ABSTRACT
Cyanobacterial harmful algal proliferations (cyanoHAPs) are increasingly associated with dog and livestock deaths when benthic mats break free of their substrate and float to the surface. Fatalities have been linked to neurotoxicosis from anatoxins, potent alkaloids produced by certain genera of filamentous cyanobacteria. After numerous reports of dog illnesses and deaths at a popular recreation site on Lady Bird Lake, Austin, Texas in late summer 2019, water and floating mat samples were collected from several sites along the reservoir. Water quality parameters were measured and mat samples were maintained for algal isolation and DNA identification. Samples were also analyzed for cyanobacterial toxins using LC-MS. Dihydroanatoxin-a was detected in mat materials from two of the four sites (0.6-133 ng/g wet weight) while water samples remained toxin-free over the course of the sampling period; no other cyanobacterial toxins were detected. DNA sequencing analysis of cyanobacterial isolates yielded a total of 11 genera, including Geitlerinema, Tyconema, Pseudanabaena, and Phormidium/Microcoleus, taxa known to produce anatoxins, including dihydroanatoxin, among other cyanotoxins. Analyses indicate that low daily upriver dam discharge, higher TP and NO3 concentrations, and day of the year were the main parameters associated with the presence of toxic floating cyanobacterial mats.
Subject(s)
Bacterial Toxins , Cyanobacteria , Tropanes , Humans , Animals , Dogs , Bacterial Toxins/genetics , Bacterial Toxins/toxicity , Bacterial Toxins/analysis , Texas , Rivers/microbiology , Cyanobacteria ToxinsABSTRACT
Exploration of the diversity in the diatom genus Homoeocladia across Micronesia revealed several clusters of undescribed species based on variations around several characters. Using ultrastructural data from scanning electron microscopy, we describe seventeen new species in three of these morphological groups. (1) A group with external thickenings includes eight new species with costae and/or bordered areolae on valve face and/or conopea and/or peri-raphe zone, and one with similar areolae but no ornamentation; this group includes the previously described H. jordanii. (2) Large, linear species, resembling H. asteropeae and H. tarangensis; we describe three new species close to the latter. (3) A sinuous-areolae group includes five new species with areola openings shaped like "~", "s", or "z" on the valve and/or girdle bands, or both, and leads to reconsideration of the diagnosis of Homoeocladia schefterae and the recognition that the globally widespread species in this complex is H. coacervata sp. nov. The three groups are based solely on morphology and no genetic relationships are implied within or between the groups, other than having the characteristics of the recently redefined genus Homoeocladia. However, the high diversity of species in Homoeocladia suggests the genus is a good candidate to test for species flocks in this region and in at least one other comparable location, incorporating DNA sampling through either culturing or metabarcoding.
ABSTRACT
Several automated molecular methods have emerged for distinguishing eukaryote species based on DNA sequence data. However, there are knowledge gaps around which of these single-locus methods is more accurate for the identification of microalgal species, such as the highly diverse and ecologically relevant diatoms. We applied genetic divergence, Automatic Barcode Gap Discovery for primary species delimitation (ABGD), Assemble Species by Automatic Partitioning (ASAP), Statistical Parsimony Network Analysis (SPNA), Generalized Mixed Yule Coalescent (GMYC) and Poisson Tree Processes (PTP) using partial cox1, rbcL, 5.8S + ITS2, ITS1 + 5.8S + ITS2 markers to delineate species and compare to published polyphasic identification data (morphological features, phylogeny and sexual reproductive isolation) to test the resolution of these methods. ASAP, ABGD, SPNA and PTP models resolved species of Eunotia, Seminavis, Nitzschia, Sellaphora and Pseudo-nitzschia corresponding to previous polyphasic identification, including reproductive isolation studies. In most cases, these models identified diatom species in similar ways, regardless of sequence fragment length. GMYC model presented smallest number of results that agreed with previous published identification. Following the recommendations for proper use of each model presented in the present study, these models can be useful tools to identify cryptic or closely related species of diatoms, even when the datasets have relatively few sequences.
