Comparison of Bacterioneuston and Bacterioplankton Dynamics during a Phytoplankton Bloom in a Fjord Mesocosm

The bacterioneuston is the community of Bacteria present in surface microlayers, the thin surface film that forms the interface between aquatic environments and the atmosphere. In this study we compared bacterial cell abundances and bacterial community structures of the bacterioneuston and the bacterioplankton (from the subsurface water column) during a phytoplankton bloom mesocosm experiment. Bacterial cell abundance, determined by flow cytometry, followed a typical bacterioplankton response to a phytoplankton bloom, with Synechococcus and high-nucleic acid content (HNA) bacterial cell numbers initially falling, probably due to selective protist grazing. Subsequently HNA and low-nucleic acid content bacterial cells increased in abundance, but Synechococcus cells did not. There was no significant difference between bacterioneuston and bacterioplankton cell abundances during the experiment. Conversely, distinct and consistent differences between the bacterioneuston and the bacterioplankton community structures were observed. This was monitored simultaneously by Bacteria 16S rRNA gene terminal restriction fragment length polymorphism and denaturing gradient gel electrophoresis. The conserved patterns of community structure observed in all of the mesocosms indicate that the bacterioneuston is distinctive and nonrandom.Determining and understanding both spatial and temporal patterns in bacterioplankton community structure are a core aim of marine microbial ecology (15). Distributions of bacterioplankton over space and time can be correlated to environmental parameters, and subsequent links can therefore be made to ecosystem function. A broad range of spatial studies made on macro- (34), meso- (20), and microscales (27) have shown clear patterns in distribution of the bacterioplankton.The sea surface microlayer is part of the air-sea interface and is generally considered to be the top 1 mm or less of the ocean (26). Surface microlayers have a fundamental role in regulating transport processes between the ocean and the atmosphere (26) and are often referred to as the neuston (28, 31). For more than 25 years it has been hypothesized that the sea surface microlayer is a hydrated gelatinous layer (40) that contains surface-active organic compounds such as carbohydrates, proteins, lipids, and humic substances in relatively high concentrations (17, 45, 48). Recently, gel-like transparent expolymer particles (TEP) have been shown to be enriched in the surface microlayer, supporting the concept of a gelatinous interfacial layer (46).Bacteria present in surface microlayers or the neuston are regarded as the bacterioneuston. There are relatively few studies which have directly compared the community structure of the bacterioneuston with that of the cognate subsurface (bacterioplankton) in the marine environment. Analysis of Bacteria 16S rRNA gene clone libraries constructed using DNA isolated from surface microlayer and subsurface water (<1 m) samples from the North Sea revealed that the bacterioneuston was dominated by two operational taxonomic units which accounted for 81% of clones analyzed (13). Community structure profiling using denaturing gradient gel electrophoresis (DGGE) of the bacterioneuston at three sites around Oahu Island in the Pacific Ocean showed that the bacterioneuston forms consistent and distinct community structures. Conversely, the archaeal community structure of the same samples using Archaea 16S rRNA gene DGGE analysis did not show the same surface microlayer-specific response, indicating that bacteria and archaea respond to their environment in fundamentally different ways in the neuston (7).Other studies have, however, reported no consistent differences between the bacterioneuston and the bacterioplankton. Samples collected from two separate sites in the Mediterranean Sea were analyzed using single-strand conformation polymorphism of Bacteria 16S rRNA genes (1). The authors did not report any significant differences between the surface microlayer and subsurface samples using this community profiling method.Nonmarine studies of the bacterioneuston and Archaea communities in estuarine (10) and freshwater (5, 19) environments have also shown distinct microbial community structures present in the surface microlayer compared to those in subsurface water ≤1 m below.Recurring phytoplankton blooms are a key feature of coastal waters and strongly influence bacterioplankton community structure and succession (4, 14, 38). Phytoplankton blooms stimulate the bacterioplankton by the release of dissolved organic matter (22) or affect bacterioplankton negatively by direct competition for resources (6). Bacterioplankton community structure may also be influenced by grazing flagellates or viral lysis (47).Mesocosm experiments have been used to study plankton ecology for many decades (33). Mesocosms facilitate study of the effects of key environmental parameters, such as temperature, on plankton communities and allow the succession of natural plankton communities that resemble those found in the marine environment (11). The enclosed water mass means that experiments can be designed which manipulate physicochemical parameters to observe biological effects. Furthermore, with replicated mesocosms, the data collected can be analyzed with statistics rigorously. In this study we monitored the dynamics of the bacterioneuston and the bacterioplankton in mesocosms of fjord surface water during an artificially induced phytoplankton bloom and compared bacterial abundances and bacterial community structures in the surface microlayer and subsurface water.     

