A new diatom (Bacillariophyceae) genus with two new species from New Mexico,USA

A new diatom (Bacillariophyceae) genus and two new species are described from the arid region of the North American southwest. The new genus, Playaensis, and new species, P. circumfimbria and P. furtiva, are distinguished by frustule morphology and autecology. Playaensis possesses unique, narrowly lunate longitudinal ribs bordering the raphe and spathulate spines, but their evolutionary relationship to known genera is unclear. In Payton Lake, New Mexico, P. circumfimbria and P. furtiva are rare in the diatom community, and their geographic and geological extent are not known, but they may be restricted to alkaline, slightly saline lakes of the region.     

Photon requirement for growth of the diatom Phaeodactylum tricornutum Bohlin (Bacillariophyceae)

Abstract Photon requirements for growth (φ_g^?1) of the diatom Phaeodactylum tricornutum were determined under nutrient-sufficient conditions at two photon flux densities corresponding to light limited and near-saturating conditions for growth. The value of φ_g^?1 based on assimilated carbon was light-dependent and varied from 8.8 to 14.0 mol photon mol C^?1 with the minimum value at the lowest photon flux density. These results are lower than might be predicted for microalgal growth based on the Z scheme of photosynthesis. Conversion of these values for carbon fixation to estimates based on oxygen evolution is problematical due to uncertainty over the appropriate assimilatory quotient (Q_a= mol O₂ mol C^?1). Minimum values based on oxygen evolution rates ranged from 6.2 to 7.6 mol photon mol O₂^?1 using a Q_a of 1.41 mol O₂ mol C^?1 obtained by Myers (1980). These estimates are similar to our previous measurements for photosynthesis and indicate a high efficiency for light energy transforming reactions during growth. The values of (φ_g^?1 obtained in this work indicate a number of inadequacies in our understanding of the energetics of microalgal growth and are inconsistent with our present knowledge of photosynthetic energy coupling in plant cells.     

Quantum requirements for growth and fatty acid biosynthesis in the marine diatom Phaeodactylum tricornutum (Bacillariophyceae) in nitrogen replete and limited conditions

We determined the quantum requirements for growth (1/?_μ) and fatty acid (FA) biosynthesis (1/?_FA) in the marine diatom, Phaeodactylum tricornutum, grown in nutrient replete conditions with nitrate or ammonium as nitrogen sources, and under nitrogen limitation, achieved by transferring cells into nitrogen free medium or by inhibiting nitrate assimilation with tungstate. A treatment in which tungstate was supplemented to cells grown with ammonium was also included. In nutrient replete conditions, cells grew exponentially and possessed virtually identical 1/?_μ of 40–44 mol photons · mol C^?1. In parallel, 1/?_FA varied between 380 and 409 mol photons · mol C^?1 in the presence of nitrate, but declined to 348 mol photons · mol C^?1 with ammonium and to 250 mol photons · mol C^?1 with ammonium plus tungstate, indicating an increase in the efficiency of FA biosynthesis relative to cells grown on nitrate of 8% and 35%, respectively. While the molecular mechanism for this effect remains poorly understood, the results unambiguously reveal that cells grown on ammonium are able to direct more reductant to lipids. This analysis suggests that when cells are grown with a reduced nitrogen source, fatty acid biosynthesis can effectively become a sink for excess absorbed light, compensating for the absence of energetically demanding nitrate assimilation reactions. Our data further suggest that optimal lipid production efficiency is achieved when cells are in exponential growth, when nitrate assimilation is inhibited, and ammonium is the sole nitrogen source.     

