Growth efficiency, growth rate and the remineralization of organic substrate by bacterioplankton - revisiting the Pirt model

The growth yield of aquatic bacteria plays a critical role in the biogeoche mical cycle of organic carbon in the sea. The Pirt model (1982) proposes a relationship of specific growth rate (mu, d(-1)), respiration rate (r, d(-1 )) and growth yield (Y, unitless) of bacteria when the growth rate is limit ed by the concentration of the organic substrate and carbon stoichiometry i s applied. Published data from natural populations of bacterioplankton with in a temperature range of 10 to 25 degrees C follow the Pirt model, where t he growth yield is approaching asymptotically a maximum value (epsilon) wit h increasing growth rate. The specific rate of the maintenance metabolism ( a, d(-1)) is the shape factor defining the curve. From the model a relation ship between the specific respiration rate and the growth rate {r= [mu(1/ep silon - 1) + a/epsilon]} can be derived. Based on the published data these model parameters were estimated: epsilon = 0.51 and a = 0.58. Our model res ults should help explain the wide range of growth efficiencies reported for natural bacterioplankton.