ENHANCEMENT OF MARINE BACTERIAL-GROWTH BY MINERAL SURFACES

The effects of sorptive inert surfaces on growth of marine bacteria an d metabolism, as well as partitioning of organic substrates, were exam ined in microcosms inoculated with bacterioplankton from a local salt marsh. Introduction of organic-free glass beads to a dilute seawater m edium (tryptic soy broth) increased yields of ATP, a surrogate for bac terial biomass, by 187% within the entire microcosm (attached + free-l iving). Growth efficiencies (bacterial C/media C) were 30% for bacteri a grown in microcosms with beads compared with 16% without beads. Surf ace enrichment increased rates of proteolytic enzyme activity and cell -specific [H-3]leucine incorporation into protein by factors of 6.8 an d 2.2, respectively. Scanning electron microscopy revealed obvious org anic coatings on all beads after 2 h of exposure, but few strongly att ached bacteria were evident, even after 40 h of exposure. Results supp ort the hypothesis that mineral surfaces facilitate bacterial utilizat ion of complex organic matter through physical-chemical processes that increase conversion efficiencies of labile substrate despite possible kinetic limitations. Furthermore, firm attachment by bacteria to thes e surfaces is apparently not a requirement to produce surface-enhanced activity.