Seasonal development of hypolimnetic ciliate communities in a eutrophic pond

Abstract The ciliated protozoan communities in the hypolimnion of a highly produtive pond were investigated over two years. Three physiological groups could be distinguished: stratified water column; (b) anaerobic ciliates with endosymbiotic methanogens; and (c) anaerobes without endosymbiotic methanogens. Both groups of anaerobes were confined to the anoxic zone of the hypolimnion. Community biomass was dominated by microaerobic ciliates which had on average 20 times larger cells than anaerobic ciliates. Abundance and biomass of microaerobic ciliates decreased over the summer, while anaerobic ciliates increased. This reflected a spatial shift in the availability of inorganic nutrients and, as a result, of ciliate food from the epi- and metalimnion to the hypolimnion. The low biomass production of anaerobic ciliates was consistent with the low theoretical growth efficiency of anaerobic metabolism. Ciliate species displayed characteristic spatial and seasonal distribution patterns within the water column which were similar in both years investigated. Spatial and temporal distribution was mainly governed by two factors: (1) the distribution of dissolved oxygen; and (2) the availability of food. Distribution patterns were not related to chemical gradients other than the oxygen gradient, but they were correlated with the distribution of major food sources.     

Depth Distribution of Bacterial Production in a Stratified Lake with an Anoxic Hypolimnion

The purpose of this study was to determine the depth distribution of bacterial biomass and production in a stratified lake and to test techniques to measure bacterial production in anaerobic waters. Bacterial abundance and incorporation of both [³H]thymidine and [³H]leucine into protein were highest in the metalimnion, at the depth at which oxygen first became unmeasurable. In contrast, [³H]thymidine incorporation into DNA was highest in the epilimnion. The ratios of incorporation into DNA/protein averaged 2.2, 0.49, and 0.95 for the epilimnion, metalimnion, and hypolimnion, respectively. Low incorporation into DNA was not due to artifacts associated with the DNA isolation procedure. Recovery of added [³H]DNA was about 90% in waters in which the portion of [³H]thymidine incorporation into DNA was about 40%. At least some obligate anaerobic bacteria were capable of assimilating thymidine since aeration of anaerobic hypolimnion waters substantially inhibited thymidine incorporation. The depth profile of bacterial production estimated from total thymidine and leucine incorporation and the frequency of dividing cells were all similar, with maximal rates in the metalimnion. However, estimates of bacterial production based on frequency of dividing cells and leucine incorporation were usually significantly higher than estimates based on thymidine incorporation (using conversion factors from the literature), especially in anaerobic hypolimnion waters. These data indicate that the thymidine approach must be examined carefully if it is to be applied to aquatic systems with low oxygen concentrations. Our results also indicate that the interface between the aerobic epilimnion and anaerobic hypolimnion is the site of intense bacterial mineralization and biomass production which deserves further study.     

Sedimentation and breakdown kinetics of organic matter in the anaerobic zone of Lake Vechten

The turnover and exchange rates, as well as the sedimentation rates concerning the input and output of carbon in the anaerobic hypolimnion and the sediment in Lake Vechten were studied. The carbon input data were derived from those on sedimentation. By comparison of C-fixation data, sedimentation rates measurements and microbial reduction rates of observed fluxes of electron acceptors a mineralization of 20–30% of the limnetic C-fixation was found in the hypolimnion. The rate-limiting step of methanogenesis in anaerobic mineralization is the breakdown of algal cell wall components to their main product, namely acetate. This intermediate has a relatively fast turnover rate to the end-products, namely the gases CH₄ and CO₂. Finally, from the data on the diffusion of low-molecular weight metabolic intermediates and on the rates of formation of CH₄ and CO₂ the output of carbon and its cycling in Lake Vechten are discussed.     

Studies on ciliated protozoa in eutrophic lakes: 2. Field and laboratory studies on the effects of oxygen and other chemical gradients on ciliate distribution

An investigation into the spatial distribution of hypolimnetic ciliates in three small eutrophic lakes during the period of summer stratification was carried out. Peak ciliate densities were found to occur at the oxic/anoxic boundary, ciliate numbers declining with increasing depth within the hypolimnion. The ciliates only occurred in aerobic water where oxygen levels were less than about 0.5 mgl^–1 Laboratory experiments demonstrated that the ciliates swim upwards under anaerobic conditions but swim rapidly downwards under aerobic conditions. Further laboratory experiments showed that although the bulk of the population occured within anaerobic water, the hypolimnetic ciliates are aerobes and cannot survive indefinite anoxia. Despite the demonstrable toxicity of high levels of ammonia and sulphide, it was probably excesive distance from an available source of oxygen that excluded the ciliates from the lowest levels of the hypolimnion. Possible mechanisms which allowed these aerobic ciliates to colonise anaerobic water are considered.     

