk in the North of Antioquia (Colombia)

The excessive and irrational use of antibiotics to control bovine mastitis and the informal trade in milk with antibiotic residues are objects of great interest for public health, due to the problems associated with the consumption of milk with antibiotic residues on human, animal, and environmental health, and antibiotic resistance. The objective of this study was to understand the attitudes of dairy farmers towards the self-consumption of milk on the farm, the use of milk with antibiotic residues, and the formal and informal milk trade that generates risks for public health. Mixed methods: cross-sectional and grounded theory. Convergent triangulation design. The study was carried out in 9 dairy municipalities in the North of Antioquia, where 216 dairy farmers participated in the quantitative component; and 17 milk producers and 9 veterinarians took part in the qualitative component. A dairy farmer characterization survey was conducted, as well as a survey on the use and marketing of milk from cows with udder health problems and/or under antibiotic treatment. Semistructured interviews were conducted on the same subject. The variable "Intention to sell milk in the village when the dairy industry does not buy it due to high BTSCC" is associated with the BTSCC variable. The variable "Type of marketing reported" is associated with the CFU variable. 5 categories: self-consumption of milk, use of milk with antibiotics, informal milk trade, control of the dairy industry, and beliefs about the elimination of antibiotics in milk, were constructed to theorize about udder health and public health. Sociocultural, political, and economic factors affect decision making in dairy farmers regarding the use and marketing of milk from cows with mastitis and antibiotic residues. These attitudes and behaviors have public health implications.

Tetracycline and sulfadiazine toxicity in human liver cells Huh-7

As typical antibiotics, tetracycline (TC) and sulfadiazine (SDZ) enter the human body through the food chain. Therefore, it is necessary to understand their individual and combined toxicity. In this study, the effects of TC, SDZ, and their mixture on cell viability, cell membrane damage, liver cell damage, and oxidative damage were evaluated in in vitro assays with human liver cells Huh-7. The results showed cytotoxicity of TC, SDZ, and their mixture, which induced oxidative stress and caused membrane and cell damage. The effect of antibiotics on Huh-7 cells increased with increasing concentration, except for lactate dehydrogenase (LDH) activity that commonly showed a threshold concentration response and cell viability, which commonly showed a biphasic trend, suggesting the possibility of hormetic responses where proper doses are included. The toxicity of TC was commonly higher than that of SDZ when applied at the same concentration. These findings shed light on the individual and joint effects of these major antibiotics on liver cells, providing a scientific basis for the evaluation of antibiotic toxicity and associated risks.

Long-term exposure of Allonais inaequalis to a mixture of antibiotics in freshwater and synthetic wastewater matrices: Reproduction, recovery, and swimming responses

Antibiotics from sulfonamide, fluoroquinolone, and diaminopyrimidine classes are widely used in human and veterinary medicine, and their combined occurrence in the aquatic environment is increasing around the world. In parallel, the understanding of how mixtures of these compounds affect non-target species from tropical freshwaters is scarce. Thus, this work aimed to study the long-term reproductive, recovery, and swimming effects of mixtures of 12 antibiotics from three different classes (up to 10 μg L-1 ) added to freshwater (FWM) and synthetic wastewater (SWM) matrices on freshwater worm Allonais inaequalis. Results revealed that at the reproduction level, the exposure to antibiotics in the SWM matrix does not cause a significant toxic effect on species after 10 days. On the other hand, exposures to initial dose mixtures (10 μg L-1 each) in FWM caused a significant reduction of offspring by 19.2%. In addition, recovery bioassays (10 days in an antibiotic-free environment) suggested that A. inaequalis has reduced offspring production due to previous exposure to antibiotic mixtures in both matrices. Furthermore, despite slight variation in swimming speed over treatments, no significant differences were pointed out. Regarding antibiotics in the water matrices after 10-day exposures, the highest concentrations were up to 2.7, 7.8, and 4.2 μg L-1 for antibiotics from sulfonamide, fluoroquinolone, and diaminopyrimidine classes, respectively. These findings suggest that a species positioned between primary producers and secondary consumers may experience late reproductive damage even in an antibiotic-free zone, after previous 10-day exposure to antibiotic mixtures. PRACTITIONER POINTS: A mixture of sulfonamide, fluoroquinolone, and diaminopyrimidine antibiotics in freshwater affects the offspring production of A. inaequalis after 10 days. After the 10-day antibiotic exposure, the reproduction of A. inaequalis remains affected in an antibiotic-free environment over the recovery period. The swimming speed of the worms does not change after 10 days of exposure to the antibiotic mixture. The concentration of dissolved solids can limit the natural degradation of sulfonamide, fluoroquinolone, and diaminopyrimidine antibiotics in the aquatic environment.

A review on the antibiotic florfenicol: Occurrence, environmental fate, effects, and health risks

Florfenicol, as a replacement for chloramphenicol, can tightly bind to the A site of the 23S rRNA in the 50S subunit of the 70S ribosome, thereby inhibiting protein synthesis and bacterial proliferation. Due to the widespread use in aquaculture and veterinary medicine, florfenicol has been detected in the aquatic environment worldwide. Concerns over the effects and health risks of florfenicol on target and non-target organisms have been raised in recent years. Although the ecotoxicity of florfenicol has been widely reported in different species, no attempt has been made to review the current research progress of florfenicol toxicity, hormesis, and its health risks posed to biota. In this study, a comprehensive literature review was conducted to summarize the effects of florfenicol on various organisms including bacteria, algae, invertebrates, fishes, birds, and mammals. The generation of antibiotic resistant bacteria and spread antibiotic resistant genes, closely associated with hormesis, are pressing environmental health issues stemming from overuse or misuse of antibiotics including florfenicol. Exposure to florfenicol at μg/L-mg/L induced hormetic effects in several algal species, and chromoplasts might serve as a target for florfenicol-induced effects; however, the underlying molecular mechanisms are completely lacking. Exposure to high levels (mg/L) of florfenicol modified the xenobiotic metabolism, antioxidant systems, and energy metabolism, resulting in hepatotoxicity, renal toxicity, immunotoxicity, developmental toxicity, reproductive toxicity, obesogenic effects, and hormesis in different animal species. Mitochondria and the associated energy metabolism are suggested to be the primary targets for florfenicol toxicity in animals, albeit further in-depth investigations are warranted for revealing the long-term effects (e.g., whole-life-cycle impacts, multigenerational effects) of florfenicol, especially at environmental levels, and the underlying mechanisms. This will facilitate the evaluation of potential hormetic effects and construction of adverse outcome pathways for environmental risk assessment and regulation of florfenicol.