Subject(s)
Diatoms , Diatoms/genetics , DNA , DNA Barcoding, Taxonomic , PhylogenyABSTRACT
Phylogenetic relationships among mediophycean diatoms with elliptical valve outline and elevated apices have long been a subject of interest and debate, particularly with respect to their relationship to pennates. However, results remain inconclusive, whether based on vegetative valve morphology, reproduction, or molecular phylogenetic data. Searching for phylogenetically informative features, we re-examined sexual reproduction, auxospore structure and development in the diatom Biddulphia biddulphiana. Several unique or unusual features and processes characterized its sexual reproduction. A unique spermatogenesis occurs with premeiotic separation of an anucleate protoplast containing all chloroplasts and likely other organelles. Additionally, their auxospore walls are some of the most complex documented, retaining earlier deposited layers that obscure layers formed during later stages of development. The oldest layer consists of thick, mostly organic incunabulum, underlain by outer and inner epizonia and finally transverse (TP) and longitudinal (LP) perizonia. The complexity of the fine structure of these layers is unprecedented. The orientation of some TP bands is also unique in mediophytes, with some perpendicular to the auxospore apical axis, parallel to each other, and open with aligned ends, as typically seen in pennates. The TP also contains rings slanting toward the apices, as in some other mediophytes, e.g., eupodiscaceans. However, both eupodiscaceans and biddulphiaceans show perizonial band structure derived from anastomosing radial scales, thus termed "scaly bands". Pinnate TP bands, common among pennate auxospores, were not found. Thus B. biddulphiana auxospore wall structure contains a mixture of characters specific to this clone but also known from mediophytes and araphid pennates. However, these features do not provide unequivocal evidence that this or the other Biddulphia species examined to date are the closest extant relatives of basal araphid pennates.
Subject(s)
Diatoms , Phylogeny , ReproductionABSTRACT
Our understanding of the importance of microbiomes on large aquatic animals-such as whales, sea turtles and manatees-has advanced considerably in recent years. The latest observations indicate that epibiotic diatom communities constitute diverse, polyphyletic, and compositionally stable assemblages that include both putatively obligate epizoic and generalist species. Here, we outline a successful approach to culture putatively obligate epizoic diatoms without their hosts. That some taxa can be cultured independently from their epizoic habitat raises several questions about the nature of the interaction between these animals and their epibionts. This insight allows us to propose further applications and research avenues in this growing area of study. Analyzing the DNA sequences of these cultured strains, we found that several unique diatom taxa have evolved independently to occupy epibiotic habitats. We created a library of reference sequence data for use in metabarcoding surveys of sea turtle and manatee microbiomes that will further facilitate the use of environmental DNA for studying host specificity in epizoic diatoms and the utility of diatoms as indicators of host ecology and health. We encourage the interdisciplinary community working with marine megafauna to consider including diatom sampling and diatom analysis into their routine practices.
Subject(s)
Diatoms , Turtles , Animals , Diatoms/genetics , Ecology , Ecosystem , Turtles/geneticsABSTRACT
Pleurosira laevis is a salt-tolerant diatom distributed around the world. The valve of P. laevis has distinct structures called ocelli, which are sharply defined areas with fine, densely packed pores. Two formae of this diatom, P. laevis f. laevis and P. laevis f. polymorpha, are distinguished from each other by their flat or dome-shaped valve faces and degree of elevation of the ocelli, respectively. In this study, we established 4 strains of P. laevis isolated from freshwaters or coastal areas in Japan and the United States, and tracked the formation of newly formed valves with the fluorescent SDV-specific dye PDMPO in culture under several salinity conditions. The result clearly demonstrated the morphological plasticity of the valves, controlled by environmental salinity. The laevis form and polymorpha form valves were produced at salinities of 2 and 7, respectively. The salinity thresholds dictating the morphological plasticity of the valve were consistent in all 4 strains. A similar morphology to the polymorpha form was reproduced in a freshwater medium with the addition of sorbitol, suggesting that osmotic pressure plays a key role in this morphological plasticity. The highly reproducible and easily manipulated change in morphology makes this diatom an ideal model for lab experiments focusing on the molecular and genetic factors involved with valve morphogenesis.
