Sublethal Exposure Research Articles

Variable Dose Rates in Realistic Radiation Exposures: Effects on Small Molecule Markers of Ionizing Radiation in the Murine Model.

Novel biodosimetry assays for use in preparedness and response to potential malicious attacks or nuclear accidents would ideally provide accurate dose reconstruction independent of the idiosyncrasies of a complex exposure to ionizing radiation. Complex exposures will consist of dose rates spanning the low dose rates (LDR) to very high-dose rates (VHDR) that need to be tested for assay validation. Here, we investigate how a range of relevant dose rates affect metabolomic dose reconstruction at potentially lethal radiation exposures (8 Gy in mice) from an initial blast or subsequent fallout exposures compared to zero or sublethal exposures (0 or 3 Gy in mice) in the first 2 days, which corresponds to an integral time individuals will reach medical facilities after a radiological emergency. Biofluids (urine and serum) were collected from both male and female 9-10-week-old C57BL/6 mice at 1 and 2 days postirradiation (total doses of 0, 3 or 8 Gy) after a VHDR of 7 Gy/s. Additionally, samples were collected after a 2-day exposure consisting of a declining dose rate (1 to 0.004 Gy/min) recapitulating the 7:10 rule-of-thumb time dependency of nuclear fallout. Overall similar perturbations were observed in both urine and serum metabolite concentrations irrespective of sex or dose rate, with the exception of xanthurenic acid in urine (female specific) and taurine in serum (VHDR specific). In urine, we developed identical multiplex metabolite panels (N6, N6,N6-trimethyllysine, carnitine, propionylcarnitine, hexosamine-valine-isoleucine, and taurine) that could identify individuals receiving potentially lethal levels of radiation from the zero or sublethal cohorts with excellent sensitivity and specificity, with creatine increasing model performance at day 1. In serum, individuals receiving a 3 or 8 Gy exposure could be identified from their pre-irradiation samples with excellent sensitivity and specificity, however, due to a lower dose response the 3 vs. 8 Gy groups could not be distinguished from each other. Together with previous results, these data indicate that dose-rate-independent small molecule fingerprints have potential in novel biodosimetry assays.

Studies on triazophos-induced oxidative stress and genotoxicity in freshwater fish Cyprinus Carpio following sublethal exposures

Triazophos (TAP), an organophosphorus insecticide, is widely used in agricultural practice for controlling various insect pests. The present research work aimed to elucidate the impact of TAP on the antioxidant status and DNA content of the freshwater fish Cyprinus carpio. The fish were grouped into batches (n=6) and received a sublethal dose of 0.3mg/L for a duration of 1 (E1), 10 (E2), 20 (E3) and 30 days (E4). Another group, devoid of any toxicant, was maintained as the control (C). Changes in the enzymatic threshold of the selected antioxidants and malondialdehyde (MDA) levels suggested the conformation of oxidative stress in the livers of the freshwater fish C. carpio due to TAP exposure. Additionally, comet assays and micronucleus tests performed on the peripheral blood of the fish suggested increased damage in the form of the percentage of tail DNA formation and a high frequency of micronucleus as compared to the control. A positive correlation was seen between the decline in antioxidant activity, the elevation in MDA and the comet length and micronucleus frequency. The study thus highlights the impact of TAP on antioxidant levels in the livers and genotoxicity in the blood of the freshwater fish C. carpio. The findings of the study confirm that the antioxidant status, along with the comet assay and micronucleus tests could be used as tools in determining the potential genotoxicity due to the TAP impact. It is therefore suggested that extensive use of TAP should be avoided as it may contribute to the decline in the C. carpio population in its natural habitats.

Study The Acute Toxicity of Zinc Oxide Nanoparticles on Cyprinus carpio's Tissues.