How did antibiotic growth promoters increase growth and feed efficiency in poultry?

It has been hypothesized that reducing the bioenergetic costs of gut inflammation as an explanation for the effect of antibiotic growth promoters (AGPs) on animal efficiency, framing some observations but not explaining the increase in growth rate or the prevention of infectious diseases. The host's ability to adapt to alterations in environmental conditions and to maintain health involves managing all physiological interactions that regulate homeostasis. Thus, metabolic pathways are vital in regulating physiological health as the energetic demands of the host guides most biological functions. Mitochondria are not only the metabolic heart of the cell because of their role in energy metabolism and oxidative phosphorylation, but also a central hub of signal transduction pathways that receive messages about the health and nutritional states of cells and tissues. In response, mitochondria direct cellular and tissue physiological alterations throughout the host. The endosymbiotic theory suggests that mitochondria evolved from prokaryotes, emphasizing the idea that these organelles can be affected by some antibiotics. Indeed, therapeutic levels of several antibiotics can be toxic to mitochondria, but subtherapeutic levels may improve mitochondrial function and defense mechanisms by inducing an adaptive response of the cell, resulting in mitokine production which coordinates an array of adaptive responses of the host to the stressor(s). This adaptive stress response is also observed in several bacteria species, suggesting that this protective mechanism has been preserved during evolution. Concordantly, gut microbiome modulation by subinhibitory concentration of AGPs could be the result of direct stimulation rather than inhibition of determined microbial species. In eukaryotes, these adaptive responses of the mitochondria to internal and external environmental conditions, can promote growth rate of the organism as an evolutionary strategy to overcome potential negative conditions. We hypothesize that direct and indirect subtherapeutic AGP regulation of mitochondria functional output can regulate homeostatic control mechanisms in a manner similar to those involved with disease tolerance.

Redefining Peptide 14D: Substitutional Analysis for Accelerated TB Diagnosis and Enhanced Activity against Mycobacterium tuberculosis

Tuberculosis (TB) caused by Mycobacterium tuberculosis remains a predominant cause of mortality, especially in low- and middle-income nations. Recently, antimicrobial peptides have been discovered that at low concentrations could stimulate the growth of M. tuberculosis (hormetic response). In this study, such a peptide was used to investigate the effects on the time to positivity (TTP). A systematic substitution analysis of peptide 14D was synthesized using Spot synthesis technology, resulting in 171 novel peptides. Our findings revealed a spectrum of interactions, with some peptides accelerating M. tuberculosis growth, potentially aiding in faster diagnostics, while others exhibited inhibitory effects. Notably, peptide NH2-wkivfiwrr-CONH2 significantly reduced the TTP by 25 h compared to the wild-type peptide 14D, highlighting its potential in improving TB diagnostics by culture. Several peptides demonstrated potent antimycobacterial activity, with a minimum inhibitory concentration (MIC) of 20 µg/mL against H37Rv and a multidrug-resistant M. tuberculosis strain. Additionally, for two peptides, a strongly diminished formation of cord-like structures was observed, which is indicative of reduced virulence and transmission potential. This study underscores the multifaceted roles of antimicrobial peptides in TB management, from enhancing diagnostic efficiency to offering therapeutic avenues against M. tuberculosis.

A novel mixture sampling strategy combining latin hypercube sampling with optimized one factor at a time method: A case study on mixtures of antibiotics and pesticides

Global sensitivity analysis in conjunction with quantitative high-throughput screening presents a novel technique for identifying the key components that induce the toxicities of mixtures. However, the mixtures currently designed with this method suffer from unequal frequency sampling, repeated mixtures, and only odd factor levels being considered. Accordingly, we use latin hypercube sampling to generate the starting points of the trajectories to achieve equal frequency sampling and non-repeated mixtures, as well as apply different one factor at a time methods for factors with odd and even levels to achieve suitability for factors with both odd and even levels. This method is called LHS-OAT. LHS-OAT was successfully applied to design 110 equal-frequency and non-repeated mixtures consisting of six antibiotics and four pesticides. It was found that four factors, roxithromycin (A5), tetracycline (A6), dichlorvos (P1), and demeton-S (P3), induce the toxicities of mixtures, and A5 and P1 in the Shaying River Basin have risk quotients ≥ 1. Additionally, we developed the toxicity deviation ratio to correct the risk quotients of interacting mixtures for effective risk assessments. This study provides a rational and effective method for mixture design that accurately identifies the important factors that induce the toxicities of mixtures.

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.

Specific Cationic Antimicrobial Peptides Enhance the Recovery of Low-Load Quiescent Mycobacterium tuberculosis in Routine Diagnostics

The culture confirmation of Mycobacterium tuberculosis (MTB) remains the gold standard for the diagnosis of Tuberculosis (TB) with culture conversion representing proof of cure. However, over 40% of TB samples fail to isolate MTB even though many patients remain infectious due to the presence of viable non-culturable forms. Previously, we have shown that two short cationic peptides, T14D and TB08L, induce a hormetic response at low concentrations, leading to a stimulation of growth in MTB and the related animal pathogen Mycobacterium bovis (bTB). Here, we examine these peptides showing they can influence the mycobacterial membrane integrity and function through membrane potential reduction. We also show this disruption is associated with an abnormal reduction in transcriptomic signalling from specific mycobacterial membrane sensors that normally monitor the immediate cellular environment and maintain the non-growing phenotype. We observe that exposing MTB or bTB to these peptides at optimal concentrations rapidly represses signalling mechanisms maintaining dormancy phenotypes, which leads to the promotion of aerobic metabolism and conversion into a replicative phenotype. We further show a practical application of these peptides as reagents able to enhance conventional routine culture methods by stimulating mycobacterial growth. We evaluated the ability of a peptide-supplemented sample preparation and culture protocol to isolate the MTB against a gold standard routine method tested in parallel on 255 samples from 155 patients with suspected TB. The peptide enhancement increased the sample positivity rate by 46% and decreased the average time to sample positivity of respiratory/faecal sampling by seven days. The most significant improvements in isolation rates were from sputum smear-negative low-load samples and faeces. The peptide enhancement increased sampling test sensitivity by 19%, recovery in samples from patients with a previously culture-confirmed TB by 20%, and those empirically treated for TB by 21%. We conclude that sample decontamination and culture enhancement with D-enantiomer peptides offer good potential for the much-needed improvement of the culture confirmation of TB.