Subject(s)
Diatoms , Salinity , Fresh Water , Osmotic Pressure , SorbitolABSTRACT
Ardissonea was resurrected from Synedra in 1986 and was included as a genus by Round, Crawford and Mann ("The Diatoms") in its own Family and Order. They commented that there might be several genera involved since the type species of the genus possesses a double-walled structure and other taxa placed in Ardissonea have only a single-walled structure. Two other genera of "big sticks," Toxarium and Climacosphenia, were placed in their own Families and Orders but share many characters with Ardissoneaceae, especially growth from a bifacial annulus. Eighteen taxa (11 new species) from Micronesia were compared with the literature and remnant material from Grunow's Honduras Sargassum sample to address the concepts of Ardissonea and Ardissoneaceae. Phylogenetic and morphological analyses showed three clades within Ardissonea sensu lato: Ardissonea emend. for the double-walled taxa, Synedrosphenia emend. and Ardissoneopsis gen. nov. for single-walled taxa. New species include Ardissoneadensistriata sp. nov.; Synedrospheniabikarensis sp. nov., S.licmophoropsis sp. nov., S.parva sp. nov., and S.recta sp. nov.; Ardissoneopsisfulgicans sp. nov., A.appressata sp. nov., and A.gracilis sp. nov. Transfers include Synedrospheniacrystallina comb. nov. and S.fulgens comb. nov. Synedraundosa, seen for the first time in SEM in Grunow's material, is transferred to Ardissoneopsisundosa comb. nov. Three more genera have similar structure: Toxarium, Climacosphenia and Grunowago gen. nov., erected for Synedrabacillaris and a lanceolate species, G.pacifica sp. nov. Morphological characters of Toxarium in our region support separation of Toxariumhennedyanum and T.undulatum and suggest additional species here and elsewhere. Climacospheniamoniligera was not found but we clarify its characters based on the literature and distinguish C.soulonalis sp. nov. from it. Climacospheniaelongata and a very long, slender C.elegantissima sp. nov., previously identified as C.elongata, were present along with C.scimiter. Morphological and molecular phylogenetics strongly suggested that all these genera belong in one family and we propose to include them in the Ardissoneacae and to reinstate the Order Ardissoneales Round.
ABSTRACT
We provide for the first time the complete plastid and mitochondrial genomes of a monoraphid diatom: Schizostauron trachyderma. The mitogenome is 41,957 bp in size and displays two group II introns in the cox1 gene. The 187,029 bp plastid genome features the typical quadripartite architecture of diatom genomes. It contains a group II intron in the petB gene that overlaps the large single-copy and the inverted repeat region. There is also a group IB4 intron encoding a putative LAGLIDADG homing endonuclease in the rnl gene. The multigene phylogenies conducted provide more evidence of the proximity between S. trachyderma and fistula-bearing species of biraphid diatoms.
Subject(s)
Diatoms/genetics , Genome, Mitochondrial , Genome, Plastid , Diatoms/classification , Diatoms/cytology , Evolution, Molecular , Open Reading Frames/genetics , Phylogeny , Sequence Analysis, DNAABSTRACT
Presented here are new insights into the marine monoraphid diatom genera Schizostauron and Astartiella, based on molecular and morphological data, including descriptions of new species. Although no unambiguous morphological synapomorphies between the two genera are currently recognized, they are closely related by DNA sequence data. Heterovalvate frustules of Schizostauron are characterized by a bifid stauros on the raphe-bearing valve and intricate areolate occlusions on the sternum valve. In Astartiella, the raphe-bearing valve is characterized by a process resembling a fistula by morphology, while the sternum valve presents a particular striation pattern. Observations by light and electron microscopy were made, along with a molecular phylogenetic analysis using a three-gene (SSU, rbcL, and psbC) concatenated dataset. Three new Schizostauron species are described (S. kajotkei, S. rawaii, S. papilliareae), and two new combinations proposed (S. citronella and S. trachyderma) for species that were previously included either in Achnanthes and Cocconeis, respectively. Likewise, six new species of Astartiella (A. almalikii, A. bornmanii, A. chunlianlii, A. marksii, A. persica, and A. wangii) are described. Molecular results exclude Schizostauron and Astartiella from three clades of exclusively monoraphid diatoms, the Achnanthaceae, Cocconeidaceae, and Achnanthidiaceae, instead placing them in the Stauroneidaceae. Morphological features of Schizostauron and Astartiella, such as the stauros, fistula, and coaxial internal proximal raphe endings, are found in other genera in this clade, whereas the only common feature with monoraphid diatoms as whole group is the heterovalvy of frustules.
