The Relative Growth Rates of Three Plankton Diatoms in Relation to Underwater Radiation and Temperature

Relative growth rates of three freshwater plankton diatoms-Asterionellaformosa, Fragilaria crotonensis, and Tabellaria flocculosa var.asterionelloides-are described from cultures suspended at variousdepths and during several seasons in the lake Windermere. Seasonalvariation in rates recorded near the surface (i m. depth) isinterpreted in terms of seasonal changes in temperature anddaylength. Rates recorded for Asterionella and Fragilaria aregenerally similar, but are approximately twice the rates obtainedwith Tabellaria. Depth profiles of relative growth rates areof similar form in all species, and normally show lightsaturationnear the surface. The shape of profiles for Asterionella isin good agreement with estimates of photosynthesis integratedover the growth periods. The parallelism between photosyntheticand relative growth rates of Asterionella is further illustratedfrom laboratory experiments: an approximate interconversion,under certain conditions, is given.     

The Isolation, Maintenance and Host Range Studies of a Chytrid Rhizophydium planktonicum Canter emend., Parasitic on Asterionella formosa Hassall

The methods of isolation and maintenance in dual clone cultureof the chytrid Rhizophydium planktonicum Canter emend, parasiticon Asterionella formosa Hass. from the plankton are described.The ability of a single fungal isolate to infect other clonesof Asterionella, Fragilaria, Tabellaria, Synedra and Cyclotella,as well as dead material was also tested. All the clones of Asterionella proved to be highly susceptibleto infection whereas only in rare instances could a sporangiumbe found which had grown and dehisced on Fragilaria and Synedra.Very few zoospores encysted on Tabellaria and Cyclotella andthose which did died without further growth. There was no evidenceto suggest that the chytrid could complete its life historyon dead material. freshwater phytoplankton, culture, parasitism, host–parasite relationships, chytridiomycetes, Rhizophydium, Zygorhizidium, diatoms, Asterionella, Fragilaria     

Isolation and identification of herbivorous ciliates from contaminated microalgal cultures

Ciliates are a common but understudied group of grazers that can invade microalgal cultures. To estimate the potential impact of ciliates on microalgal culture productivity, the identification of species that can invade these cultures is essential. Furthermore, isolation of these herbivorous ciliates allows to use them in experiments that investigate the impact of ciliate grazing on the productivity of microalgal cultures. The main aims of this study were to isolate and identify ciliates that invade cultures of the freshwater microalgae Chlorella and Chlamydomonas, and to establish a live collection of these ciliates for usage in future experiments. To this end, we optimized a method for isolating ciliates from contaminated microalgal cultures and we developed a new PCR primer set for amplifying the partial 18S rDNA of ciliates belonging to the classes Spirotrichea, Oligohymenophorea and Colpodea. As a result, we isolated 11 ciliates from microalgal enrichment cultures inoculated with non-sterile dust and various freshwater sources. Of these 11 species, 7 were found to be feeding on Chlamydomonas. Ciliate species that fed on Chlorella could not be isolated in this study. Ciliate species feeding on Chlamydomonas were identified based on a combination of morphological observations and molecular analyses of partial 18S rDNA sequences.     

Weather-driven ecology of planktonic diatoms in Lake Tovel (Trentino,Italy)

The seasonal development of planktonic diatoms in Lake Tovel has been studied from 2002 to 2004 within the SALTO research project. The objective was to investigate the role of weather conditions and lake hydrology in regulating the development of Cyclotella and Fragilaria functional species groups. The different responses of the two species to the environmental variability and their reciprocal relationships were considered. Cyclotella showed a weak relationship with the selected environmental variables and its seasonal development was difficult to interpret, also in relation to its opportunistic behaviour. On the contrary, Fragilaria complex showed a prompt response to environmental variability and its seasonal development appeared to be mainly regulated by hydrological conditions, through nitrate nitrogen and, secondarily, by silica concentrations. Water temperature and thermal stability affected only Fragilaria species, while different nutrient requirements allowed Cyclotella species to grow under conditions of limited resources for Fragilaria. Since Lake Tovel has scarce internal nutrient reserves and its hydrology is strongly affected by precipitation both in winter and summer, diatom phenology seems to be indirectly regulated by weather conditions.     