Seasonal Dynamics of Phytoplankton and Planktonic Protozoan Communities in a Northern Temperate Humic Lake: Diversity in a Dinoflagellate Dominated System

Species diversity and richness, and seasonal population dynamics of phytoplankton, planktonic protozoa, and bacterioplankton sampled from the epilimnion of Crystal Bog in 2000, were examined in order to test the hypothesis that these groups diversity and abundance patterns might be linked. Crystal Bog, a humic lake in Vilas County, Wisconsin, is part of the North Temperate Lakes Long-Term Ecological Research Site. Phytoplankton and planktonic protozoa were identified and enumerated in a settling chamber with an inverted microscope. Bacterial cells were enumerated with the use of fluorescence 4, 6-diamidino-2-phenylindole (DAPI)-staining procedures, and automated ribosomal intergenic spacer analysis (ARISA) was used to assess bacterioplankton diversity. Bacterial cell counts showed little seasonal variation and averaged 2.6 × 10⁶ cells/mL over the ice-free season. Phytoplankton and planktonic protozoan numbers varied by up to two orders of magnitude and were most numerous in late spring and summer. Dinoflagellates largely dominated Crystal Bog throughout the ice-free period, specifically Peridiniopsis quadridens in the spring, Peridinium limbatum in summer, and Gymnodinium fuscum and P. quadridens in fall. Brief blooms of Cryptomonas, Dinobryon, and Synura occurred between periods of dinoflagellate domination. The dominant dinoflagellate, Peridinium limbatum, was calculated to have a growth rate of 0.065 day^–1 and a doubling time of 10.7 days. Heterotrophic nanoflagellates (HNFs) were a consistent component of the planktonic protozoa; seasonal patterns were determined for three genera of HNFs (Monosiga, Bicosoeca, and Desmarella moniliformis). Three genera of ciliates (Coleps, Strobilidium, and Strombidium) comprised the greater part of the planktonic protozoa in Crystal Bog. The number of species of planktonic protozoa was too low to calculate a diversity index. Shannon–Weaver diversity indices for phytoplankton and bacterioplankton in the epilimnion followed very similar seasonal patterns in this lake, supporting the hypothesis that in freshwaters, diversity patterns of these groups are linked.     

Dimethylsulfoniopropionate Turnover Is Linked to the Composition and Dynamics of the Bacterioplankton Assemblage during a Microcosm Phytoplankton Bloom

Processing of the phytoplankton-derived organic sulfur compound dimethylsulfoniopropionate (DMSP) by bacteria was studied in seawater microcosms in the coastal Gulf of Mexico (Alabama). Modest phytoplankton blooms (peak chlorophyll a [Chl a] concentrations of ~2.5 μg liter⁻¹) were induced in nutrient-enriched microcosms, while phytoplankton biomass remained low in unamended controls (Chl a concentrations of ~0.34 μg liter⁻¹). Particulate DMSP concentrations reached 96 nM in the enriched microcosms but remained approximately 14 nM in the controls. Bacterial biomass production increased in parallel with the increase in particulate DMSP, and nutrient limitation bioassays in the initial water showed that enrichment with DMSP or glucose caused a similar stimulation of bacterial growth. Concomitantly, increased bacterial consumption rate constants of dissolved DMSP (up to 20 day⁻¹) and dimethylsulfide (DMS) (up to 6.5 day⁻¹) were observed. Nevertheless, higher DMSP S assimilation efficiencies and higher contribution of DMSP to bacterial S demand were found in the controls compared to the enriched microcosms. This indicated that marine bacterioplankton may rely more on DMSP as a source of S under oligotrophic conditions than under the senescence phase of phytoplankton blooms. Phylogenetic analysis of the bacterial assemblages in all microcosms showed that the DMSP-rich algal bloom favored the occurrence of various Roseobacter members, flavobacteria (Bacteroidetes phylum), and oligotrophic marine Gammaproteobacteria. Our observations suggest that the composition of the bacterial assemblage and the relative contribution of DMSP to the overall dissolved organic sulfur/organic matter pool control how efficiently bacteria assimilate DMSP S and thereby potentially divert it from DMS production.     