Thymidine incorporation in Lake Cisó: Problems in estimating bacterial secondary production across oxic-anoxic interfaces

Abstract Heterotrophic bacterial activity was measured by means of the ³H-thymidine (³H-TdR) incorporation technique in Lake Cisó, a small holomictic lake with anoxic hypolimnion. We tested several methodological questions across the vertical profile: TdR concentration at which maximal incorporation is reached, linearity of incorporation and isotope dilution, during holomixis and stratification periods. The TdR concentration at which maximal incorporation is reached changed seasonally and vertically. During holomixis, maximal incorporation was not always reached at concentrations up to 40 nM. Uptake was always linear in short incubation times and decreased from epi- to hypolimnion. The isotope dilution technique indicated a degree of participation in DNA synthesis higher than 50%, although a linear relationship between the inverse of ³H-TdR incorporation and increasing ‘cold’ thymidine concentration was not always observed. Autoradiographic experiments showed a low percentage of bacteria taking up ³H-TdR in both aerobic and anaerobic samples. The percentage of total labeled bacteria seemed to be generally higher in the metalimnion (11% maximal value) than in the hypolimnion. Labeled Amoebobacter and Chromatium cells were detected in field samples. Amoebobacter cells photoassimilated TdR in culture. Therefore, our results show that ³H-TdR incorporation is not an appropriate technique to estimate bacterial secondary production in anaerobic systems and in oxic-anoxic interfaces.     

LETTER TO THE EDITOR

SUMMARY

A two-year limnological survey between 1973 and 1975 showed that the Roodeplaat Dam is a warm monomictic impoundment which has stable thermal stratification during summer. Oxygen supersaturation of the surface waters and anaerobic conditions in the hypolimnion were encountered during summer. Water transparency was seasonal and related to existing phytoplankton populations and allochthonously-introduced clay material. Chemical stratification during summer was prominent and appeared to be caused not only by mineralization processes in the hypolimnion, but also by dilution in the surface layers during summer flooding. Because of the morphometry of the impoundment and the fact that sewage effluents are discharged into the major inflow, considerable horizontal variation in most chemical and biological characteristics was found. On the basis of the nutrient content of the waters and the magnitude of the phytoplankton populations observed, Roodeplaat Dam may be classified as a highly eutrophic water body.     

The relationship between planktonic algae and bacteria in a small lake

The seasonal changes and vertical distribution of the aerobic and anaerobic bacteria in a small edaphically eutrophic lake which exhibited thermal and chemical stratification are described. There was some correspondence between the phytoplankton and particularly the aerobic bacteria but this was not consistent. Increases in the numbers of anaerobic bacteria coincided with the low dissolved oxygen concentrations in the hypolimnion when algal populations were first senescent and then increasing actively in size.     

Effects of temperature and light on the growth and geosmin production of Lyngbya kuetzingii (Cyanophyta)

The effects of temperature and light on the growth and geosmin production of Lyngbya kuetzingii were determined. Of the three temperatures tested, 10, 25 and 35°C, the maximal geosmin concentration and geosmin productivity were yielded at 10°C, while the highest chl a production was observed at 25°C. In the studies on light intensity, the maximal geosmin concentration and geosmin productivity were observed at 10 μmol m⁻² s⁻¹, while the highest chl a production was at 20 μmol m⁻² s⁻¹. It was suggested that more geosmin was synthesized with lower chl a demand. Meanwhile, the relative amounts of extra- and intracellular geosmin were investigated. Under optimum growth conditions (20 μmol m⁻² s⁻¹, 25°C; BG-11 medium), the amounts of extracellular geosmin increased as the growth progressed and reached the maximum in the stationary phase, while the intracellular geosmin reached its maximum value in the late exponential phase, and then began to decline. However, under the low temperature (10°C) or light (10 μmol m⁻² s⁻¹) conditions, more intracellular geosmin was synthesized and mainly accumulated in the cells. The proportions of extracellular geosmin were high, to 33.33 and 32.27%, respectively, during the stationary phase at 35°C and 20 μmol m⁻² s⁻¹. It was indicated that low temperature or light could stimulate geosmin production and favor the accumulation of geosmin in cells, while more intracellular geosmin may be released into the medium at higher temperatures or optimum light intensity.     

