Average Conversion Factor Research Articles

Elemental C, N, and P cell content of individual bacteria collected at the Bermuda Atlantic Time‐series Study (BATS) site

Accurate assessments of the true elemental cellular content of carbon (C), nitrogen (N), and phosphorus (P) in bacteria have been a major difficulty in microbial research for some time. This study is the first to present single‐cell elemental C, N, and P measurements on natural populations of bacteria from the Sargasso Sea using a transmission electron microscope (TEM) equipped with an X‐ray detector unit. Elemental cell content showed a best fit as a power function of the cell size, and smaller bacteria had significantly more elemental C, N, and P per cell volume than the larger ones (scaling factor a < 1). Contrary to coastal, brackish, and freshwater systems, the bacteria collected in this study appeared to have a molar elemental P :N close to the Redfield ratio of 0.063 (N:P = 16). The geometric mean of C per cell volume analyzed in this study (148 fg C µm−3) was higher than any other estimates reported from coastal and brackish water systems. Total amount of bacterial C calculated from abundance estimates requires an average conversion factor, and the choice of a representative bacterial cell volume is therefore critical. We were able to demonstrate that the outcome of biomass assessments is highly dependant on the choice of cell‐specific conversion factors. By applying cell volumes previously reported from the BATS site, the average 0–250 m depth integration of bacterial C between 1991 and 1996 ranged between 1.7 and 2.5 times less than other recent biomass estimates for these waters.

Reconsidering transmission electron microscopy based estimates of viral infection of bacterioplankton using conversion factors derived from natural communities

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 27:103-110 (2002) - doi:10.3354/ame027103 Reconsidering transmission electron microscopy based estimates of viral infection of bacterio- plankton using conversion factors derived from natural communities Markus G. Weinbauer1,*, Christian Winter2, Manfred G. Höfle1 1GBF - German Research Centre for Biotechnology, Department of Environmental Microbiology, Mascheroder Weg 1, 38124 Braunschweig, Germany 2Netherlands Institute for Sea Research (NIOZ), Department of Biological Oceanography, PO Box 59, 1790 AB Den Burg, Texel, The Netherlands *Present address: Laboratoire d¹Océanographie de Villefranche (LOV), PB 28, 06234 Villefranche, France. E-mail: wein@obs-vlfr.fr ABSTRACT: The frequency of virus infected bacterial cells (FIC) was estimated in surface waters of the Mediterranean Sea, the Baltic Sea and the North Sea using the frequency of visibly infected cells (FVIC) as determined by transmission electron microscopy (TEM) and published average conversion factors (average 5.42, range 3.7 to 7.14) to relate FVIC to FIC. A virus dilution approach was used to obtain an independent estimation of FIC in bacterioplankton, and we provide evidence for the reliability of this approach. Across all investigated environments, FIC ranged from 2.4 to 43.4%. FIC data using both approaches were well correlated; however, the values were higher using the virus dilution approach. This indicates that the TEM approach has the potential to reveal spatiotemporal trends of viral infection; however, it may underestimate the significance of viral infection of bacteria when average conversion factors are used. Using data from the virus dilution approach and the TEM approach, we calculated new conversion factors for relating FVIC to FIC (average 7.11, range 4.34 to 10.78). Virally caused mortality of bacteria estimated from published FVIC data of marine and freshwater systems and using the new conversion factors ranged from not detectable to 129%, thus confirming that viral infection is a significant and spatiotemporally variable cause of bacterial cell death. KEY WORDS: Phage · Virus · Mortality · Lysogeny · Latent period Full text in pdf format NextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 27, No. 2. Online publication date: March 15, 2002 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2002 Inter-Research.

Characteristics and financial performance of a pediatric faculty inpatient attending service: a resource-based relative value scale analysis.

