Relationships between biovolume and carbon and nitrogen content of bacterioplankton

Abstract Cell volume, carbon and nitrogen content were determined for bacteria grown in batch cultures in water samples collected at five localities in western Florida, USA. Cultures were set up by inoculating 0.2 μm filtered water with 2.5 to 7.0% of 1.0 μm filtered water. Biovolumes of the bacteria were measured by epifluorescence photomicrography. Bacterial carbon and nitrogen contents were determined with a CHN analyser. During incubations, bacterial volumes doubled from 0.070±0.037 μ m³(mean ± S.E.) to 0.153 ± 0.036 μ m³ at early stationary phase. Bacterial C:N ratios ranged between 2.8 and 10.3, with a mean of 6.5, and were inversely correlated with cell volumes. Conversion factors for volume to carbon and nitrogen content were relatively high and variable, ranging from 0.21 to 161 pg C μm⁻³ (mean: 0.72 pg C μm⁻³) and from 0.05 to 0.25 pg N μm⁻³ (mean: 0.12 pg N μm⁻³). Small cells contained more C and N per unit volume than did large cells. The data suggested that biovolume to biomass conversion factors may be higher than previously thought and may be highly variable both temporally and geographically.     

Size-selective grazing on bacteria by natural assemblages of estuarine flagellates and ciliates

The small average cell size of in situ bacterioplankton, relative to cultured cells, has been suggested to be at least partly a result of selection of larger-sized cells by bacterivorous protozoa. In this study, we determined the relative rates of uptake of fluorescence-labeled bacteria (FLB), of various cell sizes and cell types, by natural assemblages of flagellates and ciliates in estuarine water. Calculated clearance rates of bacterivorous flagellates had a highly significant, positive relationship with size of FLB, over a range of average biovolume of FLB of 0.03 to 0.08 microns3. Bacterial cell type or cell shape per se did not appear to affect flagellate clearance rates. The dominant size classes of flagellates which ingested all types of FLB were 3- to 4-microns cells. Ciliates also showed a general preference for larger-sized bacteria. However, ciliates ingested a gram-positive enteric bacterium and a marine bacterial isolate at higher rates than they did a similarly sized, gram-negative enteric bacterium or natural bacterioplankton, respectively. From the results of an experiment designed to test whether the addition of a preferentially grazed bacterial strain stimulated clearance rates of natural bacterioplankton FLB by the ciliates, we hypothesized that measured differences in rates of FLB uptake were due instead to differences in effective retention of bacteria by the ciliates. In general, clearance rates for different FLB varied by a factor of 2 to 4. Selective grazing by protozoa of larger bacterioplankton cells, which are generally the cells actively growing or dividing, may in part explain the small average cell size, low frequency of dividing cells, and low growth rates generally observed for assemblages of suspended bacteria.     

The Contribution of Ciliated Protozoa to Plankton and Benthos Biomass in a European Ricefield

The densities and biomass of ciliates inhabiting the water-sediment interface and the water column of an experimental ricefield were investigated throughout four annual cycles. Ciliate abundance and biomass were higher at the water-sediment interface than in the water column. In both sites, large ciliates (> 10⁵μm³) contributed the higher biomass values, but the highest densities were found in the intermediate size class (10⁴-10⁵μm³). The prorodontid Coleps hirtus dominated the ciliate assemblage and usually comprised > 50% of total ciliate density. Blooms of C. hirtus , occurred in June in the water column and in July at the sediment surface. During the four cycles of rice cultivation, the average daily values for production of the entire ciliate community was 69.6 mgC/m²/d, and the net production efficiency (K₂) was 72.0%. The estimated production values in the present study are high if compared to production measured for ciliates in other freshwater ecosystems.     

