Nitzschia palea is a common freshwater diatom used as a bioindicator because of its tolerance of polluted waterways. There is also evidence it may be the tertiary endosymbiont within the “dinotom” ...dinoflagellate Durinskia baltica. A putative strain of N. palea was collected from a pond on the University of Virginia's College at Wise campus and cultured. For initial identification, three markers were sequenced—nuclear 18S rDNA, the chloroplast 23S rDNA, and rbcL. Morphological characteristics were determined using light and scanning electron microscopy; based on these observations the cells were identified as N. palea and named strain “Wise.” DNA from N. palea was deep sequenced and the chloroplast and mitochondrial genomes assembled. Single gene phylogenies grouped N. palea—Wise within a clearly defined N. palea clade and showed it was most closely related to the strain “SpainA3.” The chloroplast genome of N. palea is 119,447 bp with a quadripartite structure, 135 protein‐coding, 28 tRNA, and 3 rRNA genes. The mitochondrial genome is 37,754 bp with a single repeat region as found in other diatom chondriomes, 37 protein‐coding, 23 tRNA, and 2 rRNA genes. The chloroplast genomes of N. palea and D. baltica have identical gene content, synteny, and a 92.7% pair‐wise sequence similarity with most differences occurring in intergenic regions. The N. palea mitochondrial genome and D. baltica's endosymbiont mitochondrial genome also have identical gene content and order with a sequence similarity of 90.7%. Genome‐based phylogenies demonstrated that D. baltica is more similar to N. palea than any other diatom sequence currently available. These data provide the genome sequences of two organelles for a widespread diatom and show they are very similar to those of Durinskia baltica's endosymbiont.
Gomphonema parvulum is a cosmopolitan freshwater diatom that is used as an indicator in water quality biomonitoring. In this study, we report the culturing of two geographically separated isolates ...from southeastern North America, their morphology, and the sequencing and assembly of their mitochondrial and chloroplast genomes. Morphologically, both strains fit G. parvulum sensu lato, but the frustules from a protected habitat in South Carolina were smaller than those cited in the historic data of this species from the same location as well as a second culture from Virginia. Phylogenetic analyses using the rbcL gene placed both within a clade with G. parvulum. Genetic markers, including full chloroplast and mitochondrial genomes and the nuclear small subunit rRNA gene region were assembled from each isolate. The organellar genomes of the two strains varied slightly in size due to small differences in intergenic regions with chloroplast genomes of 121,035 bp and 121,482 bp and mitochondrial genomes of 34,639 bp and 34,654 bp. The intraspecific pairwise identities of the chloroplast and mitochondrial genomes of these two isolates were 97.9% and 95.4%, respectively. Multigene phylogenetic analysis demonstrated a close relationship between G. parvulum, Gomphoneis minuta, and Didymosphenia geminata.
While conducting a systematic investigation of phytoplankton assemblages in the northeastern Gulf of Mexico (GOM) in the aftermath of the Deepwater Horizon blowout we took the opportunity to collect ...sediment samples from off the coast of Pensacola Bay, Florida. These samples contained sufficient numbers of a monoraphid diatom initially identified as Achnanthes controversa Hustedt (Navicula marginulata Cleve) to examine its fine structure in detail. The results of these investigations clearly show that this taxon could not be accommodated in Achnanthes as currently understood, or in any currently described genus in the Achnanthidiaceae. We, therefore, propose a new genus, Vallithidium, with Vallithidium marginulatum (Cleve), J.A. Nienow & A.K.S.K Prasad as the generitype. Our investigations also show that the taxon Hustedt illustrated from Campeche Bay is not the same as the taxon described from the northeastern Gulf. We therefore describe it as a separate species in the new genus, Vallithidium campechianum sp. nov.