In many children's hospitals, inpatient attending physician services are provided by academic faculty who function as part-time inpatient specialists or hospitalists. Although some have claimed that hospitalist care can reduce length of stay and total hospital resource use and expenses, there are few benchmarks or data regarding physician productivity or the characteristics and financial performance of these programs. The resource-based relative value scale (RBRVS) is a valuable tool for developing national benchmarks and comparing the financial performance of inpatient programs at varying daily census and reimbursement levels. The objectives of this study were to 1) describe physician productivity on an inpatient service as measured by total relative value units (TRVUs) and professional charges, 2) determine whether inpatient collections were adequate to support faculty salaries for the time spent attending, and 3) develop a model to evaluate financial performance of inpatient programs at varying census and TRVU reimbursement levels. A retrospective review of hospital discharge and faculty practice billing data between June 1997 and July 1998 was conducted in a general medical service in a regional, 208-bed, university-affiliated children's hospital in the Pacific Northwest. Of 4113 patients who were admitted to the children's hospital general medical service during a 12-month period, faculty part-time hospitalists (N = 28) served as the attending physician for 1738 (42%). On an annual basis, faculty attended for an average of 29.1 days (median: 21.0; range: 7.0-97.0), with an average daily patient census (ADC) of 7.2 (median: 6.5; range: 2.8-12.0). Inpatient attendings billed for 1738 initial visits and 3957 subsequent visits. Total physician productivity for the inpatient attending group during 1 year included 12 085 TRVUs and gross professional charges of $777 743. The average payment, or conversion factor (CF), was $24.46/TRVU (71% of Medicare CF). The cash collection rate was 38%, reflecting a payor mix that included 54% Medicaid, 28% commercial payors, 12% health maintenance organization, and 6% other payors. On a weekly basis, physicians generated an average of 109 TRVUs and collected $2665 in cash. The average salary cost per RVU was $23.40, and weekly faculty salary and benefit expenses were $2550. After operating expenses and academic taxes totaling 24% were deducted ($5.87/TRVU), RBRVS-based payments and cash collections covered 79% of average faculty weekly salaries. Financial modeling showed that either an average CF of $31/TRVU or an ADC of 9 patients per day on the inpatient service would be required to generate sufficient revenue to support physician salaries and operating expenses. For a faculty inpatient attending service in a children's hospital with an ADC of 7, a $24.46 RBRVS-based CF payment is inadequate to support faculty salaries and operating expenses for the time spent attending. Inpatient services in similar payor environments with comparable expenses and staffed by faculty who care for fewer than 9 patients per day will not cover typical faculty salary costs and operating expenses.

Bronchial Rn dose survey for residences

The bronchial dosimeter for Rn progeny proposed by Yu and Guan in 1998 was employed to survey the bronchial dose from Rn progeny in 30 residences in Hong Kong. An average bronchial deposition fraction of Rn progeny was obtained as 0.0334, which gave an average dose conversion factor (DCF) of 8.5 mSv WLM −1. The mean values of potential α energy concentration (PAEC) deposited in the tracheobronchial region (PAEC T−B), total PAEC in air (PAEC T), annual effective dose ( E), concentration of Rn gas (RC) and annual dose conversion factor (ADCF) for all the residential sites combined were 0.11±0.05, 3.1±1.4 mWL, 1.2±0.5 mSv yr −1, 23±10 Bqm −3 and 0.055±0.020 (mSv yr −1 per Bqm −3), respectively, with air-conditioned sites (AC sites) and non-AC sites having significantly different mean ADCF values. The indoor relative humidity affected PAEC T and RC PAEC T−B and E with high confidence levels (>95%).

Estimating Factors to Convert Chinese ‘Total Dust’ Measurements to ACGIH Respirable Concentrations in Metal Mines and Pottery Industries

Historical data on the dust exposures of Chinese workers in metal mines (iron/copper, tin, tungsten) and pottery industries are being used in an ongoing joint Chinese/United States epidemiological study to investigate the exposure–response relationship for the development of silicosis, lung cancer, and other diseases. The historical data include ‘total dust’ concentrations determined by a Chinese method. Information about particle size distribution and the chemical and mineralogical content of airborne particles is generally not available. In addition, the historical Chinese sampling strategy is different from a typical American eight-hour time-weighted average (TWA) sampling strategy, because the Chinese samples were collected for approximately 15 minutes during production so the sample could be compared to their maximum allowable concentration (MAC) standard. Therefore, in order to assess American respirable dust exposure standards in light of the Chinese experience, factors are needed to convert historical Chinese total dust concentrations to respirable dust concentrations. As a part of the joint study to estimate the conversion factors, airborne dust samples were collected in 20 metal mines and 9 pottery factories in China during 1988 and 1989 using three different samplers: 10mm nylon cyclones, multi-stage ‘cassette’ impactors, and the traditional Chinese total dust samplers. More than 100 samples were collected and analysed for each of the three samplers. The study yielded two different estimates of the conversion factor from the Chinese total dust concentrations (measured during production processes) to respirable dust concentrations. The multivariate analysis of variance (MANOVA) reveals that, with a fixed sampling/analysis method, conversion factors were not statistically different among the different job titles within each industry. It also indicates that conversion factors among the industries were not statistically different. However, the two estimates consistently showed that conversion factors were the lowest in the pottery industry. Average conversion factors were then calculated for each of the estimates across the industries studied. A pooled mean conversion factor, 0.25±0.04, was then derived for all the job titles and industries. Respirable dust levels were estimated from the historical ‘total dust’ concentrations collected between 1952 and 1992 by adopting the American standard.

