Metabolites dynamics exacerbated by external nutrients inputs into a Ceratium hirundinella-dominated bloom in the Pengxi River, Three Gorges Reservoir, China

Tetracycline and quinolone contamination mediate microbial and antibiotic resistant gene composition in epiphytic biofilms of mesocosmic wetlands

The fate and ecological impact of antibiotics on aquatic ecosystems have not been properly elucidated in mesocosm wetlands scale. This study explored how tetracyclines (TCs, including tetracycline TC and oxytetracycline) and fluoroquinolones (QNs, including ciprofloxacin CIP and levofloxacin) affect mesocosm wetlands vegetated by V. spiralis, focusing on their impact on epiphytic biofilm microbial communities and antibiotic resistance genes (ARGs). Results showed that submerged plants absorbed more antibiotics than sediment. Both TCs and QNs disrupted microbial communities in different ways and increased eukaryotic community diversity in a concentration-dependent manner (2-4 mg/L for CIP, 4-8 mg/L for TC). TCs mainly inhibited epiphytic bacteria, while CIP increased bacterial phyla abundance. TC reduced Cyanobacteriota, Acidobacteriota, and Patescibacteria but increased Bacillota, Bacteroidota, and Armatimonadota. In contrast, CIP reduced Bacteroidota, Cyanobacteriota, and Gemmatimonadota but increased Bacillota, Planctomycetota, and Acidobacteriota. Significant differences in ARG profiles were observed between QNs and TCs, with TCs having a more substantial effect on ARGs due to their stronger impact on bacterial communities. Both antibiotics raised ARG levels with higher concentrations, particularly for multidrug resistance, tetracyclines, trimethoprim, sulfonamides, aminoglycosides, and fosfomycin, emphasizing their role in antimicrobial resistance. The study suggests that antibiotics can either stimulate or inhibit ARGs depending on their effects on bacterial communities. This study provides key evidence on the ecological mechanisms underlying the impact of TCs and QNs on epiphytic microbes of mesocosm wetlands.

Ecosystem anthropogenic enrichments enhance Chroococcus abundance and suppress Anabaena during cyanobacterial-dominated spring blooms in the Pengxi River, Three Gorges Reservoir, China

Taxa-specific responses to the increasing anthropogenic eutrophication offer promising insights for mitigating harmful algal blooms (HABs) in freshwaters. The present study evaluated the HABs species dynamics in response to the ecosystem anthropogenic enrichment during cyanobacterial-dominated spring HABs in the Pengxi River, Three Gorges Reservoir, China. Results show significant cyanobacterial dominance with a relative abundance (RA = 76.54 %). The ecosystem enrichments triggered shifts in the HABs community structure from Anabaena to Chroococcus, especially in the culture involving iron (Fe) addition (RA = 66.16 %). While P-alone enrichment caused a dramatic increase in the aggregate cell density (2.45 × 10⁸ cells L^-1), the multiple enrichment (NPFe) led to maximum biomass production (as chl-a = 39.62 ± 2.33 μgL^-1), indicating that nutrient in conjunction with the HABs taxonomic characteristics e.g., tendency to possess high cell pigment contents rather than cell density can potentially determine massive biomass accumulations during HABs. The stimulation of growth as biomass production demonstrated by both P-alone and the multiple enrichments, NPFe indicates that although P exclusive control is feasible in the Pengxi ecosystem, it can only guarantee a short-term reduction in HABs magnitude and duration, thus a lasting HABs mitigation measure must consider a policy recommendation involving multiple nutrient management, especially N and P dual control strategy. The present study would adequately complement the concerted effort in developing a rational predictive framework for freshwater eutrophication management and HABs mitigations in the TGR and elsewhere with similar anthropogenic stressors.