Physiological-biochemical responses and transcriptomic analysis reveal the effects and mechanisms of sulfamethoxazole on the carbon fixation function of Chlorella pyrenoidosa

The key molecular mechanisms of antagonism induced by combined exposure to erythromycin and roxithromycin in Chlorella pyrenoidosa

Emerging pollutants such as antibiotics have raised great concern in recent years, but the complex coexistence of multiple antibiotics in the environment poses a new challenge in the accurate assessment of the toxicity of antibiotics to aquatic organisms such as microalgae. In this study, the mechanism of action of a combination of erythromycin (ERY) and roxithromycin (ROX) on Chlorella pyrenoidosa was illustrated based on the physiological-biochemical response and transcriptomic analysis. The results revealed an inhibitory effect on the biomass of C. pyrenoidosa at 14 d in all treatment groups, whereas an antagonistic effect was observed in the coexposure groups. The photosystem was the main target despite the existence of multiple compensatory mechanisms, such as expanding the antenna size and initiating alternative electron carriers. The intercept of electrons on the donor side of PSI limited the production of energy, whereas the adjustment of the content and ratio of pigments strengthened microalgal adaptation. Enzymes and genes related to the degradation of exogenous compounds, including cytochrome P450 (P450), glutathione S-transferase (GST) and ABC transporters, mediated the detoxification of antibiotics. The upregulated expression of related genes induced by coexposure increased resistance and explained the antagonistic effects. The shift in energy allocation by increasing the proportion of lipids met the urgent requirements of microalgal physiological activities. This study reemphasizes the modes of interactions between multiple antibiotics and provides new insights into the mechanisms of antagonism induced by combinations of antibiotics.

Promote or inhibit? Transcriptomic and metabonomic insights into the effects of antibiotics on nitrogen uptake and metabolism in Myriophyllum aquaticum

Phytoremediation is an effective nitrogen removal method to alleviate eutrophication. However, the coexistence of antibiotics may inhibit nitrogen removal by aquatic macrophytes, and the underlying mechanisms remain unclear. Here, we systematically investigated the effects of three antibiotics (norfloxacin, NOR; sulfamethoxazole, SMX; and oxytetracycline, OTC) at environmental concentrations (1 μg/L and 1 mg/L) on ammonia (NH4+-N) and nitrate (NO3--N) removal by the aquatic macrophyte Myriophyllum aquaticum. NOR, SMX, and OTC reduced NH4+-N removal by M. aquaticum by 10-36 %, with low levels (1 μg/L) of NOR reducing NO3--N removal by up to 60 %. Antibiotics substantially reduced the biomass and chlorophyll contents but increased the antioxidant enzymes in M. aquaticum. While antibiotics inhibited NH4+-N removal, the promotion or inhibition effect of antibiotics on NO3--N removal by M. aquaticum depended on types and levels of antibiotics. Transcriptomic and metabonomic profile analyses revealed differentially expressed genes and metabolites, suggesting that the mechanisms underlying the promotional/inhibitory effects of antibiotics on nitrogen uptake and metabolism were related to ammonia metabolism, the tricarboxylic acid cycle, photosynthesis, and oxidative stress. Myriophyllum aquaticum exhibited better NH4+-N removal than NO3--N removal, as NH4+-N can be directly taken up by M. aquaticum and transformed into ammonium, while NO3--N must be absorbed by the plant and then reduced to ammonium. During this process, antibiotics disrupt genes associated with nitrogen uptake and metabolism. In this study, we provide multiomics insights into the mechanisms of nitrogen metabolism in aquatic macrophytes affected by antibiotics and offers a scientific basis for water pollution control.

Phycospheric Bacteria Alleviate the Stress of Erythromycin on Auxenochlorella pyrenoidosa by Regulating Nitrogen Metabolism

