Empirical Conversion Factors Research Articles

Erratum: Theoretical and empirical conversion factors for determining bacterial production in freshwater sediments via leucine incorporation

Erratum: Theoretical and empirical conversion factors for determining bacterial production in freshwater sediments via leucine incorporation

Theoretical and empirical conversion factors for determining bacterial production in freshwater sediments via leucine incorporation

Bacteria play an extraordinarily important role in carbon transformations. It is therefore crucial to accurately measure bacterial production. One of the most widely used methods is the leucine method. From rates of leucine incorporation bacterial carbon production can be derived by empirical or theoretical conversion factors (CFs). However, only few empirical CFs have been established, and no estimation of the theoretical conversion factor for freshwater systems exists until today. Therefore, we determined both, the empirical and the theoretical conversion factor, of sediment bacteria from a headwater stream. The empirical conversion factor determined from exponentially growing bacteria was 1.445 kg C mol−1. The theoretical conversion factor derived from the determination of the molar fraction of leucine in bacterial protein (0.081 ± 0.001) was 1.442 kg C mol−1. Both conversion factors are close to each other and similar to conversion factors established for marine bacterioplankton. Therefore, results of the present study indicate that high values of bacterial production determined in freshwater sediments by the leucine method in several studies were not overestimates caused by inappropriate use of CFs from marine systems but represent true high bacterial production in these environments. For studies that apply the leucine technique in freshwaters, we recommend using the theoretical conversion factor for calculation of bacterial carbon production: BCP (kg) = 1.44 × Leuinc (Leuinc = leucine incorporation in mol).

Variability and predictability of the empirical conversion factor for converting 3H-thymidine uptake into bacterial carbon production for a eutrophic lake

To assess the variability and predictability of the empirical conversion factor (CF) for converting the uptake of 3 H-thymidine (TDR) to bacterial carbon production rates in eutrophic environments, we performed 11 dilution culture experiments and results were related to a set of important concomitantly recorded environmental variables. TDR incorporation data from a field study were then converted to carbon production with the established empirical CF and a theoretical CF and compared to production estimates derived from leucine incorporation. Mean empirical CF varied between 0.5 and 7.0 x 10 6 cells (pmol TDR) -1 over the year and showed highly significant negative correlation with TDR incorporation rate and a highly significant positive correlation to temperature. Values of carbon production derived with the variable empirical CF were lower than the values obtained by the use of the theoretical CF of 1 × 10 6 cells (pmol TDR) -1 . They showed less seasonal variation than values obtained by leucine incorporation, and periods of uncoupling were observed. However, when the empirical CF was calculated from the multiple regression equation including TDR incorporation and temperature, the resulting carbon production rates showed a high correspondence with the leucine-derived production rates. Results of the analyses were interpreted as an indication that under favourable, conditions (resulting in high TDR incorporation) bacteria may be able to optimize DNA duplication over protein synthesis as a possible strategy to persist and to maintain their potential to divide under limiting conditions (e.g. decrease in temperature and substrate availability). In unfavourable conditions (resulting in low incorporation rates), bacteria may then use already produced DNA copies for rapid growth, when the environmental conditions turn favourable again. Thus, an experimental set-up causing nutrient enrichment of the sampled water by autoclaving and filtering, as generally used for dilution culture experiments, does not always reflect in situ situations, especially during periods of low nutrient concentrations.

Pelagic bacteria and phytoplankton in oceanic waters near the Canary Islands in summer

