Maintenance of clonal diversity during a spring bloom of the centric diatom Ditylum brightwellii

Maintenance of genetic diversity in eukaryotic microbes reflects a synergism between reproductive mode (asexual vs. sexual) and environmental conditions. We determined clonal diversity in field samples of the planktonic marine diatom, Ditylum brightwellii, during a bloom, when cell number increased by seven-fold because of rapid asexual division. The genotypes at three microsatellite loci were determined for 607 individual cell lines isolated during the 11 days of sampling. Genetic diversity remained high during the bloom and 87% of the cells sampled each day were genetically distinct. Sixty-nine clonal lineages were sampled two or more times during the bloom, and two clones were sampled seven times. Based on the frequency of resampled clonal lineages, capture-recapture statistics were used to determine that at least 2400 genetically distinct clonal lineages comprised the bloom population. No significant differences in microsatellite allele frequencies were observed among daily samples indicating that the bloom was comprised of a single population. No sexual stages were observed, although linkage equilibrium at two loci, high levels of allelic and genotypic diversity, and heterozygote deficiencies were all indicative of past sexual reproduction events. At the height of the bloom, a windstorm diluted cell numbers by 51% and coincided with a change in the frequency distribution of some resampled lineages. The extensive clonal diversity generated through past sexual reproduction events coupled with frequent environmental changes appear to prevent individual clonal lineages from becoming numerically dominant, maintaining genetic diversity and the adaptive potential of the population.     

Studies on the biochemistry and fine structure of silica shell formation in diatoms

Summary The sequential wall formation in the centric diatom,Ditylum brightwellii (West) Grunow, is described. The silica deposition vesicle is formed by the coalescence of small vesicles. Silicification of the new valve starts from the central labiate process area prior to the completion of cytokinesis, and the developing valve grows in a centrifugal direction. The initiation of the structures on the valve follows the sequence: labiate process, marginal ridge, and rota. A novel labiate process apparatus, which is situated in the cytoplasm close to the developing labiate process, appears prior to the initiation of the labiate process and disappears upon its maturation. Segments of the girdle bands are formed in individual silica deposition vesicles after the valve matures and is exocytosed. Three morphological forms of deposited silica have been determined: thin base layers, microfibrils, and hexagonal columns. The involvement of cytoplasmic structures in the patterning of the siliceous wall is discussed.     

Localisation of fucoxanthin chlorophyll a/c-binding polypeptides of the centric diatom Cyclotella cryptica by immuno-electron microscopy

Antisera were raised against the C termini of three fucoxanthin chlorophyll a/c-binding polypeptides, Fcp2, Fcp4, and Fcp6, of the centric diatom Cyclotella cryptica. Immunogold electron microscopy of ultrathin-sectioned cells indicated that Fcp2 and Fcp4 are present in almost the same amounts, whereas approximately 8- to 10-fold less gold label was registered for Fcp6. Immunogold electron microscopy of freeze-fracture replicas of thylakoid membranes showed that the C termini of at least Fcp2 and Fcp4 were located in the thylakoid lumen, thus demonstrating a 3-dimensional structure similar to that already described for the chlorophyll a/b-binding light-harvesting polypeptides of higher plants.     

Role of silicon in diatom metabolism

Proteins of Cylindrotheca fusiformis which incorporated significant ³²PO₄ were identified as soluble, acidic proteins, and their two-dimensions gel positions were determined. Upon addition of silicate to silicon-starved cells, at least 3 of these proteins showed a significant and rapid change in the level of phosphorylation. Under the same conditions the amount of ³²PO₄-labeled ATP, ADP, and GTP remained relatively constant. Thus silicon appears to affect phosphorylation and dephosphorylation of specific proteins, and these changes are sufficiently rapid to suggest that phosphorylation may have a role in mediating the silicon requirement for both DNA synthesis and the accumulation of specific mRNAs.     

Role of silicon in diatom metabolism

Levels of the cyclic nucleotides, cAMP and cGMP, were determined in four species of pennate diatoms; changes in their levels and ratios were monitored in silicon-starved and light-dark synchronized cultures of Cylindrotheca fusiformis. Content of both cAMP and cGMP changed during the cell cycles: when silicate was added to starved cultures, cAMP, cGMP and DNA levels rose rapidly; cAMP and cGMP declined before DNA synthesis was complete and continued to fall during the events leading to cell separation. In unstarved synchronies, net synthesis of DNA continued until cell separation; 1 h before cell separation cAMP levels fell while those of cGMP rose. The results support the proposal that cAMP and cGMP may play a part in the process of cell division in the diatom, possibly involving silicon.     

