Rates of sulfate reduction and thiosulfate consumption in a marine microbial mat

Abstract The sulfur cycle in a microbial mat was studied by determining viable counts of sulfate-reducing bacteria, chemolithoautotrophic sulfur bacteria and anoxygenic phototrophic bacteria. All three functional groups of sulfur bacteria revealed a maximum population density in the uppermost 5 mm of the mat: 1.1 × 10⁸ cells of sulfate reducers cm⁻³ sediment, 2.0 × 10⁹ cells of chemolithoautotrophs cm⁻³ sediment, and 4.0 × 10⁷ cells of anoxygenic phototrophs cm⁻³ sediment. Bacterial dynamics were studied by sulfate reduction rate measurements, both under anoxic conditions (dark incubation) and oxic conditions (incubation in the light), and determination of the vertical distribution of the potential rate of thiosulfate consumption under oxic conditions. Sulfate reduction rates in the top 5 mm of the sediment were 566 nmol cm⁻³ d⁻¹ in the absence of oxygen, and 123 nmol cm⁻³ d⁻¹ in the presence of oxygen. In the latter case, the maximum rate was found in the 5–10-mm depth horizon (361 nmol cm⁻³ d⁻¹). Biological consumption of amended thiosulfate was rapid and decreased with depth, while in the presence of molybdate, thiosulfate consumption decreased to 10–30% of the original rate.     

Light environment and synthesis of bacteriochlorophyll by populations of Chromatium okenii under natural environmental conditions

Abstract: In the meromictic alpine Lake Cadagno a dense layer of phototrophic bacteria, mainly Chromatium okenii and Amoebobacter purpureus , develop annually at the chemocline at about 10 to 11 m depth. Radiometric spectral profiles of the incident sunlight demonstrate different attenuation coefficients in the mixolimnion and in the chemocline not only for the visible light effective at each depth (photosynthetically available radiation), but also for selected photosynthetically active wavelengths used by oxygenic and anoxygenic phototrophs. Phototrophic bacteria sampled from the upper part of the layer at the maximum of cell concentration were incubated in transparent bottles at the sampling depth and at a lower depth where the light intensity is only a few percent of the one at the sampling depth. Within 4 h the specific bacteriochlorophyll concentration (Bchl protein⁻¹) increased up to 50% depending on the difference in light intensity between the sampling and the incubation depth. The specific bacteriochlorophyll concentration in the upper part of the layer remained constant (53.0 mg Bchl g⁻¹ protein, S.D. = 4.8) in spite of large changes in cell concentrations in the lake water over the season. These observations illustrate the phenomenon of light-regulated pigment synthesis under natural conditions.     

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.     

Kinetics of FeS-mediated denitrification in sediments from the Camargue (Rhone delta, southern France)

Abstract Denitrification rates were measured in sediments after the addition of different concentrations of FeS. A decrease of the denitrification rate was observed when high concentrations of ferrous iron (> 10 mM) were present. In the experiments with no significant concentrations of free Fe²⁺, the relationship between NO₃⁻ reduction and FeS concentration followed Michaelis and Menten kinetics. The maximum rate was 0.273 mmol l⁻¹ d⁻¹, 6 times as much as the basal rate 0.046 mmol l⁻¹ d⁻¹, which was attributed to organic matter; the K_s was 1.45 mM FeS. The stoichiometry of the overall reaction involving NO₃⁻ reduction and the concomitant S²⁻ oxidation was also investigated. Measured ΔS/ΔN ratios ranged between 0.55 and 0.64, with ΣH₂S + SO₄²⁻ changing less than 10%. These values agree with the theoretically expected value of 0.56.     

The Isolation and Some Characteristics of Photosynthetic Bacteria (Chromatiaceae and Chlorobiaceae) from Antarctic Marine Sediments

