Draft genome sequences of Cylindrospermopsis raciborskii strains CS-508 and MVCC14, isolated from freshwater bloom events in Australia and Uruguay

Phylogenomic and Pangenomic Assessment of a Mediterranean Strain of Raphidiopsis raciborskii Extends Knowledge of the Global Distribution and Characteristics of a Potentially Toxigenic Cyanobacterium

Among potentially toxigenic cyanobacteria, Raphidiopsis raciborskii has attracted considerable attention due to its ability to produce massive blooms and its recent spread to temperate regions. In this work, we reported for the first time a taxonomic and functional assessment of a R. raciborskii strain isolated from the Mediterranean region, contributing to filling a gap in the global distribution and characteristics of this species. The strain LT_0923 was isolated from Lake Trasimeno, a large and shallow lake in central Italy. The phylogenomic analyses based on selected marker genes and the core genome obtained from a pangenomic analysis based on a selection of available high-quality genomes showed a strong correspondence of the Lake Trasimeno strain with the North American and, at a lower average nucleotide identity, with the South American genomes. The LT_0923 genome did not show the presence of gene clusters encoding legacy cyanotoxins or emerging toxigenic compounds. The open pangenome and the large fraction of distinct gene families identified in the cloud and partly shell genome, enriched with genes specialised in environmental-specific functions and defence mechanisms, are consistent with the development of Raphidiopsis in geographically distinct regions.

Health and Environmental Impacts of Cyanobacteria and Cyanotoxins from Freshwater to Seawater

Cyanobacterial harmful algal blooms (cyanoHABs) are a natural phenomenon produced mainly by the interaction between natural and anthropogenic events. CyanoHABs are characterized by the production of cyanotoxins that can have harmful effects on different species within the food web and even affect human health. Among the most prevalent toxin groups worldwide are microcystins (MCs), anatoxins (ATXs), cylindrospermopsins (CYNs) and nodularins (NODs), which are characterized as toxins with hepatotoxic, neurotoxic, and cytotoxic effects. This review summarizes and analyzes research on the influence of cyanoHABs, the main toxin-producing cyanobacteria and the most prevalent cyanotoxins in freshwater and marine bodies, highlighting their global occurrence, toxicology, and bioaccumulation dynamics in vectors of the food web, and the main cases of acute and chronic intoxications in humans. This review is useful for understanding the dynamics of cyanoHABs' interaction with the ecosystem and their impact on human health, and how the implementation of a surveillance and management framework for cyanobacteria and cyanotoxins could generate vital information for stakeholders to establish health guidelines on the risks and hazards of cyanoHABs for the ecosystem and humans.

Cyanobacteria: A Promising Source of Antifungal Metabolites

Cyanobacteria are a rich source of secondary metabolites, and they have received a great deal of attention due to their applicability in different industrial sectors. Some of these substances are known for their notorious ability to inhibit fungal growth. Such metabolites are very chemically and biologically diverse. They can belong to different chemical classes, including peptides, fatty acids, alkaloids, polyketides, and macrolides. Moreover, they can also target different cell components. Filamentous cyanobacteria have been the main source of these compounds. This review aims to identify the key features of these antifungal agents, as well as the sources from which they are obtained, their major targets, and the environmental factors involved when they are being produced. For the preparation of this work, a total of 642 documents dating from 1980 to 2022 were consulted, including patents, original research, review articles, and theses.

Phylogenetic relationships and genetic divergence of paralytic shellfish toxin- and cylindrospermopsin- producing Cylindrospermopsis and raphidiopsis

Cylindrospermopsis and Raphidiopsis (C/R group) are closely related species responsible for cyanobacterial blooms worldwide. Paralytic shellfish toxins (PSTs) and cylindrospermopsins (CYNs) have been identified in different C/R group strains. However, the evolutionary relationship between PST- and CYN-producing strains has not been systematically evaluated. In this study, C/R group strains and their toxin biosynthesis genes were evaluated by phylogenetic analysis and sequence comparison. None of the tested strains are able to produce PSTs and CYNs simultaneously. The C/R group strains were clustered into five clades, including two non-toxic, two CYN-producing and one PST-producing clades. A high degree of similarity was observed for rpoC1 (> 96%) and ITS-L (> 97%) sequences within each clade with the exception of the ITS-L (87% to 100%) region in CYN-producing R. curvata, which has been shown to contain variable sequence insertions. Genomic analysis revealed that sxtY and sxtZ could be found in both toxic and non-toxic strains. The transposase gene IS4 was only observed in strains from the PST-producing clade. The sxt and cyr gene clusters share five gene families with similar functions. The amino acid sequences of the adenylyl-sulfate kinase genes, sxtO and cyrN, are more similar (45% to 81%) than other pairs of genes (8.0% to 40%). SxtO and CyrN proteins from C/R group strains forms an independent clade on the phylogenetic tree with a high degree of sequence similarity (78% to 100%). In conclusion, PST- and CYN- producing C/R group species can be classified into different clades based on their phylogenetic profile. The sxtO and cyrN genes have probably diverged from a single ancestral adenylyl-sulfate kinase gene, and may be specifically used for toxin biosynthesis in C/R group species.