Water blooms caused by the invasive cyanobacterium Raphidiopsis raciborskii occur in many reservoirs in the tropical and subtropical regions of China. In recent decades, this species has spread rapidly to temperate regions. Phenotypic plasticity and climate warming are thought to promote the worldwide dispersion of R. raciborskii. However, investigations into the genetic and phenotypic diversities of this species have revealed significant intraspecific heterogeneity. In particular, competition between R. raciborskii and Microcystis aeruginosa was highly strain dependent. Although the concept of an ecotype was proposed to explain the heterogeneity of R. raciborskii strains with different geographic origins, microevolution is more reasonable for understanding the coexistence of different phenotypes and genotypes in the same environment. It has been suggested that intraspecific heterogeneity derived from microevolution is a strong driving force for the expansion of R. raciborskii. Additionally, temperature, nutrient fluctuations, and grazer disturbance are critical environmental factors that affect the population establishment of R. raciborskii in new environments. The present review provides new insights into the ecological mechanisms underlying the invasion of R. raciborskii in Chinese freshwater ecosystems.

In the past decades, the taxonomic status of the cyanobacterial family Phormidiaceae has always been chaotic and problematic. In this study, filamentous cyanobacteria were investigated in the east of China, and twenty strains isolated from different locations of Zhejiang Province were characterized. Using the polyphasic approach combining morphological, molecular and phylogenetic features, these strains were grouped within the members of the genera Ancylothrix and Potamolinea, the newly recorded genera of cyanobacteria in China. Based on the collected taxonomic information of the family Phormidiaceae, cyanobacterial systematics at family level were further discussed. This study provided a simple and efficient example to perform the phylogenetic evaluation for the monophyly and rationality of currently used families of cyanobacteria by using the regional strains based on the polyphasic approach.

Ionic liquids (ILs) are known as “green solvents” and widely used in industrial applications. However, little research has been conducted on cyanobacteria. This study was conducted to investigate the toxicity of ionic liquids ([Hmim]Cl) on Microcystis aeruginosa PCC7806. The EC₅₀ (72 h) of [Hmim]Cl on the growth of Microcystis aeruginosa PCC 7806 was 10.624 ± 0.221 mg L⁻¹. The possible mechanism of toxicity of [Hmim]Cl against M. aeruginosa PCC 7806 was evaluated by measuring cell growth, photosynthetic pigment contents, chlorophyll fluorescence transients, cell ultrastructure, and transcription of the microcystin-producing gene (mcyB). The concentrations of chlorophyll a and carotenoids were significantly reduced in treated M. aeruginosa cultures. The results of chlorophyll fluorescence transients showed that [Hmim]Cl could destruct the electron-accepting side of the photosystem II of M. aeruginosa PCC 7806. Transmission electron microscopy demonstrated cell damage including changes in the structure of the cell wall and cell membrane, thylakoid destruction, and nucleoid disassembly. The transcription of the mcyB gene was also inhibited under [Hmim]Cl stress. In summary, this study provides new insights into the toxicity of [Hmim]Cl on cyanobactreia.