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 209:1-17 (2001) - doi:10.3354/meps209001 Pelagic bacteria and phytoplankton in oceanic waters near the Canary Islands in summer Antonio Bode1,*, Susana Barquero1, Manuel Varela1, Jose G. Braun2, Demetrio de Armas3 1Instituto Español de Oceanografía, Centro Oceanográfico de A Coruña, Apartado 130, Muelle de Animas s/n, 15080 A Coruña, Spain 2Universidad de La Laguna, Depto. Biología Marina, C. Astcofisico F. Sánchez s/n, 38206 La Lagune, Spain 3Instituto Español de Oceanografía, Centro Oceanográfico de Tenerife, Apartado 1373, Carretera San Andrés, 38120 Sta. Cruz de Tenerife, Spain *E-mail: antonio.bode@co.ieo.es ABSTRACT: Bacterial abundance, biomass and heterotrophic activity along with hydrographic and phytoplankton variables were measured in waters surrounding the Canary Islands during Cruise BIOCAN-98 in September 1998. Three distinct oceanographic zones, defined using temperature and phytoplankton biomass concentrations, were studied. Zone A, located NW of La Palma Island, was characterized by the presence of alternating cold and warm eddies, and generally low phytoplankton biomass. Zone B was located beween La Palma and Tenerife islands and showed a predominance of cold-core eddies and higher phytoplankton concentrations than Zone A. All stations occupied in the eastern part of the Canary Islands were grouped in Zone C and were characterized by relatively low surface temperature (<22°C) and high phytoplankton biomass. The vertical structure of the upper water column in these zones was indicative of relatively low mixing in stations of Zones A and B, while stations of Zone C displayed characteristics of frequent mixing events. Phytoplankton biomass showed deep relative maxima between 40 and 100 m at all stations. These maxima were shallower and more marked at stations with colder waters near the surface. Coccoid cyanobacteria were significantly correlated with chlorophyll a and reached abundances of up to 104 cells ml-1 in subsurface maxima. Heterotrophic bacteria were generally more abundant near the surface, and varied between 1.1 and 5.9 × 105 cells ml-1 in the upper 100 m. Bacterial abundance between 100 and 300 m was approximately constant. Bacterial production, estimated by leucine incorporation, was not correlated with bacterial abundance or chlorophyll a, and displayed relative maxima between 80 and 90 m depth but also near the surface. There were no significant differences in mean values of abundance of cyanobacteria and heterotrophic bacteria between the oceanographic zones considered, but bacterial production and growth rates were significantly higher in Zone B. Using empirical conversion factors determined during the study, we estimated bacterial production values integrated in the upper 100 m that varied between 15 and 289 mg C m-2 d-1, with population generation times between 2 and 25 d. Taking into account phytoplankton biomass and primary production values, our results suggest that pelagic bacteria are able to consume dissolved organic carbon in excess of the amount produced in situ by phytoplankton in the upper surface waters of this region. KEY WORDS: Bacterial production · Bacterial abundance · Phytoplankton biomass · Primary production · Central Eastern Atlantic Full text in pdf format NextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 209. Online publication date: January 05, 2001 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2001 Inter-Research.

High-Resolution CO Observations of Luminous Infrared Galaxies

We have performed a high-resolution imaging survey of the CO J = 1 → 0 emission in seven galaxies with infrared (IR) luminosities exceeding 3 × 1011 L☉—five of which are mergers. The resultant maps show that the molecular gas is very highly concentrated towards the cores of the mergers, with gas surface densities approaching or exceeding 104 M☉ pc-2 within 300–400 pc of the nuclei in three cases. This result supports earlier findings based on data from a smaller sample of luminous mergers. In the two mergers that show closely spaced double IR (stellar) nuclei, CO emission peaks between the nuclei and shows an extent roughly equal to the nuclear separation. The gas cores of the individual merging galaxies appear to be coalescing, while the stellar cores remain distinct. In the three single nucleus mergers, the CO peaks are coincident with the stellar nuclei, consistent with the hypothesis that these are relatively evolved merger remnants. In two of the three mergers with the most compact CO emission (Mrk 231 and NGC 6240), the empirical Galactic conversion factor from CO luminosity to molecular gas mass appears to overestimate the nuclear gas mass by a factor of more than 2 (3.6 in the case of Mrk 231). For Mrk 231, the high brightness temperature of the CO emission (Tb > 34 K) is the likeliest explanation for this overestimate. In the third such merger (NGC 2623), however, the geometry and kinematics suggest that the molecular gas mass is within a factor of 2 of the value given by using the Galactic conversion factor. Nonetheless, in all three of these objects, the molecular gas probably dominates the nuclear gravitational potential. We suggest that the molecular gas in objects with such high gas mass surface densities (~104 M☉ pc-2) is distributed in nuclear disks. These disks must be thin because of their self-gravity, with a full width of 30–40 pc (compared to radii of 300–400 pc) for a vertical velocity dispersion of 90 km s-1. The mean volume density of molecular hydrogen in such disks must be over 104 cm-3. The trend of increasing LFIR/LCO with increasing CO surface brightness is confirmed. The high concentrations of molecular gas thus appear intimately related to the high luminosities of these systems and probably serve as the fuel.

