Abstract
The hypothesis tested in this study was that inorganic particles stimulate bacterial metabolism in dilute solutions due to concentration of organic nutrients and bacteria from solution by adsorption.Measurements were made of adsorption of bacteria, glucose, and glutamic acid to inorganic particles in seawater and defined bacterial growth medium. Measurements of the metabolism of bacteria were made in the presence and absence of particles by microcalorimetry and radiorespirometry.Hydroxyapatite adsorbs glutamic acid but not glucose from the experimental medium. Hydroxyapatite also adsorbs a significant fraction of bacterial cells from the medium if the bacterial concentration is below 6*10('5) bacteria per milliliter. If bacterial concentrations are 6*10('7), then only a small fraction of cells become attached. It was therefore possible to select bacterial concentrations and organic nutrients so that bacterial attachment, organic nutrient adsorption, or both, would occur in different experiments. In this experimental system the metabolism by attached and non-attached bacteria of adsorbed and non-adsorbed organic nutrients was measured.The results of the present study do not support the initial supposition that the activity of marine bacteria is stimulated by the presence of inorganic surfaces. Bacterial activity was not enhanced at high (millimolar) concentrations of glucose or at low concentrations (micromolar) of glucose or glutamic acid. Bacterial activity was not enhanced regardless of whether the bacteria, the organic nutrient or both were associated with the surface. In fact, the activity of the attached bacteria was diminished in comparison with free bacteria.The results are discussed in terms of the possible reasons why bacteria attach to inorganic surfaces in aquatic environments.