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.