长江口塔玛亚历山大藻孢囊的形成、发展及其与赤潮动力学的关系(英文)

The toxic dinoflagellate—Alexandrium tamarense (Lebour) Balech, formed resting cysts in f/2 media with low nitrate concentrations. Among the concentrations tested, f/20 NO3^- was the most effective to induction with an encystment percentage of 2.0 in batch culture. About 73.2% and 17.6% of cysts were produced on 8 and 9 d after transferring. Newly formed cysts developed accumulation body 3d later and kept forming mucilaginous substance, which might help their dispersal and survival. The mandatory dormancy period of resting cysts was 15 and 10d when stored at 15 and 20℃ respectively. The cysts could germinate without temperature change, with germination of 75.6% 20d after formation at 20℃. The Alexandrium cyst density in the surface sediment of DG-26 station reached above 25 cysts/g in May and November of 2002, and dropped to 4.5 and 0.9 cysts/g in August of 2002 and February of 2003, suggesting that Alexandrium cysts might have germinated in spring and autumn 2002. Cysts produced during the bloom returned to water column soon, whatever the season and water temperature were. The cyst density in the surface sediment at DG-26 station in May, 2003 was only 3.3 cysts/g and the cysts were newly formed. In the Yangtse River estuary, the inoculum size was not a major factor to determine the outbreak of A.tamarense bloom.     

Population Dynamics and Production of a Planktonic Marine Copepod,. Acartia clausii,in a Small Temperate Lagoon on San Juan Island,Washington

The population dynamics and production of Acartia clausii, a planktonic marine copepod, were studied during 1973 and 1974 in a small temperate lagoon. An approach which integrated laboratory and in situ experiments with time-series sampling of the field population was used to analyze seasonal changes in the parameters of population growth (development, growth, fecundity, and mortality) and to elucidate the processes which affect these changes. The objective of the study was to understand the factors which control the seasonal cycle of abundance. The cycles of abundance were similar in the two years of study and were not affected by differences in the cycles of tidal inflow, temperature, and food availability even though the latter two factors appreciably affected growth, development, and fecundity rates. The abundance cycle is controlled by an annually consistent pattern of copepodid and adult mortality believed to be due to predation by the three-spined stickleback, the dominant fish species in the lagoon. Cannibalism and periodic tidal stimulation of hatching of accumulated eggs in the sediment help to regulate population abundance within seasonal limits. Production by the lagoon population was 229 kg C for the entire study period; 84—88% of the annual production occurred from April through July. In the area of the lagoon greater than 3-m deep the mean daily productions during the peak months of each year were 70 and 55 mg C m⁻² for 1973 and 1974, respectively.     

Viral Lysis and Bacterivory during a Phytoplankton Bloom in a Coastal Water Microcosm

