Effect of Microcystins on Proto- and Metazooplankton Is More Evident in Artificial Than in Natural Waterbodies

Quantitative detection of microcystin-LR in Bellamya aeruginosa by thin-layer chromatography coupled with surface-enhanced Raman spectroscopy based on in-situ ZIF-67/Ag NPs/Au NWs composite substrate

As a hypertoxic natural toxin, the risk of Microcystin-leucine-arginine (MC-LR) residues in Bellamya aeruginosa deserves more attention. Herein, employing the conventional thin-layer chromatography (TLC) technology and a novel surface-enhanced Raman scattering (SERS) substrate, a TLC-SERS chip was fabricated for the purification and quantitative detection of MC-LR in complex samples. The substrate exhibited excellent SERS performance with an enhancement factor of 6.6 × 107, a low detection limit of 2.27 × 10-9 mM for MC-LR, excellent uniformity and reproducibility, as well as a wide linear range. With the application of TLC, the MC-LR was efficiently purified and the concentration was increased to >3 times. Ultimately, recovery rates fluctuated between 93.28% and 101.66% were obtained from the TLC-SERS chip. On balance, the TLC-SERS chip has a robust capacity for achieving rapid and stable quantitative detection of MC-LR, which promises to improve the efficiency of food safety monitoring.

Understanding the Risks of Diffusion of Cyanobacteria Toxins in Rivers, Lakes, and Potable Water

Blue-green algae, or cyanobacteria, may be prevalent in our rivers and tap water. These minuscule bacteria can grow swiftly and form blooms in warm, nutrient-rich water. Toxins produced by cyanobacteria can pollute rivers and streams and harm the liver and nervous system in humans. This review highlights the properties of 25 toxin types produced by 12 different cyanobacteria genera. The review also covered strategies for reducing and controlling cyanobacteria issues. These include using physical or chemical treatments, cutting back on fertilizer input, algal lawn scrubbers, and antagonistic microorganisms for biocontrol. Micro-, nano- and ultrafiltration techniques could be used for the removal of internal and extracellular cyanotoxins, in addition to powdered or granular activated carbon, ozonation, sedimentation, ultraviolet radiation, potassium permanganate, free chlorine, and pre-treatment oxidation techniques. The efficiency of treatment techniques for removing intracellular and extracellular cyanotoxins is also demonstrated. These approaches aim to lessen the risks of cyanobacterial blooms and associated toxins. Effective management of cyanobacteria in water systems depends on early detection and quick action. Cyanobacteria cells and their toxins can be detected using microscopy, molecular methods, chromatography, and spectroscopy. Understanding the causes of blooms and the many ways for their detection and elimination will help the management of this crucial environmental issue.

Planktonic ciliate community driven by environmental variables and cyanobacterial blooms: A 9-year study in two subtropical reservoirs

It is well-established that environmental variability and cyanobacterial blooms have major effects on the assembly and functioning of bacterial communities in both marine and freshwater habitats. It remains unclear, however, how the ciliate community responds to such changes over the long-term, particularly in subtropical lake and reservoir ecosystems. We analysed 9-year planktonic ciliate data series from the surface water of two subtropical reservoirs to elucidate the role of cyanobacterial bloom and environmental variabilities on the ciliate temporal dynamics. We identified five distinct periods of cyanobacterial succession in both reservoirs. Using multiple time-scale analyses, we found that the interannual variability of ciliate communities was more strongly related to cyanobacterial blooms than to other environmental variables or to seasonality. Moreover, the percentage of species turnover across cyanobacterial bloom and non-bloom periods increased significantly with time over the 9-year period. Phylogenetic analyses further indicated that 84 %-86 % of ciliate community turnover was governed by stochastic dispersal limitation or undominated processes, suggesting that the ciliate communities in subtropical reservoirs were mainly controlled by neutral processes. However, short-term blooms increased the selection pressure and drove 30 %-53 % of the ciliate community turnover. We found that the ciliate community composition was influenced by environmental conditions with nutrients, cyanobacterial biomass and microzooplankton having direct and/or indirect significant effects on the ciliate taxonomic or functional community dynamics. Our results provide new insights into the long-term temporal dynamics of planktonic ciliate communities under cyanobacterial bloom disturbance.