Reactive oxygen species accelerate de novo acquisition of antibiotic resistance in E. coli

Reactive oxygen species (ROS) produced as a secondary effect of bactericidal antibiotics are hypothesized to play a role in killing bacteria. If correct, ROS may play a role in development of de novo resistance. Here we report that single-gene knockout strains with reduced ROS scavenging exhibited enhanced ROS accumulation and more rapid acquisition of resistance when exposed to sublethal levels of bactericidal antibiotics. Consistent with this observation, the ROS scavenger thiourea in the medium decelerated resistance development. Thiourea downregulated the transcriptional level of error-prone DNA polymerase and DNA glycosylase MutM, which counters the incorporation and accumulation of 8-hydroxy-2'-deoxyguanosine (8-HOdG) in the genome. The level of 8-HOdG significantly increased following incubation with bactericidal antibiotics but decreased after treatment with the ROS scavenger thiourea. These observations suggest that in E. coli sublethal levels of ROS stimulate de novo development of resistance, providing a mechanistic basis for hormetic responses induced by antibiotics.

Advances in responses of microalgal-bacterial symbiosis to emerging pollutants in wastewater

Nowadays, emerging pollutants are widely used and exist in wastewater, such as antibiotics, heavy metals, nanoparticle and microplastic. As a green alternative for wastewater treatment, microalgal-bacterial symbiosis has been aware of owning multiple merits of low energy consumption and little greenhouse gas emission. Thus, the responses of microalgal-bacterial symbiosis to emerging pollutants in wastewater treatment have become a hotspot in recent years. In this review paper, the removal performance of microalgal-bacterial symbiosis on organics, nitrogen and phosphorus in wastewater containing emerging pollutants has been summarized. The adaptation mechanisms of microalgal-bacterial symbiosis to emerging pollutants have been analyzed. It is found that antibiotics usually have hormesis effects on microalgal-bacterial symbiosis, and that microalgal-bacterial symbiosis appears to show more capacity to remove tetracycline and sulfamethoxazole, rather than oxytetracycline and enrofloxacin. Generally, microalgal-bacterial symbiosis can adapt to heavy metals at a concentration of less than 1 mg/L, but its capabilities to remove contaminants can be significantly affected at 10 mg/L heavy metals. Further research should focus on the influence of mixed emerging pollutants on microalgal-bacterial symbiosis, and the feasibility of using selected emerging pollutants (e.g., antibiotics) as a carbon source for microalgal-bacterial symbiosis should also be explored. This review is expected to deepen our understandings on emerging pollutants removal from wastewater by microalgal-bacterial symbiosis.

The challenges of defining hormesis in epidemiological studies: The case of radiation hormesis

In the current radiation protection system, preventive measures and occupational exposure limits for controlling occupational exposure to ionizing radiation are based on the linear no-threshold extrapolation model. However, currently an increasing body of evidence indicates that this paradigm predicts very poorly biological responses in the low-dose exposure region. In addition, several in vitro and in vivo studies demonstrated the presence of hormetic dose response curves correlated to ionizing radiation low exposure. In this regard, it is noteworthy that also the findings of different epidemiological studies, conducted in different categories of occupationally exposed workers (e.g., healthcare, nuclear industrial and aircrew workers), observed lower rates of mortality and/or morbidity from cancer and/or other diseases in exposed workers than in unexposed ones or in the general population, then suggesting the possible occurrence of hormesis. Nevertheless, these results should be considered with caution since the identification of hormetic response in epidemiological studies is rather challenging because of a number of major limitations. In this regard, some of the most remarkable shortcomings found in epidemiological studies performed in workers exposed to ionizing radiation are represented by lack or inadequate definition of exposure doses, use of surrogates of exposure, narrow dose ranges, lack of proper control groups and poor evaluation of confounding factors. Therefore, considering the valuable role and contribution that epidemiological studies might provide to the complex risk assessment and management process, there is a clear and urgent need to overcome the aforementioned limits in order to achieve an adequate, useful and more real-life risk assessment that should also include the key concept of hormesis. Thus, in the present conceptual article we also discuss and provide possible approaches to improve the capacity of epidemiological studies to identify/define the hormetic response and consequently improve the complex process of risk assessment of ionizing radiation at low exposure doses.

What the Hel: recent advances in understanding rifampicin resistance in bacteria

Rifampicin is a clinically important antibiotic that binds to, and blocks the DNA/RNA channel of bacterial RNA polymerase (RNAP). Stalled, nonfunctional RNAPs can be removed from DNA by HelD proteins; this is important for maintenance of genome integrity. Recently, it was reported that HelD proteins from high G+C Actinobacteria, called HelR, are able to dissociate rifampicin-stalled RNAPs from DNA and provide rifampicin resistance. This is achieved by the ability of HelR proteins to dissociate rifampicin from RNAP. The HelR-mediated mechanism of rifampicin resistance is discussed here, and the roles of HelD/HelR in the transcriptional cycle are outlined. Moreover, the possibility that the structurally similar HelD proteins from low G+C Firmicutes may be also involved in rifampicin resistance is explored. Finally, the discovery of the involvement of HelR in rifampicin resistance provides a blueprint for analogous studies to reveal novel mechanisms of bacterial antibiotic resistance.

Quorum sensing in different subcommunities becomes the key factor affecting the humification of the aerobic composting system with sauerkraut fermentation wastewater

Aerobic composting is an effective and harmless method to treat Sauerkraut fermentation wastewater (SFW). Given the limited understanding of the effect of quorum sensing (QS) on humification in subcommunities under acidic environments, a large-scale analysis was conducted to identify features that impact the response of QS to humification in different subcommunities. The results showed that the addition of SFW directly affected humification in subcommunities A and C, and the abundances of functional genes related to carbon fixation and carbon degradation were significantly increased at 7 and 15 d, respectively. In addition, subcommunity B indirectly affected humus production but regulated carbon metabolic pathways such as glycolysis/gluconeogenesis and pentose phosphate by QS with subcommunities B. These findings provide a novel perspective for analysing the regulation of humification in aerobic composting and suggest that composting has potential applications in organic wastewater treatment.