Despite nanotechnology's rapid growth and early acceptance, the health risks of prolonged exposure at varied concentrations in individuals and the environment have yet to be investigated. Due to nanomaterial use, many nanoscale products enter aquatic habitats, affecting ecosystems and human health. Nanomaterials' environmental impacts will increase. Ceramics, sunscreens, and hair care products use ZnO nanoparticles. Zinc oxide nanoparticles (ZnO NPs) may enter aquatic ecosystems, generating concerns regarding their effects on aquatic animals. This study examined how ZnO NPs affected common carp (Cyprinus carpio) diets. Toxicological studies reveal ZnO NPs harm humans and the environment. Thus, ZnO nanoparticles must be characterized for consumer and environmental health and safety. This study aims to determine ZnO nanoparticles' acute toxicity (LC50) and gill histopathology in Cyprinus carpio. 3500 mg/L ZnO nanoparticles kill C. carpio at 50%. In this work, sub-lethal Zinc Oxide nanoparticle exposure for 21 days affects the ovary, liver, and kidneys.

Expression of the <i>soxRS</i> regulon in bacterial cells exposed to various stress factors

Background. Some stress responses contribute to the formation of bacterial antibiotic resistance, including the soxRS oxidative defense regulon. Elevation of reactive oxygen species production and oxidative stress was detected in bacterial cells exposed to various environmental stresses. It can be supposed that a stress-mediated increase in the level of reactive oxygen species will activate the expression of the soxRS regulon genes, which may provide pre-adaptation to antibiotics.The aim. To study changes in the expression of soxRS regulon genes in Escherichia coli cells exposed to NaCl, acetic acid, and heating.Materials and methods. Gene expression was measured in cells bearing reporter gene fusions (soxS::lacZ, nfo::lacZ). An overnight broth culture was diluted in fresh LB broth to OD600 = 0.1 and cultivated at 37 °C without stirring until OD600 = 0.3, then the stressors were applied.Results. Exposure to NaCl and acetic acid activated the expression of soxRS regulon genes, while heating caused a decrease in gene expression. An increase in the expression level was observed in cells subjected to stresses of low intensity (which did not cause a decrease in the number of colony-forming units (CFU) by the 4th hour of exposure compared to the beginning of the stress exposure) and medium intensity (which caused a 10-fold decrease in the number of CFU), whereas high-intensity stresses (which caused a decrease in the number of CFU by more than 10 times), regardless of their nature, were accompanied by a decrease in the expression of the soxRS regulon genes.Conclusion. Under the conditions studied, only the osmotic stress caused by the addition of NaCl was accompanied by a significant activation of the soxRS regulon genes. Sublethal exposure to NaCl, causing an increase in the expression of soxRS regulon genes by 2–2.5 times, may provide pre-adaptation of bacteria to the factors that this regulon is aimed at counteracting, including antibacterial drugs.

Monitoring resistance to methomyl and synergism in the non-target Musca domestica from cotton fields of Punjab and Sindh provinces, Pakistan

Insecticides are an integral part of most of the cropping systems worldwide; however, these usually exert negative impact on the environment and non-target insects as well. Non-target insects are prone to develop resistance to insecticides due to prolonged and repeated lethal and sublethal exposures. Musca domestica is a common non-target, pollinator and nectar feeder species in cotton ecosystem, besides its status as a public health pest in human habitations. In the present work, resistance to methomyl, one of the major insecticides used for cotton pest management, was assessed in 20 M. domestica strains from the major cotton producing areas of the Punjab and Sindh provinces of Pakistan. The results revealed that toxicity values of methomyl for Punjabi and Sindhi strains ranged from 28.07 to 136.16 µg fly−1 and 29.32 to 136.87 µg fly−1, respectively. Among Punjabi strains, D.G. Khan, Lodhran, Bahawalpur, Toba Tek Singh, Bahawalnagar, Rajanpur and Jhang strains exhibited very high levels of resistance (RR > 100) to methomyl; Bhakkar, Kasur, Vehari, Layyah, Muzaffargarh and R.Y. Khan showed high resistance (RR = 51–100 fold), while the Mianwali strain showed a moderate level of resistance to methomyl (RR = 36.45 fold). In case of Sindhi strains, very high levels of resistance (> 100 fold) were reported for Sukkar and Sanghar strains, high levels of resistance (RR 51–100 fold) for Khairpur, Jamshoro and Ghotki, and moderate resistance to methomyl (38.08 fold) in the Dadu strain. There was a significant synergism of methomyl toxicity in all field strains when methomyl bioassayed along with piperonyl butoxide (PBO) and S,S,S-tributylphosphorotrithioate (DEF) providing clues of metabolic-based mechanisms of resistance to methomyl. In conclusion, insecticides used in crop farming can cause resistance development in non-target M. domestica. It is necessary to adopt the pest management activities that are safe for the environment and non-target insect species.

