Cyanobacterial blooms in China: diversity, distribution, and cyanotoxins.

Aphanizomenonaceae is a recently proposed family of Cyanobacteria encompassing 12 planktic genera. The formation and distribution of heterocytes and akinetes along the trichome are the main morphological characteristics of this family. In this context, Sphaerospermopsis and Cylindrospermopsis are close related genera both molecularly and morphologically differing by 1) rounded akinetes adjacent to the heterocytes disposed along the trichome in Sphaerospermopsis; 2) apical heterocytes and akinetes separated by a few cells (2–3) in Cylindrospermopsis. Recently, during a survey on cyanobacteria from tropical Brazilian eutrophic lakes, strains with similarities to Sphaerospermopsis and Cylindrospermopsis were isolated. Aiming to elucidate the phylogenetic placement of these strains, we performed morphological, physiological and molecular studies. The Brazilian strains were confirmed to be closely related to Sphaerospermopsis and Cylindrospermopsis, but the phylogeny, based on 16S rRNA gene and 16S–23S rRNA intergenic region, clustered them in a well-defined clade separate from these genera. According to these results, we detailed the morphology, physiology, and phylogeny of the proposed new genus Amphiheterocytum, which showed potential to create blooms in tropical shallow lakes.

Phylogenetic connection among close genera of Aphanizomenonaceae (Cyanobacteria): Amphiheterocytum gen. nov., Cylindrospermopsis and Sphaerospermopsis

Culture collections such as the Blue Biotechnology and Ecotoxicology Culture Collection (LEGE-CC) hold approximately 1200 cyanobacterial strains and are critical community resources. However, many isolates in this and other collections have not been described with a polyphasic approach, and this limits further study. Here, we employed a polyphasic methodology that integrates 16S rRNA gene phylogenetic analyses, similarity (p-distance), 16S-23S ITS rRNA region secondary structures, morphological analyses, and habitat assessments to describe four novel cyanobacterial genera from the LEGE-CC, Portugal. Pseudolimnococcus planktonicus gen. et sp. nov. (Chroococcales) is phylogenetically and morphologically related to Limnococcus. The 16S rRNA gene similarity between the types of both genera is only 93.1%. Morphologically, Pseudolimnococcus cells do not reach the original spherical shape before the next division or have aerotopes and firm mucilage, while Limnococcus cells reach the original shape, lack aerotopes, and have diffluent mucilage. Eucapsopsis lusitanus gen. et sp. nov. (Chroococcales) is morphologically similar to Eucapsis but differs from it by having aerotopes and diffluent envelope. Eucapsis lacks aerotopes and has firm mucilaginous envelopes, rarely diffluent. Both genera are phylogenetically very distant from each other and have only 90.68% 16S rRNA gene similarity. Pseudoacaryochloris arrabidensis gen. et sp. nov. (Acaryochloridales) differs from Acaryochloris by the lack of mucilaginous envelope, which is present in Acaryochloris. Both genera are phylogenetically distant and have only 94.1% 16S rRNA gene similarity. Moreover, Acaryochloris is marine (sponge symbiont), while Pseudoacaryochloris is from freshwater. Vasconcelosia minhoensis gen. et sp. nov. (Nodosilineales) is phylogenetically related to Cymatolege but has only 94.3% similarity with this genus. Morphologically both genera are distinct. Vasconcelosia has a Romeria-like structure, while Cymatolege has a Phormidium-like structure. In all cases the 16S-23S ITS rRNA region secondary structures are in agreement with the other analyses. These novel genera expand the diversity of cyanobacteria in culture collections.

Exploring the cyanobacterial diversity in Portugal: Description of four new genera from LEGE-CC using the polyphasic approach.

The taxonomic identification of cyanobacteria is essential for researchers or/and competent authorities to know their diversity and detect, manage, and control potentially toxic cyanobacteria. Microbiologists and botanists agree that polyphasic approaches are a powerful tool to identify cyanobacteria. This chapter describes the polyphasic approach, the steps to follow, and some recommendations for its correct application. The changes in taxonomy using this methodology are also explained. Finally, the applications of a polyphasic approach on genomic and metabarcoding biodiversity studies are described. The polyphasic approach is a well defined and standard tool for classifying cyanobacteria, which researchers accept, but it is continuously being revised. 