Discovery of Antimicrobial Peptides That Can Accelerate Culture Diagnostics of Slow-Growing Mycobacteria Including Mycobacterium tuberculosis

Antimicrobial peptides (AMPs) can directly kill Gram-positive bacteria, Gram-negative bacteria, mycobacteria, fungi, enveloped viruses, and parasites. At sublethal concentrations, some AMPs and also conventional antibiotics can stimulate bacterial response increasing their resilience, also called the hormetic response. This includes stimulation of growth, mobility, and biofilm production. Here, we describe the discovery of AMPs that stimulate the growth of certain mycobacteria. Peptide 14 showed a growth stimulating effect on Mycobacteria tuberculosis (MTB), M. bovis, M. avium subsp. paratuberculosis (MAP), M. marinum, M. avium-intracellulare, M. celatum, and M. abscessus. The effect was more pronounced at low bacterial inocula. The peptides induce a faster transition from the lag phase to the log phase and keep the bacteria longer in the log phase before entering stationary phase when compared to nontreated controls. In some cases, an increase in the division rate was observed. An initial screen using MAP and a collection of 75 peptides revealed 13 peptides with a hormetic effect. For MTB, a collection of 25 artificial peptides were screened and 13 were found to reduce the time to positivity (TTP) by at least 5%, improving growth. A screen of 43 naturally occurring peptides, 11 fragments of naturally occurring peptides and 5 designed peptides, all taken from the database APD3, identified a further 44 peptides that also lowered TTP by at least 5%. Lasioglossin LL-III (Bee) and Ranacyclin E (Frog) were the most active natural peptides, and the human cathelicidin LL37 fragment GF-17 and a porcine cathelicidin protegrin-1 fragment were the most active fragments of naturally occurring peptides. Peptide 14 showed growth-stimulating activity between 10 ng/mL and 10 µg/mL, whereas the stability-optimised Peptide 14D had a narrow activity range of 0.1-1 µg/mL. Peptides identified in this study are currently in commercial use to improve recovery and culture for the diagnostics of mycobacteria in humans and animals.

Removal of endocrine disruptor compounds, CO2 fixation, and macromolecules accumulation in Thermosynechococcus sp. CL-1 cultivation

Recently, concern on several environmental issues including the pollutant discharge and high concentration of CO2 have gained high interest due to its impact on ecosystem and global warming effect, respectively. Implementation of photosynthetic microorganism carries out numerous advantages including high efficiency of CO2 fixation, the great endurance under extreme conditions and generation of valuable bioproducts. Thermosynechococcus sp. CL-1 (TCL-1), a cyanobacterium, has the ability to perform CO2 fixation and accumulation of various byproducts under extreme conditions like high temperature and alkalinity, presence of estrogen, or even using swine wastewater. This study aimed to assess TCL-1 performance under various endocrine disruptor compounds (bisphenol-A, 17-β-estradiol/E2, and 17-α-ethynilestradiol/EE2), concentrations (0-10 mg/L), light intensities (500-2000 µE/m2/s), and dissolved inorganic carbon/DIC levels (0-113.2 mM). Addition of E2 content even until 10 mg/L carried out insignificant biomass growth interruption along with the improvement in CO2 fixation rate (79.8 ± 0.1 mg/L/h). Besides the influence of E2, application of higher DIC level and light intensity also enhanced the CO2 fixation rate and biomass growth. The highest biodegradation of E2 at 71% was achieved by TCL-1 in the end of 12 h cultivation period. TCL-1 dominantly produced protein (46.7% ± 0.2%), however, production of lipid and carbohydrate (39.5 ± 1.5 and 23.3 ± 0.9%, respectively) also could be considered as the potential source for biofuel production. Thus, this study can provide an efficient strategy in simultaneously dealing with environmental issues with side advantage in production of macromolecules.

Removal of tetracycline in nitrification membrane bioreactors with different ammonia loading rates: Performance, metabolic pathway, and key contributors

Membrane bioreactors (MBRs) have been widely applied for the treatment of wastewater that contains high concentrations of both ammonium and antibiotics. Nonetheless, information about tetracycline (TC) removal in nitrification MBRs with high ammonium loading rates (ALRs) is still very limited. Herein, the fate of TC at four different concentrations of 1, 5, 20, and 50 mg/L in three parallel lab-scale nitrification MBRs with different ALRs (named AN50, AN500, and AN1000) were investigated in this study. Excellent nitrification performance and high TC removal efficiency (90.46%) were achieved in AN1000 at influent TC concentration of 50 mg/L. Higher ALRs promoted the removal of TC at lower influent TC concentration (≤5 mg/L), while no significant difference was observed in TC removal efficiencies among different ALRs MBRs at higher influent TC concentration (≥20 mg/L), implying that the heterotrophic degradation could be strengthened after long-term exposure to high concentration of TC. Batch tests demonstrated that adsorption and biodegradation were the primary TC removal routes by nitrification sludge, of which both autotrophic ammonia oxidizers and heterotrophic microorganisms played an important role in the biodegradation of TC. FT-IR spectroscopy confirmed that amide groups on the sludge biomass contributed to the adsorption of TC. Mass balance analyses indicated that biodegradation (63.4-88.6% for AN50, 74.5-88.4% for AN500 and 74.4-91.4% for AN1000) was the major mechanism responsible for the removal of TC in nitrification MBRs, and its contribution increased with influent TC concentration, while only 1.1%-15.0% of TC removal was due to biosorption. TC was progressively degraded to small molecules and the presence of TC had no notable effect on membrane permeability. These jointly confirmed TC could be effectively removed via initial adsorption and subsequent biodegradation, while biodegradation was the primary mechanism in this study.