Individual variation within wild populations of an arid-zone lizard dictates oxidative stress levels despite exposure to sublethal pesticides

The relationship between sublethal pesticide exposure and oxidative stress in an ecologically relevant field setting is relatively unknown for reptiles. Oxidative stress is a multi-faceted concept that dictates key survival and fitness parameters in any organism. Fipronil and fenitrothion are two pesticides widely used globally for agricultural pest management. Using a field-based, BACI designed experiment we investigated the impact of sublethal pesticide exposure on oxidative stress biomarkers protein carbonyl and DNA damage (8-OHdG), in an arid-zone lizard species, Pogona vitticeps. A single ecologically relevant dose of pesticide was applied via oral gavage to treatment animals. Lizard condition, activity measures, and blood biomarkers were measured at relevant sampling intervals. Cholinesterase (ChE) and acetylcholinesterase (AChE) enzymatic biomarkers were measured in response to fenitrothion, and fipronil blood residues were measured for fipronil-treated lizards. Results suggested no significant treatment effect of either pesticide on parameters measured, however, 8-OHdG levels decreased by ≥ 45% for both pesticide treatment groups and not controls. Protein carbonyl levels showed a high degree of individual variation that proved more influential than pesticide exposure. Building our understanding of the macromolecular impacts of sublethal pesticide exposure on wild lizard populations is an integral step in addressing the current gap in literature and management practices. Our study has also highlighted the complex nature of studying oxidative stress in the field and the sheer necessity of future study.

Chronic larval exposure to thiacloprid impairs honeybee antennal selectivity, learning and memory performances.

The use of agricultural neonicotinoid insecticides has sub-lethal chronic effects on bees that are more prevalent than acute toxicity. Among these insecticides, thiacloprid, a commonly used compound with low toxicity, has attracted significant attention due to its potential impact on the olfactory and learning abilities of honeybees. The effect of sub-lethal larval exposure to thiacloprid on the antennal activity of adult honeybees (Apis mellifera L.) is not yet fully understood. To address this knowledge gap, laboratory-based experiments were conducted in which honeybee larvae were administered thiacloprid (0.5mg/L and 1.0mg/L). Using electroantennography (EAG), the impacts of thiacloprid exposure on the antennal selectivity to common floral volatiles were evaluated. Additionally, the effects of sub-lethal exposure on odor-related learning and memory were also assessed. The results of this study reveal, for the first time, that sub-lethal larval exposure to thiacloprid decreased honeybee antenna EAG responses to floral scents, leading to increased olfactory selectivity in the high-dose (1.0mg/L) group compared to the control group (0mg/L vs. 1.0mg/L: p = 0.042). The results also suggest that thiacloprid negatively affected odor-associated paired learning acquisition, as well as medium-term (1h) (0mg/L vs. 1.0mg/L: p = 0.019) and long-term memory (24h) (0mg/L vs. 1.0mg/L: p = 0.037) in adult honeybees. EAG amplitudes were dramatically reduced following R-linalool paired olfactory training (0mg/L vs. 1.0mg/L: p = 0.001; 0mg/L vs. 0.5mg/L: p = 0.027), while antennal activities only differed significantly in the control between paired and unpaired groups. Our results indicated that exposure to sub-lethal concentrations of thiacloprid may affect olfactory perception and learning and memory behaviors in honeybees. These findings have important implications for the safe use of agrochemicals in the environment.