The geoid constraint in global geodynamics: viscosity structure, mantle heterogeneity models and boundary conditions

SUMMARY The Earth's non-hydrostatic gravity field, or geoid, provides a first-order constraint on mantle density structure and dynamics. Geodynamic models for the geoid have proliferated since the advent of seismic mapping of mantle heterogeneity structure (tomography) because the geoid offers perhaps the best-measured independent constraint on mantle density heterogeneity. However, dynamic geoid models involve a number of questionable physical assumptions and uncertainties whose effects need to be evaluated before geodynamic inferences based upon the geoid can be considered sound. Troubling issues include the appropriate surface boundary conditions (free-slip, no-slip, plates?) and parametrization of radial viscosity variations (how many layers can be resolved?), in addition to lateral viscosity variations, possible chemical layering of the mantle, phase transitions, etc. There are also uncertainties in the density heterogeneity models used as ‘input’ to dynamic geoid models, most of which are derived from seismic tomography and require weakly constrained, empirical conversion factors to go from seismic velocity variations to density variations. Here we address several of the most straightforward problems inherent in geoid modelling, namely the issues of viscosity structure resolution, uncertainties in appropriate boundary conditions, and differences among mantle heterogeneity models. A robust feature of all models is a lower-mantle viscosity at least a factor of 30 greater than that of the upper mantle, but there is little resolution with regard to finer details such as lithospheric or uppermost mantle (‘low-viscosity zone’) viscosity. Ironically, free-slip boundary conditions result in the best fits to the geoid in all cases, but all boundary conditions exhibit predictable trade-offs with the uppermost-mantle viscosity. Models with a single viscosity layer representing the lower mantle yield similar dynamic topography estimates of the order of 700–1000 m in amplitude, regardless of the finer details of upper-mantle viscosity structure, boundary conditions or input heterogeneity models. Comparing mantle heterogeneity models based on two independent seismological determinations (Harvard and Berkeley models) and on the history of subduction, we find that these models are virtually indistinguishable regarding inferences of mantle viscosity structure and amplitude of dynamic topography, and in terms of the effects of different boundary conditions. Uncertainties concerning which type of boundary condition is appropriate are much more important than which mantle heterogeneity model is chosen. Given other uncertainties in modelling the geoid, particularly the strong effects due to lateral viscosity variations for intermediate (<10 000 km) wavelengths, we conclude that the class of dynamic geoid models explored so far cannot reliably elucidate the details of upper-mantle viscosity structure.

Bacterial productivity and protistan bacterivory in coastal and offshore communities of Lake Erie

The importance of protists as bacterivores in a coastal community and an offshore community of Lake Erie was compared during the summer of 1994. Bacterial density, cell size, and empirical conversion factors for bacterial productivity were highly variable at both sites and greater at the coastal site (P &lt; 0.01). Bacterial productivity at the coastal site was 25-50 times higher than at the offshore site. Bacterivory was estimated in situ by fluorescently labeled native bacteria. Per-cell grazing rate and filtering rate for each taxon were routinely determined. Heterotrophic nanoflagellates (HNAN) were the most important protistan bacterivores at the offshore site, while HNAN and ciliates were similarly dominant bacterivores at the coastal site. Mixotrophic bacterivory was important only at the offshore site where Dinobryon was the dominant bacterivore. Bacterial carbon flux through protists was higher at the coastal site by an order of magnitude. Offshore protists grazed virtually the entire bacterial production, while coastal protists usually grazed less than half of the bacterial production. These results suggest that coastal and offshore sites differed fundamentally in the significance of protists to carbon flux through the microbial loop to higher trophic levels.

