EXOPROTEOLYTIC ACTIVITY IN AN ATLANTIC POND (FRANCE) - ESTIMATES OF IN-SITU ACTIVITY

In order to estimate in situ bacterial exoproteolysis and its contribu tion to bacterial secondary production (BSP), we studied microbial act ivities (BSP and kinetics of exoproteolytic activity) in relation to d issolved combined amino acids (DCAA) during the survey of an Atlantic marine pond. In this pond, high concentrations of DCAA (mean = 4.27 mu M), probably generated by zooplankton grazing, allowed large bacteria l biomass development and high production (max = 10(11) cells l(-1) an d 18.8 x 10(9) cells l(-1) d(-1) respectively). Exoproteolytic enzyme activity (mean V-m = 55.9 mu M d(-1)) was tightly cou pled to bacteria l production, suggesting that protein utilization was essential for ba cterial growth. Calculation, according to the Michaelis-Menten equatio n, of the dissolved protein in situ hydrolysis rates using the kinetic parameters (V-m and K-m) and the ambient concentration of DCAA proved to be a better estimation of the actual rate of hydrolytic activity t han the potential activity based on V-m only. The rates found with thi s calculation agreed with those obtained from different environments w ith other methods (DCAA and labelled proteins uptake). Furthermore, ou r estimates of in situ proteolysis were consistent with BSP (nitrogen fluxes originating from dissolved protein hydrolysis averaging 56% of the N bacterial production), and as a result, these estimates seem to provide a realistic estimation of the actual dissolved protein hydroly sis rates.