Distribution and activity of bacteria in the headwaters of the Rhode River Estuary,Maryland, USA

A transect along the axis of the headwaters of a tidal estuary was sampled for microbial, nutrient, and physical parameters. Chlorophylla averaged 42g 1^–1 and phytoplankton comprised an estimated 80% of the total microbial biomass as determined by adenosine triphosphate (ATP). Bacterial concentrations ranged from 0.3–53.9×10⁶ cells ml^–1 and comprised about 4% of the total living microbial biomass. Bacterial production, determined by³H-methyl-thymidine incorporation was about 0.05–2.09× 10⁹ cells 1^–1 h^–1, with specific growth rates of 0.26–1.69 d^–1. Most bacterial production was retained on 0.2m pore size filters, but passed through 1.0m filters. Significant positive correlations were found between all biomass measures and most nutrient measures with the exception of dissolved inorganic nitrogen nutrients where correlations were negative. Seasonal variability was evident in all parameters and variability among the stations was evident in most. The results suggest that bacterial production requires a significant carbon input, likely derived from autotrophic production, and that microbial trophic interactions are important.     

Factors Controlling Extremely Productive Heterotrophic Bacterial Communities in Shallow Soda Pools

Dilute soda lakes are among the worlds most productive environments and are usually dominated by dense blooms of cyanobacteria. Up to now, there has been little information available on heterotrophic bacterial abundance, production, and their controlling factors in these ecosystems. In the present study the main environmental factors responsible for the control of the heterotrophic bacterial community in five shallow soda pools in Eastern Austria were investigated during an annual cycle. Extremely high cyanobacterial numbers and heterotrophic bacterial numbers up to 307 × 10⁹ L^–1 and 268 × 10⁹ L^–1 were found, respectively. Bacterial secondary production rates up to 738 µg C L^–1 h^–1 and specific growth rates up to 1.65 h^–1 were recorded in summer and represent the highest reported values for natural aquatic ecosystems. The combination of dense phytoplankton blooms, high temperature, high turbidity, and nutrient concentration due to evaporation is supposed to enable the development of such extremely productive microbial populations. By principal component analysis containing the data set of all five investigated pools, two factors were extracted which explained 62.5% of the total variation of the systems. The first factor could be interpreted as a turbidity factor; the second was assigned to as concentration factor. From this it was deduced that bacterial and cyanobacterial abundance were mainly controlled by wind-induced sediment resuspension and turbidity stabilized by the high pH and salinity and less by evaporative concentration of salinity and dissolved organic carbon. Bacterial production was clustered with temperature in factor 3, showing that bacterial growth was mainly controlled by temperature. The concept of describing the turbid water columns of the shallow soda pools as fluid sediment is discussed.     

Bacterial activity along a trophic gradient

Bacterial biomass, secondary production, and extracellular enzymatic activity [-glucosidase and leucine-aminopeptidase, measured as cleavage of artificial fluorogenic substrates 4-methyl umbelliferyl (MVF) -D-glucopyranoside and L-leucine 7-amido-4-methyl coumarin (MCA)] were measured along a trophic gradient in the Northern Adriatic Sea in four ecologically different situations. Bacterial parameters were compared with chlorophyll a and inorganic and organic nutrient concentrations. Bacterial secondary production and extracellular enzymatic activity markedly changed among different seasons and along the trophic gradient. Average bacterial secondary production increased from 0.61 to 2.09 µg Cl^–1 hour^–1 preceding a bloom, to 2.09 µg Cl^–1 hour^–1 during the bloom, decreasing again to 0.81 and 0.83 µg Cl^–1 hour^–1 in the post-bloom and summer periods, respectively (values from 0.5 m depth). Leucine-aminopeptidase activity showed more consistent trends than -glucosidase activity. Average values of leucine-aminopeptidase activity, measured by enzymatic release of MCA, increased from a pre-bloom value of 164.0 to 1,712.0 (nM MCA) hour^–1 released during a bloom, decreasing to 298.5 and 133.7 (nM MCA) hour^–1 released for the post-bloom and summer situation, respectively (values from 0.5 m depth). Average growth rates decreased during the bloom, whereas average extracellular enzymatic activity levels expressed on a cell basis increased by an average factor of 2. Along the trophic gradient, a consistent increase in bacterial secondary production could be observed in all but the summer situation (values from 0.5 m depth). Leucine-aminopeptidase activity also showed positive trends along the gradient, while -glucosidase activity did not exhibit such a clear trend. Bacterial biomass trends were less obvious considering both seasonal changes and the tropic gradient. Highly significant interrelations were detected between bacterial proteolytic activity, secondary production, chlorophyll a content, and nitrate concentrations, especially in the surface horizon. Send offprint requests to: G. J. Hemdl.     