Resource ratio and human impact: how diatom assemblages in Lake Maggiore responded to oligotrophication and climatic variability

Diatoms have been often used to track trophic changes from sedimentary records: recent studies demonstrated that these organisms can even be valuable indicators of climatic variability, although it is often difficult to discriminate the role of trophic and climatic drivers. Moving from the hypothesis that oligotrophication and climate affected the composition of the diatom assemblages by changing the resource ratio, we analysed the vernal diatoms succession in Lake Maggiore, between 1984 and 2007, using multivariate techniques (cluster analysis, canonical correspondence analysis, multivariate regression trees), in order to single out the oligotrophication effects from those attributable to climatic variability. Our results point out that Si, TP, temperature and wind emerged as key explanatory variables in species selection, with a stronger link between trophic and climatic drivers after the lake reached a stable oligotrophic status. Peculiar climate-driven events (deep mixing and floods) affected the in-lake Si:P ratio, giving an advantage to diatoms that are excellent P, but poor Si competitors. The classical role of Fragilaria and Tabellaria as early-warning indicators of eutrophication should be reconsidered, taking into account that both can be useful indicators of climate change, when links between their physiological resource needs and environmental data coming from robust limnological investigations can be established.     

Soybean Mosaic Virus: Vector Specificity and Coat Protein Properties

Aphid transmission studies of two soybean mosaic virus isolates have shown that both isolates are transmitted by Myzus persicae. Only one of the isolates is transmitted by Rhopalosiphum maidis. The R. madis non-transmissible isolate could be transmitted from plants co-infected with the R. maidis transmissible isolate; aphid acquisition factor did not seem to mediate this transmission. The two isolates could be differentiated by enzyme-linked immunosorbent assay experiments, but peptide mapping experiments revealed few differences between the isolates.     

NUTRIENT UPTAKE KINETICS IN PHYTOPLANKTON: A BASIS FOR NICHE SEPARATION1

Daily patterns of incorporation of carbon dioxide and inorganic phosphate were measured in phytoplankton from Lake George, New York, in January and February 1972. Rates of photosynthesis oscillated in phase for the entire assemblage and for individual cells of the diatoms Asterionella, Tabellaria, and Fragilaria. The photosynthetic capacity was maximal in the early afternoon. Daily patterns of phosphate uptake were also rhythmic. At ambient concentrations the assemblage takes up phosphate maximally in the morning while individual cells of the large diatom take it up maximally in the evening. A kinetic analysis of phosphate uptake indicated 2 velocities of uptake for cells of Tabellaria and Fragilaria: a hyperbolic function at small and an apparently linear relationship at relatively large concentrations. The large diatoms, in contrast to the total assemblage, functioned maximally at 2 separate times of the day: in the evening at ambient levels and in the morning at 0.4 μM and larger concentrations. Temporal stratification of the nutrient niche may be achieved by several uptake mechanisms in the algal cell that function at different times of the day or with a variable uptake velocity.     

Residual phosphate concentration under nitrogen-limiting conditions regulates curdlan production in Agrobacterium species

We investigated the influence of inorganic phosphate concentration on the production of curdlan by Agrobacterium species. A two-step culture method was employed where cells were first cultured, followed by curdlan production under nitrogen-limiting conditions. In the curdlan production step, cells did not grow but metabolized sugar into curdlan. Shake-flask experiments showed that the optimal phosphate concentration for curdlan production was in the range of 0.1–0.3 g l⁻¹. As the cell concentration increased from 0.42 to 1.68 g l⁻¹ in shake-flask cultures, curdlan production increased from 0.44 to 2.80 g l⁻¹. However, the optimal phosphate concentration range was not dependent upon cell concentration. The specific production rate was about 70 mg curdlan g-cell⁻¹ h⁻¹ irrespective of cell concentration. When the phosphate concentration was maintained at 0.5 g l⁻¹ under nitrogen-limiting conditions, as high as 65 g l⁻¹ of curdlan was obtained in 120 h. Journal of Industrial Microbiology & Biotechnology (2000) 25, 180–183. Received 25 October 1999/ Accepted in revised form 21 July 2000     

Tissue specific reactions of sorghum roots to the mycoherbicide Fusarium oxysporum f. sp. strigae versus the pathogenic F. proliferatum

Fusarium oxysporum f. sp. strigae (Foxy 2) is a mycoherbicide against Striga hermonthica. To ensure the safe use of this biocontrol agent, and as part of the risk assessment, this study was aimed at providing cytological evidence that Foxy 2 does not possess pathogenic behavior towards the non-target host sorghum. Therefore, we compared the infection processes and sorghum root tissue reactions towards the pathogenic F. proliferatum to that of Foxy 2 using light- and transmission electron microscopy. Given that during the growth process, hyphae could get into the central cylinder, tissue specific reactions of sorghum to Foxy 2 were also investigated by wounding the roots (exposing the vascular system), and testing for proliferation of hyphae within the vessels. Results showed that 2 weeks after sowing, F. proliferatum had invaded and destroyed all cell types including the central cylinder while Foxy 2 hyphae were located around the outer endodermal layer and were not able to penetrate the latter. There was an increase in blue autoflourescence in the central cylinder and especially the endodermis, probably due to increased phenolics in Foxy 2 infected roots which was not the case for F. proliferatum. This might contribute to the inability of Foxy 2 to penetrate the endodermis. Transmission electron microscopy showed extensive degradation of endodermis and vessel walls into thin translucent layers by F. proliferatum but not by Foxy 2. In the mechanically wounded and infected roots, Foxy 2 could invade the central cylinder close to the wound but was not identified a few millimeters away from the wound. This implies that it was not able to grow within or destroy the central cylinder even when already present within it; probably due to the observed increased phenolics. Thus, exposure of the vascular system did not serve as a route for the invasion of Foxy 2 which therefore could not further cause tracheomycosis. Therefore, Foxy 2 could be seen as a fungus well suited for biocontrol.     