Distribution and diversity of archaea corresponding to the limnological cycle of a hypersaline stratified lake (Solar lake, Sinai, Egypt)

The vertical and seasonal distribution and diversity of archaeal sequences was investigated in a hypersaline, stratified, monomictic lake, Solar Lake, Sinai, Egypt, during the limnological development of stratification and mixing. Archaeal sequences were studied via phylogenetic analysis of 16S rDNA sequences as well as denaturing gradient gel electrophoresis analysis. The 165 clones studied were grouped into four phylogenetically different clusters. Most of the clones isolated from both the aerobic epilimnion and the sulfide-rich hypolimnion were defined as cluster I, belonging to the Halobacteriaceae family. The three additional clusters were all isolated from the anaerobic hypolimnion. Cluster II is phylogenetically located between the genera Methanobacterium and Methanococcus. Clusters III and IV relate to two previously documented groups of uncultured euryarchaeota, remotely related to the genus Thermoplasma. No crenarchaeota were found in the water column of the Solar Lake. The archaeal community in the Solar Lake under both stratified and mixed conditions was dominated by halobacteria in salinities higher than 10%. During stratification, additional clusters, some of which may possibly relate to uncultured halophilic methanogens, were found in the sulfide- and methane-rich hypolimnion.     

Anaerobic predatory ciliates track seasonal migrations of planktonic photosynthetic bacteria

Abstract Caenomorpha medusula was the dominant anaerobic ciliated protozoon in the anoxic water of a stratified freshwater lake. The population distribution was non-random, often with a peak in the middle of the hypolimnion. Abundance was closely correlated with numbers of the photosynthetic bacterium Thiopedia sp., and the latter was selectively eaten. There was no apparent correlation with the distribution of the total bacterial count, nor with dissolved sulphide. These observations strongly suggest that planktonic anaerobic ciliates seek out specific food sources.     

Geosmin production in the cyanobacterium Oscillatoria brevis

The cyanobacterium Oscillatoria brevis (Kütz.) Gom., strain NIVA CYA 7, was used to investigate how geosmin production is related to the synthesis of chlorophyll a, phycobiliproteins and β-carotene under nitrogen (NH ₄ ⁺ ) and light limiting conditions. Chemostat samples were used to inoculate batch cultures that were treated with inhibitors of isoprenoid synthesis, norflurazon and dimethazone, and gabaculine that inhibits tetrapyrrole synthesis. Dimethazone decreased and norflurazon increased geosmin production under light limited conditions, as was expected due to their sites of action in the isoprenoid pathway. This effect was not so pronounced in nitrogen limited cultures due to the additional effect of increasing nitrogen deficiency during the experimental period. Norflurazon was the only inhibitor that uncoupled geosmin production completely from β-carotene formation which indicates a strikt coupling between geosmin and β-carotene biosynthesis. From the observed increase of geosmin production relative to pigment synthesis after norflurazon treatment it was suggested that isoprenoid precursors are directed to geosmin synthesis when the demand for pigment precursors is very low. Within the framework of this study the data strongly support the hypothesis of geosmin formation via the isoprenoid pathway in Oscillatoria brevis as was found for actinomycetes. This research was performed at the Department of Microbiology, University of Amsterdam, with financial support provided by the royal Norwegian Ministry of Foreign Affairs and the Royal Norwegian Council for Scientific and Industrial Research     

Spatial and temporal distribution of Caulobacter spp. in two mesotrophic lakes

The seasonal distribution of Caulobacter spp. has been determined in the water column of two mesotrophic lakes using most probable number (MPN) viable counting techniques from April, 1972 to March, 1973. Concentrations in Lake Washington, a monomictic lake, peaked at 1000–3300 per ml in the epilimnion during the late spring and summer and reached lows in October of less than 2 per ml prior to fall turnover. The reason for the decrease in viable numbers is not known. Caulobacter spp. began to increase gradually in December, during the winter mixing period well before the spring bloom. Concentrations in Hall Lake, a small kettle lake, were somewhat higher than in Lake Washington, ranging from 0.27 per ml in October to over 5000 per ml during May. In contrast to Lake Washington, the highest populations were found in the metalimnion and upper hypolimnion of Hall Lake. Caulobacter spp. were also found in the anaerobic depths of the hypolimnion. However, these did not grow anaerobically, suggesting that they had settled into the hypolimnion and survived in the cold anaerobic zone. The populations of Caulobacter spp. reached maximum numbers at the approximate times and depths at which algal biomass would be expected to be greatest.     