Dynamics of bacterioplankton in a mesotrophic French reservoir (Pareloup)

Bacterioplankton abundance, biomass and production were studied at a central station (35 m depth) from April 1987 to September 1988 in a mesotrophic reservoir. Bacterial production was calculated by the (³H) thymidine method.For the water column, integrated estimates of bacterioplankton abundance ranged from 2.3 10⁹ to 4.6 10⁹ cells l^–1, and carbon biomass from 0.037 to 0.068 mg C l^–1; the thymidine incorporation rates ranged from 0.8 to 17.2 picomoles l^–1 h^–1, leading to net bacterial production estimates of less than 0.7 µg C l^–1 d^–1 in winter to 18 µg C l^–1 d^–1 in summer. About 55% of the production occurred in the euphotic layers.Over the year, the bacterial carbon requirement represented 90% of the autotrophic production for the whole lake. It was five times lower than autotrophic production in spring, but twice as high in summer. This important temporal lack of balance suggests that not all the spring primary production products are consumed immediately and/or that other carbon sources probably support bacterial growth in summer.     

Nitrogen metabolism by heterotrophic bacterial assemblages in Antarctic coastal waters

Field studies to examine the in situ assimilation and production of ammonium (NH₄ ⁺) by bacterial assemblages were conducted in the northern Gerlache Strait region of the Antarctic Peninsula. Short term incubations of surface waters containing ¹⁵N-NH₄ ⁺ as a tracer showed the bacterial population taking up 0.041–0.128 g-atoms Nl^–1d^–1, which was 8–25% of total NH₄ ⁺ uptake rates. The large bacterial uptake of NH₄ ⁺ occurred even at low bacterial abundance during a rich phytoplankton bloom. Estimates of bacterial production using ³H-leucine and -adenine were l.0gCl^–1 d^–1 before the bloom and 16.2 g Cl^–1 d^–1 at the bloom peak. After converting bacterial carbon production to an estimate of nitrogen demand, NH₄ ⁺ was found to supply 35–60% of bacterial nitrogen requirements. Bacterial nitrogen demand was also supported by dissolved organic nitrogen, generally in the form of amino acids. It was estimated, however, that 20–50% of the total amino acids taken up were mineralized to NH₄ ⁺. Bacterial production of NH₄ ⁺ was occurring simultaneously to its uptake and contributed 27–55% of total regenerated NH₄ ⁺ in surface waters. Using a variety of ¹⁵N-labelled amino acids it was found that the bacteria metabolized each amino acid differently. With their large mineralization of amino acids and their relatively low sinking rates, bacteria appear to be responsible for a large portion of organic matter recycling in the upper surface waters of the coastal Antarctic ecosystem.     

Bacterial production in a mesohumic lake estimated from [14C]leucine incorporation rate

Incorporation of [¹⁴C]leucine into proteins of bacteria was studied in a temperate mesohumic lake. The maximum incorporation of [¹⁴C] leucine was reached at a concentration of 30 nm determined in dilution cultures. Growth experiments were used to estimate factors for converting leucine incorporation to bacterial cell numbers or biomass. The initially high conversion factors calculated by the derivative method decreased to lower values after the bacteria started to grow. Average conversion factors were 7.09 × 10¹⁶ cells mol^–1 and 7.71 × 10¹⁵ m³ mol^–1, if the high initial values were excluded. Using the cumulative method, the average conversion factor was 5.38 × 10¹⁵ m^–3 mol^–1 I . The empirically measured factor converting bacterial biomass to carbon was 0.36 pg C m^–3 or 33.1 fg C cell^–1. Bacterial production was highest during the growing season, ranging between 1.8 and 13.2 g C liter^–1 day^–1, and lowest in winter, at 0.2–2.9 g C liter^–1 day^–1. Bacterial production showed clear response to changes in the phytoplankton production, which indicates that photosynthetically produced dissolved compounds were used by bacteria. In the epilimnion bacterial production was, on average, 19–33% of primary production. Assuming 50% growth efficiency for bacteria, the allochthonous organic carbon could have also been an additional energy and carbon source for bacteria, especially in autumn and winter. In winter, a strong relationship was found between temperature and bacterial production. The measuring of [¹⁴C]leucine incorporation proved to be a simple and useful method for estimating bacterial production in humic water. However, an appropriate amount of [¹⁴C]leucine has to be used to ensure the maximum uptake of label and to minimize isotope dilution.     

