Background This study presents an alternative method in diatom genomics using two raphid diatoms-Campylodiscus clypeus and Plagiotropis lepidoptera-whose organellar genome characteristics have remained unexplored due to cultivation constraints. Only a small fraction of the estimated 200,000 diatom species has been cultured in the laboratory. This research showcases the use of minimal-cell genomics as a viable alternative for studying diatoms and other eukaryotic microorganisms that do not respond well to traditional laboratory culture methods. Methods Initial attempts to culture C. clypeus and P. lepidoptera were unsuccessful, hindering the acquisition of genomic data. To overcome these challenges, we employed minimal-cell whole genome amplification (mcWGA) techniques for two uncultured species, followed by metagenomic sequencing and assembly. This enabled direct genomic recovery from minimally isolated and pooled cells, eliminating the need for cultivation. Results Using mcWGA approach, we successfully obtained the complete chloroplasts and mitochondrial genomes of C. clypeus and P. lepidoptera using only 8-12 viable cells isolated from fresh environmental samples. The plastome size of C. clypeus was 143,367 bp and mitogenome size was 46,274 bp, while P. lepidoptera has plastome and mitogenome sizes of 116,161 bp and 49,356 bp, respectively. The data generated provides a valuable resource for further research, highlighting the importance of culture-independent techniques in microbial genomics.

The plastisphere can have a significant impact on the buoyancy, toxicity, and functionality of microplastics (MPs). Little is known about plastisphere structure, especially in salt-impacted lakes, despite the growing focus on the salinization of lakes. Virgin polypropylene and polyethylene terephthalate MPs were incubated for two weeks in flow-through containers in the epilimnion (low phosphorus, low salinity, high light) or hypolimnion (high P, high salinity, and low light) of a salt-impacted lake and then incubated in the lab in either their original water or water from the alternate depth to determine plastisphere response should the lake fully turn over. Environmental factors, including phosphorus concentration, light level, salinity level, and temperature, rather than polymer type, influenced community composition. Bacterial communities on MPs in the epilimnion exhibited higher diversity compared to those in the hypolimnion. Algal communities on MPs showed a similar trend, with greater diversity in the epilimnion. Overall, initial community composition had a stronger influence on community structure (priority effect) than the environment in which the plastisphere was grown. For those plastisphere communities capable of responding to species-specific desirable environmental conditions, lake mixing that results in increases in phosphorus and salinity from the hypolimnion to the epilimnion will increase the abundance of algae on MPs in the photic zone.

Light and scanning electron microscopical observations on the type population of E. rupestris W. Smith are presented. Light microscopy shows valves that are asymmetrical to the apical axis, a canal raphe positioned along the dorsal margin, and costate fibulae that extend across most of the valve. In girdle view, 'capitate costae' are evident. Scanning electron microscopy shows the valve to have a raphe with a distinct keel bordered by wide openings. Striae are very fine (ca 50 in 10 & micro;m) and are shown to lack volae externally and internally. These observations indicate that this species is morphologically more similar to species in the genus Rhopalodia O. M & uuml;ller than to the genus Epithemia Br & eacute;bisson ex K & uuml;tzing. The lack of volae in R. rupestris (W. Smith) Krammer is unique among rhopalodioid diatoms. Variations in the areolar occlusions across the Rhopalodiaceae are discussed.

We describe here the first SEM observations on the auxospores of two species of Epithemia, E. reicheltii and E. lacus-douglasi, from Douglas Lake, Michigan, USA. Both species were found in abundance with auxospores in October of 2024. The auxospores of both species were semicircular in shape, initially covered with an organic matrix, which split as incunabular caps. Internal to this matrix were transverse incunabular rows of quadrangular, imbricating scales overlapping towards the valve ends, with the longer abaxial edges fimbriate and the other edges straight. And, internal to the scales, was a single, siliceous covering - the primary longitudinal perizonial band - which had transversely-oriented fissures. Internal to the primary band were three (or four) dorsally positioned secondary longitudinal perizonial bands. The complex coverings of the auxospores of these Epithemia species are unique amongst the diatoms.