Subject(s)
Diatoms , Fistula , Diatoms/genetics , Microscopy, Electron , PhylogenyABSTRACT
Microalgal cultures are often maintained in xenic conditions, i.e., with associated bacteria, and many studies indicate that these communities both are complex and have significant impacts on the physiology of the target photoautotroph. Here, we investigated the structure and stability of microbiomes associated with a diverse sampling of diatoms during long-term maintenance in serial batch culture. We found that, counter to our initial expectation, evenness diversity increased with time since cultivation, driven by a decrease in dominance by the most abundant taxa in each culture. We also found that the site from which and time at which a culture was initially collected had a stronger impact on microbiome structure than the diatom species; however, some bacterial taxa were commonly present in most cultures despite having widely geographically separated collection sites. Our results support the conclusion that stochastic initial conditions (i.e., the local microbial community at the collection site) are important for the long-term structure of these microbiomes, but deterministic forces such as negative frequency dependence and natural selection exerted by the diatom are also at work. IMPORTANCE Natural microbial communities are extremely complex, with many more species coexisting in the same place than there are different resources to support them. Understanding the forces that allow this high level of diversity has been a central focus of ecological and evolutionary theory for many decades. Here, we used stock cultures of diatoms, which were maintained for years in continuous growth alongside populations of bacteria, as proxies for natural communities. We show that the bacterial communities remained relatively stable for years, and there is evidence that ecological forces worked to stabilize coexistence instead of favoring competition and exclusion. We also show evidence that, despite some important regional differences in bacterial communities, there was a globally present core microbiome potentially selected for in these diatom cultures. Understanding interactions between bacteria and diatoms is important both for basic ecological science and for practical science, such as industrial biofuel production.
Subject(s)
Bacteria/isolation & purification , Diatoms/microbiology , Microbiota , Bacteria/classification , Bacteria/genetics , Biodiversity , Cell Culture Techniques , Diatoms/growth & development , PhylogenyABSTRACT
The current study focuses on four species from the primarily marine diatom genus Craspedostauros that were observed growing attached to numerous sea turtles and sea turtle-associated barnacles from Croatia and South Africa. Three of the examined taxa, C. danayanus sp. nov., C. legouvelloanus sp. nov., and C. macewanii sp. nov., are described based on morphological and, whenever possible, molecular characteristics. The new taxa exhibit characters not previously observed in other members of the genus, such as the presence of more than two rows of cribrate areolae on the girdle bands, shallow perforated septa, and a complete reduction of the stauros. The fourth species, C. alatus, itself recently described from museum sea turtle specimens, is reported for the first time from loggerhead sea turtles rescued in Europe. A 3-gene phylogenetic analysis including DNA sequence data for three sea turtle-associated Craspedostauros species and other marine and epizoic diatom taxa indicated that Craspedostauros is monophyletic and sister to Achnanthes. This study, being based on a large number of samples and animal specimens analyzed and using different preservation and processing methods, provides new insights into the ecology and biogeography of the genus and sheds light on the level of intimacy and permanency in the host-epibiont interaction within the epizoic Craspedostauros species.
Subject(s)
Diatoms , Turtles , Animals , Croatia , Europe , Phylogeny , South AfricaABSTRACT
The Bacillariaceae is a very species-rich family of raphid diatoms and includes the large and taxonomically difficult genus Nitzschia, whose species are often small-celled and finely structured and have few discrete morphological characters visible in the light microscope. The classification of Nitzschia is still mostly based on one developed in the second half of the 19th century by Grunow, who separated the genus into a series of sections largely on cell shape and symmetry, the position of the raphe, transverse extension of the fibulae, and folding of the valve. We assembled and analysed single-gene and concatenated alignments of nSSU, nLSU, rbcL, psbC and cox1 to test Grunow's and subsequent classifications and to examine selected morphological characters for their potential to help define monophyletic groups. The maximum likelihood trees were equivocal as to monophyly of the family itself but showed good support for each of eight main clades of Bacillariaceae, three of which corresponded more or less to existing genera (Hantzschia, Cylindrotheca and Bacillaria). The other five main clades and some subclades comprised groups of Nitzschia species or assemblies of Nitzschia species with other genera (Pseudo-nitzschia, Fragilariopsis, Neodenticula, Tryblionella, Psammodictyon). Relationships between most of the eight main clades were not resolved robustly but all analyses recovered Nitzschia as non-monophyletic. The Grunowian classification of Nitzschia into sections was not supported, though in some respects (e.g. treatment of sigmoid species) it is better than subsequent reclassifications. Several of the main clades and subclades are cryptic (lacking morphological synapomorphies) and homoplasy is common in both light microscopical and ultrastructural characters (to the extent that organisms initially assigned to the same species sometimes prove to belong to a different main clade). Nevertheless, some characters, including the structure of the raphe canal and girdle, seem to be sufficiently conservative evolutionarily to give a provisional estimate of relationships if molecular data are unavailable. No new formal classifications are proposed but various options are explored and research needs identified.