Sediment samples taken at depths from 5 to 50 m in Borge Bay, Signy Island, Antarctica yielded purple ( Chromatiaceae ) and green ( Chlorobiaceae ) phototrophic bacteria when inoculated into Winogradsky columns or directly into Pfennig's medium. Pure cultures of Thiocapsa roseopersicina (2 strains), Thiocapsa pfennigii, Chromatium gracile, Chromatium vinosum, Thiocystis violaceae, Chlorobium limicola, Chlorobium vibrioforme and Prostaecochloris aestuarii were subsequently isolated from these enrichments. Thiocapsa roseopersicina and Chromatium vinosum were the species isolated most commonly. None of the isolates showed evidence of temperature adaptation; optimum growth was achieved between 25–30°C but all grew readily at low white light levels (spectral irradiance 160 μW/cm²) with mean generation times ranging from 8·9 to 14·2 h at 23°C depending upon the isolate. The green phototrophs grew readily in blue light (440–510 nm) of low irradiance (126 μW/cm²) which penetrates to a depth of 40–50 m in coastal waters surrounding Signy Island. Under these conditions Chlorobium limicola and Chlorobium vibrioforme had mean generation times of 22 and 12·2 h respectively compared with 10·3 and 8·9 when grown in white light of similar total irradiance. None of the purple phototrophs grew under blue light but they grew under yellow light (peak transmission 590 nm, irradiance 137 μW/cm²). Chromatium gracile and Thiocapsa roseopersicina had mean generation times of 22·3 and 18·3 h respectively compared with 14·2 and 12·3 h in white light of similar total irradiance.     

The growth and mortality of larval herring, Clupea harengus L., in the River Blackwater Estuary, 1978–1980

Herring larvae were sampled in the Outer Thames Estuary and the River Blackwater Estuary in the springs of 1978, 1979 and 1980. Data were collected on larval stage, yolk sac and post yolk sac, larval length and total larval numbers. Newly hatched larvae were 6.8±0.5 mm long and the growth rate of yolk sac larvae was estimated at 0.18 mm d⁻¹ ( L = 6.8±0.186 t ). The growth rate of post yolk sac larvae increased to 0.43mm d⁻¹ ( L = 11±48.0±43 t ). Mortality estimates, derived from total numbers in the summed estuary segments, varied between the years and the cohorts within the year. In 1979 the mortality rates were 0.061 d⁻¹ and 0.074 d⁻¹ for the two cohorts. The mean size of the larval population was estimated at 2.48×10⁹ (1.63–3.77 × 10⁹) which agreed well with population size estimates from egg laying and from catch in numbers at age together with estimated fishing mortality rates.     

Antarctic stream ecosystems: physiological ecology of a blue-green algal epilithon

SUMMARY. 1. Several dozen summer meltwater streams are located in the McMurdo Sound region (c. 78°S 165°E) of southern Victoria Land. They are characterized by a highly variable flow regime at diel, seasonal and annual times caleis; wide fluctuations in temperature and nutrient content; and a very simple epilithic community of cyanophytes ( Nostoc spp., Oscillatoriaceae), bacteria, fungi and microherbivores.
2. The epilithon survives the dark Antarctic winter as dry, frozen mats which provide a large inoculum for growth the following summer. This overwintering assemblage retains a high metabolic capacity and responds rapidly to rehydration.
3. In a series of artificial substrate experiments, biomass accumulation rates were generally less than 0.1 In units d⁻¹. Colonization and growth on the substrates was inversely related to the suspended sediment load of the stream. There was also a visual correspondence between per cent algal cover of the natural streambed and the clarity of the streamwater. Sloughing losses may limit community biomass, particularly in the turbid flowing waters.
4. During running water conditions the mature communities had very low gross photosynthetic rates per unit chlorophyll (<0,1 μg C (μg chl a .h)⁻¹ and per unit carbon (<0,2 μg C (mg biomass C.h)⁻¹). Respiration was generally a high percentage (up to 92%) of gross photosynthesis, which probably reflected the high population densities of microheterotrophs in the community.
5. The floristically simple epilithic mats slowly accumulate to extreme biomass levels (>20 μg chl a cm ⁻², <20 mg C cm⁻²). Production rates per unit biomass are low, probably in response to the cold temperatures of the Antarctic stream environment, and the accumulated biomass represents several seasons of growth.     

Role of benthic insect feces in a Rocky Mountain stream: fecal production and support of consumer growth

The feces of stream insects may be a major component of fine particulate organic matter (FPOM) available to collector organisms. In Mink Creek, Idaho, winter defecation rates for 9 species ranged from 86 mg dry feces (g dry body wt)⁻¹ d⁻¹ (Ephemerella spinifera) to 154 mg g⁻¹ d⁻¹ (Paraleptophlebia heteronea) . Detailed studies of 3 species in summer revealed that rates were much greater than in winter and exhibited high between-individual variation (e.g., 695 ± 184.8 mg (g body wt)⁻¹ d⁻¹ for Baetis tricaudatus ). By combining measured and literature values, it is estimated that the benthic insect community egests approximately 3.4 kg feces m⁻² yr⁻¹. This value lies within the range of FPOM estimated to be derived from degradation of leaf litter input (0.7–9.9 kg m⁻² yr⁻¹, depending upon assimilation efficiency of the organisms).
Short-term winter growth experiments showed that, with two exceptions, collectors fed on fecal detritus will grow as well as on other food resources; relative growth rates depend upon the species. Because fecal detritus is abundant throughout the year, and is treated by many species as a source of food, it could be a major mechanism by which seasonal fluctuation in availability of allochthonous litter input is minimized and homeostasis of structure and function maintained.     

