Polysaccharide Stalks in Didymosphenia geminata Diatom: Real World Applications and Strategies to Combat Its Spread

Didymosphenia geminata is a species of freshwater diatom that is known as invasive and is propagating quickly around the world. While invasive species are generally considered a nuisance, this paper attempts to find useful applications for D. geminata in the biomedical field and wastewater remediation. Here, we highlight the polysaccharide-based stalks of D. geminata that enable versatile potential applications and uses as a biopolymer, in drug delivery and wound healing, and as biocompatible scaffolding in cell adhesion and proliferation. Furthermore, this review focuses on how the polysaccharide nature of stalks and their metal-adsorption capacity allows them to have excellent wastewater remediation potential. This work also aims to assess the economic impact of D. geminata, as an invasive species, on its immediate environment. Potential government measures and legislation are recommended to prevent the spread of D. geminata, emphasizing the importance of education and collaboration between stakeholders.

Impact of Algicidal Bacillus mycoides on Diatom Ulnaria acus from Lake Baikal

Algae–bacteria interactions play an important role in water ecosystems. In this work, the BS2-15 algicidal strain was isolated from the bottom sediments of Lake Baikal and identified as Bacillus mycoides on the basis of 16S rDNA sequencing, its described ultrastructure, and biochemical properties. B. mycoides BS2-15 was demonstrated to have a strong algicidal effect against a freshwater diatom culture of Ulnaria acus, inhibiting its growth and increasing frustules fragility. By analyzing the impact of bacterial filtrate onto the cells of U. acus, we demonstrated that perhaps an algicidal compound is produced by bacteria independently in the presence of diatoms in a medium. Using methods of TUNEL and confocal microscopy, we revealed that the bacterial algicidal effect on the diatom cells results in DNA fragmentation, nucleus destruction, and neutral lipid accumulation. This phenomenon highlights the complexity of algae–bacteria interactions and their potential role in regulating water ecosystem microbial populations.

Encyonema chebalingense sp. nov., a new freshwater diatom species (Cymbellales, Bacillariophyceae) from Guangdong Province, China

During a survey of freshwater diatoms from Mojiang River, Chebaling Nature Preserve in Shaoguan City, Shixing County, Guangdong Province, China, a new Encyonema species, Encyonema chebalingense sp. nov., was discovered. Based on observations with light and scanning electron microscopy, a detailed morphological description of E. chebalingense is here presented. The main features of E. chebalingense include: conspicuously asymmetrical and dorsiventral, semielliptical to semielliptical–lanceolate valves, with a filiform raphe; dorsal margin clearly arched and ventral margin nearly straight or slightly concave; central area on the ventral side formed by 1–2 shorter central striae; and short tectullae projecting within the striae. The new species was compared with some similar species, all of which show similarities to E. chebalingense but differ in features such as dimensions, internal valve structure, stria density and valve shape. This genus is common and abundant in relatively clean waters, and other new species most likely will be recorded in the future from China.

Taxonomy and phylogeny of Aphanomycopsis bacillariacearum, a holocarpic oomycete parasitoid of the freshwater diatom genus Pinnularia

Investigations into simple holocarpic oomycetes are challenging, because of the obligate biotrophic nature of many lineages and the periodic presence in their hosts. Thus, despite recent efforts, still, the majority of species described remains to be investigated for their phylogenetic relationships. One of these species is Aphanomycopsis bacillariacearum, the type species of the genus Aphanomycopsis. Species of Aphanomycopsis are endobiotic holocarpic parasites of diverse hosts (e.g., diatoms, desmids, dinoflagellates). All species classified in this genus were assigned to it based on the presence of branching hyphae and the formation of two generations of zoospores, of which the first one is not motile. Originally, Aphanomycopsis with its type species, A. bacillariacearum, had been classified in the Saprolegniaceae. However, the genus has undergone multiple taxonomic reassignments (to Ectrogellaceae, Lagenidiaceae, and Leptolegniellaceae) in the past. To settle the taxonomy and investigate the phylogenetic placement of Aphanomycopsis, efforts were undertaken to isolate A. bacillariacearum from its original host, Pinnularia viridis and infer its phylogenetic placement based on nrSSU (18S) sequences. By targeted isolation, the diatom parasitoid was rediscovered from Heiðarvatn lake, Höskuldsstaðir, Iceland. Phylogenetic reconstruction shows that A. bacillariacearum from Pinnularia viridis is embedded within the Saprolegniales, and largely unrelated to both diatom-infecting oomycetes in the Leptomitales (Ectrogella, Lagenisma) and those placed within the early-diverging lineages (Miracula, Diatomophthora) of the Oomycota.

Encyonema oblonga (Bacillariophyta, Cymbellaceae), a new species from Shanxi Province, China

A new species, Encyonema oblonga Liu & Xie, is collected during a survey of the freshwater diatom flora of Manghe River, Shanxi, China. The valves of this new species are oblong with rounded apices and have the features typical of Encyonema, including complex areolae. We compare the new species with the most similar taxa, E. leei, E. leei var. sinensis and E. appalachianum and consider that E. leei var. sinensis is the valid name. The morphology of E. oblonga is documented with light and scanning electron microscopy.