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Appl Environ Microbiol. 1974 March; 27(3): 488-495
Copyright © 1974 American Society for Microbiology. All Rights Reserved.

Heterotrophic Potential for Amino Acid Uptake in a Naturally Eutrophic Lake¹

^a Department of Microbiology and School of Oceanography, Oregon State University, Corvallis, Oregon 97331

ABSTRACT

The uptake of sixteen ¹⁴C-labeled amino acids by the indigenous heterotrophic microflora of Upper Klamath Lake, Oregon, was measured using the kinetic approach. The year-long study showed a seasonal variation in the maximum uptake velocity, V_max, of all the amino acids which was proportional to temperature. The maximum total flux of amino acids by the heterotrophic microflora ranged from 1.2 to 11.9 µmol of C per liter per day (spring to summer). Glutamate, asparagine, aspartate, and serine had the highest V_max values and were respired to the greatest extent. The percentages of the gross (net + respired) uptake of the amino acids which were respired to CO₂ ranged from 2% for leucine to 63% for glutamate. Serine, lysine, and glycine were the most abundant amino acids found in Upper Klamath Lake surface water; at intermediate concentrations were alanine, aspartate, and threonine; and the remaining amino acids were always below 7.5 x 10^-8 M (10 µg/liter). The amino acid concentrations determined chemically appear to be the sum of free and adsorbed amino acids, since the values obtained were usually greater than the (K_t + S_n) values obtained by the heterotrophic uptake experiments.

² Present address: Canada Centre for Inland Waters, Lakes Research Division, Burlington, Ontario, Canada.

¹ Published as technical paper no. 3727, Oregon Agricultural Experiment Station.