Microbial and classical food webs: A visit to a hypertrophic lake

Abstract: Plankton community structure and fluxes of carbon for bacteria (production and bacterivory) were investigated in the urban, hypertrophic Lake Rodó (Uruguay) using a short time interval for sampling (5–15 d) during one year. The lake sustains a high phytoplankton biomass (up to 335 μg l⁻¹ chlorophyll a ) always dominated by the filamentous cyanobacteria Planktothrix agardhii . The zooplankton community was numerically dominated by rotifers and ciliates; cladocerans were rare during most of the year. The rotifer abundance was very high (up to 10⁵ individual l⁻¹), the bacterivorous Anuraeopsis fissa being the most abundant species. Predation rates of heterotrophic nanoflagellates (HNF) on bacteria (range: 31–130 bacteria HNF⁻¹ h⁻¹) were higher than those reported in the literature for field studies. A carbon budget showed that HNF can consume on average 91 and 76% of the bacterial carbon production in summer and winter, respectively. Bacterial turnover times are the lowest reported until now from field conditions (5 to 42 h). Consequently, bacterial carbon production was extremely high (72 to 1071 μg C l⁻¹ d⁻¹). Bacterial production was positively correlated to bacterial abundance but the relationship was significantly improved by the inclusion of temperature (82% variability explained). My results support the general trend for increased bacterial production with increasing trophic status, and suggest a lower energy transfer efficiency to higher trophic levels in hypertrophic lakes due to the many trophic interactions involved.     

Phototrophic sulfur bacteria and sulfate-reducing bacteria causing red waters in a shallow brackish coastal lagoon (Prévost Lagoon, France)

Abstract In the shallow lagoon of Prévost (43°30'N, 3°54'E; French Mediterranean coast), red waters occurring periodically during warm summers are a consequence of a succession of ecological events beginning in the early spring with a bloom of algae ( Ulva lactuca ). In summer 1977, a red water was analyzed; in the early summer, the water turned anoxic and became rich in sulfide which originated from sulfate reduction in the first 10 cm of the sediment. Numbers of both phototrophic and sulfate-reducing bacteria (SRB) increased during spring and summer, and the genera in the prevailing populations did not change: Thiocapsa (80%) among the phototrophic bacteria and Desulfovibrio and Desulfobacter among the SRB. They were also dominant during the period of red waters. A few Chromatium and Thiocystis species were also identified. During red water periods, these bacteria grew very actively, removing all the sulfide produced by SRB, and accumulated in the whole water column. Consequently, the sulfate level increased to 5 mmol·1⁻¹ higher than the theoretical sulfate level calculated from salinity, showing the active oxidation of sulfide by phototrophic bacteria. After the dystrophic crisis, oxic conditions were reestablished and the phototrophic bacterial biomass was partly grazed by zoobenthos organisms which densely populated the sediment surface.     

Effect of plant succession, ploughing, and fertilization on the microbiological oxidation of atmospheric methane in a heathland soil

Abstract: The effect of plant succession on methane uptake was measured on intact soil cores collected from seven heathland sites. Six of the sites had undergone either secondary succession with grass or oak, ammonium fertilization or ploughing, while the seventh site was located in the native heathland. There was a positive relationship between methane uptake rate and time elapsed since the plant invasion had taken place in the native heathland. The native heathland site showed an insignificant atmospheric methane uptake of 0.01 mg CH₄ m⁻² d⁻¹, whereas the established oak brushwood (70 years old) and the grass invaded heathland (13 years old) showed rates of 1.36 mg CH₄ m⁻² d⁻¹ and 0.73 mg CH₄ m⁻² d⁻¹, respectively. In the fertilized heathland plot (112 kg N ha⁻¹ six years prior to this study) grass had become the dominating species and showed a methane oxidation rate of 0.28 mg CH₄ m⁻² d⁻¹. Ploughing of the heathland resulted in methane oxidation rates seven times the rates measured in the native heathland. The results suggested that an increased future atmospheric nitrogen deposition in heathlands and other nutrient poor ecosystems may have a stimulating effect on the soil sink for atmospheric methane.     