The cytotoxic and photodynamic inactivation of micro-organisms by Rose Bengal

Rose Bengal was cytotoxic to the following bacteria at the concentrations given in parentheses (highest concentrations of dye in mol/1 at which growth occurred on nutrient medium): Brochothrix thermosphacta and Deinococcus radiodurans (1 times 10^-6 or less); Streptococcus, Micrococcus, Staphylococcus, Bacillus, Arthrobacter and Kurthia spp. (1 times 10^-5–1 x 10^-4), and Pseudomonas spp. and Enterobacteriaceae (5 times 10^-3–1 x 10^-2 or greater). These organisms were killed rapidly when suspended in illuminated (170 μE/m²/s) solutions of Rose Bengal (1 times 10^-4 mol/1) providing oxygen was present. Singlet oxygen was identified as the lethal agent, because the rate of killing was increased by dissolving the dye in deuterium oxide while the organisms were protected against photoinactivation by L-histidine or crocetin. Yeasts from chilled foods were killed in illuminated solutions of Rose Bengal but a light intensity of 315 μE/m²/s was needed for a death rate comparable with that of bacteria. The yeasts present in a range of chilled meat and dairy products failed to form colonies on Rose Bengal (5 times 10^-5 mol/1) media exposed continuously to modest illumination (55–80 μE/m²/s).     

Effects of light and temperature on the cell size and some biochemical components in two freshwater cryptophytes

The effects of light and temperature on cell size and cellular composition (chlorophyll, protein, carbohydrate) of two freshwater cryptophytes were studied with batch cultures. Neither of the species had a constant cell size but the size varied with growth conditions. At each temperature the smallest cells were recorded at the lowest experimental photon flux density. The smallest cells of Cryptomonas 979/67 had an average volume of 232 μm³ and the largest ones 1 020 μm³. In Cryptomonas 979/62 the smallest and largest cells measured 4 306 μm³ and 12 450 μm³. Both species increased their cellular chlorophyll content when PFB dropped below 110–120 μmol m^-2 s^-1. The highest and lowest chlorophyll contents of 979/67 were 7.45 fg μm^-3 and 0.55 fg μm^-2 respectively. For 979/62 the corresponding values were 10.23 fg μm^-3 and 0.93 fg μm^-3. In both species the protein content remained stable at PFDs higher than 110–120 μmol m^-2 S^-1. The highest content of protein measured in 979/67 was 638 fg μm^-3 and the lowest 147 fg μm^-3. For 979/62 these values were 1 036 fg μm^-3 and 148 fg μm^-3 respectively. The carbohydrate results were less clear and no pattern either in response to photon flux density or temperature was obvious. The lowest and highest contents recorded for 979/67 were 62 fg μm^-3 and 409 fg μ^-3 and for 979162, 36 fg μm^-3 and 329 fg μm^-3     

Bacterivory by the ciliate Euplotes in different states of hunger

Abstract: The feeding of the marine ciliate Euplotes mutabilis was studied using bacteria ( Vibrio natriegens ) doubly labelled with ³H-thymidine and ¹⁴C-leucine. In the presence of abundant bacteria (30 × 10⁶ bacteria ml⁻¹), an average Euplotes cell (initially without food vacuoles) with a protein content of 12 ng consumed 16 × 10³ bacteria in the first hour and 27 × 10³ bacteria over four hours, accumulating about 60% of the bacterial protein into ciliate macromolecules. Euplotes which had been starved or under-fed to reduce cell protein biomass to 7 or 9 ng consumed significantly fewer bacteria, but the gross growth efficiency for protein did not change. The rate of consumption of bacteria by large Euplotes of protein content 15 ng was initially less than that of 12 ng cells, and it decreased markedly before the end of a 4-hour experiment. Recently divided cells ingested bacteria rapidly, but showed a reduced gross growth efficiency of about 40%. At low bacterial concentrations (6 × 10⁶ bacteria ml⁻¹) the rates of ingestion were markedly reduced to between     and     of maximal levels; the smallest cells could not sustain feeding activity at the low prey concentration and gross growth efficiency fell from 43 to 20% during a 4-hour experiment. The strategy adopted by Euplotes in response to local fluctuations in food supply involves rapid consumption with high growth efficiency in times of plenty, but slow shrinkage without cell division to survive in times of shortage.     