Seasonal change in the proportion of bacterial and phytoplankton production along a salinity gradient in a shallow estuary

We intended to evaluate the relative contribution of primary production versus allochthonous carbon in the production of bacterial biomass in a mesotrophic estuary. Different spatial and temporal ranges were observed in the values of bacterioplankton biomass (31–273 g C l^–1) and production (0.1–16.0 g C l^–1 h^–1, 1.5–36.8 mg C m^–2 h^–1) as well as in phytoplankton abundance (50–1700 g C l^–1) and primary production (0.1–512.9 g C l^–1 h^–1, 1.5–512.9 mg C m^–2 h^–1). Bacterial specific growth rate (0.10–1.68 d^–1) during the year did not fluctuate as much as phytoplankton specific growth rate (0.02–0.74 d^–1). Along the salinity gradient and towards the inner estuary, bacterio- and phytoplankton biomass and production increased steadily both in the warm and cold seasons. The maximum geographical increase observed in these variables was 12 times more for the bacterial community and 8 times more for the phytoplankton community. The warm to cold season ratios of the biological variables varied geographically and according to these variables. The increase at the warm season achieved its maximum in the biomass production, particularly in the marine zone and at high tide (20 and 112 times higher in bacterial and phytoplankton production, respectively). The seasonal variation in specific growth rate was most noticeable in phytoplankton, with seasonal ratios of 3–26. The bacterial community of the marine zone responded positively – generating seasonal ratios of 1–13 in bacterial specific growth rate – to the strong warm season increment in phytoplankton growth rate in this zone. In the brackish water zone where even during the warm season allochthonous carbon accounted for 41% (on average) of the bacterial carbon demand, the seasonal ratio of bacterial specific growth rate varied from about 1 to 2. During the warm season, an average of 21% of the primary production was potentially sufficient to support the whole bacterial production. During the cold months, however, the total primary production would be either required or even insufficient to support bacterial production. The estuary turned then into a mostly heterotrophic system. However, the calculated annual production of biomass by bacterio- and phytoplankton in the whole ecosystem showed that auto- and heterotrophic production was balanced in this estuary.     

Heterotrophic bacterial production in Lake Xolotlán (Managua) during 1988–1989

The biomass and production (thymidine incorporation) of heterotrophic bacterioplankton has been assessed from July, 1988, to October, 1989. in Lake Xolotlán, Nicaraqua. Bacterial abundance was high, 2–3.10¹⁰ cells.l^–1, and bacterial biomass averaged ca. 0.75 mg C.l^–1, or roughly 20% of the partivculate organic carbon. Bactrial production averaged between 3.5–5 g C.l^–1.h^–1 and on a areal basis was 650–959 mg C.m^–2.d^–1 or 13–20% ofthe primary production. Although bacterial production (volumetric basis) was typical for eutrophic lakeks, the bacterial specific growth rate was low, the bacteial population doubling time was ca. 1 week, perhaps indicating that there was a low grazing pressure on the bacteria.     