Pyoverdin cheats fail to invade bacterial populations in stationary phase

Microbes engage in cooperative behaviours by producing and secreting public goods, the benefits of which are shared among cells, and are therefore susceptible to exploitation by nonproducing cheats. In nature, bacteria are not typically colonizing sterile, rich environments in contrast to laboratory experiments, which involve inoculating sterile culture with few bacterial cells that then race to fill the available niche. Here, we study the potential implications of this difference, using the production of pyoverdin, an iron‐scavenging siderophore that acts as a public good in the bacteria Pseudomonas aeruginosa. We show that (1) nonproducers are able to invade cultures of producers when added at the start of growth or during early exponential growth phase, but not during late exponential or stationary phase; (2) the producer strain does not produce pyoverdin in the late exponential and stationary phases and so is not paying the cost of cooperating during those phases. These results suggest that whether a nonproducing mutant can invade will depend upon when the mutation arises, as well as the population structure, and raise a potential difficulty with the use of antimicrobial treatment strategies that propose to exploit the invasive abilities of cheats.     

The effect of bacteria on interspecific relationships between the euryhaline rotifer Brachionus rotundiformis and the harpacticoid copepod Tigriopus japonicus

Inconsistent results have been obtained on the population growth of Brachionus rotundiformis and Tigriopus japonicus, when results from single-species and two-species mixed cultures are compared. Bacteria growth was not regulated in these experiments, which could be the cause for this. In order to test this possibility, we conducted similar experiments under axenic and synxenic (with presence of one species of bacteria) conditions. The population growth of B. rotundiformis was suppressed by the presence of T. japonicus in axenic cultures. T. japonicus could not persist in axenic cultures, but its population increased when grown in synxenic cultures. T. japonicus used RT bacteria strain as a food source, while these bacteria were toxic to B. rotundiformis. These results suggest that bacteria can modify the interspecific relationship between B. rotundiformis and T. japonicus.     

Growth and anthocyanin production by carrot suspension cultures grown under chemostat conditions with phosphate as the limiting nutrient

Chemostat cultures of carrot suspension cultures, where growth was limited by the concentration of phosphate in the input medium, were achieved by replacing a fixed proportion of the culture with fresh medium at daily intervals. In the range 0.05–0.30mM phosphate in the input medium and at a specific growth rate of 0.357 days^?1, steady-state culture density but not anthocyanin in the cells was strictly proportional to the input phosphate concentration with no intercept. At a phosphate concentration of 0.10mM and growth rates from 0.105 to 0.430 days^?1, the steady-state culture density could not be described by Monod's model of chemostat cultures, but could be described by Nyholm's model. The steady-state levels of anthocyanin were not strictly proportional to the steady-state biomass under all conditions, showing that anthocyanin production is not completely growth associated.     

Studies on Enzymatic Production of ATP

A study of the microflora of radurized Vienna sausages which did not contain preservatives revealed gram-negative diplococci and paired short rods. These radio-resistant isolates were the main residual flora in radurized viennas. The cultures were aerobic, oxidase positive and non-motile, and sugars were oxidized or not attacked at all. The population at the low temperature incubation from 0 to 10°C was abundant and these isolates may be psychrophilic bacteria. The cultures are also capable of growing in media supplemented with 7.5% sodium chloride. The present study has demonstrated that all of these organisms should be tentatively classified as an Intermediate type of Moraxella and Acinetobacter.

D₁₀ values of typical isolates ranged from 44 to 54 krad when irradiated in 0.067 m phosphate buffer, pH 7.0, and were about 4 times larger than that of Acinetobacter calcoaceticus.     

