The uptake of %-labeled organic compounds has been used by many workers to study heterotrophic microorganisms in natural waters. IIowevcr, if flux rates of organic compounds are to be mcasurcd, the loss of '"CO2 during incubation becomes an important source of error. A method is proposed in which the experiment is run in a closed system and the l'C02 collected after killing and acidification.Phenethylamine on Chromatographic paper is the absorbing agent and the paper is counted by liquid scintillation.Studies of 19 compounds from pond water showed that 60% (aspartic acid) to 8% (arginine) of the labeled material cntcring the microorganisms was respired. INTRODUCITONDissolved organic compounds exist in natural waters at such low concentrations (a few pg/liter) that only radioactive tracer techniques arc sensitive enough to Eollow their flux. Aquatic bacteria appear to be chiefly responsible for the removal of these compounds from the water, and various modiRcations of the basic Parsons and Strickland (1963) technique have been devclopcd to quantify the kinetics of uptake (Wright and Hobbie 1966;Vaccaro and Jannasch 1967). These methods all underes.timate the total uptake because of loss of 14co2. Hamilton and Austin (1967) estimated that more than half of the labeled 14C ( as glucose) taken up by a culture of bacteria was immediately respired. Respiration loss in natural plankton was measured with an ion chamber and electromcter by IIobbie, Crawford, and Webb ( 1968), but the method allowed only six o,r seven experim,ents a day. The method presented here can be used with more than a hundred samples per day, yet is as accurate as ion chamber counting. METHODSThe basic technique consists of adding different amounts of a labeled compound,
The importance of vacteria in the cycling of carbon in the Pamlico River estuary was studied by measuring the rates of uptake of organic compounds. Our methods allowed analysis with the Michaelis—Menten kinetics equations, and both the rates of uptake of dissolved free amino acids (DFAA) and glucose as well as the percentage of carbon subsequently respired as CO2 were determined. In addition, the concentrations of the amino acids in the water were determined using ion exchange chromatography. Other tests included measurements of primary productivity and of the effects of the other amino acids in the water upon the uptake of one amino acid. There was considerable variation in the heterotrophic activity over time and distance probably caused by patchiness in distribution of plankton and dissolved compounds in the water. Although there is some competition between amino acids being taken up, the effect upon kinetics measurements is probably negligible. Tests made every 3 hr showed a coefficient of variability (CV) of the measured maximum velocity of uptake (Vmax) of aspartic acid to be only 26%, and a similar CV was found for daily samples. In several instances the uptake of one amino acid was found to be competitively inhibited by the presence of another amino acid, but the concentrations necessary to inhibit were far above natural concentrations and such effects are probably unimportant in nature. Mutual inhibition was found between the similar amino acid pairs glutamic acid and aspartic acid, threonine and serine, glycine and alanine, and leucine and alanine. Highest Vmax values were found during the summer months and early fall and ranged from a high of 69.42 mg C/1°hr for alanine in August to less than 0.20 mg C/1°hr for most of the substrates tested in the colder months. The Vmax values for glucose uptake (0.06 to 9.64 mg C/1°hr) indicate that this estuarine system is one of the most microbially—active environments tested. The DFAA were presented in the water at concentrations of from 10 to 30 mg C/1; over half of this was ornithine, glycine, and serine. The DFAA were only about 0.2% of the total dissolved organic carbon in the water. Further, seasonal variations of DFAA concentrations, generally paralleling those of primary productivity, suggested that the amino acids originated from algal excretion and the decay of algal cells. The orders of abundance and concentrations of individual amino acids were similar to those reported for other bodies of water. When the natural concentration of a substrate is known the actual velocity of uptake (Vn) or flux for that substrate may be found. Flux rates were only 1%—10% of the Vmax values in the coldest months; the highest values were found in the warmest months. At each experimental concentration of amino acid, a certain amount was taken up, and a percentage of this amount was oxidized to caron dioxide. This percentage was constant for a particular amino acid in spite of varying experimental times, substrate concentrations, and temperatures. Leucine had the lowest percen...
Dissolved organic matter in York River estuary included 38 micrograms of free amino acids per liter. The highest concentrations were of glycine, serine, and ornithine. Of the 14 amino acids studied for uptake by planktonic bacteria, glycine, methionine, and serine had the greatest flux rates. The total amino acid flux represented from 1 to 10 percent of the daily photosynthetic carbon fixation.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.