A novel equal frequency sampling of factor levels (EFSFL) method is applied to identify the dominant factor inducing the combined toxicities of 13 factors

The research framework combining global sensitivity analysis (GSA) with quantitative high-throughput screening (qHTS), called GSA-qHTS, provides a potentially feasible way to screen for important factors that induce toxicities of complex mixtures. Despite its value, the mixture samples designed using the GSA-qHTS technique still have a shortage of unequal factor levels, which leads to an asymmetry in the importance of elementary effects (EEs). In this study, we developed a novel method for mixture design that enables equal frequency sampling of factor levels (called EFSFL) by optimizing both the trajectory number and the design and expansion of the starting points for the trajectory. The EFSFL has been successfully employed to design 168 mixtures of 13 factors (12 chemicals and time) that each have three levels. By means of high-throughput microplate toxicity analysis, the toxicity change rules of the mixtures are revealed. Based on EE analysis, the important factors affecting the toxicities of the mixtures are screened. It was found that erythromycin is the dominant factor and time is an important non-chemical factor in mixture toxicities. The mixtures can be classified into types A, B, and C mixtures according to their toxicities at 12 h, and all the types B and C mixtures contain erythromycin at the maximum concentration. The toxicities of the type B mixtures increase firstly over time (0.25 ∼ 9 h) and then decrease (12 h), while those of the type C mixtures consistently increase over time. Some type A mixtures produce stimulation that increases with time. With the present new approach to mixture design, the frequency of factor levels in mixture samples is equal. Consequently, the accuracy of screening important factors is improved based on the EE method, providing a new method for the study of mixture toxicity.

Fluoroquinolone Residues in the Environment Rapidly Induce Heritable Fluoroquinolone Resistance in Escherichia coli

Extensive antibiotic use increases the environmental presence of their residues and may accelerate the development of antibiotic resistance, although this remains poorly understood at environmentally relevant concentrations. Herein, susceptible Escherichia coli K12 was continuously exposed to five antibiotics at such concentrations for 100 days. The de novo-evolved mutants rapidly obtained fluoroquinolone resistance within 10 days, as indicated by the 4- and 16-fold augmentation of minimum inhibitory concentrations against enrofloxacin and ciprofloxacin, respectively. Moreover, the mutants maintained heritable fluoroquinolone resistance after the withdrawal of antibiotics for 30 days. Genomic analysis identified Asp87Gly or Ser83Leu substitutions in the gyrA gene in the mutants. Transcriptomics data showed that the transcriptional response of the mutants to fluoroquinolones was primarily involved in biofilm formation, cellular motility, porin, oxidative stress defense, and energy metabolism. Homologous recombination and molecular docking revealed that mutations of gyrA primarily mainly conferred fluoroquinolone resistance, while mutations at different positions of gyrA likely endowed different fluoroquinolone resistance levels. Collectively, this study revealed that environmentally relevant concentrations of antibiotics could rapidly induce heritable antibiotic resistance; therefore, the discharge of antibiotics into the environment should be rigorously controlled to prevent the development of antibiotic resistance.

Dose-dependent joint resistance action of antibacterial mixtures in their hormetic effects on bacterial resistance based on concentration addition model

The judgment of joint resistance action is significant for evaluating the resistance risk of antibacterial mixture. Using bacterial mutation frequency (MF) and conjugative transfer frequency (CTF) to respectively characterize the bacterial endogenous and exogenous resistance, mutation unit and conjugative transfer unit have been proposed to judge the joint resistance action of antibacterial mixture at a certain dose. However, these methods could not evaluate the antibacterial mixture's joint resistance action at a larger concentration-range. In this study, the concentration addition for bacterial resistance (CA-BR) approach was used to judge the joint resistance actions between kanamycin sulfate (KAN) and some other typical antibacterial agents, including sulfonamides (SAs), sulfonamide potentiators (SAPs), and silver antibacterial compounds (SACs). Through comparing the hormetic dose-response curves of the binary mixtures on the MF (or CTF) in Escherichia coli (E. coli) and the corresponding CA-BR curves calculated from the hormetic dose-responses of the single agents, the joint resistance actions between KAN and other agents were judged to exhibit dose-dependent feature: with the increase of mixture concentration, the joint mutation actions between KAN and SAs (or SAPs) were fixed at synergism, and the joint mutation actions between KAN and SACs varied from antagonism to synergism; the joint conjugative transfer actions between KAN and other agents changed from antagonism to synergism. Mechanistic explanation suggested that the heterogeneous pattern of joint resistance action had a close relationship with the interplays among the agents' modes of action, and meanwhile was significantly influenced by their joint survival pressure on E. coli. This study reveals the dose-dependent feature for the joint resistance action of antibacterial mixture and highlights the importance of exposure concentration, which will benefit clarifying the resistance risk of antibacterial mixture in the environment.

Blue Light Improves Antimicrobial Efficiency of Silver Sulfadiazine Via Catalase Inactivation

Background: Blue light exhibits the ability to deactivate catalase present in pathogens, significantly improving the antimicrobial performance of compounds such as hydrogen peroxide (H2O2). However, H2O2 is not used within clinical settings due to its short half-life, limiting its potential applications. In this study, we explore the usage of Food and Drug Administration-approved and clinically used silver sulfadiazine (SSD) as a potential alternative to H2O2, acting as a reactive oxygen species (ROS)-producing agent capable of synergizing with blue light exposure. Materials and methods: For in vitro studies, bacterial strains were exposed to a continuous wave 405 nm light-emitting diode (LED) followed by treatment with SSD for varying incubation times. For in vivo studies, bacteria-infected murine abrasion wounds were treated with daily treatments of 405 nm LED light and 1% SSD cream for up to 4 days. The surviving bacterial population was quantified through agar plating and colony-forming unit quantification. Results: Through a checkerboard assay, blue light and SSD demonstrated synergistic interactions. Against both gram-negative and gram-positive pathogens, blue light significantly improved the antimicrobial response of SSD within both phosphate-buffered saline and nutrient-rich conditions. Examination into the mechanisms reveals that the neutralization of catalase significantly improves the ROS-producing capabilities of SSD at the exterior of the bacterial cell, producing greater amounts of toxic ROS capable of exerting antimicrobial activity against the pathogen. Additional experiments reveal that the incorporation of light improves the antimicrobial performance of SSD within methicillin-resistant Staphylococcus aureus (MRSA)- and Pseudomonas aeruginosa strain 1 (PAO-1)-infected murine abrasion wounds. Conclusions: As an established, clinically used antibiotic, SSD can act as a suitable alternative to H2O2 in synergizing with catalase-deactivating blue light, allowing for better translation of this technology to more clinical settings and further implementation of this treatment to more complex animal models.

