Vertical distribution of major sulfate-reducing bacteria in a shallow eutrophic meromictic lake

The vertical distribution of sulfate-reducing bacteria was investigated in a shallow, eutrophic, meromictic lake, Lake Harutori, located in a residential area of Kushiro, Japan. A steep chemocline, characterized by gradients of oxygen, sulfide and salinity, was found at a depth of 3.5–4.0 m. The sulfide concentration at the bottom of the lake was high (up to a concentration of 10.7 mM). Clone libraries were constructed using the aprA gene, which encodes adenosine-5′-phosphosulfate reductase subunit A, in order to monitor sulfate-reducing bacteria. In the aprA clone libraries, the most abundant sequences were those from the Desulfosarcina–Desulfococcus (DSS) group. A primer set for a DSS group-specific 16S rRNA gene was used to construct another clone library, analysis of which revealed that the uncultured group of sulfate-reducing bacteria, SEEP SRB-1, accounted for nearly half of the obtained sequences. Quantification of the major bacterial groups by catalyzed reporter deposition-fluorescence in situ hybridization demonstrated that the DSS group accounted for 3.2–4.8% of the total bacterial community below the chemocline. The results suggested that the DSS group was one of the major groups of sulfate-reducing bacteria and that these presumably metabolically versatile bacteria might play an important role in sulfur cycling in Lake Harutori.     

Trophic relationships between bacteria and protozoa in the hypolimnion of a meromictic mesostrophic lake

The development of ciliated protozoan biomass in the hypolimnion of Piburger See, a small subalpine lake, was demonstrated to depend mainly on two factors. Firstly, the availability of oxygen or nitrate as electron acceptors determines the depth profiles of ciliates. Large quantities of ciliates and even maximum numbers were found at depths where no oxygen could be detected. If nitrate also disappeared during the summer stagnation period, the biomass of protozoa was strongly reduced. Nitrite peaks generally corresponded with ciliate peaks. An extension of Finlay's findings (dissimilatory nitrate reductase within the inner mitochondrial membrane) to other ciliate groups is hypothesized.Secondly, the biomass development of hypolimnetic ciliates was strongly correlated with the bacterial biomass registered approx. 2 weeks before (r² = 0.891, n = 14). The biomass of bacteria, on the other hand, was dependent upon the sedimentation rate of organic carbon (r² = 0.850, n = 15), if a time lag of approx. 2 weeks was taken into account. Therefore a total time lag of approx. 4 weeks was assumed to take place between sedimentation of organic substance and the corresponding increase in ciliate biomass (r² = 0.853, n = 14). Bacteria were shown to be an important intermediate link in the food chain of the hypolimnion. They appear to represent the principal energy source for pelagic ciliates. Sedimentation of organic carbon, nitrogen and phosphorus is the driving force for the establishment of the hypolimnetic microbial community.     

Grazing rates of a calanoid copepod (Paralabidocera antarctica) in a continental Antarctic lake

The presence of crustaceans in some Antarctic lakes adds a level of complexity to the food webs of these environments. The grazing pressure of the crustaceans on phytoplankton and other protists, and the role they play in controlling food web structure, has not yet been examined in any detail. This paper presents the first data on grazing pressure of crustacean zooplankton in continental Antarctic lakes. In this study the grazing rates of Paralabidocera antarctica in saline Ace Lake, Vestfold Hills, were assessed using a radio-tracer method. Clearance rates ranged from approximately 1 to 8 ml ind.⁻¹ day⁻¹, depending on developmental stage. Due to their high abundance, nauplii exhibited the highest daily carbon ingestion rates. The population cleared about 3% of the water column per day, accounting for a significant fraction of primary production. P. antarctica has a considerable impact on the carbon cycle in Ace Lake and, by inference, in the other lakes in which it occurs. Accepted: 30 October 1999     

Depth distribution of euryhaline halophilic bacteria in Suribati Ike, a meromictic lake in East Antarctica

Euryhaline halophiles grow over a wide range of salinity, from <3% NaCl (seawater equivalent) to >15% NaCl and even saturation level (about 30% NaCl). Several species of euryhaline halophiles occur worldwide, especially in marine environments and also in aquatic and terrestrial habitats of the Antarctic ice-free areas. A biogeographic view of Antarctic halophiles is that their migration among lakes on land is more difficult than in marine setting. Ponds and lakes on land may thus serve as “islands” which facilitate the selection and separation of unique species. We isolated euryhaline halophiles from the saline lake, Suribati Ike, near Syowa Station and placed them into seven groups, each demonstrating a clear depth-related distribution. Six of the seven groups probably represent new species of the genera Halomonas and Marinobacter. This result suggests that Antarctic saline lakes exhibit high selectivity of unique euryhaline halophiles and possibly of other microbial groups.     

Bacterial population dynamics in a meromictic lake.