Competition between anoxygenic phototrophic bacteria and colorless sulfur bacteria in a microbial mat

Abstract The populations of chemolithoautotrophic (colorless) sulfur bacteria and anoxygenic phototrophic bacteria were enumerated in a marine microbial mat. The highest population densities were found in the 0–5 mm layer of the mat: 2.0 × 10⁹ cells cm⁻³ sediment, and 4.0 × 10⁷ cells cm⁻³ sediment for the colorless sulfur bacteria and phototrophs, respectively. Kinetic parameters for thiosulfate-limited growth were assessed for Thiobacillus thioparus T5 and Thiocapsa roseopersicina M1, both isolated from microbial mats. For Thiobacillus T5, growing at a constant oxygen concentration of 43 μmol l⁻¹, μ_max was 0.336 h⁻¹ and K _s 0.8 μmol l⁻¹. Phototrophically grown Thiocapsa strain M1 displayed a μ_max of 0.080 h⁻¹ and a K _s of 8 μmol l⁻¹ when anoxically grown under thiosulfate limitation. In a competition experiment with thiosulfate as electron donor, Thiocapsa became dominant during a 10-h oxic/14-h anoxic regimen at continuous illumination, despite the higher affinity for thiosulfate of Thiobacillus .     

A cytological characterization of the parasitic action of ultramicrobacteria NF1 and NF3 of the genus Kaistia on chemoorganotrophic and phototrophic bacteria

Two strains (NF1 and NF3) of free-living chemoorganotrophic bacteria have been isolated from multiyear oil slime and Pedilanthus tithymaloides rhizosphere and ascribed to the genus Kaistia of the class Alphaproteobacteria on the basis of the nucleotide sequences of 16S rRNA gene and phenotypic characteristics. These strains can be assigned to ultramicrobacteria as their populations are represented by two subpopulations: (1) ultrasmall cells, on average 200–300 nm in diameter and <0.1 μm³ in volume, of up to 60% of the total number of cells in a population, and (2) cells 400–800 nm in diameter and 0.15–0.5 μm³ in volume, of up to 40% of the total number of cells in a population. The interaction of the isolated ultramicrobacteria strains (IUMB) with different bacterial species has been studied in cocultures grown under starvation and in complete nutrient media. It has been found that IUMB can be facultative parasites on certain species of chemoorganotrophic and phototrophic bacteria. The interaction of IUMB with prey bacteria exhibits the extracellular type of parasitism and involves establishing stable cell–cell contacts between the parasites and their prey to cause destruction of host cells.     

Microbial community structure in autotrophic nitrifying granules characterized by experimental and simulation analyses

This study evaluates the community structure in nitrifying granules (average diameter of 1600 μm) produced in an aerobic reactor fed with ammonia as the sole energy source by a multivalent approach combining molecular techniques, microelectrode measurements and mathematical modelling. Fluorescence in situ hybridization revealed that ammonia-oxidizing bacteria dominated within the first 200 μm below the granule surface, nitrite-oxidizing bacteria a deeper layer between 200 and 300 μm, while heterotrophic bacteria were present in the core of the nitrifying granule. Presence of these groups also became evident from a 16S rRNA clone library. Microprofiles of NH₄⁺, NO₂^–, NO₃^– and O₂ concentrations measured with microelectrodes showed good agreement with the spatial organization of nitrifying bacteria. One- and two-dimensional numerical biofilm models were constructed to explain the observed granule development as a result of the multiple bacteria–substrate interactions. The interaction between nitrifying and heterotrophic bacteria was evaluated by assuming three types of heterotrophic bacterial growth on soluble microbial products from nitrifying bacteria. The models described well the bacterial distribution obtained by fluorescence in situ hybridization analysis, as well as the measured oxygen, nitrite, nitrate and ammonium concentration profiles. Results of this study are important because they show that a combination of simulation and experimental techniques can better explain the interaction between nitrifying bacteria and heterotrophic bacteria in the granules than individual approaches alone.     

A Description of Occurrence and Morphology of a New Species of Red-Water Forming Strombidium (Spirotrichea, Oligotrichia)

We describe a red-water ciliate, Strombidium lingulum n. sp., collected from a marine fjord in British Columbia (BC), Canada. In August, 1995, red-brown streaks were observed in the waters of Kyuquot Sound. BC. These streaks were composed of a ciliate population with an abundance in the surface of ˜ 1.5 × 10³ cells ml^-1. Density was reduced to < 50 cells ml^-1 below the surface. The bloom persisted for only a few hours; cells were observed for 3-4 days and were only occasionally observed in the weeks after the bloom. The red waters were speculated to be formed by a combination of downwelling events and an observed phototactic migration of the ciliate. As the ciliate was positively phototactic and pigmented, it may be mixotrophic; it was certainly heteroirophic, as it contained dinoflagellates and small ciliates in food vacuoles. Ciliates were preserved in Lugol's iodine and then both protargol stained and prepared for scanning electron microscopy.     

