Seasonal variation in structural and functional distribution of periphyton in a macrolide antibiotics-contaminated river.

Periphyton, a microbial assemblage of autotrophic and heterotrophic organisms, is vital to aquatic ecosystems. While exposure to macrolide antibiotics has been confirmed to reduce the biodiversity and damage the critical ecological functions in indoor microcosm bioassays, the distribution of periphyton along a macrolide antibiotic pollution gradient in a river has yet to be determined. Herein, we established the spatiotemporal distribution of five major macrolides, i.e., azithromycin (AZI), roxithromycin (ROX), erythromycin (ERY), clarithromycin (CLA), and anhydro erythromycin (ERY-H2O) in water and periphyton of Zao River (Xi'an, China), after which we evaluated the effects on the structures, photosynthetic activity, and carbon utilization capacity of periphyton in March, June, and September 2023. In contrast with the reference sites, the macrolides were identified in all sewage treatment plants (STPs) impacted sites with concentrations ranging from 0.05 to 2.18 µg/L in water and from not detected - 9.67 µg/g in periphyton. Regarding community structure, the occurrence of macrolides was negatively linked to FirmicutesExiguobacterium undae and Exiguobacterium sibiricum, CyanobacteriaOscillatoriales and Vischeria sp., and ChlorophytaMonostroma grevillei, Selenastrum sp. LU21 and Desmodesmus subspicatus. At the functional level, only the metabolism of phenolic acids was significantly decreased in river reach with high antibiotic levels in June, compared to the other five carbon sources that were not altered. The overall photosynthetic activity of periphytic photosystem II remained unchanged in both reference and STPs impacted groups throughout three seasons. Overall, the macrolides released from STPs were correlated with the altered periphytic structures in the river, whereas a similar trend was not detected for the community functions owing to the functional redundancy. A mesocosm experiments warrants further consideration to validate the field results.

Highly sensitive ultra-performance liquid chromatography coupled with triple quadrupole mass spectrometry detection method for levoglucosan based on Na+ enhancing its ionization efficiency.

The sensitive determination of levoglucosan in aqueous samples has great significance for the study of biomass burning. Although some sensitive high-performance liquid chromatography/mass spectrometry (HPLC/MS) detection methods have been developed for levoglucosan, there are still plenty of shortcomings, such as complicated sample pre-treatment procedures, large-amount sample requirements, and poor reproducibility. Herein, a new method for the determination of levoglucosan in the aqueous sample was developed using ultra-performance liquid chromatography with triple quadrupole mass spectrometry (UPLC-MS/MS). In this method, we firstly found that compared with H+, Na+ could effectively enhance the ionization efficiency of levoglucosan, even though the content of H+ is higher in the environment. Moreover, the precursor ion m/z 185.1 [M + Na]+ could be used as a quantitative ion to sensitively detect levoglucosan in aqueous samples. Only 2 µL of un-pretreated sample is required for one injection in this method, and great linearity was obtained (R 2 = 0.9992) using the external standard method when the concentration of levoglucosan was 0.5-50 ng mL-1. The limit of detection (LOD) and quantification (LOQ) were 0.1 ng mL-1 (0.2 pg absolute mass injected) and 0.3 ng mL-1, respectively. Acceptable repeatability, reproducibility, and recovery were achieved. This method has the advantages of high sensitivity, good stability, good reproducibility, and simple operation, which could be widely used for the detection of different concentrations of levoglucosan in various water samples, especially for the detection of samples with low content such as ice core or snow samples.

Effects of erythromycin and roxithromycin on river periphyton: Structure, functions and metabolic pathways.

Macrolides have been frequently detected in the surface waters worldwide, posing a threat to the aquatic microbes. Several studies have evaluated the ecotoxicological effects of macrolides on single algal and bacterial strains. However, without considering the species interaction in the aquatic microbial community, these results cannot be extrapolated to the field. Thus, the present study aimed to evaluate the effects of two macrolides (erythromycin and roxithromycin) on the structure, photosynthetic process, carbon utilization capacity, and the antibiotic metabolic pathways in river periphyton. The colonized periphyton was exposed to the graded concentration (0 µg/L (control), 0.5 µg/L (low), 5 µg/L (medium), 50 µg/L (high)) of ERY and ROX, respectively, for 7 days. Herein, high levels of ERY and ROX altered the community composition by reducing the relative abundance of Chlorophyta in the eukaryotic community. Also, the Shannon and Simpson diversity indexes of prokaryotes were reduced, although similar effects were seldomly detected in the low and medium groups. In contrast to the unchanged carbon utilization capacity, the PSII reaction center involved in the periphytic photosynthesis was significantly inhibited by macrolides at high levels. In addition, both antibiotics had been degraded by periphyton, with the removal rate of 51.63-66.87% and 41.85-48.27% for ERY and ROX, respectively, wherein the side chain and ring cleavage were the main degradation pathways. Overall, this study provides an insight into the structural and functional toxicity and degradation processes of macrolides in river periphyton.

Metabolomic profiles in a green alga (Raphidocelis subcapitata) following erythromycin treatment: ABC transporters and energy metabolism.

A recent study showed that erythromycin (ERY) exposure caused hormesis in a model alga (Raphidocelis subcapitata) where the growth was promoted at an environmentally realistic concentration (4 µg/L) but inhibited at two higher concentrations (80 and 120 µg/L), associated with opposite actions of certain signaling pathways (e.g., xenobiotic metabolism, DNA replication). However, these transcriptional alterations remain to be investigated and verified at the metabolomic level. This study uncovered metabolomic profiles and detailed toxic mechanisms of ERY in R. subcapitata using untargeted metabolomics. The metabolomic analysis showed that metabolomic pathways including ABC transporters, fatty acid biosynthesis and purine metabolism were associated with growth promotion in algae treated with 4 µg/L ERY. An overcompensation was possibly activated by the low level of ERY in algae where more resources were reallocated to efficiently restore the temporary impairments, ultimately leading to the outperformance of growth. By contrast, algal growth inhibition in the 80 and 120 µg/L ERY treatments was likely attributed to the dysfunction of metabolomic pathways related to ABC transporters, energy metabolism and metabolism of nucleosides. Apart from binding of ERY to the 50S subunit of ribosomes to inhibit protein translation as in bacteria, the data presented here indicate that inhibition of protein translation and growth performance of algae by ERY may also result from the suppression of amino acid biosynthesis and aminoacyl-tRNA biosynthesis. This study provides novel insights into the dose-dependent toxicity of ERY on R. subcapitata.