Efficient utilization of dissolved free amino acids by suspended marine bacteria

Abstract

Incorporation of a mixture of 14C-labeled amino acids by bacteria averaged 79% of assimilation (incorporation plus respiration) but varied with time and location in the salinity gradient of the Newport River estuary, North Carolina, over a 9-month period. The incorporation ranged from an average of 86% at a high (34.2%.) to 74 % at a low (4.1%.) average salinity location. Incorporation at the high salinity location generally was greater than values previously reported in the literature because we accounted for amino acids lost from the paniculate fraction as a result of the acidification required to liberate 14CO 2 from the water. Loss of label due to acidification for estuarine water and for neritic water collected from Florida to Massachusetts was up to 79% of the incorporated amino acids and varied inversely with the amount of incorporated label. The data affirm that suspended marine bacteria efficiently utilize dissolved free amino acids and that acidification should not be used to stop the incubation of samples to be filtered for measurement of substrate incorporation.