Transfer pattern of hormesis into personal care product mixtures from typical hormesis-inducing compounds

Some personal care products (PCPs) and their chemical components showed a hormetic effect in the freshwater photobacterium Vibrio qinghaiensis sp. -Q67 (Q67) after long-term exposure. However, how hormesis transfers between chemical components and PCP mixture, and which chemical component plays a major role remain unknown. To this end, according to the seven compounds detected in one skin lotion (SK5) and their concentration ratios, many mixture rays were constructed to simulate the SK5. Of these seven compounds, three presented monotonic concentration-response curves (CRC) to Q67 at 0.25 and 12 h (called a S-shaped compound). The other four compounds showed hormetic CRCs after 12 h and monotonic CRCs at 0.25 h (called a J-shaped compound). Based on their mixture ratios, we designed one ternary mixture ray of all S-shaped compounds, one quaternary mixture ray of all J-shaped compounds, and four quaternary mixture rays of one J-shaped and three S-shaped compounds. It was shown that SK5 could be approximately simulated by the mixture ray of the seven compounds detected in SK5 and only the mixture rays containing at least one hormesis-inducing compound produced hormesis to Q67 at 12 h. Based on the concentration ratios of various compounds and comparison of four hormetic characteristic parameters to those of various mixture rays, it was found that the compound betaine (BET) is a key compound affecting the hormesis of mixtures. Additionally, we studied the hormesis mechanism of BET on Q67 via quorum sensing (QS). This preliminarily indicated that the autoinducer-2 triggered the QS pathway. This study elucidated the transfer pattern of hormesis into mixtures, which would be an efficient method to identifying the potential components that affect hormesis transfer in mixtures. We expect that this study will provide new insights into hormesis and its mixtures.

On the meta-analysis of hormetic effects

The evidence for hormetic responses with chemical effects at doses lower than the no-observed-adverse-effect-level (sub-NOAEL) is increasing, creating a need for meta-analyses of sub-NOAEL effects across studies. However, the distinct features of hormetic responses complicate the procedures of meta-analyses aiming to study sub-NOAEL, hormetic effects, and there is no standardized methodology to serve as a guideline. In this piece, a protocol is proposed, which covers the selection of more holistic keywords to be integrated into the literature search queries, the designation of control, and the identification of NOAEL (and thus sub-NOAEL dose responses). It also considers the selection of the response indicators and the incorporation of time and dose as sources of variation. This protocol can serve as a reference point for a harmonized and more robust methodology to meta-analyze sub-NOAEL effects of chemicals on living organisms.

Extracellular DNAses Facilitate Antagonism and Coexistence in Bacterial Competitor-Sensing Interference Competition

Over the last 4 decades, the rate of discovery of novel antibiotics has decreased drastically, ending the era of fortuitous antibiotic discovery. A better understanding of the biology of bacteriogenic toxins potentially helps to prospect for new antibiotics. To initiate this line of research, we quantified antagonists from two different sites at two different depths of soil and found the relative number of antagonists to correlate with the bacterial load and carbon-to-nitrogen (C/N) ratio of the soil. Consecutive studies show the importance of antagonist interactions between soil isolates and the lack of a predicted role for nutrient availability and, therefore, support an in situ role in offense for the production of toxins in environments of high bacterial loads. In addition, the production of extracellular DNAses (exDNases) and the ability to antagonize correlate strongly. Using an in domum-developed probabilistic cellular automaton model, we studied the consequences of exDNase production for both coexistence and diversity within a dynamic equilibrium. Our model demonstrates that exDNase-producing isolates involved in amensal interactions act to stabilize a community, leading to increased coexistence within a competitor-sensing interference competition environment. Our results signify that the environmental and biological cues that control natural-product formation are important for understanding antagonism and community dynamics, structure, and function, permitting the development of directed searches and the use of these insights for drug discovery. IMPORTANCE Ever since the first observation of antagonism by microorganisms by Ernest Duchesne (E. Duchesne, Contribution à l'étude de la concurrence vitale chez les microorganisms. Antagonism entre les moisissures et les microbes, These pour obtenir le grade de docteur en medicine, Lyon, France, 1897), many scientists successfully identified and applied bacteriogenic bioactive compounds from soils to cure infection. Unfortunately, overuse of antibiotics and the emergence of clinical antibiotic resistance, combined with a lack of discovery, have hampered our ability to combat infections. A deeper understanding of the biology of toxins and the cues leading to their production may elevate the success rate of the much-needed discovery of novel antibiotics. We initiated this line of research and discovered that bacterial reciprocal antagonism is associated with exDNase production in isolates from environments with high bacterial loads, while diversity may increase in environments of lower bacterial loads.

Metagenomic evidence for increasing antibiotic resistance in progeny upon parental antibiotic exposure as the cost of hormesis

Antibiotics are widely consumed in the intensive mariculture industry. A better understanding of the effect of antibiotics on intergenerational antibiotic resistance in organisms is urgent since intergenerational transmission is crucial for the spread of antibiotic resistance genes (ARGs) in the environment. Herein, marine medaka (Oryzias melastigma) chronically exposed to low doses of sulfamethazine (SMZ) hormetically affected the progeny, characterized by increased richness and diversity of fecal microbiota and intestinal barrier-related gene up-regulation. Progeny immunity was modulated and caused by genetic factors due to the absence of significant SMZ accumulation in F1 embryos. In addition, some of the top genera in the progeny were positively correlated with immune diseases, while the expression of some immune-related genes, such as TNFα, IL1R2, and TLR3 changed significantly. This further indicated that the host selection caused by changes in progeny immunity was probably the primary determinant of progeny intestinal microbial colonization. Metagenomic analysis revealed that Proteobacteria represented the primary carriers of ARGs, while parental SMZ exposure facilitated the distribution and enrichment of multiple ARGs involved in the antibiotic inactivation in the progeny by promoting the diversity of Gammaproteobacteria and Bacteroidetes, further illustrating that antibiotic selection pressure persisted even if the offspring were not exposed. Therefore, SMZ induced hormesis in the progeny at the expense of increasing antibiotic resistance. Collectively, these findings provide a comprehensive overview of the intergenerational effect of antibiotics and serve as a reminder that the ARG transmission induced by the intergenerational impact of antibiotics on organisms should not be ignored.