Estimating Factors to Convert Chinese ‘Total Dust’ Measurements to ACGIH Respirable Concentrations in Metal Mines and Pottery Industries

Historical data on the dust exposures of Chinese workers in metal mines (iron/copper, tin, tungsten) and pottery industries are being used in an ongoing joint Chinese/United States epidemiological study to investigate the exposure–response relationship for the development of silicosis, lung cancer, and other diseases. The historical data include ‘total dust’ concentrations determined by a Chinese method. Information about particle size distribution and the chemical and mineralogical content of airborne particles is generally not available. In addition, the historical Chinese sampling strategy is different from a typical American eight-hour time-weighted average (TWA) sampling strategy, because the Chinese samples were collected for approximately 15 minutes during production so the sample could be compared to their maximum allowable concentration (MAC) standard. Therefore, in order to assess American respirable dust exposure standards in light of the Chinese experience, factors are needed to convert historical Chinese total dust concentrations to respirable dust concentrations. As a part of the joint study to estimate the conversion factors, airborne dust samples were collected in 20 metal mines and 9 pottery factories in China during 1988 and 1989 using three different samplers: 10mm nylon cyclones, multi-stage ‘cassette’ impactors, and the traditional Chinese total dust samplers. More than 100 samples were collected and analysed for each of the three samplers. The study yielded two different estimates of the conversion factor from the Chinese total dust concentrations (measured during production processes) to respirable dust concentrations. The multivariate analysis of variance (MANOVA) reveals that, with a fixed sampling/analysis method, conversion factors were not statistically different among the different job titles within each industry. It also indicates that conversion factors among the industries were not statistically different. However, the two estimates consistently showed that conversion factors were the lowest in the pottery industry. Average conversion factors were then calculated for each of the estimates across the industries studied. A pooled mean conversion factor, 0.25±0.04, was then derived for all the job titles and industries. Respirable dust levels were estimated from the historical ‘total dust’ concentrations collected between 1952 and 1992 by adopting the American standard.

Conversion of Nitrogen to Protein and Amino Acids in Wild Fruits

Protein content of plant tissues is usually estimated by multiplying total nitrogen by a conversion factor of 6.25. This technique assumes that all nitrogen originates from protein. When applied to fruit pulp, it overestimates protein content because pulp typically contains free amino acids and many nitrogenous secondary metabolites. At issue is the extent of error and, consequently, what the conversion factor between nitrogen and protein should be. We calculated a conversion factor based on pulp samples from 18 species collected in the southeastern United States. We also report a new and simple method of estimating protein and free amino acids in fruit pulp. Because previous studies have found high variation in protein and secondary metabolite content among fruit species, use of a single conversion factor for all species will generate error. In an attempt to reduce such error, we calculated protein contents and conversion factors separately for two common fruit types: lipid-rich/carbohydrate-poor and lipid-poor/carbohydrate-rich. We found no difference between these types of fruit and hence combined results in calculating an average conversion factor of 5.64. Use of an accurate conversion factor is important in estimating protein consumption by wild animals and in formulating diets of captive animals. It can also reveal whether loss of body mass in captive animals on fruit diets is due to insufficient protein consumption, secondary metabolite toxicity, or an imbalance of amino acids.

