BACTERIAL-GROWTH EFFICIENCY ON NATURAL DISSOLVED ORGANIC-MATTER

Bacterial growth efficiency was examined in batch cultures and continuous flow cultures by inoculating natural assemblages of pelagic bacteria from different localities into particle-free water. Growth efficiencies were determined from direct measurements of particulate organic carbon (POC) produced and dissolved organic carbon (DOC) used. On average, 6% of the DOC was consumed during growth m batch cultures. Depending on sampling locality, the DOC consumed was converted to bacterial biomass with efficiencies ranging from 26 to 61%. The efficiency did not correlate with either concentration of DOC or temperature. In continuous flow cultures, growth efficiency increased progressively with increasing ammonium concentration but decreased with increasing substrate C : N ratio. These results suggest that the C : N ratio of the substrate can be a major determinant of bacterial growth efficiency and that differences in growth efficiency between sampling stations can be attributed to differences in the concentration of usable N in the substrate.