Morphology and molecular phylogeny of the marine diatom genus Nagumoea (Bacillariophyceae) from Japan

The canal-bearing diatom genus Nagumoea, described based on only morphological evidence, was tentatively assigned to the order Bacillariales, although its phylogenetic position remained unclear. Because three isolates of Nagumoea (SK002, SK024 and SK053) were successfully established from Japanese coasts, we performed their morphological observations and molecular phylogenetic analyses to discuss the phylogeny and taxonomic position of this genus. Strains SK002 and SK024 were identified as Nagumoea africana, whereas SK053 conformed with Nagumoea serrata. There was high interspecific divergence between N. africana and N. serrata in the rbcL sequences (8.03–8.17%), indicating their distinctness. Furthermore, intraspecific variations were detected within N. africana (2.35%) in the rbcL, implying its cryptic diversity. The maximum likelihood and Bayesian phylogenetic trees inferred from the plastid rbcL, psbC and nuclear 18S rDNA genes recovered Nagumoea as monophyletic with strong statistical support and embedded within an unresolved, poorly supported lineage containing Achnanthes, Craspedostauros, Staurotropis and Undatella in the canal-bearing order Bacillariales (= the family Bacillariaceae). Although the constrained tree based on the monophyly of Nagumoea and the other canal-bearing clade (Surirellales and Rhopalodiales) was statistically rejected by the topology tests, the phylogenetic position of Nagumoea with other Bacillarialean members remains equivocal. The possession of two plastids positioned fore and aft, observed in the present study, and lack of keel, typical of the Bacillariales, indicate the possibility of Nagumoea being part of the ingroup of the Bacillariales or its closely related outgroup.     

Temperature requirements for growth and survival of macroalgae from Disko Island (Greenland)

The temperature requirements for growth and upper temperature tolerance were determined in 16 macroalgal species collected on Disko Island (Greenland). The upper survival temperatures were examined in 1°C steps, and growth measured at 5°C intervals between 0 and 20°C using a refined method, where the fresh weight was determined weekly or fortnightly over a period of 5 or 6 weeks. To express temperature-growth responses, growth rates of temperature-acclimated plants were taken. Two groups with different temperature requirements were identified: (1) A stenothermal group includingAcrosiphonia arcta, Acrosiphonia sonderi, Urospora penicilliformis, Devaleraea ramentacea, Desmarestia aculeata, Pilayella littoralis, growing between 0 and (10 to) 15 (or 20)°C with optima between 0 and 10°C. The upper survival temperatures in these species and inChromastrum secundatum, Chromastrum virgatulum, Chordaria flagelliformis were between 17 and 23°C (duration of experiment: 2 weeks). (2) A eurythermal group includingEnteromorpha clathrata, Enteromorpha intestinalis andPolysiphonia urceolata growing between 0 and 20°C with growth optima at 10 or 15°C. The upper survival temperatures in these species and inChaetomorpha tortuosa, Bangia atropurpurea andEudesme virescens were between 24 and 31°C. These algal species showed little adaptation to the Arctic temperatures. In contrast, algae from the first group exhibited a relatively high adaptation to low temperatures — approaching the low temperature requirements of Antarctic algae. The results are discussed in relation to the geographic distribution of individual species.     

Morphology of the marine epiphytic diatom Cocconeis heteroidea (Bacillariophyceae)

The morphology and fine valve structure of the marine epiphytic diatom Cocconeis heteroidea Hantzsch have been investigated. The entire frustule, including the internal and external structure of the raphid valve (RV) and araphid valve (AV), and the complete cingulum, are described using light microscopy and scanning and transmission electron microscopy, using a bleaching method. The strongly sigmoid raphe terminates in elongate hooked helictoglossae internally. The hymenes, with perforations arranged in a centric array, are located near the internal openings of the areolae in the RV. The striae in the AV consist of alveoli occluded by hymenes, that have perforations arranged in a parallel array and are located near the outer surface. The complete cingulum of AV consists of three open bands without fimbriae: a valvocopula, a copula with a ligula and a pleura with a small ligula. The RV has only a valvocopula which is open type and not fimbriate.     