Micro-Raman analysis of residual stresses and phase transformations in crystalline silicon under microindentation

Vickers microindentations obtained with loads between 0.05 N and 2 N were performed on crystalline (100) silicon. The residual stress field and the different structural states induced by loading were studied by mapping the indented zones by their micro-Raman response. A Raman signature of amorphous silicon is found in the center of the impression. The energy of the Γ25 zone center phonon is found to vary from 522 cm−1 when probing the silicon at a distance of 80 μm from the center of the indentation up to 527 cm−1 when probing the pileup region of the impression. When probing cracked zones in the vicinity of the pileup region, wave numbers as high as 536 cm−1 are measured. The stress components induced by a point indentation (1 N) have been calculated from analytical expressions given in the literature. For an average conversion factor of 3.2 cm−1/GPa, the residual local stresses after unloading are found of the same order of magnitude or even larger than the calculated stresses that are generated during loading. A tentative explanation is proposed. Finally a systematic laser-induced thermal treatment of the central area and of the pileup region of indentations was performed. It is shown that the amorphous silicon in the center can partly recrystallize but that the residual stress state in the pileup region cannot be completely relaxed by local laser heating.

Biological phosphorus removal by pure culture of Lampropedia spp.

Lampropedia spp. is a Gram-negative, Neisser-positive coccus that was isolated from EBPR (enhanced biological phosphate removal) activated sludge laboratory plants operating on dairy and piggery wastewaters. In aerobic growth tests carried out on sodium acetate, Lampropedia spp. stored PHB up to 12% w/w. Biomass yield was estimated at 0.55 g VSS.g −1 HAc and specific growth rate at 0.045 h −1. The experimental maximum acetic acid removal rate was 71.86 mg HAc.g −1 VSS.h −1 with a semisaturation constant of 71.78 mg.l −1. Batch tests were carried out to check whether Lampropedia spp. was capable of enhanced biological phosphorus removal. Under anaerobic conditions, Lampropedia spp. sequestered acetate and stored PHB with an average conversion factor of 0.33 mg PHB.mg −1 HAc. The measured maximum PHB storage capacity was 31% w/w, with a maximum specific PHB accumulation rate of 17 mg PHB.g −1 VSS.h −1 and a specific anaerobic acetate uptake rate of 57 mg HAc.g −1 VSS.h −1. The experimental ratio between phosphorus released and acetate taken up was low, on average 0.044 mg PO 4-P.mg −1 HAc, with a specific rate ranging from 1.7 to 3.6 mg PO 4-P.g −1 VSS.h −1 at pH 7.5. Despite the low figure, fractionation analyses showed that in anaerobic conditions the released phosphate comes from cell polyphosphate degradation. Therefore, all the results allow us to conclude that Lampropedia spp. can be classified amongst the phosphorus accumulating bacteria

Surface Radiative Fluxes in Sub-Sahel Africa

Abstract This paper reports results of observations of radiative fluxes measured in sub-Sahel Africa during a 2-yr period (1992–94). Shortwave radiation in the solar spectrum (0.2–4.0 μm), photosynthetically active radiation (0.4–0.7 μm), and longwave radiation (4.0–50.0 μm) were observed. In this study, the annual variability and the effects of dust on these fluxes (in particular, on the ratio of photosynthetically active radiation to the total shortwave radiation) were characterized. This ratio, known as the conversion factor, is important in modeling net primary productivity and the total CO2 budget. In the past, this ratio was assumed to be constant. The authors’ observations indicate that the daily average conversion factor has a strong annual cycle with a minimum of 0.41 in the middle of the dry season and a maximum of 0.55 in the first half of the rainy season, which is consistent with theoretical computations. The 2-yr mean is 0.49, only about 2% less than the nominal value of 0.50. The 2-yr mean ...

A Cohort Study with Regard to the Risk of Haematological Malignancies in Patients treated with X-Rays for Benign Lesions in the Locomotor System: II. Estimation of Absorbed Dose in the Red Bone Marrow

A cohort study with regard to the risk of haematological malignancies was performed on about 20,000 patients who in 1950-1964 received roentgen treatment for benign conditions in the locomotor system. In order to estimate the mean absorbed red bone marrow dose the treatments were classified as concerning 10 sites (cervical spine, thoracic spine, lumbar spine, sacral region, shoulder, hip, elbow, wrist, knee and ankle). The four last-mentioned sites do not normally contain red bone marrow in adults and their contribution to the mean absorbed dose was regarded as zero. For the other 6 sites random samples consisting of 30 patients for each site were drawn from the cohort. By use of the treatment records and data from the literature on some physical parameters and red bone marrow distribution in normal adult persons, average conversion factors were calculated by which the subscribed surface dose could be converted into mean absorbed dose in red bone marrow. These conversion factors were then applied on the whole cohort and used for stratification of it according to different levels of exposure.