The relative roles of multiple drivers on benthic ciliate communities in an intertidal zone

Intertidal biodiversity is being severely disrupted as a result of increased anthropogenic activity. However, our knowledge about how natural gradients, human induced disturbance and biotic interactions affect biodiversity is limited. So, we investigated how three facets of alpha diversity and community composition of benthic ciliates responded to environmental and biological gradients in the intertidal zone of Zhejiang, China. The key determinants and their relative effects on ciliate communities were identified using structural equation modeling, distance-based redundancy analysis and variation partitioning analysis. Our results revealed that sediment grain size was the most important factor affecting alpha diversity and community composition. Human induced eutrophication had significant effects on phylogenetic alpha diversity and community composition. However, the effects of biotic interactions on ciliate communities were relatively small. Moreover, we found community composition was more sensitive to human disturbance than alpha diversity, thus, more suitable for indicating human-induced eutrophication.

Interactions between Ciliate Species and Aphanizomenon flos-aquae Vary Depending on the Morphological Form and Biomass of the Diazotrophic Cyanobacterium

Aphanizomenon flos-aquae can form extensive blooms from freshwater to the brackish environment and, being a diazotrophic species, contribute significantly to the nitrogen and carbon cycle. It occurs as single filaments or aggregates and could be used as an alternative nutrients source for bacteria and ciliates. Ciliates are a group of organisms playing a crucial role in the transfer of nitrogen from primary producers to higher trophic levels in aquatic food webs. The aim of the experiment was to study the effects of the cyanobacterium A. flos-aquae on the community of five ciliate species (Spirostomum minus, Euplotes aediculatus, Strobilidium sp., Vorticella sp. and Paramecium tetraurelia). The response of each species to the presence of a low/high cyanobacterial biomass and to the different morphological forms of A. flos-aquae (single filaments or aggregates) was demonstrated. The results of the experiment showed the variability of interactions between the cyanobacterium A. flos-aquae and ciliates and pointed out the possible benefits that A. flos-aquae provides to the ciliates (e.g., a substrate for the development of bacteria as food for ciliates or as a source of nitrogen and carbon).

Studies of the liposolubility and the ecotoxicity of MC-LR degradation by-products using computational molecular modeling and in-vivo tests with Chlorella vulgaris and Daphnia magna

Computational molecular modelling, mass spectrometry and in-vivo tests with Chlorella vulgaris (C. vulgaris) and Daphnia magna (D. magna) were used to investigate the liposolubility and ecotoxicity of MC-LR degradation by-products generated after oxidation by OH^• radicals in Fenton process. Exposure of MC-LR (5 µg.L^-1) to the most severe oxidation conditions (Fe²⁺ 20 mM and H₂O₂ 60 mM) resulted in a reduction in the toxin concentration of 96% (0.16 µg.L^-1), however, with the formation of many by-products. The by-product of m/z 445 was the most resistant to degradation and retained a toxic structure of diene bonds present in the Adda amino acid. Computational modeling revealed that m/z 445 (tPSA = 132.88 Ų; KOW = 2.02) is more fat-soluble than MC-LR (tPSA = 340.64 Ų; KOW = 0.68), evidencing an easier transport process of this by-product. Given this, toxicity tests using C. vulgaris and D. magna indicated greater toxicity of the by-product m/z 445 compared to MC-LR. When the conversion of MC-LR to by-products was 77%, the growth inhibition of C. vulgaris and the D. magna immobility were, respectively, 6.14 and 0%, with 96% conversion; growth inhibition and the immobility were both 100%  for both species.

Disentangling the relative roles of natural and anthropogenic-induced stressors in shaping benthic ciliate diversity in a heavily disturbed bay

Coastal areas are facing biodiversity loss and degradation of habitats due to intensified human activities. However, our understanding of the relative contribution of natural gradients and human induced disturbance to biodiversity is limited. Here, we investigated the response of three facets of alpha and beta diversity of benthic ciliates to environmental gradients in a highly disturbed estuarine bay in China. We used linear regression and distance-based redundancy analysis to determine the key driving factors for biodiversity. Variation partitioning was further used to examine the relative influence of natural gradients and anthropogenic disturbances on ciliate communities. Our results revealed that ciliate alpha diversity and functional composition remained similar despite notable variation in species composition along salinity gradient. Sediment grain size, together with heavy metals were the strongest determinants in shaping both alpha and beta diversity. After controlling for the effect of natural factors, heavy metals still had significant impacts on beta diversity. Human induced nitrogen enrichment was positively correlated with algivorous functional group with possible impacts on benthic food webs. These results suggest that beta diversity is overall more sensitive to anthropogenic stressors than alpha diversity and give important insights into the role of anthropogenic disturbance on coastal diversity, being also useful for developing ecosystem protection and conservation strategies.