Biochemical and histopathological responses of Biomphalaria alexandrina to RIPEX (plant growth regulator)

BackgroundPlant growth regulators are widely used in agriculture for increasing the growth and ripening of plants, but they endanger the aquatic ecosystem. The current study assessed the effect of sublethal exposure to RIPEX 48% EC concentrations (8 and 16 µL/L) on oxidative stress parameters, sex hormones, immune potential enzymes, differential hemocyte counts, and the histopathology of digestive glands and ovotestis in Biomphalaria alexandrina snails.ResultsRIPEX exposure caused an overall increase in Superoxide dismutase and Glutathione-S-Transferase activities in B. alexandrina. However, extreme RIPEX exposure inhibits SOD activity in snails. Malondialdehyde activity showed an increase in B. alexandrina exposed to both concentrations after all exposure periods. RIPEX also caused a significant increase in testosterone in snails exposed to 16 µL/L, it did, however, reduce hormone levels in snails exposed to 8 µL/L at 7 days. Regarding estradiol, there was a significant increase after 3 days of exposure to 16 µl/L and 7 days of exposure to 8 µL/L. RIPEX exposure also increased the activities of Myeloperoxidase and Adenosine deaminase enzymes in the digestive glands of snails. It increased the total hemocyte count of exposed snails as well as the number of granulocytes. Snail digestive glands and ovotestis showed pathological alterations after 7 days of RIPEX exposure.ConclusionsThese findings suggest that RIPEX is toxic to B. alexandrina and that this snail can be used as a bioindicator for environmental contamination with plant growth regulators.

Lethal and sublethal implications of low temperature exposure for three intertidal predators

Benthic invertebrate predators play a key role in top-down trophic regulation in intertidal ecosystems. While the physiological and ecological consequences of predator exposure to high temperatures during summer low tides are increasingly well-studied, the effects of cold exposure during winter low tides remain poorly understood. To address this knowledge gap, we measured the supercooling points, survival, and feeding rates of three intertidal predator species in British Columbia, Canada — the sea stars Pisaster ochraceus and Evasterias troschelii and the dogwhelk Nucella lamellosa — in response to exposure to sub-zero air temperatures. Overall, we found that all three predators exhibited evidence of internal freezing at relatively mild sub-zero temperatures, with sea stars exhibiting an average supercooling point of −2.50 °C, and the dogwhelk averaging approximately −3.99 °C. None of the tested species are strongly freeze tolerant, as evidenced by moderate-to-low survival rates after exposure to −8 °C air. All three predators exhibited significantly reduced feeding rates over a two-week period following a single 3-h sublethal (−0.5 °C) exposure event. We also quantified variation in predator body temperature among thermal microhabitats during winter low tides. Predators that were found at the base of large boulders, on the sediment, and within crevices had higher body temperatures during winter low tides, as compared to those situated in other microhabitats. However, we did not find evidence of behavioural thermoregulation via selective microhabitat use during cold weather. Since these intertidal predators are less freeze tolerant than their preferred prey, winter low temperature exposures can have important implications for organism survival and predator-prey dynamics across thermal gradients at both local (habitat-driven) and geographic (climate-driven) scales.

Cold atmospheric pressure plasma-antibiotic synergy in Pseudomonas aeruginosa biofilms is mediated via oxidative stress response