Thalassiosira antarctica (Bacillariophyceae): Vegetative and resting stage ultrastructure of an ice-related marine diatom

Summary The ultrastructure of T. antarctica var. antarctica vegetative and resting stages are compared using light and transmission electron microscopy. Resting spores contain noticeably more lipid reserves than do vegetative cells. Numerous mitochondria and generally fewer numbers of other organelles are eliminated from spores into an abortive daughter cell when the spore formation division sequence is terminated. The remaining spore contents are a compact arrangement of organelles with lipid bodies predominating. These two stages are thus ultrastructurally distinct, and differences in their chemical composition can be manifested as cytological modifications.     

Electron requirements for carbon incorporation along a diel light cycle in three marine diatom species

Diatoms account for about 40% of primary production in highly productive ecosystems. The development of a new generation of fluorometers has made it possible to improve estimation of the electron transport rate from photosystem II, which, when coupled with the carbon incorporation rate enables estimation of the electrons required for carbon fixation. The aim of this study was to investigate the daily dynamics of these electron requirements as a function of the diel light cycle in three relevant diatom species and to apprehend if the method of estimating the electron transport rate can lead to different pictures of the dynamics. The results confirmed the species-dependent capacity for photoacclimation under increasing light levels. Despite daily variations in the photosynthetic parameters, the results of this study underline the low daily variability of the electron requirements estimated using functional absorption of the photosystem II compared to an estimation based on a specific absorption cross section of chlorophyll a. The stability of the electron requirements throughout the day would suggest it is potentially possible to estimate high-frequency primary production by using autonomous variable fluorescence measurements from ships-of-opportunity or moorings, without taking potential daily variation in this parameter into consideration, but this result has to be confirmed on natural phytoplankton assemblages. The results obtained in this study confirm the low electron requirements of diatoms to perform photosynthesis, and suggest a potential additional source of energy for carbon fixation, as recently described in the literature for this class.     

Observation of developmental processes in loosely attached diatom (Bacillariophyceae) communities

The succession of attached algal communities was studied in Lake Biwa and the Omiya River. After the ‘climax’ which was characterized by large numbers of Cymbella turgidula Grunow and Gomphoneis quadripunctatum (Østrup) P. Dawson, the community was dominated by species attached directly to stalks or tangled among stalks. Stalks produced by species of the previous phase are important as secondary substrata. The dominant species of the new phase were ‘loosely attached species’, as defined by Hudon and Bourget (1983). I propose a new model consisting of phase 1, characterized by the first colonizers, including large rosette‐type species and motile type species; phase 2, characterized by the stalk‐producing species; and phase 3, characterized by the growth of loosely attached species.     

Heterotrophic growth and nutritional aspects of the diatom Cyclotella cryptica (Bacillariophyceae): effect of nitrogen source and concentration

To investigate the nutritional value of the diatom Cyclotella cryptica Reimann, Lewin, and Guillard as an alternative feed for the use in the aquaculture industry, the heterotrophic growth characteristics, total fatty acids, and the resultant fatty acid profile of the microalga were studied when cultivated with sodium nitrate, ammonium chloride, or urea. All three nitrogen sources supported growth under heterotrophic conditions, and their uptake affected the pH of the cultivation medium, even when buffered. The use of sodium nitrate or urea resulted in a significant increase in the pH of the cultivation media, whereas the use of ammonium chloride caused a minor decrease in the pH of the cultivation media. The maximum specific growth rate was highest when urea and ammonium chloride were supplied at a low concentration; however, the total fatty acid content was not significantly affected (P = 0.101) by the nitrogen source when supplied at 10.7 mM nitrogen. The total fatty acid content and fatty acid profile of C. cryptica was more affected by the growth phase (predominately influenced by the initial nitrogen concentration) than by the source of nitrogen.     