Grazing of the copepod Diaptomus connexus on purple sulphur bacteria in a meromictic salt lake

A meromictic lake ecosystem (Mahoney Lake, BC, Canada) was investigated to elucidate the significance of chemocline bacteria in the total carbon cycle under natural conditions. In this lake, primary production by oxygenic phototrophs was insufficient to support the observed net secondary production of the calanoid copepod Diaptomus connexus and the rotifer Brachionus plicatilis , indicating the presence of additional food sources for consumers. Mahoney Lake harbours the densest population of phototrophic sulphur bacteria ever reported in a natural body of water. This layer is located at the interface between oxic and anoxic water layers and is dominated by the purple sulphur bacterium Amoebobacter purpureus . The transfer rates of A. purpureus carbon to D. connexus determined in stratified mesocosms were very low (0.71 ngC copepod⁻¹ day⁻¹) and accounted for only 0.6% of the observed net biomass increase in the zooplankter. Stable stratification within the mesocosms prevented an upwelling of A. purpureus into the oxic part. However, measurements of carbon fluxes, infrared fluorescence microscopy and stable carbon analysis provided cumulative evidence that, under in situ conditions, the cell carbon of purple sulphur bacteria indeed enters the aerobic food chain via the grazing activity of D. connexus . Based on a two-source isotopic mixing model, A. purpureus represents at least 75–85% of the diet of D . connexus . Autumnal upwelling into oxic water layers and aggregation of A . purpureus cells appear to be the main factors determining the high carbon flux from purple sulphur bacteria to zooplankton under natural conditions, and most probably also play a key role in other aquatic ecosystems. Through this pathway, over 53% of the reduced organic matter of purple sulphur bacteria trapped in anoxic bottom waters is returned to the oxic realm.     

Primary productivity and biomass of epiphytes on Phragmites australis in a eutrophic Danish lake

A field incubator based on a closed flow system was applied for primary productivity measurements in situ. The seasonal development of epiphytes showed a pronounced productivity maximum in May (610 mg C m⁻² Phragmites stand d⁻¹) and a maximum chlorophyll a content of 414 mg m⁻² Phragmites stand. Substratum limitation was indicated during the spring maximum. Primary productivity and biomass decreased to low values in late summer, mainly due to shading from the aerial shoots. Significant quantitative heterogeneities in epiphyte biomass occurred over a few decimeter of Phragmites stem. Productivity and biomass were higher on old stems than on new ones throughout the growth period. The annual epiphyte production (23,7 g C m⁻² Phragmites stand) was mainly a result of the spring maximum. The fact that 64% was produced on old stems emphasizes the importance of the highly variable degree to which these may be destroyed. The host plant phenology appears from this investigation to be a key factor affecting epiphyte growth in the emergent vegetation determined by (1) the amount of available substratum and (2) the light penetration through the canopy.     

Comparative primary productivity of algal epiphytes on three species of macrophyte in the littoral zone of Lake Ohrid, Yugoslavia

Primary productivity of algal epiphytes on the surfaces of Phragmites, Potamogeton , and Nuphar was measured seasonally from June 1978, through June 1979, in the littoral zone of Lake Ohrid, using ¹⁴C methodology. Surface areas of individual macrophytes were determined throughout the study period through the use of a non-miscible surfactant and a calibration curve of surfactant weight versus known, calculated surface areas.
Mean total surface area available for epiphytic colonization during the study period was 1.032 m² macrophyte surface per m² of littoral zone for Phragmites , 0.810 m² for Potamogeton , and 0.167 m² for Nuphar . Seasonal rates of mean primary productivity of algal epiphytes on Phragmites from the surface to the light-compensation depth ranged from 84–1406 mg C m⁻² littoral zone d⁻¹; ranges for epiphytes on Potamogeton and Nuphar were 77–586 and 69–268 mg C m⁻² littoral zone d⁻¹, respectively. Maximum rates were observed typically during June; minimum rates were observed typically during August to December. Mean daily productivity rates over the 12 month period were for epiphytes on Potamogeton 167.0, on Nuphar 100.4 and on Phragmites 671.2 mg C m⁻² littoral zone d⁻¹. Calculated annual production for epiphytes on Nuphar was 36.65, on Potamogeton 60.95 and on Phragmites 245.0 g C m⁻² littoral zone yr⁻¹. Epiphytic production data were typically considerably higher than production data obtained for littoral and pelagial planktonic algae and compare favorably with published data for epiphytic and periphytic production in Lawrence Lake, Marion Lake, and Borax Lake.     