Bacterial carbon production in the northern Baltic:a comparison of thymidine incorporation and FDC based methods

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 153:59-66 (1997) - doi:10.3354/meps153059 Bacterial carbon production in the northern Baltic: a comparison of thymidine incorporation and FDC based methods Tuomi P Bacterial production in the open Gulf of Finland was estimated by 3H-thymidine incorporation rate (TTI) and by the frequency of dividing cells (FDC), counted by transmission electron microscopy (TEM). To relate TTI and FDC to bacterial growth rate, batch cultures with the natural bacterial community from the study area were used. Conversion factors between 0.2 and 7.2 x 1018 cells mol-1 TdR, or 0.3 and 24.3 x 1017 µm3 mol-1 TdR, were obtained for TTI, depending on the season and calculation model used (integrative, cumulative, or modified derivative). From FDC and growth rate (µ) based on bacterial cell numbers, the following equation was derived: µ = 0.002FDC - 0.001. Bacterial carbon production in the study area, estimated using the FDC method, was 20 to 80% higher than TTI-based estimates. Virus abundances were followed in the batch cultures and in the field study. Viral lysis may have been a significant cause of bacterial mortality in the field, but it remains to be shown whether viral-induced mortality was already included in the empirical conversion factor. Bacteria · 3H-thymidine incorporation rate · Frequency of dividing cells · Baltic Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 153. Publication date: July 10, 1997 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1997 Inter-Research.

Microbial processes in cold oceans. I. Relationship between temperature and bacterial growth rate

Despite the obvious relevance of the high latitude oceans to models and budgets of biogenic carbon, the seasonal patterns of energy flow through the lower food web in this region are poorly understood. It has been suggested that, in high latitude and cold oceans, the rates of bacterial metabolism and growth are low and are depressed to a much greater degree than those of co-occurring phytoplankton and metazoan heterotrophs. The low-temperature suppression of bacterial growth would reduce microbial food web activity, bacteria would consume and recycle less primary production and more phytoplankton carbon would be available to metazoan grazers. The implications of this scenario for models of oceanic carbon flow are profound. In this paper, we present an analysis of 66 published studies on temperature and growth rate for bacteria from the World Ocean, including polar regions, and examine the results of a field investigation of bacterioplankton growth in seasonally cold Newfoundland (eastern Canada) coastal waters. Based upon the analysis of published data, where approximately 50 % of the observations were from environments less than or equal to 4 degrees C, we report a weak (r(2) - 0.058, n = 231) relationship between specific growth rate (SGR) and temperature with a Q(10) = 1.5. The mean (0.39 to 0.41 d(-1)) and median (0.25 to 0.29 d(-1)) SGR of bacteria from cold (less than or equal to 4 degrees C) and warm (>4 degrees C) waters were not significantly different. For both the published data as well as for the field study in Conception Bay, Newfoundland, the SGR was significantly greater (p < 0.01) when computed from empirical thymidine conversion factors than from theoretical or literature derived thymidine conversion factors. Our analysis suggests that the growth rates of bacterioplankton from cold and temperate oceans are similar at their respective ambient temperatures, when the appropriate conversion factors are used to compute growth. We propose that bacteria-based food webs and microbial trophic pathways are as important in overall energy and material cycling in high latitude oceans as they are at lower latitudes.

Conversion factors for estimation of cell production rates of soil bacteria from [ 3H]thymidine and [ 3H]leucine incorporation

Thymidine and leucine incorporation into NaOH-extractable macromolecules were examined as methods for estimating bacterial production rates in soil. Six out of ten bacterial strains isolated from soil incorporated thymidine and all incorporated leucine. Three of the strains which incorporated [ 3H]thymidine were grown as a mixture in four continuous cultures with generation times of 1.12–4.12 days. Empirical conversion factors were determined by simultaneous measurement of thymidine and leucine incorporation and bacterial cell and carbon production. Isotope dilution was determined at each generation time to enhance the accuracy of incorporation measurements. Empirical conversion factors for thymidine ranged from 0.2 to 1.1 × 10 18 cells mol −1 with a mean of 0.54 × 10 18 cells mol −1. Empirical conversion factors for leucine (0.38–1.8 × 10 16 cells mol −1) were low when compared to previously determined conversion factors. Significant differences among empirical conversion factors measured for leucine at the four generation times were found, suggesting a dependence of the empirical conversion factor for leucine on generation time. Addition of gamma-sterilized soil before incorporation measurements did not effect thymidine incorporation. Leucine incorporation, however, was significantly increased by an enhanced extraction of leucine-labelled macromolecules. We conclude that conversion factors for calculation of in situ cell production of soil bacteria from [ 3H]thymidine incorporation are in the same range as conversion factors published for aquatic bacteria. Thymidine incorporation offers a direct quantitative estimate of bacterial cell production in soil. A drawback of the thymidine method is that not all soil bacteria are able to incorporate thymidine, which may lead to conservative production estimates. The leucine method needs further investigation before it is applicable to natural soil samples.