A new marine diatom, Cocconeis shikinensis sp. nov. (Bacillariophyceae) from Japan

A new species of Cocconeis has been found growing on the green seaweed Caulerpa racemosa (Forsskål) J. Agardh var. laete‐virens (Montagne) Weber van Bosse from Shikine Island in the Izu Islands on the Pacific coast of Japan; we propose the name Cocconeis shiki‐nensis Hid. Suzuki and describe the species by light microscopy (LM) and electron microscopy (EM). This taxon was also collected from the plastic plates used for rearing in seed production systems of the abalone Nordotis discus hannai Ino and the horned turban Turbo cornutus Solander in the Toyama Prefectural Fisheries Research Institute facing the Sea of Japan. The main morphological features of C. shikinensis are as follows. The valves are elliptic. The valve face of the raphid valve (RV) is slightly concave and that of the araphid valve (AV) is complementary to the RV and convex. The single plastid is flat, C‐shaped and elaborately lobed. The raphe on the RV is straight. The each terminal area expands to both sides along the valve margin, forming an arrowhead‐shaped, thickened hyaline area. The striae consist of small, round areolae and are radiate and uniseriate. On the AV, the striae consist of several alveoli. Each alveolus opens internally by means of a circular foramen. The valvocopula of each valve is fimbriate and open. The cingulum attached to the AV consists of three girdle bands; a valvocopula and two bands (copula and pleura), which are open and have ligulae. The relationship between C. shikinensis and similar members of the genus Cocconeis is discussed.     

Inorganic and organic nitrogen uptake by the toxigenic diatom Pseudo-nitzschia australis (Bacillariophyceae)

The nitrogen uptake capabilities of the toxigenic diatom Pseudo-nitzschia australis (Frenguelli), freshly isolated from Monterey Bay California, were examined in unialgal laboratory cultures at saturating photosynthetic photon flux densities (100 μmol photons m⁻² s⁻¹) and 15 °C. The kinetics of nitrogen (nitrate, ammonium, urea and glutamine) uptake as a function of substrate concentration were estimated from short (20.5 min) incubations using the ¹⁵N-tracer technique. Based on the estimated maximum specific uptake rates and measures of N affinity (the initial slope of the uptake versus nutrient concentration curve), nitrate is the preferred nitrogen substrate, followed by glutamine and ammonium, which are equivalent. Rates of urea uptake by P. australis did not saturate at concentrations as high as 36 μg-at N L⁻¹, and urea uptake as a function of concentration could not be described by Michaelis–Menten kinetics over the concentration gradient tested. Although there is a clear preference for nitrate at equivalent concentrations (compared to ammonium, urea, and glutamine), these laboratory results demonstrate the capability of this pennate diatom to utilize both inorganic and organic forms of nitrogen, supporting field observations that P. australis blooms during both upwelling and non-upwelling conditions off the west coast of North America. Substantial differences in the nitrogenous nutrition of P. australis can be expected in these environments, and anthropogenic inputs of N substrates such as ammonium and urea can support its growth, and may contribute significantly to both harmful diatom blooms and the maintenance of seed populations at non-bloom abundances, particularly during periods of reduced or absent upwelling.     

Allocation of photoassimilated carbon into major algal metabolite fractions: Variation between two diatom species isolated from the Weddell Sea (Antarctica)

Distribution of photoassimilated carbon into major metabolite classes differed between two Antarctic diatom species, Nitzschia curta and a small unicellular Chaetoceros sp.. Time course uptake studies (over 54 h) revealed that ¹⁴C allocation appeared to be equilibrated after approximately 8 h at light saturated photosynthesis. During short term dark periods (6 h), polysaccharides as well as low-molecular-weight compounds were catabolised to sustain protein synthesis in the dark, whilst lipid reserves were not mobilised for this process. Experiments with these two species were conducted at 0 and -1.5°C, although no difference in the distribution of radiolabel was measured between the two temperatures. It is hypothesised that under near-optimal conditions fast growing species are characterised by a high carbon turnover associated with a rapid flow of newly assimilated carbon into polymeric compound classes. On the other hand, slower growing species (such as N. curta) may store a significant amount of surplus carbon in the low-molecular-weight metabolite fraction. Species specific preferences were observed when comparing the accumulation of radiolabel into the lipid pools.