Kinetics of glucose and amino acid uptake by attached and free-living marine bacteria in oligotrophic waters

Kinetics of glucose and amino acid uptake by attached and free-living bacte ria were compared in the upper 70 m of the oligotrophic north-western Medit erranean Sea. Potential uptake rates of amino acids were higher than those of glucose in all the samples analysed. Cell-specific potential uptake rate s of attached bacteria were up to two orders of magnitude higher than those of total bacteria, both for amino acids and glucose (0.72-153 amol amino a cids cell(-1) h(-1) and 0.05-58.42 amol glucose cell(-1)h(-1) for attached bacteria and 0.34- 1.37 amol amino acids cell(-1) h(-1) and 0.07-0.22 amol glucose cell(-1) h(-1) for total bacteria). The apparent K, values were als o higher in attached bacteria than in total bacteria, both for amino acids and glucose. These results would reflect the presence of different uptake s ystems in attached and free-living bacteria, which is in accordance with th e different nutrient characteristics of their microenvironments, ambient wa ter and particles. Attached bacteria show transport systems with low affini ty, which characterise a bacterial community adapted to high concentration of substrates.