Variations in zooplankton functional groups density in freshwater ecosystems exposed to cyanobacterial blooms

The recently observed decline of biodiversity has become a major problem on Earth. Anthropogenically-driven climate change and eutrophication of natural habitats represent great threats to both terrestrial and aquatic ecosystems. Particularly vulnerable are freshwater ecosystems, where the mentioned changes promote development of cyanobacteria. Extension of the cyanobacterial bloom period, increase of cyanobacterial biomass production and toxicity may involve numerous changes in freshwater ecosystem functioning. We conducted a study in water bodies exposed to cyanobacterial blooms of different duration: short-lasting and long-lasting cyanobacterial blooms. We tested the impact of cyanobacterial biomass on densities of zooplankton species grouped into functional groups (functional groups densities) under conditions of different bloom length periods. The functional groups of zooplankton were identified on the basis of three functional traits of each species: mean body length (BL), potential food source (FS) and feeding type (FT). The results of the study showed that assembling species into functional groups may be helpful in understanding the interactions between biotic components of ecosystem. The results showed that the response of each functional group density for cyanobacterial biomass development depends on the functional traits of the animals (i.e. how the species interact with the whole food web) and may be different depending on the bloom intensity, which acts like a factor selecting adapted species.

Vertical distribution of the relic species Eurytemora lacustris (Copepoda, Calanoida) in stratified mesotrophic lakes

The aim of this study was to determine factors affecting the vertical distribution of Eurytemora lacustris in mesotrophic lakes (Wigry, Hańcza, Szurpiły; north-eastern Poland) during the summer stagnation. Eurytemora lacustris was found in all of the studied lakes, with the highest abundance (8 ind. L^-1) in Lake Wigry. In Lake Szurpiły, E. lacustris has never been recorded before. The results of this study revealed that E. lacustris was most numerous in thermocline zones, suggesting that this species could temporarily tolerate warmer water and lower oxygen concentrations due to better food resources. During the study, it was found that a large part of the E. lacustris population had epibiont ciliates, in contrast to other species of zooplankton that did not have any epibionts. The improvement in the water quality of many deep lakes could lead to an increase in the abundance of E. lacustris. However, epibiont ciliates may be a threat for this species and may play a substantial role in determining the production, distribution, and community dynamics of E. lacustris.

Characterization of bacterial and microbial eukaryotic communities associated with an ephemeral hypoxia event in Taihu Lake, a shallow eutrophic Chinese lake

While the important roles of microbial communities in oceanic hypoxic zones were beginning to be understood, little is known about microbial community associated with this phenomenon in shallow lakes. To address this deficit, both the bacterial and microbial eukaryotic communities of an ephemeral hypoxic area of Taihu Lake were characterized. The hypoxia provided nutritional niches for various bacteria, which results in high abundance and diversity. Specific bacterial groups, such as vadinBC27 subgroup of Bacteroidetes, Burkholderiales, Rhodocyclales, Pseudomonas, and Parcubacteria, were dominated in hypoxic sites and relevant to the fermentation, denitrification, nitrification, and sulfur metabolism. Conversely, most of microbial eukaryotes disappeared along with the decline of DO. An unexpected dominance of fungi was observed during hypoxia, which partly explained by the accumulation of toxic algae. Mucor was the single dominant genus in the hypoxic zone. We proposed that this group might cooperate with bacterial communities in the anaerobic degradation of algal biomass and woody materials. Generally, the hypoxic microbiome in shallow lakes is mainly involved in fermentative metabolism depending on phytodetritus and is potentially influenced by terrestrial sources. This study provided new insights into the unique microbiome in short-term hypoxia in shallow lakes and lays the foundation for studies that will enhance our understanding of the microbial players associated with hypoxia and their adaption strategy on the global scale.