Live Diatoms Research Articles

Continuous reproduction of planktonic foraminifera in laboratory culture.

Planktonic foraminifera were long considered obligate sexual outbreeders but recent observations have shown that nonspinose species can reproduce by multiple fission. The frequency of multiple fission appears low but the survival rate of the offspring is high and specimens approaching fission can be distinguished. We made use of this observation and established a culturing protocol aimed at enhancing the detection and frequency of fission. Using this protocol, we selectively cultured specimens of Neogloboquadrina pachyderma and raised the frequency of reproduction by fission in culture from 3% in randomly selected specimens to almost 60%. By feeding the resulting offspring different strains of live diatoms, we obtained a thriving offspring population and during the subsequent 6 months of culturing, we observed two more successive generations produced by fission. This provides evidence that in nonspinose species of planktonic foraminifera, reproduction by multiple fission is likely clonal and corresponds to the schizont phase known from benthic foraminifera. We subsequently tested if a similar culturing strategy could be applied to Globigerinita glutinata, representing a different clade of planktonic foraminifera, and we were indeed able to obtain offspring via multiple fission in this species. This work opens new avenues for laboratory-based experimental work with planktonic foraminifera.

A method for bone marrow extraction of diatoms for forensic science applications.

Diatoms show potential as trace evidence indicators, particularly as evidence of drowning. Often, the diatom test to diagnose drowning is done on soft tissue or bone marrow from a recently deceased individual. This method presented here combines elements from previous forensic literature and methods of diatom isolation in phycology to extract diatoms from bone marrow of skeletal remains for forensic use. This diatom extraction method is time-efficient, minimizes contamination risk, and produces samples of intact diatoms. This method is designed to complete sample preparation within 24 h, sampling the bone for diatoms internally and externally. This method was developed using porcine long bones submerged in water with live diatoms for up to 3 months. Three marrow samples were extracted from each bone so the method was developed using 102 marrow samples. Additionally, 132 surficial bone and environmental samples were collected and prepared during method development. To briefly summarize the method, the bone joints were cut off with an angle grinder in a biosafety hood to expose the marrow, which was removed from the hip, knee, and shaft as separate samples. The marrow was digested with nitric acid at 400°C in glass beakers before being centrifuged with DI water, plated onto microscope slides, and observed with a compound microscope. Observation found good preservation of unbroken diatom cell walls throughout the process. This method can be used to prepare diatoms as forensic trace evidence.

Composição e estrutura da comunidade de diatomáceas bentônicas de marismas do sul do Brasil e sua relação com variáveis ambientais

Abstract: Aim This study focused on the spatiotemporal variation of the benthic diatom community structure in salt marshes from the Patos Lagoon estuary and their relationship with environmental variables. Methods Samplings were carried out in the winter of 2010 and summer of 2011 (during El Niño and La Niña) in sites with different sediment granulometry, salinity, and distances from the Atlantic Ocean. The surface sediment was collected using a core (10 cm in diameter and 2 cm in depth) and the benthic diatoms were removed following the Trapping method, allowing the observation of live diatoms. Results The richness values (18 and 48 taxa), evenness (0.41 and 0.68), and Shannon diversity indices (2.02 and 3.31 bits/ind.) variations were not significative between the sites and seasons, although temperature and salinity differed significatively between winter and summer. However, the diatom's composition and distribution were related to temperature, salinity, and sediment particle size. Mainly the species Hippodonta hungarica, Luticola simplex Navicula cf. cryptotenelloides, N. erifuga, N. jacobii, Nitzschia filiformis var. conferta, Planothidium frequentissimum and Tryblionella calida were associated with lower temperature and lower salinity in the winter. The species Navicula cf. cryptocephala, N. phylleptosomaformis, Nitzschia pusilla, N. frustulum, N. scalpelliformis and Pseudostaurosiropsis geocollegarum were associated with higher temperature and higher salinity in the summer. Birraphid diatom taxa, mainly species of the genus Navicula and Nitzschia, were frequent or abundant in sandy sediments, and monoraphids, such as Planothidium frequentissimum, were frequent in sites where silt and clay predominated. Conclusions The composition of the benthic diatoms revealed variation between the sites in the winter and summer seasons, during El Niño and La Niña episodes. In winter, high rainfall and freshwater runoff maintained oligohaline condition in the marshes, while in summer, flooding with meso-poly-euhaline waters changed the diatom composition. The granulometry was an important factor in explaining the distribution of the birraphid and monorhapid taxa.