Comparison of Rates of Flagellate Bacterivory and Bacterial Production in a Marine Coastal System

Protozoan predation on bacteria and bacterioplankton secondary production were simultaneously determined in La Salvaje Beach water during 1990. Protozoan grazing on bacterioplankton was measured from fluorescently labeled bacterium uptake rates; estimates of bacterial secondary production were obtained from [H]thymidine incorporation rates. Two different conversion factors were used to transform thymidine incorporation rates into bacterial production rates; both of them were specific for La Salvaje Beach and were calculated by using empirical and semitheoretical approaches. The average flagellate predation rate was 14.0 bacteria flagellate h; the average population predation rate was 7.35 x 10 bacteria liter h. The estimates of bacterial production differed greatly depending on the conversion factor used, and so did the percentages of bacterial production consumed by flagellated protozoa (4.6% when the empirical conversion factor for La Salvaje Beach was used and 113% when the semitheoretical conversion factor specific for this system was used). The ecological implications of each of these values are discussed.

Incorporation of thymidine and leucine in the subarctic Pacific application to estimating bacterial production

This study examines the use of incorporation rates of thymidine (TdR) and leucine (Leu) in order to estimate bacterial production in the oceanic subarctic Pacific. Incorporation rates at different concentrations suggest that isotope dilution is low when 5 nM TdR is used, but other data indicate at least 3-fold and 2-fold dilution for TdR and Leu, respectively. The ratio of incorporation into the hot acid insoluble fraction, compared to the cold acid insoluble fraction, is 0.66 for TdR and 0.86 for Leu. Empirical conversion factors were measured in experiments during four 1 mo-long cruises. Conversion factors did not vary systematically and were not affected by additions of organic compounds or ammonium. Average conversion factors were 1.74 X 10 cells mol-' of incorporated TdR (SD = 0.89 X 10 cells mol-') and 0.108 X 10 cells mol-' of incorporated Leu (SD = 0.085 X 10'%ells mol-l). It was possible to estimate 'bottle-less' conversion factors during May 1988 when bacterial numbers increased greatly; in situ bottle-less conversion factors were 1.55 and 0.185 X 10'' cells mol-' for TdR and Leu, respectively. Estimates of bacterial production based on the TdR and Leu methods agreed within and 25 % for 0 to 40 m (ca the mixed layer) and 40 to 80 m (bottom half of the euphotic zone). respectively.

DNA Synthesis and Tritiated Thymidine Incorporation by Heterotrophic Freshwater Bacteria in Continuous Culture

Continuous cultivation of heterotrophic freshwater bacteria was used to assess the relationship between DNA synthesis and tritiated thymidine incorporation. The bacteria were grown on a yeast extract medium with generation times of 0.25 to 3.7 days. In six different continuous cultures, each inoculated with a grazer-free mixed bacterial sample from Lake Vechten (The Netherlands), tritiated thymidine incorporation into a cold trichloroacetic acid precipitate and bacterial cell production were measured simultaneously. Empirical conversion factors were determined by division of both parameters. They ranged from 0.25 x 10 to 1.31 x 10 cells mol of tritiated thymidine (mean, 0.60 x 10 cells mol of tritiated thymidine). In addition, DNA concentrations were measured by fluorometry with Hoechst 33258. The validity of this technique was confirmed. Down to a generation time of 0.67 day, bacterial DNA content showed little variation, with values of 3.8 to 4.9 fg of DNA cell. Theoretical conversion factors, which can be derived from DNA content under several assumptions, were between 0.26 x 10 and 0.34 x 10 cells mol of thymidine (mean, 0.30 x 10 cells mol of thymidine). Isotope dilution was considered the main factor in the observed discrepancy between the conversion factors. In all experiments, a tritiated thymidine concentration of 20 nM was used. Control experiments indicated maximum incorporation at this concentration. It was therefore concluded that the observed difference resulted from intracellular isotope dilution which cannot be detected by current techniques for isotope dilution analysis.