Polyclonal antibodies against nine different bacteria isolated from Lake Saelenvannet in western Norway were produced, and the population dynamics of these strains in the lake were monitored through two spring seasons by immunofluorescence staining. The total counts of bacteria varied over time and space from 1.5 x 10(6) to 1.5 x 10(7) cells ml-1. The counts of specific bacteria were in the range of 10(3) to 10(4) cells ml-1 or less; in sum, they generally made up less than 1% of the bacterial community. Some populations showed significant changes in abundance, with blooms lasting 1 to 3 weeks. The rate of change (increase and decrease) in abundance during blooms was estimated to be 0.2 to 0.6 day-1. The average virus-to-bacteria ratio was 50, and there was a significant correlation between the abundances of virus and bacteria. Both protozoan grazing and lytic virus infection were assessed as possible mechanisms driving the variations in bacterial population density.     

Nutrient-phytoplankton relationships in a tropical meromictic soda lake

Seasonal variation through one year in total nitrogen (TN), total phosphorus (TP), phytoplankton biomass, phytoplankton species composition and other environmental factors were examined in Lake Sonachi, a tropical meromictic soda lake. Mean concentrations of TN and TP were 11 000 µg N l^-1 and 100 µg P l^-1, respectively. Maximum concentrations of TN and TP occurred in the monimolimnion. Phytoplankton biomass ranged from 350 to 1260 mg m^-3. Synechococcus bacillaris, a small coccoid cyanophyte, dominated the phytoplankton. The mean chlorophyll a concentration of 37 mg · m^-3 was a modest value when compared with those of other tropical soda lakes. High TN:TP ratios indicated phosphorus limitation in the lake.     

Diurnal residence of the larger stages of the calanoid copepod Acartia tonsa in the anoxic monimolimnion of a tropical meromictic lake in New Guinea

We studied diel vertical migration of the calanoid copepod Acartiatonsa in a coastal meromiclic lake (Lake Nagada, Papua New Guinea).During the day, the animals migrate several metres below theoxycline to just above or into the sediments, and remain inanoxic water. Vertical migration patterns differ between ontogeneticstages; adults and larger copepodites do not occur in appreciablenumbers in the water samples during the day (deepest sampletaken at {small tilde}0.5 m above the sediment). Around sunset,the larger copepodites gradually appear in the water column,reaching the near-surface food layer (0–2 m) only wellafter sunset. Our results suggest that the evening ascent ofthe copepods in this tropical lake is related to relative changesin light intensity, and that there are age- and sex-relateddifferences in the responses to these stimuli.     

Formation of purple membranes during salt bacteria cultivation]

Experiments have been carried out on cultivation of halophile with probe selection in the interval of 1--2 hours to record the spectra of repeated disturbed completed inner reflection. Periodicity in the changes of spectral characteristics of the culture with the interval of 20--24 hours is revealed. A clearly expressed dichroism of the amid II band of the membrane complex is found, the absence of this dichroism in the protein isolated from the membrane complex is stated. It is suggested that dichroism revealed is a specific feature of the presence of purpuric membranes in the cells. Spontaneous plane orientation of protein macromolecules in purpuric membranes is established. The level of dichroism of amid II band is shown to depend on fermentation conditions of salt bacteria.     

Assessment of grazing by the freshwater copepod Diaptomus minutus using carotenoid pigments: a caution

In order to assess feeding selectivity in freshwater zooplankton, we conducted feeding trials using Diaptomus minutus isolated from two Wisconsin lakes. Copepods were fed an algal assemblage comprised of an equal biomass of a centric diatom, a cryptomonad and a coccal green alga. The total amounts of photopigments were tracked using high-performance liquid chromatography. The removals of carotenoids and a-type phorbins (chlorophyll a and phaeopigments) from feeding suspensions were compared with their presence in the guts of animals, in fecal pellets, and in the final suspension. Diaptomus minutus generally removed either the diatoms primarily or all three algal cells equally. These removals were not reflected in gut extracts of the animals, however, where alloxanthin (marker of cryptomonads) was always present, but where fucoxanthin and diadinoxanthin (markers of diatoms) were never observed. Pigment disappearance was variable for total a-type phorbins, but frequently >90% for carotenoids, particularly for fucoxanthin and diadinoxanthin. Phaeophytin a was the major a-type phorbin detected after gut passage. Our results indicate that evaluations of zooplankton grazing which assume that algal carotenoids remain detectable throughout gut passage must be made with substantial caution and that differences in pigment processing are likely to occur among zooplankton species. Furthermore, grazing experiments designed to evaluate decreases of specific pigments in feeding suspension, rather than their appearance in animals' guts, may prove a more valuable approach to understanding the feeding selectivity of copepods.      