Hydrogen economy and storage by nanoporous microalgae diatom: Special emphasis on designing photobioreactors

Storing multiple energy forms from microalgae is not only facile but also lowers the cost of culturing the microalgae. Among many microalgae, diatoms are microscopic glass menageries which are responsible for converting stored lipids and biomass into hydrogen, besides fixing 25% of global CO2. Besides this their silica frustules are also nature's naturally available bionanomaterials which have immense applications in nanotechnology for hydrogen production and other energy storage. The diatom frustules get hybridized with various chemical and biological components to generate or store hydrogen in various fuel cells. In laboratory these live diatoms can be allowed to culture in various designed solar panel photobioreactors better known as diatom solar panels for high and low value-added products essentially biofuel and fucoxanthin. The present review thus discusses about possible scope and approaches to produce hydrogen from live diatom and as well as from its biomass in specially designed photobioreactors. This truly has economic aspects of hydrogen production from diatoms in comparison to other microalgae which needs to be explored for its wide applications due to its robustness and abundance occurrence.

Live diatoms as potential biocatalyst in a microbial fuel cell for harvesting continuous diafuel, carotenoids and bioelectricity

Microbial fuel cell (MFC) with live diatoms (Nitzschia palea) displacing bacteria in the anodic chamber generated electrical potential. Unlike other microalgae, diatoms fix 25% of atmospheric CO2, thus releasing O2. They perform photolysis of water by photosynthesis in the plastid during light photoperiod and cellular respiration in the mitochondria during dark, producing electrons and protons, respectively. The electrogenic property of diatom was explored and evaluated by comparing the potential changes with reference fuel cell without diatoms and that operated with diatoms in the anodic chamber. Such photosynthetic diatom microbial fuel cell (PDMFC) employed f/2 media rich in nitrates, phosphates, metasilicates, trace metals and vitamins as the anolyte and potassium permanganate as catholyte enhanced the output voltage by 3rd day. The maximum power density for PDMFC was 12.62 mWm−2 and coulombic efficiency of 22.95%. Besides this, the fixed diatom cells at anode showed about 64.28% increase in lipid production on 15th day compared to that on 1st day along with the increment in formation of complex fatty acid methyl esters and carotenoids during its operation. Hence, diatoms can be envisaged to substitute bacteria in the anodic chamber of MFC to simultaneously produce bioelectricity and other valuable compounds. Further their silica nanoporous architecture serve as good absorbents for heavy metal removal found in many wastewaters.

Resonance Raman and SERRS of fucoxanthin: Prospects for carotenoid quantification in live diatom cells

Fucoxanthin, one of the most abundant carotenoids in brown algae or in unicellular diatoms, plays a crucial role in photosynthetic processes and has a significant contribution to the natural pigments industry and biomedical application as colouring and bioactive agent. Many carotenoids are widely identified using resonance Raman (RR) spectroscopy, however, quantitative estimation of this pigment in solutions and in live cells from RR data is challenging. Here we investigated the concentration dependence resonance Raman and surface-enhanced resonance Raman scattering (SERRS) spectra of fucoxanthin, to prospect the capability of the techniques for quantitative estimation of the carotenoid in live diatom species, Cylindrotheca closterium and Skeletonema costatum. Furthermore, since pools of carotenoids are usually present in live photosynthetic microorganisms, we compared their SERRS signal when exposed to Ag nanoparticles and found distinct SERRS carotenoids signature. Regarding fucoxanthin quantification, we found a nonlinear increase in the resonance Raman intensity of the ν(C=C) mode in the concentration range from 1.190 µM to 3.035 mM and a linear increase in SERRS intensity in the 0.12 to 1.186 µM concentration range, comparable with the signal intensity collected from single diatom cells. Particularly, S. costatum, an opportunistic diatom causing harmful bloom in certain conditions, could provide important information from carotenoids monitoring in relation with its adaptability to various environmental factors, which would certainly consolidate such monitoring approaches relying on Raman spectroscopy techniques.