Effects of solar radiation,humic substances and nutrients on phytoplankton biomass and distribution in Lake Solumsjö, Sweden

Impacts of solar radiation, humic substances and nutrients on phytoplankton abundance at different depths were investigated in a temperate dimictic lake, Lake Solumsjö. Penetration of solar radiation profiles at different depths, represented as light attenuation coefficient (K _d) were examined. Water sampling and downward irradiance of photosynthetically active radiation (PAR), ultraviolet-A (UV-A, 320–400 nm) and ultraviolet-B (UV-B, 280–320 nm) radiation were performed once a week and at three different times of the day (08.00, 12.00 and 16.00 hrs, local time) between September 13 and November 1, 1999. During the period of investigation, solar radiation above the water surface declined from 474 to 94 mol m^–2 s^–1 for PAR, from 1380 to 3.57 W m^–2 for UV-A and from 13.1 to 0.026 W m^–2 for UV-B, respectively. The attenuation coefficient (K _d) for UV-B radiation ranged from 3.7 to 31 m^–1 and UV-B radiation could not be detected at depths greater than 0.25 m. Humic substances measured at 440 nm ranged from 35.5 to 57.7 Pt mg l^–1. Mean values of biomass, estimated from chlorophyll a, in the whole water column (0–10 m) varied between 2.3 and 5.6 g l^–1 and a diel fluctuation was observed. During stratified conditions, high levels of iron (1.36 mg l^–1) and manganese (4.32 mg l^–1) were recorded in the hypolimnion, suggesting that the thermocline played a major role in the vertical distribution of phytoplankton communities in Lake Solumsjö. The high levels of iron and manganese stimulated the growth of Trachelomonas volvocinopsis in the hypolimnion at a depth of 10 m. Negative impacts of UV-B radiation on phytoplankton in lake Solumsjö are reduced due to the high levels of humic substances and the high degree of solar zenith angle at the latitude studied.     

Labile dissolved organic carbon and water temperature as regulators of heterotrophic bacterial activity and production in the lakes of Sub-Antarctic Marion Island

Summary The objectives of the 3 year study were to determine the relationship between bacterial numbers and phytoplankton standing crops (chlorophyll a) in sub-antarctic Marion Island lakes (33) and to determine the relative importance of labile dissolved organic carbon and water temperature as regulators of heterotrophic bacterial activity and production. Bacterial activity (the incorporation and respiration rates of ¹⁴C-labelled substrates) and production (the rate of [methyl-³H]thymidine incorporation into DNA) were measured in oligotrophic Lava Lake and Gentoo Lake, an elephant seal wallow. Samples were incubated under ambient conditions as well as at increased temperature and with additions of labile dissolved organic carbon (DOC). Bacterial numbers ranged from 2.13 × 10⁵ cell ml^–1 to 15.17 × 10⁶ cells ml^–1 in the lake survey. The chlorophyll range was 0.18 to >75 g 1^–1. Bacterial numbers were not correlated to chlorophyll concentration in waters where the chlorophyll content was 5 g 1^–1 but were correlated in waters with larger algal contents. Heterotrophic bacterial activity and production, which were similar to rates recorded for equivalent lower latitude systems, were higher in Gentoo Lake than in Lava Lake. As a result of qualitative and quantitative differences in the DOC pools, DOC was the stronger regulator of bacterial activity and production in Lava Lake, while temperature was the stronger factor in Gentoo Lake.     

Bacteria in the sea-ice zone between Elephant Island and the South Orkneys during the Polish sea-ice zone expedition, (December 1988 to January 1989)

During austral summer 1988/89, total bacterial Acridine Orange Direct Counts (AODC) in seawater, mean 6.0×10⁶ l^–1, were three to ten times lower than generally reported for the Bransfield Strait to north Weddell Sea area. In contrast, numbers of viable bacteria (Colony Forming Units, CFU), mean 10.6×10³ l^–1 were two to three times higher than reported. Bacterial abundance here shows large seasonal and spatial changes. On the basis of bacterial, diatom, detritus, and amino acid data from this study, two main regions were defined: Cold winter water in the west with high salinity and low CFU, AODC, and other parameters. In the east, lower salinity and higher values for all parameters were found in warmer meltwater at the surface. CFU and AODC values in ice were respectively six and 85 times higher than in surrounding seawater. Taxonomic studies indicate considerable diversity in genera and nutritional requirements of isolated bacteria. Sea-ice and water column bacterial communities differed. Many isolated strains, however, were found in both habitats. Sea-ice seems to be important in regulating surrounding bacterioplankton.     