Macrolide pollution has attracted a great deal of attention because of its ecotoxic effects on microalgae, but the role of phycospheric bacteria under antibiotic stress remains unclear. This study explored the toxic effects of erythromycin (ERY) on the growth and nitrogen metabolism of Auxenochlorella pyrenoidosa; then, it analyzed and predicted the effects of the composition and ecological function of phycospheric bacteria on microalgae under ERY stress. We found that 0.1, 1.0, and 10 mg/L ERY inhibited the growth and chlorophyll of microalgae, but the microalgae gradually showed enhanced growth abilities over the course of 21 days. As the exposure time progressed, the nitrate reductase activities of the microalgae gradually increased, but remained significantly lower than that of the control group at 21 d. NO3- concentrations in all treatment groups decreased gradually and were consistent with microalgae growth. NO2- concentrations in the three treatment groups were lower than those in the control group during ERY exposure over 21 d. ERY changed the community composition and diversity of phycospheric bacteria. The relative abundance of bacteria, such as unclassified-f-Rhizobiaceae, Mesorhizobium, Sphingopyxis, Aquimonas, and Blastomonas, varied to different degrees. Metabolic functions, such ABC transporters, the microbial metabolism in diverse environments, and the biosynthesis of amino acids, were significantly upregulated in the treatments of higher concentrations (1.0 and 10 mg/L). Higher concentrations of ERY significantly inhibited nitrate denitrification, nitrous oxide denitrification, nitrite denitrification, and nitrite and nitrate respiration. The findings of this study suggest that phycospheric bacteria alleviate antibiotic stress and restore the growth of microalgae by regulating nitrogen metabolism in the exposure system.

Palmatine Alleviates Particulate Matter-Induced Acute Lung Injury by Inhibiting Pyroptosis via Activating the Nrf2-Related Pathway

Particulate matter (PM) induces and enhances oxidative stress and inflammation, leading to a variety of respiratory diseases, including acute lung injury. Exploring new treatments for PM-induced lung injury has long been of interest to researchers. Palmatine (PAL) is a natural extract derived from plants that has been reported in many studies to alleviate inflammatory diseases. Our study was designed to explore whether PAL can alleviate acute lung injury caused by PM. The acute lung injury model was established by instilling PM (4 mg/kg) into the airway of mice, and PAL (50 mg/kg and 100 m/kg) was administrated orally as the treatment groups. The effect and mechanism of PAL treatment were examined by immunofluorescence, immunohistochemistry, Western Blotting, ELISA, and other experiments. The results showed that oral administration of PAL (50 mg/kg and 100 m/kg) could significantly alleviate lung inflammation and acute lung injury caused by PM. In terms of mechanism, we found that PAL (50 mg/kg) exerts anti-inflammatory and anti-damage effects mainly by enhancing the activation of the Nrf2-related antioxidant pathway and inhibiting the activation of the NLRP3-related pyroptosis pathway in mice. These mechanisms have also been verified in our cell experiments. Further cell experiments showed that PAL may reduce intracellular reactive oxygen species (ROS) by activating Nrf2-related pathways, thereby inhibiting the activation of NLRP3-related pyroptosis pathway induced by PM in Beas-2B cell. Our study suggests that PAL can be a new option for PM-induced acute lung injury.

Mechanisms of hormetic effects of ofloxacin on Chlorella pyrenoidosa under environmental-relevant concentration and long-term exposure

Antibiotics are frequently detected in surface water and pose potential threats to organisms in aquatic ecosystem such as microalgae. The occurrence of biphasic dose responses raised the possibility of stimulation of microalgal biomass by antibiotics at environmental-relevant concentration and caused potential ecological risk such as algal bloom. However, the underlying mechanisms of low concentration-induced hormetic effects are not well understood. In this study, we evaluated the hormesis of ofloxacin on Chlorella pyrenoidosa under environmental-relevant concentration and long-term exposure. Results showed the hormetic effects of ofloxacin on cell density and carbon fixation rate (RC). The predicted maximum promotion was 17.45 % by 16.84 μg/L and 20.08 % by 15.78 μg/L at 21 d, respectively. The predicted maximum concentration of non-effect on cell density and RC at 21 d was 3.24 mg/L and 1.44 mg/L, respectively. Ofloxacin induced the mobilization of pigments and antioxidant enzymes to deal with oxidative stress. PCA analysis revealed Chl-a/Chl-b could act as a more sensitive biomarker under acute exposure while chlorophyll fluorescence parameters were in favor of monitoring long-term implication. The hormesis in increased secretion of extracellular organic matters was regarded as a defensive mechanism and accelerated indirect photodegradation of ofloxacin. Bioremoval was dominant and related to biomass accumulation in the total dissipation while abiotic removal appeared slight contributions. This study provided new insights into the understanding of hormesis of microalgae induced by antibiotics.