Shift in benthic diatom community structure and salinity thresholds in a hypersaline environment of solar saltern, Korea

The community dynamics of benthic diatoms in the hypersaline environment are investigated to advance our understanding how salinity impacts marine life. Diatoms were sampled in the two salterns encompassing salt Ponds, ditches, and seawater reservoirs (n = 11), along the salinity gradient (max = 324 psu), and nearby tidal flats (n = 2). The floral assemblages and distributions across sites and stations showed great variations, with a total of 169 identified taxa. First, not surprisingly, higher diversity of benthic diatoms was found at natural tidal flats than salterns. The saltern diatoms generally showed salinity dependent distributions with distinct spatial changes in species composition and dominant taxa. Biota-environment and principal component analysis confirmed that salinity, mud content, and total nitrogen were key factors influencing the overall benthic community structure. Some dominant species, e.g., Nitzschia scalpelliformis and Achnanthes sp. 1, showed salinity tolerance / preference. The number of diatom species at salinity of >100 psu reduced over half and no diatoms were found at maximum salinity of 324 psu. The highest salinity for the observed live diatoms was 205 psu, however, a simple regression indicated a theoretical salinity threshold of ~300 psu on the survival. Finally, the indicator species were identified along the salinity gradient in salterns as well as natural tidal flats. Overall, high species numbers, varying taxa, and euryhaline distributions of saltern diatoms collectively reflected a dynamic saltern ecosystem. The present study would provide backgrounds for biodiversity monitoring of ecologically important microalgal producers in some unique hypersaline environment, and elsewhere. Key words: benthic diatom; hypersaline; indicator species; salinity gradient; saltern

Learning Diatoms Classification from a Dry Test Slide by Holographic Microscopy.

Diatoms are among the dominant phytoplankters in marine and freshwater habitats, and important biomarkers of water quality, making their identification and classification one of the current challenges for environmental monitoring. To date, taxonomy of the species populating a water column is still conducted by marine biologists on the basis of their own experience. On the other hand, deep learning is recognized as the elective technique for solving image classification problems. However, a large amount of training data is usually needed, thus requiring the synthetic enlargement of the dataset through data augmentation. In the case of microalgae, the large variety of species that populate the marine environments makes it arduous to perform an exhaustive training that considers all the possible classes. However, commercial test slides containing one diatom element per class fixed in between two glasses are available on the market. These are usually prepared by expert diatomists for taxonomy purposes, thus constituting libraries of the populations that can be found in oceans. Here we show that such test slides are very useful for training accurate deep Convolutional Neural Networks (CNNs). We demonstrate the successful classification of diatoms based on a proper CNNs ensemble and a fully augmented dataset, i.e., creation starting from one single image per class available from a commercial glass slide containing 50 fixed species in a dry setting. This approach avoids the time-consuming steps of water sampling and labeling by skilled marine biologists. To accomplish this goal, we exploit the holographic imaging modality, which permits the accessing of a quantitative phase-contrast maps and a posteriori flexible refocusing due to its intrinsic 3D imaging capability. The network model is then validated by using holographic recordings of live diatoms imaged in water samples i.e., in their natural wet environmental condition.

Biosilica slab photonic crystals as an alternative to cleanroom nanofabrication?

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.

Algal Community Dynamics Within the Savannah River Estuary, Georgia Under Anthropogenic Stress

Estuaries are naturally dynamic ecosystems mixing fresh and marine waters, while consistently varying in depth and discharge due to diurnal tide shifts. Anthropogenic alterations impacting the Savannah River are expected to change the hydrology of the ecosystem and effect algal community structure and composition. The Savannah Harbor Expansion Project began recently with the aim of widening and deepening the river by more than a meter. It is anticipated that tidal height, influx of salt water, and sedimentation rates will be affected, which will disturb algal communities upstream. Baseline data from the Savannah River mudflats were obtained in 2011 as part of a biodiversity assessment. Algal community indices were also examined and related to species alterations in the community. Living algal species were classified as freshwater, marine, or brackish in addition to planktonic, epipelic, and epipsammic. Live diatoms were replaced by filamentous cyanobacteria representatives like Phormidium and green filamentous algae. There was a decrease in abundance of live chain-forming marine plankton species potentially due to sediment accumulation. Species richness within the diatom communities analyzed in clean material decreased (mean = 40 ± 6.6 standard deviation to 26 ± 4.6) and the 95% confidence interval narrowed when before and during dredging was compared. Cymatosira belgica Grunow remained as the dominant species with an average of 38% relative abundance at low tide and 33% relative abundance at high tide. With exposure to dredging and increased sediment deposition diatom communities showed significant change due to potential increase in turbidity and lower light availability.