Heterotrophic microbial activity in shallow aquifer sediments of Long Island,New York

Bacterial numbers and activities (as estimated by glucose uptake and total thymidine incorporation) were investigated at two sites in Long Island, New York aquifer sediments. In general, bacterial activities were higher in shallow (1.5–4.5 m below the water table or BWT), oxic sediments than in deep (10–18 m BWT), anoxic sediments. The average total glucose uptake rates were 0.18 ± 0.10 ng gdw^–1 h^–1 in shallow sediments and 0.09 ± 0.11 ng gdw^–1 h^–1 in deep sediments; total thymidine incorporation rates were 0.10 ± 0.13 pmol gdw^–1 h^–1 and 0.03 ± 0.03 pmol gdw^–1 h^–1 in shallow and deep sediments, respectively. Incorporation of glucose was highly efficient, as only about 10% of added label was recovered as CO₂. Bacterial abundance (estimated from acridine orange direct counts) was 2.5 ± 2.0 × 10⁷ cells gdw^–1 and 2.0 ± 1.3 × 10⁷ cells gdw^–1 in shallow and deep sediments, respectively. These bacterial activity and abundance estimates are similar to values found in other aquifer environments, but are 10- to 1000-fold lower than values in soil or surface sediment of marine and estuarine systems. In general, cell specific microbial activities were lower in sites from Connetquot Park, a relatively pristine site, when compared to activities found in sites from Jamesport, which has had a history of aldicarb (a pesticide) contamination. To our knowledge, this is the first report of bacterial activity measurements in the shallow, sandy aquifers of Long Island, New York.Correspondence to: D.G. Capone     

Bacterial productivity and microbial biomass in tropical mangrove sediments

Bacterial productivity (³H-thymidine incorporation into DNA) and intertidal microbenthic communities were examined within five mangrove estuaries along the tropical northeastern coast of Australia. Bacteria in mangrove surface sediments (0–2 cm depth) were enumerated by epifluorescence microscopy and were more abundant (mean and range: 1.1(0.02–3.6)×10¹¹ cells·g DW^–1) and productive (mean: 1.6 gC·m^–2· d^–1) compared to bacterial populations in most other benthic environments. Specific growth rates (¯x=1.1) ranged from 0.2–5.5 d^–1, with highest rates of growth in austral spring and summer. Highest bacterial numbers occurred in winter (June–August) in estuaries along the Cape York peninsula north of Hinchinbrook Island and were significantly different among intertidal zones and estuaries. Protozoa (10⁵–10⁶·m^–2, pheopigments (0.0–24.1g·gDW^–1) and bacterial productivity (0.2–5.1 gC·m^–2·d^–1) exhibited significant seasonality with maximum densities and production in austral spring and summer. Algal biomass (chlorophylla) was low (mean: 1.6g·gDW^–1) compared to other intertidal sediments because of low light intensity under the dense forest canopy, especially in the mid-intertidal zone. Partial correlation analysis and a study of possible tidal effects suggest that microbial biomass and bacterial growth in tropical intertidal sediments are regulated primarily by physicochemical factors and by tidal flushing and exposure. High microbial biomass and very high rates of bacterial productivity coupled with low densities of meiofaunal and macroinfaunal consumers observed in earlier studies suggest that microbes may be a sink for carbon in intertidal sediments of tropical mangrove estuaries.     

Benthic bacterial biomass and production in the Hudson River estuary

Bacterial biomass, production, and turnover were determined for two freshwater marsh sites and a site in the main river channel along the tidally influenced Hudson River. The incorporation of [methyl-³H]thymidine into DNA was used to estimate the growth rate of surface and anaerobic bacteria. Bacterial production at marsh sites was similar to, and in some cases considerably higher than, production estimates reported for other aquatic wetland and marine sediment habitats. Production averaged 1.8–2.8 mg C·m^–2·hour^–1 in marsh sediments. Anaerobic bacteria in marsh sediment incorporated significant amounts of [methyl-³H]thymidine into DNA. Despite differences in dominant vegetation and tidal regime, bacterial biomass was similar (1×10³±0.08 mg C·m^–2) inTrapa, Typha, andNuphar aquatic macrophyte communities. Bacterial abundance and productivity were lower in sandy sediments associated withScirpus communities along the Hudson River (0.2×10³±0.05 mg C·m^–2 and 0.3±0.23 mg C·m^–2·hour^–1, respectively).     