An explanation for the variability in the conversion factor deriving bacterial cell production from incorporation of [3 H] thymidine

The empirical conversion factor deriving bacterial cell production from incorporation of [3H]thymidine (cells nmol−1) varies by orders of magnituide in the literature. An empirical conversion factor is not realistic unless the concentration of [3H]thymidine used maximizes the degree of participation (DP) of [3H]thymidine in DNA synthesis equally in both unaltered lakewater samples and in lake-water cultures. I find that a higher [3H]thymidine concentration (>20 nM) than normally used for routine samples (5–10 nM) may be required for maximal incorporation into DNA in lake-water cultures, at least in spring. Thus a conversion factor with the latter [3H]thymidine concentrations will be an overestimate. This hypothesis is supported by an analysis of the literature indicating that with concentrations of [3H]thymidine > 10 nM, the empirical conversion factors most often approach the expected theoretical factor (≈1 × 1018 cells mol−1).

Protozoan Grazing and Bacterial Production in Stratified Lake Vechten Estimated with Fluorescently Labeled Bacteria and by Thymidine Incorporation

In stratified Lake Vechten, The Netherlands, protozoan grazing was estimated on the basis of uptake of fluorescently labeled bacteria and compared with bacterial production estimated on the basis of thymidine incorporation. By using a grazer-free mixed bacterial population from the lake in continuous culture, an empirical relationship between cell production and thymidine incorporation was established. Thymidine incorporation into total cold-trichloroacetic-acid-insoluble macromolecules yielded a relatively constant empirical conversion factor of ca. 10 (range, 0.38 x 10 to 1.42 x 10) bacteria mol of thymidine at specific growth rates (mu) ranging from 0.007 to 0.116 h. Although thymidine incorporation has been assumed to measure DNA synthesis thymidine incorporation appeared to underestimate the independently measured bacterial DNA synthesis by at least 1.5- to 13-fold, even if all incorporated label was assumed to be in DNA. However, incorporation into DNA was found to be insignificant as measured by conventional acid-base hydrolysis. Methodological problems of the thymidine technique are discussed. Like the cultures, Lake Vechten bacteria showed considerable thymidine incorporation into total macromolecules, but no significant incorporation into DNA was found by acid-base hydrolysis. This applied not only to the low-oxygen hypo- and metalimnion but also to the aerobic epilimnion. Thus, the established empirical conversion factor for thymidine incorporation into total macromolecules was used to estimate bacterial production. Maximum production rates (141 x 10 bacteria liter h; mu, 0.012 h) were found in the metalimnion and were 1 order of magnitude higher than in the epi- and hypolimnion. In all three strata, the estimated bacterial production was roughly balanced by the estimated protozoan grazing. Heterotrophic nanoflagellates were the major consumers of the bacterial production and showed maximum numbers (up to 40 x 10 heterotrophic nanoflagellates liter) in the microaerobic metalimnion.

Validity of the empirical conversion factors for assessing bacterial production from3H thymidine incorporation rates

3H thymidine incorporation into bacterial production were determined from samples laken in a mesotrophic lake. Twenty five diluted water cultures were conducted at « in situ » temperature (4-22° C) from April 1987 to February 1989. The conversion factors varied through the year ; the average conversion factor was 6.29 x I0 9 cells (2-10.7) per nanomole of thymidine incorporated into cold TCA precipitate and 7.18 x 10 9 cells (3.47-10.7) nmoM, when corrected for the increase in cell biomass which occured during the incubations. The validity of these factors, higher than the theoretical conversion factors values, is discussed considering the diluted water culture conditions and the data analysis methods.