Subject(s)
Diatoms/classification , Chloroplasts/classification , Chloroplasts/genetics , Diatoms/genetics , Diatoms/physiology , Electron Transport Complex IV/classification , Electron Transport Complex IV/genetics , Likelihood Functions , Microscopy, Electron, Scanning , Phylogeny , RNA, Ribosomal, 18S/classification , RNA, Ribosomal, 18S/genetics , RNA, Ribosomal, 28S/classification , RNA, Ribosomal, 28S/geneticsABSTRACT
Photonics, the manipulation of light at nanoscale, is a key enabling technology with impact in health and energy applications, among others. In most cases photonics still relies on materials and fabrication methods inherited from other disciplines, usually requiring expensive, time-consuming and environmentally-unfriendly processes. Recent experiments demonstrated that advanced photonic materials, as complex as those known as 2.5 dimensional slab photonic crystals, also occur naturally in diatoms. These microscopic algae precipitate silicic acid from water to produce silicon dioxide membranes, relying on intracellular biomineralization mechanisms. Addressing some important aspects for the potential industrial utilization of these structures, we here propose that optical materials produced by the diatoms could serve as cost-effective and environmentally friendly alternatives to cleanroom nanofabrication. We demonstrate that photonic materials grown by the diatom species Coscinodiscus granii can be separated based on its hydrokinetic characteristics. We further show that the photonic membranes present low defect rates of ca. 1/100 unit cells and that variation in pore diameter, as observed between individual membranes, can affect the photonic properties at large, but only marginally at low refractive index contrast. Finally, we list algal culture collections operating worldwide, thus providing a global network for live diatoms and diatom materials. We discuss the feasibility and bottlenecks related to scaled-up growth for direct utilization of photonic materials from diatoms.
Subject(s)
Optics and Photonics , Silicon Dioxide/chemistry , Crystallization , Diatoms/chemistry , Kinetics , Nanostructures/chemistryABSTRACT
Although previous phylogenetic analyses suggested that the araphid diatom family Plagiogrammaceae is monophyletic, there is still not a clear understanding of relationships among the genera, and the taxonomy of several genera--Dimeregramma and Plagiogramma--remains questionable in light of paraphyly for both genera using molecular and morphological data. We have expanded the available DNA for molecular work for dozens of plagiogrammacean clones and analyzed 29 morphological characters from plagiogrammarian taxa and closely related genera, to increase understanding of the evolutionary history and systematics of the family and re-evaluate the current taxonomical classification of plagiogrammacean genera. The addition of more taxa and more data confirm the results from previous molecular phylogenies: most plagiogrammacean genera are monophyletic, except for Dimeregramma and Plagiogramma. Interestingly, the morphological analysis resolves only Talaroneis and Glyphodesmis as monophyletic. Given these results, we feel there is limited support for retaining Dimeregramma and Plagiogramma as distinct genera, and formally propose amending Plagiogramma and transferring six Dimeregramma species. As the Plagiogrammaceae is also one of the first-diverging clades of pennate diatoms, we also used these molecular data to estimate the age of the family, based on multiple calibration points derived from fossil taxa within or close to the Plagiogrammaceae. The results indicated that the Plagiogrammaceae evolved more than 114 million year ago and its diversification appears to correspond to a time of climate cooling. Additionally, we described a new monotypic genus (Coccinelloidea) with one new species C. gracilis, and five new species within established genera, e.g. Plagiogramma marginalis, Plagiogramma harenae, Plagiogramma porcipellis, Neofragilaria montgomeryii and Psammogramma anacarae.
