The Utilization of Dissolved Free Amino Acids by Estuarine Microorganisms

Abstract

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...

Attached and Free-Floating Bacteria in the Fraser River Estuary, British Columbia, Canada

“…Heterotrophic activity Uptake expressed as pg glucose I-' h-'. Percent respiration calculated as respired uptake divided by total uptake ( a ) JH-glucose uptake (After Azam and Holm-Hansen, 1973) Cruise River Plume Strait T V,,, , , T=Turnover time in hours V,,,, expressed in pg glucose 1-' h-' K t + Sn expressed in pg glucose 1-' Hobbie and Crawford (1969b) Pamlico River Estuary "C 3.25-9.5 Crawford et al (1974) Pamlico River Estuary I4C 0.15-24.1 0.2-22 0.83-49.9 Vaccaro and Jannasch (1966) Woods Hole Dock 1 4~ 0.275 1.6 Seki et al (1969) Nanaimo River Estuary I4C' 0.187-156 Wood and Chua (1973) Toronto Harbour "C 0.51-10.59 12-304 20-37 1 Seki et al (1975) Tokyo Bay 14C 18 8.7 155…”

Nutrient limitation of bacterioplankton growth in Lake Dillon, Colorado

“…On an annual areal basis, C equivalent to 60% (1987) and 66% (1988) of net primary production was converted to bacterioplankton biomass. If the growth efficiency of bacterioplankton varies between 40 and 60% (most common values vary between 10 and 90% depending on substrate: Hobbie and Crawford 1969;Crawford et al 1974;Bell 1984;Jorgensen 1986), then C equivalent to l-2 times net primary production was processed by the bacterioplankton of the lake.…”

Utilization of inorganic and organic nitrogen by bacteria in marine systems1

“…In both cases uptake rates were low, and the exact specific activity has little effect. Individual amino acids were estimated as 0.10 PM, and total free amino acids as 0.30 PM (Crawford et al 1974). …”