Microbial growth and macromolecular synthesis in the northwestern Atlantic Ocean

Simultaneous time-course measurements of 35SO42-, 32PO43-, 15NH4+, and [14C]acetate, glucose, and glutamate uptake were made at three stations in the northwestern Atlantic Ocean, using water samples taken from well below the euphotic zone. Marked deviations from linearity were observed in 14 of the 15 cases. At the two most inshore stations uptake of 15NH4+ or incorporation of 35SO42- into protein was undetectable for 16-30 h, followed by very rapid increases in the rates of activity. The sudden burst of SO42-and NH4+ uptake was accompanied by a major increase in the incorporation of 32P into RNA and lipid fractions of the microbial population at a continental slope station. At a station in Sargasso Sea, all substrates were taken up without lag. Extended incubations led to a growth plateau which may be a measure of the total biologically labile organic nutrient supply. In all cases tested, chloramphenicol severely restricted uptake. One of the inshore stations was revisited a year later with similar results. The combined data demonstrate the utility of using inorganic nutrient uptake and subcellular incorporation patterns to measure microbial growth and metabolism and stress the necessity of time-course rather than end-point incubations