Microalgal paste production of the diatom Chaetoceros calcitrans using electrolytic flocculation method at optimum culture conditions

The optimum culture conditions of the local strain Chaetoceros calcitrans were determined to improve biomass and reduce cost of production. Under outdoor culture conditions, higher cell density was attained when the cultures were enriched with Tungkang Marine Research Laboratory (TMRL) medium composed of cheap technical grade reagents and cultured at 25 g L−1 salinity. The cultures were lighted with two 40 W cool-white GE fluorescent tubes (24–35 μmol photon m−2 s−1). Using semi-continuous culture system under established optimum culture conditions, C. calcitrans can be re-cultured thrice and concentrated at each culture cycle using electrolytic flocculation method to produce 4.6 kg m−3 of diatom paste. The viability of concentrated C. calcitrans after 3 months of storage was comparable to live diatom cells. Simple preservation technique by low-temperature storage is convenient for storing algal concentrates for use as starter cultures and for feeding invertebrates. The paste costs USD 8.24 kg−1 inclusive of the assets and flocculation materials for culturing and harvesting the diatom, respectively. This study established the suitable conditions for mass culture of C. calcitrans and produced concentrated diatoms in paste form that is readily available for aquaculture hatcheries at a lower cost.

Interaction of Freshwater Diatom with Gold Nanoparticles: Adsorption, Assimilation, and Stabilization by Cell Exometabolites

The rising concern about the potential toxicity of synthetic gold nanoparticles (AuNPs) in aquatic environments requires a rigorous estimation of physico-chemical parameters of reactions between AuNPs and major freshwater microorganisms. This study addresses the interaction of 10-nm size, positively charged AuNPs with periphytic freshwater diatoms (Eolimna minima). The adsorption experiments on viable cells were performed in 10 mM NaCl and 5 mM NaCl + 5 mM NaHCO3 solution at a variable pH (3–10), at an AuNPs concentration from 1 µg/L to 10,000 µg/L, and an exposure time from a few minutes to 55 days. Three types of experiments, adsorption as a function of time (kinetics), pH-dependent adsorption edge, and constant-pH “Langmuirian” type isotherms, were conducted. In addition, long-term interactions (days to weeks) of live diatoms (under light and in the darkness) were performed. The adsorption was maximal at a pH from 3 to 6 and sizably decreased at a pH of 6 to 10. Results of adsorption experiments were modeled using a second order kinetic model, a Linear Programming Model, Freundlich isotherm, and a ligand binding equation for one site competition. The adsorption of AuNPs(+) most likely occurred on negatively-charged surface sites of diatom cell walls such as carboxylates or phosphorylates, similar to previously studied metal cations. Under light exposure, the AuNPs were stabilized in aqueous solution in the presence of live cells, probably due to the production of exometabolites by diatoms. The adsorbed amount of AuNPs decreased after several days of reaction, suggesting some AuNPs desorption. In the darkness, the adsorption and assimilation were stronger than under light. Overall, the behavior of positively charged AuNPs at the diatom–aqueous solution interface is similar to that of metal cations, but the affinity of aqueous AuNPs to cell exometabolites is higher, which leads to the stabilization of nanoparticles in solution in the presence of diatoms and their exudates. During photosynthetic activity and the pH rising above 9 in the vicinity of diatom cells, the adsorption of AuNPs strongly decreases, which indicates a decreasing potential toxicity of AuNPs for photosynthesizing cells. The present study demonstrates the efficiency of a thermodynamic and kinetic approach for understanding gold nanoparticles interaction with aquatic freshwater peryphytic microorganisms.

Live diatoms as indicators of urban stormwater runoff.