Short-term thermal acclimation induces adaptive changes in the inner mitochondrial membranes of fish skeletal muscle

In the oxidative muscles (musculi laterales superficiales) of crucian carp Carassius carassius acclimated for 6 weeks to either 5 or 25° C, the volume density and the surface density of fibres per tissue did not differ significantly between the control and experimental groups. The correlation ratio (μ²) for these values was below 50, 39·3 and 43·9 respectively. After acclimation to 5° C, the surface density of outer mitochondrial membrane per fibre increased significantly from 0·93 to 1·23m² cm⁻³ in the summer population but dropped from 0·94 to 0·67 m² cm⁻³ in the winter population. The surface density of outer mitochondrial membrane per mitochondrion increased from 3·24 to 4·52 m² cm⁻³ in summer fish. After acclimation to 25° C, the surface density of inner mitochondrial membranes per muscle fibre decreased from 4·04 to 1·79 m² cm⁻³ in summer fish and from 3·86 to 1·07 m² cm⁻³ in winter fish. The surface density of inner mitochondrial membranes per mitochondrion increased from 14·17 to 15·60 m²cm⁻³ in summer fish but dropped from 13·91 to 10·67 m² cm⁻³ in winter fish. Correlation matrices demonstrate a negative correlation of the surface density of outer mitochondrial membrane per mitochondrion with the volume density of mitochondria per fibre and temperature, suggesting cold-induced proliferation of small mitochondria. It was concluded that short-term cold acclimation increased surface area of the inner mitochondrial membranes in summer fish.     

Photoautotrophic growth in suspension culture of cells from the moss, Barbula unguiculata

Chlorophyllous cells in suspension culture from the moss, Barbula unguculata Hedw., grown under photoheterotrophic conditions were transferred to photoautotrophic conditions. The cells started to grow photoautotrophically without selection. Maximum growth was observed under irradiances of more than 5 W m² and in an atmosphere enriched with 1% (v/v) CO₂. Under optimum growth conditions, dry weight and chlorophyll content in the culture had increased 20-fold after 20 days of cell growth. High concentration of chlorophyll [10–20 μg (mg dry weight)⁻¹] and high photosynthetic actively [30–70 μmol O₂ evolved (mg chlorophyll)⁻¹ h⁻¹] were observed throughout the culture period. In sugar-free culture medium, cell growth did not occur in the dark or in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) under light, although cell growth was observed in glucose-containing medium under those conditions. When cells that were grown photoautotrophically for one year were transferred to glucose-containing medium under ordinary air, they started to grow heterotrophically both in the light and in the dark.     

GROWTH OF HETEROSIGMA CARTERAE (RAPHIDOPHYCEAE) ON NITRATE AND AMMONIUM AT THREE PHOTON FLUX DENSITIES: EVIDENCE FOR N STRESS IN NITRATE-GROWING CELLS

The marine alga Heterosigma carterae Hulburt (Raphidophyta) was grown in N-limiting batch cultures using either nitrate or ammonium as the N source, at photon flux densities (PFDs) of 50, 200, and 350 μmol·m^-2·s^-1 in a 12:12 h LD cycle. Carbon content could be estimated from biovolume (μg C = 0.278 × nL; R = 0.98) but not reliably from pigment content. During exponential growth, ammonium-grown cells (in comparison with nitrate-grown cells at the same PFD) attained higher growth rates by at least 20%, contained more N, and had a lower C:N ratio, higher concentrations of intracellular free amino acids, and higher ratios of glutamine: glutamate (Gln: Glu) and asparagine: aspartate (Asn:Asp). Growth was nearly light-saturated on ammonium at 200 μmol·m^-2·s^-1 (cell-specific growth rate of 1.2 d^-1) but probably not saturated in nitrate-grown cells at 350 μmol·m^-2·s^-1. PFD did not affect Gln: Glu or Asn: Asp for a given N source. These results indicate that the nitrate-growing cells were more N-stressed than those using ammonium (which in contrast were relatively C-stressed) and that this organism would show an enhanced competitive advantage against other species when supplied with a transient supply of ammonium rather than nitrate .     

