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D M Karl

Publications and source records attributed to D M Karl.

31 records · Page 2Linked to original sources
PubMed1984

Laboratory calibrations of the [h]adenine technique for measuring rates of RNA and DNA synthesis in marine microorganisms.

The nucleic acid synthesis rates of several marine phytoplankton and bacteria grown in chemostat and batch cultures were measured by using [H]adenine. The [H]adenine synthesis rates showed excellent agreement with the known rates of synthesis estimated from chemical RNA and DNA data. Under certain conditions, RNA turnover and ATP pool compartmentalization produce inaccuracies in synthesis measurements made with [H]adenine. However, accurate measurements of the rates of microbial RNA and DNA synthesis can be made in any environmental situation provided a few simple precautions are observed. First, time course experiments are recommended. Second, experiments should be conducted for periods long enough to avoid problems arising from disequilibria of internal ATP pools. Finally, exogenous [H]adenine should remain in the medium over the length of the time course.

Journal Article↗
PubMed1983

ATP as a biomass indicator for closed ecosystems.

Nucleotide measurements have been used as biomass indicators in microbial ecology. We report the use of this metric in materially closed, energetically open microbial ecosystems. Our results indicate that: (i) both ATP concentrations and pO2 show an increase from time of closure; (ii) ATP concentrations (0.2 1.2 ng/ml) are approximately 2 3 times higher than open ocean water; (iii) there is an apparent oscillation of ATP concentrations on the order of 50 days; and (iv) within experimental limitations the ratios of ATP concentrations to observed total cell counts is constant.

Adenosine Triphosphate↗
PubMed1982

Selected nucleic Acid precursors in studies of aquatic microbial ecology.

The use of radiolabeled nucleosides and nucleic acid bases to estimate the rates of RNA and DNA synthesis in naturally occurring microbial assemblages requires numerous assumptions, several of which are evaluated herein. Comparative time series analyses of the uptake and incorporation, labeling specificity, and extent of catabolism of [2-H]adenine, [methyl-H]thymidine, and [5-H]uridine were performed with pure bacterial and algal cultures, as well as with environmental samples. [H]thymidine yielded the most variable results, especially with regard to the extent of nonspecific macromolecular labeling. The pathways of [H]thymidine and [H]adenine metabolism were further evaluated by isotope dilution methods and by comparing incorporation patterns of thymidine labeled at different sites of the molecule. The advantages, uncertainties, and limitations of the use of radiolabeled nucleic acid precursors in studies of aquatic microbial ecology are discussed and a prospectus for future studies presented.

Journal Article↗
PubMed1981

Simultaneous rates of ribonucleic Acid and deoxyribonucleic Acid syntheses for estimating growth and cell division of aquatic microbial communities.

A method for measuring rates of ribonucleic acid (RNA) and deoxyribonucleic acid (DNA) syntheses using a single radioactive precursor has been devised and tested using bacterial cultures and natural assemblages of marine and freshwater microorganisms. The procedure is based upon the uptake and incorporation of exogenous [H]adenine into cellular adenosine triphosphate and deoxyadenosine triphosphate pools which serve as the immediate precursors for the adenine incorporated into RNA and DNA, respectively. It is proposed that the DNA/RNA rate ratio is correlated with the specific growth rate of microorganisms and can be used as an index for estimating and comparing the productivities of microbial assemblages in nature. This technique can also be used to detect discontinuous growth and cell division processes which frequently occur in surface plankton populations. The DNA/RNA rate ratios measured in a variety of aquatic ecosystems ranged from 3.3 to 31.8% without significant correlation to total microbial biomass.

Journal Article↗
PubMed1980

Effects of alkaline phosphatase activity on nucleotide measurements in aquatic microbial communities.

Alkaline phosphatase (APase) activity was detected in aquatic microbial assemblages from the subtropics to Antarctica. The occurrence of APase in environmental nucleotide extracts was shown to significantly affect the measured concentrations of cellular nucleotides (adenosine triphosphate, adenosine diphosphate, adenosine monophosphate, guanosine triphosphate, uridine triphosphate, and cytidine triphosphate), adenylate energy charge, and guanosine triphosphate/adenosine triphosphate ratios, when conventional methods of nucleotide extraction were employed. Under the reaction conditions specified in this report, the initial rate of hydrolysis of adenosine triphosphate was directly proportional to the activity of APase in the sample extracts and consequently can be used as a sensitive measure of APase activity. A method was devised for obtaining reliable nucleotide measurements in naturally occurring microbial populations containing elevated levels of APase activity. The metabolic significance of APase activity in microbial cells is discussed, and it is concluded that the occurrence and regulation of APase in nature is dependent upon microscale inorganic phosphate limitation of the autochthonous microbial communities.