Recent trends of polyphasic approach in taxonomy and cyanobacterial diversity

Abstract Cyanobacterial mats supplanting coral and spreading coral diseases in tropical reefs, intensified by environmental shifts caused by human‐induced pressures, nutrient enrichment, and global climate change, pose grave risks to the survival of coral ecosystems. In this study, we characterized Okeanomitos corallinicola gen. and sp. nov., a newly discovered toxic marine heterocyte‐forming cyanobacterium isolated from a coral reef ecosystem of the South China Sea. Phylogenetic analysis, based on the 16S rRNA gene and the secondary structure of the 16S–23S rRNA intergenic region, placed this species in a clade distinct from closely related genera, that is, Sphaerospermopsis stricto sensu, Raphidiopsis , and Amphiheterocytum . The O. corallinicola is a marine benthic species lacking gas vesicles, distinguishing it from other members of the Aphanizomenonaceae family. The genome of O. corallinicola is large and exhibits diverse functional capabilities, potentially contributing to the resilience and adaptability of coral reef ecosystems. In vitro assays revealed that O. corallinicola demonstrates notable cytotoxic activity against various cancer cell lines, suggesting its potential as a source of novel anticancer compounds. Furthermore, the identification of residual saxitoxin biosynthesis function in the genome of O. corallinicola , a marine cyanobacteria, supports the theory that saxitoxin genes in cyanobacteria and dinoflagellates may have been horizontally transferred between them or may have originated from a shared ancestor. Overall, the identification and characterization of O. corallinicola provides valuable contributions to cyanobacterial taxonomy, offering novel perspectives on complex interactions within coral reef ecosystems. 

Okeanomitos corallinicola gen. and sp. nov. (Nostocales, Cyanobacteria), a new toxic marine heterocyte‐forming Cyanobacterium from a coral reef

The recently established genus Sphaerospermopsis was characterized by spherical akinetes located on one or both sides of heterocytes. The establishment of the new genus was supported by the clustering of the 16S rRNA gene. Natural populations of the genus may be overlooked when akinetes are absent. In this study, a new Sphaerospermopsis species, Sphaerospermopsis crassa, and other Sphaerospermopsis species were taxonomically evaluated by combining morphology and molecular data on the 16S rRNA gene and the 16S–23S rRNA internally transcribed spacer (ITS). New insights into the taxonomy of the genus Sphaerospermopsis were obtained. The ITS secondary structures from seven Sphaerospermopsis strains of three species showed the same pattern of D1–D1′, Box-B and V3 helices, which distinguished them from other heterocytous genera. Furthermore, the V2 helix was quite variable and useful for species delimitation within Sphaerospermopsis.

New insights into the taxonomy of the genus Sphaerospermopsis (Nostocales, Cyanobacteria) with the description of Sphaerospermopsis crassa sp. nov.

The taxonomy of coccoid cyanobacteria has been largely revised in recent years. In this study, a novel coccoid cyanobacterial strain was isolated from a watercourse at the Poyang Lake Model Research Base, Jiangxi province, Eastern China. A polyphasic approach combining morphological and molecular testing was used to characterize this strain referred to as CHAB 4018. Regarding colonial form and cellular spatial arrangement, this strain was morphologically similar to strains of the genus Eucapsis. The maximum 16S rRNA gene sequence similarity of this strain to the currently described cyanobacteria genera was 93.40%, exceeding the cutoff for genus delimitation in bacteriology. Furthermore, a phylogenetic tree based on 16S rRNA gene sequences indicated that strain CHAB 4018 formed a unique clade in the family Chroococcaceae and was phylogenetically close to the recently established genus Cryptococcum but distant from the Chroococcus 'sensu stricto' clade and from Eucapsis. Thus, a novel coccoid cyanobacterial genus with a new species is here described as Neochroococcus gongqingensis. A large phylogenetic tree using more strains suggested phylogenetic intermixture of Chroococcus-like and Eucapsis-like cyanobacteria, suggesting the need for further studies on the phylogeny and taxonomy of coccoid cyanobacteria.

/pdf/neochroococcus-gongqingensis-gen-et-sp-nov-a-new-member-of-3qxx8qaot6.pdf

Neochroococcus gongqingensis gen. et sp. nov., a new member of coccoid cyanobacteria from a watercourse, Eastern China

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New insights into the taxonomy of the genus Sphaerospermopsis (Nostocales, Cyanobacteria) with the description of Sphaerospermopsis crassa sp. nov.

Neochroococcus gongqingensis gen. et sp. nov., a new member of coccoid cyanobacteria from a watercourse, Eastern China