Growth of an aerobic bacterium with trichloroacetic acid as the sole source of energy and carbon

The aerobic microbial decomposition of trichloroacetic acid (TCA) was studied. A TCA-decomposing culture was enriched in continuous-flow and batch experiments on a medium containing TCA as the only organic component. Pure cultures of TCA degraders were isolated from the enrichment on TCA agar plates. Characterization of several isolates proved them all to be representatives of the same bacterium, a Gram-negative, catalase-positive and cytochrome C-oxidase-positive, non-motile, somewhat irregular rod. The bacterium could not be identified on the basis of its carbon-source-utilization pattern, but a partial sequencing of the 16S rDNA gene showed the isolate to belong to the gamma sub-group of Proteobacteria, and to be phylogenetically close to Acinetobacter calcoaceticus. The isolated bacterium grew exponentially with TCA as the sole source of energy and carbon. The maximum growth rate (µ_max) and the growth yield on TCA (Y _X/S ) were determined to be 0.027 h^–1 and 0.027 g biomass/g TCA, respectively. The bacterium was not able to grow on mono- or dichloroacetic acid, but it could grow on acetate.     

Habitat selection in the larvae of two species of Zygoptera (Odonata): biotic interactions and abiotic limitation

Field and laboratory experiments were set up to obtain data on the reasons for different habitat selection of Enallagma cyathigerum and Platycnemis pennipes. (1) Rearing of larvae in two different ponds showed that while P. pennipes was not able to survive conditions of low oxygen content, 50% of the E. cyathigerum larvae survived. (2) In field predation experiments with sticklebacks and dragonflies as predators, we found that E. cyathigerum suffered highest predation by the fish. In P. pennipes, mortality was highest with Anax imperator. (3) Experiments regarding larval behaviour showed that E. cyathigerum was generally more active and had higher foraging success than P. pennipes. Both species reduced activity in the presence of fish, but E. cyathigerum did so to a minor extent. In contrast to P. pennipes, E. cyathigerum showed escaping behaviour. (4) In the laboratory, the growth of E. cyathigerum was faster than that of P. pennipes.     

Establishment and growth characteristics of Glycyrrhiza glabra hairy root cultures

Hairy root cultures of Glycyrrhiza glabra producing considerable amounts of phenolic compounds were successfully established by using Agrobacterium strain C58C18(pRT GUS 104). The effect of phosphate, ammonia, nitrate and ferric-EDTA concentrations of culture medium on growth and total phenolics production of the cultures were studied. By employing statistical experimental design and linear regression analysis an improved B5 medium (B50-M) could be developed. When cultivating G. glabra hairy roots in B50-M medium we were able to obtain 9 g dried roots/l in 25 days which was twice as much as when using the initial B50 medium. According to tentative analyses the cultures did not contain glycyrrhyzin, but they produced liquiritigenin and isoliquiritigenin. The production of total phenolic substances (mg g^-1 dw) was higher in the improved medium resulting in significantly higher volumetric productivity (mg phenolic compounds l^-1). This will further enable the extraction and identification of the phenolic compounds produced by the cultures.     

Some but not All Tetrahymena Species Destroy Monolayer Cultures of Cells from a Wide Range of Tissues and Species

The activities of Tetrahymena corlissi, Tetrahymena thermophila, and Tetrahymena canadensis were studied in coculture with cell lines of insects, fish, amphibians, and mammals. These ciliates remained viable regardless of the animal cell line partner. All three species could engulf animal cells in suspension. However, if the animal cells were monolayer cultures, the monolayers were obliterated by T. corlissi and T. thermophila. Both fibroblast and epithelial monolayers were destroyed but the destruction of human cell monolayers was done more effectively by T. thermophila. By contrast, T. canadensis was unable to destroy any monolayer. At 4 °C T. thermophila and T. corlissi did not carryout phagocytosis and did not destroy monolayers, whereas T. canadensis was able to carryout phagocytosis but still could not destroy monolayers. Therefore, monolayer destruction appeared to require phagocytosis, but by itself this was insufficient. In addition, the ciliates expressed a unique swimming behavior. Tetrahymena corlissi and T. thermophila swam vigorously and repeatedly into the monolayer, which seemed to loosen or dislodge cells, whereas T. canadensis swam above the monolayer. Therefore, differences in swimming behavior might explain why T. corlissi has been reported to be a pathogen but T. canadensis has not.     

Kinetic Behavior of Some Polyphosphate-Accumulating Bacteria Isolates in the Presence of Nitrate and Oxygen

This paper studies the phosphate uptake by pure cultures of Aeromonas hydrophila, Klebsiella oxytoca, Agrobacterium tumefaciens, and Aquaspirillum dispar in the presence of both nitrate and oxygen. It is shown that species were able to respire both electron acceptors for phosphate accumulation. A. tumefaciens and A. dispar accumulated overall phosphate both in oxic and anoxic culture conditions, whereas A. hydrophila and K. oxytoca eliminated overall phosphate only in oxic conditions. A. dispar was able to remove phosphate by reducing oxygen and nitrate simultaneously with the production of dinitrogen gas. The anoxic denitrification observed in the cultures of adapted and nonadapted cells to nitrate showed that only A. dispar have a denitrification rate superior when the cells were adapted to nitrate. Received: 15 December 1998 / Accepted: 21 January 1999