During a systematic investigation of phytoplankton assemblages in the northeastern Gulf of Mexico (GOM) in the aftermath of the Deepwater Horizon blowout we encountered a population of diatoms ...morphologically similar to Nitzschia ossiformis (Taylor) Simonsen located about 75 km offshore and concentrated at a depth of 60—120 meters. The density of individuals in the population was sufficient to make detailed observations using light and electron microscopy. Our specimens were frequently united into short ribbon—like colonies. This, plus features of the fine structure of valve (biseriate striae, raphe canal without pores and flush with the valve surface) suggest the GOM population is more closely related to Fragilariopsis than to Nitzschia sensu stricto. The presence of a unique feature, described here for the first time, a transverse sulcus in the exterior surface of one of the poles, coupled with the characteristic shape of the valve, suggest our taxon cannot be accommodated in Fragilariopsis, or any other genus hitherto known within the family Bacillariaceae. We, therefore, propose a new genus, Sulcatonitzschia for this diatom and any other nitzschioid diatom with a transverse sulcus, with a new species, Sulcatonitzschia novossiformis as the generitype. Published descriptions suggest that some populations identified as Nitzschia ossiformis may be conspecific with S. novossiformis, but the type of N. ossiformis as delineated by Taylor is not. Examination of the fine structure of the valves is necessary to resolve these relationships.
Our examination of net phytoplankton collected from coastal localities in Odisha on the east coast of India, including Chilka Lake, Chandrabhaga Beach and Puri, in December 2015, revealed the ...overwhelming dominance of
Thalassiosira mala
, a gelatinous colony-forming, potentially harmful, marine planktonic diatom. The large numbers of cells allowed us to observe details of the cingulum not previously reported. The epicingulum is composed of four open bands including an areolated valvocopula, an areolated copula and two non-areolated pleurae. The immature hypocingulum includes at least two bands. Openings of alternate bands are arranged in a dextral pattern. Based on previous reports from the west coast and our current findings,
Thalassiosira mala
appears to be a common, widely distributed primary producer in Indian coastal waters. The presence of morphologically similar species, especially those <20 μm in diameter, underscores the importance of reliable species-level taxonomy using appropriate techniques for meaningful ecological and biogeographic considerations and for monitoring potentially harmful algae in India’s economically important coastal waters. Published reports suggest that
Thalassiosira mala
is widely distributed in temperate and tropical waters, present in 26 of 232 ecoregions and 18 of 62 provinces recognized in a recent classification of coastal marine ecoregions.
A population of the rarely reported diatom Nanoneis longta was observed over a period of more than two years in the northeastern Gulf of Mexico. This permitted a detailed examination of the fine ...structure of the valve in scanning and transmission electron microscopy. The population matched the basic features of the original description of the species, but displayed a greater size range. Our use of SEM revealed the presence of a novel structure, the porticus marginalis, along the perimeter of the valve. The species was most abundant below the thermocline, at depths between 25 and 125 m, and from summer to early fall. An emended definition of the species to accommodate the observed size range and the new feature is included.
Prasad A.K.S.K and Nienow J.A. 2011. Livingstonia (Thalassiosirales, Bacillariophyta), a new genus of fultoportulate centric diatoms from an Atlantic coastal plain river in Florida, southeastern ...United States. Phycologia 50: 264-280. DOI: 10.2216/09-89.1
A morphological and taxonomic account of Livingstonia palatkaensis, a new genus and species of centric diatoms belonging to the order Thalassiosirales Glezer & Makarova, is provided. Descriptions are based on material collected from the St. Johns River, a major, highly colored blackwater river in the Atlantic coastal plain in the southeastern United States. Scanning electron microscopic observations clearly show that although the valve structure in Livingstonia shares broad similarities with the genera Thalassiosira and Skeletonema, the types of the two fultoportulate families Thalassiosiraceae and Skeletonemataceae, respectively, it is sufficiently dissimilar to warrant the description of a new genus. Livingstonia is characterized by the presence of compound marginal processes, each formed from the external extension of a fultoportula and a semielliptical hyaline hood or cover. The areolae have semicontinuous internal cribra. A single rimoportula is present near the valve center. No fultoportulae are found at or near the center of the valve face. Furthermore, Livingstonia lacks connecting threads of marginal fultoportulae and an external extension of the rimoportula on the valve face, a combination of features that is unusual in the genus Skeletonema. Livingstonia is also distinguished from two recently described freshwater genera in the Thalassiosiraceae from the southeastern United States, Cyclotubicoalitus and Spicaticribra, in having a rimoportula away from the margin but close to the center of the valve and in other key characteristics. A note on another freshwater, co-occurring, more frequent and widespread, chain-forming, closely related diatom, Skeletonema potamas, is also included. Livingstonia is tentatively placed in the family Thalassiosiraceae.