Ultrastructural Study of Golgi Duplication in Trypanosoma brucei

Golgi duplication in the protozoan parasite Trypanosoma brucei has been tracked using serial thin section three-dimensional reconstructions of transmission electron micrographs. The old Golgi maintains a constant size (∼0.060 μm³) throughout the cell cycle. A morphologically identifiable new Golgi appears at ∼0.20 of the cell cycle (defined by the size of the nucleus and lasting about 9 h) and grows from ∼0.018 μm³ until it is the same size as the old Golgi (by ∼0.55 of the cell cycle). Morphologically identifiable late Golgi appear at ∼0.58 of the cell cycle, but their volume (∼0.036 μm³) did not change significantly. Cryoimmunoelectron microscopy was used to identify candidates for the earliest new Golgi structures, and these comprised clusters of vesicles containing Golgi reassembly stacking protein (GRASP) near an endoplasmic reticulum exit site. These results, combined with earlier fluorescence data, suggest that the new Golgi begins functioning before cisternal stacks are formed.     

Bacterivory by starved marine heterotrophic nanoflagellates of two species which feed differently, estimated by uptake of dual radioactive-labelled bacteria

Abstract: The rates of ingestion of bacteria and of accumulation of bacterial biomass by hungry Pteridomonas danica and Paraphysomonas imperforata were measured using dual radioactive-labelled bacteria in experiments lasting 4–8 h. Pteridomonas continuously consumed 4–5 bacteria h⁻¹ throughout experiments lasting 8 h, irrespective of bacterial concentration above a threshold of about 5 × 10⁵ bacteria ml⁻¹, and continued to catch bacteria even below this density. The clearance rate of about 1 nl cell⁻¹ h⁻¹ at higher bacterial concentrations increased three or four times as bacterial numbers fell. Paraphysomonas cells, with only half the biomass of Pteridomonas , ingested up to 10 bacteria h⁻¹ at high bacterial concentrations, and gradually reduced the feeding rate, effectively ceasing to feed at 10⁶ bacteria ml⁻¹; their initial clearance rate of 1–2.5 nl cell⁻¹ h⁻¹ subsequently fell as low as 0.1 nl cell⁻¹ h⁻¹. Estimation of feeding rate by extrapolation from short-term experiments on such flagellates requires extreme caution. These flagellates, starved to levels typical of the natural environment, accumulated ingested bacterial biomass at an efficiency of between 16 and 21%, indicating that in nature they would recycle 80% or more of the nutrients contained in their food.     

Comparisons of the diets and reproductive performances of two sympatric rotifers, Asplanchna girodi and Asplanchna priodonta

SUMMARY. 1. Diet composition and the production of embryos were measured in Asplanchna girodi and Asplanchna priodonta collected through 3 years in the San Joaquin-Sacramento delta of California. The two species are sympatric in low to moderate densities for 5 months of the year.
2. Despite marked differences in the structure of the trophi, both species consumed the same array of prey species. Percentage composition of the diet varied both intra- and interspecifically. The food niches of the two species appear to differ little from one another.
3. Individuals of Asplanchna girodi had a larger mean number of prey in the gut per individual than did those of A. priodonta , due to their larger size. Per unit volume, each species prey gathering performance was the same. Asplanchna priodonta produced more embryos per calculated unit volume of prey ingested than did A. girodi .
4. During spring, when both species were present in the plankton, A. priodonta did not capture Size Class 2 and 5 animals (volumes 0.09–1.0 μm³×10⁶ and 3.0–3.5 μm³X10⁶ respectively) nor large Synchaeta . Both these prey classes were in the diet during the summer and autumn months. Several hypotheses are examined as possible explanations for this phenomenon.     

