MEASUREMENT OF THE INCORPORATION RATES OF 4 AMINO-ACIDS INTO PROTEINSFOR ESTIMATING BACTERIAL PRODUCTION

In aquatic ecosystems, [H-3]thymidine incorporation into bacterial DNA and [H-3]leucine incorporation into proteins are usually used to esti mate bacterial production. The incorporation rates of four amino acids (leucine, tyrosine, lysine, alanine) into proteins of bacteria were m easured in parallel on natural freshwater samples from the basin of th e river Meuse (Belgium). Comparison of the incorporation into proteins and into the total macromolecular fraction showed that these differen t amino acids were incorporated at more than 90% into proteins. From i ncorporation measurements at four subsaturated concentrations (range, 2-77 nM), the maximum incorporation rates were determined. Strong corr elations (r > 0.91 for all the calculated correlations) were found bet ween the maximum incorporation rates of the different tested amino aci ds over a range of two orders of magnitude of bacterial activity. Bact erial production estimates were calculated using theoretical and exper imental conversion factors. The productions calculated from the incorp oration rates of the four amino acids were in good concordance, especi ally when the experimental conversion factors were used (slope range, 0.91-1.11, and r > 0.91). This study suggests that the incorporation o f various amino acids into proteins can be used to estimate bacterial production.