A.K.S.K. Prasad and J.A. Nienow. 2006. The centric diatom genus Cyclotella, (Stephanodiscaceae: Bacillariophyta) from Florida Bay, USA, with special reference to Cyclotella choctawhatcheeana and ...Cyclotella desikacharyi, a new marine species related to the Cyclotella striata complex. Phycologia 45: 127-140. DOI: 10.2216/05-13.1
A new marine species of the centric diatoms of the genus Cyclotella, Cyclotella desikacharyi A.K.S.K. Prasad collected from several localities in Florida Bay, USA, where it is a dominant part of the planktonic assemblage, is described by means of light and scanning electron microscopy. Cyclotella desikacharyi is characterized by the presence of dense striae (14-19 in 10 µm) in the marginal zone and small granules all through the surface of the valve, including the central area, fultoportulae on the valve mantle located on every second or third interstria, each surrounded by three satellite pores, a pronounced tangential undulation, 3-17 valve-face fultoportulae in an arc on the uplift of the undulation and numerous discoid plastids. The new species is compared with Cyclotella striata complex; C. desikacharyi closely resembles C. striata in valve dimensions and in the structure and arrangement of alveolate striae, and in the presence of three satellite pores surrounding each fultoportula on the valve mantle; it differs from it in the stria density and the presence of siliceous granules on the entire valve surface. The new species is compared with the other closely related marine members of the genus, Cyclotella stylorum and Cyclotella litoralis. Cyclotella choctawhatcheeana Prasad, originally described from the northern Gulf Coast of Florida, is also recorded in several localities in Florida Bay and its global distribution is discussed. The evolution of euryhalinity in the genus Cyclotella is also discussed in brief.
Long-term observations of a marine planktonic plicate Thalassiosira species, T. cedarkeyensis Prasad, from the Gulf coasts of Florida, Alabama, and Mississippi and the Atlantic coasts of Florida and ...Georgia demonstrate its wide occurrence in the southeastern United States and its ability to form extensive blooms. We also report for the first time its ability to form typical Thalassiosira chains, linking sibling cells by threads of chitin. A closely related and co-occurring diatom, T. livingstoniorum, is described on the basis of investigations conducted during 2000–2011 as a new species from many localities in Apalachee Bay on the Gulf coast and Indian River Lagoon on the Atlantic coast of Florida. It differs from T. cedarkeyensis in areola density, presence of continuous cribra on loculate areolae, arrangement and distribution of valve processes, and the number of satellite pores surrounding the valve-face fultoportulae. We have not yet found any evidence of chain formation in T. livingstoniorum. Thalassiosira cedarkeyensis and T. livingstoniorum can be easily distinguished in Naphrax-mounted preparations in light microscopy (LM), and they represent two different groups (lineages?) of plicate species with reference to internal cribrum structure of the loculate areolae. Their differences may justify placement in two different genera. Although T. cedarkeyensis (which has individual cribra on the proximal siliceous layer like T. hyperborea) is abundant and widespread on the Gulf and Atlantic coasts of the southeastern United States, T. livingstoniorum (which has continuous cribra like T. lacustris) has been found, thus far, only in Florida coastal waters. Comparisons are made between these two species and the other morphologically similar extant and extinct plicate species. Thalassiosira livingstoniorum and T. cedarkeyensis, although widespread and frequently encountered during warmer months, may be easily overlooked sources of primary production in the nutrient-rich northeastern Gulf of Mexico.
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