Protozoan Grazing, Bacterial Activity, and Mineralization in Two-Stage Continuous Cultures

In two-stage continuous cultures, at bacterial concentrations, biovolumes, and growth rates similar to values found in Lake Vechten, ingestion rates of heterotrophic nanoflagellates (HNAN) increased from 2.3 bacteria HNAN . h at a growth rate of 0.15 day to 9.2 bacteria . HNAN . h at a growth rate of 0.65 day. On a yeast extract medium with a C/N/P ratio of 100:15:1.2 (Redfield ratio), a mixed bacterial population showed a yield of 18% (C/C) and a specific carbon content of 211 fg of C . mum. The HNAN carbon content and yield were estimated at 127 fg of C . mum and 47% (C/C). Although P was not growth limiting, HNAN accelerated the mineralization of PO(4)-P from dissolved organic matter by 600%. The major mechanism of P remineralization appeared to be direct consumption of bacteria by HNAN. N mineralization was performed mainly (70%) by bacteria but was increased 30% by HNAN. HNAN did not enhance the decomposition of the relatively mineral-rich dissolved organic matter. An accelerated decomposition of organic carbon by protozoa may be restricted to mineral-poor substrates and may be explained mainly by protozoan nutrient regeneration. Growth and grazing in the cultures were compared with methods for in situ estimates. Thymidine incorporation by actively growing bacteria yielded an empirical conversion factor of 1.1 x 10 bacteria per mol of thymidine incorporated into DNA. However, nongrowing bacteria also showed considerable incorporation. Protozoan grazing was found to be accurately measured by uptake of fluorescently labeled bacteria, whereas artificial fluorescent microspheres were not ingested, and selective prokaryotic inhibitors blocked not only bacterial growth but also protozoan grazing.

The Influence of Raingage Integration Time, on Measured Rainfall-intensity Distribution Functions

Rainfall-rate statistics are frequently derived on the basis of raingage recordings having effective integration times of five minutes or more. The conversion of such data to equivalent statistics for an effective integration time of one minute is important in the prediction of microwave system performance. High-resolution tipping-bucket precipitation records for 45 locations in Canada have been analyzed to yield empirical conversion factors appropriate for five- or ten-minute sampling times. Two modes of expression are examined. In one, the ratio of equiprobable one-minute to τ-minute rainfall rates is treated as a function of their probability of occurrence, while in the other it is considered a function of the observed τ-minute rainfall intensity. In each instance the entire Canadian semicontinent could conveniently be divided into three characteristic regions with appropriate raingage correction factors for each region expressed in the form of a power-law over the range of practical interest These results are compared with earlier efforts in Europe, Africa and Australia.

Automatic Determination of Bacterioplankton Biomass by Image Analysis

Image analysis was applied to epifluorescense microscopy of acridine orange-stained plankton samples. A program was developed for discrimination and binary segmentation of digitized video images, taken by an ultrasensitive video camera mounted on the microscope. Cell volumes were estimated from area and perimeter of the objects in the binary image. The program was tested on fluorescent latex beads of known diameters. Biovolumes measured by image analysis were compared with directly determined carbon biomasses in batch cultures of estuarine and freshwater bacterioplankton. This calibration revealed an empirical conversion factor from biovolume to biomass of 0.35 pg of C mum (+/- 0.03 95% confidence limit). The deviation of this value from the normally used conversion factors of 0.086 to 0.121 pg of C mum is discussed. The described system was capable of measuring 250 cells within 10 min, providing estimates of cell number, mean cell volume, and biovolume with a precision of 5%.

Production of planktonic bacteria in Lake Michigan

Bacterial production rates were estimated for the surface waters of a station 100‐m deep in southeastern Lake Michigan during 1984. Production was calculated from incorporation of [3H‐methyl]thymidine and from empirical conversion factors determined from dilution experiments performed throughout the study. The conversion factors (with typical C.V. &lt;40%) varied between 4.7 and 18.3 × l09 cells produced per nanomole of thymidine incorporated into ice‐cold trichloroacetic acid extracts. Our estimates yielded bacteria exponential growth rates between 0.05 and 0.24 h‐1 (C.V. typically &lt;50%) based on the empirical conversion factors. The growth estimates are much lower (0.004–0.020 h‐1) when based on measured 47% thymidine incorporation into DNA and a theoretical conversion factor. The higher growth estimates appear more consistentwith estimated grazing losses. Carbon flux estimates are less certain, due to the possible range of bacterial carbon content and growth efficiencies, but most of the higher growth estimates imply a bacterial carbon demand higher than concurrent 14C‐based primary production measurements. This may mean that a source other than recent primary production is needed to meet this demand.