Summer bacterial populations in Mississippi River Pool 19: implications for secondary production

Bacterial populations were sampled at 37 sites in Mississippi River Pool 19. Bacterial biomass was calculated from direct epifluorescent cell counts. Bacterial production was estimated by incubating cells in situ in predator-free water inside membrane chambers and the frequency of dividing cells. Bacterial biomass in the water column ranged from 0.05 to 1.13 mg C ^-1, biomass in the vegetated areas of the pool was significantly higher than that in other habitats (P < 0.05, ANOVA). Biomass in sediments (to a depth of 10 cm) ranged from 24 to 1,073 mg C m^-2, biomass in muddy sediments was significantly higher (P < 0.05) than that in sandy sediments. Biomass on the submersed surfaces of hydrophytes was 0.06–4.90 mg bacterial C g^-1 dry weight of plant material. The vegetated habitat (water column plus vegetation) contained approximately 45 times the concentration of bacterial carbon found in nonvegetated main channel border areas and more than 100 times the concentration in the main river channel.Bacterial production rates in the water column of a vegetated section of the pool ranged from 0.03 to 3.28 g C m ^-3 s d ^-1 ; production (m ^-3) in a vegetation bed was 5.5 times that in the adjacent nonvegetated channel border areas and approximately 50 times that in the main channel. Aquatic macrophytes and associated microorganisms may be capable of providing significant inputs of carbon to secondary consumers in the pool during the summer low flow.     

Influence of hydrological seasonality on bacterioplankton in two neotropical floodplain lakes

Seasonal fluctuation in river stage strongly affects the ecological functioning of tropical floodplain lakes. This study was conducted to assess the influence of hydrological seasonality on bacterial production and abundance in two floodplain lakes of the Autana River, a blackwater river in the Middle Orinoco basin, Venezuela. Water samples for nutrient chemistry, chlorophyll a, and microbiological determinations were collected in two floodplain lakes and in the mainstem of the river during 1997–98. DOC and chlorophyll a concentrations were similar between mainstem and lake sites during high water when river and lakes were well connected but became different during the period of low water when the interaction was minimal. Higher values of bacterial production were observed in the floodplain lakes (0.62–1.03 g C l^–1 h^–1) compared to the mainstem sites (0.17–0.19 g C l^–1 h^–1) during the period of low water, while during the period of high water river and lake sites showed similar levels (0.04 g C l^–1 h^–1). Bacterial numbers followed bacterial production in the floodplain lakes, reaching higher numbers during the period of low water (1.41–2.40 × 10⁶ cells ml^–1). Availability of substrate and inorganic nutrients, pH, and inputs and losses of bacterial cells could be determining the observed seasonal patterns in bacterial production and abundance. The Autana lakes exhibited a strong seasonal pattern in the chemical and biological conditions, showing higher productivity during the lentic phase that lasted between 5 and 6 months.     

Variability of phytoplankton distribution and primary production around Elephant Island,Antarctica, during 1990–1993

The distribution and abundance of phytoplankton within a sampling grid of 50×10³ km² around Elephant Island were determined from early January to mid-March of 4 successive years, 1990–1993. The number of stations where physical-optical-biological data were obtained from the surface to a maximum of 750 m ranged from 74 in 1990 to 206 in 1993. Contour maps of chlorophyll-a (chl-a) concentrations showed marked mesoscale patchiness that varied from month to month and also interannually. The distribution patterns for chl-a were similar when plotting surface concentrations or integrated values to 100 m. Three major zones could be distinguished that differed in both physical and biological characteristics. Stations in the northwest portion of the grid (Drake Passage waters) and in the southeast portion of the grid (Bransfield Strait waters) showed the most pronounced interannual variations, with phytoplankton biomass and rates of primary production being considerably higher in 1990–91 than in 1992–93. The central portion of the sampling grid, which included the major frontal system north of Elephant Island, showed the smallest interannual variations in both biological and physical parameters and the highest rates of primary production. Phytoplankton biomass and rates of primary production were correlated with depth of the upper mixed layer (UML), which in turn was correlated with the measured wind stress. The mean depth of the UML was 50 m, while the mean depth of the euphotic zone was 90 m. Using the measured mean surface solar irradiance (550 Einsteins m^–2 s^–1), the mean irradiance experienced by cells in the UML of 50 m would be around 105 E m^–2 s^–1, which is similar to the measured I_k (light saturation) value for photosynthesis (101 Em^–2 s^–1). The mean value from all cruises for chl-a in surface waters was 0.7 mg m^–3, while the mean rate of primary production was 374 mg Cm^–2 day^–1.     