The relative importance of viral lysis and bacterivory as causes of bacterial mortality were estimated. A laboratory experiment was carried out to check the kind of control that viruses could exert over the bacterial assemblage in a non-steady-state situation. Virus-like particles (VLP) were determined by using three methods of counting (DAPI [4′,6-diamidino-2-phenylindole] staining, YOPRO staining, and transmission electron microscopy). Virus counts increased from the beginning until the end of the experiment. However, different methods produced significantly different results. DAPI-stained VLP yielded the lowest numbers, while YOPRO-stained VLP yielded the highest numbers. Bacteria reached the maximal abundance at 122 h (3 × 10⁷ bacteria ml⁻¹), after the peak of chlorophyll a (80 μg liter⁻¹). Phototrophic nanoflagellates followed the same pattern as for chlorophyll a. Heterotrophic nanoflagellates showed oscillations in abundance throughout the experiment. The specific bacterial growth rate increased until 168 h (2.6 day⁻¹). The bacterivory rate reached the maximal value at 96 hours (0.9 day⁻¹). Bacterial mortality due to viral infection was measured by using two approaches: measuring the percentage of visibly infected bacteria (%VIB) and measuring the viral decay rates (VDR), which were estimated with cyanide. The %VIB was always lower than 1% during the experiment. VDR were used to estimate viral production. Viral production increased 1 order of magnitude during the experiment (from 10⁶ to 10⁷ VLP ml⁻¹ h⁻¹). The percentage of heterotrophic bacterial production consumed by bacterivores was higher than 60% during the first 4 days of the experiment; afterwards, this percentage was lower than 10%. The percentage of heterotrophic bacterial production lysed by viruses as assessed by the VDR reached the highest values at the beginning (100%) and at the end (50%) of the experiment. Comparing both sources of mortality at each stage of the bloom, bacterivory was found to be higher than viral lysis at days 2 and 4, and viral lysis was higher than bacterivory at days 7 and 9. A balance between bacterial losses and bacterial production was calculated for each sampling interval. At intervals of 0 to 2 and 2 to 4 days, viral lysis and bacterivory accounted for all the bacterial losses. At intervals of 4 to 7 and 7 to 9 days, bacterial losses were not balanced by the sources of mortality measured. At these time points, bacterial abundance was about 20 times higher than the expected value if viral lysis and bacterivory had been the only factors causing bacterial mortality. In conclusion, mortality caused by viruses can be more important than bacterivory under non-steady-state conditions.     

Size-Dependent Chemosensory Responses to Familiar and Unfamiliar Conspecific Faecal Pellets by the Iberian Rock-Lizard, Lacerta monticola

We conducted a field study to analyse the social relationships between males of the Iberian rock lizard (Lacerta monticola). The degree of familiarity was determined based on the degree of overlap between their home ranges. We then designed a laboratory experiment to test whether the same males were able to discriminate between familiar and unfamiliar conspecifics using faecal pellet odours. Differential tongue‐flick rates suggest that large males (snout‐to‐vent length, SVL > 75 mm), at least, may discriminate between odours of familiar and unfamiliar males. The behavioural responses were dependent on relative differences in body size between the responding male and the male that donated the faecal pellet. Thus, as responding small males increased in size relative to their corresponding familiar male, their rate of tongue‐flicking significantly decreased; this was not the case in response to unfamiliar males. In contrast, there were no significant correlations between the response of large males to familiar or unfamiliar male stimuli, regardless of size differences. These results suggest that chemical cues contained in faecal pellets allow individual recognition in male L. monticola, and that the response depends on body size. We suggest that faecal pellets might be used to scent‐mark home ranges, which would contribute to lowering the costs of aggressive interactions.     

Substrate-Specific Clades of Active Marine Methylotrophs Associated with a Phytoplankton Bloom in a Temperate Coastal Environment

Marine microorganisms that consume one-carbon (C₁) compounds are poorly described, despite their impact on global climate via an influence on aquatic and atmospheric chemistry. This study investigated marine bacterial communities involved in the metabolism of C₁ compounds. These communities were of relevance to surface seawater and atmospheric chemistry in the context of a bloom that was dominated by phytoplankton known to produce dimethylsulfoniopropionate. In addition to using 16S rRNA gene fingerprinting and clone libraries to characterize samples taken from a bloom transect in July 2006, seawater samples from the phytoplankton bloom were incubated with ¹³C-labeled methanol, monomethylamine, dimethylamine, methyl bromide, and dimethyl sulfide to identify microbial populations involved in the turnover of C₁ compounds, using DNA stable isotope probing. The [¹³C]DNA samples from a single time point were characterized and compared using denaturing gradient gel electrophoresis (DGGE), fingerprint cluster analysis, and 16S rRNA gene clone library analysis. Bacterial community DGGE fingerprints from ¹³C-labeled DNA were distinct from those obtained with the DNA of the nonlabeled community DNA and suggested some overlap in substrate utilization between active methylotroph populations growing on different C₁ substrates. Active methylotrophs were affiliated with Methylophaga spp. and several clades of undescribed Gammaproteobacteria that utilized methanol, methylamines (both monomethylamine and dimethylamine), and dimethyl sulfide. rRNA gene sequences corresponding to populations assimilating ¹³C-labeled methyl bromide and other substrates were associated with members of the Alphaproteobacteria (e.g., the family Rhodobacteraceae), the Cytophaga-Flexibacter-Bacteroides group, and unknown taxa. This study expands the known diversity of marine methylotrophs in surface seawater and provides a comprehensive data set for focused cultivation and metagenomic analyses in the future.     