Calculation of Air Kerma to Average Glandular Tissue Dose Conversion Factors for Mammography

Among the quantities used for dose specification in mammography the average absorbed dose in glandular tissue is most appropriate for risk assessments. Generally, average absorbed dose in glandular tissue is derived from measurement of air kerma free-in-air combined with conversion factors obtained from radiation transport calculations in mathematical breast models. Air kerma to glandular tissue dose conversion factors are published by various authors as a function of half-value layer (HVL) for simple breast phantoms. Calculations by different authors differ in radiation transport codes, photon interaction data, photon spectra, composition and thickness of superficial layer (representing skin and subcutaneous adipose tissue), presence of compression plate, and are not performed with the tissue compositions recommended by the ICRU. Protocols for dosimetry in mammography in different European countries (UK, Netherlands, Sweden) use results from different authors. To study the influence of the parameters indicated, air kerma to glandular tissue dose conversion factors, g, are calculated using the MCNP radiation transport code. Use of different spectra can cause differences in g values up to about 7%. The use of a compression plate results in a 4.5±1.5% smaller g value for the same HVL. The use of MCPLIB cross sections results in 10% higher g values compared to the use of XCOM data. The influence of the backscatter material (composition and thickness) on the g value is marginal (<1%). The different superficial layers used result in differences in g values of up to 19%. When the breast thickness is changed from 2 cm to 8 cm, g values decrease by a factor of about 4. Employing Hammerstein's tissue compositions compared to those from the ICRU results in differences in g values up to about 14%.

Calculation of Air Kerma to Average Glandular Tissue Dose Conversion Factors for Mammography

Calculation of Air Kerma to Average Glandular Tissue Dose Conversion Factors for Mammography

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

Incorporation of [(14)C]leucine into proteins of bacteria was studied in a temperate mesohumic lake. The maximum incorporation of [(14)C] 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 × 10(16) cells mol(-1) and 7.71 × 10(15) μm(3) mol(-1), if the high initial values were excluded. Using the cumulative method, the average conversion factor was 5.38 × 10(15) μm(-3) mol(-1) I . The empirically measured factor converting bacterial biomass to carbon was 0.36 pg C μm(-3) or 33.1 fg C cell(-1). Bacterial production was highest during the growing season, ranging between 1.8 and 13.2 μg C liter(-1) day(-1), and lowest in winter, at 0.2-2.9 μg 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 [(14)C]leucine incorporation proved to be a simple and useful method for estimating bacterial production in humic water. However, an appropriate amount of [(14)C]leucine has to be used to ensure the maximum uptake of label and to minimize isotope dilution.

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.

Determination of bacterioplankton biomass, net production and growth efficiency in the Southern Ocean

Several conversion factors are r e q w e d for the eshmation of bacterial biomass, net production and carbon demand from epifluorescence microscopy and measurements of [3 H]-thymidlne and [3 H]-leucine incorporation rates. These conversion factors were evaluated simultaneously in mixed cultures of bacterial assemblages from the Weddell/Scoha Confluence of the Southern Ocean. The cultures were grown in the dark at + l 'C. Conversion factors were calculated for each culture by regression analyses of cumulative parameters. Average conversion factors were: 1.1 X 1018 cells per m01 thymidme incorporated into cold TCA precipitate, 7.5 X 1015 pm3 of biovolume per m01 leucine incorporated into cold TCA precipitate, 0 4 pgC biomass per wm3 of biovolume, and 40% carbon growth yield.