Effect of temperature on light-limited growth of the harmful diatom Eucampia zodiacus Ehrenberg, a causative organism in the discoloration of Porphyra thalli

The diatom Eucampia zodiacus Ehrenberg is one of the harmful diatoms which indirectly cause, through nutrient depletion, discoloration of Porphyra thalli. The effect of temperature on light-limited growth of E. zodiacus was examined at 13 irradiance levels (5–350 μmol m⁻² s⁻¹) in combination with five temperatures (8.0–25.0 °C). The results showed that all the parameters of growth-irradiance curves, such as the maximum growth rate (μ_m), half saturation constant (K_s), threshold value of irradiance (I₀) and saturation irradiance for growth (S), increased with increasing temperature. On the basis of the relationship between temperature and growth-irradiance curves and seasonal fluctuation of the light environment in Harima-Nada, the effect of irradiance on the population dynamics of E. zodiacus during the period from October to March was evaluated using two indices, depth of the threshold irradiance for growth (D_t) and depth where a half of its maximum growth rate is attained (D_k). D_t and D_k remained almost stable from October to December, but gradually increased in early March. This indicates that the range of depth at which E. zodiacus was able to grow increased markedly in early spring when E. zodiacus blooms in Harima-Nada. As the vegetative cells of E. zodiacus tend to distribute in relatively deeper water layers, where growth is limited by irradiance, the increase in the depth range over which E. zodiacus is able to grow is concluded to be an important factor allowing development of its blooms.     

Studies on the biochemistry and fine structure of silica shell formation in diatoms

Summary The morphogenesis of the different types of labiate processes is compared among three species of centric diatoms [Stephanopyxis turns (Greville) Ralfs,Odontella sinensis (Greville) Grunow, andOdontella aurita (Lyngbye) Agardh]. In all species, a cytoplasmic structure,i.e., the labiate process apparatus, situated close to the developing labiate process, appears before the labiate process begins to form and disappears upon its maturation. The possibility that the labiate process apparatus is implicated in the phylogeny of the labiate process is discussed.     

Photosynthetic oscillation in individual cells of the marine diatom <Emphasis Type="Italic">Coscinodiscus wailesii</Emphasis> (Bacillariophyceae) revealed by microsensor measurements

Oscillations with a period of 1–2 min in the rate of photosynthesis have been found in leaves of C₃ and C₄ land plants under invariant, saturating, light and carbon dioxide. This article reports the occurrence of similar oscillations with a period of 2–2.5 min in individual cells of the marine diatom Coscinodiscus wailesii. These oscillations were determined by measurements of both oxygen (oxygen microelectrode) and carbon dioxide (pH microelectrode) just outside the plasmalemma. These oscillations were found in less than 1% of the cells examined. The occurrence of oscillations in unicelluar diatoms rules out for these organisms hypotheses as to the origin of oscillations in land plant leaves that are based on cell–cell interactions.     

5alpha, 8alpha-Epidioxysterol sulfate from a diatom Odontella aurita

A 5alpha,8alpha-epidioxysterol sulfate was isolated from the cultured diatom Odontella aurita (NIES 589), and its structure was elucidated by spectroscopic methods.     

Surfactant-producing microorganisms isolated from the gut of a Eucalyptus-feeding sawfly,Perga affinis affinis

Summary Microorganisms which produce surfactants were isolated from the gut of a eucalypt-feeding sawfly. It is possible that surfactants in the guts of some defoliators may be microbiologically-produced.Deceased     

The special Golgi-ER-mitochondrium unit in the diatom genusCoscinodiscus

As an exception among diatoms, dictyosomes inCoscinodiscus wailesii andC. centralis form throughout the vegetative cell cycle a complex functional unit with a mitochondrium via an ER-cisterna. Ultrathin sections of spermatogonangia ofC. wailesii revealed that these G-ER-M (Golgi-ER-Mitochondrium) associations are maintained also during spermatogenesis. A dissociation of the G-ER-M-unit occurred however, whenC. wailesii cells formed protoplasts under the influence of the antimicrotubular herbicide APM, leading also to the dissociation of the Golgi stack itself. Lamellar membrane profiles, resembling Golgi membranes were seen to align with the plasmalemma of the protoplasts. These observations are discussed in comparison to the G-ER-M-units found in the xanthophyte algaVaucheria and the oomyceteSaprolegnia. Dedicated to Prof. DrElisabeth Tschermak-Woess on the occasion of her 70th birthday.     