Structure and Dynamics of Veiled Virgin Olive Oil: Influence of Production Conditions and Relation to its Antioxidant Capacity

Structure and dynamics of the colloidal dispersions in veiled virgin olive oil (VVOO), the fresh olive juice, were for the first time investigated with different scattering techniques and related to the extraction conditions applied by the olive oil producers. VVOO samples were produced with either the three-phase extraction procedure (oil/externally added water) at different malaxation times, or by the dual-phase extraction procedure (no externally added water). Static light scattering (Small angle light scattering apparatus SALSA), dynamic light scattering, based on a 3D cross-correlation system, a flat cell and a red HeNe-Laser with 632,8 nm wavelength (3D-DLS), classical dynamic light scattering using a goniometer with cylindrical cells and a green laser with 532 nm wavelength, (Green-DLS), and small angle X-ray scattering (SAXS), are the scattering techniques that were used for the analysis of the samples. In addition, samples of VVOO were analyzed with a confocal microscope. SAXS technique gave almost the same results for all the samples of VVOO indicating comparable nano-structure due to the triglyceride backbone. When 3D-DLS and Green DLS were applied to the VVOO samples, quite different results were obtained. In addition, from the microscopic study of the VVOO samples discrete droplets but no anisotropic crystals could be observed. Finally, radical scavenging activity measurements applying Electron Paramagnetic Resonance spectroscopy showed that the antioxidant capacity of the veiled VVO was higher than the one of the filtered oils. Between the two oil extraction systems the dual phase one seems to be more appropriate for the production of stable and rich in minor constituents olive oils.     

Dynamics of Bacterial Community Composition and Activity during a Mesocosm Diatom Bloom

Bacterial community composition, enzymatic activities, and carbon dynamics were examined during diatom blooms in four 200-liter laboratory seawater mesocosms. The objective was to determine whether the dramatic shifts in growth rates and ectoenzyme activities, which are commonly observed during the course of phytoplankton blooms and their subsequent demise, could result from shifts in bacterial community composition. Nutrient enrichment of metazoan-free seawater resulted in diatom blooms dominated by a Thalassiosira sp., which peaked 9 days after enrichment (≈24 μg of chlorophyll a liter⁻¹). At this time bacterial abundance abruptly decreased from 2.8 × 10⁶ to 0.75 × 10⁶ ml⁻¹, and an analysis of bacterial community composition, by denaturing gradient gel electrophoresis (DGGE) of PCR-amplified 16S rRNA gene fragments, revealed the disappearance of three dominant phylotypes. Increased viral and flagellate abundances suggested that both lysis and grazing could have played a role in the observed phylotype-specific mortality. Subsequently, new phylotypes appeared and bacterial production, abundance, and enzyme activities shifted from being predominantly associated with the <1.0-μm size fraction towards the >1.0-μm size fraction, indicating a pronounced microbial colonization of particles. Sequencing of DGGE bands suggested that the observed rapid and extensive colonization of particulate matter was mainly by specialized α-Proteobacteria- and Cytophagales-related phylotypes. These particle-associated bacteria had high growth rates as well as high cell-specific aminopeptidase, β-glucosidase, and lipase activities. Rate measurements as well as bacterial population dynamics were almost identical among the mesocosms indicating that the observed bacterial community dynamics were systematic and repeatable responses to the manipulated conditions.     