Cold atmospheric-pressure plasma (CAP) has emerged as a potential alternative or adjuvant to conventional antibiotics for the treatment of bacterial infections, including those caused by antibiotic-resistant pathogens. The potential of sub-lethal CAP exposures to synergise conventional antimicrobials for the eradication of Pseudomonas aeruginosa biofilms is investigated in this study. The efficacy of antimicrobials following or in the absence of sub-lethal CAP pre-treatment in P. aeruginosa biofilms was assessed. CAP pre-treatment resulted in an increase in both planktonic and biofilm antimicrobial sensitivity for all three strains tested (PAO1, PA14, and PA10548), with both minimum inhibitory concentrations (MICs) and minimum biofilm eradication concentrations (MBECs) of individual antimicrobials, being significantly reduced following CAP pre-treatment of the biofilm (512-fold reduction with ciprofloxacin/gentamicin; and a 256-fold reduction with tobramycin). At all concentrations of antimicrobial used, the combination of sub-lethal CAP exposure and antimicrobials was effective at increasing time-to-peak metabolism, as measured by isothermal microcalorimetry, again indicating enhanced susceptibility. CAP is known to damage bacterial cell membranes and DNA by causing oxidative stress through the in situ generation of reactive oxygen and nitrogen species (RONS). While the exact mechanism is not clear, oxidative stress on outer membrane proteins is thought to damage/perturb cell membranes, confirmed by ATP and LDH leakage, allowing antimicrobials to penetrate the bacterial cell more effectively, thus increasing bacterial susceptibility. Transcriptomic analysis, reveals that cold-plasma mediated oxidative stress caused upregulation of P. aeruginosa superoxide dismutase, cbb3 oxidases, catalases, and peroxidases, and upregulation in denitrification genes, suggesting that P. aeruginosa uses these enzymes to degrade RONS and mitigate the effects of cold plasma mediated oxidative stress. CAP treatment also led to an increased production of the signalling molecule ppGpp in P. aeruginosa, indicative of a stringent response being established. Although we did not directly measure persister cell formation, this stringent response may potentially be associated with the formation of persister cells in biofilm cultures. The production of ppGpp and polyphosphate may be associated with protein synthesis inhibition and increase efflux pump activity, factors which can result in antimicrobial tolerance. The transcriptomic analysis also showed that by 6 h post-treatment, there was downregulation in ribosome modulation factor, which is involved in the formation of persister cells, suggesting that the cells had begun to resuscitate/recover. In addition, CAP treatment at 4 h post-exposure caused downregulation of the virulence factors pyoverdine and pyocyanin; by 6 h post-exposure, virulence factor production was increasing. Transcriptomic analysis provides valuable insights into the mechanisms by which P. aeruginosa biofilms exhibits enhanced susceptibility to antimicrobials. Overall, these findings suggest, for the first time, that short CAP sub-lethal pre-treatment can be an effective strategy for enhancing the susceptibility of P. aeruginosa biofilms to antimicrobials and provides important mechanistic insights into cold plasma-antimicrobial synergy. Transcriptomic analysis of the response to, and recovery from, sub-lethal cold plasma exposures in P. aeruginosa biofilms improves our current understanding of cold plasma biofilm interactions.

Post-fumigation sub-lethal activities of phosphine and ethyl formate on survivorship, fertility and female sex pheromone production of Callosobruchus chinensis (L.)

Phosphine (PH3) and ethyl formate (EF), the two popular fumigant disinfectants of stored product insect pests, are primarily evaluated for their knock down effects without considering their post-fumigation sub-lethal activities. The sub-lethal activities (adult survivorship, fecundity, sterility and female sex pheromone production) of the fumigants were evaluated on a field-to-storage insect pest adzuki bean beetle, Callosobruchus chinensis (L.). The adults’ survivorship and female fecundity, both were dose-dependently affected by sub-lethal PH3 and EF fumigation exposures. Hatchability of the eggs laid by fumigated female adults were also significantly affected. Gas-chromatography mass-spectrometry analysis of solid-phase micro-extraction from virgin fumigated C. cinensis females revealed that the PH3 LC25 (the lethal concentration required to kill the 25% of the population) fumigated female C. chinensis released significantly less amount of the pheromone components. In contrast, EF LC25 exposure did not affect the pheromone release. This study unveils the facts that the EF and PH3 fumigation have detrimental bioactivities against C. chinensis. Notably, this suggests to consider the sub-lethal EF and PH3 fumigation rather than the dose required to instantly kill all the C. chinensis individuals for disinfestation of stored adzuki bean.

In vitro interaction between essential oil compounds and halquinol against zoonotic pathogenic bacteria

The use of growth-promoting antibiotics has led to an increase in antimicrobial resistance; therefore, the search for new alternatives is essential. As many producers are afraid of applying new technologies, the association between conventional and new methods is an opportunity to introduce innovative approaches. The objective of this research was to evaluate the interaction between halquinol and allyl isothiocyanate (AITC), cinnamaldehyde (CIN), and carvacrol (CA). The minimum inhibitory concentrations were evaluated against Salmonella and Escherichia coli, in addition to their fractional inhibitory concentration index (FICindex), the potential for antimicrobial resistance, and the reversal of halquinol resistance. The compounds were effective when used isolated, with an emphasis on AITC, effective in concentrations between 31.25 and 500 μL/L. Halquinol was effective in the range from 18.75 to 600 μg/mL, working within the range recommended by the manufacturer (30–60 ppm) for most bacteria. The FICindex has shown that the combinations of halquinol with CIN and CA presented mostly synergistic and additive effects. In sublethal exposures, prolonged exposure to EOC mainly led to the potentiation of their effects, and exposure to halquinol led to resistance, increasing its inhibitory concentration by approximately 10 times. Resistance reversal tests showed that AITC and CIN have the potential to minimize resistance to halquinol in vitro.