Growth of thermophilic obligately autotrophic hydrogen-oxidizing bacteria on thiosulfate

Thermophilic obligately autotrophic H₂-oxidizing bacteria from Icelandic hot springs were tested for growth on thiosulfate. Ten strains were tested and all grew on thiosulfate but not on sulfite or sulfur. The product of thiosulfate oxidation was sulfate. The growth rate on thiosulfate was slower (μ=0.12 h^-1) than on H₂ (μ=0.34 h^-1). Washed cells which had been grown on thiosulfate could oxidize thiosulfate rapidly but H₂-grown cells oxidized thiosulfate much more slowly and with about a 3 h lag time. The bacteria would not grow on agar medium under H₂ but grew on agar medium containing thiosulfate.     

Taxonomic composition and biomass of heterotrophic flagellates in relation to lake trophy and season

1. Taxonomic composition and abundance of heterotrophic flagellates (HF) were studied in 55 lakes with different trophy in northern Germany using a live-counting technique.
2. Mean abundances and biomasses of HF ranged from 169 cells L⁻¹ and 22 μg L⁻¹ in mesotrophic lakes to 2439 cells mL^–1 and 475 μg L⁻¹ in hypertrophic lakes, respectively. Highest values were generally observed in spring, but mesotrophic lakes showed maximum values in early summer.
3. The taxonomic composition of HF was not significantly influenced by lake trophy and season. The major fraction of HF consisted of chrysomonads and Protista incertae sedis; other important groups were choanoflagellates and bicosoecids. The size distribution of HF changed with lake trophy and season, with a higher proportion of large HF (> 10 μm) in hypertrophic lakes and in spring, respectively.
4. Correlation analyses revealed a strong negative impact of cladocerans on total HF biomass and especially on large HF. Ciliates and large bacteria (> 10 μm) were strongly positively correlated with HF biomass; small bacteria (< 2 μm) showed a weak positive correlation.
5. Analyses at the level of species and genera revealed distinct distribution patterns of some taxa. Paraphysomonas , Aulacomonas and Quadricilia as large-bodied HF showed highest abundance in hypertrophic lakes and in spring. Attached taxa (e.g. Monosiga , Salpingoeca amphoridium ) were highly abundant in late summer and autumn, whereas Spumella and Kathablepharis occurred frequently in most samples.     

The regulation of Mn2+ and Cu2+ uptake in cells of the yeast Candida utilis grown in continuous culture

Abstract Transport of Mn²⁺ was repressed in Candida utilis cells grown in continuous culture in high-Mn²⁺ (100 μM Mn²⁺) medium as compared to cells grown in basic (0.45 μM Mn²⁺) and low-Mn²⁺ (< 0.05 μM Mn²⁺) media. In contrast, no repression of Cu²⁺ uptake occurred in high-Cu²⁺-grown (25 μM Cu²⁺) cells as compared to cells grown in basic medium (0.54 μM Cu²⁺). Cu²⁺-limited cells did not hyperaccumulate Cu²⁺ and there was not significant difference in initial uptake rates for all 3 Cu²⁺ conditions. Mn²⁺ uptake appears to be regulated by a mechanism sensitive to the external Mn²⁺ concentration, whereas Cu²⁺ transport is not governed in this way by the external Cu²⁺.     

Heterotrophic bacterioplankton production and grazing mortality rates in an Ethiopian rift-valley lake (Awassa)

SUMMARY. 1. Heterotrophic bacterioplankton growth and production rates were estimated in a tropical lake by various methods. Mean growth rates, determined by tritiated thymidine incoporation into DNA, frequency of dividing cells and increase in cell density varied between 0.013 and 0.014 (with a range of 0.006–0.026) h⁻¹ corresponding to bacterial production of 1.16–1.22 (0.34–3.63) mg C m⁻³ h⁻¹.
2. Heterotrophic bacterial production estimated from oxygen and inorganic carbon consumption in the dark were compared with these values. The oxygen method gave similar results, while values from dark carbon uptake were as much as 2.5 times higher.
3. Although the different estimates of rates of bacterial production showed different patterns, the existence of spatial (vertical) and temporal (diel and seasonal) variation was demonstrated. Bacterial production was 13–41% of the net primary production and 10–30% of gross primary production.
4. Bacterial grazing mortality rate was estimated from size-fractionation and metablic inhibitor experiments. Average grazing rates were between 0.34 and 3.77 mg C m⁻³ h⁻¹ corresponding to 76–120% of the mean bacterial production rate. Organisms 1–12 μm in size, possibly mainly ciliates. were implicated as important bacterial grazers.