The antimicrobial peptide DGL13K is active against drug-resistant gram-negative bacteria and sub-inhibitory concentrations stimulate bacterial growth without causing resistance

Antimicrobial peptides may be alternatives to traditional antibiotics with reduced bacterial resistance. The antimicrobial peptide GL13K was derived from the salivary protein BPIFA2. This study determined the relative activity of the L-and D-enantiomers of GL13K to wild-type and drug-resistant strains of three gram-negative species and against Pseudomonas aeruginosa biofilms. DGL13K displayed in vitro activity against extended-spectrum beta-lactamase (ESBL)-producing and Klebsiella pneumoniae carbapenemase (KPC)-producing Klebsiella pneumoniae (MICs 16–32 μg/ml), MDR and XDR P. aeruginosa, and XDR Acinetobacter baumannii carrying metallo-beta-lactamases (MICs 8–32 μg/ml). P. aeruginosa showed low inherent resistance to DGL13K and the increased metabolic activity and growth caused by sub-MIC concentrations of GL13K peptides did not result in acquired bacterial resistance. Daily treatment for approximately two weeks did not increase the MIC of DGL13K or cause cross-resistance between LGL13K and DGL13K. These data suggest that DGL13K is a promising antimicrobial peptide candidate for further development.

Hormesis-Like Effects of Tetrabromobisphenol A on Anaerobic Digestion: Responses of Metabolic Activity and Microbial Community

Tetrabromobisphenol A (TBBPA) has extensive applications in various fields; its release into ecosystems and the potential toxic effects on organisms are becoming major concerns. Here, we investigated the effects of TBBPA on anaerobic digestion, whose process is closely related to the carbon cycles under anaerobic conditions. The results revealed that TBBPA exhibited dose-dependent hormesis-like effects on methane production from glucose, i.e., the presence of 0.1 mg/L TBBPA increased the methane production rate by 8.79%, but 1.0-4.0 mg/L TBBPA caused 3.45-28.98% of decrement. We found that TBBPA was bound by the tyrosine-like proteins of the extracellular polymeric substances of anaerobes and induced the increase of reactive oxygen species, whose slight accumulation stimulated the metabolism activities but high accumulation increased the apoptosis of anaerobes. Owing to the differences between individual anaerobes in tolerance, TBBPA at 0.1 mg/L stimulated the acidogenesis and hydrogenotrophic methanogenesis, whereas higher levels (i.e., 1.0-4.0 mg/L) severely restrained all of the processes of acidogenesis, acetogenesis, and methanogenesis. Along with the accumulation of bisphenol A (BPA) produced from TBBPA by Longilinea sp. and Pseudomonas sp., the methanogenic pathway was partly shifted from acetate-dependent to hydrogen-dependent direction, and the activities of carbon monoxide dehydrogenase and acetyl-CoA decarbonylase/synthase were inhibited, while acetate kinase and F420 were hormetically affected. These findings elucidated the mechanism of anaerobic syntrophic consortium responses to TBBPA, supplementing the potential environmental risks of brominated flame retardants.

Growth and physiological responses in a submerged clonal aquatic plant and multiple-endpoint assessment under prolonged exposure to ciprofloxacin

Ciprofloxacin is ubiquitous and poses a potential threat to aquatic ecosystems. However, the comprehensive effect of prolonged ciprofloxacin exposure on the submerged clonal plant Vallisneria natans (Lour.) Hara remains unknown. Growth and physiological responses in V. natans exposed to ciprofloxacin at concentrations of 0, 0.05, 0.25, 1.25, 2.5, 5 and 10 mg/L were repeatedly evaluated on Days 7, 14, 28, 42 and 56. V. natans maintained good growth properties under 0.05-0.25 mg/L ciprofloxacin treatments, while the inhibition effect on plant growth induced by higher-concentration treatments increased over time. The IC50 values of ciprofloxacin for growth endpoints ranged from 1.6 mg/L to 5.3 mg/L and displayed time-dependent decreases. Pigment contents were significantly stimulated by ciprofloxacin on Day 7 but decreased to varying degrees as the exposure time was extended. Soluble protein and hydrogen peroxide content rose significantly over the first 14 days of treatment with 0.25-10 mg/L ciprofloxacin but decreased under 1.25-10 mg/L ciprofloxacin treatments since Day 28. Antioxidants including superoxide dismutase, catalase, guaiacol peroxidase, ascorbate peroxidase and proline functioned well in mitigating oxidative stress under different ciprofloxacin concentrations, lowering the comprehensive toxic effects of ciprofloxacin on V. natans during the period from Day 14 to Day 42, as evidenced by decreased IBR (integrated biomarker response) values. However, the toxic pressure of ciprofloxacin on V. natans peaked on Day 56. These findings suggest that exposure time can influence the responses of V. natans exposed to ciprofloxacin and that IBR can be employed to evaluate the integrated impacts of prolonged ciprofloxacin contamination in aquatic settings.

Hormesis induced by silver iodide, hydrocarbons, microplastics, pesticides, and pharmaceuticals: Implications for agroforestry ecosystems health

Increasing amounts of silver iodide (AgI) in the environment are expected because of the recent massive expansion of weather modification programs. Concurrently, pharmaceuticals, microplastics, hydrocarbons, and pesticides in terrestrial ecosystems continue contaminating forests and agroforests. Our review supports that AgI induces hormesis, a biphasic dose response characterized by often beneficial low-dose responses and toxic high-dose effects, which adds to the evidence for pharmaceuticals, microplastics, hydrocarbons, and pesticides induced hormesis in numerous species. Doses smaller than the no-observed-adverse-effect-level (NOAEL) positively affect defense physiology, growth, biomass, yields, survival, lifespan, and reproduction. They also lead to negative or undesirable outcomes, including stimulation of pathogenic microbes, pest insects, and weeds with enhanced resistance to drugs and potential negative multi- or trans-generational effects. Such sub-NOAEL effects perplex terrestrial ecosystems managements and may compromise combating outbreaks of disease vectors that can threaten not only forest and agroforestry health but also sensitive human subpopulations living in remote forested areas.

