Enhancement of marine bacterial growth by mineral surfaces

The effects of sorptive inert surfaces on growth of marine bacteria and metabolism, as well as partitioning of organic substrates, were examined in microcosms inoculated with bacterioplankton from a local salt marsh. Introduction of organic-free glass beads to a dilute seawater medium (tryptic soy broth) increased yields of ATP, a surrogate for bacterial biomass, by 187% within the entire microcosm (attached + free-living). Growth efficiencies (bacterial C /media C) were 30% for bacteria grown in microcosms with beads compared with 16% without beads. Surface enrichment increased rates of proteolytic enzyme activity and cell-specific [³H]leucine incorporation into protein by factors of 6.8 and 2.2, respectively. Scanning electron microscopy revealed obvious organic coatings on all beads after 2 h of exposure, but few strongly attached bacteria were evident, even after 40 h of exposure. Results support the hypothesis that mineral surfaces facilitate bacterial utilization 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 these surfaces is apparently not a requirement to produce surface-enhanced activity.