Geosmin production and polyphasic characterization of Oscillatoria limosa Agardh ex Gomont isolated from the open canal of a large drinking water system in Tianjin City,China

Taste and odor (T & O) episodes always cause strong effects on drinking water supply system. Luanhe River diversion into Tianjin City in China is an important drinking water resource. Massive growth of a benthic filamentous cyanobacterium with geosmin production in the open canal caused a strong earthy odor episode in Tianjin. On the basis of the morphological and molecular identification of this cyanobacterium as Oscillatoria limosa Agardh ex Gomont, the genetic basis for geosmin biosynthesis and factors influencing growth and geosmin production of O. limosa CHAB 7000 were studied in this work. A 2268-bp open reading frame, encoding 755 amino acids, was amplified and characterized as the geosmin synthase gene (geo), followed by a cyclic nucleotide-binding protein gene (cnb). Phylogenetic analysis implied that the evolution of the geosmin genes in O. limosa CHAB 7000 might involve a horizontal gene transfer event. Examination on the growth and geosmin production of O. limosa CHAB 7000 at different light intensities showed that the maximum geosmin production was observed at 10 μmol photons m⁻² s⁻¹, while the optimum growth was at 60 μmol photons m⁻² s⁻¹. Under three temperature conditions (15 °C, 25 °C, and 35 °C), the maximum growth and geosmin production were observed at 25 °C. Most amounts of geosmin were retained in cells during the growth phase, but high temperature and low light intensity increased the release of geosmin into the medium, implying that O. limosa CHAB 7000 had a high potential harm for the release of geosmin from its cells at these adverse conditions.     

Distribution and Diversity of Archaea Corresponding to the Limnological Cycle of a Hypersaline Stratified Lake (Solar Lake, Sinai, Egypt)

The vertical and seasonal distribution and diversity of archaeal sequences was investigated in a hypersaline, stratified, monomictic lake, Solar Lake, Sinai, Egypt, during the limnological development of stratification and mixing. Archaeal sequences were studied via phylogenetic analysis of 16S rDNA sequences as well as denaturing gradient gel electrophoresis analysis. The 165 clones studied were grouped into four phylogenetically different clusters. Most of the clones isolated from both the aerobic epilimnion and the sulfide-rich hypolimnion were defined as cluster I, belonging to the Halobacteriaceae family. The three additional clusters were all isolated from the anaerobic hypolimnion. Cluster II is phylogenetically located between the genera Methanobacterium and Methanococcus. Clusters III and IV relate to two previously documented groups of uncultured euryarchaeota, remotely related to the genus Thermoplasma. No crenarchaeota were found in the water column of the Solar Lake. The archaeal community in the Solar Lake under both stratified and mixed conditions was dominated by halobacteria in salinities higher than 10%. During stratification, additional clusters, some of which may possibly relate to uncultured halophilic methanogens, were found in the sulfide- and methane-rich hypolimnion.     

Natural populations of bacteria in Lake Kinneret: Observations with scanning electron and epifluorescence microscopy

The bacterioplankton assemblage in Lake Kinneret, Israel, sampled on 6 occasions representative of different seasonal conditions was studied with scanning electron microscopy (SEM) and epifluorescence microscopy after acridine-orange staining. In near-surface (1–3 m) samples taken in October 1981 and March 1983, several unusual types of budding, appendaged, and filamentous cells were found. During lake stratification, typical large anaerobic forms (including photosynthetic green sulphur bacteria) were observed in samples from the metalimnion and deep (40 m) hypolimnion. Epifluorescence counts indicated that bacteria in the water column ranged from 0.55 to 2.67 × 10⁶ cells ml^–1.     

Effects of farnesol and the off-flavor derivative geosmin on Streptomyces tendae.

Effects of the sesquiterpene farnesol (3,7,11-trimethyl-2,6,10-dodecatrien-1-ol) and the sesquiterpene derivative geosmin (1,10-trans-dimethyl-trans-9-decalol) were investigated in a geosmin-producing actinomycete, Streptomyces tendae. Exposure to 300 microM farnesol reduced biomass (fresh matter) accumulation by 97% compared with biomass accumulation by controls, whereas an equal amount of geosmin did not affect biomass accumulation. Increasing exposure to farnesol corresponded with reduced optical density of the culture, reduced levels of geosmin, and reduced metabolic heat production compared with controls, while exogenous geosmin did not affect these parameters. Geosmin dissipated from unioculated medium more rapidly than farnesol, indicating that in addition to the lower toxicity of geosmin, the actual exposure to geosmin over time may be less than exposure to an equal amount of farnesol. Cultures grown on Actinomyces-B medium contained 99.5% less geosmin and were more sensitive to farnesol than those grown on Hickey-Tresner medium, indicating that geosmin synthesis was associated with reduced sensitivity to farnesol. Consumption of farnesyl moieties during geosmin synthesis may reduce the potential for farnesol-induced inhibition of growth and metabolism.     