Diatom bioassessment of streams/rivers does not distinguish between live (cells with intact chloroplasts) and dead (empty cells) individuals, even though most diatom samples collected from the field will be composed of a mixture of both. This study aimed to evaluate whether percentage of live diatoms (PLD), live diatom density and chlorophyll a, and diatom species compositions can be used as indicators of hydrologic disturbance in an urban stream. We deployed artificial substrates on a monthly basis and collected periphyton samples weekly over the course of one calendar year (n=182) in three tributaries of urbanized Ruddiman Creek (Michigan, USA). We also collected samples before and after six major storm events (>0.5cm rain). We found no temporal patterns in PLD (Mann-Kendall test p>0.05) or species composition (non-metric multidimensional scaling (NMDS) ordination), which may be explained by a diatom composition already tolerant to frequent disturbance. There was no difference in PLD before and after storm events, which might partially be explained by their disturbance resistance due to different assemblage ages (1, 2, and 4weeks old) before the storms. High flow had differential effects on diatom species; loosely attached Navicula and Nitzschia species were more easily removed compared to stalk-forming Gomphonema parvulum. The most important environmental variable that was found to affect live diatom density and chlorophyll was stream width, which has an indirect effect (as a measure of discharge) on periphyton assemblages. In conclusion, PLD was found to be unsuitable metric for assessing stormwater runoff in urban streams where periphyton may not have enough time to form mature communities.

Assessing the dietary sources of two cichlid species in River Nile sub-branches: Stomach contents, fatty acids and stable isotopes analyses

We assess the importance of four different food sources as dietary components of Oreochromis niloticus and Sarotherodon galilaeus in Nile sub-branches using stomach contents, fatty acids (FA) and stable isotopes (SI) analyses. Diatoms were the dominant food items, whereas sand and mud constitute a major part of the stomach contents of both cichlids in the northern ElBehery canal. FAs and SI were compared in cichlids and four potential food sources. Carbon isotopes excluded the fresh macrophyte Myriophyllum spicatum and its epiphytes as a potential food source, whereas FA biomarkers indicated that M. spicatum is assimilated in cichlids’ muscles as detrital materials. FA profiles of cichlids’ muscles were highly enriched by live diatom markers whereas decayed diatoms and bacterial markers were partially present. Carbon isotope signatures of cichlids were much close to that of suspended particulate organic matter (SPOM) which elucidated that SPOM was the source of diatoms and bacterial detritus incorporated in cichlids muscles. Cichlids were highly enriched with nitrogen signatures which was a result of increased anthropogenic effects and incorporation of bacterial films. SI and FA analyses precisely indicated that live diatoms and bacteria, detrital macrophytes are the main sources of organic matter incorporated in cichlids muscles.

Nutrient treatments alter microbial mat colonization in two glacial meltwater streams from the McMurdo Dry Valleys, Antarctica.

Microbial mats are abundant in many alpine and polar aquatic ecosystems. With warmer temperatures, new hydrologic pathways are developing in these regions and increasing dissolved nutrient fluxes. In the McMurdo Dry Valleys, thermokarsting may release both nutrients and sediment, and has the potential to influence mats in glacial meltwater streams. To test the role of nutrient inputs on community structure, we created nutrient diffusing substrata (NDS) with agar enriched in N, P and N + P, with controls, and deployed them into two Dry Valley streams. We found N amendments (N and N + P) to have greater chlorophyll-a concentrations, total algal biovolume, more fine filamentous cyanobacteria and a higher proportion of live diatoms than other treatments. Furthermore, N treatments were substantially elevated in Bacteroidetes and the small diatom, Fistulifera pelliculosa. On the other hand, species richness was almost double in P and N + P treatments over others, and coccoid green algae and Proteobacteria were more abundant in both streams. Collectively, these data suggest that nutrients have the potential to stimulate growth and alter community structure in glacial meltwater stream microbial mats, and the recent erosion of permafrost and accelerated glacial melt will likely impact resident biota in polar lotic systems here and elsewhere.

The nature of the diatom Leptocylindrus mediterraneus (Bacillariophyceae), host of the enigmatic symbiosis with the stramenopile Solenicola setigera

:The consortium between the colonial stramenopile Solenicola setigera and the centric chain-forming diatom Leptocylindrus mediterraneus is cosmopolitan throughout the world ocean yet rarely abundant. However, the nature of the association remains enigmatic. A mutualistic symbiosis requires a live diatom host, but the frustule of L. mediterraneus is apparently empty, lacking protoplasm and plastids. The parasitism requires free-living host cells to be infected, but there is no evidence of populations of the free-living diatom. During experiments attempting to culture the heterotrophic S. setigera, we successfully obtained a strain of the host diatom. In the small-subunit (SSU) rDNA phylogeny, L. mediterraneus was closely related to Dactyliosolen blavyanus and to a new sequence of Dactyliosolen sp. while distantly related to the genus Leptocylindrus. We proposed the reinstatement of L. mediterraneus in the genus Dactyliosolen as D. mediterraneus. Even under optimal growth conditions, the frustule was nearly empty with reduced protoplasm concentrated in the middle. When compared with congeneric species, D. mediterraneus showed a double-layered structure that acts as substrate for Solenicola. The free-living diatom lacked the convex walls that D. mediterraneus showed as host of Solenicola. The diatom in consortium with Solenicola maintained the photosynthetic machinery to eventually proliferate as a free-living organism. The ecological and morphological observations suggested that the diatom was successfully adapted to the mutualistic symbiosis with Solenicola. We discarded a parasitic relationship in this exceptional example of symbiosis.