Cross-Platform Comparison of Amino Acid Metabolic Profiling in Three Model Organisms Used in Environmental Metabolomics.

Environmental metabolomics is a promising approach to study pollutant impacts to target organisms in both terrestrial and aquatic environments. To this end, both nuclear magnetic resonance (NMR)- and mass spectrometry (MS)-based methods are used to profile amino acids in different environmental metabolomic studies. However, these two methods have not been compared directly which is an important consideration for broader comparisons in the environmental metabolomics field. We compared the quantification of 18 amino acids in the tissue extracts of Daphnia magna, a common model organism used in both ecotoxicology and ecology, using both 1H NMR spectroscopy and liquid chromatography with tandem MS (LC-MS/MS). 1H NMR quantification of amino acids agreed with the LC-MS/MS quantification for 17 of 18 amino acids measured. We also tested both quantitative methods in a D. magna sub-lethal exposure study to copper and lithium. Again, both NMR and LC-MS/MS measurements showed agreement. We extended our analyses with extracts from the earthworm Eisenia fetida and the plant model Nicotiana tabacum. The concentrations of amino acids by both 1H NMR and LC-MS/MS, agreed and demonstrated the robustness of both techniques for quantitative metabolomics. These findings demonstrate the compatibility of these two analytical platforms for amino acid profiling in environmentally relevant model organisms and emphasizes that data from either method is robust for comparisons across studies to further build the knowledge base related to pollutant exposure impacts and toxic responses of diverse environmental organisms.

Comparative phosphoproteomics analysis provides insights into the responses of Chilo suppressalis to sublethal chlorantraniliprole exposure.

Sublethal exposure to insecticides causes changes in insect behaviors and physiologies including feeding, mobility, communication, hormone homeostasis, development and fecundity, however, the underlying molecular mechanisms were largely unclear. Our previous studies revealed that sublethal chlorantraniliprole exposure disturbed the hormone homeostasis, reduced the weight and longevity and prolonged the developmental duration of Chilo suppressalis. In the present study, the potential phosphorylation modification regulation mechanisms in C. suppressalis in response to sublethal chlorantraniliprole exposure were explored using comparative and quantitative phosphoproteomics. A total of 2640 phosphopeptides belonging to 1144 phosphoproteins were identified, among which 446 phosphopeptides derived from 303 unique phosphoproteins were differentially phosphorylated between the chlorantraniliprole-treated and control larvae. The phosphorylation levels of differentially phosphorylated phosphopeptides were further validated using parallel reaction monitoring (PRM). Functional classification and protein-protein interaction of the differentially phosphorylated proteins (DPPs) were analyzed. Generalized analysis of the DPPs and the differentially expressed genes (DEGs) identified in our previous study showed that sublethal chlorantraniliprole exposure significantly changed the transcription and phosphorylation levels of genes/proteins associated with carbohydrate and lipid metabolism, cytoskeleton, signal transduction, transcription, translation and post-translational modification, leading to the dysfunctions of energy metabolism, transcription regulation, protein synthesis and modification, and signal transduction in C. suppressalis. Further analysis of the phosphorylation motifs in DPPs revealed that the MAPKs, CDKs, CaMK II, PKA, PKC and CK II protein kinases might be directly responsible for the phosphoproteomics response of C. suppressalis to chlorantraniliprole treatment. Our results provide abundant phosphorylation information for characterizing the protein modification in insects, and also provide valuable insights into the molecular mechanisms of insect post-translational modifications in response to sublethal insecticide exposure. © 2023 Society of Chemical Industry.

Modeling disruption of Apis mellifera (honey bee) odorant-binding protein function with high-affinity binders.