The diatom Order Rhopalodiales comprises canal-bearing taxa with nitrogen-fixing cyanobacterial endosymbionts, but its genus-level systematics remains unresolved due to the paraphyly of Rhopalodia. We characterized two Northern California strains of Rhopalodia californica sp. nov. using valve morphology, complete organellar and spheroid body (SB) genomes, and multi-gene phylogenetics. Chloroplast (133,208-133,222 bp), mitochondrial (35,955-36,097 bp), and SB (3.064 Mbp) genomes were all structurally conserved and identical in gene content. Phylogenetic analysis of nuclear (18S, 28S), chloroplast (rbcL, psbC), and mitochondrial (cob) genes placed R. californica with Epithemia sp. GazosCreekCA in a strongly supported ‘californica’ clade, distinct from other clades of Epithemia and Rhopalodia species. Genome-wide nucleotide similarity was high within the clade (>97.6%) but markedly lower (<95%) when compared to other Rhopalodiales, a pattern that aligns with distinctions observed in the SB, chloroplast, and mitochondrial datasets. Evolutionary rate was fastest for the mitochondrion, followed by the SB and then the chloroplast. Synteny analysis revealed that gene order and structure were highly conserved between the two R. californica strains and remained well conserved even in comparison with Epithemia sp. GazosCreekCA. These results demonstrate that the ‘californica’ group is a genetically and morphologically cohesive lineage within Rhopalodia sensu lato, supporting its recognition in future taxonomic studies.

We compared type material of Epithemia argentina described by Brun, as well as other collections with type material of two purported synonymous taxa, E. debyi and E. multicostata, described by Pantocsek, based on light and scanning electron microscopy. All three taxa were transferred to the genus Rhopalodia by M & uuml;ller. R. argentina has robust costate fibulae, a large tubular canal raphe, striae in single to double rows of areolae, and volate occlusions with a single point of attachment and positioned internally. R. argentina is distinguished from R. debyi and R. multicostata by costate fibula density and shape of the valves. The latter two species are considered heterotypic synonyms of each other. The distributions of these species over time and space are discussed.

A new species of Rhopalodia is described from fossil sediments from Mexico based on light and scanning electron microscope observations. The new Rhopalodia species has valve features that place it within the R. gibba group of the genus, including a raphe in a short keel on the dorsal side of the valve and girdle bands that have small extensions that clasp over the costate fibulae. The species is distinguished from R. gibba and other allied species by valve shape. This is the first extinct fossil species of Rhopalodia described outside of Europe.

We present light and scanning electron microscopical observations of two species from North America that resemble the original concept of Epithemia reicheltii Fricke. We review the history of that taxon, its similarity with Epithemia cistula, and present data to suggest the two North American species considered herein, which are sympatric in their distribution in Douglas Lake, Michigan, are different from one another. One of those species is described as new, Epithemia lacusdouglasi sp. nov. and we discuss the possibility of sympatric speciation in this locality. Epithemia reicheltii has also been reported from South Africa, and we review that report with original material. Based on our observations of the size diminution series of the taxon, we propose E. schoemanii sp. nov. and discuss its systematic position based on its valve morphology.

We report the complete chloroplast genomes of two closely related taxa, Nitzschia nienhuisii and Epithemia catenata. The plastids share 96.85% nucleotide similarity and exhibit similar genomic structure. The N. nienhuisii plastome is 128,415 bp with 129 protein-coding genes, whereas E. catenata plastome is 140,525 bp with 130 protein-coding genes, including a duplicated psaJ in the inverted repeat. Both genomes encode 30 tRNAs, one tmRNA, six rRNAs, and two pseudogenes (tyrC and ycf42). The larger E. catenata genome likely reflects 12 unique ORFs. Maximum likelihood phylogenetic analysis supports a close relationship between these taxa.

Starry stonewort (Nitellopsis obtusa (Desvaux) J. Groves) is an invasive freshwater green macroalga in North America that is widespread in the Laurentian Great Lakes Basin and forms thick monotypic meadows in littoral zones. However, little is known about its development throughout the growing season. The objectives of this study were to document the growth and development of N. obtusa in two Lake Michigan drowned river mouth lakes and relate this growth to temperature, nutrients, and other submerged aquatic vegetation. These lakes are significant because they serve as direct connections from the landscape to the Great Lakes system and offer pathways for further range expansion of N. obtusa. Snorkel surveys were conducted in 2020 (biomass) and 2021 (reproductive structure development) at four sites that differed in management and use, three in Pentwater Lake and one in Muskegon Lake. Low biomass of N. obtusa was recorded in mid-July, with exponential growth through mid-August, and stabilization through late summer into October. Biomass was highest at the marina site, and the lowest relative biomass was recorded at the reference site. Water parameters did not explain the growth of N. obtusa well, but were consistent with prior studies. Male reproductive structures (antheridia) developed later than in the other study of N. obtusa in its native range, and females (oogonia) were not observed. Our study suggests N. obtusa growth patterns can differ among lakes and at sites within lakes; marinas should be targeted for management efforts to limit the spread of N. obtusa within and among lakes.