Estimation of diffusion limitation after pneumonectomy from carbon monoxide diffusing capacity

In three foxhounds, diffusing capacity for carbon monoxide (D l CO) was reduced by 25–30% after left pneumonectomy. Based on previous morphometric data in animals and physiologic data in humans, this reduction should not result in any impairment in gas exchange. However, experimental evidence indicates that diffusion limitation develops during exercise after pneumonectomy. Our objective is to determine whether this diffusion limitation to gas exchange can be predicted from physiologic measurements of D l CO. D l CO measured by the rebreathing technique was translated into diffusing capacity for O 2 (D l O 2 ) using an average conversion factor for canids obtained morphometrically (Weibel et al., Respir. Physiol. 54: 173–188, 1983). Arterial O 2 saturation (Sa O 2 ) at various intensities of stead state exercise was calculated from D l O 2 and measured values of O 2 consumption, alveolar P O 2 , hemoglobin and arterial pH, and compared to observed Sa O 2 . After pneumonectomy, Sa O 2 declined progressively with increasing exercise load. In all dogs, the observed pattern of arterial O 2 saturation could be predicted from D l CO measured at similar work loads. The relationship between predicted (Pr) and observed (Ob) Sa O 2 is: Sa O 2(Pr) = 22.73 + 0.77Sa O 2(Ob) , r = 0.92. The slope is significantly less than 1.0 ( P<0.005), indicating that other factors must also contribute to arterial desaturation. We conclude that physiologic measurement of D l CO is a meaningful indicator of diffusion limitation to gas exchange. In the foxhound, a modest reduction in D l CO significantly impairs O 2 transport during exercise; but other gas exchange abnormalities, e.g. ventilation perfusion inhomogeneity, must also develop.

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.

Calculation of Cell Production from [ 3 H]Thymidine Incorporation with Freshwater Bacteria

The conversion factor for the calculation of bacterial production from rates of [H]thymidine incorporation was examined with diluted batch cultures of freshwater bacteria. Natural bacterial assemblages were grown in aged, normal, and enriched media at 10 to 20 degrees C. The generation time during 101 growth cycles covered a range from 4 to >200 h. The average conversion factor was 2.15 x 10 cells mol of thymidine incorporated into the trichloroacetic acid (TCA) precipitate (standard error = 0.29 x 10; n = 54), when the generation time exceeded 20 h. At generation times of <20 h, the average conversion factor was 11.8 x 10 cells mol of thymidine incorporated into TCA precipitate (standard error = 1.72 x 10; n = 47). The amount of radioactivity in purified DNA increased with decreasing generation time and increasing conversion factor (calculated from the TCA precipitate), corresponding to a decrease in the percentage in protein. The conversion factors calculated from purified DNA or from the TCA precipitate gave the same variability. Conversion factors did not change significantly with the medium, but were significantly higher at 20 degrees C than at 15 and 10 degrees C. A detailed examination of the [H]thymidine concentrations that were needed to achieve maximum labeling in DNA was carried out 6 times during a complete growth cycle. During periods with low generation times and high conversion factors, 15 nM [H]thymidine was enough for the maximum labeling of the TCA precipitate. This suggests that incorporation of [H]thymidine into DNA is probably limited by uptake during periods with generation times of <20 h and that freshwater bacterioplankton cell production sometimes is underestimated when a conversion factor of 2.15 x 10 cells mol of thymidine incorporated is used.

Energy content of macrobenthic invertebrates: general conversion factors from weight to energy

In ecological studies, especially in those dealing with energy circulation in nature, determinations of the energy content of organisms are inevitable. Energy determinations are, however, laborious and time-consuming. Average conversion factors based on different species form various areas and seasons may often be a shortcut for overcoming this problem. To establish general energy conversion factors for aquatic invertebrate groups, we used 376 values of J · mg −1 DW and 255 values of J · mg −1 AFDW, representing 308 and 229 species, respectively. The dry-weight-to-energy factors were highly variable both within and between taxonomic groups, e.g.: Porifera, 6.1 J · mg −1 DW; insect larvae, 22.4 J · mg −1 DW (median values). The energy-conversion factors related to AFDW showed a much smaller dispersion with a minimum median value of 19.7 J · mg −1 AFDW (Ascidiacea) and a maximum of 23.8 J · mg −1 AFDW (insect larvae). Within taxonomic groups, the 95% confidence intervals (AFDW) were only a few percent of the median values. The use of energy-conversion factors based on AFDW is preferable due to their lower dispersion. For aquatic macrobenthic invertebrates, a general conversion factor of 23 J · mg −1 AFDW can be used.