Live diatoms facing Ag nanoparticles: surface enhanced Raman scattering of bulk cylindrotheca closterium pennate diatoms and of the single cells

Live diatoms exposed to AgNPs revealed SERS mechanism dependent on the nanoparticles type while the SERS output allowed detection of extracellular substances.

The Hurst exponents of Nitzschia sp. diatom trajectories observed by light microscopy

We present the results of an experiment with light microscopy performed to capture the trajectories of live Nitzschia sp. diatoms. The time series corresponding to the motility of this kind of cells along ninety-five circular-like trajectories have been obtained and analyzed with the scaling statistical method of detrended fluctuation analysis optimized via a wavelet transform. In this way, we determined the Hurst parameters, in two orthogonal directions, which characterize the nature of the motion of live diatoms in light microscopy experiments. We have found mean values of these directional Hurst parameters between 0.70 and 0.63 with overall standard errors below 0.15. These numerical values give evidence that the motion of Nitzschia sp. diatoms is of persistent type and suggest an active cell motility with a kind of memory associated with long-range correlations on the path of their trajectories. For the collected statistics, we also find that the values of the Hurst exponents depend on the number of abrupt turns that occur in the diatom trajectory and on the type of wavelet, although their mean values do not change much.

Natural nanoporous silica frustules from marine diatom as a biocarrier for drug delivery

The possible use of natural silica nanoporous biomaterial from marine diatom for drug delivery applications was explored. Coscinodiscus concinnus have a homogeneous size distribution with radius of 220 ± 15 µm with surface featuring a mounded topography with about 2 µm wide porous domes organized on the surface in pentagonal packing. Streptomycin, used as a hydrophilic drug to demonstrate the in vitro oral drug delivery model based on diatom structure, mainly adsorbed on to the diatom silica surface (foramen), inside pores (cribrum) and into the internal hollow diatom structure (cribellum). The maximum drug loading capacity of streptomycin was 33.33 ± 2 %. The release was biphasic, involving initial burst release (first 6 h) mainly from the surface of diatom foramen, and sustained drug release (upto 7 days) from cribrum and cribellum. The study indicated that the live diatoms from marine environment, due to their unique features (easy cultivable, low-cost and biocompatibility), are a potential and alternative natural source of nanoporous siliceous material for in vitro oral drug delivery applications.

Morphological and molecular phylogenetic studies on Fistulifera saprophila

Accurate taxonomic identification provides the foundation for a number of diatom applications, such as the ecological monitoring of waters and the reconstruction of past environments. Despite significant recent developments in diatom taxonomy and phylogenetics, to date, only a few taxa have been studied extensively using a wide range of techniques. In this paper, data gained from intensive research on the morphology of live and cleaned diatom cells of two Fistulifera saprophila (Lange-Bertalot & Bonik) Lange-Bertalot strains isolated from the Gulf of Gdańsk are discussed. This study suggests that because specimens of F. saprophila have very delicate frustules prone to dissolution, the species has not been fully investigated and, therefore, a revised description is presented. Data on live cells and colony morphology, as well as interesting findings on the discrepancies between measurements of wet-mounted, dried and Naphrax-mounted diatom cells are also shown. The geographical distribution and ecological tolerance of F. saprophila is probably much wider than previously reported, but needs further investigation. The results of molecular phylogenetic analyses confirm the clear separation of Fistulifera Lange-Bertalot from Navicula Bory, also showing that its sister genera are Craticula Grunow, Eolimna Lange-Bertalot and Stauroneis Ehrenberg. Surprisingly, genera considered to have similar morphological characteristics, such as Mayamaea Lange-Bertalot and Sellaphora Mereschkowsky fall on a separate phylogenetic branch.