Heterotrophic bacterial activity and primary production in a hypertrophic African lake

The relationship between heterotrophic bacteria and phytoplankton in the epilimnion (0–10 m) of hypertrophic Hartbeespoort Dam, South Africa, was examined by statistically analyzing three years of parallel measurements of heterotrophic bacterial activity (glucose uptake) and phytoplankton particulate and dissolved organic carbon production. Algal biomass ranged between 4.0 and 921.1 mg Chl a m^-3 at the surface. Primary production varied between 69.5 and 3010.0 mg C m^-2h^-1 while algal production of dissolved organic carbon (EDOC) ranged from 2.5 to 219.2 mg C m^-2h^-1. Bacterial numbers reached a summer peak of 44.23 × 10⁶ cells ml^-1 in the first year and showed no depth variation. The maximum rate of glucose uptake, V_max, reached a peak of 5.52 g C l^-1h^-1. V_max, maximum glucose concentration (K_t + S_n) and glucose turnover time (T_t) were usually highest at the surface and decreased with depth concomitant with algal production. At the surface, V_max was correlated to EDOC (r = 0.59, n = 67, p < 0.001) and primary production (r = 0.71, n = 70, p < 0.001). At 5 and 10 m, V_max was correlated to integral euphotic zone (~ 4 m) algal production and bacterial numbers. Glucose turnover time was inversely related to integral algal production (r = -0.72, n = 70, p < 0.001) and less strongly to bacterial numbers. The data indicated that although bacterial numbers and biomass were low relative to algal biomass in this hypertrophic lake, the heterotrophic bacteria attained high rates of metabolic activity as a result of enhanced algal production of available organic carbon.     

Bacterial productivity in ponds used for culture of penaeid prawns

The quantitative role of bacteria in the carbon cycle of ponds used for culture of penaeid prawns has been studied. Bacterial biomass was measured using epifluorescence microscopy and muramic acid determinations. Bacterial growth rates were estimated from the rate of tritiated thymidine incorporation into DNA. In the water column, bacterial numbers ranged from 8.3×10⁹ 1^–1 to 2.57×10¹⁰ 1^–1 and production ranged from 0.43 to 2.10 mg Cl^–1 d^–1. In the 0–10 mm zone in sediments, bacterial biomass was 1.4 to 5.8 g C m^–2 and production was 250 to 500 mg C m^–2 d^–1. The results suggested that most organic matter being supplied to the ponds as feed for the prawns was actually being utilized by the bacteria. When the density of meiofauna increased after chicken manure was added, bacterial biomass decreased and growth rates increased.     

Absence of red-light enhancement of phototropism in pea seedlings at limiting irradiances of blue light

The effect of different light qualities (blue, green, white, red and far-red) on ethylene production in leaf discs and flower petal discs of Begonia × hiemalis cv. Schwabenland Red was studied. All the light qualities, except far-red, reduced the ACC-conversion to ethylene in leaf discs by about 70% at a photosynthetic photon flux density (PPFD) of 20 mol m^–2s^–1.Blue and green light were less inhibitory than white and red light at lower PPFD. In all treatments far-red light at 0.5 mol m^–2s^–1 of photon flux density (PFD) stimulated the ACC-conversion to ethylene in leaf discs by about 60–90% compared to the dark-incubated control. White and red light strongly inhibited the -naphthalene-acetic acid (NAA) stimulated ethylene synthesis in leaf discs. The results may suggest that the ethylene production is controlled by phytochrome in the leaves but not in the petals. Lack of coaction of any light quality with silver ions on ethylene production in leaf and petal discs was also observed.Abbreviations ACC 1-aminocyclopropane-1-carboxylic acid - EFE ethylene forming enzyme - NAA -naphthalene-acetic acid - PFD photon flux density - PPFD photosynthetic photon flux density - RH relative air humidity - SAM S-adenosylmethionine - STS silver thiosulphate