Effects of farnesol and the off-flavor derivative geosmin on Streptomyces tendae.

Effects of the sesquiterpene farnesol (3,7,11-trimethyl-2,6,10-dodecatrien-1-ol) and the sesquiterpene derivative geosmin (1,10-trans-dimethyl-trans-9-decalol) were investigated in a geosmin-producing actinomycete, Streptomyces tendae. Exposure to 300 microM farnesol reduced biomass (fresh matter) accumulation by 97% compared with biomass accumulation by controls, whereas an equal amount of geosmin did not affect biomass accumulation. Increasing exposure to farnesol corresponded with reduced optical density of the culture, reduced levels of geosmin, and reduced metabolic heat production compared with controls, while exogenous geosmin did not affect these parameters. Geosmin dissipated from unioculated medium more rapidly than farnesol, indicating that in addition to the lower toxicity of geosmin, the actual exposure to geosmin over time may be less than exposure to an equal amount of farnesol. Cultures grown on Actinomyces-B medium contained 99.5% less geosmin and were more sensitive to farnesol than those grown on Hickey-Tresner medium, indicating that geosmin synthesis was associated with reduced sensitivity to farnesol. Consumption of farnesyl moieties during geosmin synthesis may reduce the potential for farnesol-induced inhibition of growth and metabolism.     

Freundlich adsorption isotherms of agricultural by-product-based powdered activated carbons in a geosmin-water system

The present study was designed to model the adsorption of geosmin from water under laboratory conditions using the Freundlich isotherm model. This model was used to compare the efficiency of sugarcane bagasse and pecan shell-based powdered activated carbon to the efficiency of a coal-based commercial activated carbon (Calgon Filtrasorb 400). When data were generated from Freundlich isotherms, Calgon Filtrasorb 400 had greater geosmin adsorption at all geosmin concentrations studied than the laboratory produced steam-activated pecan shell carbon, steam-activated bagasse carbon, and the CO2-activated pecan shell carbon. At geosmin concentrations < 0.07 microg/l for the phosphoric acid-activated pecan shell carbon and below 0.08 microg/l for a commercially produced steam-activated pecan shell carbon obtained from Scientific Carbons, these two carbons had a higher calculated geosmin adsorption than Filtrasorb 400. While the commercial carbon was more efficient than some laboratory prepared carbons at most geosmin concentrations, the results indicate that when the amount of geosmin was below the threshold level of human taste (about 0.10 microg/l), the phosphoric acid-activated pecan shell carbon and the Scientific Carbons sample were more efficient than Filtrasorb 400 at geosmin removal.     

Evaluation of Bacillus as a practical means for degradation of geosmin

Summary A specific method for analysis of geosmin in bacterial cultures was developed which used a minimum of manipulation. Strains of Bacillus cereus, previously reported to degrade geosmin, were tested for their ability to degrade synthetic geosmin. The initial concentration of geosmin in media was not appreciably changed by the growth of the Bacillus strains. The natural isomer of geosmin was also tested with one of these strains and was not degraded. Previous evidence for the degradation of geosmin by Bacillus is discussed critically.NRCC No 26104     

Potential sites of geosmin production by streptomycetes in and around reservoirs

Water from several oligotrophic reservoirs of the North West Water Authority at Longridge, Lancashire, supported only sparse growth of streptomycetes isolated from the reservoirs. Growth was enhanced by nutrient-amendment of the water and one common isolate, identified as Streptomyces albidoflavus , produced geosmin in water which was supplemented with sufficient concentrations of available carbon, nitrogen and phosphorus. The minimum concentrations required for geosmin production were higher than those recorded in natural reservoir water. Synthesis of geosmin in water also required a minimum temperature of about 15dEC. Sterilized samples of reservoir sediment, sediment extract, plant debris from banks and surrounding soil also supported geosmin production by S. albidoflavus. Both bank debris and exposed sediment developed earthy odours without inoculation. The structure of reservoir banks influenced the quantity of plant growth and accumulation of litter, and therefore also the potential for contamination of reservoir water by geosmin. The potential of these various sites of geosmin production to contaminate reservoir water is assessed.