The phylogenetic placement of the diatom genera Denticula and Grunowia has remained unresolved for almost over 200 years, with Denticula having been assigned to the disparate families Fragilariaceae, Bacillariaceae, and Epithemiaceae. Recent molecular investigations have placed Denticula within Bacillariaceae; however, these studies included sequence data from only a single taxon, D. kuetzingii, and did not account for the morphological diversity within the genus. To date, no sequence data exists for the genus Grunowia. In this study, we generated sequence data (SSU, rbcL, psbC) for four Denticula species, including the generitype Denticula tenuis, as well as the type species of Grunowia, G. sinuata, to assess their evolutionary relationships. Maximum-likelihood inference reveals that Denticula is not monophyletic, with the four Denticula species distributed across three distinct clades. Denticula tenuis formed a clade with G. sinuata, distinct from Denticula valida and D. elegans, which grouped together, and from D. kuetzingii, which aligned within a broader clade that includes Nitzschia amphibia and N. inconspicua. These phylogenetic groupings demonstrate that historically diagnostic features for Denticula such as transverse fibulae and scalloped valvocopulae are homoplastic within the Bacillariaceae.

We conducted a preliminary survey of the valve morphology and ultrastructure of 14 different taxa of the diatom genus Epithemia Br & eacute;bisson ex K & uuml;tzing. We documented the structure of the areolae, structure and course of the raphe system, girdle bands with and without septa, and the variation in size and outline of the valves via size diminution across populations from North America, South America and Europe. Based on these preliminary observations, and a comprehensive review of the literature, we classified the genus into five groups, distinguished from one another on the course of the raphe, areolar structure and organization of the frustule. We also provide a review of the genus in terms of nomenclature. This study has been developed to begin comprehensive revisionary studies of the genus.

As part of revisionary studies of the diatom order Rhopalodiales, in this work, we are initiating a review of the species described by Josef Pantocsek, including the typification of his species. Pantocsek presented 5 new genera and over 280 species of diatoms, 2 of the genus Epithemia, from a locality listed as & Eacute;lesd, now part of Romania. We present the first light and scanning electron micrographs of Epithemia bihariensis Pantocsek and designate a lectotype for this species. By virtue of its highly biarcuate raphe system that almost reaches the dorsal margin at the centre of the valve, Epithemia bihariensis is assigned to the E. sorex group. Its ecology, as a marine species, and some ultrastructural features, such as segment-like frustules and the raphe contained in a narrow keel, suggest the retention of some ancestral features in the Rhopalodiales. A second species presented by Pantocsek, E. costata, is shown to be a superfluous name, as is the name E. pantocsekites Van Landingham. The Miocene epoch, which is the earliest period for which we currently have verified specimens of the Rhopalodiales, was apparently a time of morphological diversification of this taxon.

We describe species of Rhopalodiales found in samples from Swan Lake, Oregon, deposited in the Tempère and Peragallo Collection in the Museum National d'Histoire Naturelle (Paris) and the Academy of Natural Sciences (Philadelphia). A total of eight different taxa have been recognized, and these are detailed with light and, in some cases, scanning electron microscopy. Six of the species are of the genus Epithemia sensu stricto. Within this genus, we describe one species new to science and make two new combinations. Species found in the Swan Lake material belong to the Turgida (one species), Argus (one species), Sorex (two species), and Adnata (two species) groups of Epithemia. Variation is described relative to the course and position of the raphe branches, the structure and organization of the areolae, and the central area. Two species of Rhopalodia sensu stricto are reported, including one newly described species. A checklist of the Epithemia and Rhopalodia species reported from the USA is also presented.

Despite their ecological significance and unique endosymbiotic capabilities, diatoms in the genus Rhopalodia remain poorly represented in genomic databases, particularly with respect to the availability of complete genomes from multiple organellar compartments. This study addresses that gap by presenting, for the first time, the complete chloroplast (133,086 bp), mitochondrial (36,786 bp), and spheroid body (3,024,495 bp) genomes of Rhopalodia sterrenburgii, a nitrogen-fixing diatom with a cyanobacterial endosymbiont. Phylogenetic reconstruction based on five genes from different cellular compartments (18S, 28S, rbcL, psbC, cob) placed R. sterrenburgii as a basal lineage relative to R. gibba (Rhopalodia sensu lato) and the Epithemia sensu stricto species E. argus, E. turgida, and E. sorex, providing new insights into evolutionary relationships within Rhopalodiales. Additionally, pathway analysis revealed the progressive loss of genes involved in vitamin B12 and chlorophyll a biosynthesis in more recently diverged Rhopalodia and Epithemia lineages. Our findings support a pattern of genome reduction in symbiotic diazotrophic diatoms, potentially driven by coevolution with their endosymbionts, and an increasing reliance on integrated metabolic functions between the host and the endosymbiont.