Description of a new dinoflagellate with a diatom endosymbiont, <Emphasis Type="Italic">Durinskia capensis</Emphasis> sp. nov. (Peridiniales,Dinophyceae) from South Africa

A new dinoflagellate Durinskia capensis Pienaar, Sakai et Horiguchi sp. nov. (Peridiniales, Dinophyceae), from tidal pools along the west coast of the Cape Peninsula, Republic of South Africa, is described. The dinoflagellate produces characteristic dense orange-red colored blooms in tidal pools. The organism is characterized by having a eukaryotic endosymbiotic alga. Ultrastructure study revealed the organism has a cellular construction similar to that of other diatom-harboring dinoflagellates. The cell is thecate and the plate formula is: Po, x, 4', 2a, 6', 5c, 4s, 5', 2', which is the same as that of Durinskia baltica, the type species of the genus Durinskia. D. capensis can, however, be distinguished from D. baltica by overall cell shape, the relative size of the 1a and 2a plates, the degree of cingular displacement, and the shape of the eyespot. Our molecular analysis based on SSU rDNA revealed that D. capensis is closely allied to D. baltica, thus supporting the assignment of this new species to this genus. This Durinskia clade takes a sister position to another diatom-harboring dinoflagellate clade, which includes Kryptoperidinium foliaceum and Galeidinium rugatum. Molecular analysis based on the rbcL gene sequence and ultrastructure study revealed that the endosymbiont of D. capensis is a diatom. The SSU rDNA gene trees indicated that four species with a diatom endosymbiont formed a clade, suggesting a single endosymbiotic origin.     

Electron microscopical observations onPseudaphelidium drebesii Schweikert and Schnepf, a parasite of the centric diatomThalassiosira punctigera

Summary Ultrastructural observations revealed details of the infection process and the fine structure ofPseudaphelidium drebesii Schweikert and Schnepf, a parasite of the marine centric diatomThalassiosira punctigera (Castracane) Hasle. After attachment and encystment of the zoospore an intracellular infection tube is generated. This structure is everted between the overlap of the girdle bands or the gap between the valve and the girdle band of the host diatom. The bulk of thePseudaphelidium protoplast enters the silica shell of the diatom via the infection tube but does not pierce the host plasma membrane. Parts of the host cytoplasm are phagocytized with microfilament involvement.Pseudaphelidium drebesii is characterized by unusual microbodies containing tubular inclusions and by closed mitosis with a perinuclear spindle. The taxonomic position ofP. drebesii is discussed.     

Assessment of Potential Impacts of Exotic Species on Populations of a Threatened Species, White Sands Pupfish, Cyprinodon tularosa

The potential impact of introduced species on rare taxa is of particular concern to conservation biologists. We evaluate the impacts of western mosquitofish (Gambusia affinis) and virile crayfish (Orconectes virilis) on experimental populations of a threatened species, the White Sands pupfish (Cyprinodon tularosa). Forty experimental pupfish populations were exposed to one of four treatments; (a) 1 crayfish, (b) 4 crayfish, (c) 5 adult mosquitofish and (d) control. Pupfish population size and biomass was monitored over the duration of one breeding season. A repeated measure multiple analysis of covariance revealed a significant effect of treatments on response variables (population size and biomass) (P<0.0001). Mosquitofish had a significant effect on population size and biomass (P=0.0330). The effect of one crayfish was not significant (P=0. 0683). However, 4 crayfish had a significant effect (P<0.0001) on population size. We use these data, along with information on environmental tolerances of crayfish and mosquitofish, to evaluate risks for specific pupfish populations. An erratum to this article is available at .     

Effects of germanium dioxide,an inhibitor of diatom growth,on the microscopic laboratory cultivation stage of the kelp, <Emphasis Type="Italic">Laminaria saccharina</Emphasis>

The kelp, Laminaria saccharina, is an economically and biologically valuable seaweed used in integrated multi-trophic aquaculture. The development of the initial microscopic phase of the life cycle of this species is carried out in the laboratory. A treatment of germanium dioxide (GeO₂) can be applied to algal laboratory cultures to inhibit the growth of contaminating diatoms. Previous studies reported inhibitory effects also affecting the macroscopic stage of the life cycle of L. saccharina, the sporophyte, but the effects on the microscopic gametophytic life stage are unknown. To determine the effects, cultures of L. saccharina were treated with varying concentrations of GeO₂ and the resulting lengths and surface area of the juvenile sporophytes produced were measured. It was determined that GeO₂ follows a typical dose-effect pattern, increasing the growth rate of juvenile sporophytes until a critical point at which an inhibitory effect was observed. To obtain juvenile sporophytes ready for deployment to aquaculture sites in the shortest time and to successfully reduce diatom contamination, it was determined that a concentration between 0.10 and 0.50mL of GeO₂ per litre of seawater, applied at day 8, was the most efficient.     