Journal Article↗
PubMed1979

Measurement of microbial activity and growth in the ocean by rates of stable ribonucleic Acid synthesis.

A relatively simple and extremely sensitive technique for measuring rates of stable ribonucleic acid (RNA) synthesis was devised and applied to bacterial cultures and seawater samples. The procedure is based upon the uptake and incorporation of exogenous radiolabeled adenine into cellular RNA. To calculate absolute rates of synthesis, measurements of the specific radioactivity of the intracellular adenosine 5'-triphosphate pools (precursor to RNA) and of the total amount of radioactivity incorporated into stable cellular RNA per unit time are required. Since the rate of RNA synthesis is positively correlated with growth rate, measurements of RNA synthesis should be extremely useful for estimating and comparing the productivities of microbial assemblages in nature. Adenosine 5'-triphosphate, adenylate energy charge, and rates of stable RNA synthesis have been measured at a station located in the Columbian Basin of the Caribbean Sea. A subsurface peak in RNA synthesis (and therefore growth) was located within the dissolved oxygen minimum zone (450 m), suggesting in situ microbiological utilization of dissolved molecular oxygen. Calculations of the specific rates of RNA synthesis (i.e., RNA synthesis per unit of biomass) revealed that the middepth maximum corresponded to the highest specific rate of growth (420 pmol of adenine incorporated into RNA.day) of all depths sampled, including the euphotic zone. The existence of an intermediate depth zone of active microbial growth may be an important site for nutrient regeneration and may serve as a source of reduced carbon for mesopelagic and deep sea environments.

Journal Article↗
PubMed1978

Occurrence and ecological significance of GTP in the ocean and in microbial cells.

A comparison between the ATP concentrations based on peak height light emission values (0 to 3 s) and integrated light flux determinations (15 to 75 s) for a variety of seawater samples revealed that the integrated method of light detection consistently yielded higher ATP concentrations, ranging from 1.38 to 2.35 times larger than the corresponding peak ATP values. A significant correlation (r = 0.923) was observed for a plot of DeltaADP (i.e., integrated ATP - peak ATP) versus GTP + UTP, suggesting that the analytical interference on the ATP assay was the result of the presence of non-adenine nucleotide triphosphates. Size-fractionation studies revealed an enrichment of the non-adenine nucleotide triphosphates, relative to ATP, in the smallest size fraction analyzed (<10 mum). Investigations were conducted with 20 species of unicellular marine algae to determine their intracellular nucleotide concentrations, and these determinations were compared to the levels measured in lab cultures of the marine bacterium Serratia marinorubra. These results indicated that the intracellular GTP/ATP ratios in S. marinorubra increase in direct proportion to the rate of cell growth, and that the GTP/ATP ratios in bacteria are much greater than in growing algae, presumably due to the differences in rates of cellular biosynthesis. It is concluded that quantitative determinations of GTP/ATP ratios in environmental sample extracts may be useful for measuring microbial growth.

Journal Article↗
PubMed1975

Parathyroid hormone status and renal responsiveness in familial hypophosphatemic rickets.

Basal serum and urinary biochemical parameters and their response to PTH or calcium infusion were examined in 14 untreated patients with familial hypophosphatemic rickets (FHR) from 5 kindreds and 9 normal control subjects after a period of dietary equilibration. FHR subjects exhibited significantly elevated basal serum iPTH levels (FHR: 11.4 +/- 0.8, controls: 5.1 +/- 0.5 ng/ml, P less than 0.001) and urinary cAMP excretion (FHR: 7.83 +/- 0.81, controls: 3.78 +/- 0.46 nmol/mg creatinine P less than 0.001). In response to PTH infusion (6 units/kg over 4 hours) FHR subjects exhibited a mean 34% decrease in TRP and a 22-fold increase in cAMP excretion, both comparable to the control response. Calcium infusion (10 mg/kg over 1 h) rapidly suppressed serum iPTH and urinary cAMP values in FHR subjects. However, TRP remained inappropriately low for the level of serum phosphate. Basal and post-calcium infusion serum iPTH levels correlated positively with urinary cAMP in FHR subjects and controls. Pre- and post-calcium infusion iPTH levels correlated with serum calcium in FHR subjects. Mean Salivary phosphate concentration was significantly reduced in FHR subjects (FHR: 12.68 +/- 0.87, controls: 22.47 +/- 2.16 mg/100 ml, P less than 0.001). However, calculated salivary phosphate clearance rates were similar in FHR and control subjects. PTH or calcium infusion did not significantly alter salivary phosphate concentration or clearance rates in either patients or controls. We concluded that untreated FHR patients exhibit a state of mild secondary hyperparathyroidism and an at least normal renal phosphaturic response to PTH. In addition, there is no evidence for increased salivary phosphate excretion in FHR.

25-Hydroxyvitamin D3 1-alpha-Hydroxylase↗