Attached and free-floating bacteria in a diverse selection of water bodies

The contribution of attached and free-floating bacteria to the bacterial numbers and heterotrophic uptake in 44 diverse aquatic environments was studied. A factor analysis reduced the variability of the raw data base to three major factors explaining 53.6% of total variance. These factors were (i) salinity, (ii) heterotrophic uptake, and (iii) particulate load. A cluster analysis categorized the 44 habitats into five distinct environmental types based on these three factors. There was no significant pattern in the distribution of attached versus free-floating bacteria when assessed by epifluorescent microscopy. However the contribution of attached bacteria to the uptake of an amino acids mix was reduced in marine waters. Heavy particulate loads resulted in an increased percentage uptake of amino acids and glucose from the attached bacteria. Uptake response was found to be substrate specific especially in oliogotrophic freshwater. Amino acid uptake was more associated with the attached fraction, whereas glucose uptake was mediated more by the free-floating fraction.