Characteristics of assimilatory sulfate transport in Rhodobacter sulfidophilus

Abstract Sulfate uptake was investigated with four species of phototrophic sulfur bacteria. Rhodobacter sulfidophilus and Chromatium vinosum took up ³⁵S-labeled sulfate added in micromolar concentrations. Sulfate uptake by C. vinosum was expressed only under sulfate starvation. R. sulfidophilus took up 10 μM sulfate almost completely and accumulated it up to 5300-fold, also when grown with excess sulfate. Sulfite (1 mM) as an intermediate of sulfate assimilation inhibited sulfate uptake completely within 1 min. Moderate inhibition was observed with cysteine (1 mM) and none with sulfide (1 mM). Transport was not dependent on the cations K⁺, Na⁺, Li⁺ or protons, but was sensitive to uncouplers and to the ATPase inhibitor dicyclohexylcarbodiimide (DCCD). The accumulation of sulfate correlated with the ATP concentration in the cells, indicating an ATP-dependent uptake mechanism.     

High organic loading influences the physical characteristics of aerobic sludge granules

Aims:  The effect of high organic loading rate (OLR) on the physical characteristics of aerobic granules was studied.
Methods and Results:  Two column-type sequential aerobic sludge blanket reactors were fed with either glucose or acetate as the main carbon source, and the OLR was gradually raised from 6 to 9, 12 and 15 kg chemical oxygen demand (COD) m⁻³ d⁻¹. Glucose-fed granules could sustain the maximum OLR tested. At a low OLR, these granules exhibited a loose fluffy morphology dominated by filamentous bacteria. At higher OLRs, these granules became irregularly shaped, with folds, crevices and depressions. In contrast, acetate-fed granules had a compact spherical morphology at OLRs of 6 and 9 kg COD m⁻³ d⁻¹, with better settling and strength characteristics than glucose-fed granules at similar OLRs. However, acetate-fed granules could not sustain high OLRs and disintegrated when the OLR reached 9 kg COD m⁻³ d⁻¹.
Conclusions:  The compact regular microstructure of the acetate-fed granules appeared to limit mass transfer of nutrients at an OLR of 9 kg COD m⁻³ d⁻¹. The looser filamentous microstructure of the glucose-fed granules and the subsequent irregular morphology delayed the onset of diffusion limitation and allowed significantly higher OLRs to be attained.
Significance and Impact of the Study:  High organic loading rates are possible with aerobic granules. This research would be helpful in the development of aerobic granule-based systems for high-strength wastewaters.     

Milk consumption and estimates of growth energetics in pouch young of the northern brown bandicoot, Isoodon macrourus (Peramelidae, Marsupialia), in captivity

Milk consumption was measured in pouch young of the northern brown bandicoot, Isoodon macrourus , using the ²²Na turnover technique. Milk consumption rates increased from about 2.3 ml young⁻¹ d⁻¹ at 23 days post-partum to about 17.2ml young⁻¹ d⁻¹ at 52 days, just prior to weaning. Young increased in mass from 8.5 g to around 112 g over the same period. Masś gained for each ml of milk consumed ranged from 0.28 to 0.65 gml⁻¹. The efficiency with which young converted milk energy and protein into body energy and protein ranged from 16.1 to 39.6% and 38.4 to 82.3%, respectively.     

Sinking rates of planktonic diatoms in an unstratified lake: a comparison of field and laboratory observations

SUMMARY. 1. Natural population sinking rates were calculated by fitting an exponential regression to 6 years'observations on declining crops of Melosira italica subarctica O. Müll. and Stephanodiscus astraea (Ehr.) Grun.
2. Losses were described by an exponential model which yielded still water sinking rates of 0.86 md⁻¹ for M. italica and 0.45md⁻¹ for S. astraea.
3. Laboratory measurements of the sinking rate of natural populations showed that the rate increased abruptly from less than 0.2 m d⁻¹ in growing populations to 0.4 m d⁻¹ after silica depletion.
4. The measured sinking rate of S. astraea agreed well with that observed in the field. Where as populations of M. italica appeared to sink more quickly in the lake than could be accounted for by laboratory observations.     

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.