Mycosporine-like amino acids (MAAs) are widespread in various microbes and protect them against harsh environments. Here, four different Aphanizomenon species were isolated from severely eutrophic waterbodies, Lake Dianchi and the Guanqiao fishpond. Morphological characters and molecular phylogenetic analysis verified that the CHAB5919, 5921, and 5926 strains belonged to the Aphanizomenon flos-aquae clade while Guanqiao01 belonged to the Aphanizomenon gracile clade. Full wavelength scanning proved that there was obvious maximal absorption at 334 nm through purified methanol extraction, and these substances were further analyzed by HPLC and UPLC-MS-MS. The results showed that two kinds of MAAs were discovered in the cultured Aphanizomenon strains. One molecular weight was 333.28 and the other was 347.25, and the daughter fragment patterns were in accordance with the previously articles reported shinorine and porphyra-334 ion characters. The concentration of the MAAs was calibrated from semi-prepared MAAs standards from dry cells of Microcystis aeruginosa PCC7806 algal powder, and the purity of shinorine and porphyra-334 were 90.2% and 85.4%, respectively. The average concentrations of shinorine and porphyra-334 were 0.307–0.385 µg/mg and 0.111–0.136 µg/mg in Aphanizomenon flos-aquae species, respectively. And there was only one kind of MAAs (shinorine) in Aphanizomenon gracile species.,with a content of 0.003–0.049 µg/mg dry weight among all Aphanizomenon gracile strains. The shinorine concentration in Aphanizomenon flos-aquae was higher than that in Aphanizomenon gracile strains. The total MAAs production can be ranked as Aphanizomenon flos-aquae > Aphanizomenon gracile.

Lead (Pb) is a hazardous pollutant in water environments that can cause significant damage to aquatic animals and humans. In this study, crucian carp (Carassius auratus) were exposed to waterborne Pb for 96 h; then, histopathological analysis, quantitative qPCR analysis, and 16S high-throughput sequencing were performed to explore the effects of Pb on intestinal bioaccumulation, structural damage, oxidative stress, immune response, and microbiota imbalance of C. auratus. After Pb exposure, the intestinal morphology was obviously damaged, including significantly increasing the thickness of the intestinal wall and the number of goblet cells and reducing the depth of intestinal crypts. Pb exposure reduced the mRNA expressions of Claudin-7 and villin-1 while significantly elevated the level of GST, GSH, CAT, IL-8, IL-10, IL-1, and TNF-α. Furthermore, 16S rRNA analysis showed that the Shannon and Simpson indices decreased at 48 h after Pb exposure, and the abundance of pathogenic bacteria (Erysipelotrichaceae, Weeksellaceae, and Vibrionaceae) increased after Pb exposure. In addition, the correlation network analysis found that Proteobacteria were negatively correlated with Firmicutes and positively correlated with Bacteroidetes. Functional prediction analysis of bacteria speculated that the change in intestinal microbiota led to the PPAR signaling pathway and peroxisome function of the intestine of crucian carp was increased, while the immune system and membrane transport function were decreased. Finally, canonical correlation analysis (CCA) found that there were correlations between the intestinal microbiota, morphology, antioxidant factors, and immune factors of crucian carp after Pb exposure. Taken together, our results demonstrated that intestinal flora dysbiosis, morphological disruption, oxidative stress, and immune injury are involved in the toxic damage of Pb exposure to the intestinal structure and function of crucian carp. Meanwhile, Pb exposure rapidly increased the abundance of pathogenic bacteria, leading to intestinal disorders, further aggravating the damage of Pb to intestinal structure and function. These findings provide us a basis for the link between gut microbiome changes and heavy metal toxicity, and gut microbiota can be used as biomarkers for the evaluation of heavy metal pollution in future.

A cyanobacterial strain (ZJJ01), morphologically identified as a Leptolyngbya-like species was isolated from a freshwater pond in Zhangjiajie National Forest Park, China, and it was characterized through a polyphasic study based on morphological, ecological, and molecular data. Morphologically, the strain fits the description of Leptolyngbya well, but under further examination, it formed a distinctive structure, namely nodules, which confirmed that it belonged to the genus of Nodosilinea. The 16S rRNA gene threshold value and 16S rRNA phylogenetic analyses clearly confirmed that the studied strain belongs to the genus Nodosilinea but that it is phylogenetically distinct from the 10 other species of Nodosilinea. Furthermore, The D1–D1’ and Box–B helix of the 16S–23S ITS region of the strain ZJJ01 were also different from those of previously described Nodosilinea species. On the basis of this polyphasic approach, here, we provide a description of the new taxon: Nodosilinea hunanesis sp. nov.

River–lake systems in the middle and lower reaches of the Yangtze River Basin function as critical ecological interfaces for maintaining regional water security and biodiversity. However, the complex interplay between environmental factors and biological communities in these systems remains poorly understood, limiting evidence-based management strategies essential for achieving sustainable development goals. This study investigated the spatiotemporal heterogeneity of environmental variables and their relationships with biological communities across 36 sampling sites (4 rivers, 5 lakes) from January to November 2022. Significant spatial differences were observed between river and lake systems, with lakes exhibiting higher concentrations of biochemical oxygen demand (BOD₅), chlorophyll-a, permanganate index (CODMn), loss on ignition (LOI), sediment total nitrogen (STN), total organic carbon (TOC), and turbidity, while rivers showed elevated total nitrogen levels. These patterns reflected fundamental differences in hydrodynamic mechanisms, particularly water retention time and sedimentation processes. Environmental parameters displayed distinct seasonal variations, with BOD₅ increasing markedly in autumn, and chlorophyll-a showing system-specific peaks in lakes (May) and rivers (September). Multivariate analyses revealed that water temperature, organic matter, and nutrients (particularly phosphorus) were key drivers shaping both phytoplankton and benthic communities. The structural equation model identified a strong cascade pathway from turbidity through phosphorus to phytoplankton richness, and uncovered a “phosphorus paradox” wherein total phosphorus exhibited contrasting effects on different biological components—positive for phytoplankton richness but negative for benthic richness. The positive relationship between phytoplankton and benthic macroinvertebrate richness provided evidence for benthic–pelagic coupling in this river–lake system. These findings advance our understanding of the complex mechanisms linking physical factors, nutrient dynamics, and biological communities across river–lake continuums, providing a quantitative framework for ecosystem-based management that supports sustainable development in the Yangtze River Basin and similar freshwater systems globally.