Community dynamics within microbial mat assemblages are complex, likely involving intricate metabolic linkages. Interactions between microbes shape these communities, particularly in extreme habitats such as those found in the Middle Island Sinkhole (MIS), Lake Huron. Herein, euxinic waters resemble early-Earth ocean conditions, and diverse microbial groups form benthic mats. The goal of this study was to examine interspecific relationships among culturable cyanobacteria (two strains of Anagnostidinema) and diatoms (Craticula cuspidata and Nitzschia palea) isolated from MIS mats in a co-culture factorial experiment. Although most crosses showed limited interactions, a significant increase in abundance of one Anagnostidinema strain was found when grown with Craticula cuspidata compared to other taxa (P < 0.0001). Nitzschia palea growth was significantly reduced when grown with either strain of cyanobacteria (P = 0.0040). Addition of both cells and filtrates from C. cuspidata cultures caused increases in Anagnostidinema percent cover. Unique metabolic capabilities of C. cuspidata may benefit some cyanobacteria, and cyanobacteria may inhibit N. palea growth via interference competition. These interactions may be masked in the mat community in situ by environmental factors or other interspecific interactions, or allow species to survive in low abundance in an otherwise unfavorable habitat.

We detail the diatom taxa described by F.T. Kutzing across three of his publications that have been referred to the diatom genera Epithemia and Rhopalodia. Taxa considered include Frustulia adnata, F. picta, E. alpestris, E. musculus, E. porcellus, E. proboscidea, E. sorex, E. ventricosa, E. vertagus, E. ventricosa beta. gregaria and E. reticulata. For these 12 taxa, this represents the first time Kutzing's specimens have been illustrated with light microscopy. Most of the material consulted here is from the Natural History Museum, London, though we also reviewed material from the Academy of Natural Sciences for E. adnata. We present light microscope images of the Kutzing taxa and complement these observations with images of the type slides, material packets and both herbarium (unpublished) and published drawings. In some cases, modern concepts of K & uuml;tzing species are supported, but in others it is likely that species concepts will be changed by the specimens in the type material. Lectotypes are designated for Epithemia adnata and Epithemia reticulata.

Abstract High‐sulfur, low‐oxygen environments formed by underwater sinkholes and springs create unique habitats populated by microbial mat communities. To explore the diversity and biogeography of these mats, samples were collected from three sites in Alpena, Michigan, one site in Monroe, Michigan, and one site in Palm Coast, Florida. Our study investigated previously undescribed eukaryotic diversity in these habitats and further explored their bacterial communities. Mat samples and water parameters were collected from sulfur spring sites during the spring, summer, and fall of 2022. Cyanobacteria and diatoms were cultured from mat subsamples to create a culture‐based DNA reference library. Remaining mat samples were used for metabarcoding of the 16S and rbcL regions to explore bacterial and diatom diversity, respectively. Analyses of water chemistry, alpha diversity, and beta diversity articulated a range of high‐sulfur, low‐oxygen habitats, each with distinct microbial communities. Conductivity, pH, dissolved oxygen, temperature, sulfate, and chloride had significant influences on community composition but did not describe the differences between communities well. Chloride concentration had the strongest correlation with microbial community structure. Mantel tests revealed that biogeography contributed to differences between communities as well. Our results provide novel information on microbial mat composition and present evidence that both local conditions and biogeography influence these unique communities.

Denticula costata Hustedt was originally described from fossil material from Sumatra and later assigned to the genus Tetralunata. Although Tetralunata was thought to be endemic to Indonesia, D. costata has been reported from wetwalls from South Africa. This disparity in locality prompted us to investigate the D. costata in South Africa further. D. costata (now T. costata) specimens and the species reported from South Africa were different in size, shape, and structure of the raphe system. These differences, as well as comparisons to other Denticula species, allowed us to determine that the South African specimens have not been described previously. Valve ultrastructure, including the canal raphe, areolae with volate occlusions, and presence/structure of the septa suggest this new species belongs to the genus Tetralunata. This is the first report of Tetralunata from outside of Indonesia. Herein, we describe Tetraluanata schoemanii sp. nov. and its systematic placement close to, but separate from, Epithemia. This first report of Tetralunata from outside of Indonesia, increases our understanding of the genus range and displays a unique biogeographical pattern that warrants further investigation in the future.

We contest the recently reported findings that suggest the presence of female gametangia in the North American range of the invasive macroalga Nitellopsis obtusa (Harrow-Lyle, T.J., Ginn, B.K., Kirkwood, A.E., and Melles, S.J. 2023. First report of female gametangia in the invasive macroalga starry stonewort ( Nitellopsis obtusa) in North America. Botany, 101: 61–64. doi:10.1139/cjb-2022-0096). The claims do not clearly show identifying morphology of N. obtusa female gametangia, are inconsistent with known characeaen developmental biology, and do not provide the evidence commensurate with such a claim. More convincing observational data are required. To date, only male thalli of N. obtusa have been confirmed either with herbarium vouchers or clear images. The appearance of female gametangia would have significant implications for the invasion biology of N. obtusa as well as approaches to managing its spread.