Hormetic dose responses induced by organic flame retardants in aquatic animals: Occurrence and quantification

The organic flame retardants (OFRs) have attracted global concerns due to their potential toxicity and ubiquitous presence in the aquatic environment. Hormesis refers to a biphasic dose response, characterized by low-dose stimulation and high-dose inhibition. The present study provided substantial evidence for the widespread occurrence of OFRs-induced hormesis in aquatic animals, including 202 hormetic dose response relationships. The maximum stimulatory response (MAX) was commonly lower than 160% of the control response, with a combined value of 134%. Furthermore, the magnitude of MAX varied significantly among multiple factors and their interactions, such as chemical types and taxonomic groups. Moreover, the distance from the dose of MAX to the no-observed-adverse-effect-level (NOAEL) (NOAEL: MAX) was typically below 10-fold (median = 6-fold), while the width of the hormetic zone (from the lowest dose inducing hormesis to the NOAEL) was approximately 20-fold. Collectively, the quantitative features of OFRs-induced hormesis in aquatic animals were in accordance with the broader hormetic literature. In addition, the implications of hormetic dose response model for the risk assessment of OFRs were discussed. This study offered a novel insight for understanding the biological effects of low-to-high doses of OFRs on aquatic animals and assessing the potential risks of OFRs in the aquatic environment.

Microbiomes and glyphosate biodegradation in edaphic and aquatic environments: recent issues and trends

Glyphosate (N-(phosphonomethyl)glycine) has emerged as the top-selling herbicide worldwide because of its versatility in controlling annual and perennial weeds and the extensive use of glyphosate-resistant crops. Concerns related to the widespread use of glyphosate and its ubiquitous presence in the environment has led to a large number of studies and reviews, which examined the toxicity and fate of glyphosate and its major metabolite, aminomethylphosphonic acid (AMPA) in the environment. Because the biological breakdown of glyphosate is most likely the main elimination process, the biodegradation of glyphosate has also been the object of abundant experimental work. Importantly, glyphosate biodegradation in aquatic and soil ecosystems is affected not only by the composition and the activity of microbial communities, but also by the physical environment. However, the interplay between microbiomes and glyphosate biodegradation in edaphic and aquatic environments has rarely been considered before. The proposed minireview aims at filling this gap. We summarize the most recent work exploring glyphosate biodegradation in natural aquatic biofilms, the biological, chemical and physical factors and processes playing on the adsorption, transport and biodegradation of glyphosate at different levels of soil organization and under different agricultural managements, and its impact on soil microbial communities.

A simple judgment method for joint action of antibacterial agents on bacterial resistance

The severe pollution of bacterial resistance induced by the wide and even indiscriminate use of antibacterial agents has posed serious threats to human health and ecological safety. Furthermore, the combined effects of antibacterial agents have a closer relationship with the pollution of bacterial resistance than single antibacterial agent. However, there is little information regarding how multiple antibacterial agents interplay to induce bacterial resistance. Here, we developed a simple judgment method with five basic procedures for the joint action of antibacterial agents on bacterial resistance, involving toxicity determination, mutation frequency determination, conjugative transfer frequency determination, dose-response relationship fitting, key parameters obtaining, and joint resistance action judgment. This proposed approach was validated through investigating the joint resistance action between silver nanoparticle (AgNP) and 1-pyrrolidino-1-cyclohexene (1P1C, a kind of quorum sensing inhibitors). According to the procedures, the mutation unit and conjugative transfer unit for the AgNP-1P1C mixture were calculated to be 64.27 and 5.10, respectively, indicating the antagonism for their joint resistance action. This method can not only benefit the mechanistic explanation for how mixed antibacterial agents stimulate the bacterial resistance, but also guide the environmental risk assessment and clinical use of combined antibacterial agents in the related fields. • We present a novel method to judge the joint resistance action of antibacterial agents, taking the emergence and dissemination of antibiotic resistance genes into account. • Toxicity determination can help to design the mixtures of antibacterial agents and confirm the appropriate test concentration range of antibacterial agents used in mutation frequency and conjugative transfer frequency determination. • The mutation unit and conjugative transfer unit were proposed according to the toxic unit in the judgment of joint toxic action.

Antimicrobial Resistance in Rivers: A Review of the Genes Detected and New Challenges

River ecosystems are very important parts of the water cycle and an excellent habitat, food, and drinking water source for many organisms, including humans. Antibiotics are emerging contaminants which can enter rivers from various sources. Several antibiotics and their related antibiotic resistance genes (ARGs) have been detected in these ecosystems by various research programs and could constitute a substantial problem. The presence of antibiotics and other resistance cofactors can boost the development of ARGs in the chromosomes or mobile genetic elements of natural bacteria in rivers. The ARGs in environmental bacteria can also be transferred to clinically important pathogens. However, antibiotics and their resistance genes are both not currently monitored by national or international authorities responsible for controlling the quality of water bodies. For example, they are not included in the contaminant list in the European Water Framework Directive or in the US list of Water-Quality Benchmarks for Contaminants. Although ARGs are naturally present in the environment, very few studies have focused on non-impacted rivers to assess the background ARG levels in rivers, which could provide some useful indications for future environmental regulation and legislation. The present study reviews the antibiotics and associated ARGs most commonly measured and detected in rivers, including the primary analysis tools used for their assessment. In addition, other factors that could enhance antibiotic resistance, such as the effects of chemical mixtures, the effects of climate change, and the potential effects of the coronavirus disease 2019 pandemic, are discussed. Environ Toxicol Chem 2022;41:687-714. © 2022 SETAC.

Disinfectant-induced hormesis: An unknown environmental threat of the application of disinfectants to prevent SARS-CoV-2 infection during the COVID-19 pandemic?

Massive additional quantities of disinfectants have been applied during the COVID-19 pandemic as infection preventive and control measures. While the application of disinfectants plays a key role in preventing the spread of SARS-CoV-2 infection, the effects of disinfectants applied during the ongoing pandemic on non-target organisms remain unknown. Here we collated evidence from multiple studies showing that chemicals used for major disinfectant products can induce hormesis in various organisms, such as plants, animal cells, and microorganisms, when applied singly or in mixtures, suggesting potential ecological risks at sub-threshold doses that are normally considered safe. Among other effects, sub-threshold doses of disinfectant chemicals can enhance the proliferation and pathogenicity of pathogenic microbes, enhancing the development and spread of drug resistance. We opine that hormesis should be considered when evaluating the effects and risks of such disinfectants, especially since the linear-no-threshold (LNT) and threshold dose-response models cannot identify or predict their effects.