Links between Phytoplankton and Bacterial Community Dynamics in a Coastal Marine Environment

Bacteria and phytoplankton dynamics are thought to be closely linked in coastal marine environments, with correlations frequently observed between bacterial and phytoplankton biomass. In contrast, little is known about how these communities interact with each other at the species composition level. The purpose of the current study was to analyze bacterial community dynamics in a productive, coastal ecosystem and to determine whether they were related to phytoplankton community dynamics. Near-surface seawater samples were collected in February, May, July, and September 2000 from several stations in the Bay of Fundy. Savin et al. (M.C. Savin et al., Microb Ecol 48: 51-65) analyzed the phytoplankton community in simultaneously collected samples. The attached and free-living bacterial communities were collected by successive filtration onto 5 m and 0.22 m pore-size filters, respectively. DNA was extracted from filters and bacterial 16S rRNA gene fragments were amplified and analyzed by denaturing gradient gel electrophoresis (DGGE). DGGE revealed that diversity and temporal variability were lower in the free-living than the attached bacterial community. Both attached and free-living communities were dominated by members of the Roseobacter and Cytophaga groups. Correspondence analysis (CA) ordination diagrams showed similar patterns for the phytoplankton and attached bacterial communities, indicating that shifts in the species composition of these communities were linked. Similarly, canonical CA revealed that the diversity, abundance, and percentage of diatoms in the phytoplankton community accounted for a significant amount of the variability in the attached bacterial community composition. In contrast, ordination analyses did not reveal an association between free-living bacteria and phytoplankton. These results suggest that there are specific interactions between phytoplankton and the bacteria attached to them, and that these interactions influence the composition of both communities.     

Sedimentary Losses in the Reservoir Saidenbach: Flux and Sinking Velocities of Dominant Phytoplankton Species

Sedimentation of phytoplankton was studied in the meso/eutrophic reservoir Saidenbach for two years and measured as biovolume in a sedimentation trap near the bottom. It comes to an annual average of 2.76cm³/m² × d (0.4… 10.9) and is statistically significant dependent on the free water concentration measured 14 days before. This allows flux to be reliably calculated without any direct measurement. The bottom is reached above all by diatoms which form 90% of the deposited algae. The sinking velocity of the diatoms is mainly determined by their physiological state: During growth phases low sinking velocities (0.1 … 2m/d) were found, while in decline phases they increased considerably (>6m/d). The highest average sinking velocities found among large diatoms were calculated for Fragilaria crotonensis (3…4m/d), the lowest for Melosira italica (1.5…2m/d). The values for Asterionella formosa, Synedra acus and Diatoma elongatum were between them. Turbulence has no influence on sinking velocity (usually, spring full circulation sees the highest sedimentary losses), but plays an essential part in the survival of the population in free water. Permanent redistribution prevents diatoms from sinking out from the euphotic layer, this “inoculation” making further development possible. On an annual average, phytoplankton forms approximately only one quarter of the whole trap sediment (max. 62%). The flux of the dry weight of seston (2.33g/m² x d on an average) reflects the changes in phytoplankton flux negligibly only and does not reveal any relation to it. so that seston flux is not suitable for determining phytoplankton sedimentation. But it is possible to calculate this at a probability of 65 to 94%, by using the free water concentration measured 14 days before.     

Primary Production of Phytoplankton in a Strongly Stratified Temperate Lake

Lake Verevi (12.6 ha, maximum depth 11.0 m, mean depth 3.6 m) is a strongly eutrophic and stratified lake. Planktothrix agardhii is the most characteristic phytoplankton species in summer and autumn, while photosynthesizing sulphur bacteria can occur massively in the metalimnion. Primary production (PP) and chlorophyll a concentration (Chl a) were seasonally studied in 1991, 1993, 2000, and 2001. Vertical distribution of PP was rather complex, having usually two peaks, one at or near the surface (0–1 m), and another deeper (at 3–7 m) in the metalimnion. The values of dark fixation of CO₂ in the metalimnion were in most cases higher than those in the upper water layer. Considering the average daily PP 896 mg C m⁻² and yearly PP 162 mg C m⁻², Secchi depth 2.34 m, and epilimnetic concentrations of chlorophyll a (19.6 mg m⁻³), total nitrogen and total phosphorus (TP, 52 mg m⁻³) in 2000, L. Verevi is a eutrophic lake of a ‘good’ status. Considering the total amounts of nutrients stored in the hypolimnion, the average potential concentrations in the whole water column could achieve 1885 mg m⁻³ of TN and 170 mg m⁻³ of TP reflecting hypertrophic conditions and a ‚bad’ status. Improvement of the epilimnetic water quality from the 1990s to the 2000s may have resulted from incomplete spring mixing and might not reflect the real improvement. A decreased nutrient concentration in the epilimnion has supported the establishment of a ‘clear epilimnion state’ allowing light to penetrate into the nutrient-rich metalimnion and sustaining a high production of cyanobacteria and phototrophic sulphur bacteria.     