Production and decomposition processes in a saline meromictic lake

Bacterial and phytoplankton cell number and productivity were measured in the mixolimnion and chemocline of saline meromictic Mahoney Lake during the spring (Apr.–May) and fall (Oct.) between 1982 and 1987. High levels of bacterial productivity (methyl ³H-thymidine incorporation), cell numbers, and heterotrophic assimilation of ¹⁴C-glucose and ¹⁴C-acetate in the mixolimnion shifted from near surface (1.5 m), at a secondary chemocline, to deeper water (4–7 m) as this zone of microstratification gradually weakened during a several year drying trend in the watershed. In the mixolimnion, bacterial carbon (13–261 µgC 1^–1) was often similar to phytoplankton carbon (44–300 µgC 1^–1) and represented between 14–57% of the total microbial (phytoplankton + bacteria) carbon depending on the depth interval. Phototrophic purple sulphur bacteria were stratified at the permanent primary chemocline (7.5–8.3 m) in a dense layer (POC 250 mg 1^–1, bacteriochlorophyll a 1500–70001µ 1^–1), where H₂S changed from 0.1 to 2.5 mM over a 0.2 m depth interval. This phototrophic bacterial layer contributed between 17–66% of the total primary production (115–476 mgC m^–2 d^–1) in the vertical water column. Microorganisms in the phototrophic bacterial layer showed a higher uptake rate for acetate (0.5–3.7 µC 1^–1 h^–1) than for glucose (0.3–1.4 µgC 1^–1 h^–1) and this heterotrophic activity as well as bacterial productivity were 1 to 2 orders of magnitude higher in the dense plate than in the mixolimnetic waters above. Primary phytoplanktonic production in the mixolimnion was limited by phosphorus while light penetration appeared to regulate phototrophic productivity of the purple sulphur bacteria.     

Microbial sulfate reduction in a brackish meromictic steppe lake

Patterns of sulfate reduction were studied in water and sediments of Lake Shira, South Siberia, Russia. The lake was characterized by a high level of sulfate (91-116 mM). The concentration of hydrogen sulfide in the anoxic waters of the lake reached 0.6 mM. In summer the sulfate reduction rate in the water column, measured by radiometric technique, varied from 0.25 to 9.81 mol sulfate l^-1 d^-1. There were two peaks of sulfate reduction activity: just below the chemocline and near the sediment surface. Sulfate reduction rate in the profundal silts ranged from 4.1 to 90.6 mol l^-1 d^-1. The zone of the most active sulfate reduction was restricted to the surface sediment layers. The acceleration of sulfate reduction rate (up to 236 mol l^-1 d^-1) and the increase of density of viable sulfate reducers (up to 2 x 10⁵ cells ml^-1) were recorded in the littoral sediments adjacent to the mouth of the Son River and sewage discharge. It was apparently caused by the input of allochthonous organic substrates and also by a high environmental temperature. On an areal basis, sulfate reduction rate in the water was approximately 8 times higher than that in the profundal sediments. Sulfate reduction was the most important process of anaerobic oxidation of organic carbon in Lake Shira. In summer in the profundal zone of the lake, sulfate reducers were able to mineralize about 67% of the daily integrated primary production of phototrophic and chemotrophic organisms.     

Factors influencing the induction of diapausing egg production in the calanoid copepod Diaptomus leptopus

Field and laboratory studies were carried out between 1995 and 1997 on four populations of Diaptomus leptopus found in seasonally temporary, occasionally temporary, and a permanent environment to assess the relative importance of photoperiod and temperature regimes versus other proximate local cues in inducing diapause egg production. Patterns of diapausing and subitaneous egg production were determined by observation of individual females bearing clutches that were produced in the field. A laboratory common-garden experiment was performed to assess the effects of four different regimes of temperature and photoperiod on the induction of diapause. Patterns of diapausing egg production differed among ponds: diapause occurred early in the seasonally temporary environment and occurred rarely in the permanent environment. In the common-garden experiment, populations exhibited substantial changes in the onset of diapause when compared to patterns found under field conditions. These results provide indirect evidence that the different populations respond to available cues of environmental change in different ways in nature, or that environmental cues vary among habitats.     

Vertical distribution of planktonic rotifers in a karstic meromictic lake

Vertical distribution of planktonic rotifers is described in relation to temperature and oxygen in Lake La Cruz, a single-doline, closed karstic lake (121 m diameter and 25 m maximum depth) which shows iron meromixis. Samples were taken by peristaltic pumping at 10 cm depth intervals in the oxycline zone from June 1987 to September 1988. A model of rotifer vertical structure in stratified lakes is proposed. Rotifers concentrate their populations at the depths with intense gradients. As stratification develops some rotifer populations show a downward migration following the thermocline and some others show an upward migration following the oxycline. The production-respiration balance in the lake, and so the position of the oxycline with respect to the thermocline and the layer of maximum production, depends on meteorological conditions. A shift in the dominance of congeneric or related species can occur in consecutive years. In Lake La Cruz, mixing conditions and subterranean inflow in spring were much more intense in 1988 than 1987, and the distance between production and decomposition depths was smaller in 1988. Anuraeopsis miraclei, an oxycline-bound species with high abundance in 1987, was displaced by A. fissa in 1988. A. fissa, which was a metalimnetic species during early summer, reached peak densities (3 × 10⁴ ind l^–1) at the oxycline, equaling the abundance of A. miraclei the preceeding year.