Growth efficiency and respiration at different growth rates in glucose-limited chemostats with natural marine bacteria populations

Chemostats with glucose-enriched seawater and inoculated with natural populations of heterotrophic marine bacteria were run at different dilution rates (0.05 to 1.0 d(-1)), at constant temperature (22degreesC) and with low organic substrate medium (20 muM glucose). The following parameters were measured: cell abundance, POC, PON and total CO2 produced. The results demonstrated an increase in growth efficiency with higher specific growth rates within the growth rate range investigated here that is typical for oceanic samples. The results were parameterized according to the Pirt model, with a maximum efficiency of substrate conversion (F = 0.57) and a specific rate of maintenance metabolism (a = 0.41 d(-1)), although the experimental results within the limited growth rate range investigated here are not statistically different from a linear relationship. On first principals it can be argued that the growth efficiency has to pass through the origin and have a maximum efficiency below 1.0, thus suggesting an asymptotic relationship like the Pirt model. Applying the iterative method of model parameter adjustment to previously published data, similar growth efficiency versus growth rate relationships were arrived at, Our results confirm that at a particular temperature a proportionately higher fraction of dissolved organic material is remineralized in oligotrophic oceans that support lower growth rates than in waters supporting higher growth rates. Consequently, in the latter waters, the efficiency of transfer of dissolved organic material into the particulate form is supposed to be higher.