Bacterioplankton growth yield in continuous seawater cultures

Estuarine planktonic bacteria were grown in gas-tight continuous cultures on filtered seawater with reduced content of inorganic carbon. Production of CO, (respiration) and of particulate organic matter (net production) were measured by infrared gas analysis, and growth yield was calculated as net production divided by the sum of respiration and net production. Cultures grown at 6, l 0 and 15 "C showed an average growth yield of 20.7 % ( k l . l , 95 % CL) with minor correlations to both temperature and generation time. This value is considerably lower than the generally assumed growth yield of 60 %, based on short term uptake of radiolabelled substrates. Bacterioplankton gross production and substrate demand might thus have been severely underestimated in previous studies.