Subject(s)
Diatoms/classification , Diatoms/genetics , Phylogeny , Animals , Bayes Theorem , Climate Change , Diatoms/cytology , Diatoms/ultrastructure , Fossils , Sequence Analysis, DNAABSTRACT
Detailed morphological documentation is provided for established Proschkinia taxa, including the generitype, P. bulnheimii, and P. complanata, P. complanatula, P. complanatoides and P. hyalosirella, and six new species. All established taxa are characterized from original material from historical collections. The new species described in this paper (P. luticola, P. staurospeciosa, P. impar, P. modesta, P. fistulispectabilis, and P. rosowskii) were isolated from the Western Pacific (Yellow Sea coast of Korea) and the Atlantic (Scottish and Texas coasts). Thorough documentation of the frustule, valve and protoplast architecture revealed the combination of characters diagnostic of the genus Proschkinia: a single-lobed chloroplast; a broad girdle composed of U-shaped, perforated bands; the position of the conopeate raphe-sternum relative to the external and internal valve surface; and the presence of an occluded process through the valve, termed the "fistula". Seven strains of Proschkinia were grown in culture and five of these were sequenced for nuclear ribosomal SSU and plastid-encoded rbcL. Phylogenetic analysis recovered a clade of Proschkinia with Fistulifera, another fistula-bearing diatom genus, and together these were sister to a clade formed of the Stauroneidaceae; in turn, all of these were sister to a clade composed of Parlibellus and two monoraphid genera Astartiella and Schizostauron. Despite morphological similarities between Proschkinia and the Naviculaceae, these two taxa are distant in our analysis. We document the variation in the morphology of Proschkinia, including significant variability in the fistula, suggesting that fistula ultrastructure might be one of the key features for species identification within the genus.
Subject(s)
Diatoms , Phylogeny , Republic of KoreaABSTRACT
New molecular and morphological insights are presented on Campylosira africana and two new species, Extubocellulus cupola sp. nov. and Plagiogrammopsis castigatus sp. nov. Species descriptions were based on LM/SEM micrographs and a data set with concatenated sequences of SSU, rbcL and psbC loci constructed from 56 cymatosiroid strains isolated from global geographic locations. Extubocellulus cupola is distinguished by a mesh-like marginal ridge and dome-shaped areolation, and P. castigatus, by a prominent marginal extension at the valve center. Campylosira africana, a species from South Africa described by Professor Malcolm Giffen, has never been documented through LM or SEM, which led some authors to place it in synonymy under Campylosira cymbelliformis. We confirm that C. africana is a distinct species and provide microphotographic documentation and DNA sequences. We present morphological evidence for the well-known cymatosiroid species Extubocellulus spinifer possessing complete pili, and we emend the generic description of Extubocellulus.
Subject(s)
Diatoms , Phylogeny , South AfricaABSTRACT
The diatom genus Orthoseira Thwaites (Bacillariophyta) is a ubiquitous taxon in aerial diatom assemblages, with species found globally. Cylindrical cell shape and radial symmetry of this genus has led to its historical placement in the Coscinodiscophyceae ('radial centric' diatoms), but its systematic relationships have remained uncertain. We present a five-gene phylogeny, based on nuclear (nSSU rDNA) and chloroplast (rbcL, psbC, psbA, and psaB) genes to determine the phylogenetic placement of Orthoseira among the diatoms. The concatenated multi-gene phylogenies and nSSU-only gene tree demonstrate that Orthoseira is deeply embedded within a clade of the Mediophyceae ('multipolar centric' diatoms). Throughout all phylogenetic analyses, Orthoseira was shown to be sister to the genera Terpsinoë and Hydrosera. Through comparison of topologies reflecting competing hypotheses about the placement of Orthoseira, it was determined that the hypothesis that Orthoseira, represented here by O. dendroteres and O. roeseana, is a member of the Melosirales should be rejected. Therefore, lack of morphological similarity between Hydrosera, Orthoseira, and Terpsinoë is hypothesized to be the result of changes in habitat preferences that lead to an ancient divergence event between the Orthoseirales and the Hydrosera, Terpsinoë clade.