Chemical toxins pose a great threat to honey bee health because they affect memory and cognition, diminish immunity, and increase susceptibility to infection, resulting in decreased colony performance, reproduction, and survival. Although the behavioral effects of sub-lethal chemical exposure on honey bees have been intensively studied, how xenobiotics affect olfaction, at the molecular level, still needs to be elucidated. In the present work, in silico tools, such as molecular docking, binding free energy calculations, and molecular dynamics simulations are used to predict if environmental chemicals have stronger binding affinities to honey bee antennal odorant-binding protein 14 (OBP14) than the representative floral odors citralva, eugenol, and the fluorescent probe 1-N-phenylnaphthylamine. Based on structural analysis, 21 chemicals from crop pesticides, household appliances, cosmetics, food, public health-related products, and other sources, many of which are pervasive in the hive environment, have higher binding affinities than the floral odors. These results suggest that chemical exposures are likely to interfere with the honey bee's sense of smell and this disruptive mechanism may be responsible for the lower associative learning and memory based on olfaction found in bees exposed to pesticides. Moreover, bees mainly rely on olfactory cues to perceive their environment and orient themselves as well as to discriminate and identify their food, predators, nestmates, and diseased individuals that need to be removed with hygienic behavior. In summary, sub-lethal exposure to environmental toxins can contribute to colony collapse in several ways from the disruption of proper olfaction functioning.

Sublethal Biochemical Effects of Polyethylene Microplastics and TBBPA in Experimentally Exposed Freshwater Shrimp Palaemonetes argentinus

The biochemical effects of sublethal exposure to polyethylene microplastics (PEM) of 40-48 µm particle size and the flame retardant tetrabromobisphenol A (TBBPA), a plastic additive, on the freshwater shrimp Palaemonetes argentinus were assessed. Here, we postulate that the use of enzyme and thyroid hormones as biomarkers contributes to the knowledge of the effects of microplastics and plastic additives on freshwater crustaceans. To address this, we evaluated the activities of acetylcholinesterase (AChE), glutathione S-transferase (GST), and carboxilesterase (CbE, using 1-naphthyl acetate (NA) as substrate) and levels of the thyroid hormones thyroxine (T4) and triiodothyronine (T3) after shrimp were exposed (for 96 h) to these xenobiotics at environmentally realistic concentrations. The results showed that the mixture of both xenobiotics led to a decrease in AChE and GST activities and increased T4 levels. We suggest that physiological processes could be compromised in freshwater organisms when exposed to microplastics and TBBPA together, and this could ultimately affect upper levels of the food web.

Exposure of Shewanella oneidensis MR-1 to Sublethal Doses of Ionizing Radiation Triggers Short-Term SOS Activation and Longer-Term Prophage Activation.

Currently, there is a lack of bacterial biomarkers indicative of exposure to ionizing radiation (IR). IR biomarkers have applications for medical treatment planning, population exposure surveillance, and IR sensitivity studies. In this study, we compared the utility of signals originating from prophages and the SOS regulon as biomarkers of IR exposure in the radiosensitive bacterium Shewanella oneidensis. Using RNA sequencing, we demonstrated that 60 min after exposure to acute doses of IR (40, 1, 0.5, and 0.25 Gy), the transcriptional activation of the SOS regulon and the lytic cycle of the T-even lysogenic prophage So Lambda are comparable. Using quantitative PCR (qPCR), we showed that 300 min after exposure to doses as low as 0.25 Gy, the fold change of transcriptional activation of the So Lambda lytic cycle surpassed that of the SOS regulon. We observed an increase in cell size (a phenotype of SOS activation) and plaque production (a phenotype of prophage maturation) 300 min after doses as low as 1 Gy. While the transcriptional responses of the SOS and So Lambda regulons have been examined in S. oneidensis after lethal IR exposures, the potential of these (and other transcriptome-wide) responses as biomarkers of sublethal levels of IR (<10 Gy) and the longer-term activity of these two regulons have not been investigated. A major finding is that after exposure to sublethal doses of IR, the most upregulated transcripts are associated with a prophage regulon and not with a DNA damage response. Our findings suggest that prophage lytic cycle genes are a promising source of biomarkers of sublethal DNA damage. IMPORTANCE The bacterial minimum threshold of sensitivity to ionizing radiation (IR) is poorly understood, which hinders our understanding of how living systems recover from the doses of IR experienced in medical, industrial, and off-world environments. Using a transcriptome-wide approach, we studied how in the highly radiosensitive bacterium S. oneidensis, genes (including the SOS regulon and the So Lambda prophage) are activated after exposure to low doses of IR. We found that 300 min after exposure to doses as low as 0.25 Gy, genes within the So Lambda regulon remained upregulated. As this is the first transcriptome-wide study of how bacteria respond to acute sublethal doses of IR, these findings serve as a benchmark for future bacterial IR sensitivity studies. This is the first work to highlight the utility of prophages as biomarkers of exposure to very low (i.e., sublethal) doses of IR and to examine the longer-term impacts of sublethal IR exposure on bacteria.