Algal proliferation is a significant potential risk factor for the formation of disinfection by-products (DBPs) in drinking water during long-distance water transfer. Taking a water treatment plant along the Middle Route of the South-to-North Water Diversion Project as our research site, we combined year-round field monitoring with indoor experiments to characterize seasonal algal community succession. We demonstrate that algal species specificity is the decisive factor shaping the DBP formation profile upon chlorination. Among factors examined, algal species composition exerts the greatest influence on trihalomethane (THM) formation (relative contribution 43.6 %), markedly higher than chlorine dosage (15.9 %) and algal density (1.1 %). Under high biomass, common algae (e.g., Synedra, Desmodesmus, and Chlorella) act as high-risk precursors of carcinogenic N-nitrosamines, including N-nitrosodipropylamine (NDPA), N-nitrosodiethylamine (NDEA), and N-nitrosodimethylamine (NDMA). Notably, Synedra produced NDPA up to 4.73 × 10³ ng/L, while Desmodesmus generated NDEA at 44.5 ng/L, exceeding its 0.2 ng/L threshold by two orders of magnitude. Chlorella also accumulates NDMA. Furthermore, the picocyanobacterium Cyanobium generates high NDPA concentrations (up to 2.94 × 10³ ng/L) even at low chlorine doses, far exceeding the California 10 ng/L notification level, indicating that picocyanobacteria may be underappreciated high-risk N-nitrosamine precursors. These observations suggest that conventional treatment processes can regulate total THM concentrations but remain inadequate to fully address emerging toxic DBPs from specific dominant algal taxa. Consequently, this study furnishes critical scientific justification for reorienting drinking water safety management—moving from a strategy of total algal biomass reduction to one of precise, species-specific early warning.

The middle route of the South-to-North Water Diversion Project supplies high-quality water to various water treatment plants along its path and increases the diversity of cyanobacteria present in the raw water. A filamentous cyanobacterium Leptodesmis xinxiangensis HNU2023 was successfully isolated from a drinking water plant in Xinxiang, which receives its water supply from this middle route. Morphologically, this strain exhibits similarities to cyanobacterial taxa within the genera Leptodesmis and Phormidesmis. Phylogenetic analysis, based on 16S rRNA gene sequences, indicates that this strain is closely related to Leptodesmis, forming a well-supported clade. The 16S rRNA gene sequences of the strain show between 95.5% and 98% similarity to known Leptodesmis species, suggesting that it represents a new species within this genus. Moreover, the distinctive patterns observed in the D1-D1′ and Box-B helix regions of the 16S–23S rRNA internal transcribed spacer (ITS) secondary structure further confirm that this strain is a novel species. Consequently, the comprehensive analysis of the isolated strain, in conjunction with morphological characteristics, 16S rRNA gene sequencing, and ITS secondary structure, substantiates the classification of Leptodesmis xinxiangensis sp. nov. as a new species within the genus Leptodesmis.

Nostoc sphaeroides (N. sphaeroides) is a commercially cultivated cyanobacterium, its flocculation activity has remained entirely unexplored. Here, we report the first systematic investigation of the flocculation performance, underlying mechanisms, and key influencing factors of N. sphaeroides homogenates against toxigenic Microcystis aeruginosa 7806 (M. aeruginosa) and natural water samples. Using kaolin as a test suspension, a flocculation efficiency of 91.7% was achieved under optimized conditions (0.5 g/L homogenate, 5 mmol/L CaCl2, and 50 min reaction time). The bioactive components were predominantly water-soluble extracellular polymeric substances, comprising 92.9% polysaccharides and only 1.8% proteins, identifying extracellular polysaccharides as the principal functional moiety driving flocculation. Calcium ions markedly enhanced flocculation via an adsorption-bridging mechanism, corroborated by a dose-dependent increase in calcium-binding capacity. The homogenate retained high flocculating activity across a temperature range of 30-90 °C, with optimal performance at pH 8.0, and multivalent cations (Ca2+, Mg2+, Fe3+) acted as superior coagulant aids compared to monovalent counterparts. Notably, post-flocculation, the Fv/Fm ratio and cellular surface integrity of M. aeruginosa remained intact, whereas extracellular microcystin concentrations in the culture medium declined substantially. This indicates that the flocculation process does not immediately compromise cell viability while effectively mitigating toxin-associated risks. In preliminary field trials with natural water, turbidity removal reached 47.9%, accompanied by measurable reductions in total nitrogen, total phosphorus, and ammonia nitrogen. Collectively, these findings establish, for the first time, that N. sphaeroides possesses both high flocculation efficiency and nutrient-removal capacity, positioning it as a promising, environmentally benign bioflocculant for natural water remediation.