Subject(s)
Diatoms/classification , Diatoms/genetics , Phylogeny , Chloroplast Proteins/genetics , Cluster Analysis , DNA, Algal/chemistry , DNA, Algal/genetics , DNA, Chloroplast/chemistry , DNA, Chloroplast/genetics , DNA, Ribosomal/chemistry , DNA, Ribosomal/genetics , RNA, Ribosomal, 18S/genetics , Sequence Analysis, DNAABSTRACT
Until now only one group of diatoms, the Bacillariaceae, was known to contain heterotrophic representatives. We show that a second group, represented by species in the genus Tursiocola, has undergone evolutionary loss of photosynthesis within the Bacillariophyta. Heterotrophy was evidenced by the presence of only apochlorotic cells in live and motile specimens. Three species of Tursiocola (T. bondei sp. nov., T. alata sp. nov., and T. gracilis sp. nov.), of which at least two are apochlorotic, are described as new to science from the skin of Florida manatees. T. ziemanii and T. varicopulifera were also observed to be apochlorotic. A new morphological feature termed a "fastigium" was observed on some Tursiocola spp. and is described as an extension of the mantle margin at the valve apex that overhangs the apex and extends towards the valve face. The presence of greatly elevated marginal ridges on the valve face of T. alata sp. nov. is a newly observed morphological character within the genus. Phylogenetic analyses using ribosomal RNA sequences indicate that Tursiocola is monophyletic, though morphological character analysis suggests paraphyly as species of the closely related Epiphalaina genus are embedded within a larger Tursiocola clade.
Subject(s)
Diatoms/isolation & purification , Trichechus manatus/microbiology , Animals , Diatoms/classification , Diatoms/ultrastructure , Skin/microbiologyABSTRACT
The diatom Phaeodactylum tricornutum has been used as a model for cell biologists and ecologists for over a century. We have incorporated several new raphid pennates into a three gene phylogenetic dataset (SSU, rbcL, psbC), and recover Gomphonemopsis sp. as sister to P. tricornutum with 100% BS support. This is the first time a close relative has been identified for P. tricornutum with robust statistical support. We test and reject a succession of hypotheses for other relatives. Our molecular data are statistically significantly incongruent with placement of either or both species among the Cymbellales, an order of diatoms with which both have been associated. We believe that further resolution of the phylogenetic position of P. tricornutum will rely more on increased taxon sampling than increased genetic sampling. Gomphonemopsis is a benthic diatom, and its phylogenetic relationship with P. tricornutum is congruent with the hypothesis that P. tricornutum is a benthic diatom with specific adaptations that lead to active recruitment into the plankton. We hypothesize that other benthic diatoms are likely to have similar adaptations and are not merely passively recruited into the plankton.
Subject(s)
Databases, Nucleic Acid , Diatoms/classification , Diatoms/genetics , Phylogeny , Phytoplankton/genetics , Diatoms/ultrastructure , Phytoplankton/ultrastructureABSTRACT
Several lineages of raphe-bearing diatoms possess a "stauros," which is a transverse, usually thickened area free of pores across the center of the valve. It has been suggested that this structure has evolved several times across the raphid diatoms, but we have noticed similarities beyond the stauros between two marine genera-Craspedostauros and Staurotropis-in the structure of their pore occlusions. We have isolated, cultured and extracted DNA from several strains of both genera to infer the phylogenetic relationship between these taxa, as well as test the suggested relationship of Craspedostauros to Achnanthes and Mastogloia based on plastid morphology. DNA sequence data (nuclear-encoded rRNA SSU, plastid-encoded rbcL and psbC) suggest that, except for Mastogloia, these genera are closely-related, though not sister taxa. The DNA phylogeny also suggests that the Mastogloiales are not monophyletic, with clades containing Achnanthes and Craspedostauros sister to clades containing taxa in the Bacillariales. Using evidence from molecular and morphological data, we describe the following new taxa: Craspedostauros alyoubii and C. paradoxa from the Red Sea and Guam, respectively; Staurotropis khiyamii and S. americana from the Red Sea and the Gulf of Mexico, respectively; and Dreuhlago cuneata n. gen., n. sp. from Guam.