Sublethal exposure to imidacloprid in commercial Apis mellifera colonies in early spring: performance of honey bees and insecticide transference between in-hive products

Sublethal exposure to imidacloprid in commercial Apis mellifera colonies in early spring: performance of honey bees and insecticide transference between in-hive products

Daphnia magna sub-lethal exposure to phthalate pollutants elicits disruptions in amino acid and energy metabolism

Phthalic acid esters (PAEs) are a class of chemicals that are usually incorporated as additives in the manufacturing of plastics. PAEs are not covalently bound to the material matrix and can, consequently, be leached into the environment. PAEs have been reported to act as endocrine disruptors, neurotoxins, metabolic stressors, and immunotoxins to aquatic organisms but there is a lack of information regarding the impact of sub-lethal concentrations to target organisms. The freshwater crustacean Daphnia magna, a commonly used model organism in aquatic toxicity, was exposed to four phthalate pollutants: dimethyl phthalate (DMP), diethyl phthalate (DEP), monomethyl phthalate (MMP), and monoethyl phthalate (MEP). Liquid chromatography-tandem mass spectrometry (LC-MS/MS) was employed in a targeted metabolomic approach to quantify polar metabolites extracted from a single Daphnia body. Individual metabolite percent changes and hierarchical clustering heatmap analysis showed unique metabolic profiles for each phthalate pollutant. Metabolite percent changes were mostly downregulated or presented opposing responses for the low and high concentrations tested. Meanwhile, pathway analyses suggest the disruption of related and unique pathways, mostly connected with amino acid and energy metabolism. The pathways aminoacyl-tRNA biosynthesis, arginine biosynthesis, and glutathione metabolism were disrupted by most selected PAEs. Overall, this study indicates that although phthalate pollutants can elicit distinct metabolic perturbations to each PAE, they still impacted related biochemical pathways. These chemical-class based responses could be associated with a common toxic mechanism of action. The reported findings show how targeted metabolomic approaches can lead to a better understanding of sub-lethal exposure to pollutants, revealing metabolomic endpoints do not hold a close relationship with traditional acute toxicity endpoints.

Hormesis effects of sulfoxaflor on Aphis gossypii feeding, growth, reproduction behaviour and the related mechanisms

Sulfoxaflor, an important alternative insecticide in integrated pest management (IPM) strategies, can effectively control sap-feeding insect pests such as Aphis gossypii. Although the side effects of sulfoxaflor have recently attracted widespread attention, its toxicological characteristics and mechanisms are still largely undefined. Therefore, the biological characteristics, life table and feeding behaviour of A. gossypii were studied to evaluate the hormesis effect of sulfoxaflor. Then, the potential mechanisms of induced fecundity associated with the vitellogenin (Ag. Vg) and vitellogenin receptor (Ag. VgR) genes were investigated. Although the LC10 and LC30 concentrations of sulfoxaflor significantly reduced the fecundity and net reproduction rate (R0) of the directly exposed sulfoxaflor-resistant and susceptible aphids, hormesis effects on fecundity and R0 were observed in the F1 generation of Sus A. gossypii when the parental generation was exposed to the LC10 of sulfoxaflor. Moreover, the hormesis effects of sulfoxaflor on phloem feeding were observed in both A. gossypii strains. Additionally, enhanced expression levels and protein content of Ag. Vg and Ag. VgR were observed in progeny generations when F0 was subjected to the trans- and multigenerational sublethal sulfoxaflor exposure. Therefore, sulfoxaflor-induced resurgence might occur in A. gossypii after exposure to sublethal concentrations. Our study could contribute to a comprehensive risk assessment and provide convincing reference to optimize sulfoxaflor in IPM strategies.