Impact of mass mortality of a mosquito fish,Gambusia affinison the ecology of a fresh water eutrophic lake (Lake Naini Tal,India)

Between 28th March and 4th April, 2000 a fungal infection killed >80% of the most abundant planktivorous fish, Gambusia affinis in Lake Naini Tal, Uttaranchal, India. In response to this mortality, planktonic communities and some eutrophication-related parameters viz., primary productivity, phosphate–phosphorus, nitrate–nitrogen and transparency of the water, were considerably changed. Total zooplankton number more than doubled, phytoplankton number reduced nearly to half, primary production and phosphate-phosphorus was dramatically reduced, while nitrate–nitrogen and water clarity increased. The phytoplankton decline was caused by increased zooplankton grazing (top-down control) rather than phosphorus deficiency (bottom-up control). After 3 months, Gambusia and planktonic communities and nutrient levels reverted back almost to their pre-mortality state. Thus removal of G. affinis could improve water quality of Lake Naini Tal.     

Evolution of a new chromosomal lineage in a laboratory population ofDrosophila through centric fission

Structural rearrangements of chromosomes have played a decisive role in the karyotypic evolution of species. It is also known that inversions, translocations, fusions, fissions, heterochromatin variations and other chromosomal changes occur as transient events in natural populations. Herein we report the occurrence of a rare event of centric fission of a metacentric chromosome in a laboratory population ofDrosophila, called Cytorace 1. This centric fission has been fixed in a sub-population of Cytorace 1, resulting in a new chromosomal lineage called Fissioncytorace-1.     

Upward cascading effects of nutrients: shifts in a benthic microalgal community and a negative herbivore response

We evaluated the effects of nutrient addition on interactions between the benthic microalgal community and a dominant herbivorous gastropod, Cerithidea californica (California horn snail), on tidal flats in Mugu Lagoon, southern California, USA. We crossed snail and nutrient (N and P) addition treatments in enclosures on two tidal flats varying from 71 to 92% sand content in a temporally replicated experiment (summer 2000, fall 2000, spring 2001). Diatom biomass increased slightly (~30%) in response to nutrient treatments but was not affected by snails. Blooms of cyanobacteria (up to 200%) and purple sulfur bacteria (up to 400%) occurred in response to nutrient enrichment, particularly in the sandier site, but only cyanobacterial biomass decreased in response to snail grazing. Snail mortality was 2–5 times higher in response to nutrient addition, especially in the sandier site, corresponding to a relative increase in cyanobacterial biomass. Nutrient-related snail mortality occurred only in the spring and summer, when the snails were most actively feeding on the microalgal community. Inactive snails in the fall showed no response to nutrient-induced cyanobacterial growths. This study demonstrated strongly negative upward cascading effects of nutrient enrichment through the food chain. The strength of this upward cascade was closely linked to sediment type and microalgal community composition.     

Studies on the biochemistry and fine structure of silica shell formation in diatoms

In diatoms, the siliceous cell walls are enveloped by an organic component which includes 4-hydroxyproline and 3,4-dihydroxy-L-proline. The formation of these two amino acids were studied in Nitzschia angularis in Si-starvation synchrony. Both appear to arise from peptidyl proline. Its conversion to peptidyl hydroxyproline was shown in cell-free extracts and in kinetic studies using [¹⁴C]proline. Two lines of evidence indicate that dihydroxyproline does not arise from the further hydroxylation of peptidyl hydroxyproline: First, there was a lag of several minutes between the incorporation of [¹⁴C]proline into protein and the appearance therein of [¹⁴C]hydroxyproline but no such lag for the appearance of dihydroxyproline. Second, ,-dipyridyl blocked the formation of hydroxyproline, but not of dihydroxypyroline, from peptidyl proline. Cell walls made in the presence of dipyridyl differed little in overall chemical composition from walls made in its absence and were morphologically identical. [¹⁴C]dehydroproline was rapidly metabolized in the cells, with [¹⁴C]dihydroxyproline a prominent product. Studies of the conversion of [¹⁴C]proline to [¹⁴C]hydroxyproline at various stages of wall formation showed an increased synthesis of [¹⁴C]dihydroxyproline at the end of cell separation.     

Dr Han L. Golterman,a Limnologist: a tribute on the occasion of his 65th birthday and retirement

The green algae D. tertiolecta, the flagellate I. galbana and the diatom C. gracilis were grown in batch cultures. The organisms were analysed for lipid class composition at the logarithmic and stationary growth phases using the Chromarod-Iatroscan thin layer chromatography with flame ionization detection (TLC-FID) system.There were major differences in lipid class production among the organisms investigated, but few differences in lipid class distribution between log phase and stationary phase cultures of D. tertiolecta and I. galbana. C. gracilis displayed the general trend exhibited in diatom metabolism, which can be characterized by an increase in triacylglycerol synthesis in situations of stress.