Phytoplankton and Primary Production of Lakes in the Matamek Watershed,Quebec

The productivity of three Shield lakes on Quebec's North Shore was found to be comparable with that of the most oligotrophic lakes known. Factors contributing to this condition may be that the moderately sized lakes of this study are deep relative to their surface areas, highly stained by humic substances, of very low conductivity, and contain little dissolved CO₂. Standing crops of phytoplankton are very low, never exceeding 600 mg/m³. Chrysophyceae are dominant over all other classes of algae in both biomass and numbers, comprising approximately 50% of the fresh weight throughout the season. The abundance of micro-flagellates implies a large surface area to volume ratio and the ability to move are an advantage in a nutrient poor environment. Much of the phytoplankton present may grow heterotrophically and energy additions from the terrestrial environment may be extremely important to the productivity of northern lakes when photosynthetic production is not significant.     

Bacterioplankton cell growth and macromolecular synthesis in seawater cultures during the North Atlantic Spring Phytoplankton Bloom,May, 1989

We performed a series of seawater culture experiments on surface mixed layer samples during the spring phytoplankton bloom in the North Atlantic Ocean. Diluted (20% unfiltered + 80% 0.22 m filtered) and untreated whole seawater samples were incubated up to 40 hour and sampled periodically for cell numbers, biovolume, and incorporation of ³H-thymidine and -leucine. Abundance and biovolume increased exponentially at similar rates in diluted and whole samples, suggesting that removal by bacteriovores was low compared with growth. The exponential increase in biovolume was due to increases in cell numbers and mean cell volume. Generation times (i.e., 0.693/) averaged 36–53 hour in these surface (10 m) samples. Ninety percent of the tritiated thymidine incorporation (TTI) into cold trichloroacetic acid-insoluble cell fractions was recovered after extraction with NaOH and phenolchloroform, indicating that catabolism of thymidine and its appearance in RNA or protein was very low. The percentage of thymidine recovered in DNA did not change over the 40 hour of incubation and was the same as in water column samples. Rates of thymidine and leucine incorporation also increased exponentially. Incorporation rates tended to increase more rapidly than cell numbers or biovolume, though the differences were not significantly different, due to the small number of samples and variability over the time courses. Differential rates of increase in cellular properties during growth might indicate a lack of coupling between incorporation and production over time scales of hours-days. This in turn may reflect unbalanced growth of bacterial assemblages, which is an adaptation to variable conditions in the upper ocean in this season. Nonequality of rate constants for cells and incorporation yields conversion factors that are either higher or lower than would be calculated from balanced growth (i.e., rates of increase in numbers and incorporation rates equal), depending on the calculation approach chosen. An alternative approach to calculating conversion factors (the modified derivative approach) is proposed, which is insensitive to differential rates of increase of abundance and incorporation.     

Growth Characteristics of the Thermophilic Fungus Scytalidium thermophilum in Relation to Production of Mushroom Compost

Scytalidium thermophilum is an important thermophilic fungus in the production of mushroom compost. I investigated the characteristics of this organism and present a simple model with which fungal growth in compost can be described. The model is used to predict better circumstances for rapid indoor production of mushroom compost. I conclude that inoculation of the starting material with prepared compost either before or after the pasteurization phase has only a minor effect on the shortening of the composting process. This is because the initial growth rate of the fungus is much higher than its growth rate later. A lower temperature (53.5°C instead of the usual 56 to 58°C) during the pasteurization phase may be most profitable for rapid compost production; such a temperature may reduce the time that is needed for the last phase of the production process by at least 1 day.     

Ice Nucleus Production of Fusarium moniliforme var. subglutinans in Relation to Its Growth Characteristics

The effects of culture conditions on the ice nucleus production of Fusarium moniliforme var. subglutinans isolated from the gut of larvae of the rice stem borer (Chilo suppressalis Walker) were examined. The ice nucleus production was only affected by cultivation temperature and pH: the optimum temperature and pH were 15°C to 20°C and 4.0 to 6.0, respectively.